Thermoplastic polymer powders for 3D printing by sintering

Abstract

The present invention mainly relates to a thermoplastic polymer powder suitable for use in 3D printing by sintering, which powder exhibits: - a volume average diameter Dv50 of less than 150 μm, a volume average diameter Dv10 of more than 15 μm and a volume average diameter Dv90 of less than 300 μm, as measured by laser diffraction according to ISO standard 13320:2009; and - a thermal signature characterized by: (i) the presence of two melting peaks Tf1 and Tf2, in which Tf1 is smaller than Tf2, a. the ratio between the associated melting enthalpies (formula (I)) is less than 0.5, as determined according to NF EN ISO standard 11357-3:2018; and b. the difference between the two melting peaks (Tf2-Tf1) is less than 40° C.; or (ii) an asymmetric melting peak characterized by a ratio σ (formula (II)) that is greater than the extrapolated melting onset temperature Tf2. eim , peak melting temperature T pm and the extrapolated melting end temperature T efm a thermal signature characterized by the presence of an asymmetric melting peak, determined from a DSC thermogram measured at a heating rate of 20°C / min in accordance with NF EN ISO standard 11357-3:2018.

Description

[Technical field]

[0001] This patent application relates to a thermoplastic polymer composition for use in 3D printing by sintering, a process for its manufacture, and its use in 3D printing by sintering. [Background technology]

[0002] The construction of 3D articles is often used to produce prototypes or models of parts ("rapid prototyping") or to produce finished parts in small series ("rapid manufacturing"), for example in the automotive, nautical, aviation, aerospace, medical (prostheses, hearing systems, tissue, etc.), textiles, clothing, fashion, decoration, housings for electronic devices, telephony, home automation, computers, lighting, sports and industrial tools sectors.

[0003] Among the techniques for producing 3D articles, the manufacturing process by sintering is particularly advantageous. According to this process, a layer of polymer powder is heated and then selectively and briefly irradiated with electromagnetic radiation (e.g. laser beam, infrared, ultraviolet) in a chamber, resulting in the melting of powder particles bombarded by the radiation. The melted particles coalesce and solidify to form a solid mass. This process allows the production of 3D articles in a simple manner by successively and repeatedly irradiating freshly applied layers of powder.

[0004] The quality of the parts produced and their mechanical properties depend on the properties of the polymer powder. Thermoplastic polymers are valued for their mechanical properties combined with heat and chemical resistance.

[0005] The main brake on the development of 3D printing by laser sintering is the cost of the powder, which can be substantially reduced if the latter is recyclable, for example by adding a certain amount of used powder to a new powder charge.

[0006] The recycling rate depends in particular on the build temperature, which is the temperature to which the powder is exposed throughout the build process, which can last several hours. Under the influence of temperature, polymer powders generally change, in particular their color and / or viscosity, thus limiting the benefits or even the possibilities of reuse.

[0007] In fact, the build temperature is even more difficult to regulate. This is because if the build temperature is too low, curling phenomena occur, i.e. deformation of the built part under the influence of internal stresses that appear when the polymer layer crystallizes too quickly. Curling generally damages all parts assembled in the chamber. Furthermore, problems with agglomeration of the powder bath, which is necessary to support the part during the build, as well as melting defects that affect the mechanical properties of the printed part, may be observed. Conversely, if the build temperature is too high, caking phenomena are observed, i.e. agglomeration of the polymer powder bath under the influence of partial melting of the particles. Powders agglomerated in this way cannot be reused.

[0008] It is known to take into account the thermal properties of the polymer during the development of powders for 3D printing by sintering. The width of the working window, related to the gap between the melting peak and the crystallization peak, is of particular importance, especially in avoiding curling and caking problems. Nevertheless, apart from the specific case of polymorphic polymers, little attention has been paid so far to the influence of the specific shape of the melting peak and the presence of other peaks.

[0009] There is therefore a need to provide thermoplastic polymer powders that exhibit lower costs while allowing better recyclability. Summary of the Invention

[0010] This patent application is based on the unexpected observation that the use of polymer powders exhibiting a specific thermal signature makes it possible to reduce the build temperature. Indeed, reducing the bath temperature can limit the degradation of the powder and therefore increase its recyclability. Furthermore, lowering the bath temperature can widen the working window of a given polymer, thus making the printing process more robust, for example with respect to temperature non-uniformities within the bath, and / or improving the T f and T c It is possible to envisage the use of polymers with a small gap between

[0011] Thus, according to a first aspect, the subject of the present invention is a thermoplastic polymer powder suitable for use in p3D printing by sintering, - a volume mean diameter Dv50 of less than 150 μm, a volume mean diameter Dv10 of more than 15 μm and a volume mean diameter Dv90 of less than 300 μm, as measured by laser diffraction according to ISO standard 13320:2009; a thermal signature, (i) In the two melting peaks Tf1 and Tf2, Tf1 is smaller than Tf2, and the melting peaks are a. Ratio between related enthalpies of fusion: TIFF2024539018000002.tif10170 is less than 0.5, as determined in accordance with NF EN ISO standard 11357-3:2018; and b. The gap between the two melting peaks (Tf2-Tf1) is less than 40°C; or the presence of two melting peaks Tf1 and Tf2, characterized by (ii) Ratio σ: Presence of asymmetric melting peaks characterized by TIFF2024539018000003.tif8170 It is characterized by: Here, the extrapolated melting onset temperature T eim , peak melting temperature T pm , and the extrapolated melting end temperature T efmis determined from DSC thermograms measured at a heating rate of 20 °C / min according to NF EN ISO standard 11357-3:2018, Heat Signature Shows.

