Thermoplastic polymer powder for 3D printing by sintering

Abstract

The invention relates mainly to a thermoplastic polymer powder suitable for use in 3D printing by sintering, having: a volume mean diameter Dv50 less than 150 µm, a volume mean diameter Dv10 greater than 15 µm and a volume mean diameter Dv90 less than 300 µm, as measured by laser diffraction according to ISO 13320:2009, and a thermal signature characterized by the presence of: (i) two melting peaks Tf1 and Tf2, Tf1 being less than Tf2, said melting peaks being characterized in that: a. the ratio between the associated enthalpies of melting, as determined according to NF EN ISO 11357-3:2018 is less than 0.5; 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 : σ = > 2.0 where the extrapolated start-melting temperature Teim, peak melting temperature Tpm and end-melting temperature Tefm are determined from a DSC thermogram measured with a heating rate of 20°C / min, according to standard NF EN ISO 11357-3:2018.

Description

Title of the invention: Thermoplastic polymer powder for 3D printing by sintering Technical field

[0001] This patent application relates to a thermoplastic polymer composition useful for 3D printing by sintering, its manufacturing process and its use in 3D printing by sintering. Prior art

[0002] The construction of 3D articles is often used to produce prototypes, models of parts (“rapid prototyping”) or to produce finished parts in small series (“rapid manufacturing”), for example in the fields of: automotive, nautical, aeronautical, aerospace, medical (prostheses, hearing systems, cellular tissues, etc.), textiles, clothing, fashion, decoration, cases for electronics, telephony, home automation, IT, lighting, sport, industrial tools.

[0003] Among the techniques for manufacturing 3D articles, the sintering process is particularly interesting. According to this process, a layer of polymer powder is heated and then selectively and briefly irradiated in a chamber by electromagnetic radiation (e.g., laser beam, infrared radiation, UV radiation). As a result, the powder particles impacted by the radiation melt. The molten particles coalesce and solidify, leading to the formation of a solid mass. This process can easily produce 3D articles by the repeated irradiation of successive layers of freshly applied powder.

[0004] The quality of the manufactured parts as well as their mechanical properties depend on the characteristics of the polymer powder. Thermoplastic polymers are appreciated for their mechanical properties associated with their thermal and chemical resistance.

[0005] A major obstacle to the development of 3D printing by laser sintering is the cost of the powder. This cost of the polymer powder can be reduced substantially if it is recyclable, for example by adding a specific quantity of powder already used to a load of new powder.

[0006] The recyclability rate in turn depends in particular on the construction temperature, the temperature to which the powder is exposed throughout the construction process, which can last several hours. Under the effect of temperature, the polymer powder most often changes, in particular in color and / or viscosity, thus limiting the interest or even the possibility of its reuse.

[0007] However, the build temperature is also difficult to control. Indeed, if the build temperature is too low, "curling" phenomena occur, meaning a deformation of the built part under the effect of internal stresses appearing when the polymer layers crystallize too quickly. The appearance of "curling" most often compromises all the parts built in the chamber. Furthermore, problems with the cohesion of the powder bath, necessary for supporting the part being built, can be observed, as well as fusion defects that affect the mechanical properties of the printed part. Conversely, when the build temperature is too high, "caking" phenomena occur, meaning an agglomeration of the polymer powder bath due to partial melting of the grains. Powder that has agglomerated in this way cannot be recycled.

[0008] It is known to consider the thermal properties of the polymer when developing a powder for 3D printing by sintering. The width of its 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. However, little attention has been paid so far to the effect of the specific shape of the melting peak and the existence of other peaks, except in the specific case of polymorphic polymers.

[0009] There therefore remains a need to propose a thermoplastic polymer powder having a lower cost while allowing better recyclability. Summary of the invention

[0010] This application is based on the unexpected finding that using a polymer powder with a specific thermal signature made it possible to lower the build temperature. Reducing the bath temperature limits powder aging and therefore increases its recyclability. A lower bath temperature also widens the working window for a given polymer, thus making the printing process more robust, for example, with respect to temperature inhomogeneities in the bath, and / or allowing the use of polymers with a small difference between the build temperature and the thermal conductivity.

[0011] Also, according to a first aspect, the invention relates to a thermoplastic polymer powder suitable for use in 3D printing by sintering, having: - a volume average diameter Dv50 of less than 150 pm, a volume average diameter Dv10 of greater than 15 pm and a volume average diameter Dv90 of less than 300 pm, as measured by laser diffraction according to the ISO 13320: 2009 standard, and - a thermal signature characterized by the presence of:

[0012] (i) of two fusion peaks Tfi and Tf2, Tfi being less than Tf2, said fusion peaks being characterized in that: a. the ratio between the associated enthalpies of fusion, as determined according to standard NF EN ISO 11357-3:2018 is less than 0.5; and b. the difference between the two melting peaks (Tf2-Tfi) is less than 40°C; or

[0013] (ii) of an asymmetric melting peak, characterized by a ratio o:

[0014] O = Uefm-Teim) > 2.0 (Tefm-Tpm)

[0015] where the extrapolated start-of-melting temperature Teim, peak-of-melting temperature Tpm and end-of-melting temperature Tefm are determined from a DSC thermogram measured with a heating rate of 20°C / min, according to standard NF EN ISO 11357-3:2018.

[0016] Preferably, the thermoplastic polymer powder has a volume average diameter Dv50 of between 45 and 130 μm.

[0017] A powder having a ratio between 0.05 and 0.2 is particularly ahTj2 favorite.

