Thermoplastic polymer powder having a large particle size distribution

Abstract

The invention relates to a thermoplastic polymer powder that has a Hausner index of 1.30 or less and comprises particles of which the particle size distribution is characterized by a SPAN of 1.0 or more. The invention also relates to the use of such a powder for the construction of a three-dimensional article, for coating a surface and for manufacturing an article by rotational molding. The invention also relates to a method for preparing a thermoplastic polymer powder and to a method for encapsulating a thermoplastic polymer particle with at least one additive.

Description

[0001] Description

[0002] Title: Thermoplastic polymer powder with wide particle size distribution

[0003] Field of invention

[0004] The present invention relates to a thermoplastic polymer powder, its use in a method of constructing a three-dimensional article, coating or rotational molding, as well as an article manufactured therefrom. The invention also relates to a method of preparing a thermoplastic polymer powder, as well as a method of encapsulating thermoplastic polymer particles with at least one additive.

[0005] Technical background

[0006] The construction of three-dimensional (3D) articles can be used to produce prototypes or various parts, for example in the automotive, nautical, aeronautical, aerospace, medical (notably for the manufacture of prostheses, hearing systems, cellular tissues, etc.) fields, textiles, clothing, fashion, decoration, housings for electronics, telephony, home automation, IT, lighting, sport and industrial tools.

[0007] Among the techniques for manufacturing 3D articles, the sintering manufacturing process is particularly interesting. According to this process, a layer of polymer powder is, in a conventional manner, selectively and briefly irradiated in a chamber by electromagnetic radiation (e.g. laser beam, infrared radiation, UV radiation), the result being that the powder particles impacted by the radiation melt. The molten particles coalesce and solidify to lead to the formation of a solid mass. This process can produce, in a simple manner, 3D articles by the repeated irradiation of a succession of freshly applied powder layers.

[0008] Polymer powders used in layer-by-layer 3D article manufacturing processes are often produced by a milling process, which leads to particles with very varied and angular shapes and generally with a broad particle size distribution. Due to these irregular shapes and the presence of acute angles and protruding edges in the particles, powders produced by milling have a relatively low packing (characterized by a high Hausner index), which results in reduced flowability (or free-flowing ability) and spreadability of the powder and can therefore hinder the implementation of polymer powder in 3D article manufacturing processes and in particular by sintering. Indeed, difficulty in free-flowing the powder leads to a risk of creating voids when stacking the particles to form an object (in particular by selective laser sintering or SLS).Furthermore, poor free flow of powder can lead to surface appearance defects (clusters, powder flow lines) in other technologies such as rotational molding, fluidized bed dipping or electrostatic spraying.

[0009] In addition, grinding very often generates the creation of fibrils or short fibers that disrupt flow and spreading. In the case of a 3D article manufacturing process, these particles, due to their particular shape, are often the cause of appearance defects on the parts produced if they are placed on the edges of the parts to be built. In addition, during powder transfer, these fibers or fibrils tend to combine with each other to form balls which are sources of defects in the majority of powder implementation processes.

[0010] Finally, a milled powder often has a greater developed surface area than a powder obtained by dissolution / precipitation, which is often more spherical and therefore has a lower developed surface area. The latter powder will require, in the case of a dry mixture, fewer additives (e.g., flow agents) to achieve the same flow capacity.

[0011] Alternatively, powders can be produced by a dissolution / precipitation process. However, such a process typically results in a powder comprising monodisperse particles (i.e., having a narrow particle size distribution), which can lead to poor particle coalescence when the powder is used (e.g., in 3D printing or during surface coating or molding processes). Indeed, unlike a monodisperse system, a broad particle size distribution allows the finest particles in this distribution to fit between the larger ones and thus minimize interparticle voids.

[0012] In addition, powders with a low SPAN (i.e. narrow particle size distribution) often exhibit significant flow (from certain particle sizes depending on the powder material). This "fluid" nature of the flow can impair the proper spreading of the powder layer in SLS by forming a wave in front of the scraper or leveling roller. In rotational molding, high powder fluidity often generates parts with poorly controlled thicknesses, mainly in the concave areas of the mold (due to centrifugation). The use of a low SPAN powder in rotational molding is also not favorable for the following reason: a wide particle size distribution allows the film coating the mold to build up gradually.Indeed, since the finer particles reach their softening (or melting) temperature before the larger particles, the construction of the coating is progressive from the mold wall towards the internal face of the part, thus avoiding the creation of porosities.

[0013] An example of a powder for 3D printing applications is described in document US 2021 / 0130608. This document relates to a biocompatible polymer powder intended in particular for use in 3D printing of medical devices, comprising in particular a bioceramic as a flow agent.

[0014] There is therefore a real need to provide polymer powders with better flowability and spreadability and allowing the manufacture, particularly when used for the construction of 3D articles, of objects that are less porous, more rigid and with a smoother surface.

[0015] Summary of the invention

[0016] The invention relates firstly to a thermoplastic polymer powder having a Hausner index less than or equal to 1.30 and comprising particles whose particle size distribution is characterized by a SPAN greater than or equal to 1.0.

[0017] In embodiments, the thermoplastic polymer is a semi-crystalline thermoplastic polymer.

[0018] In embodiments, the thermoplastic polymer is selected from the group consisting of polyamides, vinylidene fluoride homopolymers and copolymers, polyamide block and polyether block copolymers, thermoplastic polyurethanes, polyester block and polyether block copolymers, polycarbonate, polystyrene, polyaryletherketones, polyolefins, and combinations thereof.

[0019] In embodiments, the thermoplastic polymer is at least one polyamide, preferably a polyamide 11, a polyamide 12 and / or a polyamide 6, and / or a copolymer with polyamide blocks and polyether blocks in which preferably the polyamide blocks are blocks of polyamide 6, polyamide 11, polyamide 12, polyamide 6.10, polyamide 10.10 and / or polyamide 10.12 and the polyether blocks are blocks derived from polyethylene glycol, propylene glycol, polytrimethylene glycol and / or polytetrahydrofuran.

[0020] In embodiments, the powder has a Hausner index of less than or equal to 1.28, preferably less than or equal to 1.20, more preferably less than or equal to 1.15.

[0021] In embodiments, the powder comprises particles having a particle size distribution characterized by a SPAN of 1.0 to 2.5, preferably 1.0 to 2.0.

[0022] In embodiments, the powder comprises at least one additive, preferably selected from the group consisting of flow agents, mineral fillers, fibers, polymer powders, colorants, pigments, flame retardant additives, antioxidant stabilizers, light stabilizers, impact suppressants, antistatic agents, flame retardants, and mixtures thereof.

[0023] The invention also relates to the use of a powder as described above for the construction of a three-dimensional article, preferably layer by layer, more preferably by sintering, even more preferably by sintering caused by electromagnetic radiation.

[0024] The invention also relates to the use of a powder as described above for coating a surface, preferably metallic. The invention also relates to the use of a powder as described above for manufacturing an article by rotational molding.

[0025] The invention also relates to a method for preparing a powder of the thermoplastic polymer, comprising the following steps: a) providing a powder of the thermoplastic polymer; b) heating said powder by means of an energy source with a temperature of 600 to 10000°C, preferably 600 to 8000°C, more preferably 1000 to 3000°C; c) preferably pulverizing the powder; d) cooling the powder; and e) collecting the powder.