[0012] Preferably, the thermoplastic polymer powder exhibits a volume average diameter Dv50 between 45 μm and 130 μm.

[0013] In particular, ratios between 0.05 and 0.2: Powder showing TIFF2024539018000004.tif10170 is preferred.

[0014] According to a preferred embodiment, the thermal signature is characterized by the presence of two peaks Tf1 and Tf2, the gap between these melting peaks extending over a temperature interval ranging from 5° C. to 30° C. Advantageously, it is characterized by an asymmetric peak exhibiting a ratio σ greater than 2.3.

[0015] Advantageously, the melting peak(s) Tf1 and Tf2 extend over a temperature interval ranging from 2°C to 40°C, preferably from 5°C to 30°C, and in particular from 10°C to 20°C.

[0016] Preferably, the thermoplastic polymer powder comprises at least two different thermoplastic polymers.

[0017] According to one embodiment, the thermoplastic polymer powder comprises at least two thermoplastic polymers differentiated by at least one property, in particular viscosity or chemical nature.

[0018] Advantageously, the thermoplastic polymer powder exhibits an inherent viscosity of between 0.65 dl / g and 1.8 dl / g.

[0019] According to a preferred embodiment, the thermoplastic polymer powder comprises at least one polymer selected from polyamides and thermoplastic elastomers, more preferably PA11, PA12, and polyether block amides.

[0020] According to a second aspect, the present invention provides a method for producing a composition comprising the steps of: (i) milling at least one thermoplastic polymer to obtain a powder having a volume average diameter Dv50 of less than 150 μm, a volume average diameter Dv10 of more than 15 μm, and a volume average diameter Dv90 of less than 300 μm, as measured by laser diffraction according to ISO standard 13320:2009; and, if appropriate, (ii) blending said thermoplastic polymer with another thermoplastic polymer before, during, or after step (i). The present invention relates to a method for producing such a thermoplastic polymer powder, comprising the steps of: This ensures that the powder obtained at the end of the process exhibits the thermal signature defined above.

[0021] According to a third aspect, the present invention is directed to the use of a thermoplastic polymer powder as defined above for 3D printing by sintering, in particular by laser sintering.

[0022] The invention will be better understood in light of the following description and drawings. [Brief description of the drawings]

[0023] [Figure 1] Device for 3D printing by sintering using the SLS (Selective Laser Sintering) method [Diagram 2] Thermogram of the polyamide powder according to Example 1 showing the heat flow Q (in W / g) required to heat the sample at a given rate of 20° C. / min as a function of temperature T. [Diagram 3] Thermogram of the polyamide powder according to Example 2 showing the heat flow Q (in W / g) required to heat the sample at a given rate of 20° C. / min as a function of temperature T. [Figure 4] Thermogram of the polyamide powder according to Example 3 showing the heat flow Q (in W / g) required to heat the sample at a given rate of 20° C. / min as a function of temperature T. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] [Definition] The term "powder" is understood to mean a solid substance in finely divided form; this is generally provided in the form of particles of very small size, generally of the order of a few hundred micrometers or less.

[0025] The term "melting temperature" is understood to refer to the temperature at which an at least partially crystalline compound passes into a viscous liquid state, measured according to NF EN ISO standard 11357-3:2018. Unless otherwise indicated, this is more particularly the peak melting temperature, as defined below.

[0026] More specifically, the following terms related to melting temperatures are understood to be defined in accordance with ISO standard 11357-1:2016: "Peak" refers to a portion of a thermogram obtained by differential scanning calorimetry (DSC) that deviates from the baseline of the specimen, reaches a maximum or minimum, and then returns to the baseline of the specimen. Such a peak may represent a first-order transition; "Endothermic peak" refers to a peak where the heat flow delivered to the specimen crucible is greater than that of the reference crucible. This corresponds to a transition that absorbs heat; "Baseline" refers to the part of the recorded thermogram that does not involve any transition, in this case specifically a first order transition of melting type. In the transition zone, a virtual baseline can be determined: this is an imaginary line plotted through the transition zone, where the heat due to the transition is assumed to be zero. The virtual baseline can be plotted by interpolating the baseline of the specimen with a straight line; "Peak area" refers to the area bounded by the peak and the interpolated virtual baseline. This corresponds to the transition enthalpy expressed in J / g; "Extrapolated melting onset temperature" T eim denotes the intersection of the interpolated virtual baseline with the tangent at the inflection point of the peak onset; "Peak melting temperature" T pmindicates the temperature at which the distance between the thermogram and the virtual baseline during the peak is maximum; "Extrapolated End Temperature" T efm indicates the intersection point between the virtual baseline and the tangent at the inflection point at the peak end.

[0027] The term "enthalpy of fusion" is understood to mean the heat required to melt a composition, which corresponds to the area under the melting peak(s) on the thermogram, measured in accordance with NF EN ISO standard 11357-3:2018.

[0028] The term "Dv50" is understood to mean the value of the diameter of the powder particles for which the cumulative distribution function of the diameters of the particles weighted by volume is equal to 50%. The value of "Dv50" is measured by laser diffraction, for example using a Malvern Mastersizer 2000® diffractometer, in accordance with ISO standard 13320:2009. Similarly, "Dv10" and "Dv90" are the corresponding diameters for which the cumulative distribution function of the diameters of the particles weighted by volume is equal to 10% and 90%, respectively. The rules for the expression of the results of the particle size distribution are given by ISO standard 9276-parts 1 to 6.

