Polyamide powder manufacturing process for 3D printing

Abstract

The invention relates to a process for manufacturing a polyamide powder by anionic polymerization in a solvent, comprising the following steps: a) the formation of a reaction medium comprising the introduction of at least one lactam monomer into said solvent, the introduction of at least one catalyst into said solvent, and the introduction of at least one activator into said solvent at a given temperature; b) the polymerization of the lactam monomer to polyamide in the reaction medium; c) the precipitation of the polyamide in powder form in the reaction medium; and d) heating, after step a), of the reaction medium to a temperature higher than the temperature at which at least one activator was introduced, in the range of 140 to 200°C. The invention also relates to a powder obtained by such a process and to uses of such a powder. Figure 1 is shown in the abstract.

Description

Title of the invention: Process for manufacturing polyamide powder for 3D printing. Field of the invention

[0001] The present invention relates to a method for manufacturing a polyamide powder by anionic polymerization in a solvent medium. The invention also relates to a powder obtained by such a method, as well as its use in a method for constructing three-dimensional articles. Technical background

[0002] The construction of three-dimensional (3D) articles can be used to produce prototypes or various parts, for example in the automotive, nautical, aeronautical, aerospace, medical (in particular for the manufacture of prostheses, hearing systems, cellular tissues...), textile, clothing, fashion, decoration, housings for electronics, telephony, home automation, computer science, lighting, sports and industrial tooling fields.

[0003] Among the techniques for manufacturing 3D articles, the polyamide powder sintering process (also called powder fusion sintering) is particularly interesting. This technology makes it possible, for example, to obtain fine and complex geometries that are impossible to achieve using conventional molding techniques. According to this process, a layer of polyamide powder is, conventionally, selectively and briefly irradiated in a chamber by radiation, generally electromagnetic (e.g., laser beam, infrared radiation, UV radiation). As a result, the powder particles impacted by the radiation melt. The molten particles coalesce and solidify, leading to the formation of a solid mass. This process can produce 3D articles by the repeated irradiation of successive layers of freshly applied powder.

[0004] In the case of selective laser sintering (SLS), the procedure is typically carried out as follows. A thin layer of polyamide powder is deposited onto a horizontal plate held in a chamber heated to a temperature between the crystallization temperature Te and the melting temperature Tf of the polyamide powder. The laser agglomerates powder particles at different points in the powder layer according to a geometry corresponding to the object, for example, using a computer that stores the shape of the object and reproduces it as slices. Next, the horizontal plate is lowered by a value corresponding to the thickness of a powder layer (for example, between 0.05 and 2 mm and generally on the order of 0.1 mm), and then the powder is deposited. A new layer of powder is applied, and the laser agglomerates the powder particles according to a geometry corresponding to this new slice of the object. The procedure is repeated until the entire object has been created. The entire assembly is then slowly cooled, and the object solidifies as soon as its temperature drops below the crystallization temperature (Te). The unagglomerated parts remain in powder form. Inside the chamber, the resulting object is surrounded by powder. After cooling, the object is separated from the powder, which can then be reused for another operation.

[0005] Immediately after the laser beam is applied, the sample temperature is higher than the crystallization temperature Te of the powder. However, the addition of a new, cooler layer of powder can cause the part temperature to drop rapidly. When this temperature falls below Te, it leads to deformation (a phenomenon known as "curling") in the manufactured object. Similarly, when the powder temperature in the machine gets too close to the powder's melting temperature (Tf), it causes caking around the parts. This manifests as lumps or clumps of powder in certain areas of the object's surface, instead of a well-defined final object. When caking occurs, it is then necessary to clean the parts to remove the remaining powder before they can be used.This cleaning is generally done by sandblasting, which can lead to the degradation of certain thin and / or fragile elements of the 3D printed parts.

[0006] To avoid these phenomena, it is therefore important to keep the temperature difference (Te) of the powder as far apart as possible from the temperature difference (Tf) of the powder. The difference between the Tf and Te of the powder defines the working temperature window of the device used to agglomerate the powder particles by radiation-induced fusion. In this text, the term "working window" refers to the build temperature range applicable to a powder when used in 3D printing, as defined below. The working window is defined by its upper and lower temperature limits. The upper limit of the working window corresponds to the temperature of the build chamber above which agglomeration or "caking" occurs. The lower limit of the working window corresponds to the temperature of the build chamber below which distortion, deformation, or "curling" occurs.Having a wide working window allows for greater flexibility in terms of the objects built. Furthermore, it helps to mitigate the significant temperature variations typically observed in 3D printing machines, which are generally on the order of + / -3°C.

