Method for producing sintered bodies with improved roughness - Patent Application 20070122997

Abstract

The present invention is primarily directed to a polyamide powder composition useful for powder bed additive manufacturing, comprising: (a) 10% by weight to 90% by weight of a polyamide powder A having an intrinsic viscosity calculated according to equation (1) from the flow rate of a solution of the polymer and the solvent, measured in an Ubbelohde viscometer in accordance with ISO Standard 307:2019, apart from the use of m-cresol as the solvent and at a temperature of 20°C, of ​​0.8 to 2.8 with a span between 0.4 and 1.40; (b) 90% to 10% by weight of a polyamide powder B different from the polyamide powder A, having an intrinsic viscosity calculated as above of 0.8 to 2.8 with a span between 0.4 and 1.40; (c) 0 to 40 wt. % of additives selected from flow agents, stabilizers, optical brighteners, and energy absorbing additives and / or fillers; The present invention relates to a polyamide powder composition comprising: It is understood that polyamide powder B is derived from polyamide powder A, and the difference in intrinsic viscosity between powders A and B does not exceed 0.6 in absolute value.

Description

[Technical Field]

[0001] This patent application relates to a process for the production by 3D printing of sintered bodies with improved roughness, to such sintered bodies, and to compositions useful for the production thereof. [Background technology]

[0002] Additive manufacturing (e.g., SLS, MJF, HSS) on a thermoplastic polymer powder bed allows for the creation of complex shaped workpieces, including serially arranged ones. This allows for the simultaneous production of many workpieces with excellent resolution and very good mechanical properties, giving it an advantage over other additive manufacturing processes such as fused wire deposition.

[0003] However, these processes are very demanding in terms of the properties of the polymer powder. For example, the powder must be able to form a powder bed with the properties required for additive manufacturing processes. Specifically, the powder must not only be able to spread in a thin layer of uniform thickness, but also to form a cohesive powder bed that can support the weight of the workpiece being built.

[0004] The properties of polymer powders are also important for obtaining defect-free objects with particularly low roughness. In particular, the surface roughness of printed workpieces is often inadequate for certain applications, such as bearing cages, seals, turbines, pistons, rings, compressor valves, or engine parts, which require precisely sized workpieces. This problem arises particularly in connection with the recycling of residual powder recovered at the end of each printing run, which is required for economic reasons. It has been found that such powder recycling, in particular, does not guarantee the production of high-quality workpieces with a consistent roughness.

[0005] It is known to improve the surface condition of workpieces obtained by additive manufacturing by physical and / or chemical treatments, but these treatments significantly increase production time and therefore costs.

[0006] U.S. Patent Publication No. 2011 / 0237731 discloses powders for 3D printing by laser sintering that contain 10% to 30% by weight of a polyamide 12 powder with low thermal viscosity change, mixed with a more advanced polyamide 12 powder. However, within these mixtures, some components have very different properties, which can lead to inhomogeneity in the manufactured article and affect its mechanical properties.

[0007] US Patent Publication No. 2018 / 094103 proposes polyamide powders for 3D printing by sintering, which have a viscosity in solution according to ISO 307 of 1.55 to 1.75, and which change from 10% to 40% after 24 hours under nitrogen at 10°C below the melting point. 3D printing with these powders does not always produce workpieces with a satisfactory roughness for applications requiring precisely sized workpieces, such as bearing cages, seals, turbines, pistons, rings, compressor valves or engine parts. Summary of the Invention

[0008] The object of the present invention is therefore to propose a polyamide powder composition for 3D printing by laser sintering, which allows the production of workpieces that are in particular partially recycled and have good surface quality and low roughness.

[0009] In particular, the invention is based on the observation that mixtures of specially selected polyamide powders, in particular having an intrinsic viscosity difference of less than 0.6, allow the production of articles with good surface quality and in particular low roughness.

[0010] Thus, according to a first aspect, one subject of the invention is a method for treating a cancer cell comprising: (a) 10% by weight to 90% by weight of polyamide powder A having an intrinsic viscosity calculated according to equation (1) from the flow rate of a solution of polymer and solvent, measured with an Ubbelohde viscometer in accordance with ISO Standard 307:2019, apart from the use of m-cresol as solvent and at a temperature of 20°C, of ​​0.8 to 2.8 with a span between 0.4 and 1.40; (b) 90% to 10% by weight of a polyamide powder B different from the polyamide powder A, having an intrinsic viscosity calculated as above of 0.8 to 2.8 with a span between 0.4 and 1.40; (c) 0% to 40% by weight of additives and / or fillers It is understood that the difference in intrinsic viscosity between powders A and B does not exceed 0.6 in absolute value.