[0018] According to a preferred embodiment, the thermal signature is characterized by the presence of two peaks Tfi and Tf2, the difference between these melting peaks extending over a temperature range from 5 to 30°C. Advantageously, it is characterized by an asymmetrical peak having a ratio greater than 2.3.

[0019] Advantageously, the melting peak(s) Tfi and Tf2 are spread over a temperature range of 2 to 40°C, preferably from 5 to 30°C and particularly from 10 to 20°C.

[0020] Preferably, the thermoplastic polymer powder comprises at least two distinct thermoplastic polymers.

[0021] According to one embodiment, the thermoplastic polymer powder comprises at least two thermoplastic polymers distinct by at least one of their properties, in particular by their viscosity or by their chemical nature.

[0022] Advantageously, the thermoplastic polymer powder has an inherent viscosity of 0.65 dl / g to 1.8 dl / g.

[0023] According to a preferred embodiment, the thermoplastic polymer powder comprises at least one polymer selected from thermoplastic polyamides and elastomers, and further preferred from PA 11, PA 12 and polyetherblock amides.

[0024] According to a second aspect, the invention relates to a method for manufacturing such a thermoplastic polymer powder, comprising the steps of: i. grinding at least one thermoplastic polymer into a powder exhibiting a volume mean diameter Dv50 less than 150 pm, volume mean diameter DvlO greater than 15 pm and volume mean diameter Dv90 less than 300 pm, as measured by laser diffraction according to ISO 13320:2009, and, where applicable, ii. mixing said thermoplastic polymer with another thermoplastic polymer, before, during or after step (i),

[0025] so that the powder obtained from the process has a thermal signature as defined above.

[0026] According to a third aspect, the invention relates to the use of a thermoplastic polymer powder as defined above for 3D printing by sintering, in particular by laser sintering. Brief description of the drawings

[0027] The invention will be better understood with regard to the following description and the figures, which show:

[0028] [Fig-1]: a 3D printing device by SLS type sintering (English acronym for “selective laser sintering”;

[0029] [Fig.2]: a thermogram of a polyamide powder according to example 1, showing the heat flux Q (in W / g) required to heat the sample at the imposed rate of 20°C / min, as a function of the temperature T;

[0030] [Fig.3]: a thermogram of a polyamide powder according to example 2 showing the heat flux Q (in W / g) required to heat the sample at the imposed rate of 20°C / min, as a function of the temperature T; and

[0031] [Fig.4]: a thermogram of a polyamide powder according to example 3 showing the heat flux Q (in W / g) required to heat the sample at the imposed rate of 20°C / min, as a function of the temperature T. Description of the embodiments

[0032] [Definitions]

[0033] The term "powder" is understood to mean a solid material in finely divided form, generally in the form of very small particles, generally of the order of a few hundred micrometers or less.

[0034] The term "melting temperature" is understood to mean the temperature at which an at least partially crystalline compound passes into the viscous liquid state as measured according to standard NF EN ISO 11357-3:2018. Unless otherwise indicated, this is more particularly the peak melting temperature as defined below.

[0035] More specifically, the following terms relating to melting temperature are defined as defined in ISO 11357-1:2016: • A “peak” refers to the part of the thermogram obtained by differential calorimetry Differential scanning calorimetry (DSC) which deviates from the baseline of the specimen to reach a maximum or a minimum, then returns to the baseline of the specimen. Such a peak may indicate a first-order transition; • An "endothermic peak" refers to a peak where the heat flux supplied to the test specimen crucible is greater than that of the reference crucible. This corresponds to a transition that absorbs heat; • A “baseline” refers to the portion of the recorded thermogram without any transitions, specifically here without any first-order transitions such as melting. At a transition zone, a virtual baseline can be determined: this is an imaginary line drawn through the transition zone, assuming that the heat due to the transition is zero. The virtual baseline can be drawn by interpolating the specimen's baseline using a straight line; • a “peak area” refers to the area delimited by the peak and the interpolated virtual baseline. It is similar to a transition enthalpy, expressed in J / g; • an “extrapolated melting start temperature” Teim designates the point of intersection of the interpolated virtual baseline and the tangent at the inflection point of the peak start; • a “peak melting temperature” Tpm designates the temperature at which the distance is greatest between the thermogram and the virtual baseline during a peak; • an “extrapolated end temperature” Tefm denotes the point of intersection of the virtual baseline and the tangent at the inflection point of the end of the peak.

[0036] The term "enthalpy of fusion" means the heat required to melt the composition, corresponding to the melting peak(s) on the thermogram, measured according to standard NF EN ISO 11357-3:2018.

[0037] The term "Dv50" refers to the value of the powder particle diameter such that the volume-weighted cumulative particle diameter distribution function is equal to 50%. The value of "Dv50" is measured by laser diffraction according to ISO 13320:2009, for example, on a Malvern Mastersizer 2000® diffractometer. Similarly, "Dv10" and "Dv90" are the corresponding diameters such that the volume-weighted cumulative particle diameter function is equal to 10% and 90%, respectively. The rules for representing the results of a particle size distribution are given by ISO 9276 - parts 1 to 6.

[0038] The term "viscosity" refers to the inherent viscosity as measured according to ISO 307:2007. The term "viscosity" also refers to the inherent viscosity as measured in a Ubbelohde-type viscometer according to ISO 307:2019, except when m-cresol is used as the solvent and the temperature is 20°C. The inherent viscosity has the dimensions of the inverse of a concentration and is equal to the natural logarithm of the relative viscosity, divided by the concentration of polymer dissolved in the solvent.