[0007] If, in order to widen the working window, it is desirable to have a large Tf-Tc gap (since this includes the working window), other parameters also come into play in defining the working window. Thus, widening the working window does not necessarily result from an increase in the Tf-Tc gap.

[0008] The enlargement of the working window of a powder is determined for a certain 3D printing system; however, this enlargement of the working window of a powder will occur on any device, although not necessarily in the same proportions.

[0009] Various processes for preparing or treating polyamide powder have been described to obtain powders suitable for use in 3D printing.

[0010] Document WO 2013 / 090174 relates to a process for treating a thermoplastic polymer powder in which a polymerized and insulated powder is subjected to heat treatment by heating for one or more hours at a temperature relatively close to its melting point as determined prior to this operation. This heat treatment process aims to change the melting point, the recrystallization point, and / or the enthalpy of fusion of the polymer.

[0011] Document EP 1571173 describes a process for preparing a polyamide 12 powder by anionic polymerization of lauryllactam in a solvent of said lauryllactam, in the presence of an organic or mineral filler and an amide in particular proportions relative to the lauryllactam. In the examples in this document, the polymerization process includes a step in which the polymerization ingredients in the solvent are heated for 2 hours at 120°C after the activator has been added, to complete the polymerization.

[0012] Document FR 3095205 relates to a process for preparing a polyamide powder by anionic polymerization in a solvent to obtain a powder in which the particles comprise a polyamide core and a polyamide shell, the shell having an inherent viscosity in solution and a melting point higher than those of the core. In the examples in this document, the polymerization process includes a step of heating the polymerization medium to 130°C for 3 hours after the end of the introduction of the activator.

[0013] There is a real need to provide a process for preparing polyamide powder for use in 3D printing, in particular by sintering, which allows for an expanded working window for the construction temperature of 3D printing devices, while remaining simple to implement. Summary of the invention

[0014] The invention relates primarily to a process for manufacturing a polyamide powder by anionic polymerization in a solvent, comprising the following steps:

[0015] a) the formation of a reaction medium comprising: • the introduction of at least one lactam monomer into said solvent; • the introduction of at least one catalyst into said solvent; and • the introduction of at least one activator into said solvent at a temperature data;

[0016] b) the polymerization of the lactam monomer to polyamide in the reaction medium;

[0017] c) the precipitation of the polyamide in powder form in the reaction medium; and

[0018] d) heating, after step a), of the reaction medium to a temperature above the temperature of the introduction of at least one activator and being between 140 and 200°C.

[0019] In embodiments, the heating in step d) is carried out for a period of 2 hours or more, preferably 3 hours or more, preferably 5 hours or more, preferably for a period of 8 to 15 hours, more preferably 10 to 12 hours.

[0020] In embodiments, step a) further includes the introduction of at least one filler into the solvent, the at least one filler preferably being a mineral filler, preferably silica, and / or an organic filler, preferably a polyamide powder.

[0021] In embodiments, step a) further includes the introduction of at least one amide into the solvent, the at least one amide preferably being an N,N'-alkylene bisamide, more preferably N,N'-Ethylene bis-stearamide and / or N,N'-Ethylene bis-oleamide.

[0022] In embodiments, at least one lactam monomer is chosen from the group consisting of 2-pyrrolidone, caprolactam, 2-azacyclononanone, lauryllactam and mixtures thereof.

[0023] In embodiments, at least one catalyst is chosen from the group consisting of sodium, potassium, alkali metal hydrides and hydroxides, alkali metal alkoxides, and mixtures thereof, preferably from the group consisting of sodium hydride, potassium hydride, sodium, sodium methylate, sodium ethoxide, and mixtures thereof.

[0024] In embodiments, at least one activator is chosen from the group consisting of N-carboxyanilide lactams, (mono)isocyanates, polyisocyanates, carbodiimides, cyanamides, acyllactams and acylcarbamates, triazines, ureas, N-substituted imides, esters, phosphorus trichloride and mixtures thereof.

