Method for producing a polyamide powder

Abstract

The invention relates to a method for producing a polyamide powder having a single-mode melting endotherm and a single melting point (Tf1max), the method comprising the steps of: i) bringing a polyamide into contact with a solvent in order to obtain a mixture; ii) heating the mixture in order to solubilize the polyamide in the solvent; iii) cooling the mixture to the temperature (Tp) of precipitation of the polyamide from the solvent, thereby obtaining a powder characterized by a non-single-mode melting endotherm and more than one melting point, (Tf1max) being the highest melting point; iv) keeping the temperature of the mixture at a temperature that is at most equal to Tp, in particular within the range from Tp - 0.1°C to Tp - 15°C, until the precipitated polyamide powder is characterized by a single-mode melting endotherm and one melting point (Tf1max); and v) recovering the obtained polyamide powder.

Description

[0001] Description

[0002] Title: Process for manufacturing a polyamide powder

[0003] Field of invention

[0004] The present invention relates to a method for manufacturing a polyamide powder having an increased gap between the melting temperature and the crystallization temperature (Tn - T c ) polyamide powder.

[0005] A big gap between the Tfi and the T c of a polyamide-based powder is useful in many uses, and in particular in the technology of agglomeration of powder by fusion or sintering caused by radiation such as for example a laser beam (laser sintering), infrared radiation or UV radiation or any source of electromagnetic radiation allowing the powder to be melted to manufacture objects.

[0006] The present invention also relates to the polyamide powders obtained according to this process.

[0007] Finally, it concerns the use of this powder and the articles manufactured from it.

[0008] Prior art

[0009] The technology of agglomerating polyamide powders under a laser beam is used to manufacture three-dimensional objects such as prototypes and models in various fields.

[0010] A thin layer of polyamide powder is deposited on a horizontal plate held in an enclosure heated to a temperature between the crystallization temperature T cand the melting temperature T of the polyamide powder. The laser agglomerates powder particles at different points of the powder layer according to a geometry corresponding to the object, for example using a computer that stores the shape of the object and restores it in the form of slices. The powder areas exposed to the laser solidify as soon as their temperature falls below the crystallization temperature Tc. Then, the horizontal plate is lowered by a distance corresponding to the thickness of a layer of powder, then a new layer of powder is deposited and the laser agglomerates powder particles according to a geometry corresponding to this new slice of the object, and so on. The procedure is repeated until the entire object has been manufactured. Inside the enclosure, an object surrounded by non-agglomerated powder is obtained. The whole is then gently cooled.After complete cooling, the object is separated from the powder which can possibly be reused for another operation.

[0011] Immediately after the action of the laser beam, the temperature of the exposed area is higher than the crystallization temperature (T c ) of the powder. But when the temperature drops too quickly below this temperature, for example by adding a new layer of colder powder, this leads to deformations of the part being printed (the phenomenon of "curling" in English). Similarly, when the temperature of the powder gets too close to the melting temperature (Tfi) of the powder, this leads to caking around the parts, which manifests itself by the formation of lumps of powder affecting the quality of the print.

[0012] To avoid these phenomena, it is therefore important to have powders with a temperature Tc as far as possible from the T . The difference Tfi - Tc of the powder determines the working temperature window of the device used to agglomerate the powder particles by fusion caused by radiation. This working window is defined by its upper temperature limit and its lower temperature limit. The upper limit of the working window corresponds to the temperature at which agglomeration or "caking" occurs. The lower limit of the working window corresponds to the temperature at which distortion or deformation or "curling" occurs. It is desirable that this working window is greater than the temperature variation within 3D printing machines, which is generally of the order of + / -3°C.

[0013] Furthermore, a high enthalpy of fusion (AHf) is advantageous in order to optimize the geometric definition of the manufactured parts. Indeed, if the latter is too low, the energy provided by the laser risks sintering, by thermal conduction, the powder particles surrounding the part under construction, which limits the geometric precision of the part obtained.

[0014] It is clear that everything that has just been explained for the agglomeration of polyamide powders under a laser beam is valid regardless of the electromagnetic radiation that causes the fusion, whether the fusion process is selective or non-selective.

[0015] Document US 5,932,687 discloses a process for preparing a precipitated polyamide powder having a narrow particle distribution and low porosity. This process comprises a first step of cooling the polyamide previously dissolved in an alcohol solvent to a temperature Ti (higher than the precipitation temperature of the polyamide in the solvent) so as to obtain nucleation of the polyamide, followed by a second cooling step so as to obtain supersaturation of the medium and thus precipitation of the polyamide at a temperature T2. The suspension obtained is directly cooled and dried to recover the polyamide powder.

[0016] Document US 2008 / 0166496 discloses a polyamide 11 powder that can be used in a powder agglomeration process, in particular for preparing three-dimensional objects. These powders are prepared according to a process comprising a step of cooling the polyamide previously dissolved in ethanol to a temperature at which the polyamide precipitates. The heat generation induced by the precipitation maintains the medium at this temperature for 25 minutes, then the temperature decreases slightly and a 35-minute isotherm is achieved. At the end of this stage, the mixture is cooled to isolate the precipitated polyamide powder.

[0017] However, the inventors were able to observe that the processes of the state of the art made it possible to obtain polyamide powders whose analysis by differential scanning calorimetry, in 1 èreheating, shows the presence of two temperature peaks, associated with two relatively close but distinct melting points, revealing the presence of distinct crystalline phases. However, for the reasons mentioned above, this heterogeneity of the thermal characteristics of the powder reduces the working window and is therefore likely to harm the quality of objects manufactured using the powder agglomeration process by fusion using electromagnetic radiation, in particular their definition.

[0018] There is therefore a real need for a process for preparing polyamide powders, useful for powder agglomeration technologies by fusion caused by electromagnetic radiation, which can overcome these drawbacks.

[0019] Summary of the invention

[0020] The inventors have now developed a dissolution / precipitation process that can effectively increase the T - Te difference of existing polyamides, obtaining a monomodal melting endotherm.

[0021] More particularly, it was discovered that by introducing, at the end of the polyamide precipitation phase, a temperature plateau of sufficient duration, it was possible to convert a powder characterized by a non-monomodal melting endotherm and more than one melting temperature (Tfi), (Tfi max ) being the highest melting temperature, in a polyamide powder characterized by a monomodal melting endotherm, and a single melting temperature (Tfi ) equal to (Tfi max ) and thus increase the temperature difference (Tfi - T c). The inventors were able to demonstrate that this temperature level allowed for crystalline improvement, and thus to obtain a single crystalline phase.

[0022] The polyamide powders obtained are thus particularly advantageous for use in a powder agglomeration process by fusion using electromagnetic radiation, in particular in that they make it possible to widen the working window and therefore to improve the quality and / or definition of the objects manufactured from these powders.