[0029] The term "viscosity" is understood to denote the inherent viscosity measured according to ISO standard 307:2007. The term "viscosity" is understood to denote the inherent viscosity measured with a Ubbelohde viscometer according to ISO standard 307:2019, except that m-cresol is used as the solvent and the temperature is 20° C. The inherent viscosity has the dimension of the reciprocal of the concentration and is equal to the natural logarithm of the relative viscosity divided by the concentration of the polymer dissolved in the solvent.

[0030] The term "3D printing by sintering" is understood to refer to a technique aimed at the production of parts by additive manufacturing, in which powder is selectively melted by means of a laser or electromagnetic radiation, such as infrared light.

[0031] The term "crystallinity" is understood to refer to the degree of crystallinity calculated from wide-angle X-ray scattering (WAXS) measurements on a Nano-inXider® type device under the following conditions: - Wavelength: Main Kα1 line of copper (1.54 Angstroms). - Generator power: 50kV - 0.6mA. - Observation mode: Transmit - Counting time: 10 minutes

[0032] In this way, a spectrum of the scattering intensity as a function of the diffraction angle is obtained. This spectrum makes it possible to confirm the presence of crystals if, in addition to the amorphous halo, peaks are visible on the spectrum. In this spectrum, the area of ​​the crystalline peak (designated A) and the area of ​​the amorphous halo (designated AH) can be measured. The proportion (by weight) of crystalline polymer in the sample is estimated by the ratio (A) / (A+AH).

[0033] The thermograms referred to in this patent application are obtained by differential scanning calorimetry (DSC) analysis of about 10 mg of the test composition on the first heat using a temperature gradient of 20° C. / min, in accordance with NF EN ISO standard 11357-3:2018. In particular, the start temperature can be about 20° C. and the end temperature can be about 260° C. Thermograms such as those shown in the figures can be obtained using a Q2000 differential scanning calorimeter sold by TA Instruments.

[0034] Indefinite and definite articles such as "a", "an" or "the" by default mean, in the context of the present description, "at least one" and "said at least one", respectively.

[0035] A. Thermoplastic polymer powder The thermoplastic polymer powder provided according to the present invention comprises - a volume mean diameter Dv50 of less than 150 μm, a volume mean diameter Dv10 of more than 15 μm and a volume mean diameter Dv90 of less than 300 μm, as measured by laser diffraction according to ISO standard 13320:2009; a heat signature, (i) In the two melting peaks Tf1 and Tf2, Tf1 is smaller than Tf2, and the melting peaks are a. Ratio between related enthalpies of fusion: TIFF2024539018000005.tif10170 is less than 0.5, as determined in accordance with NF EN ISO standard 11357-3:2018; and b. The gap between the two melting peaks (Tf2-Tf1) is less than 40°C; the presence of two melting peaks Tf1 and Tf2, (ii) Ratio σ: Presence of asymmetric melting peaks characterized by TIFF2024539018000006.tif8170 Thermal signatures, indicates, Here, the extrapolated melting onset temperature T eim , peak melting temperature T pm , and the extrapolated melting end temperature T efm is determined from DSC thermograms measured at a heating rate of 20° C. / min according to NF EN ISO standard 11357-3:2018.

[0036] Thermoplastic polymers that can be used in the context of the present invention can be chosen in particular from polyolefins such as polypropylene and polyethylene (olefin-based waxes do not depart from the scope of the invention), polycarbonates, polymethylmethacrylate (PMMA), polyamides such as polyether block amides (PEBA) and thermoplastic elastomers, polyesters with polyether blocks (COPE), thermoplastic polyurethanes (TPU), or blends thereof.

[0037] Aliphatic polyamides are particularly preferred, in particular long-chain aliphatic polyamides, ie those containing at least 8 carbon atoms per amide group, especially PA11 and PA12, and also polyether block amides.

[0038] Polyether block amides are copolymers comprising polyamide blocks and polyether blocks. Preferably, they are linear (non-crosslinked) copolymers.

[0039] PEBA copolymers can result from the polycondensation of a polyamide (PA) block having a reactive end and a polyether (PE) block having a reactive end. Examples include: - polyamide blocks having diamine chain ends polycondensed with polyoxyalkylene blocks having dicarboxylic chain ends; - a polyamide block having dicarboxylic chain ends polycondensed with a polyoxyalkylene block having diamine chain ends; or - polyamide blocks with dicarboxylic chain ends polycondensed with polyether diols (the resulting products are in this case polyether ester amides).

[0040] The polyamide blocks with dicarboxyl chain ends result, for example, from the condensation of polyamide precursors in the presence of a chain-limiting dicarboxylic acid. The polyamide blocks with diamine chain ends result, for example, from the condensation of polyamide precursors in the presence of a chain-limiting diamine. These polyamide blocks can be homopolyamides or copolyamides. It can concern in particular one of the polyamide PA11, PA12 or PA6 blocks or blends thereof.

[0041] The polyether blocks of PEBA essentially comprise or consist of alkylene oxide units. They can be obtained from alkylene glycols, such as PEG (polyethylene glycol), PPG (polypropylene glycol), PO3G (polytrimethylene glycol) or PTMG (polytetramethylene glycol), preferably PTMG. They can also result from copolyethers containing different alkylene oxides, either uniformly in the chain, in particular in blocks, or randomly distributed. Polyether blocks can also be obtained by oxyethylation of bisphenols, such as bisphenol A. These products are described, in particular, in EP 613 919 A1. The polyether blocks can also be ethoxylated primary amines. The polyether blocks can finally comprise or consist of polyoxyalkylene blocks with NH2 chain ends, such blocks being obtainable by cyanoacetylation of polyether diols. Such polyethers are sold by Huntsman under the name Jeffamine® or Elastamine® (e.g. Jeffamine® D400, D2000, ED2003, or XTJ 542).