[0025] In embodiments, the solvent is a cut of paraffinic hydrocarbons having a boiling temperature range between 120 and 170°C.

[0026] In embodiments, the heating temperature at step d) is from 140 to 170°, preferably from 145 to 160°C, preferably still from 145 to 155°C.

[0027] In embodiments, the temperature of the introduction of at least one activator is from 50 to 150°C, preferably from 60 to 135°C.

[0028] In embodiments, the process further includes a step of introducing into the solvent one or more additives chosen from the group consisting of pigments, dyes, carbon black, carbon nanotubes, antioxidants, anti-UV agents and plasticizers.

[0029] The invention also relates to a polyamide powder obtained by a manufacturing process as described above.

[0030] The invention also relates to the use of a powder as described above, for the construction of a three-dimensional article, preferably layer by layer, more preferably by sintering, even more preferably by sintering caused by electromagnetic radiation.

[0031] The invention also relates to the use of a powder as described above, for the manufacture of a composite, a substrate coating, a transfer paper, a liquid or solid ink composition, a liquid or solid paint, a structural adhesive, a cosmetic composition or a pharmaceutical composition.

[0032] The invention also relates to a method for manufacturing a three-dimensional article comprising the following steps: • the manufacture of a powder by a process as described above; • the deposition, preferably in the form of a layer, of said powder; and • sintering of the powder, preferably using radiation electromagnetic.

[0033] The present invention addresses the need expressed above. More specifically, it provides a method for manufacturing a polyamide powder with a higher melting point, resulting in a wider operating temperature window for 3D printing. Thus, when used in 3D printing, this allows for the production of higher-quality parts with improved definition and / or facilitates, reduces, or even eliminates the need for mechanical cleaning that could damage the manufactured parts, particularly thin ones. Consequently, the powders prepared according to the invention enable the 3D printing of a wider range of part geometries.

[0034] This is accomplished by carrying out a so-called "cooking" step of the anionic polymerization reaction medium, comprising heating said medium The reaction occurs after the introduction of reagents and other compounds involved in polymerization, at a specific temperature. Without being bound by any particular theory, the inventors believe that the baking stage leads to a physical and chemical modification of the powder particle surface, for example, a crystalline refinement at the surface, which allows for a wider working window.

[0035] The heat treatment described in document WO 2013 / 090174 is an additional step, which takes place after the synthesis of the powder particles, on a powder that has already been polymerized and isolated from its synthesis medium. In contrast, the baking step according to the present invention, carried out on the reaction medium, is an integral part of the anionic polymerization phase in a solvent medium, and it enables the crystalline refinement of the precipitated powder particles. Brief description of the figures

[0036] [Fig. 1] represents a photograph showing an illustrative example of a pull-up barbell of type IB (15 cm long and 4 mm thick) undergoing the deformation measurement test as described in the "Examples" section below.

[0037] [Fig.2] represents a photograph showing the measurement of the deformation of the same dumbbell illustrative during the deformation measurement test as described in the "Examples" section below. In this illustrative example, the dumbbell deformed by 5 mm between its two ends.

[0038] [Fig.3] represents a photograph showing four examples of parts having 10 holes of varying sizes manufactured by selective laser sintering with polyamide powders as described in the "Examples" section below. These parts illustrate different sensitivities to caking and the scores that can be assigned to evaluate these sensitivities based on the number of open holes, as described in the "Examples" section below. Part A has a score of 0 / 10, part B a score of 6 / 10, part C a score of 8 / 10, and part D a score of 10 / 10. Detailed description

[0039] The invention is now described in more detail and in a non-limiting manner in the following description.

[0040] Unless otherwise indicated, all percentages relating to quantities are mass percentages.

[0041] In this text, the quantities indicated for a given species may apply to that species according to all its definitions (as mentioned in this text), including more restricted definitions. Powder manufacturing

[0042] The invention relates primarily to a process for manufacturing a polyamide powder by anionic polymerization in a solvent medium. Unless otherwise indicated, the steps of the process, and in particular steps a), b), c) and d) as defined above, may take place at least partly simultaneously.

[0043] Anionic polymerization takes place by opening of the lactamate ring. It generally comprises three steps: an initiation step to form a lactamate penion, then an activation reaction which leads to the formation of an acyllactam and finally the propagation (or polymerization) step.