[0026] In embodiments, the prepared powder is a powder as defined above.

[0027] In embodiments, the step of providing the thermoplastic polymer powder comprises grinding the thermoplastic polymer, or dissolving the thermoplastic polymer in a solvent and precipitating said thermoplastic polymer in the solvent.

[0028] The invention also relates to a method for encapsulating thermoplastic polymer particles with at least one additive, comprising the following steps: a) providing thermoplastic polymer particles; b) mixing the thermoplastic polymer particles with at least one additive, preferably selected from the group consisting of flow agents, mineral fillers, fibers, polymer powders, dyes, pigments, fire retardant additives, antioxidant stabilizers, light stabilizers, impact suppressants, antistatic agents, flame retardants, and mixtures thereof, so as to form a thermoplastic polymer powder; c) heating said powder using an energy source with a temperature of 600 to 10000°C, preferably 600 to 8000°C, more preferably 1000 to 3000°C; d) spraying the powder, if applicable; e) cooling the powder;and (f) the collection of the powder.;

[0029] In embodiments, the step of providing thermoplastic polymer particles comprises grinding the thermoplastic polymer, or dissolving the thermoplastic polymer in a solvent and precipitating said thermoplastic polymer in the solvent.

[0030] In embodiments, cooling is performed by contacting the powder with a cold gas, preferably compressed air, or cold water.

[0031] In embodiments, the collection of the powder is carried out in a collection bin or in a cyclone.

[0032] In embodiments, the method further comprises a step of sieving the collected powder and / or a step of mixing the collected, and optionally sieved, powder with at least one additive, preferably selected from the group consisting of flow agents, mineral fillers, fibers, polymer powders, dyes, pigments, fire retardant additives, antioxidant stabilizers, light stabilizers, impact suppressants, antistatic agents, flame retardants, and mixtures thereof.

[0033] The invention also relates to a three-dimensional article manufactured from a powder as described above or from a composition as described above, preferably by layer-by-layer printing, more preferably by sintering.

[0034] The present invention makes it possible to meet the need expressed above. More particularly, it provides a thermoplastic polymer powder having higher flowability, better spreadability and improved coalescence ability during its use. In addition, when the powder is used for the construction of three-dimensional objects, such as by a sintering process, it makes it possible to obtain objects having a smoother and more homogeneous surface, which in particular makes it possible to facilitate subsequent treatments of the surface of said objects, and having a higher density, and therefore good mechanical properties, in particular higher rigidity. The powder according to the invention also allows good stacking of the particles, which ensures good dimensional stability of the successive layers deposited and thus good maintenance of the parts under construction.In addition, the powder according to the invention has improved thermal stability, which makes it possible to improve the recyclability of the powder in other construction processes.

[0035] This is accomplished by providing a powder that has both a low Hausner index, reflecting a high untapped density of the powder compared to its tapped density, while also having a relatively broad particle size distribution (high SPAN).

[0036] The invention also provides a method for preparing a thermoplastic polymer powder making it possible to obtain a powder having both a wide particle size distribution (high SPAN) and a high flowability (low Hausner index). In addition, the method according to the invention makes it possible to eliminate at least a portion of the very fine particles, which may in particular be responsible for fouling 3D printing or rotational molding devices when the powder is used and which are difficult to remove by other selection methods such as sieving.

[0037] This is accomplished by applying a powder treatment comprising a heating step using an energy source with a temperature of 600 to 10000°C followed by cooling.

[0038] The invention also provides a method for encapsulating thermoplastic polymer particles with at least one additive, allowing the maintenance of a homogeneous distribution of the additive in the powder over time and capable of reducing the coalescence of the particles. In particular embodiments in which the additive comprises fibers, the method according to the invention allows the maintenance of the random orientation of the fibers over time and thus the maintenance of the isotropic properties of the powder.

[0039] Brief description of the figures

[0040] [Fig. 1] represents a snapshot obtained by scanning electron microscopy (SEM, magnification x160) of powder no. T as described in example 1 below.

[0041] [Fig. 2] represents a photograph obtained by scanning electron microscopy (magnification x160) of powder no. A' as described in example 1 below.

[0042] [Fig. 3] represents a snapshot obtained by scanning electron microscopy (magnification x160) of powder no. 2' as described in example 1 below.

[0043] [Fig. 4] represents a photograph obtained by scanning electron microscopy (magnification x160) of powder no. B' as described in example 1 below.

[0044] [Fig. 5] represents a snapshot obtained by scanning electron microscopy (magnification x160) of powder no. C' as described in example 1 below.

[0045] Detailed description

[0046] The invention is now described in more detail and in a non-limiting manner in the following description.

[0047] Unless otherwise stated, all percentages relating to quantities are percentages by mass.

[0048] In this text, the quantities indicated for a given species may apply to this species according to all its definitions (as mentioned in this text), including the more restricted definitions.

[0049] Powder

[0050] The invention relates to a thermoplastic polymer powder. By "thermoplastic polymer powder" is meant a powder comprising at least particles comprising at least one thermoplastic polymer; for the purposes of the present invention, the "thermoplastic polymer powder" may thus comprise components other than a thermoplastic polymer (in the particles comprising the thermoplastic polymer or in particles devoid of thermoplastic polymer), for example additives.

[0051] The thermoplastic polymer may be semi-crystalline or amorphous, and is preferably semi-crystalline.

[0052] “Semi-crystalline thermoplastic polymer” means a thermoplastic polymer having: a) a crystallization temperature (Te), which is determined according to ISO 11357-3:2013, during the cooling step at a rate of 20 K / min in DSC (differential scanning calorimetry); b) a melting temperature (Tf), which is determined according to ISO 11357-3:2013 during the heating step at a rate of 20 K / min in DSC; and c) and an enthalpy of fusion (AHf), determined according to ISO 11357-3:2013 during the heating step at a rate of 20 K / min in DSC, which is greater than 5 J / g, preferably greater than 10 J / g, for example greater than 20 J / g and generally less than 200 J / g, preferably less than 150 J / g, for example less than 100 J / g, or less than 50 J / g.

[0053] Advantageously, the semi-crystalline thermoplastic polymer has a melting temperature Tf of 100 to 300°C, and preferably of 120 to 200°C. The Tf is measured as indicated above, and corresponds to the Tf measured during the first heating.

[0054] The semi-crystalline thermoplastic polymer may have a crystallization temperature Te of 40 to 250°C, preferably 45 to 200°C, for example 45 to 150°C. The Te is measured as indicated above.

[0055] Typically, Tf and Te are determined directly from the semi-crystalline thermoplastic polymer powder. When the powder is a polymer blend, Tf is taken to mean the lowest melting temperature of the polymer blend and Te is taken to mean the highest temperature of the polymer blend.

[0056] Preferably, the thermoplastic polymer is selected from the group consisting of polyamides (PA), vinylidene fluoride homopolymers and copolymers (PVDF), polyamide block and polyether block copolymers (PEBA), thermoplastic polyurethanes (TPU), polyester block and polyether block copolymers (COPE), polycarbonate (PC), polystyrene (PS), polyaryletherketones, such as polyetheretherketone (PEEK), polyolefins, such as polyethylene and polypropylene, and combinations thereof. The thermoplastic polymer according to the invention may thus comprise, or be, at least one polyamide. It may be a homopolyamide or a copolyamide, or a mixture thereof.