[0023] According to a first aspect, the invention thus aims to provide a method for manufacturing a polyamide powder having a monomodal melting endotherm and a single melting temperature (Tfi max), said method comprising the steps of: i) bringing a polyamide into contact with a solvent in order to obtain a mixture; ii) heating the mixture in order to solubilize the polyamide in the solvent; ii) cooling the mixture to the precipitation temperature (T P ) of the polyamide in said solvent, whereby a powder characterized by a non-monomodal melting endotherm and more than one melting temperature is obtained, (Tfi max ) being the highest melting temperature; iv) maintaining the temperature of the mixture at a temperature at most equal to T P , notably included in the range from T P - 0.1 °C at T P -15°C, until the precipitated polyamide powder is characterized by a monomodal melting endotherm and a melting temperature (Tfi max ); and v) recovery of the polyamide powder obtained.

[0024] Advantageously, the method further has one or more of the following additional characteristics.

[0025] Thus, in embodiments, the method according to the invention is a method:

[0026] - in which the solvent which is brought into contact with the polyamide is an alcohol, in particular a C1-C4 aliphatic alcohol, preferably ethanol;

[0027] - wherein the heating of the mixture is carried out at a temperature of 100°C to 200°C, and preferably of 120°C to 160°C; and / or wherein the heating of the mixture has a duration of 1 to 6 hours, and preferably of 1 to 3 hours;

[0028] - wherein the cooling of the mixture in step iii) is carried out at a rate of 1°C to 100°C per hour and preferably of 10°C to 60°C per hour;

[0029] - in which the polyamide is polyamide 11, polyamide 6, or polyamide 10.10, or polyamide 10.12, or polyamide 6.10;

[0030] - in which the precipitation temperature T P polyamide is between 80°C and 130°C, in particular between 100 and 120°C;

[0031] - in which in step iv), the mixture is maintained at a temperature at most equal to T P for a period of at least 2 hours, in particular between 3 and 12 hours, from the start of precipitation of the polyamide;

[0032] - further comprising a step vi) of drying the precipitated polyamide powder recovered in step v) or obtained at the end of step iv), in particular at a temperature between 10°C and 150°C, more particularly between 50 and 100°C; and / or

[0033] - in which the drying of the precipitated polyamide powder is carried out at a pressure ranging from 10 mbar to atmospheric pressure.

[0034] According to a second aspect, the present invention also aims to provide a polyamide powder having a monomodal melting endotherm and a single melting temperature (Tfi max ) capable of being obtained by the process according to the invention.

[0035] Advantageously, the powder also has one or more of the following additional characteristics.

[0036] Thus, in embodiments, the powder is a powder:

[0037] - characterized in that it has a volume average diameter of between 10 and 200 pm, in particular between 20 and 100 pm, and preferably between 40 and 80 pm;

[0038] - characterized in that it has a diameter Dv10 greater than 5 pm, in particular between 10 and 70 pm, and preferably between 20 and 60 pm;

[0039] - characterized in that it has a diameter Dv90 of less than 350 pm, in particular between 30 and 200 pm, and preferably between 50 and 150 pm;

[0040] - characterized in that it has a median diameter Dv50 of between 10 and 200 pm, in particular of between 20 and 100 pm, and preferably of between 30 and 90 pm;

[0041] - characterized in that it has a span factor of between 0.1 and 1.5, preferably between 0.1 and 1.0 and more preferably between 0.5 and 1.0;

[0042] - in which the polyamide is polyamide 11;

[0043] - characterized in that it has a melting temperature (Tfi max ) between 195 and 205°C; and / or

[0044] - in which the difference between the melting temperature (Tfi max ) and the crystallization temperature (T c ) is between 35 and 45°C.

[0045] According to a third aspect, the present invention also relates to a polyamide 11 powder having a monomodal melting endotherm and a single melting temperature (Tfi max ) between 195°C and 205°C, also having at least one of the following characteristics:

[0046] - a volume average diameter of between 10 and 200 pm, in particular between 20 and 100 pm, and preferably between 40 and 80 pm;

[0047] - a diameter Dv10 greater than 5 pm, in particular between 10 and 70 pm, and preferably between 20 and 60 pm;

[0048] - a median volume diameter Dv50 of between 10 and 200 pm, in particular between 20 and 100 pm, and preferably between 30 and 90 pm;

[0049] - a diameter Dv90 of less than 350 pm, in particular between 30 and 200 pm, and preferably between 50 and 150 pm; - a span factor of between 0.1 and 1.5, preferably between 0.1 and 1, and more preferably between 0.5 and 1.0;

[0050] - a fusion enthalpy greater than 100 J / g; and preferably between 110 and 160 J / g; and / or

[0051] - an inherent viscosity between 0.8 and 1.8, and preferably between 1.0 and 1.5.

[0052] According to a fourth aspect, the invention relates to a composition in powder form for 3D printing, in particular by laser sintering, comprising:

[0053] - a polyamide powder according to the invention; and

[0054] - at least one filler or additive.

[0055] According to a fifth aspect, the invention relates to a method for manufacturing polyamide objects by agglomeration of powder by fusion using electromagnetic radiation, the powder being as defined in the present description.

[0056] According to a sixth aspect, the invention relates to a manufactured article obtained by melting using electromagnetic radiation a powder or a composition according to the invention.

[0057] According to a seventh aspect, the invention relates to the use of a method according to the invention for increasing the difference (Tfi -Te) between the melting temperature (Tfi) and the crystallization temperature (T c ) of a polyamide.

[0058] Figures

[0059] [Fig.1] represents the thermograms, illustrating the heat flow as a function of temperature, obtained by differential scanning calorimetry of polyamide 11 of comparative example 2, as follows:

[0060] (a): first heating, (b) subsequent cooling and (c) second heating, with the corresponding enthalpy of fusion AHf;

[0061] [Fig. 2] represents the thermograms, illustrating the heat flow as a function of temperature, obtained by differential scanning calorimetry of polyamide 11 of example 3, as follows:

[0062] (a): first heating, (b) subsequent cooling and (c) second heating, with the corresponding enthalpy of fusion AHf; and [Fig. 3] represents the thermograms, illustrating the heat flux as a function of temperature, obtained by differential scanning calorimetry of polyamide 11 of comparative example 4, as follows:

[0063] (a): first heating, (b) subsequent cooling and (c) second heating, with the corresponding enthalpy of fusion AHf.

[0064] Detailed description

[0065] The invention is now described in more detail and in a non-limiting manner in the following description.

[0066] Definitions

[0067] It is specified that the expressions “from ... to ...” and “between ... and ...” used in this description must be understood as including each of the limits mentioned.

[0068] The term "powder" means 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.

[0069] Powders are generally characterized by thermograms obtained by differential scanning calorimetry (DSC) according to:

[0070] - a first heating, allowing the characterization of the melting phenomenon of the polyamide powder;

[0071] - cooling to characterize the crystallization phenomenon of the polyamide material;

[0072] - a 2nd heating allowing the characterization of the melting phenomenon of the polyamide material itself.

[0073] The following terms are understood to mean in relation to thermal properties, as defined in ISO 11357-1:2016:

[0074] - a “peak” means the part of the thermogram obtained by differential scanning calorimetry (DSC) which deviates from the baseline to reach a local maximum or a local minimum, then returns to the baseline. Such a peak may indicate a first-order transition (crystallization exotherm or melting endotherm); a melting peak, as used herein, may in particular comprise several peaks or shoulders before the signal returns to the baseline.