[0011] According to one embodiment, polyamide powder A and polyamide powder B are each chosen from PA 6, PA 66, PA613, PA1010, PA 1012, PA 11, PA 12, PA 11 / 10T and copolymers thereof.

[0012] According to one embodiment, polyamide powder B is derived from polyamide powder A.

[0013] According to one embodiment, polyamide powders A and / or B have an intrinsic viscosity between 0.90 and 1.50.

[0014] According to one embodiment, the difference in intrinsic viscosity between polyamide powder A and polyamide powder B does not exceed, in absolute value, 0.5, preferably 0.4 and most particularly 0.3.

[0015] According to one embodiment, the polyamide powder composition comprises polyamide powder A in an amount of 20% to 80% by weight, preferably 30% to 70% by weight, most particularly 40% to 60% by weight.

[0016] According to one embodiment, the polyamide powder composition comprises 20% to 80% by weight of polyamide powder B, preferably 30% to 70% by weight, most particularly 40% to 60% by weight.

[0017] According to a second aspect, the present invention provides a method for producing a medicament for the treatment of a medicament comprising: (i) virgin polyamide powder A having an intrinsic viscosity calculated according to equation (1) from the flow rate of a solution of polymer and solvent, measured with an Ubbelohde viscometer in accordance with ISO Standard 307:2019, apart from the use of m-cresol as solvent and at a temperature of 20°C, of ​​0.8 to 2.8 with a span between 0.4 and 1.40; (ii) a polyamide powder B having an intrinsic viscosity calculated as above of 0.8 to 2.8, with a span between 0.4 and 1.40, which has been previously used in 3D printing by laser sintering; and (iii) Optional additives and / or fillers wherein the difference in intrinsic viscosity of each is understood to be no more than 0.6 in absolute value.

[0018] According to yet another aspect, the present invention provides a method for producing a sintered body by 3D printing with laser sintering, comprising: (i) preparing a polyamide powder composition as defined above; (ii) 3D printing the polyamide powder batch by laser sintering to obtain a sintered body. The process includes the steps of:

[0019] According to one embodiment, polyamide powder A and polyamide powder B are each chosen from PA 6, PA 66, PA613, PA1010, PA 1012, PA 11, PA 12, PA 11 / 10T and copolymers thereof.

[0020] According to one embodiment, polyamide powder B is derived from polyamide powder A.

[0021] According to one embodiment, the difference in intrinsic viscosity between polyamide powder A and polyamide powder B does not exceed, in absolute value, 0.5, preferably 0.4 and most particularly 0.3.

[0022] According to one embodiment, the polyamide powders A and / or B have an intrinsic viscosity between 0.9 and 1.5.

[0023] And according to a final aspect, the invention relates to a sintered body comprising particles of a polyamide powder composition as defined above, assembled by partial melting, characterized in that the surface roughness, measured under the conditions described in the examples, is Rz<50 μm and Ra<10 μm. DETAILED DESCRIPTION OF THE INVENTION

[0024] Definition of Terms The nomenclature used to describe polyamides follows ISO standard 1874-1. In particular, in the PA X designation, X represents the number of carbon atoms in the polyamide unit resulting from the condensation of an amino acid or a lactam. In the PA XY designation, which refers to a polyamide resulting from the condensation of a diamine with a dicarboxylic acid or a difunctional acid derivative, X represents the number of carbon atoms in the diamine and Y represents the number of carbon atoms in the dicarboxylic acid or acid derivative. The designation PA X / Y refers to a copolyamide where X and Y are two different monomers.

[0025] The term "powder bed additive manufacturing" is understood to denote a process in which a powder bed, which is a layer of polymer powder, is irradiated with electromagnetic radiation (e.g., laser beam, infrared, ultraviolet) to selectively melt the powder particles bombarded by the radiation. The molten particles coalesce and solidify to form a solid mass. This method can produce articles by repeatedly irradiating freshly applied layers of powder.

[0026] Furthermore, the term "volume mean diameter" or "Dv" refers to the volume average diameter of a powder material measured by laser diffraction according to ISO standard 13320:2009, for example, using a Malvern Insitec® diffractometer. Similarly, "Dv10" and "Dv90" are the corresponding diameters at which the cumulative volume-weighted particle diameter function is equal to 10% and 90%, respectively. More specifically, Dv50 refers to the volume median diameter. Rules for the presentation of particle size distribution results are specified in ISO standard 9276 - Parts 1 to 6.