[0057] In embodiments, the thermoplastic polymer may in particular be an elastomeric thermoplastic polymer, more particularly chosen from a PEBA copolymer, a TPU and / or a COPE copolymer.

[0058] Of course, the designation PEBA in the present description of the invention relates, in particular, to PEBAX® marketed by Arkema, to Vestamid® marketed by Evonik®, to Grilamid® marketed by EMS, as well as to Pelestat® type PEBA marketed by Sanyo or to any other PEBA from other suppliers.

[0059] In embodiments, the elastomeric thermoplastic polymer may also be selected from styrenic block copolymers (TPS), thermoplastic polyolefin elastomers (TPO), and / or thermoplastic vulcanizates (TPV). Examples of commercial elastomeric thermoplastic polymers are, for example, CAWITON®, THERMOLAST K®, THERMOLAST M®, Sofprene®, Dryflex® and Laprene ® (TPS), Desmopan® or Elastollan® (TPU), Santoprene®, Termoton®, Solprene®, THERMOLAST V®, Vegaprene®, or Forprene® (TPV), and For-Tec E® or Engage. Ninjaflex® (TPO).

[0060] In embodiments, the thermoplastic polymer comprises or is a polymer selected from homopolymers and copolymers of polyoxymethylene (POM), polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyphthalamides (PPA), poly(p-phenylene terephthalamide), and mixtures thereof.

[0061] In embodiments, the thermoplastic polymer may comprise, or be, a polycarbonate (PC).

[0062] In embodiments, the thermoplastic polymer may comprise, or be, polystyrene (PS).

[0063] In embodiments, the thermoplastic polymer may comprise, or be, a polyetheretherketone (PEEK).

[0064] The thermoplastic polymer may consist of a single polymer, in particular as described above, or may comprise or consist of a mixture of thermoplastic polymers (preferably semi-crystalline), in particular a mixture of any of the thermoplastic polymers (preferably semi-crystalline) as described above. The thermoplastic polymer powder according to the invention has a Hausner index of less than or equal to 1.30. In a known manner, the Hausner index of a powder is defined as the ratio of the packed density of the powder to its unpacked density (also called aerated density or bulk density). The packed and aerated densities can be measured according to ISO 3953:2011, for example using a STAV II packing volume meter.Advantageously, the thermoplastic polymer powder has a Hausner index less than or equal to 1.28, preferably less than or equal to 1.25, more preferably less than or equal to 1.20, more preferably less than or equal to 1.15, more preferably less than or equal to 1.12, more preferably less than or equal to 1.10. In embodiments, the powder has a Hausner index of less than or equal to 1.07, or less than or equal to 1.05, or less than or equal to 1.02, or a Hausner index of 1.0 to 1.05, or 1.05 to 1.10, or 1.10 to 1.15, or 1.15 to 1.20, or 1.20 to 1.22, or 1.22 to 1.25, or 1.25 to 1.28, or 1.28 to 1.30. The lower the Hausner index of the powder, the better its flowability (or free flow) will be.

[0065] The thermoplastic polymer powder according to the invention is characterized by a SPAN greater than or equal to 1. 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, in which:

[0066] Dv90 denotes the particle size at 90 ème percentile, in volume, of the cumulative distribution of particle sizes (in other words it is the corresponding diameter so that the cumulative function of particle diameters, weighted by volume, is equal to 90%),

[0067] Dv10 denotes the particle size at io ème percentile, in volume, of the cumulative distribution of particle sizes (in other words it is the corresponding diameter so that the cumulative function of particle diameters, weighted by volume, is equal to 10%), and

[0068] Dv50 is the volume median diameter of the particles and corresponds to the particle size at 50 ème percentile (by volume) of the cumulative particle size distribution.

[0069] Dv50, Dv90 and Dv10 can be measured by laser diffraction particle size analysis according to ISO 13320:2009, for example on a Malvern Insitec® type diffractometer.

[0070] Preferably, the SPAN of the particles of the powder is from 1.0 to 2.5, even more preferably from 1.0 to 2.0, even more preferably from 1.2 to 2.0. In particular, the particles of the powder may have a SPAN of 1.0 to 1.2, or from 1.2 to 1.5, or from 1.5 to 1.7, or from 1.7 to 2.0, or from 2.0 to 2.2, or from 2.2 to 2.5.

[0071] Preferably, the particles of the powder have a Dv50 of 20 to 500 pm, more preferably of 30 to 250 pm, even more preferably of 40 to 120 pm.

[0072] Preferably, the particles of the powder have a Dv90 of 50 to 800 pm, more preferably of 60 to 500 pm, even more preferably of 70 to 130 pm.

[0073] Preferably, the particles of the powder have a Dv10 of 5 to 100 pm, more preferably of 10 to 80 pm, even more preferably of 15 to 60 pm.

[0074] In embodiments, the powder contains a cumulative fraction of particles of size less than or equal to 10 μm less than or equal to 1% by weight, preferably less than or equal to 0.8% by weight, relative to the total weight of the powder.

[0075] In embodiments, the powder contains a cumulative fraction of particles of size less than or equal to 30 μm less than or equal to 10% by weight, preferably less than or equal to 5% by weight, even more preferably less than or equal to 2% by weight, or less than or equal to 1% by weight, relative to the total weight of the powder.

[0076] The cumulative fraction of particles is measured according to ISO 13320:2009.

[0077] For the purposes of the present invention, the size of a particle means the volume equivalent average diameter of said particle.

[0078] A powder containing a low cumulative fraction of fine particles (in particular, particles of size less than or equal to 30 pm, preferably less than or equal to 10 pm) as defined above has certain advantages for 3D printing or rotational molding processes, because these fine particles can in particular be responsible for the fouling of 3D printing or rotational molding devices when the powder is used and are difficult to remove by other selection processes such as sieving.

[0079] In embodiments, the powder according to the invention consists, or consists essentially, of at least one thermoplastic polymer.

[0080] The powder may further comprise one or more additives. Preferably, the powder may comprise one or more additives selected from the group consisting of flow agents, mineral fillers, fibers, polymer powders, colorants, pigments, flame retardant additives, antioxidant stabilizers, light stabilizers, impact suppressants, antistatic agents, flame retardants, and mixtures thereof.

[0081] The powder may comprise at least one flow agent. By "flow agent" is meant an agent which makes it possible to improve the flowability as well as the leveling of the powder, in particular during a sintering process.

[0082] The flow agent may for example be chosen from silicas, in particular precipitated silicas, hydrated silicas, vitreous silicas, fumed silicas and pyrogenic silicas, vitreous oxides, in particular vitreous phosphates and vitreous borates, alumina, such as amorphous alumina, TiO2, calcium silicates, magnesium silicates, such as talc, mica, kaolin, attapulgite, waxes and mixtures thereof.

[0083] The flow agent may be present in the composition in an amount less than or equal to 5% by weight, preferably less than or equal to 3% by weight, relative to the total weight of the composition. This amount of flow agent may more particularly be from 0.1 to 2.5%, preferably from 0.1 to 2%, more preferably from 0.5 to 2%, for example from 0.5 to 1.5%, relative to the total weight of the composition.