[0075] - a “baseline” means the part of the recorded thermogram without any transition, in particular here without any first-order transition of the melting or crystallization type. At a transition zone, a virtual baseline can be determined: it 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 baseline of the specimen by means of a straight line;

[0076] - a "peak area" means the area delimited by the peak and the interpolated virtual baseline. It is similar to a transition enthalpy, expressed in J / g. The term "enthalpy of fusion" is intended to denote the heat required to melt the composition, corresponding to the area under the melting peak on the thermogram, measured according to ISO 11357-3:2018;

[0077] The term "melting temperature" is understood to mean the temperature representative of the melting phenomenon during which the polyamide powder or the at least partially crystalline polyamide material passes into the viscous liquid state as measured according to ISO 11357-3:2018. Thus, within the meaning of this description, a melting peak, which would comprise several peaks or shoulders, would be associated with several melting temperatures, namely a melting temperature for each peak or shoulder.

[0078] By "melting temperatures in 1 ère and 2 ème heating”, we mean melting temperatures, noted respectively Tfi for 1 ère heat and Tf2, for 2 èmeheating, measured by DSC, according to the ISO11357-3: 2018 standard, and corresponding respectively to the maximum intensity of the melting peak signal in the first heating and in the second heating, both carried out with a temperature ramp of 20°C / min. Thus, within the meaning of this description, if several melting temperatures (Tfi) are detected in the first heating, then the one which must be used in the calculation of the difference (Tfi

[0079] - Te) is the temperature T corresponding to the lowest melting temperature, namely Tfi min . Tfi maxdenotes the highest melting temperature (Tfi) and corresponds to the single melting temperature (Tfi) obtained at the end of step iv). By "crystallization temperature", hereinafter referred to as Te, is meant the temperature at which the at least partially crystalline compound passes from the viscous liquid state to the semi-crystalline state as measured according to ISO 11357-3:2018, with a temperature ramp of -20°C / min. The crystallization temperature corresponds more particularly to that measured during cooling after the first melting of the compound (1 ère heating) and before the second fusion (2 ème heating), the first melting allowing the thermal history of the compound to be erased. Unless otherwise indicated, this is the temperature of the crystallization peak, corresponding to the maximum signal intensity in DSC. Thus, for the purposes of this description, if several crystallization temperatures are detected upon cooling, then Tc corresponds to the highest crystallization temperature and it is this value which must be used in the calculation of the difference (Tfi - T c ).

[0080] By "monomodal melting endotherm" of polyamide powder is meant the part of the thermogram obtained by differential scanning calorimetry (DSC) corresponding to the first melting of the polyamide powder, and which is characterized by a single melting temperature Tfi. In other words, the melting peak corresponding to the first heating comprises only one single peak. Conversely, a multimodal melting endotherm is characterized by a melting peak at 1 ère heating with several peaks, or several melting peak temperatures. Similarly, a melting endotherm whose melting peak in 1 ère heating would present a shoulder would not be considered a monomodal endotherm within the meaning of this description.

[0081] By "precipitation temperature", hereinafter referred to as T P , we mean the temperature at which the mixture, formed by the polyamide and the solvent used in the process, passes from a homogeneous state to a heterogeneous state. The precipitation temperature is detected by means of a temperature probe (PT100 type) coupled to a dynamic thermoregulation system (for example a “small flower” system sold by the company Huber). At the time of precipitation, the thermoregulation system cannot compensate for the exothermicity instantaneously. Also, the precipitation temperature is detected precisely in the form of a disturbance on the derivative of the temperature of the reaction medium as a function of the time to be detected. The temperature corresponding to the start of the disturbance of the derivative is assimilated to the precipitation temperature (T P). The term "Dv50" is understood to mean the value of the volume median diameter of the powder particles so that the cumulative function of particle diameter distribution, weighted by their volume, is equal to 50%. Similarly, "Dv10" and "Dv90" are respectively the corresponding diameters so that the cumulative function of particle diameters, weighted by their volume, is equal to 10%, and respectively, to 90%. These values ​​are measured according to ISO 13319-1:2021, for example on a Coulter counter multisizer 3 granulometer. The rules for representing results of a particle size distribution are given by ISO 9276 - parts 1 to 6.

[0082] By “span” factor, we mean a factor characterizing the width of the particle size distribution, defined by: span = (Dv90-Dv10) / Dv50, the diameters “Dv10”, “Dv50” and “Dv90” being as defined previously.

[0083] The term "average diameter" is understood to mean the value of the volume-average diameter of the particles corresponding to the arithmetic mean of the particle diameters weighted by their volume. This value is measured according to ISO 13319-1:2021, for example on a Coulter counter multisizer 3 granulometer.

[0084] The term "viscosity" is understood to mean the inherent viscosity as measured in an Ubbelohde-type viscometer according to ISO 307:2019, except when using m-cresol as the solvent and a temperature of 20°C. Inherent viscosity has the dimension of the inverse of a concentration and is equal to the natural logarithm of the relative viscosity, all divided by the concentration of polymer dissolved in the solvent.

[0085] The term "3D printing" refers to a technique for producing parts through additive manufacturing, by selectively melting a powder using electromagnetic radiation such as a laser or infrared light. Process for manufacturing a polyamide powder

[0086] According to a first aspect, the invention thus aims to provide a method for manufacturing a polyamide powder having a monomodal melting endotherm and a single melting temperature (Tfi max ), said method comprising the steps of: i) contacting a polyamide with a solvent in order to obtain a mixture; ii) heating the mixture in order to dissolve the polyamide in the solvent; ii) cooling the mixture to the precipitation temperature (T P ) in said solvent, whereby a powder characterized by a non-monomodal melting endotherm and more than one melting temperature is obtained, (Tfi max) being the highest melting temperature; iv) maintaining the temperature of the mixture at a temperature at most equal to T P , notably included in the range from T P to T P - 15°C, until the precipitated polyamide powder is characterized by a monomodal melting endotherm and a single melting temperature (Tfi max ); and v) recovery of the polyamide powder obtained.

[0087] The term "monomer" in the following description should be taken to mean "repeating unit". The case where a repeating unit is made up of the association of a diamine with a diacid is special. It is considered that it is the association of a diamine and a diacid, that is to say the diamine.diacid pair, which corresponds to the monomer. This is explained by the fact that individually, the diamine or the diacid does not allow amide-type functions to be obtained.

[0088] For the purposes of the invention, the term "polyamide" means the condensation products of lactams, amino acids or diamine-diacid pairs. It may be a homopolymer, i.e. a polymer resulting from the condensation of the same repeating unit, i.e. the same monomer, or a copolymer resulting from the condensation of at least two repeating units, i.e. two different monomers, called "co-monomers", i.e. at least one monomer and at least one co-monomer (monomer different from the first monomer) to form a copolymer such as a copolyamide (abbreviated CoPA), as defined below. The term "copolyamide" (abbreviated CoPA) means the polymerization products of at least two different monomers chosen from:

[0089] - amino acid or aminocarboxylic acid monomers, and preferably alpha, omega-aminocarboxylic acids;

[0090] - lactam-type monomers;

[0091] - pairs of monomers of the “diamine-diacid” type resulting from the reaction between a diamine and a dicarboxylic acid; and

[0092] - their mixtures, with monomers with different carbon numbers in the case of mixtures between an amino acid type monomer and a lactam type monomer.