[0027] The term "span" refers to a ratio that describes the width of the particle size distribution of a powder and is given by the following formula: [Number 1] Represented by TIFF2026500500000001.tif19170, During the ceremony, Dv10 denotes the diameter at which less than 10% by volume of the particles of the polymer powder fall; - Dv50 denotes the diameter at which less than 50% by volume of the particles of the polymer powder are contained (by definition, Dv50 is also the volume median diameter), and Dv90 denotes the diameter at which less than 90% by volume of the particles of the polymer powder fall; These diameters are measured as described above.

[0028] The term "intrinsic viscosity" refers to the viscosity calculated from the flow rate of a solution of polymer and solvent measured in an Ubbelohde-type viscometer according to ISO standard 307:2019, apart from the use of m-cresol as the solvent and a temperature of 20°C. Intrinsic viscosity is calculated according to the following equation (1): [Number 2] Calculated according to TIFF2026500500000002.tif15170. Intrinsic viscosity is equal to the natural logarithm of the ratio of the flow time of the polymer solution, t, divided by the flow time of the solvent, t0, as a mass percentage, divided by the concentration, c, of the polymer dissolved in the solvent. The dimension of intrinsic viscosity is the reciprocal of the concentration, where it is unitless when the concentration is given as a mass percent.

[0029] A. Polyamide Powder Composition Polyamide powder compositions useful for powder bed additive manufacturing according to the present invention include those comprising: (a) 10% by weight to 90% by weight of polyamide powder A having an intrinsic viscosity calculated according to equation (1) from the flow rate of a solution of polymer and solvent, measured with an Ubbelohde viscometer in accordance with ISO Standard 307:2019, apart from the use of m-cresol as solvent and at a temperature of 20°C, of ​​0.8 to 2.8 with a span between 0.4 and 1.40; (b) 90% to 10% by weight of a polyamide powder B different from the polyamide powder A, having an intrinsic viscosity calculated as above of 0.8 to 2.8 with a span between 0.4 and 1.40; (C) 0% to 40% by weight of additives and / or fillers It is understood that the difference in intrinsic viscosity between powders A and B does not exceed 0.6 in absolute value.

[0030] Polyamide powder A and polyamide powder B are different. They may be the same polyamide powder or different polyamide powders. Preferably, they are the same polyamide powder. The polyamide powders differ in at least one property. This property is in particular their appearance, such as color, intrinsic viscosity, particle size, crystallinity, or thermal properties.

[0031] In particular, one of the polyamide powders in the composition may be derived from the other polyamide powder in the composition, in particular by recycling.

[0032] The polyamide powders A and B have intrinsic viscosities whose difference remains moderate in order to avoid non-uniformity in the sintered workpiece. Thus, according to the present invention, these polyamide powders have an intrinsic viscosity difference of no more than 0.6, in particular 0.5, more preferably 0.4, and most particularly 0.3, as an absolute value. Preferably, the intrinsic viscosity difference, as an absolute value, is 0 to 0.6, in particular 0.05 to 0.5, and most particularly 0.1 to 0.3.

[0033] Furthermore, according to the invention, these polyamide powders have an intrinsic viscosity of at least 0.8, preferentially at least 1, more preferably at least 1.2. According to the invention, these polyamide powders have an intrinsic viscosity of less than or equal to 2.8, preferentially less than or equal to 2.5.

[0034] These viscosity ranges are particularly advantageous, making 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).

[0035] The viscosity of polyamide powders depends not only on the nature of the polyamide but also on its molecular weight in particular, so that polyamides with higher molecular weights will have a higher viscosity than polyamides with the same lower molecular weight.

[0036] Most commercially available polyamides are available in a variety of viscosity grades, so it is easy to select from the range of polyamides offered those with the specified viscosity difference.

[0037] Furthermore, if powders A and B are the same polyamide powder but differ in that one is recycled and the other is not or only rarely recycled, they will generally also have a difference in viscosity, which can vary significantly and is easily measurable depending on the powder formulation and the temperature and time of use of the recycled powder.

[0038] According to the present invention, the polyamide powder composition further has a specific particle size, characterized in particular by its span.

[0039] Specifically, the particle size distribution of polyamide powders can have a significant impact on the performance of additive manufacturing by sintering, especially on roughness.

[0040] Thus, according to the invention, the polyamide powder has a span, as defined above, between 0.4 and 1.40, in particular between 0.6 and 1.10, in particular between 0.8 and 1.0.

[0041] According to one embodiment, the polyamide powder in the composition preferably has a volume average diameter Dv10 greater than 15 μm. According to certain embodiments, the polyamide powder has a volume average diameter Dv10 between 15 μm and 50 μm, or between 25 μm and 45 μm, or between 30 μm and 40 μm.

[0042] According to one embodiment, the volume average diameter Dv50 of the powder is preferably between 30 μm and 60 μm. According to one particular embodiment, the polyamide powder has a volume average diameter Dv50 between 35 μm and 55 μm, or between 40 μm and 50 μm.