[0044] By "polyamide powder" is meant a powder comprising at least particles comprising at least one polyamide; in the context of the present invention, the "polyamide powder" may thus comprise components other than polyamide (in particles comprising polyamide or in particles devoid of polyamide).

[0045] Anionic polymerization can be carried out continuously or discontinuously (also called "batch"). Preferably, it is carried out discontinuously.

[0046] In the process according to the invention, at least one lactam monomer, at least one catalyst, and at least one activator, and preferably at least one amide, and preferably at least one filler, are contacted in a solvent. In the present text, the solvent comprising at least one of the various compounds involved in the polymerization is called the "reaction medium." The compounds mentioned above may be introduced all simultaneously, all successively, or partly simultaneously and partly successively.

[0047] Preferably, the solvent is introduced into any suitable device, for example a reactor, followed by the lactam monomer(s), the amide(s) (when present), the filler(s) (when present), the catalyst(s), and the activator(s), either simultaneously or sequentially. Advantageously, the solvent, the lactam monomer(s), the amide(s) (when present), and the filler(s) (when present) are first introduced into the polymerization device, and then the water present in the reaction medium is removed, for example by azeotropic distillation, before the catalyst(s) are added to the anhydrous medium. Preferably, the activator(s) are not added all at once to the reaction medium. This prevents clogging or loss of control of the polymerization.Thus, the activator(s) are preferably added incrementally, or injected continuously over a certain period, according to one or more introduction rates. Preferably, the activator(s) are introduced into the reaction medium after the introduction of the lactam monomers, amides (when present), fillers (when present), and catalyst(s).

[0048] Preferably, the solvent used dissolves (at least partially) the lactam monomer(s) and the amide(s). However, the solvent does not dissolve the polyamide which form during polymerization (that is, the polyamide is insoluble in said solvent under the polymerization conditions). Thus, the polymerization of the polyamide leads to its precipitation directly in the form of particles (and therefore powder) in the solvent.

[0049] The solvent can be supersaturated with lactam monomer at the activator introduction temperature. Various methods can be used to supersaturate the solvent with monomer. One such method may include the steps of saturating the solvent with monomer at a temperature higher than the activator introduction temperature, and then lowering the temperature to the latter.

[0050] Alternatively, the polymerization can be carried out in a solvent not supersaturated with lactam monomer. In this case, the reaction medium preferably contains the monomer(s) dissolved in the solvent at a concentration far from saturation at the activator introduction temperature.

[0051] Any solvent inert to the lactam monomers with respect to the polymerization reaction can be used. The solvent is preferably a paraffinic hydrocarbon fraction (preferably a mixture of isoparaffin, N-paraffin and cycloparaffin) with a boiling range advantageously between 120 and 200°C, preferably between 140 and 170°C.

[0052] The lactam monomers are preferably selected from the group consisting of lauryllactam (lactam 12), caprolactam (lactam 6), 2-pyrrolidone (lactam 4), 2-azacyclononanone (lactam 8) and mixtures thereof. Even more preferably, the lactam monomers are lauryllactam and / or caprolactam.

[0053] Most preferably, the amide that can be introduced into the reaction medium comprises, or is, one (or more) N,N'-alkylene bisamide(s). Even more advantageously, the amide is chosen from among the N,N'-alkylene bisamides of fatty acids, and is more preferentially chosen from the group consisting of N,N'-ethylene bis-stearamide (formula Ci7H35-C(=O)-NH-CH2-CH2-NH-C(=O)-Ci7H35 and abbreviated EBS), N,N'-ethylene bis-oleamide (formula Ci7H33-C(=O)-NH-CH2 CH2-NH-C(=O)-Ci7H33 and abbreviated EBO), N,N'-alkylene bis-palmitamide (in particular N,N'-ethylene bis-palmitamide), N,N'-alkylene bis-gadoleamide (in particular N,N'-ethylene bis-gadoleamide), N,N'-alkylene bis-ketoleamide (in particular N,N'-ethylene bis-ketoleamide), N,N'-alkylene bis-erucamide (in particular N,N'-ethylene bis-erucamide), and mixtures thereof. Preferably, the amide is selected from EBS, EBO, and mixtures thereof.The amide may comprise a primary amide preferably containing 12 to 22 carbon atoms, preferably in combination with an N,N'-alkylene bisamide as described above. This primary amide is preferably selected from the group consisting of oleamide, N-stearamide, isostearamide, erucamide, and mixtures thereof.