[0093] These monomers can be linear or branched or substituted where appropriate.

[0094] According to embodiments, the polyamide is a homopolymer.

[0095] According to a first type, the polyamide comes from the condensation of an aliphatic, cycloaliphatic or aromatic dicarboxylic acid, in particular containing from 4 to 36 carbon atoms, preferably from 6 to 18 carbon atoms, and an aliphatic, cycloaliphatic or aromatic diamine, in particular containing from 2 to 20 carbon atoms, preferably from 6 to 14 carbon atoms.

[0096] Examples of dicarboxylic acids include 1,4-cyclohexyldicarboxylic acid, butanedioic acid, adipic acid, azelaic acid, suberic acid, sebacic acid, dodecanedicarboxylic acid, octadecanedicarboxylic acid, terephthalic acid and isophthalic acid, as well as dimerized fatty acids.

[0097] Examples of diamines include tetramethylenediamine, hexamethylenediamine, 1,10-decamethylenediamine, dodecamethylenediamine, trimethylhexamethylenediamine, isomers of bis(4-aminocyclohexyl)methane (BACM), bis(3-methyl-4-aminocyclohexyl)methane (BMACM), 2,2-bis(3-methyl-4-aminocyclohexyl)propane (BMACP), para-aminodicyclohexylmethane (PACM), isophoronediamine (IPDA), 2,6-bis(aminomethyl)norbornane (BAMN) and piperazine (Pip). Advantageously, the polyamide is selected from PA 4.6, PA 4.10, PA 4.12, PA 4.14, PA 4.18, PA 6.10, PA 6.12, PA 6.14, PA 6.18, PA 9.12, PA 10.10, PA 10.12, PA 10.14 and PA 10.18. In the PA XY notation, X represents the number of carbon atoms derived from the diamine residues and Y represents the number of carbon atoms derived from the diacid residues, as is conventional.

[0098] In some embodiments, the polyamide is selected from polyamide 11, polyamide 6, polyamide 10.10, polyamide 10.12, or polyamide 6.10. Preferably, the polyamide is PA 11.

[0099] Steps i) and ii)

[0100] The indefinite article “a” or definite article “the” before the term “polyamide” used in the process according to the invention means, within the framework of this disclosure, “at least one polyamide”, and respectively “said at least one polyamide”.

[0101] Thus, in a first step i), “at least one” polyamide is brought into contact with a solvent in order to obtain a mixture.

[0102] Preferably, only one polyamide is used in the process.

[0103] It is however possible to use a mixture of several, in particular two, polyamides. Preferably, such a mixture comprises a majority polyamide, representing in particular more than 80% by weight of the total weight of polyamides used in step i), and this in such a way as to obtain a coprecipitation of the mixture of polyamides.

[0104] In some embodiments, the solvent that is contacted with the polyamide may be selected from: ethanol, propanol, butanol, isopropanol, heptanol, formic acid, acetic acid, N-methylpyrrolidone, N-butylpyrrolidone, butyrolactam, caprolactam. Preferably, the solvent that is contacted with the polyamide is a C1-C4 aliphatic alcohol, more preferably ethanol, and even more preferably technical grade ethanol of 96% purity (containing water and denatured with 2-butanone and propan-2-ol).

[0105] The polyamide may have a weight fraction in the solvent of 0.01 to 0.30; and preferably of 0.1 to 0.3. It may in particular have a weight fraction of 0.01 to 0.05; 0.05 to 0.1; or of 0.1 to 0.15 or of 0.15 to 0.2; or of 0.2 to 0.25; or of 0.25 to 0.3.

[0106] The mixture obtained is then heated in step ii) to dissolve the polyamide, i.e. until a homogeneous mixture is obtained. The heating of the mixture may in particular be carried out at a temperature between 100°C and 200°C, and preferably between 120°C and 160°C.

[0107] In some embodiments, heating the mixture may for example be carried out at a temperature of 100°C to 105°C; or 105°C to 110°C; or 110°C to 115°C; or 115°C to 120°C; or 120°C to 125°C; or 125°C to 130°C; or 130°C to 135°C; or 135°C to 140°C; or 140°C to 145°C; or 145°C to 150°C; or 150°C to 155°C; or 155°C to 160°C; or 160°C to 165°C; or 165°C to 170°C; or from 170°C to 175°C; or from 175°C to 180°C; or from 180°C to 185°C; or from 185°C to 190°C; or from 190°C to 195°C; or from 195°C to 200°C.

[0108] In some embodiments, heating the mixture, including maintaining the mixture at the dissolution temperature, may have a duration of

[0109] 1 to 6 hours, and preferably 1 to 3 hours. Thus, heating the mixture can last from 1 hour to 1 hour and 30 minutes; or from 1 hour and 30 minutes to

[0110] 2 hours; or from 2 hours to 2 hours and 30 minutes; or from 2 hours and 30 minutes to 3 hours; or from 3 hours to 3 hours and 30 minutes; or from 3 hours and 30 minutes to 4 hours; or from 4 hours to 4 hours and 30 minutes; or from 4 hours and 30 minutes to 5 hours; or from 5 hours to 5 hours and 30 minutes; or from 5 hours and 30 minutes to 6 hours.

[0111] In some embodiments, the heating comprises at least one step during which the temperature increases in order to reach a maximum temperature between 100°C and 200°C, in particular between 120°C and 160°C.

[0112] In some embodiments, the heating comprises at least one step in which the temperature remains essentially constant at a value between 100°C and 200°C, in particular between 120°C and 160°C.

[0113] Step iii)

[0114] Then, in step iii), the mixture is cooled in order to cause the precipitation of the polyamide in powder form.

[0115] The precipitation temperature (T P ) can vary for the same polyamide depending on the solvent. Similarly, for the same solvent, it can vary depending on the polyamide. Indeed, the precipitation of the polyamide is accompanied by a release of heat leading to a slight rise in the internal temperature. At the end of precipitation there is no more release of heat and the internal temperature drops back to its set temperature. This precipitation temperature can be between 80°C and 130°C, particularly between 100 and 120°C, especially when the solvent is a C1-C4 aliphatic alcohol.

[0116] This cooling can be carried out to a temperature greater than or equal to 50°C. Thus, the cooling can, for example, be carried out to a temperature of 50°C. Thus, the cooling can, for example, be carried out to a temperature ranging from 50°C to 60°C; or from 60°C to 70°C; or from 70°C to 80°C; or from 80°C to 90°C; or from 90°C to 100°C; or from 100°C to 110°C; or from 110°C to 120°C; or from 120°C to 130°C.