[0043] According to one embodiment, the polyamide powder has a volume average diameter Dv90 of less than 120 μm, in particular less than 100 μm, most particularly less than 90 μm. According to certain embodiments, the polyamide powder has a volume average diameter Dv90 of between 40 μm and 120 μm, or between 45 μm and 100 μm, or between 50 μm and 80 μm.

[0044] Finally, the polyamide powder advantageously has a volume average diameter Dv of less than 55 μm. According to certain embodiments, the polyamide powder has a volume average diameter Dv90 of between 30 μm and 55 μm, or between 35 μm and 50 μm, or between 40 μm and 45 μm.

[0045] The polyamide may in particular be chosen from aliphatic polyamides, semicrystalline polyamides, and copolymers and blends thereof.

[0046] Mention may in particular be made of aliphatic polyamides such as PA 6, PA 66, PA 613, PA 1010, PA 1012, PA 11, PA 12 and their copolymers, and semi-aromatic polyamides such as PA 11 / 10T.

[0047] Advantageously, the composition comprises 20% to 80% by weight, preferably 25% to 70% by weight, and most particularly 30% to 60% by weight of polyamide powder A. According to one particular embodiment, the polyamide powder composition comprises 10% to 20% by weight, or 20% to 30% by weight, or 30% to 40% by weight, or 40% to 50% by weight, or 50% to 60% by weight, or 60% to 70% by weight, or 70% to 80% by weight, or 80% to 90% by weight of polyamide powder A relative to the total weight of the polyamide powder composition.

[0048] Advantageously, the composition comprises 20% to 80% by weight, preferably 25% to 70% by weight, and most particularly 30% to 60% by weight of polyamide powder B. According to one particular embodiment, the polyamide powder composition comprises 10% to 20% by weight, or 20% to 30% by weight, or 30% to 40% by weight, or 40% to 50% by weight, or 50% to 60% by weight, or 60% to 70% by weight, or 70% to 80% by weight, or 80% to 90% by weight of polyamide powder B relative to the total weight of the polyamide powder composition.

[0049] Preferably, the polyamide powder composition does not contain other polyamides.

[0050] The remainder of the composition may consist of other compounds, in particular fillers and / or additives. The polyamide powder composition may, in addition to polyamide powders A and B, in particular comprise 0 to 40% by weight of one or more conventional additives and fillers.

[0051] The additives generally account for less than 5% by weight of the total weight of the composition. Preferably, the additives account for less than 1% by weight of the total weight of the powder. The additives may include flow agents, stabilizers (light stabilizers, especially UV stabilizers and heat stabilizers), optical brighteners, colorants, pigments, and energy absorbing additives (including UV absorbers). Advantageously, the composition does not contain pigments or colorants.

[0052] The flow agent may be, for example, hydrophilic or hydrophobic silica. The flow agent advantageously represents 0.01% to 0.4% by weight relative to the total weight of the composition. In another embodiment, the powder composition does not contain a flow agent.

[0053] The polyamide powder composition may also contain one or more fillers, which generally represent less than 40% by weight, in particular less than 30% by weight, and preferably less than 25% by weight, relative to the total weight of the final powder composition. Fillers may include reinforcing fillers, in particular mineral fillers such as carbon black, talc, carbon or non-carbon nanotubes, and fibers, in particular crushed or non-crushed glass or carbon fibers, or glass in other forms, such as flakes or hollow or filled balls.

[0054] B. 3D printing method using laser sintering The processes of interest for the present invention are in particular selective laser sintering (SLS) processes, sintering processes of the MJF (Multi Jet Fusion) type or sintering processes of the HSS (High Speed ​​Sintering) type.

[0055] The SLS method is widely known and in this connection reference may be made in particular to US Pat. No. 6,136,948 and WO 96 / 06881.

[0056] According to this type of sintering method, a thin layer of powder is deposited on a horizontal plate held in a chamber heated to a temperature known as the build temperature. Heating to the build temperature is typically achieved using IR radiation lamps, e.g., halogen lamps, which generally have an emission maximum at wavelengths between 750 nm and 1250 nm. The build temperature refers to the temperature to which the powder bed of the constituent layers of the three-dimensional object being built is heated during the layer-by-layer sintering process. Electromagnetic radiation, e.g., in the form of a laser, then provides the energy necessary to sinter the powder particles at different points in the powder layer according to the shape corresponding to the object, using a computer that stores the shape of the object in memory and reproduces it in slice form. The horizontal plate is then lowered a distance corresponding to the thickness of the powder layer, and a new layer of powder is sprayed, heated, and sintered in the same manner. This procedure is repeated until the object is manufactured.