[0039] The term “3D printing by sintering” is understood to mean a technique aimed at producing parts by additive manufacturing, by selectively melting a powder using electromagnetic radiation such as a laser or infrared light.

[0040] The term “crystallinity rate” is understood to mean the crystallinity rate as calculated from wide angle X-ray scattering (WAXS) measurements, on a Nano-inXider® type device with the following conditions: • Wavelength: main Kal line of copper (1.54 Angstroms). • Generator power: 50 kV - 0.6 mA. • Observation mode: transmission • Counting time: 10 minutes

[0041] This yields a spectrum of the scattered intensity as a function of the diffraction angle. This spectrum allows the presence of crystals to be identified when peaks are visible in the spectrum in addition to the amorphous halo. The spectrum allows the area of ​​the crystalline peaks (denoted A) and the area of ​​the amorphous halo (denoted AH) to be measured. The (mass) proportion of crystalline polymer in the sample is estimated by the ratio (A) / (A+AH).

[0042] The thermograms referred to in this application are obtained by differential scanning calorimetry (DSC) analysis according to standard NF EN ISO 11357-3:2018, using a first heating of approximately 10 mg of the composition to be tested, and a temperature ramp of 20°C / min. The initial temperature may, in particular, be approximately 20°C and the final temperature approximately 260°C. Thermograms such as those shown in the figures can be obtained using a Q2000 differential scanning calorimeter, marketed by TA Instruments.

[0043] Indefinite and definite articles such as "a", "an" or "the" mean in the context of this exposition by default "at least one", and respectively "the said at least one" or "the said at least one". A. Thermoplastic polymer powder

[0044] The thermoplastic polymer powder proposed according to the invention has: - a volume average diameter Dv50 of less than 150 pm, a volume average diameter in volume DvlO greater than 15 pm and a mean volume diameter Dv90 less than 300 pm, as measured by laser diffraction according to ISO 13320:2009, and - a thermal signature characterized by the presence of: i. of two fusion peaks Tfi and Tf2, Tfi being less than Tf2, said fusion peaks being characterized in that: a. the ratio between the associated enthalpies of fusion, such as de-ahtj2 completed according to standard NF EN ISO 11357-3:2018 is less than 0.5; and b. the difference between the two melting peaks (Tf2-Tfi) is less than 40°C; or ii. of an asymmetrical melting peak, characterized by a ratio o:

[0045] O = (Tefm-Teim) > 2.0 (Tefm-Tpm)

[0046] where the extrapolated start-of-melting temperature Teim, peak-of-melting temperature Tpm and end-of-melting temperature Tefm are determined from a DSC thermogram measured with a heating rate of 20°C / min, according to standard NF EN ISO 11357-3:2018.

[0047] The thermoplastic polymers that can be used in the context of the present invention can in particular be chosen from polyolefins such as polypropylene and polyethylene (olefinic base waxes would not fall outside the scope of the invention), polycarbonate, polymethylmethacrylate (PMMA), polyamides and thermoplastic elastomers such as polyetherblock amides (PEBA), polyesters and polyether blocks (COPE), thermoplastic polyurethanes (TPU) or their mixtures.

[0048] Aliphatic polyamides, in particular long chain, i.e. having at least 8 carbon atoms per amide group, and in particular PA 11 and PA 12 as well as polyetherblock amides are particularly preferred.

[0049] Polyetherblock amides are copolymers comprising polyamide blocks and polyether blocks. Preferably, they are linear (non-crosslinked) copolymers.

[0050] PEBA copolymers can result from the polycondensation of reactive-end polyamide (PA) blocks with reactive-end polyether (PE) blocks. For example, they may include: - polyamide blocks with polycondensed diamine chain ends with polyoxyalkylene blocks with dicarboxylic chain ends; - polyamide blocks with polycondensed dicarboxylic chain ends and polyoxyalkylene blocks with diamine chain ends; or - polyamide blocks with polycondensed dicarboxylic chain ends with polyetherdiols, the products obtained in this case being polyether-teramides.

[0051] Polyamide blocks with dicarboxylic acid ends are obtained, for example, from the condensation of polyamide precursors in the presence of a chain-limiting dicarboxylic acid. Polyamide blocks with diamine chain ends are obtained, for example, from the condensation of polyamide precursors in the presence of a chain-limiting diamine. These polyamide blocks may be homopolyamides or copolyamides. They may include, in particular, PA 11, PA 12, PA 6 polyamide blocks or mixtures thereof.

[0052] The polyether blocks of PEBA essentially comprise or are composed of alkylene oxide units. The polyether blocks may be derived from alkylene glycols such as PEG (polyethylene glycol), PPG (propylene glycol), PO3G (polytrimethylene glycol), or PTMG (polytetramethylene glycol), preferably PTMG. They may also be derived from copolyethers comprising different alkylene oxides distributed in the chain in a regular manner, particularly by blocks, or statistically. The polyether blocks may also be obtained by oxyethylation of bisphenols, such as bisphenol A. These products are described, in particular, in document EP 613919 AL. The polyether blocks may also be ethoxylated primary amines. Finally, the polyether blocks may comprise or be composed of polyoxyalkylene blocks with NH2 chain ends. Such blocks can be obtained by cyanoacetylation of polyetherdiols.Such polyethers are sold by the Huntsman company under the name Jeffamine® or Elastamine® (for example Jeffamine® D400, D2000, ED 2003, XTJ 542).

[0053] 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, 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.