[0117] Furthermore, this cooling may be carried out at a rate of between 1 and 100°C per hour, preferably between 10 and 60°C per hour, and more preferably between 20 and 50°C per hour. For example, the cooling may be carried out at a rate of 1 to 5°C per hour; 5 to 10°C per hour; 10 to 15°C per hour; or 15 to 20°C per hour; or 20 to 25°C per hour; or 25 to 30°C per hour; or 30 to 35°C per hour; or 35 to 40°C per hour; or 40 to 45°C per hour; or 45 to 50°C per hour; or 50 to 55°C per hour; or 55 to 60°C per hour; or 60 to 65°C per hour; or from 65 to 70°C per hour; or from 70 to 75°C per hour; or from 75 to 80°C per hour; or from 80 to 85°C per hour; or from 85 to 90°C per hour; or from 90 to 95°C per hour; or from 95 to 100°C per hour.

[0118] In certain embodiments, and in order to promote precipitation, a quantity of polyamide may be introduced in step i) of loading the raw materials. Preferably, this quantity of polyamide is less than or equal to 20% by mass, and preferably less than or equal to 10% by mass relative to the total mass of polyamide used in this step. The polyamide may be identical or different from that dissolved in the solvent, preferably identical. The polyamide may in particular be chosen from polyamide 11, polyamide 6, polyamide 10.10, polyamide 10.12 and polyamide 6.10.

[0119] Thus, the added quantity of polyamide may represent from 0.1% to 1% by mass; or from 1% to 2% by mass; or from 2% to 3% by mass; or from 3% to 4% by mass; or from 4% to 5% by mass; or from 5% to 8% by mass; or from 8% to 12% by mass; or from 12% to 16% by mass; or from 16% to 20% by mass relative to the total mass of polyamide used in this step. Step iii) is advantageously carried out with stirring. For a given stirring system, the stirring speed makes it possible to control the volume average diameter of the particles. As a general rule, the higher the stirring speed, the lower the average diameter of the polyamide particles. Conversely, the lower the stirring speed, the higher the average diameter of the polyamide particles.

[0120] During the cooling step, when the precipitation temperature of the polyamide in said solvent is reached, a precipitation phase begins. The start of this precipitation phase corresponds to the start of step iv) of the process according to the invention.

[0121] In step iv), the mixture is maintained at a temperature close to the precipitation temperature (T P ) of the polyamide in the solvent, at most equal to and in particular included in the range from -0.1°C to -15°C of this precipitation temperature, and this for a sufficient duration to allow the production of a precipitated polyamide powder having a monomodal melting endotherm and an increased melting temperature.

[0122] In other words, the process includes in step iv) a temperature stage during which the temperature is kept constant for a duration t. More particularly, the temperature is kept constant throughout the duration of the polyamide precipitation phase, namely a period ti, then for an additional duration t2 making it possible to perfect the crystalline mesh of the precipitated polyamide and thus to obtain a polyamide powder having a monomodal melting endotherm and an increased melting temperature.

[0123] Generally speaking, the duration ti is generally much less than the duration t2, so that the total duration t of the temperature plateau is generally very close to t2.

[0124] The additional time required to obtain a monomodal melting endotherm can be determined by analyzing samples taken at different intervals by differential scanning calorimetry (DSC) according to ISO11357-3.

[0125] For example, at the end of the precipitation phase of polyamide 11, i.e. at the end of period ti, the inventors were able to observe by DSC, in 1 ère heating, obtaining a bimodal melting endotherm, characterized by two distinct melting temperatures. By maintaining the temperature constant at a temperature close to the precipitation temperature of the polyamide in the solvent, for a sufficient additional duration t2, the inventors were able to observe the transformation of the bimodal melting endotherm of polyamide particles into a monomodal melting endotherm, reflected on the DSC thermogram by the disappearance of the peak associated with the lowest melting temperature, in favor of the peak associated with the highest melting temperature. Advantageously, this temperature plateau of a total duration ti+t2 therefore makes it possible both to increase the difference T -Te but also to obtain a monomodal melting endotherm.

[0126] According to embodiments, in step iv), the mixture is maintained at a constant temperature for a duration t2 of at least 2 hours, in particular between 3 and 12 hours, preferably at least 4 hours, in particular between 4 and 12 hours, from the end of the precipitation of the polyamide. This additional duration after the end of the precipitation of the polyamide may be 2 to 3 hours; or 3 to 4 hours; or 4 to 5 hours; or 5 to 6 hours; or 6 to 7 hours; or 7 to 8 hours or 8 to 9 hours; or 9 to 10 hours; or 10 to 11 hours; or 11 to 12 hours. In certain embodiments, in step iv), the mixture is maintained at a constant temperature for a duration t of at least 2 hours, in particular between 3 and 12 hours, preferably at least 4 hours, in particular between 4 and 12 hours, from the start of precipitation of the polyamide.This duration from the start of precipitation of the polyamide can be 2 to 3 hours; or 3 to 4 hours; or 4 to 5 hours; or 5 to 6 hours; or 6 to 7 hours; or 7 to 8 hours or 8 to 9 hours; or 9 to 10 hours; or 10 to 11 hours; or 11 to 12 hours.

[0127] Step v) and vi)

[0128] At the end of the temperature plateau carried out in step iv), the precipitated polyamide particles are recovered from the mixture in the form of a powder in step v) by conventional solid-liquid separation means.

[0129] This step generally includes cooling the mixture obtained so that the reactor can be emptied and thus the precipitated polyamide particles obtained from the solvent can be separated, in particular by filtration.

[0130] The process for manufacturing the polyamide powder may also comprise a step vi) of drying the polyamide powder obtained in step iv) or recovered in step v). The drying step may for example be carried out in a stirred or rotary dryer.

[0131] In some embodiments, the drying may be carried out at a temperature of 10°C to 150°C, in particular 50°C to 100°C, preferably 25°C to 85°C, and more preferably 70°C to 80°C. The drying may for example be carried out at a temperature of 10°C to 20°C; or 20°C to 30°C; or 30°C to 40°C; or 40°C to 50°C; or 50°C to 60°C; or 60°C to 70°C; or 70°C to 80°C; or 80°C to 90°C; or 90°C to 100°C; or 100°C to 110°C; or 110°C to 120°C; or from 120°C to 130°C; or from 130°C to 140°C; or from 140°C to 150°C; or from 150°C to 160°C.

[0132] In some embodiments, the drying may be carried out under vacuum at a pressure of less than 100 mbar, preferably less than 50 mbar. Thus, the drying may be carried out at a pressure of 1 to 10 mbar; or 10 to 20 mbar; 20 to 30 mbar; 30 to 40 mbar; 40 to 50 mbar; 50 to 60 mbar; 60 to 70 mbar; 70 to 80 mbar; 80 to 90 mbar; 90 to 100 mbar; 100 to 150 mbar; 150 to 200 mbar; 200 to 250 mbar; or 250 to 300 mbar; or 300 to 500 mbar; or 500 to 700 mbar; or from 700 mbar to less than 1 bar (absolute pressure).

[0133] Alternatively, drying can be carried out at atmospheric pressure.

[0134] Polyamide powder capable of being obtained according to the manufacturing process of the invention

[0135] According to a second aspect, the invention relates to a polyamide powder having a monomodal melting endotherm and a single melting temperature (Tfi max) capable of being obtained by the process as described above.