[0054] The amide, for example the N,N'-alkylene bisamide(s), can be introduced into the reaction medium in an amount of 0.001 to 4 moles, preferably 0.075 to 2 moles, per 100 moles of lactam monomer; in particular the amount of amide (for example of N,N'-alkylene bisamide) can be 0.001 to 0.05 moles, or 0.05 to 0.1 moles, or 0.1 to 0.5 moles, or 0.5 to 1 mole, or 1 to 1.5 moles, or 1.5 to 2 moles, or 2 to 3 moles, or 3 to 4 moles, per 100 moles of lactam monomer. Adding an amide as described above helps to adjust the apparent specific surface area (measurable by the BET method) of the polyamide powder particles. The greater the amount of amide added, the higher the apparent specific surface area will be.

[0055] The filler, if any, introduced into the reaction medium is intended to serve as a crystallization seed. It may be mineral or organic, or comprise one (or more) mineral filler and one (or more) organic filler. Suitable mineral fillers for the invention include silica, carbon black, and / or talc. Appropriate organic fillers include polymer powders (thermoplastic or thermosetting) insoluble in the synthesis solvent, and more particularly polyamide, homopolyamide, or copolyamide powders, especially PA 4, PA 6, PA 8, PA 11, PA 12, PA 6 / 12, PA 6.12, PA 6.13, PA 6.10, PA 6.6, and / or PA 10.10. Examples of such polyamide powders include Arkema's Orgasol® powders, Arkema's Rilsan® fine powders, Evonik's Vestosint® powders and Chemopharma's MICROPAN® powders.In advantageous embodiments, the filler is a mineral filler and is more particularly silica. In other advantageous embodiments, the filler is an organic filler and is more particularly a polyamide powder such as PA 12 powder.

[0056] Preferably, the charge according to the invention is a charge of finely divided particles, in particular having a volume average diameter of 0.01 to 40 µm, preferably from 10 to 30 µm. Such ranges of average diameter make it possible to obtain powder particles having a volume average diameter suitable in particular for use in a process for constructing a 3D article. The value of the volume average diameter of the particles corresponds to the arithmetic mean of the particle diameters weighted by the volume of said particles. It can be determined according to ISO 13319:2007, for example using a Multisizer 3 Coulter Counter particle size analyzer from Beckman Coulter. The weight ratio of the charge introduced into the reaction medium to the lactam monomers introduced into the reaction medium, expressed as a percentage, can range from 0.001 to 65%, preferably from 0.005 to 45%, more preferably from 0.01 to 30%, or even higher. Preferably from 0.05 to 20%. In some embodiments, this weight ratio may be from 0.001 to 0.1%, or from 0.01 to 0.05%, or from 0.05 to 0.1%, or from 0.1 to 0.3%, or from 0.3 to 0.5%, or from 0.5 to 1%, or from 1 to 2%, or from 2 to 5%, or from 5 to 10%, or from 10 to 20%, or from 20 to 30%, or from 30 to 45%, or from 45 to 65%. The proportion of filler relative to the amount of lactam monomer, as well as the average diameter of the filler, influences the average diameter of the resulting polyamide particles. The lower the proportion of filler relative to the amount of lactam monomer, the higher the average volume diameter of the powder particles will be. The larger the average volume diameter of the charge, the larger the average volume diameter of the powder particles will be.

[0057] The catalyst can be any catalyst usable in an anionic polymerization process of lactams. More particularly, the catalyst is a base strong enough to lead to the formation of a lactamate after reaction with the lactam. The catalyst can be selected from alkali metals (in particular sodium and potassium), alkali metal hydrides and hydroxides, alkali metal alkoxides, and mixtures thereof. By way of non-limiting examples of suitable catalysts, sodium hydride, potassium hydride, sodium, sodium methylate, and / or sodium ethoxide may be mentioned. The catalyst according to the invention can be a mixture of several catalysts, in particular as described above.Advantageously the amount of catalyst is 0.1 to 5 moles, preferably between 0.3 and 3 moles, per 100 moles of lactam monomer, for example 0.1 to 0.3 moles, or 0.3 to 0.5 moles, or 0.5 to 0.7 moles, or 0.7 to 1 mole, or 1 to 1.5 moles, or 1.5 to 2 moles, or 2 to 3 moles, or 3 to 5 moles, per 100 moles of lactam monomer.