[0054] A two-step method for preparing PEBA having ester bonds between PA blocks and PE blocks is described in document FR 2846332 AL. A method for preparing PEBA having amide bonds between PA blocks and PE blocks is described in document EP 1482011 AL. Polyether blocks can also be mixed with polyamide precursors and a diacid chain limiter to prepare PEBA by a one-step process.

[0055] While PEBAs generally comprise a polyamide block and a polyether block, they can also comprise two, three, four or even more different blocks.

[0056] According to one embodiment, the mass proportion of polyether blocks in the copolymer is at least 50% relative to the total weight of the copolymer. Preferably, the mass proportion of polyether blocks is 55 to 85% relative to the total weight of the copolymer, and more preferably 60 to 80%, relative to the total weight of the copolymer. The mass proportions of blocks in the copolymer can be determined from the number-average molar masses of the blocks.

[0057] Particularly preferred PEBAs are those having an instantaneous hardness (Shore D hardness), as determined according to ISO 868:2003, of less than 50 and more preferably between 35 and 45.

[0058] Of course, the designation PEBA in the present description of the invention relates 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] According to one embodiment, the thermoplastic polymer powder has an enthalpy of fusion greater than 25 J / g, or from 25 to 30 J / g, or from 30 to 40 J / g, or from 40 to 50 J / g, or from 50 to 60 J / g, or from 60 to 70 J / g, or from 70 to 80 J / g, or from 80 to 90 J / g, or from 90 to 100 J / g, or from 100 to 110 J / g, or from 110 to 120 J / g, or from 120 to 130 J / g. A thermoplastic polymer powder with an enthalpy of fusion between 30 and 110 J / g is particularly advantageous. More specifically, the enthalpy of fusion varies depending on the polymer considered. Thus, the enthalpy of fusion for a polyamide can be between 70 and 110 J / g, while the enthalpy of fusion for a PEBA will preferably be between 25 and 50 J / g.

[0060] The thermoplastic polymer powder generally comprises at least 50% by weight of thermoplastic polymer relative to the total weight of powder. According to certain embodiments, the powder comprises at least 75%, or at least 80%, or at least 85%, or at least 90%, or at least 92.5%, or at least 95%, or at least 97.5%, or at least 98%, or at least 98.5%, or at least 99%, or at least 99.5% by weight of thermoplastic polymer relative to the total weight of the thermoplastic polymer powder of the invention.

[0061] According to some embodiments, the thermoplastic polymer powder may comprise a single thermoplastic polymer, for example only a polyolefin, a polyamide, or even a polyetherblock amide.

[0062] Alternatively, the thermoplastic polymer powder may comprise two or more distinct thermoplastic polymers. These polymers may be distinguished in particular by their chemical nature, for example a mixture of polyolefins, polyamides or polyetherblock amides.

[0063] According to certain embodiments, the powder according to the invention comprises several polymers, of the same chemical nature or not, distinct by at least one of their properties. These properties may in particular be viscosity, crystallinity and crystallization speed. Thus, the powder according to the invention may for example include a polyamide or polyether block amide and a polyolefin wax.

[0064] In order to be suitable for 3D printing by sintering, the thermoplastic polymer powder must meet certain criteria, particularly in terms of particle size.

[0065] According to the invention, the thermoplastic polymer powder has a volume average diameter Dv50 of less than 150 pm. According to certain embodiments, the thermoplastic polymer powder has a volume average diameter Dv50 between 45 and 130 pm, in particular between 50 and 120 pm and especially between 55 and 100 pm.

[0066] Besides the average diameter alone, the particle size distribution of the thermoplastic polymer powder can also have a significant impact on the performance in 3D printing by sintering.

[0067] Thus, according to the invention, the thermoplastic polymer powder has a volume average diameter DvlO greater than 15 pm. According to certain embodiments, the thermoplastic polymer powder has a volume average diameter DvlO between 20 and 60 pm, in particular between 25 and 45 pm and especially between 30 and 40 pm.

[0068] Thus, according to the invention, the thermoplastic polymer powder has a volume average diameter Dv90 of less than 300 pm. According to certain embodiments, the thermoplastic polymer powder has a volume average diameter Dv90 of between 100 and 300 pm, in particular between 120 and 250 pm and very particularly between 140 and 200 pm.

[0069] The polymer powder compositions according to the invention are further characterized by a specific thermal signature. This signature is unique because the melting peak is not symmetrical and singular as is conventionally the case. According to the invention, this thermal signature comprises either two melting peaks or an asymmetrical melting peak, for example, due to the presence of another transition close to the melting point.

[0070] This type of thermal signature is observed, for example, when other phase transitions are located close to the melting point. Usually, such phase transitions are considered a risk of disrupting or even preventing 3D printing by sintering to a satisfactory quality.

[0071] However, it has unexpectedly turned out that such thermal signatures can, by allowing a lower temperature start to melting, make it possible to lower the build temperature and thus reduce the thermal aging of the powder during the build process and thus increase the possibilities of reuse, thereby considerably reducing the cost of the printing material.

[0072] According to the invention, the thermal signature of the thermoplastic polymer powder can be characterized by the presence of two melting peaks Tfi and Tf2, which are close together, i.e. not more than 40°C apart, and characterized by the fact that the melting peak Tfi at the lower temperature is significantly smaller than the melting peak Tf2 located at the higher temperature, so that the ratio between the enthalpy of fusion associated with these peaks ^Tfi is less than 0.5. AHrfi

[0073] Alternatively, the thermal signature of the thermoplastic polymer powder can be characterized by the presence of an asymmetric peak. The asymmetry is expressed by the ratio o as follows:

[0074] O = (Tefm-Teim) > 2.0 (Tefm-Tpm)

[0075] where the extrapolated melting start temperature Teim, the melting peak temperature Tpm and the extrapolated melting end temperature Tefm are determined from a DSC thermogram measured with a heating rate of 20°C / min, according to standard NF EN ISO 11357-3:2018.