[0042] The number average molar mass (Mn) of the polyamide blocks in the PEBA is preferably from 400 to 1500 g / mol, more preferably from 500 to 1200 g / mol, even more preferably from 500 to 1000 g / mol. The number average molar mass (Mn) of the polyether blocks is preferably from 400 to 1500 g / mol, more preferably from 500 to 1200 g / mol, and even more preferably from 500 to 1000 g / mol.

[0043] A two-step process for the preparation of PEBA with ester bonds between the PA and PE blocks is described in FR 2 846 332. A process for the preparation of PEBA with amide bonds between the PA and PE blocks is described in EP 1 482 011. The polyether block can also be mixed with a polyamide precursor and a diacid chain limiter to prepare PEBA in a one-step process.

[0044] PEBAs generally comprise polyamide blocks and polyether blocks, but they can also comprise two, three, four or indeed even more different blocks.

[0045] According to one embodiment, the proportion by weight of the polyether blocks in the copolymer is at least 50% relative to the total weight of the copolymer. Preferably, the proportion by weight of the polyether blocks is between 55% and 85% relative to the total weight of the copolymer, more preferably between 60% and 80% relative to the total weight of the copolymer. The proportion by weight of the blocks in the copolymer can be determined from the number-average molar mass of the blocks.

[0046] Particularly preferred PEBAs are those that exhibit an instantaneous hardness (Shore D) of less than 50, more preferably between 35 and 45, measured according to ISO standard 868:2003.

[0047] It will be appreciated that the designation PEBA in this description of the invention relates to Pebax® products sold by Arkema, Vestamid® products sold by Evonik®, and Grilamid® products sold by EMS, as well as to Pelestat® type PEBA products sold by SANYO Electric Co., Ltd., or any PEBA products of other suppliers.

[0048] According to one embodiment, the thermoplastic polymer powder exhibits a melting enthalpy of more than 25 J / g, or between 25 and 30 J / g, or between 30 and 40 J / g, or between 40 and 50 J / g, or between 50 and 60 J / g, or between 60 and 70 J / g, or between 70 and 80 J / g, or between 80 and 90 J / g, or between 90 and 100 J / g, or between 100 and 110 J / g, or between 110 and 120 J / g, or between 120 and 130 J / g. Particularly advantageous are thermoplastic polymer powders exhibiting a melting enthalpy between 30 and 110 J / g. More particularly, the melting enthalpy varies depending on the polymer envisaged. Thus, the melting enthalpy of polyamides may in particular be between 70 and 110 J / g, whereas the melting enthalpy of PEBA will preferably be between 25 and 50 J / g.

[0049] The thermoplastic polymer powder generally comprises at least 50% by weight of thermoplastic polymer, based on the total weight of the powder. According to some embodiments, the powder comprises at least 75% by weight, or at least 80% by weight, or at least 85% by weight, or at least 90% by weight, or at least 92.5% by weight, or at least 95% by weight, or at least 97.5% by weight, or at least 98% by weight, or at least 98.5% by weight, or at least 99% by weight, or at least 99.5% by weight of thermoplastic polymer, based on the total weight of the thermoplastic polymer powder of the invention.

[0050] According to some embodiments, the thermoplastic polymer powder may include only a single thermoplastic polymer, for example one polyolefin, one polyamide, or one polyether block amide.

[0051] Alternatively, the thermoplastic polymer powder can include two or more different thermoplastic polymers, which can be distinguished in particular by their chemical nature, for example blends of polyolefins, polyamides, or polyether block amides.

[0052] According to some embodiments, the powder according to the invention comprises several polymers, whether of the same chemical nature or not, that are differentiated by at least one property. These properties may in particular be viscosity, crystallinity and crystallization rate. Thus, the powder according to the invention may comprise, for example, a polyamide or polyether block amide and a polyolefin wax.

[0053] To be suitable for 3D printing by sintering, thermoplastic polymer powders must meet certain criteria, especially with regard to particle size distribution.

[0054] According to the invention, the thermoplastic polymer powder exhibits a volume average diameter Dv50 of less than 150 μm. According to some embodiments, the thermoplastic polymer powder exhibits a volume average diameter Dv50 of between 45 μm and 130 μm, in particular between 50 μm and 120 μm, and more particularly between 55 μm and 100 μm.

[0055] In addition to the average diameter, the particle size distribution of thermoplastic polymer powders can have a significant impact on the performance quality of 3D printing by sintering.

[0056] Thus, according to the invention, the thermoplastic polymer powder exhibits a volume average diameter Dv10 of more than 15 μm. According to some embodiments, the thermoplastic polymer powder exhibits a volume average diameter Dv10 of between 20 μm and 60 μm, in particular between 25 μm and 45 μm, in particular between 30 μm and 40 μm.

[0057] Thus, according to the invention, the thermoplastic polymer powder exhibits a volume average diameter Dv90 of less than 300 μm. According to some embodiments, the thermoplastic polymer powder exhibits a volume average diameter Dv90 of between 100 μm and 300 μm, in particular between 120 μm and 250 μm, in particular between 140 μm and 200 μm.

[0058] The polymer powder composition according to the invention is further characterized by a specific thermal signature, which is characteristic because the melting peak is not symmetrical, as is the case conventionally, but unique, and according to the invention, this thermal signature comprises either two melting peaks or an asymmetric melting peak, for example due to the presence of another transition close to the melting point.