[0136] In some embodiments, the polyamide powder has an inherent viscosity of 0.8 to 1.7, and preferably 1.0 to 1.5. Thus, the powder may for example have an inherent viscosity of 0.8 to 0.9; or 0.9 to 1.0; or 1.0 to 1.1; or 1.1 to 1.2; or 1.2 to 1.3; or 1.3 to 1.4; or 1.4 to 1.5; or 1.5 to 1.6; or 1.6 to 1.7. In the above, the inherent viscosity is expressed in (g / 100 g) -1 .

[0137] The inherent viscosity is measured using a micro-Ubbelohde tube. The measurement is carried out at 20°C on a 75 mg sample of powder at a concentration of 0.5% (m / m) in m-cresol. The inherent viscosity is expressed in (g / 100 g) -1 and is calculated according to the following formula:

[0138] Inherent viscosity = ln(t s / to) x 1 / C, with C = m / px 100, in which t sis the flow time of the solution, to is the flow time of the solvent, m is the mass of the sample whose viscosity is determined and p is the mass of the solvent.

[0139] In some embodiments, the precipitated polyamide powder may have a crystallization temperature (T c ) from 100°C to 200°C, and preferably from 130°C to 180°C. The polyamide powder may in particular have a crystallization temperature of 100°C to 110°C; or from 110°C to 120°C; or from 120°C to 130°C; or from 130°C to 140°C; or from 140°C to 150°C; or from 150°C to 160°C; or from 160°C to 170°C; or from 170°C to 180°C; or from 180°C to 190°C; or from 190°C to 200°C.

[0140] In certain embodiments, the polyamide powder has a fusion enthalpy greater than or equal to 60 J / g, preferably greater than or equal to 100 J / g. This fusion enthalpy may for example be 60 to 80 J / g; or 80 to 100 J / g; or 100 to 110 J / g; or 110 to 120 J / g; or 120 to 130 J / g; or 130 to 140 J / g; or 140 to 150 J / g; or 150 to 160 J / g.

[0141] In some embodiments, the polyamide powder may have a melting temperature Tfi of between 130°C and 260°C, and preferably between 160°C and 210°C. The polyamide powder may in particular have a melting temperature of 130°C to 140°C; or 140°C to 150°C; or 150°C to 160°C; or 160°C to 170°C; or 170°C to 180°C; or 180°C to 190°C; or 190°C to 200°C; or 200°C to 210°C; or 210°C to 220°C; or 220°C to 230°C; or 230°C to 240°C; or from 240°C to 250°C; or from 250°C to 260°C.

[0142] The melting temperature (Tfi) of the precipitated polyamide powder is determined during the first heating as explained above. According to the method of the invention, a single melting temperature of the polyamide is observed at the end of the temperature plateau at the end of step iv).

[0143] In some embodiments, the polyamide powder may have an apparent specific surface area of ​​0.1 to 50 m 2 / g, and preferably 1 to 10 m 2 / g. The precipitated polyamide powder can therefore have a specific surface area of ​​0.1 to 1 m 2 / g; or from 1 to 5 m 2 / g; or 5 to 10 m 2 / g; or 10 to 20 m 2 / g; or 20 to 30 m 2 / g; or 30 to 50 m 2 / g. The apparent specific surface area (ASS) is measured according to the BET (BRUNAUER-EMMET-TELLER) method, known to those skilled in the art. It is notably described in The Journal of the American Chemical Society, volume 60, page 309, February 1938, and corresponds to the international standard ISO 9277: 2010. The specific surface area measured according to the BET method corresponds to the surface porosity of the powder, i.e. it includes the surface formed by the pores on the surface of the particles.

[0144] According to certain embodiments, the polyamide powder obtained according to the process of the invention is characterized in that it has:

[0145] - a volume average diameter of between 10 and 200 pm, in particular between 20 and 100 pm, and preferably between 40 and 80 pm;

[0146] - a diameter Dv10 greater than 5 pm, in particular between 10 and 70 pm, and preferably between 20 and 60 pm;

[0147] - a median volume diameter Dv50 of between 10 and 200 pm, in particular between 20 and 100 pm, and preferably between 30 and 90 pm;

[0148] - a diameter Dv90 less than 350 pm, in particular between 30 and 200 pm, and preferably between 50 and 150 pm;

[0149] - a span factor between 0.1 and 1.5; and preferably between 0.5 and 1.0.

[0150] - a fusion enthalpy greater than 60 J / g; and preferably between 100 and 160 J / g

[0151] - an inherent viscosity between 0.5 and 2.0, and preferably between 1.0 and 1.5.

[0152] In a preferred embodiment, the polyamide powder has a monomodal melting endotherm and a single melting temperature (Tfi max) capable of being obtained by the process, is characterized in that it has a span factor of between 0.1 and 1.5, preferably between 0.1 and 1.0 and more preferably between 0.5 and 1.0.

[0153] Polyamide 11 powder

[0154] According to another aspect, the invention relates to a polyamide 11 powder characterized in that it has a monomodal melting endotherm and a single melting temperature at 1 ère heating Tfi equal to Tfi max between 195°C and 205°C, in particular around 200°C and / or a crystallization temperature T c between 150 and 165°C, especially around 158°C.

[0155] The polyamide 11 powder is in particular a powder characterized by one or more of the following characteristics, preferably by all of the following characteristics:

[0156] - a volume average diameter of between 10 and 200 pm, in particular between 20 and 100 pm, and preferably between 40 and 80 pm; - a diameter Dv10 greater than 5 pm, in particular between 10 and 70 pm, and preferably between 20 and 60 pm;

[0157] - a median volume diameter Dv50 of between 10 and 200 pm, in particular between 20 and 100 pm, and preferably between 30 and 90 pm;

[0158] - a diameter Dv90 less than 350 pm, in particular between 30 and 200 pm, and preferably between 50 and 150 pm;

[0159] - a span factor between 0.1 and 1.5; and preferably between 0.5 and 1.0.

[0160] - a fusion enthalpy greater than 100 J / g; and preferably between 110 and 160 J / g

[0161] - an inherent viscosity between 0.8 and 1.8, and preferably between 1.0 and 1.5.

[0162] Preferably, the polyamide 11 powder is characterized in that it has a monomodal melting endotherm, a single melting temperature in 1 ère heating Tfi equal to Tfi max between 195°C and 205°C, and a span factor between 0.1 and 1.5, preferably between 0.1 and 1 and more preferably between 0.5 and 1.0.

[0163] Composition in powder form for 3D printing, in particular by selective laser sintering.

[0164] According to yet another aspect, the invention relates to a composition in powder form for 3D printing, in particular by selective laser sintering, comprising a polyamide powder as defined above, in association with one or more usual fillers or additives, i.e. suitable for 3D printing technologies.

[0165] This composition is advantageously ready to use.

[0166] This composition may include additives that help improve the processing properties of the powder for its use in 3D printing technologies.

[0167] 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 the composition. 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). Among the flow agents, mention may be made, for example, of a hydrophilic or hydrophobic silica. Advantageously, the flow agent represents from 0.01 to 0.5% by weight relative to the total weight of the composition. Preferably, the composition comprises 0.1 to 0.4% by weight of flow agent.