[0076] When the thermoplastic polymer powder has several melting peaks, these are preferably spread over a temperature range of 2 to 40°C, preferably from 5 to 30°C and particularly from 10 to 20°C.

[0077] Indeed, it is generally preferable that the melting peaks not be too far apart. Thus, for example in 3D printing by laser fusion (SLS), a build temperature lower than the melting temperature Tfb and too far from the temperature Tf2 requires the use of excessive laser power or passing it through several times (multiscan).

[0078] According to the invention, the ratio between the enthalpy of fusion associated with these peaks is less than 0.5. Advantageously, this ratio can be between 0.02 and 0.4, and in particular between 0.05 and 0.2.

[0079] According to one embodiment, the enthalpy of fusion associated with the peak melting temperature Tfi is greater than 2 J / g, or from 2 to 5 J / g, or from 5 to 10 J / g, or from 10 to 15 J / g, or from 15 to 20 J / g, or from 20 to 25 J / g, or from 25 to 30 J / g, or from 30 to 35 J / g, or from 35 to 40 J / g, or from 40 to 50 J / g, or from 50 to 60 J / g, or from 60 to 70 J / g. Particularly advantageous is a thermoplastic polymer powder having an enthalpy of fusion associated with the peak melting temperature Tfi between 2 and 40 J / g.

[0080] According to another embodiment, the enthalpy of fusion associated with the melting peak Tf2 is greater than 15 J / g, or from 15 to 20 J / g, or from 20 to 30 J / g, or from 30 to 40 J / g, or from 40 to 50 J / g, or from 50 to 60 J / g, or from 60 to 70 J / g, or from 70 to 80 J / g, or from 80 to 100 J / g, or from 100 to 120 J / g, or from 120 to 130 J / g. Particularly advantageous is a thermoplastic polymer powder having an enthalpy of fusion associated with the melting peak Tf2 between 20 and 130 J / g.

[0081] When the thermoplastic polymer powder exhibits an asymmetrical peak, this- ci is characterized by a value of o greater than 2.0, and preferably greater than 2.3. Advantageously, o is between 2.0 and 6.0, in particular between 2.2 and 5.0, and very particularly between 2.3 and 4.0.

[0082] According to certain embodiments, the thermoplastic polymer powder has an inherent viscosity of 0.65 dl / g to 1.8 dl / g, preferably of 0.9 dl / g to 1.4 dl / g, and more preferably of 1.0 dl / g to 1.3 dl / g. These powders are particularly advantageous in that they allow a good compromise to be obtained for having both good coalescence properties during sintering (sufficiently low viscosity) and good mechanical properties of the sintered object (sufficiently high viscosity).

[0083] The thermoplastic polymer powder may include, in addition to the thermoplastic polymer(s), one or more usual additives and fillers.

[0084] The additives generally represent less than 5% by weight relative to the total weight of the composition. Preferably, the additives represent less than 1% by weight of the total weight of powder. Among the additives, mention may be made of flow agents, stabilizing agents (light, in particular UV, and heat), optical brighteners, dyes, pigments, energy-absorbing additives (including UV absorbers).

[0085] Examples of flow agents include hydrophilic or hydrophobic silica. Advantageously, the flow agent represents 0.01 to 0.5% by weight relative to the total weight of the composition. Preferably, the thermoplastic polymer powder comprises 0.1 to 0.4% by weight of the flow agent.

[0086] The thermoplastic polymer powder may also comprise one or more fillers. The fillers generally represent less than 50% by weight, and preferably less than 40% by weight relative to the total weight of the final powder. Among the fillers, we can cite reinforcing fillers, in particular mineral fillers such as carbon black, talc, nanotubes, carbon or not, fibers (glass, carbon, etc.), ground or not.

[0087] B. Process for manufacturing thermoplastic polymer powder

[0088] The thermoplastic polymer powder can in particular be obtained by grinding thermoplastic polymer in the form of extruded granules or flakes, according to conventional techniques.

[0089] The grinding can be carried out on equipment known for this purpose, for example, using a counter-rotating pin mill, a hammer mill, or a whirl mill. When the powder contains several polymers and / or certain additives and / or certain reinforcing fillers, some or all of them can be incorporated by mixing in the melt state, for example, by extrusion (compounding) and granulation followed by grinding the granules. Alternatively, it is also possible to add other polymers and / or certain additives and / or certain reinforcing fillers by dry blending. Preferably, the flow agent is added by dry blending.

[0090] According to one embodiment, and in particular for polyamides, the method of manufacturing the powder composition comprises the steps of: a. Prepolymerization of the thermoplastic polymer monomer(s) and subsequent granulation b. Grinding and possible subsequent sieving of the prepolymer powder obtained; c. Subjecting the prepolymer powder obtained, optionally sieved, to solid-phase polycondensation to obtain a polymer powder.

[0091] The additives and / or reinforcing fillers may be added to the prepolymer by melt mixing (compounding) before grinding or by dry mixing. Alternatively, the additives and / or reinforcing fillers may also be added subsequently to the polymer powder by dry mixing. C. Use of the powder

[0092] The described thermoplastic polymer powder is particularly useful in 3D printing processes by sintering.

[0093] Preferably, the composition of the invention is used in a selective laser sintering (SLS) process, an MJF (Multi Jet Fusion) type sintering process or an HSS (High Speed ​​Sintering) type sintering process.