[0084] The flow agent is generally in powder form, preferably with particles of substantially spherical shape. The flow agent in the composition may have particles having a volume median diameter (Dv50) less than or equal to 20 pm, preferably less than or equal to 15 pm, more preferably less than or equal to 10 pm, even more preferably less than or equal to 1 pm. For example, the median diameter Dv50 of the particles of the flow agent may be from 10 nm to 100 nm, or from 100 nm to 1 pm, or from 1 pm to 20 pm.

[0085] The powder may alternatively be free of flow agent, and in particular of flow agent as described above.

[0086] The powder may comprise one or more mineral fillers, for example, selected from carbonate mineral fillers, including calcium carbonate, magnesium carbonate, dolomite and / or calcite, barium sulfate, calcium sulfate, dolomite, alumina hydrate, wollastonite, montmorillonite, zeolite, perlite, nanofillers (fillers in the nanometer range) such as nanoclays and / or carbon nanotubes, carbon black, glass fibers, carbon fibers, and combinations thereof.The powder according to the invention may comprise organic additives such as, more particularly, polymer powders (other than thermoplastic polymer), in particular those having a melting temperature higher than the maximum temperature experienced by the powder during its use (for example during a layer-by-layer 3D article construction process), in particular those with a Young's modulus greater than or equal to 1000 MPa.

[0087] In embodiments, the powder is free of mineral fillers and / or (preferably and) organic additives, in particular free of polymer powder other than the thermoplastic polymer.

[0088] The powder may comprise the mineral fillers and the organic additives in a mass quantity less than or equal to 60%, preferably less than or equal to 30%, more preferably less than or equal to 1%, relative to the total weight of the composition, for example in a mass quantity of 0.05 to 60%, preferably 1 to 30%, preferably 1 to 20%, preferably 1 to 10%.

[0089] The powder of the invention may also comprise one or more additives chosen from dyes, pigments, in particular pigments for coloring and pigments for infrared absorption, fire-resistant additives, antioxidant stabilizers, light stabilizers, shock-resistant agents, antistatic agents, flame-retardant agents and mixtures thereof. These additives are preferably in the form of powder with a Dv50 of less than or equal to 20 μm. These additives may be present in the composition in a mass quantity of 0.05 to 5%, relative to the total weight of the composition.

[0090] In embodiments, the powder consists essentially of, or consists of, particles comprised of thermoplastic polymer and one or more additives selected from flow agents, mineral fillers, polymer powders, colorants, pigments, flame retardant additives, antioxidant stabilizers, light stabilizers, impact suppressants, antistatic agents, flame retardants, and mixtures thereof.

[0091] Manufacturing processes

[0092] The invention also relates to a process for preparing a thermoplastic polymer powder, in particular a thermoplastic polymer powder as described above.

[0093] The preparation method comprises providing a powder of the thermoplastic polymer and heating it by means of an energy source with a temperature of 600 to 10000°C, preferably a flame. In the context of the present invention, it should be understood that the temperature ranges indicated for the energy source characterize the temperature of the energy source itself (at its center) and not the temperature of the heated powder particles. The use of such an energy source allows very rapid heating of the particles by increasing thermal conduction.

[0094] The step of providing the powder may comprise the manufacture of such a powder. The thermoplastic polymer powder provided may be obtained by any suitable means. Advantageously, the powder is obtained by grinding the thermoplastic polymer (which is for example in the form of granules). In these embodiments, the thermoplastic polymer (or the mixture of thermoplastic polymers) is preferably pre-melted (for example at a temperature between 150 and 300°C), then ground after its solidification. The grinding may be carried out using any suitable grinding device, such as a pin mill, a hammer mill, a classifer mill or a fluid bed air jet mill. Advantageously, the grinding is cryogenic grinding.In this case, the thermoplastic polymer is, in a first step, cooled to a temperature lower than its glass transition temperature, for example to a temperature 10 to 50°C lower than the glass transition temperature of the thermoplastic polymer. Thus, the thermoplastic polymer can be cooled to a temperature lower than or equal to -10°C, preferably lower than or equal to -50°C, and more preferably lower than or equal to -80°C. The cooling of the thermoplastic polymer before grinding can be carried out for example with liquid nitrogen, or with liquid carbon dioxide, or with dry ice, or with liquid helium.

[0095] Alternatively, the provided powder may be obtained by a dissolution / precipitation process (particularly when the thermoplastic polymer is a polyamide and / or a PEBA). In these embodiments, the process comprises dissolving the thermoplastic polymer in a solvent and precipitating the thermoplastic polymer in the solvent. More particularly, the process may comprise the steps of contacting the thermoplastic polymer (e.g., in the form of granules) with a solvent to obtain a mixture; heating the mixture to dissolve the copolymer in the solvent; and cooling the mixture to obtain the precipitated polymer in powder form. The solvent in which the thermoplastic polymer is dissolved may be selected from ethanol, propanol, butanol, isopropanol, heptanol, formic acid, acetic acid, N-methylpyrrolidone, N-butylpyrrolidone, butyrolactam, and / or caprolactam.The thermoplastic polymer may have a mass fraction in the solvent of 0.05 to 0.5, and preferably of 0.1 to 0.3. The heating of the thermoplastic polymer / solvent mixture may in particular be carried out at (or up to) a temperature of 100 to 160°C, and preferably of 120 to 150°C; and / or have a duration of 1 to 6 hours, and preferably of 1 to 3 hours. Then, the mixture is cooled in order to cause crystallization and thus precipitation of the copolymer in powder form. This cooling may be carried out to a temperature greater than or equal to 50°C, for example a temperature in the range of 50 to 90°C; and may be carried out at a rate of 10 to 100°C per hour, preferably of 10 to 60°C per hour. The dissolution / precipitation process may include a step of drying the thermoplastic polymer powder after cooling the mixture, for example carried out in an oven.Drying can be carried out at a temperature of 10 to 150°C, preferably 25 to 85°C, and can be carried out under vacuum (in particular at a pressure greater than 10 mbar, preferably greater than 50 mbar) or under atmospheric pressure.

[0096] Preferably, the powder provided is a powder obtained by grinding. This makes it possible to obtain powders with a higher SPAN.

[0097] Whatever its manufacturing process, the powder may be subjected to a selection step, in particular carried out on a sieve or by a dynamic selector.

[0098] The provided thermoplastic polymer powder is then subjected to the heating step. Preferably, the powder is heated by means of a blowtorch or any other means for generating a hot gas flow, more preferably by means of a blowtorch. Advantageously, the blowtorch is an oxy-fuel blowtorch (i.e. using dioxygen O2 as an oxidant), more preferably oxy-propane (i.e. using dioxygen and propane as oxidants), oxy-butane (i.e. using dioxygen and butane as oxidants) or oxy-acetylene (i.e. using dioxygen and acetylene as oxidants), even more preferably oxy-propane.

[0099] Most preferably, the method comprises a step of spraying the powder. Preferably, the steps of heating the powder and spraying the powder are partly simultaneous. In particular, they can be carried out using the same device.

[0100] Preferably, a flame spray device is used as a blowtorch. Such a device allows the powder, advantageously transported by a carrier gas, in particular air, to be sprayed through the flame. For example, a MiniSprayJet F311 FX model device from IBEDA can be used. This autonomous equipment only requires a power connection to be operational.