[0168] The composition may also include one or more fillers, in particular to improve the mechanical properties (breaking stress and elongation at break) of parts obtained by 3D printing.

[0169] 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.

[0170] The additives or fillers may be mixed with the polyamide before the polyamide powder manufacturing process, during the polyamide powder manufacturing process (e.g., in step i) before dissolving the polyamide or in step iv) after precipitation), or after the polyamide powder manufacturing process. Preferably, the additives are introduced after the polyamide powder manufacturing process, by mixing the polyamide powder and said additives.

[0171] The composition may comprise the polyamide in a weight proportion preferably greater than or equal to 80%, or 81%, or 82%, or 83%, or 84%, or 85%, or 86%, or 87%, or 88%, or 89%, or 90%, or 91%, or 92%, or 93%, or 94%, or 95%, or 96%, or 97%, or 98%, or 99%, or 99. 1%, or 99.2%, or 99.3%, or 99.4%, or 99.5%, or 99.6%, or 99.7%, or 99.8%, or 99.9%, or 99.91%, or 99.92%, or 99.93%, or 99.94%, or 99.95%, or 99.96%, or 99.97%, or 99.98%, or 99.99%.

[0172] In embodiments, the polyamide contained in the composition is polyamide 11.

[0173] In embodiments, polyamide 11 has a melting temperature (Tfi) of between 185°C and 205°C. In embodiments, the difference between the melting temperature (Tn) and the crystallization temperature (T c ) of polyamide 11 is between 35 and 45°C.

[0174] Use of a polyamide powder obtained according to the process of the invention or of a composition in powder form comprising it, in a process for agglomerating powder by fusion

[0175] The invention also relates to a method for manufacturing a polyamide object by agglomeration of powder by fusion using electromagnetic radiation, the powder being a polyamide powder or a composition in powder form as defined above.

[0176] The electromagnetic radiation can be infrared, ultraviolet, or visible radiation. Preferably, it is laser radiation (the manufacturing process is then called "selective laser sintering").

[0177] In this process, a thin layer of powder is deposited on a horizontal plate held in an enclosure heated to a so-called build temperature. The term "build temperature" refers to the temperature to which the powder bed, of a constituent layer of a three-dimensional object under construction, is heated during the layer-by-layer sintering process of the powder. This temperature is chosen within the range T - T cpolyamide powder resulting from the manufacturing process, preferably between Tfi - 5°C and Tc + 5°C, and more preferably between T - 10°C and Tc + 10°C. The electromagnetic radiation 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 reproducing this shape in the form of slices).

[0178] The horizontal plate is then lowered by a distance corresponding to the thickness of a layer of powder and a new layer is deposited. The thickness of a layer is typically between 0.05 and 2 mm and generally of the order of 0.1 mm. The electromagnetic radiation provides the energy necessary to sinter the powder particles into a geometry corresponding to this new slice of the object and so on. The procedure is repeated until the object is manufactured. Powders are used in the fusion agglomeration or sintering process. These powders can have a volume average diameter of 10 pm up to 200 pm and are advantageously of a volume average diameter between 20 and 100 pm.

[0179] Preferably the volume average diameter is between 40 and 80 pm.

[0180] The invention also relates to a manufactured article, in particular by 3D printing, obtained by sintering using electromagnetic radiation of a powder as previously described.

[0181] This article can be chosen from prototypes and models, particularly in the automotive, nautical, aeronautical, aerospace, medical (prosthetics, hearing systems, cellular tissues, etc.), textile, clothing, fashion, decoration, housings for electronics, telephony, home automation, IT, lighting fields.

[0182] More generally, the invention also relates to the use of a manufacturing method as previously described to increase the difference (Tfi -Te) between the melting temperature (Tfi) and the crystallization temperature (Te) of a polyamide.

[0183] Examples

[0184] The following examples illustrate embodiments of the present invention without limiting it.

[0185] In all the following examples:

[0186] - The particle size distribution of the powders was characterized by measuring the particle size distribution on a Coulter Counter-Multisizer 3 device (Beckmann Coulter) in accordance with ISO 13319-1:2021. From this, the volume average diameter as well as the diameters Dv10, Dv50 and Dv90 were determined. The span value is calculated from these volume average diameters.

[0187] - the analysis of thermal characteristics is carried out by DSC according to the ISO 11357-3 standard "Plastics - Differential Scanning Calorimetry (DSC) Part 3: Determination of temperature and enthalpy of melting and crystallization". The temperatures of particular interest here are the melting temperature during the first heating (Tfi) and the crystallization temperature (T c ). Indeed, in a manner known to those skilled in the art (in the field of manufacturing 3D objects by agglomeration of powder by fusion), the gap “Tf - Te” corresponds to T - T c .

[0188] - The inherent viscosity of polyamides is measured in an Ubbelohde type viscometer according to ISO 307:2019, except when using m-cresol as solvent and a temperature of 20°C.

[0189] - acidity (similar to the concentration at the COOH chain end of the polyamide) and basicity (similar to the concentration at the NH2 chain end of the polyamide) are measured by potentiometry. Acidity is measured according to the following method: a sample of polyamide is dissolved in benzyl alcohol at a concentration of 0.6% by mass; then, this sample is assayed by potentiometry with a 0.02N tetrabutylammonium hydroxide solution. Basicity is measured according to the following method: a sample of polyamide is dissolved in meta-cresol at a concentration of 0.6% by mass; then, this sample is assayed by potentiometry with a 0.02N perchloric acid solution.

[0190] Example 1: preparation of a polyamide 11

[0191] Polyamide 11 is obtained by polycondensation of 11-aminoundecanoic acid in the presence of 3,000 ppm of ortho-phosphoric acid used as a catalyst. This PA11 has an inherent viscosity of 1.40 associated with a COOH chain end concentration equal to 55 mmol / kg and NH2 equal to 51 mmol / kg as well as a melting temperature of 189°C (2 e DSC heating according to ISO 11357-3:2018).

[0192] Example 2 (comparative)

[0193] In a reactor (1 L useful), 85 g of the PA11 produced in example 1 and 425 g of technical ethanol (purity 96%) are loaded, mechanical stirring is carried out using propeller turbine blades. The stirrer is started at a speed of 500 rpm throughout the test, then the medium is heated to 160°C, followed by a one-hour isotherm to solubilize the polyamide 11. Controlled cooling at a rate of -60°C / h down to 20°C is carried out to precipitate the polyamide. The precipitation temperature is 120°C. Then, the reactor is drained and the dispersion is dried in an oven at 75°C at atmospheric pressure.

[0194] The PA11 powder obtained has the following characteristics: an inherent viscosity of 1.25, a volume average diameter of 66 pm as well as diameters Dv10 = 33 pm, Dv50 = 75 pm, Dv90 = 108 pm and therefore a span = 1.00. DSC analysis of this PA11 powder shows a bimodal melting endotherm in 1 èreheating with two distinct peaks at 191°C and 199°C associated with a fusion enthalpy of 137 J / g (Fig.1), as well as a single crystallization temperature T c = 159°C. The lower of the two melting temperatures is used to calculate the T - T gap c which is therefore equal to 32°C.