[0094] The SLS process is widely known. In this context, reference can be made in particular to documents US 6,136,948 and WO 96 / 06881.

[0095] In this type of process, a thin layer of powder is deposited onto a horizontal plate held in a chamber heated to a temperature called the build temperature. Most often, heating to the build temperature is achieved using IR radiation lamps, for example halogen lamps, which generally have a maximum emission at a wavelength between 750 nm and 1250 nm.

[0096] The build temperature refers to the temperature to which the powder bed, of a constituent layer of a three-dimensional article under construction, is heated during the layer-by-layer sintering process of the powder.

[0097] Electromagnetic radiation, for example in the form of a laser, then provides the energy necessary to sinter the powder particles at different points of the powder layer according to a geometry corresponding to an object, for example using a computer having in memory the shape of an object and restoring the latter in the form of slices. Then, the horizontal plate is lowered by a height corresponding to the thickness of a layer of powder, and a new layer of powder is The material is spread out, heated, and then sintered in the same way. The procedure is repeated until the object has been made.

[0098] The layer of powder deposited on a horizontal plate may, before sintering, have a thickness of, for example, 20 to 200 µm, and preferably 50 to 150 µm. After sintering, the thickness of the agglomerated material layer is somewhat less, and may have, for example, a thickness of 10 to 150 µm, and preferably 30 to 100 µm.

[0099] In the MJF and HSS processes, the entire layer of the building material is exposed to radiation, but only a portion coated with a melting agent is melted to become a layer of a 3D part. The melting agent is a compound capable of absorbing radiation and converting it into thermal energy, for example, black ink. It is applied selectively to the selected region of the building material. The melting agent is able to penetrate the layer of the building material and transfers the absorbed energy to the adjacent building material, causing it to melt or be sintered. Through the melting, bonding, and subsequent hardening of each layer of the building material, the object is formed.

[0100] In the particular case of MJF, a detailing agent is further added to the edges of the area to be melted to allow the parts to have a better definition.

[0101] Advantageously, the use of the polymer powder composition of the invention in these processes does not require any particular modification. As mentioned above, it does, however, make it possible to obtain parts with lower roughness and better definition.

[0102] The polymer powder composition according to the invention can be recycled and reused in several successive constructions. In this case, it can be reused alone or in a mixture with other recycled or non-recycled powders.

[0103] As an example, the use of the thermoplastic polymer powder described in a method of constructing a three-dimensional object layer by layer by sintering caused by electromagnetic radiation in a device 1, such as that shown diagrammatically in [Fig.l], is described below.

[0104] The electromagnetic radiation may, for example, be infrared radiation, ultraviolet radiation, or preferably laser radiation. In particular, in a device 1 such as that shown schematically in [Fig. 1], the electromagnetic radiation may comprise a combination of infrared radiation 100 and laser radiation 200.

[0105] The sintering process is a layer-by-layer manufacturing process for building a three-dimensional object 80.

[0106] The device 1 comprises a sintering chamber 10 in which are arranged a feed tray 40 containing the thermoplastic polymer powder and a movable horizontal plate 30. The horizontal plate 30 can also act as support for the three-dimensional object 80 under construction. However, objects made from thermoplastic polymer powder generally do not require additional support and can usually be self-supported by the unsintered powder from previous layers.

[0107] According to the process, thermoplastic polymer powder is taken from the feed tray 40 and deposited onto the horizontal plate 30, forming a thin layer 50 of powder that constitutes the three-dimensional object 80 under construction. The powder layer 50 is heated by infrared radiation 100 to reach a substantially uniform temperature equal to the predetermined minimum construction temperature Te.

[0108] The energy required to sinter the thermoplastic polymer powder particles at different points of the powder layer 50 is then provided by a laser beam 200 from the laser 20 moving in the (xy) plane, according to a geometry corresponding to that of the object. The molten powder re-solidifies forming a sintered portion 55 while the remainder of the layer 50 remains in the form of unsintered powder 56. A single pass of a single laser beam 200 is generally sufficient to ensure sintering of the powder. However, in certain embodiments, several passes at the same location and / or several electromagnetic radiations reaching the same location may also be envisaged to ensure sintering of the powder.

[0109] Next, the horizontal plate 30 is lowered along the (z) axis by a distance corresponding to the thickness of a powder layer, and a new layer is deposited. The laser 20 provides the energy necessary to sinter the powder particles according to a geometry corresponding to this new slice of the object, and so on. The procedure is repeated until the object 80 has been fabricated.

[0110] The temperature in the sintering chamber 10 of the layers below the layer being built may be lower than the build temperature. However, this temperature generally remains above, or even well above, the glass transition temperature of the powder. It is particularly advantageous for the temperature at the bottom of the chamber to be maintained at a temperature Tb, known as the "bottom of the chamber temperature," such that Tb is less than Te by less than 40°C, preferably less than 25°C, and even more preferably less than 10°C.

[0111] Once the object 80 is finished, it is removed from the horizontal plate 30 and the unsintered powder 56 can be sieved before being returned, at least partially, to the feed bin 40 to serve as recycled powder. Recycling the powder is possible because the build temperature Te is generally lower than that of traditional build processes, which helps to mitigate the aging of the unsintered powder, which has been subjected to the temperature conditions of at least one sintering build. The recycled thermoplastic polymer powder can be used as is or alternatively mixed with virgin powder.