[0059] This type of thermal signature is observed, for example, when other phase transitions are present near the melting point. Normally, such phase transitions are considered a risk that would prevent, and in fact prohibit, 3D printing with sintering of satisfactory quality.

[0060] Indeed, it has been unexpectedly found that such thermal signatures can allow for lower build temperatures in that they can enable melting to begin at a lower temperature, thus reducing thermal degradation of the powder during the build process and therefore increasing the potential for reuse, thereby significantly reducing the cost of printing materials.

[0061] According to the invention, the thermal signature of the thermoplastic polymer powder can be characterized by the presence of two melting peaks Tf1 and Tf2 close to each other, i.e. not more than 40° C. apart from each other, and the melting peak Tf1 at the lower temperature is significantly smaller than the melting peak Tf2 at the higher temperature, whereby the ratio between the melting enthalpies associated with these peaks is: It is characterized by the fact that TIFF2024539018000007.tif10170 is less than 0.5.

[0062] Alternatively, the thermal signature of a thermoplastic polymer powder can be characterized by the presence of an asymmetric peak. The asymmetry is determined by the ratio σ: TIFF2024539018000008.tif8170, where the extrapolated melting onset temperature T eim , peak melting temperature T pm , and the extrapolated melting end temperature T efmis determined from DSC thermograms measured at a heating rate of 20° C. / min according to NF EN ISO standard 11357-3:2018.

[0063] If the thermoplastic polymer powder exhibits several melting peaks, preferably the melting peaks are spread over a temperature interval ranging from 2°C to 40°C, preferably from 5°C to 30°C, especially from 10°C to 20°C.

[0064] This is because it is generally preferable that the melting peaks are not too far apart: thus, for example, in 3D printing by selective laser melting (SLS), if the build temperature is below the melting temperature Tf1 and too far away from the temperature Tf2, then it is necessary to use too high a laser power or to make several passes of the laser (multi-scan).

[0065] According to the invention, the ratio between the melting enthalpies associated with these peaks: TIFF2024539018000009.tif10170 is less than 0.5. Advantageously, this ratio may be between 0.02 and 0.4, in particular between 0.05 and 0.2.

[0066] According to one embodiment, the melting enthalpy associated with the melting peak Tf1 is greater than 2 J / g, or between 2 and 5 J / g, or between 5 and 10 J / g, or between 10 and 15 J / g, or between 15 and 20 J / g, or between 20 and 25 J / g, or between 25 and 30 J / g, or between 30 and 35 J / g, or between 35 and 40 J / g, or between 40 and 50 J / g, or between 50 and 60 J / g, or between 60 and 70 J / g. Particularly advantageous are thermoplastic polymer powders that exhibit a melting enthalpy associated with the melting peak Tf1 between 2 and 40 J / g.

[0067] According to another embodiment, the melting enthalpy associated with the melting peak Tf2 is greater than 15 J / g, or between 15 and 20 J / g, or between 20 and 30 J / g, or between 30 and 40 J / g, or between 40 and 50 J / g, or between 50 and 60 J / g, or between 60 and 70 J / g, or between 70 and 80 J / g, or between 80 and 100 J / g, or between 100 and 120 J / g, or between 120 and 130 J / g. Particularly advantageous are thermoplastic polymer powders that exhibit a melting enthalpy associated with the melting peak Tf2 between 20 and 130 J / g.

[0068] If the thermoplastic polymer powder exhibits an asymmetric peak, the asymmetric peak is characterized by a σ value greater than 2.0, preferably greater than 2.3. Advantageously, σ is between 2.0 and 6.0, in particular between 2.2 and 5.0, and especially between 2.3 and 4.0.

[0069] According to some embodiments, the thermoplastic polymer powders have an inherent viscosity of 0.65 dl / g to 1.8 dl / g, preferably 0.9 dl / g to 1.4 dl / g, and more preferably 1.0 dl / g to 1.3 dl / g. These powders are particularly advantageous in that they make it possible to obtain a good compromise between good coalescence properties during sintering (sufficiently low viscosity) and good mechanical properties of the sintered body (sufficiently high viscosity).

[0070] The thermoplastic polymer powder may contain, in addition to the thermoplastic polymer(s), one or more conventional additives and fillers.

[0071] 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 relative to the total weight of the powder. Among the additives, mention may be made of flow agents, stabilizers (light stabilizers, especially UV stabilizers and heat stabilizers), optical brighteners, dyes, pigments, and energy absorbing additives (including UV absorbers).

[0072] Among the flow agents, mention may be made, for example, of hydrophilic or hydrophobic silica. Advantageously, the flow agent represents from 0.01% to 0.5% by weight relative to the total weight of the composition. Preferably, the thermoplastic polymer powder comprises from 0.1% to 0.4% by weight of flow agent.

[0073] The thermoplastic polymer powder may also contain one or more fillers. The fillers generally represent less than 50% by weight, preferably less than 40% by weight, relative to the total weight of the final powder. Among the fillers, mention may be made, inter alia, of reinforcing fillers, in particular inorganic fillers such as carbon black, talc, carbon nanotubes or non-carbon nanotubes, fibers (glass, carbon, etc.), whether or not ground.

[0074] B. Manufacturing process of thermoplastic polymer powder The thermoplastic polymer powder can in particular be obtained by comminuting a thermoplastic polymer in the form of extruded granules or flakes, according to conventional techniques.

[0075] The grinding can be carried out using items of equipment known for this purpose, such as pin mills, hammer mills, or whirl mills. If the powder contains some polymers and / or certain additives and / or certain reinforcing fillers, some or all of them can be incorporated by melt mixing, e.g. extrusion (compounding) and granulation, followed by grinding the granules. Alternatively, other polymers and / or certain additives and / or certain reinforcing fillers can be added by dry blending. Preferably, the flow agent is added by dry blending.