[0057] The powder layer deposited on the horizontal plate may have a thickness of, for example, 20 to 200 μm, preferably 50 to 150 μm, before sintering. After sintering, the layer of agglomerated material may have a slightly lower thickness, for example, 10 to 150 μm, preferably 30 to 120 μm.

[0058] In the MJF and HSS processes, the entire layer of build material is exposed to radiation, but only the portions covered by the fluxing agent melt into layers of the 3D workpiece. The fluxing agent is a compound capable of absorbing radiation and converting it into thermal energy, such as black ink. It is selectively applied to selected areas of the build material. The fluxing agent is able to penetrate the layers of build material, transferring the absorbed energy to adjacent build materials, causing them to melt or sinter. The melting, bonding, and subsequent hardening of each layer of build material forms the object.

[0059] In the particular case of MJF, a detailing agent is also added to the edge of the melting zone to give the workpiece better definition.

[0060] Advantageously, the use of the polyamide powder compositions described below in these methods does not require any special modifications, but allows for the production of highly detailed workpieces with good surface appearance and particularly low roughness.

[0061] Advantageously, this method allows the polyamide powder composition to be used for several successive builds, where it may be recycled alone or compounded with other recycled or non-recycled powders.

[0062] C. Method for Producing Polyamide Powder The polyamide powder contained in the composition can in particular be obtained by grinding polyamide in the form of extruded granules or flakes, according to conventional techniques.

[0063] The grinding can be carried out in equipment known for this purpose, such as counter-rotating pin mills, hammer mills or orbital mills.

[0064] If the powder contains, in addition to the polyamide powder, certain additives and / or certain reinforcing fillers, these additives and / or fillers can be incorporated by melt kneading, for example by extrusion (compounding) and granulation, followed by grinding of the granules. Alternatively, it is also possible to add other polymers and / or certain additives and / or certain reinforcing fillers by dry kneading. Preferably, the flow agent is added by dry kneading.

[0065] According to one embodiment, the process for producing a polyamide powder comprises the following steps: (i) prepolymerizing polyamide monomers followed by granulation; (ii) grinding to a powder; (iii) optionally sieving the resulting prepolymer powder; (iv) treating the prepolymer powder by contacting it with water or water vapor at a temperature close to its crystallization temperature Tc for a time sufficient to increase its melting temperature and / or heat of fusion, to bring it into a solid state, separating the water or water vapor from the prepolymer powder, and drying; this step allows the addition of a powder with the desired phosphoric acid content. (v) subjecting the resulting treated prepolymer powder to solid-state polycondensation to obtain a polymer powder.

[0066] A method for treating prepolymer powders is described in particular in EP 1 413 595 A1.

[0067] Alternatively, the polyamide powder may also be produced via other processes known in the art, for example by precipitation anionic polymerization as described in EP 1814931 B1 or FR 06 / 56024 B1.

[0068] The intrinsic viscosity of the polyamide powder thus obtained depends greatly on the polycondensation parameters and, in the case of the process described, on the solid-state polycondensation.

[0069] It should further be noted that the intrinsic viscosity of the polyamide powder may increase during aging of the powder, i.e., with time, especially exposure to heat. The rate at which the intrinsic viscosity of the polyamide powder increases depends, among other things, on the temperature and also on the presence or absence of antioxidants or catalysts. Catalysts may include, among other things, phosphorous acid, especially hypophosphorous acid, phosphorous acid, and phosphoric acid.

[0070] As mentioned above, it is particularly preferred to combine the polyamide powder in a composition with recycled polyamide powder that has been used in 3D printing, in particular by laser sintering, and has therefore been exposed to temperatures close to the melting point for a significant period of time. Particularly advantageous are compositions that contain the same recycled polyamide powder as the polyamide powder.

[0071] Such polyamide powder compositions can be produced in particular by combining a primary polyamide powder having the required properties with a recycled polyamide powder having the required properties, the intrinsic viscosity of each being adjusted so that the viscosity difference between the powders does not exceed a certain value.

[0072] The additives and / or reinforcing fillers may be added to the prepolymer by melt compounding or dry compounding between process steps (i) and (ii), or they may be added to the composition later, in particular by dry compounding.

[0073] If the span of a powder is too low, it can be increased by adding finer or larger particles, and conversely, if the span of a powder is too high, it can be reduced by separating out the finest or largest particles, for example by sieving or defining.

[0074] D. Manufacturable workpieces The use of the composition according to the invention therefore allows the production of three-dimensional workpieces of good quality, in particular of good surface quality, and in particular these articles may have a low roughness.