[0112] In particular, in embodiments where the thermoplastic polymer powder consists of a mixture of PI powder and P2 powder, the build temperature can be lower than that which would be used for a traditional build process using a composition consisting of PI powder (which is not according to the invention). This allows for the possibility of improved recycling of unsintered powder compositions in subsequent build processes. Advantageously, the mixture of powders to be recycled is mixed with virgin P and / or P2 powder, so as to maintain a build temperature Te lower than that of traditional build processes.

[0113] The invention will be explained in more detail in the following examples. Examples

[0114] In the following examples, several thermoplastic polymer powders with different particle sizes and thermal signatures were examined for their behavior in 3D printing by sintering. EXAMPLE 1

[0115] For reference purposes, a polyamide 11 powder, formulated for 3D printing, marketed by ARKEMA France under the name Rilsan® In vent Natural (RIN), was used.

[0116] The thermal signature of the polyamide 11 powder was characterized by differential scanning calorimetry (DSC) performed on a TA Instruments Q2000 calorimeter, in accordance with ISO 11357-3:2013. In the thermogram shown in [Fig. 2], the dashed lines represent the baseline and the solid lines the tangents of the flanks from the melting peak to the inflection point. The temperatures Teim and Tefm are the temperatures at which the baseline is intersected by the flank tangents. The temperature Tpm is that at the minimum of the melting peak. The temperatures Tpm, Teim, and Tefm were determined from the thermogram shown in [Fig. 2] and are given in Table 2 below.

[0117] This powder was further characterized by its average diameter Dv50 of 49 pm, its average diameter Dv10 of 23 pm and its average diameter Dv90 of 90 pm, by laser diffraction on a Malvern Insitec diffractometer and RTSizer software, according to the ISO 13320: 2009 standard in the dry process, choosing a pressure of 7.5 bars and an air flow rate of 10 m3 / h. EXAMPLE 2

[0118] A thermoplastic polymer powder was prepared by dry mixing 90% by weight of polyamide 11 powder marketed by ARKEMA France under the name Rilsan® Invent Natural with 10% by weight of heat-treated polyamide 11. uniquely, obtained according to the following process.

[0119] First, a polyamide 11 prepolymer was synthesized from 1.2 kg of amino-11-undecanoic acid in the presence of 0.5 kg of water, 5 g of hypophosphorous acid, and 9.8 g of phosphoric acid. The mixture was heated to 190°C in 2 hours with stirring, starting as soon as the temperature reached 160°C or the pressure exceeded 8.5 bar. During the synthesis, the water initially containing amino-11-undecanoic acid was removed by evaporation at constant pressure (P = 10 bar). After removing 430 g of water, the molten prepolymer was extruded using a twin-screw extruder. The mixture was then cooled using two steel rollers with circulating cold water to solidify, cool and crush into flakes.

[0120] The recovered prepolymer is then ground in a hammer mill equipped with an internal selector until a powder with a volume median diameter Dv50 of 49 µm is obtained. The powder thus obtained is then subjected to solid-phase polycondensation in a vacuum dryer at 180°C to increase the viscosity of the polyamide to 1.1 dl / g.

[0121] The polyamide 11 powder obtained was then sieved through a 150 μm square mesh.

[0122] The resulting powder exhibits a thermal signature characterized by the temperatures Tpm, Teim, and Tefm shown in Table 2. These temperatures were determined from a thermogram measured by differential scanning calorimetry (DSC) on a TA Instruments Q2000 calorimeter, in accordance with ISO 11357-3:2013. In the thermogram shown in [Fig. 3], the dashed lines represent the baseline and the solid lines the tangents to the flanks of the melting peak at the inflection point. The temperatures Teim and Tefm are the temperatures at which the baseline is intersected by the flank tangents. The temperature Tpm is that at the minimum of the peak. The angle of the tangent was adjusted to account for the low-temperature spreading preceding the melting peak.

[0123] This powder was further characterized by its average diameter Dv50 of 49 pm, its average diameter Dv10 of 23 pm and its average diameter Dv90 of 90 pm, by laser diffraction according to the ISO 13320: 2009 standard, on a Malvern Insitec diffractometer as explained in example 1. EXAMPLE 3

[0124] A thermoplastic polymer powder was prepared by dry mixing 90% by weight of polyamide 11 powder marketed by ARKEMA France under the name Rilsan® Invent Natural with 10% by weight of polyamide 12 marketed by ARKEMA under the name Orgasol Invent Smooth, having a DvlO of 31 pm, a Dv50 of 40 pm and a Dv90 of 50 pm.

[0125] The resulting powder exhibits a thermal signature characterized by two melting temperatures, Tfi and Tf2, shown in Table 2. These temperatures were determined from the thermogram illustrated in [Fig. 4], measured by differential scanning calorimetry (DSC) on a TA Instruments Q2000 calorimeter, in accordance with ISO 11357-3:2013. The difference between the two melting peaks, Tfi and Tf2, is 19°C. The ratio of the enthalpy of Tfi to that of Tf2 is 0.1.

[0126] This powder was further characterized by its mean diameter Dv50 of 49 pm, its mean diameter DvlO of 23 pm and its mean diameter Dv90 of 90 pm, by laser diffraction according to ISO 13320:2009, on a Malvern Master sizer 2000® diffractometer as explained in Example 1.