[0076] According to one embodiment, particularly for polyamides, the process for producing the powder composition comprises: (a) prepolymerization of the monomer(s) of the thermoplastic polymer, followed by granulation; (b) grinding the resulting prepolymer powder, followed by optional sieving; (c) subjecting the obtained, optionally sieved, prepolymer powder to solid-state polycondensation to obtain a polymer powder; Includes stages.

[0077] The additives and / or reinforcing fillers can be added to the prepolymer by melt blending (compounding) before grinding or by dry blending. Alternatively, the additives and / or reinforcing fillers can be added subsequently to the polymer powder by dry blending.

[0078] C. Use of Powder The described thermoplastic polymer powders are particularly useful in processes for 3D printing by sintering.

[0079] Preferably, the compositions of the invention are used in selective laser sintering (SLS) processes, MJF (multi-jet fusion) type sintering processes, or HSS (high speed sintering) type sintering processes.

[0080] The SLS process is widely known: in this connection reference may be made in particular to US Pat. No. 6,136,948 and WO 96 / 06881.

[0081] In this type of process, a thin layer of powder is deposited on a horizontal plate maintained in a chamber heated to a temperature called the build temperature. In most cases, heating to the build temperature is performed using IR radiating lamps, e.g. halogen lamps, with emission maxima generally at wavelengths between 750 nm and 1250 nm.

[0082] The build temperature refers to the temperature to which the powder bed of the constituent layers of the three-dimensional article being built is heated during the layer-by-layer sintering process of the powder.

[0083] Then, electromagnetic radiation, for example in the form of a laser, supplies the energy necessary to sinter the powder particles at different points of the powder layer according to the shape corresponding to the object, for example using a computer that stores the shape of the object in memory and recreates it in the form of slices. The horizontal plate is then lowered a height corresponding to the thickness of the powder layer and a new layer of powder is similarly spread, heated and then sintered. This procedure is repeated until the object is produced.

[0084] The powder layer deposited on the horizontal plate may have a thickness of, for example, 20 μm to 200 μm, preferably 50 μm to 150 μm, before sintering. After sintering, the thickness of the layer of agglomerated material is slightly reduced and may have a thickness of, for example, 10 μm to 150 μm, preferably 30 μm to 100 μm.

[0085] In the MJF and HSS processes, the entire layer of build material is exposed to radiation, but only the portions covered with a fuser melt into layers of the 3D part. The fuser is a compound, such as black ink, that can absorb radiation and convert it into thermal energy. It is selectively applied to selected areas of the build material. The fuser can penetrate the layer of build material and transfer the absorbed energy to adjacent build material, thereby melting or sintering the build material. The melting, bonding, and subsequent hardening of each layer of build material forms the object.

[0086] In the specific case of MJF, more detailing agents are added to the edges of the melted zone to allow the part to have greater definition.

[0087] Advantageously, the use of the polymer powder composition of the invention in these processes does not require any special modifications, while making it possible to obtain parts that exhibit lower roughness and better definition, as mentioned above.

[0088] The polymer powder composition according to the invention can be recycled and reused in several successive build-ups, either alone or mixed with other recycled or non-recycled powders.

[0089] As an example, the use of the described thermoplastic polymer powder in a process for layer-by-layer building of three-dimensional objects by sintering induced by electromagnetic radiation in a device 1 as shown diagrammatically in FIG. 1 is described below.

[0090] The electromagnetic radiation may for example be infrared, ultraviolet or preferably laser radiation. In particular, in a device 1 as shown diagrammatically in figure 1, the electromagnetic radiation may comprise a combination of infrared 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 chamber 10 in which is arranged a supply tank 40 containing a thermoplastic polymer powder and a movable horizontal plate 30. The horizontal plate 30 can also function as a support for the three-dimensional object 80 to be built. Nevertheless, objects produced from thermoplastic polymer powder generally do not require additional supports and can generally be self-supported by the unsintered powder of the previous layer.

[0093] According to this process, thermoplastic polymer powder is drawn from a supply tank 40 and deposited on a horizontal plate 30 to form a thin layer 50 of constituent powder of the three-dimensional object 80 to be built. The powder layer 50 is heated by infrared radiation 100 to a predetermined minimum build temperature T c A substantially uniform temperature equal to

[0094] The energy required to sinter the particles of the thermoplastic polymer powder at various points of the powder layer 50 is then contributed by the laser radiation 200 of the mobile laser 20 in the plane (xy), according to a shape corresponding to the shape of the object. The molten powder resolidifies to form a sintered part 55, while the remaining part of the layer 50 remains in the form of unsintered powder 56. Generally, a single pass of a single laser radiation 200 is sufficient to ensure sintering of the powder. Nevertheless, in some embodiments, it is also possible to envisage several passes over the same location and / or multiple electromagnetic radiations impinging on the same location to ensure sintering of the powder.

[0095] The horizontal plate 30 is then lowered along the axis (z) a distance corresponding to the thickness of the powder layer and a new layer is deposited. The laser 20 provides the energy necessary to sinter the powder particles according to the shape corresponding to this new slice of the object, etc. This procedure is repeated until the object 80 is produced.