[0075] This polyamide powder composition allows for the additive manufacturing by sintering of workpieces having properties, particularly surface characteristics, that are at least close to, if not better than, workpieces obtained with conventional polyamide powders, particularly with regard to roughness.

[0076] According to the present patent application, the roughness of the sintered body is evaluated by a roughness meter, in particular a non-contact roughness meter, such as the AltiSurf® 500 surface condition characterization station from AltiMet, using an AltiProbe Optic optical sensor with a measurement point acquisition rate of 1000 Hz. The roughness measured in this way is expressed by the usual parameters Ra, which indicates the arithmetic mean roughness of the profile, and Rz, which indicates the maximum roughness of the profile.

[0077] The sintered body may therefore comprise particles of a polyamide powder composition as described above assembled by partial melting, and is characterized by a surface roughness, measured under the conditions described in the examples, of Rz<50 μm and Ra<10 μm.

[0078] The present invention is further illustrated in the following examples.

[0079] Unless otherwise indicated, percentages listed are percentages by weight based on the weight of the final composition. [Example]

[0080] A. Particle size The powders were characterized in terms of particle size using a Malvern Insitec laser diffractometer equipped with RT Sizer software according to ISO standard 13320:2009.

[0081] A laser beam is shone on particles moving through the air. Objects scatter and re-emit light, with smaller particles scattering more light than larger particles. The diffracted (scattered) light is received by a series of photodetectors positioned at different angles. This creates a diffraction image of the sample. This image is used to measure particle size using a light scattering theory known as Mie theory.

[0082] The measurement is carried out on 30 g of powder. The measured particle size distribution parameters Dv10, Dv50, Dv90 and span are recorded.

[0083] B. Viscosity measurement Apart from the use of m-cresol as solvent and a temperature of 20 °C, the intrinsic viscosity of the powder was determined from the flow time of the solution and solvent measured with a viscometer equipped with a micro-Ubbelohde type 538-23 IIC tube in accordance with ISO standard 307:2019.

[0084] Polyamide 11 A: Rilsan® Invent Natural sold by Arkema with 6000 ppm H3PO4, inherent viscosity 1.2; Polyamide 11 B: Polyamide 11 A aged in a vacuum oven at 180°C for 7 hours, intrinsic viscosity 1.7; Polyamide 11 C: Rilsan® Invent Natural sold by Arkema with 10,000 ppm H3PO4, inherent viscosity 1.2; Polyamide 11 D: Polyamide 11 C, inherent viscosity 1.3, aged in a vacuum oven at 180°C for 7 hours; Polyamide 11 E: Rilsan® Invent Natural sold by Arkema with 600 ppm H3PO4, inherent viscosity 1.2; Polyamide 11 F: Polyamide 11 E, inherent viscosity 2.5, aged in a vacuum oven at 180°C for 7 hours; Polyamide 12 G: Orgasol® Invent Smooth, intrinsic viscosity 1.3, available from Arkema; Polyamide 12 H: Polyamide 12 G, inherent viscosity 1.3, aged in a vacuum oven at 170°C for 7 hours; Polyamide 11 I: Polyamide 11 F, inherent viscosity 3.0, aged in a vacuum oven at 180°C for 7 hours; [Table 1] JPEG2026500500000003.jpg66170

[0085] Example 1 50% by weight of polyamide 11 powder A and 50% by weight of polyamide 11 powder B were dry-mixed in a Henschel mixer at a rotation speed of 900 rpm for 100 seconds. The properties of each powder are shown in Table 1 above.

[0086] The resulting powder compositions were characterized for particle size and intrinsic viscosity as described above.

[0087] - Dv10=19μm - Dv50=45μm - Dv90=79μm - Span=1.33 - IV=1.45 The resulting polyamide powder composition was used to produce 1A XY test specimens (test specimen 1A according to ISO standard 527-2, called "XY" because it was printed on the horizontal plane of the printer) by 3D printing with laser sintering on a P100 machine (sold by EOS) while adjusting the powder layer thickness to 100 μm. The printing parameters used were as follows: Laser output: 24W Laser speed: 3000mm / s Distance between two laser paths: 0.25mm The roughness of the test specimens was determined using a non-contact roughness tester (e.g., AltiMet's AltiSurf® 500 Surface State Characterization Station) using an Alti Probe Optic optical sensor with a point acquisition rate of 1000 Hz. Roughness is expressed by the usual parameters Ra and Rz. The roughness of the top surface of the sintered test specimens is measured horizontally. The results are listed in Table 2 below. It can be seen that by using this powder it is possible to obtain sintered workpieces with low roughness.

[0088] Example 2 50% by weight of polyamide 11 powder C and 50% by weight of polyamide 11 powder D were dry-mixed in a Henschel mixer at a rotation speed of 900 rpm for 100 seconds. The properties of each powder are shown in Table 1 above.