[0127] [Tableauxl] Composition of powders, relative to the weight of the composition Composition Example 1 (Ref) Example 2 Example 3 PA 11 Rilsan Invent Nat [% by weight] 100 90 90 PA 11 treated [% by weight] - 10 - PA 12 Orgasol Invent Smooth [% by weight] - - 10

[0128] [Tables2] Thermal characteristics Example Tpm [°C] Teim [°C] Tetm [°C] o AH [ J / g] Tf2 [°C] zÀHffj / zÀ HTf2 1 (reference) 201 196 215 1.4 115 - - 2 201 183 215 2.3 111 - - 3 182 NDNDND 113 201 0.1 Behavior of powders in 3D printing

[0129] The polymer powders obtained were then used to manufacture, by 3D printing using laser sintering, a 1BA XY test specimen (1BA test specimen according to the standard ISO 527-1BA, called "XY" because it is printed in the printer's horizontal plane) on a P100 machine (marketed by EOS) with the powder layer thickness set to 100 µm. The printing parameters used are as follows:

[0130] Laser power: 24W

[0131] Laser speed: 3000mm / s

[0132] Distance between 2 laser passes: 0.25mm

[0133] It was found on the one hand that the powder of example 2 could be sintered at a construction temperature of 9°C below the temperature of powder 1 (183°C for powder 1 vs 174°C for the powder of example 2). The test pieces obtained from powders 1 and 2 nevertheless had comparable mechanical properties. However, a reduction in the construction temperature makes it possible to reuse powder 2 more widely, as it has undergone less thermal aging during the construction process, and therefore to significantly reduce the cost of the material for 3D printing.

[0134] It was also observed that the powder of example 3 also made it possible to obtain good quality test specimens at a construction temperature below the temperature of powder 1. Thus, the presence of several melting peaks can be taken advantage of as long as they are not too far apart.

[0135] These examples highlight that a powder with a specific particle size associated with a complex thermal signature, characterized either by the presence of two melting peaks separated by less than 40°C and having a ratio between the associated melting enthalpies AHf, and AH[2 <0.5 or by an asymmetric melting peak characterized by a ratio o > 2.0, can make it possible to lower the build temperature during 3D printing, thus limiting thermal aging and therefore the cost of the material. List of cited documents

[0136] [US 6,136,948]

[0137] [WO 96 / 06881]

Claims

Claims

1. Thermoplastic polymer powder suitable for use in 3D printing by sintering, having: - a volume average diameter Dv50 of less than 150 pm, a volume average diameter Dv10 of greater than 15 pm and a volume average diameter Dv90 of less than 300 pm, as measured by laser diffraction according to ISO 13320: 2009, and - a thermal signature characterized by the presence of: (i) two melting peaks Tfi and Tf2, Tfi being less than Tf2, said melting peaks being characterized in that: a. the ratio between the associated melting enthalpies, as de- &HTf> determined according to NF EN ISO 11357-3:2018 is less than 0.5; and b. the difference between the two melting peaks (Tf2-Tfi) is less than 40°C; or (ii) an asymmetric melting peak, characterized by a ratio o: 0 = (Tefm-Teim) > 2.0 (Tefm-Tpm) where the extrapolated melting start temperature Teim, the melting peak temperature Tpm and the extrapolated melting end temperature Tefm are determined from a DSC thermogram measured with a heating rate of 20°C / min, according to standard NF EN ISO 11357-3:2018.

2. Thermoplastic polymer powder according to claim 1, characterized in that it has a volume average diameter Dv50 of between 45 and 130 pm.

3. Thermoplastic polymer powder according to claim 1 or 2, wherein the ratio ^rfi is between 0.05 and 0.

2. XI!; _

4. Thermoplastic polymer powder according to one of claims 1 to 3, in which the thermal signature is characterized by the presence of two peaks Tfi and Tf2, the difference between these melting peaks extending over a temperature interval from 5 to 30°C.

5. Thermoplastic polymer powder according to one of claims 1 to 4, characterized in that the thermal signature is characterized by an asymmetrical peak having a ratio o greater than 2.

3.

6. Thermoplastic polymer powder according to one of claims 1 to 5, in which the melting peak(s) Tfi and Tf2 extend over a temperature range from 2 to 40°C, preferably from 5 to 30°C and very particularly from 10 to 20°C.

7. Thermoplastic polymer powder according to one of claims 1 to 6, comprising at least two distinct thermoplastic polymers.

8. Thermoplastic polymer powder according to one of claims 1 to 7, comprising at least two thermoplastic polymers distinct by at least one of their properties, in particular by their viscosity.

9. Thermoplastic polymer powder according to one of claims 1 to 7, comprising at least two distinct thermoplastic polymers differing in their chemical nature.

10. Thermoplastic polymer powder according to one of claims 1 to 9, having an inherent viscosity of 0.65 dl / g to 1.8 dl / g as measured in an Ubbelohde type viscometer according to ISO 307:2019, except using m-cresol as solvent and a temperature of 20°C.

11. Thermoplastic polymer powder according to one of claims 1 to 10, comprising at least one polymer chosen from polyamides and thermoplastic elastomers.

12. Thermoplastic polymer powder according to claim 11, comprising at least one polymer chosen from PA 11, PA 12 and polyetherblock amides.

13. A method of manufacturing a thermoplastic polymer powder according to one of claims 1 to 12, comprising the steps of: a. Grinding at least one thermoplastic polymer into a powder having a volume average diameter Dv50 of less than 150 pm, a volume average diameter Dv10 of greater than 15 pm and a volume average diameter Dv90 of less than 300 pm, as measured by laser diffraction according to ISO 13320:2009, and, where appropriate, b. mixing said thermoplastic polymer with another thermoplastic polymer, before, during or after step (i), so that the powder obtained from the method has a thermal signature as defined in claim 1.

14. Use of a powder according to one of claims 1 to 13 for 3D printing by sintering.

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

Images