[0101] Advantageously, the method according to the invention makes it possible, by appropriate adjustment of the energy source (preferably the flame), to improve the particle size of the powder by eliminating by combustion at least a portion of the very fine particles (in particular, particles of size less than or equal to 30 pm, preferably less than or equal to 10 pm), these very fine particles being difficult to eliminate by other selection methods such as sieving. A significant presence of very fine particles (in particular, particles of size less than or equal to 30 pm, preferably less than or equal to 10 pm) can in certain methods cause fouling of the devices used, in particular SLS 3D printing devices and rotational molding devices.

[0102] Preferably, the energy source (preferably the flame) has a temperature of 600 to 8000°C, more preferably 600 to 4000°C, preferably 1000 to 3000°C. The energy source may in particular have a temperature of 600 to 800°C, or 800 to 1000°C, or 1000 to 1200°C, or 1200 to 1500°C, or 1500 to 1700°C, or 1700 to 2000°C, or 2000 to 2200°C, or 2200 to 2500°C, or 2500 to 2700°C, or 2700 to 3000°C, or 3000 to 3500°C, or 3500 to 4000°C, or 4000 to 6000°C, or 6000 to 8000°C, or 8000 to 10000°C.

[0103] The contact time between the powder and the energy source (preferably the flame) is advantageously between 0.01 s and 1 s, preferably from 0.02 s to 0.1 s, in particular the contact time between the powder and the flame may be from 0.01 to 0.02 s, or from 0.02 to 0.04 s, or from 0.04 to 0.06 s, or from 0.06 to 0.08 s, or from 0.08 to 0.1 s, or from 0.1 to 0.25 s, or from 0.25 to 0.5 s, or from 0.5 to 0.75 s, or from 0.75 to 1 s.

[0104] Heating the thermoplastic polymer powder using the energy source as defined above causes partial melting of the powder particles at their surface, leading to rounding, or even spheronization (i.e., complete rounding), of the powder particles. This results in a reduction of the Hausner index of the powder, and an improvement in its flowability.

[0105] Generally, during powder manufacturing, the Hausner index of the powder can be decreased by increasing the energy of the powder heating process (which allows fusion at the particle surface). This can be done for example: by increasing the flow rate of the sprayed powder; by increasing the flow rate of the transport air (or gas); by increasing the flow rate of the oxidant; by increasing the flow rate of the fuel; by increasing the pressure of the cooling air (or gas); by increasing the heating time of the particles by increasing the distance between the energy source (e.g. the sprayer) and the collection device.

[0106] The method according to the invention also has the advantage of reducing the SPAN of the starting powder very little, or not at all, which makes it possible to obtain powders having a SPAN greater than or equal to 1.00.

[0107] The transport gas flow rate can be from 0 to 0.08 MPa, especially from 0 to 0.05 MPa.

[0108] The oxidant flow rate can be from 15 to 70 L / min, in particular from 20 to 60 L / min.

[0109] The fuel flow rate can be from 10 to 40 L / min, especially from 15 to 25 L / min.

[0110] The cooling gas pressure can be from 0.15 to 0.8 MPa, especially from 0.2 to 0.6 MPa.

[0111] Most preferably, the powder is then cooled. Preferably, the powder can be cooled by contacting it with a fluid; in particular a cold gas and / or a cold liquid. For the purposes of the present invention, the term "cold gas" means a gas having a temperature of at most 30°C and for the purposes of the present invention, the term "cold liquid" means a liquid having a temperature of at most 20°C. The cold gas is more preferably air, and more particularly compressed air. The cold liquid is advantageously water.

[0112] The preparation method preferably comprises a step of collecting the powder. Advantageously, the collection of the powder takes place at least partly simultaneously with its cooling. The collection of the powder very preferably comprises bringing the powder into contact with a fluid (gas and / or liquid), in particular the fluid used to cool the powder. The fluid, and in particular when it is a gas, may be in motion, so as to entrain the powder particles, for example a rotational movement. Bringing the powder into contact with a fluid (in particular in motion) makes it possible to reduce the agglomeration of the powder particles which may occur before the end of their cooling.

[0113] Powder collection can be carried out in a suitable collection device, such as a collection bin or, preferably, a suitable cyclone. The use of a cyclone is particularly advantageous because it allows the powder particles to be separated from the transport gas (the particles being collected at one end of the device while the powder transport gas is discharged at another end of the device). Compared to a collection bin, the use of a cyclone allows for reduced product losses and therefore improved powder yield.

[0114] The collection device may in particular contain, and / or be surrounded by, the fluid used to cool the powder.

[0115] Preferably, the distance between the energy source, preferably the flame (at its base) (for example the tip of the gun in the case of a spray device), and the collection device is from 1 to 2.5 m, preferably from 1.3 to 2.2 m, for example 1.5 m or 2 m.

[0116] The method may include a step of selecting the particles of the collected powder according to their desired particle size, in particular by sieving.

[0117] The method may comprise mixing the thermoplastic polymer particles with any other components of the powder (in particular, additives as described above), if any.

[0118] Advantageously, the mixture is a dry mixture of the components of the powder, in powder form. When the powder comprises more than two components, the mixture can be carried out in one step (the components all being added to the mixture simultaneously) or in several steps (a premixing of some components being carried out first before the addition of other components), the components being able to be mixed in any order. The mixture can be carried out in any device suitable for mixing powders.

[0119] Alternatively, the additives, in whole or in part, may be mixed with the thermoplastic polymer before preparing the thermoplastic polymer powder according to the invention, during the step of providing a thermoplastic polymer powder. Thus, in the case of manufacturing the powder by grinding, the additives may be mixed with the thermoplastic polymer before it is melted or mixed with the ground thermoplastic polymer powder. In the case of manufacturing the powder by dissolution / precipitation, the additives may be mixed with the thermoplastic polymer before it is dissolved in the solvent, or they may be mixed with the thermoplastic polymer after it is dissolved in the solvent and before it is precipitated, or they may be mixed with the precipitated thermoplastic polymer powder.When only a part of the additives are mixed with the thermoplastic polymer before the preparation of the powder according to the invention by heating using an energy source with a temperature of 600 to 10000°C (for example a flame), the rest of the additives are mixed with said powder by dry mixing.

[0120] In embodiments, at least one additive is added to the thermoplastic polymer powder before the heating step and the method comprises a step of spraying the powder. In these embodiments, the heating and spraying steps make it possible to encapsulate at least a portion of the powder particles by at least a portion of said additive. Encapsulating the powder particles by an additive has the advantage of making the thermoplastic polymer and the additive integral, which makes it possible to reduce the segregation of the additive-containing powder and to maintain a homogeneous distribution of the additive in the powder. Encapsulation can also allow a reduction in the coalescence of the particles. In addition, when the additive is a fiber, the encapsulation makes it possible to maintain the fibers in a random orientation, which gives isotropic properties to the powder.

[0121] Defining process

[0122] The invention also relates to a method for defining a powder. By "defining" is meant the reduction of the quantity of particles of a size less than or equal to 30 μm, preferably 10 μm in the powder. The quantity of particles of a size less than or equal to a given size in the powder can be determined by laser diffraction particle size analysis according to ISO 13320:2009, for example on a Malvern diffractometer of the Insitec® type.