[0195] In a reactor (1 L useful), 85 g of the PA11 produced in Example 1 and 425 g of technical ethanol (purity 96%) are loaded into a reactor, mechanical stirring is carried out using propeller turbine type blades. The stirrer is started at a speed of 500 rpm throughout the test, then the medium is heated to 160°C, followed by a one-hour isotherm to solubilize the polyamide 11. Controlled cooling at a rate of -60°C / h to 115°C is carried out to precipitate the polyamide, followed by a 4-hour isotherm at 115°C to achieve crystalline perfection. The precipitation temperature (TP ) is 120°C. Then, controlled cooling is restarted at the same rate of -60°C / h down to 20°C, the reactor is then drained and the dispersion is dried in an oven at 75°C at atmospheric pressure.

[0196] The PA11 powder obtained has the following characteristics: an inherent viscosity of 1.28, a volume average diameter of 40 pm as well as diameters Dv10 = 27 pm, Dv50 = 42 pm and Dv90 = 53 pm therefore a span = 0.62. The DSC analysis of this PA11 powder shows a monomodal melting endotherm in 1 ère heating with a single melting temperature at 200°C associated with a fusion enthalpy of 140 J / g (Fig.1), as well as a single crystallization temperature Tc = 157°C (Fig. 2). The difference Tfi - Tc is now equal to 43°C.

[0197] Example 4 (comparative) following US 2008 / 0166496

[0198] A diamine terminated PA 11 is prepared by polymerization of 250 g of 11-aminoundecanoic acid in the presence of 1.25 g of 4, 4'-diaminocyclohexylmethane (PACM, mixture of isomers) of inherent viscosity 1.42 associated with a concentration of COOH groups at the end of the chain equal to 19 mmol / kg and of NH2 groups at the end of the chain equal to 67 mmol / kg.

[0199] In a reactor (1 L useful), 85 g of this diamine-terminated PA11 and 425 g of technical ethanol (purity 96%) are loaded, mechanical stirring is carried out using propeller turbine blades. The stirrer is started at a speed of 500 rpm throughout the test. The medium is heated to 152°C, followed by a one-hour isotherm at this temperature. The medium is then cooled to 112°C at a speed of -25°C / h and then maintained at this temperature for one hour. The precipitation temperature (T P) is 112°C. Then the medium is cooled to room temperature at a rate of -25°C / h. The reactor is then drained and the ethanol is distilled in a stirred dryer at 70°C / 400 mbar then the powder is dried at 84°C / 20 mbar. The PA11 powder obtained has the following particle size characteristics: a volume average diameter of 89 pm as well as diameters Dv10 = 65 pm, Dv50 = 93 pm and Dv90 = 123 pm therefore a span = 0.62. The DSC analysis of this PA11 powder shows a bimodal melting endotherm in 1 ère heating with a shoulder at 193°C and a peak at 202°C associated with a fusion enthalpy of 140 J / g (Fig.1), as well as a single crystallization temperature T c = 162°C (Fig.3). It is the lower of the two melting temperatures that is used to calculate the T - T difference c which is therefore equal to 29°C.

Claims

Claims 1. Process for manufacturing a polyamide powder having a monomodal melting endotherm and a single melting temperature (Tfi max ), said method comprising the steps of: i) bringing a polyamide into contact with a solvent in order to obtain a mixture; ii) heating the mixture in order to solubilize the polyamide in the solvent J ill) cooling of the mixture to the precipitation temperature (T P ) of the polyamide in said solvent, whereby a powder characterized by a non-monomodal melting endotherm and more than one melting temperature is obtained, (Tfi max ) being the highest melting temperature; iv) maintaining the temperature of the mixture at a temperature at most equal to T P , notably included in the range from T P - 0.1 °C at T P-15°C, until the precipitated polyamide powder is characterized by a monomodal melting endotherm and a melting temperature (Tfi max ); and v) recovery of the polyamide powder obtained.

2. Method according to claim 1, in which the solvent which is brought into contact with the polyamide is an alcohol, in particular a C1-C4 aliphatic alcohol, preferably ethanol.

3. A method according to any one of claims 1 or 2, wherein the polyamide is polyamide 11, polyamide 6, or polyamide 10.10, or polyamide 10.12, or polyamide 6.

10.

4. Method according to any one of the preceding claims, in which in step iv), the mixture is maintained at a temperature at most equal to T P for a period of at least 2 hours, in particular between 3 and 12 hours, from the end of the precipitation of the polyamide.

5. Polyamide powder exhibiting a monomodal melting endotherm and a single melting temperature (Tfi max ) capable of being obtained by the process according to one of claims 1 to 4.

6. Polyamide powder according to claim 5, characterized in that it has a median diameter Dv50 of between 10 and 200 pm, in particular of between 20 and 100 pm, and preferably of between 30 and 90 pm.

7. Polyamide powder according to any one of claims 5 or 6, characterized in that it has a span factor of between 0.1 and 1.5, preferably between 0.1 and 1.0 and more preferably between 0.5 and 1.

0.

8. Powder according to any one of claims 5 to 7, in which the polyamide is polyamide 11.

9. Powder according to claim 8, characterized in that it has a melting temperature (Tfi max ) between 195 and 205°C.

10. Powder according to any one of claims 8 or 9, in which the difference between the melting temperature (Tfi max ) and the crystallization temperature (T c ) is between 35 and 45°C.

11. Polyamide 11 powder exhibiting a monomodal melting endotherm and a single melting temperature (Tfi max ) between 195°C and 205°C, also having at least one of the following characteristics: - a volume average diameter of between 10 and 200 pm, in particular between 20 and 100 pm, and preferably between 40 and 80 pm; - a diameter Dv10 greater than 5 pm, in particular between 10 and 70 pm, and preferably between 20 and 60 pm; - a median volume diameter Dv50 of between 10 and 200 pm, in particular between 20 and 100 pm, and preferably between 30 and 90 pm; - a diameter Dv90 less than 350 pm, in particular between 30 and 200 pm, and preferably between 50 and 150 pm; - a span factor between 0.1 and 1.5, preferably between 0.1 and 1, and more preferably between 0.5 and 1.0; - a fusion enthalpy greater than 100 J / g; and preferably between 110 and 160 J / g; and / or - an inherent viscosity of between 0.8 and 1.8, and preferably between 1.0 and 1.

5. Composition in powder form for 3D printing, in particular by laser sintering, comprising: - a polyamide powder according to any one of claims 5 to 11; and - at least one filler or additive. Method for manufacturing polyamide objects by agglomeration of powder by fusion using electromagnetic radiation, the powder being as defined in any one of claims 5 to 12. Manufactured article obtained by fusion using electromagnetic radiation of a powder according to any one of claims 5 to 11 or of a composition according to claim 12. Use of a method according to any one of claims 1 to 4 to increase the gap (Tfi min -Te) between the melting temperature (Tfi min ) and the crystallization temperature (T c ) of a polyamide.

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