[0089] The resulting powder compositions were characterized for particle size and intrinsic viscosity as described above.

[0090] - Dv10=19μm - Dv50=45μm - Dv90=79μm - Span=1.33 - IV=1.25 The resulting polyamide powder composition was used to fabricate 1A XY test specimens by 3D printing with laser sintering, as shown in Example 1.

[0091] The roughness of the test specimens was determined as shown in Example 1. The results are listed in Table 2 below, which shows that this powder is capable of obtaining sintered workpieces with very low roughness.

[0092] Example 3 50% by weight of polyamide 12 powder G and 50% by weight of polyamide 12 powder H were dry-mixed in a Henschel mixer at a rotation speed of 900 rpm for 100 seconds. The properties of each powder are shown in Table 1 above.

[0093] The resulting powder compositions were characterized for particle size and intrinsic viscosity as described above.

[0094] - Dv10=33μm - Dv50=40μm - Dv90=50μm - Span=0.43 - IV=1.3 The resulting polyamide powder composition was used to fabricate 1A XY test specimens by 3D printing with laser sintering, as shown in Example 1.

[0095] The roughness of the test specimens was determined as shown in Example 1. The results are listed in Table 2 below, which shows that this powder is capable of obtaining sintered workpieces with very low roughness.

[0096] Example 4 (Comparative) 50% by weight of polyamide 12 powder F and 50% by weight of polyamide 12 powder I were dry-mixed in a Henschel mixer at a rotation speed of 900 rpm for 100 seconds. The properties of each powder are shown in Table 1 above.

[0097] The resulting powder compositions were characterized for particle size and intrinsic viscosity as described above.

[0098] - Dv10=19μm - Dv50=45μm - Dv90=79μm - Span=1.33 - IV=2.75 The resulting polyamide powder composition was used to fabricate 1A XY test specimens by 3D printing with laser sintering, as shown in Example 1.

[0099] The roughness of the specimens was determined as shown in Example 1. The results are listed below in Table 2. It is observed that the use of this powder results in sintered workpieces with high roughness.

[0100] Example 5 70% by weight of polyamide 11 powder C and 30% by weight of polyamide 11 powder D were dry-mixed in a Henschel mixer at a rotation speed of 900 rpm for 100 seconds. The properties of each powder are shown in Table 1 above.

[0101] The resulting powder compositions were characterized for particle size and intrinsic viscosity as described above.

[0102] - Dv10=19μm - Dv50=45μm - Dv90=79μm - Span=1.33 - IV=1.3 The resulting polyamide powder composition was used to fabricate 1A XY test specimens by 3D printing with laser sintering, as shown in Example 1.

[0103] The roughness of the test specimens was determined as shown in Example 1. The results are listed in Table 2 below, which shows that this powder is capable of obtaining sintered workpieces with very low roughness.

[0104] Example 6 70% by weight of polyamide 12 powder G and 30% by weight of polyamide 12 powder H were dry-mixed in a Henschel mixer at a rotation speed of 900 rpm for 100 seconds. The properties of each powder are shown in Table 1 above.

[0105] The resulting powder compositions were characterized for particle size and intrinsic viscosity as described above.

[0106] - Dv10=33μm - Dv50=40μm - Dv90=50μm - Span=0.43 - IV=1.3 The resulting polyamide powder composition was used to fabricate 1A XY test specimens by 3D printing with laser sintering, as shown in Example 1.

[0107] The roughness of the test specimens was determined as shown in Example 1. The results are listed in Table 2 below, which shows that this powder is capable of obtaining sintered workpieces with very low roughness.

[0108] Example 7 (Comparative) 50% by weight of polyamide 11 powder E and 50% by weight of polyamide 11 powder F were dry-mixed in a Henschel mixer at a rotation speed of 9000 rpm for 100 seconds. The properties of each powder are shown in Table 1 above.

[0109] The resulting powder compositions were characterized for particle size and intrinsic viscosity as described above.

[0110] - Dv10=19μm - Dv50=45μm - Dv90=79μm - Span=1.33 - IV=1.85 The resulting polyamide powder composition was used to fabricate 1A XY test specimens by 3D printing with laser sintering, as shown in Example 1.

[0111] The roughness of the specimens was determined as shown in Example 1. The results are listed below in Table 2. It is observed that the use of this powder produces sintered workpieces with high roughness. [Table 2] JPEG2026500500000004.jpg61170

[0112] The surface properties of the sintered workpiece are considered acceptable if the roughness of the 1A XY specimen is characterized by an Rz of less than 50 μm and an Ra of less than 10 μm. Conversely, an Rz of more than 50 μm and an Ra of more than 10 μm is considered poor.