[0123] This method according to the invention comprises the following steps: a) providing a powder of the thermoplastic polymer; b) heating said powder by means of an energy source with a temperature of 600 to 10000°C, preferably 600 to 8000°C, more preferably 1000 to 3000°C; c) preferably, spraying the powder; d) cooling the powder; and e) collecting the powder.

[0124] What has been described in the previous section in relation to the process of preparing a thermoplastic polymer powder can be applied in the same way to this process.

[0125] Generally speaking, the higher the temperature of the energy source, the smaller the quantity of particles smaller than or equal to 10 pm will be.

[0126] Advantageously, the defining process allows a reduction in the quantity of particles of size less than or equal to 20 pm and / or a reduction in the quantity of particles of size less than or equal to 30 pm in the powder.

[0127] Advantageously, the collected powder contains a cumulative fraction of particles of size less than or equal to 10 μm less than or equal to 1% by weight, preferably less than or equal to 0.8% by weight, relative to the total weight of the powder.

[0128] Advantageously, the powder contains a cumulative fraction of particles of size less than or equal to 30 μm less than or equal to 10% by weight, preferably less than or equal to 5% by weight, even more preferably less than or equal to 2% by weight, or less than or equal to 1% by weight, relative to the total weight of the powder.

[0129] Advantageously, the collected powder (i.e., the defined powder) is as described above in the “Powder” section and, in particular, has a Hausner index of less than or equal to 1.30 and comprises particles whose particle size distribution is characterized by a SPAN of greater than or equal to 1.0.

[0130] Encapsulation process

[0131] The invention also relates to a method for encapsulating thermoplastic polymer particles with at least one additive.

[0132] This method according to the invention comprises the following steps: a) providing thermoplastic polymer particles; b) mixing the thermoplastic polymer particles with at least one additive, so as to form a thermoplastic polymer powder; c) heating said powder by means of an energy source with a temperature of 600 to 10000°C, preferably 600 to 8000°C, more preferably 1000 to 3000°C; d) spraying the powder, if necessary; e) cooling the powder; and f) collecting the powder.

[0133] The at least one additive is advantageously in powder form. Preferably, it is chosen from the additives mentioned above in the previous sections.

[0134] The mixing of the thermoplastic polymer particles with the at least one additive is preferably carried out by dry mixing.

[0135] Preferably, the heating and spraying steps are at least partly simultaneous.

[0136] What has been described in the previous section in relation to the process for preparing a thermoplastic polymer powder may be applied in the same way to this process. The step of providing thermoplastic polymer particles may be as described in the step of providing the thermoplastic polymer powder in the "Manufacturing Methods" section above.

[0137] Advantageously, the collected powder (i.e., the encapsulated powder) is as described above in the “Powder” section and, in particular, has a Hausner index of less than or equal to 1.30 and comprises particles whose particle size distribution is characterized by a SPAN of greater than or equal to 1.0.

[0138] The powder or composition as described above can be used in a process for constructing 3D articles, preferably layer by layer (also called 3D printing process), more preferably by sintering, even more preferably by sintering caused by electromagnetic radiation, for example infrared, ultraviolet radiation, or preferably a laser.

[0139] Preferably, the composition of the invention is used in a selective laser sintering (SLS) process. The composition can also be used in a sintering process of the M JF (Multi Jet Fusion) type and HSS (High Speed ​​Sintering).

[0140] The invention also relates to a method of constructing a three-dimensional article comprising: a) depositing, preferably in the form of a layer, powder as described above or a composition as described above, in powder form; and b) sintering the powder, preferably by means of an electromagnetic radiation beam.

[0141] Preferably, steps a) and b) are repeated, so as to form the three-dimensional article.

[0142] The powder, as described above, can be recycled and reused in several successive constructions. It can for example be used as such or in a mixture with other recycled or non-recycled powders. Advantageously, the non-agglomerated powder after step b), preferably after each step b) of the process, can be recycled in the same construction process, to carry out a subsequent deposition step a), or in another construction process.

[0143] What has been described above in relation to the use of the powder or composition for the construction of a three-dimensional article applies similarly to the method of constructing a three-dimensional article.

[0144] The invention also relates to an article manufactured from a powder or a composition as described above, preferably by means of a process as described above.

[0145] In other embodiments, the powder or composition according to the invention may be used for coating a surface. The surface may be coated in whole or in part. Advantageously, the coating is a film obtained by melting the thermoplastic polymer powder described above or the composition described above in powder form (in particular, a film 100 to 550 μm thick, more preferably 200 to 500 μm thick).

[0146] The surface may be of any type, including a metal surface, for example the surface of a part selected from the group consisting of ordinary or galvanized steel parts and aluminum or aluminum alloy parts.

[0147] The invention also relates to a method for coating a surface comprising the following steps: bringing the surface into contact with the powder as described above or with the composition as described above, in powder form; melting the powder.

[0148] Before bringing the surface into contact with the powder, the coating process may include a step of applying a mask to the surface, particularly when the object to be coated is only to be partially covered by the coating. The application of a mask makes it possible to selectively coat only certain parts of the part to be coated. The powder is then brought into contact with unmasked parts of the surface to be coated.

[0149] The powder may be applied to or contacted with a surface by many coating techniques well known to those skilled in the art. Preferably, the coating is carried out by a method selected from the group consisting of fluidized bed dipping, electrostatic spraying and hot powder coating.

[0150] Thus, the coating can be carried out by electrostatic spraying. The step of bringing the surface into contact with the powder or the composition in powder form can then comprise the steps of: electrically charging the powder; spraying the electrically charged powder onto the surface; heating the powder-coated surface to a temperature above the melting temperature of the thermoplastic polymer.

[0151] Electrostatic spray coating involves depositing electrostatically charged powder particles onto a surface, particularly at room temperature. The powder can be electrostatically charged as it passes through the nozzle of a spraying device. The charged powder can then be sprayed onto the object comprising the surface to be coated, which is connected to a zero potential. The coated object can then be placed in an oven at a temperature that allows the powder to melt.

[0152] The equipment for projecting (or spraying) the powder can be of any type. Preferably, the nozzle is brought to a high potential of between ten and one hundred kilovolts, of negative or positive polarity. Preferably, the equipment for projecting the powder is an electrostatic gun which charges the powder by Corona effect and / or by triboelectrification. Preferably, the powder flow rate in the projection equipment is from 10 to 200 g / min, and more preferably, from 50 to 120 g / min. Preferably, the electrostatic application temperature of the powder is from 15 to 25°C. Preferably, the residence time of the surface in the oven is from 3 to 15 minutes. Advantageously, the heating temperature of the surface can be from 180 to 300°C, preferably from 200 to 250°C.The heating temperature of the powder-coated surface may preferably be at least 30°C higher than the melting temperature of the thermoplastic polymer, more preferably 30 to 60°C higher than the melting temperature of the thermoplastic polymer. The surface may then be cooled, for example, to room temperature. If a mask has been used, it may be removed.

[0153] Alternatively, the coating may be carried out by dipping in a fluidized bed. Thus, the step of contacting the surface with the powder may comprise the steps of: heating the surface to a temperature above the melting temperature of the thermoplastic polymer; dipping the surface into a fluidized bed comprising the powder.