[0058] The activator's role is to induce the formation of the acyllactam and to control the polymerization. The activator is advantageously chosen from among the N-carboxyanilide lactams, (mono)isocyanates, polyisocyanates, carbodiimides, cyanamides, acyllactams and acylcarbamates, triazines, ureas, N-substituted imides, esters, phosphorus trichloride, carbon dioxide and mixtures thereof. Preferably, the molar ratio of the catalyst to the activator is 0.2 to 2, preferably 0.8 to 1.2, for example 0.2 to 0.5, or 0.5 to 0.8, or 0.8 to 0.9, or 0.9 to 1, or 1 to 1.1, or 1.1 to 1.2, or 1.2 to 1.5, or 1.5 to 2.

[0059] In embodiments, other additives may be added to the reaction medium, such as pigments, dyes, carbon black, carbon nanotubes, antioxidants, anti-UV agents, and / or plasticizers.

[0060] Polymerization is preferably carried out at atmospheric pressure or at a slightly higher pressure (partial pressure of the hot solvent). It can be carried out under an atmosphere of an inert gas, for example under nitrogen.

[0061] Preferably, the temperature applied to the reaction medium during the introduction of the activator (called the "activator introduction temperature") is between 50°C and 150°C, and more preferably between 60 and 135°C, and even more preferably between 75 and 125°C. In particular, it may be between 50 and 65°C, or between 65 and 75°C, or between 75 and 85°C, or between 85 and 95°C, or between 95 and 105°C, or between 105 and 115°C, or between 115 and 125°C, or between 125 and 135°C, or between 135 and 150°C.

[0062] The activator introduction temperature can be applied to the reaction medium at any time before or during the activator addition. Advantageously, this temperature is applied to the reaction medium after the lactam monomer, the amide (when present), and the feedstock (when present) have been added to the solvent, and before the catalyst is added and the activator is injected. Before the activator introduction temperature is applied, the reaction medium may, for example, be at room temperature (i.e., for example, at a temperature of 15 to 30°C).

[0063] The activator introduction temperature can be maintained for a certain period after the activator introduction has begun. Preferably, it is maintained until the activator introduction is complete. The activator introduction temperature can be maintained for a period of at least 1 hour, preferably from 1 to 12 hours, preferably from 3 to 10 hours, for example, from 1 to 2 hours, or from 2 to 3 hours, or from 3 to 4 hours, or from 4 to 5 hours, or from 5 to 6 hours, or from 6 to 7 hours, or from 7 to 8 hours, or from 8 to 9 hours, or from 9 to 10 hours, or from 10 to 11 hours, or from 11 to 12 hours. Advantageously, the activator introduction temperature is applied for a period equal to or substantially equal to the activator introduction time.

[0064] The process according to the invention further comprises a step of heating the reaction medium to a temperature of 140 to 200°C, which is carried out once the introductions of the lactam monomer, the catalyst, and the activator into the reaction medium have been completed. This step is also referred to as the "baking step" in this text. According to the present invention, this baking step is carried out on the reaction medium, that is, while the ingredients and polymerization products are still in the solvent. The baking step allows polymerization to continue by chain-elongation reactions, once the activator has been completely added to the reaction medium.

[0065] Preferably, the temperature of this cooking step (referred to as the "cooking temperature" in this text) is different from the activator introduction temperature, and more preferably higher than the introduction temperature of the activator. Preferably, the cooking step as defined in this text is carried out after the lactam monomer, the amide when present, the filler when present, the catalyst and the activator have been added (or brought into contact) in the solvent.

[0066] The cooking step is preferably carried out in the same device (e.g., reactor) as the steps described above. Advantageously, after the introduction of the activator, the reaction medium is heated to the cooking temperature, preferably gradually, for example over a period of 15 to 60 min, preferably 20 to 40 min, in particular about 30 min.