[0113] The results in Table 2 above demonstrate the advantages of polyamide powder compositions with specific intrinsic viscosities and spans, with limited intrinsic viscosity differences. Specifically, sintered bodies made from these powders have good surface properties, particularly low roughness.

[0114] References list U.S. Patent Publication No. 2011 / 0237731 U.S. Patent Publication No. 2018 / 094103

Claims

1. 1. A polyamide powder composition comprising: (a) The flow rate of a solution of polymer and solvent, measured with an Ubbelohde viscometer according to ISO standard 307:2019, excluding the use of m-cresol as the solvent and a temperature of 20° C., is calculated from the formula (1): [Number 3]. 10% to 90% by weight of polyamide powder A, having an intrinsic viscosity calculated according to (b) 90% to 10% by weight of a polyamide powder B different from the polyamide powder A, having an intrinsic viscosity calculated as above of from 0.8 to 2.8 with a span between 0.4 and 1.40; (c) 0 to 40 wt. % of additives selected from flow agents, stabilizers, optical brighteners, and energy absorbing additives and / or fillers; wherein polyamide powder B is derived from polyamide powder A, and it is understood that the difference in intrinsic viscosity between powders A and B does not exceed 0.6 in absolute value.

2. 2. The polyamide powder composition according to claim 1, wherein polyamide powder A and polyamide powder B are each selected from PA 6, PA 66, PA613, PA1010, PA 1012, PA 11, PA 12, PA 11 / 10T and copolymers thereof.

3. 3. The polyamide powder composition according to claim 1 or 2, wherein polyamide powder A and / or polyamide powder B has a diameter Dv50 between 30 μm and 60 μm.

4. 4. Polyamide powder composition according to claim 1, wherein polyamide powder A and / or polyamide powder B has an intrinsic viscosity between 0.90 and 1.

50.

5. 5. Polyamide powder composition according to any one of claims 1 to 4, wherein the difference in intrinsic viscosity between polyamide powder A and polyamide powder B does not exceed, in absolute value, 0.5, preferably 0.4, most particularly 0.

3.

6. 6. Polyamide powder composition according to any one of claims 1 to 5, comprising 20 to 80% by weight, preferably 30 to 70% by weight, most particularly 40 to 60% by weight of polyamide powder A.

7. 7. Polyamide powder composition according to any one of claims 1 to 6, comprising 20% ​​to 80% by weight, preferably 30% to 70% by weight, most particularly 40% to 60% by weight of polyamide powder B.

8. The polyamide powder composition according to any one of claims 1 to 7, (i) The flow rate of the polymer and solvent solution measured with an Ubbelohde viscometer according to ISO standard 307:2019, excluding the use of m-cresol as the solvent and the temperature of 20° C., is calculated by the following equation (1): [Number 4]. Virgin polyamide powder A, having an intrinsic viscosity calculated according to (ii) a polyamide powder B having an intrinsic viscosity calculated as above of between 0.8 and 2.8, with a span between 0.4 and 1.40, which has been previously used in 3D printing by laser sintering, and (iii) optional additives and / or fillers wherein polyamide powder B is derived from polyamide powder A, and it is understood that the difference in their respective intrinsic viscosities does not exceed 0.6 in absolute value.

9. 1. A method for producing a sintered body by 3D printing with laser sintering, comprising: (i) preparing a polyamide powder composition according to any one of claims 1 to 7, and (ii) 3D printing the polyamide powder batch by laser sintering to obtain a sintered body. A method comprising the steps of:

10. 10. The process according to claim 9, wherein polyamide powder A and polyamide powder B are each selected from PA 6, PA 66, PA 613, PA 1010, PA 1012, PA 11, PA 12, PA 11 / 10T and copolymers thereof.

11. The method according to claim 9 or 10, wherein the polyamide powder B is derived from the polyamide powder A.

12. 12. Process according to any one of claims 9 to 11, wherein the difference in intrinsic viscosity between polyamide powder A and polyamide powder B does not exceed, in absolute value, 0.5, preferably 0.4, most particularly 0.

3.

13. 13. The process according to any one of claims 9 to 12, wherein polyamide powder A and / or polyamide powder B has an intrinsic viscosity between 0.9 and 1.

5.

14. 8. A sintered body comprising particles of the polyamide powder composition according to claims 1 to 7 assembled by partial melting, characterized in that it has a surface roughness measured by a non-contact profilometer (AltiMet AltiSurf® 500 surface condition characterization station) using an Alti Probe Optic optical sensor with a measurement point acquisition rate of 1000 Hz, characterized in that Rz<50 μm and Ra<10 μm.

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