[0154] The surface to be coated is preheated to a temperature that allows the powder according to the invention to melt. The surface is then immersed in a fluidized bed comprising the powder. The powder melts upon contact with the surface and forms a coating thereon. The coated surface is then preferably cooled, for example in ambient air. When present, the mask can then be removed. Preferably, the fluidized air for fluidizing the powder is cold, clean and oil-free. Preferably, the surface heating temperature is from 180 to 450°C, preferably from 250 to 350°C. More preferably, the surface heating is carried out at a temperature at least 30°C higher than the melting temperature of the thermoplastic polymer, more preferably at a temperature 30 to 120°C higher than the melting temperature of the thermoplastic polymer.Preferably, the duration of soaking of the surface in the fluidized bed is from 1 to 10 seconds, more preferably from 3 to 7 seconds. The soaking of the surface in the fluidized bed can take place one or more times (each soaking preferably having a duration of 1 to 10 s, more preferably from 3 to 7 s).

[0155] In other embodiments, the coating is carried out by hot powder coating. The step of contacting the surface with the powder then comprises the steps of: heating the surface to a temperature above the melting temperature of the thermoplastic polymer; spraying the powder onto the surface.

[0156] The heating temperature of the surface may be as described above in relation to fluidized bed dip coating. It is preferably at least 30°C higher than the melting temperature of the thermoplastic polymer, more preferably 30 to 120°C higher than the melting temperature of the thermoplastic polymer. The surface may then be cooled, for example, to room temperature. When a mask has been used, it may be removed. The sprayed powder may or may not be electrostatically charged.

[0157] The characteristics described above in relation to the use of powder for coating a surface (in particular concerning the description of the surface and the thickness of the coating film) can be applied in the same way to coating processes.

[0158] The invention also relates to an object having a surface covered at least in part with a coating obtained (or capable of being obtained) by the fusion of a powder or composition as described above, preferably an object obtained (or capable of being obtained) by a method as described above.

[0159] Another subject of the invention relates to the use of the powder as described above or of a composition as described above, in powder form, for the manufacture of an article by rotational molding (also called rotational molding).

[0160] The invention also relates to a method of manufacturing an article comprising the following steps: providing a powder as described above or a composition as described above, in powder form; and rotational molding of said powder.

[0161] Rotational molding is a molding process in which powder is introduced into a mold, which can be of variable size, shape, thickness, and material. The mold is then heated while being rotated, which causes the powder to heat up, by conduction in contact with the mold wall, to its melting point. Total or partial rotation of the mold (advantageously at a speed of 2 to 40 rpm), preferably along one or two axes (preferably orthogonal), allows the molten material to cover the entire internal surface of the mold. The mold is then advantageously cooled, preferably with air or water spray, and preferably while being kept rotating. After solidification of the polymeric material, the article can be demolded.

[0162] Advantageously for the mold heating step, the mold is introduced into an oven. The mold is preferably heated to a temperature of 20°C to 60°C above the melting point of the polymer, preferably 20°C to 40°C above its melting point.

[0163] Rotational molding processes from polymer powder are well known to those skilled in the art. The invention also relates to an article obtained (or capable of being obtained) by a rotational molding process as described above.

[0164] Examples

[0165] The following examples illustrate the invention without limiting it.

[0166] Example 1

[0167] The following powders have been prepared or used:

[0168] Powder 1: Pebax® 3533 commercial powder (Arkema).

[0169] Powder 2: Pebax® 40R53 commercial powder (Arkema).

[0170] Powder 3: Pebax® 4533 commercial powder (Arkema).

[0171] Powder 4: Rilsan® Fine Powders T BLUE 7443 commercial powder (Arkema).

[0172] Powder 5: Rilsan® Fine Powders T Nat BHV (Arkema) commercial powder.

[0173] Powder 6: Orgasol® Invent SMOOTH commercial powder (Arkema).

[0174] Powder 7: Commercial powder PA2200 (EOS).

[0175] Powder 8: Rilsan® Invent Natural commercial powder (Arkema).

[0176] Part of powders No. 1, 2, 3, 4, 5 and 6 underwent the following treatment: the powders were pumped with air from a vibrating tank and then transported to an oxy-propane flame sprayer MiniSprayJet F311 FX from IBEDA (flame temperature of 2000-2600°C). The powders were then sprayed using the flame sprayer. The sprayed powders were collected in a cyclone-type recuperator where they were cooled by circulating compressed air around the cyclone.

[0177] The following powders were obtained using the operating parameters indicated in the table below.

[0178] [Table 1]

[0179] For all powder treatments, the inlet dry air pressure is 0.6 MPa, the propane pressure is 0.14 MPa, the oxygen pressure is 0.25 MPa, the powder transport pipe to the sprayer has an Inner Diameter (mm) / Length (mm) ratio of 11 / 2000 and the transport air pressure is 0 MPa, except for powder treatment No. 1 for which it is 0.04 MPa.

[0180] Powders 1, A, 2, B, C, 3 and D were then dry blended with one or more flow agents in a Henschel IAM 6L mixer for 100 s, at room temperature and with stirring at 9000 rpm. The flow agents and their quantity (weight percentage) are indicated in the table below. The additivated powders are subsequently referred to as powders no. T, A', 2', B', C', 3' and D', respectively.

[0181] [Table 2]

[0182] Powders Nos. A', B', C', D', E and F are powders according to the invention; powders Nos. T, 2', 3', 4, 5, 6, 7 and 8 are comparative powders.

[0183] The Hausner index and SPAN of the powders were then determined according to the methods described above.

[0184] The results are presented in the table below.

[0185] [Table 3]

[0186] It is found that powders comprising a low Hausner index (i.e., high free-flowability) combined with a high SPAN could be obtained. In contrast, commercial powders 6 and 7 have a SPAN less than 1 and commercial powder 8 has a Hausner index greater than 1.30.

[0187] Pictures of the particles of powders No. T, A', 2', B' and C' are shown in Figure 1, Figure 2, Figure 3, Figure 4 and Figure 5 respectively. It is observed that the application of the powder treatment by the pulverizer makes it possible to round off, or even spheronize (case of powder No. C') the particles of the ground powders.

[0188] Example 2

[0189] The powders 3' and D' as described in Example 1 above were used to manufacture by 3D printing by sintering, more specifically by SLS, 1 BA XY (in the build plane) specimens according to the ISO 527 standard, on a Sharebot Snowwhite machine, under the temperature conditions (of the powder and the enclosure) indicated in Table 4 below. The laser parameters used are the same for the entire print and for each of the two powders tested, and are as follows: each layer of powder to be sintered is scanned by a 6.3 W power laser applied to the layer in points spaced from each other by 0.06 mm at a speed of 40,000 points per second.

[0190] During construction, the temperature of the powder on the surface of the build tank was imposed, and was measured at the surface using an infrared thermal sensor. The air temperature in the enclosure was measured using a temperature probe placed inside the machine, less than 10 cm from the build tank.

[0191] The following properties of the specimens thus constructed were then measured:

[0192] Density: measured by the Archimedes' buoyancy method described in ISO 1183-1:2019; the average density of 5 specimens was calculated.

[0193] Tensile modulus: measured on an INSTRON 5966 machine according to ISO 527-2; the average of the tensile moduli of 5 specimens was calculated.

[0194] A high density indicates good sintering of the powder particles together and successful transformation of the powder into a part.