[0096] The temperature of the layer below the layer being built, in the sintering chamber 10, may be lower than the build temperature. However, this temperature generally remains above the glass transition temperature of the powder, and in fact much higher than the transition temperature. The temperature at the bottom of the chamber is referred to as T b T c A temperature T, known as the "tank bottom temperature", which is less than 40° C. lower, preferably less than 25° C. lower, and more preferably less than 10° C. lower. b It is particularly advantageous to keep

[0097] Once the object 80 is completed, it is removed from the horizontal plate 30 and the unsintered powder 56 is sieved before being at least partially returned to the supply tank 40 to serve as recycled powder. Recycling of the powder is accomplished by removing the build temperature T cis generally lower than in conventional shaping processes, which makes it possible to reduce the degradation of the green powder subjected to the temperature conditions of at least one shaping by sintering. The recycled thermoplastic polymer powder can be used as it is or blended with new powder.

[0098] In particular, in the embodiment in which the thermoplastic polymer powder consists of a blend of powders P1 and P2, the build temperature can be lower than that used in a conventional build process using a composition (not according to the invention) consisting of powder P1. This makes it possible to envisage an improved recycling of the unsintered powder composition in subsequent builds. Advantageously, the recycled powder blend can be subjected to a build temperature T lower than the build temperature of the conventional build process. c To maintain the consistency, it is blended with fresh powders P and / or P2.

[0099] The present invention is explained in further detail in the following examples. EXAMPLES

[0100] In the following examples, several thermoplastic polymer powders exhibiting different particle size distributions and thermal signatures were examined for their behavior in 3D printing by sintering.

[0101] Example 1 As a reference, a polyamide 11 powder formulated for 3D printing sold under the name Rilsan® Invent Natural (RIN) by Arkema France was used.

[0102] The thermal signature of the polyamide 11 powder was characterized by differential scanning calorimetry (DSC) performed on a TA Instruments Q2000 calorimeter according to ISO standard 11357-3:2013. In the thermogram shown in Figure 2, the dotted line represents the baseline and the solid line represents the tangent to the edge of the melting peak at the inflection point. Temperature T eim and T efmis the temperature at which the baseline intersects the tangent to the edge. pm is the minimum temperature of the melting peak. Temperature T pm , T eim , and T efm was determined from the thermogram shown in FIG. 2 and is shown in Table 2 below.

[0103] The powder was then analyzed by laser diffraction with a Malvern Insitec diffractometer and RTSizer software, on a dry route, at a pressure of 7.5 bar and 10 m, in accordance with ISO standard 13320:2009. 3 / h air flow rate, its Dv50 average diameter is 49 μm, its Dv10 average diameter is 23 μm, and its Dv90 average diameter is 90 μm.

[0104] Example 2 The plastic polymer powder was prepared by dry blending 90% by weight of polyamide 11 powder sold under the name Rilsan® Invent Natural by Arkema France with 10% by weight of heat-treated polyamide 11 obtained according to the following process:

[0105] First, polyamide 11 prepolymer was synthesized from 1.2 kg of 11-aminoundecanoic acid in the presence of 0.5 kg of water, 5 g of hypophosphorous acid, and 9.8 g of phosphoric acid. As soon as the temperature reached 160°C or the pressure exceeded 8.5 bar, the mixture was heated to a temperature of 190°C for 2 hours with stirring. During the synthesis, the water with which the 11-aminoundecanoic acid was initially added was removed by evaporation at constant pressure (P = 10 bar). After removing 430 g of water, the molten prepolymer was extruded in a twin-screw extruder. The mixture was then cooled, solidified, cooled and crushed to obtain flakes using two steel rollers while circulating cold water.

[0106] The recovered prepolymer is then ground in a hammer mill equipped with an internal selector until a powder having a volume median diameter Dv50 of 49 μm is obtained. The powder thus obtained is then subjected to solid-state polycondensation in a dryer at 180° C. under vacuum to increase the viscosity of the polyamide to 1.1 dl / g.

[0107] The resulting polyamide 11 powder was then sieved on a 150 μm square mesh.

[0108] The obtained powder was heated at a temperature T pm , T eim , and T efm These temperatures were determined from thermograms measured by differential scanning calorimetry (DSC) on a TA Instruments Q2000 calorimeter in accordance with ISO standard 11357-3:2013. In the thermograms shown in FIG. 3, the dotted line represents the baseline and the solid line represents the tangent to the edge of the melting peak at the inflection point. Temperature T eim and T efm is the temperature at which the baseline intersects the tangent to the edge. pm is the minimum temperature of the peak. The angle of the tangent line has been adjusted to take into account the low temperature spread preceding the melting peak.

[0109] Furthermore, this powder is characterized by its Dv50 average diameter of 49 μm, its Dv10 average diameter of 23 μm, and its Dv90 average diameter of 90 μm, as measured by laser diffraction on a Malvern Insitec diffractometer, according to ISO standard 13320:2009, as described in Example 1.

[0110] Example 3 The thermoplastic polymer powder was prepared by dry blending 90% by weight of polyamide 11 powder sold under the name Rilsan® Invent Natural by Arkema France with 10% by weight of polyamide 12 sold under the name Orgasol Invent Smooth by Arkema, exhibiting a Dv10 of 31 μm, a Dv50 of 40 μm and a Dv90 of 50 μm.

[0111] The powder obtained exhibits a thermal signature characterized by two melting temperatures Tf1 and Tf2, as shown in Table 2. These temperatures were determined from the thermogram shown in Figure 4, measured by differential scanning calorimetry (DSC) in a TA Instruments Q2000 calorimeter according to ISO standard 11357-3:2013. The difference between the two melting peaks Tf1 and Tf2 is 19°C. The ratio of the enthalpy of Tf1 to that of Tf2 is 0.1.