[0195] The results are presented in Table 4 below.

[0196] [Table 4]

[0197] The powder D' according to the invention, having a lower Hausner index, allows the construction of parts having better density and better mechanical properties.

[0198] The thermal stability of the 3' and D' powders was also evaluated. For this, the powders were subjected to aging as follows: for each of the powders, 100 successive layers were deposited using an EOS Formiga P100 machine, at a temperature of 125°C, without using a laser. For each of the powders, the tapped and untapped densities before and after aging were measured. The delta density, corresponding to the difference between the density of the powder after aging and the density of the aging powder, was calculated.

[0199] The results are shown in the table below. [Table 5]

[0200] It is observed that the comparative powder loses density (unpacked and packed) after passing through the printing machine. Agglomeration of the powders and / or loss of efficiency of the flow agent due to partial anchoring of this agent on the powder particles can explain this phenomenon.

[0201] On the contrary, not only does the powder according to the invention not suffer any loss of density after passing through the printing machine, but it even has a higher unpacked and packed density. This powder can therefore easily be recycled in a new printing process.

[0202] Example 3

[0203] A powder No. G was prepared by subjecting powder No. 8 described in Example 1 to a treatment as described in Example 1 (process according to the invention) but with the following operating parameters:

[0204] - Powder pumping air pressure: 0.32 MPa;

[0205] - Cooling air pressure: 0.35 MPa;

[0206] - Propane flow rate: 17.5 L / min;

[0207] - Oxygen flow rate: 24.5 L / min;

[0208] - Distance from spray gun to collector: 2 m;

[0209] - Transport air pressure: MPa.

[0210] A particle size analysis of powders No. T, A', 3', D', 4, E, 5, F and 8 described in Example 1 and of powder No. G was carried out by laser diffraction according to ISO 13320: 2009 on a Malvern Insitec® type diffraction apparatus. The cumulative fractions (in percentage) of particles less than or equal to 5 pm, less than or equal to 10 pm, less than or equal to 20 pm and less than or equal to 30 pm are reported in the table below. [Table 6]

[0211] It is noted that the application of the method according to the invention makes it possible to reduce the quantity of fine and very fine particles.

Claims

Claims 1. Thermoplastic polymer powder having a Hausner index less than or equal to 1.30 and comprising particles whose particle size distribution is characterized by a SPAN greater than or equal to 1.

0.

2. Powder according to claim 1, in which the thermoplastic polymer is a semi-crystalline thermoplastic polymer.

3. Powder according to claim 1 or 2, wherein the thermoplastic polymer is selected from the group consisting of polyamides, vinylidene fluoride homopolymers and copolymers, polyamide block and polyether block copolymers, thermoplastic polyurethanes, polyester block and polyether block copolymers, polycarbonate, polystyrene, polyaryletherketones, polyolefins and combinations thereof.

4. Powder according to one of claims 1 to 3, in which the thermoplastic polymer is at least one polyamide, preferably a polyamide 11, a polyamide 12 and / or a polyamide 6, and / or a copolymer with polyamide blocks and polyether blocks in which preferably the polyamide blocks are blocks of polyamide 6, polyamide 11, polyamide 12, polyamide 6.10, polyamide 10.10 and / or polyamide 10.12 and the polyether blocks are blocks derived from polyethylene glycol, propylene glycol, polytrimethylene glycol and / or polytetrahydrofuran.

5. Powder according to one of claims 1 to 4, having a Hausner index less than or equal to 1.28, preferably less than or equal to 1.20, more preferably less than or equal to 1.

15.

6. Powder according to one of claims 1 to 5, comprising particles whose particle size distribution is characterized by a SPAN of 1.0 to 2.5, preferably of 1.0 to 2.

0.

7. Powder according to one of claims 1 to 6, in which the cumulative fraction of particles of size less than or equal to 10 μm is less than or equal to 1% by weight, preferably less than or equal to 0.8% by weight, relative to the total weight of the powder and / or the fraction cumulative particle size less than or equal to 30 μm is less than or equal to 10% by weight, preferably less than or equal to 5% by weight, even more preferably less than or equal to 2% by weight, or less than or equal to 1% by weight, relative to the total weight of the powder.

8. Powder according to one of claims 1 to 7, further comprising at least one additive, preferably chosen from the group consisting of flow agents, mineral fillers, fibers, polymer powders, dyes, pigments, fire-resistant additives, antioxidant stabilizers, light stabilizers, impact-resistant agents, antistatic agents, flame-retardant agents, and mixtures thereof.

9. Use of a powder according to one of claims 1 to 8 for the construction of a three-dimensional article, preferably layer by layer, more preferably by sintering, even more preferably by sintering caused by electromagnetic radiation.

10. Use of a powder according to one of claims 1 to 8 for coating a surface, preferably metallic.

11. Use of a powder according to one of claims 1 to 8 for the manufacture of an article by rotational molding.

12. A method for preparing a thermoplastic polymer powder, comprising the following steps: a) providing a thermoplastic polymer powder; b) heating said powder by means of an energy source with a temperature of 600 to 10000°C, preferably 600 to 8000°C, more preferably 1000 to 3000°C; c) preferably pulverizing the powder; d) cooling the powder; and e) collecting the powder.

13. A method according to claim 12, wherein the powder prepared is a powder according to one of claims 1 to 8.

14. The method of claim 12 or 13, wherein the step of providing the thermoplastic polymer powder comprises grinding the thermoplastic polymer, or dissolving the thermoplastic polymer in a solvent and precipitating said thermoplastic polymer in the solvent.

15. A method for encapsulating thermoplastic polymer particles with at least one additive, comprising the following steps: a) providing thermoplastic polymer particles; b) mixing the thermoplastic polymer particles with at least one additive, preferably selected from the group consisting of flow agents, mineral fillers, fibers, polymer powders, dyes, pigments, fire retardant additives, antioxidant stabilizers, light stabilizers, impact suppressants, antistatic agents, flame retardants, and mixtures thereof, so as to form a thermoplastic polymer powder; c) heating said powder using an energy source with a temperature of 600 to 10000°C, preferably 600 to 8000°C, more preferably 1000 to 3000°C; d) spraying the powder, if applicable; e) cooling the powder; and f) collecting the powder.

16. The method of claim 15, wherein the step of providing thermoplastic polymer particles comprises grinding the thermoplastic polymer, or dissolving the thermoplastic polymer in a solvent and precipitating said thermoplastic polymer in the solvent.

17. Method according to one of claims 12 to 16, in which the cooling is carried out by bringing the powder into contact with a cold gas, preferably compressed air, or cold water.

18. Method according to one of claims 12 to 17, in which the collection of the powder is carried out in a recovery tank or in a cyclone.

19. Method according to one of claims 12 to 18, further comprising a step of sieving the collected powder and / or a step of mixing the collected, and optionally sieved, powder with at least one additive, preferably chosen from the group consisting of flow agents, mineral fillers, fibers, polymer powders, dyes, pigments, fire-resistant additives, antioxidant stabilizers, light stabilizers, shock-resistant agents, antistatic agents, flame-retardant agents, and mixtures thereof.

20. Three-dimensional article manufactured from a powder according to one of claims 1 to 8, preferably by layer-by-layer printing, more preferably by sintering.

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