[0112] Furthermore, this powder is characterized by its Dv50 average diameter of 49 μm, its Dv10 average diameter of 23 μm, and its Dv90 average diameter of 90 μm, as measured by laser diffraction on a Malvern Mastersizer 2000® diffractometer, according to ISO standard 13320:2009, as described in Example 1. [Table 1] TIFF2024539018000010.tif55170[Table 2] TIFF2024539018000011.tif33170

[0113] Powder behavior in 3D printing The resulting polymer powder was then used to produce specimen 1BA XY (specimen 1BA, based on ISO standard 527-1BA, called "XY" because it is printed on the horizontal plane of the printer) on a P100 machine (sold by EOS) by 3D printing with laser sintering, adjusting the powder layer thickness to 100 μm. The printing parameters used were: Laser power: 24W Laser speed: 3000mm / sec Distance between two laser paths: 0.25mm

[0114] On the one hand, it was found that the powder of Example 2 could be sintered at a build temperature 9° C. lower than that of Powder 1 (183° C. for Powder 1 vs. 174° C. for Powder 2). Nevertheless, the specimens obtained from Powders 1 and 2 had comparable mechanical properties. In fact, the reduction in build temperature makes it possible to reuse Powder 2, which is less thermally degraded during the build process, to a great extent, thus allowing a significant reduction in material costs for 3D printing.

[0115] On the other hand, it was observed that the powder of example 3 also makes it possible to obtain good quality test pieces at a lower shaping temperature than that of powder 1. As a result, it is therefore possible to take advantage of the presence of several melting peaks, as long as they are not too far apart.

[0116] These examples are characterized by the presence of two melting peaks separated by less than 40° C. and the associated melting enthalpy ΔH f1 and ΔH f2 It has been shown that powders with a specific particle size distribution, characterized by a ratio between σ and σ <0.5, combined with a complex thermal signature, make it possible to reduce the build temperature during 3D printing, thus limiting thermal degradation and therefore reducing material costs.

[0117] [References list] [U.S. Patent No. 6,136,948] [International Publication No. 96 / 06881]

Claims

1. A thermoplastic polymer powder suitable for use in 3D printing by sintering, - having a volume average diameter Dv50 of less than 150 μm, a volume average diameter Dv10 of more than 15 μm, and a volume average diameter Dv90 of less than 300 μm, measured by laser diffraction in accordance with ISO standard 13320:2009, and - a thermal signature, (i) Two melting peaks Tf １ and Tf ２ In this case, Tf １ is Tf ２ Smaller, a. the ratio between the associated enthalpies of fusion: being less than 0.5, determined in accordance with NF EN ISO standard 11357-3:2018; and b. The gap between the two melting peaks (Tf ２ -Tf １ ) is less than 40°C; Two melting peaks Tf １ and Tf ２ The existence of, or (ii) the ratio σ: an asymmetric melting peak characterized by an extrapolated melting onset temperature T ｅｉｍ , peak melting temperature T ｐｍ , and the extrapolated melting end temperature T ｅｆｍ is determined from a DSC thermogram measured at a heating rate of 20°C / min in accordance with NF EN ISO standard 11357-3:2018; the presence of an asymmetric melting peak, characterizing the thermal signature is shown by the thermoplastic polymer powder.

2. The thermoplastic polymer powder according to claim 1, characterized in that it exhibits a volume average diameter Dv50 between 45 μm and 130 μm.

3. The ratio: is between 0.05 and 0.2, of the thermoplastic polymer powder according to claim 1.

4. Thermal signature with two peaks Tf １ and Tf ２ and the gap between these melting peaks is spread over a temperature interval ranging from 5°C to 30°C.

5. The thermoplastic polymer powder according to claim 1, characterized in that the thermal signature exhibits an asymmetric peak with a ratio σ greater than 2.

3.

6. One or more melting peaks Tf １ and Tf ２ 2. The thermoplastic polymer powder according to claim 1, wherein V extends over a temperature interval ranging from 2°C to 40°C, preferably from 5°C to 30°C, in particular from 10°C to 20°C.

7. The thermoplastic polymer powder according to claim 1, comprising at least two different thermoplastic polymers.

8. The thermoplastic polymer powder according to claim 1, comprising at least two thermoplastic polymers distinguished by at least one property, particularly viscosity.

9. The thermoplastic polymer powder according to claim 1, comprising at least two different thermoplastic polymers with different chemical properties.

10. The thermoplastic polymer powder according to claim 1, having an inherent viscosity of 0.65 dl / g to 1.8 dl / g, measured with an Ubbelohde viscometer in accordance with ISO standard 307:2019, except that m-cresol is used as the solvent and the temperature is 20°C.

11. The thermoplastic polymer powder according to claim 1, comprising at least one polymer selected from polyamide and thermoplastic elastomer.

12. The thermoplastic polymer powder according to claim 11, comprising at least one polymer selected from PA11, PA12, and polyether block amide.

13. a. grinding at least one thermoplastic polymer to obtain a powder having a volume average diameter Dv50 of less than 150 μm, a volume average diameter Dv10 of more than 15 μm, and a volume average diameter Dv90 of less than 300 μm, as measured by laser diffraction according to ISO standard 13320:2009; and, if appropriate, b. blending said thermoplastic polymer with another thermoplastic polymer before, during, or after step (i); comprising the steps of: whereby at the end of the process the powder obtained exhibits the thermal signature according to claim 1. A method for producing the thermoplastic polymer powder according to any one of claims 1 to 12.

14. 10. Use of the powder according to claim 1 for 3D printing by sintering.

15. 15. Use according to claim 14 for 3D printing by laser sintering.

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