[0067] The cooking temperature is from 140 to 200°C, preferably from 145 to 160°C, more preferably from 145 to 155°C. In particular, the cooking temperature may be from 140 to 145°C, or from 145 to 150°C, or from 150 to 155°C, or from 155 to 160°C, or from 160 to 165°C, or from 165 to 170°C, or from 170 to 175°C, or from 175 to 180°C, or from 180 to 185°C, or from 185 to 190°C, or from 190 to 195°C, or from 195 to 200°C.

[0068] Advantageously, the cooking temperature is higher than the activator introduction temperature by at least 20°C, preferably by at least 40°C. In particular, the activator introduction temperature may be higher by at least 20°C, or at least 30°C, or at least 40°C, or at least 50°C, or at least 60°C, or at least 70°C, or at least 80°C, or at least 90°C.

[0069] The duration of the cooking step (also referred to as "cooking time" in this text) is preferably greater than or equal to 2 hours, preferably even greater than or equal to 3 hours, and even more preferably greater than or equal to 5 hours. Even more advantageously, it is from 8 to 15 hours, preferably from 10 to 12 hours. For example, the cooking time may be from 2 to 3 hours, or from 3 to 4 hours, or from 4 to 5 hours, or from 5 to 6 hours, or from 6 to 7 hours, or from 7 to 8 hours, or from 8 to 9 hours, or from 9 to 10, or from 9 to 10, or from 10 to 11 hours, or from 11 to 12 hours, or from 12 to 13 hours, or from 13 to 14 hours, or from 14 to 15 hours.

[0070] After the cooking step, the reaction medium can be cooled, preferably to a temperature ranging from room temperature to 110°C, more preferably to a temperature of 60 to 90°C.

[0071] The polyamide obtained by polymerization precipitates in the solvent as a powder. Thus, the polyamide powder is dispersed in the solvent (i.e., it is not dissolved in the solvent). The polyamide powder can be separated from the solvent by any solid / liquid separation method known to those skilled in the art, such as decantation, dewatering, etc.

[0072] The polyamide powder can be subjected to a drying step, in particular vacuum drying, to remove solvent residues, for example in an oven.

[0073] The powder obtained by polymerization is preferably a polyamide powder chosen from the group consisting of PA 4, PA 6, PA 12, PA 12 / 6, PA 12 / 4, PA 4 / 6, PA 4 / 6 / 12 and mixtures thereof.

[0074] The invention also relates to a powder obtained by, or capable of being obtained by, a process as described above.

[0075] The polyamide powder preferably has a volume average diameter of 10 to 100 pm, preferably 20 to 80 pm, more preferably 25 to 60 pm, and more preferably 30 to 50 pm. In some embodiments, the volume average diameter of the powder is 10 to 20 pm, or 20 to 30 pm, or 30 to 35 pm, or 35 to 40 pm, or 40 to 45 pm, or 45 to 50 pm, or 50 to 60 pm, or 60 to 70 pm, or 70 to 80 pm, or 80 to 90 pm, or 90 to 100 pm. The volume average diameter of the powder can be determined as described above.

[0076] Preferably, the temperature difference Tf-Tc of the powder is at least 20°C, preferably at least 25°C, preferably at least 28°C, more preferably at least 30°C, and even more preferably at least 33°C. The crystallization and melting temperatures can be measured according to ISO 11357-3:2018 Plastics — Differential scanning calorimetry (DSC) — Part 3.

[0077] The polyamide powder may have an inherent viscosity of 0.8 to 1.7 (g / 100 g), preferably 1.0 to 1.5 (g / 100 g). The inherent viscosity is measured according to ISO 307:2019, preferably in a Ubbelohde-type viscometer, except that m-cresol is used as the solvent and the temperature is 20°C. The inherent viscosity has the dimensions of the inverse of a concentration and is equal to the natural logarithm of the relative viscosity, divided by the concentration of polymer dissolved in the solvent. Use of powder

[0078] The invention also relates to the use of a polyamide powder as described above for the manufacture (or construction) of a three-dimensional article.

[0079] The polyamide powder according to the invention can be used in a 3D printing process. For the purposes of this invention, "3D printing" or "additive manufacturing" means any process for manufacturing three-dimensional parts by adding or agglomerating powder, layer by layer. For the purposes of this invention, "3D printing" or "additive manufacturing" also includes selective sintering technologies using an absorber, in particular the technologies known as "High Speed ​​Sintering" (HSS) and "Multi-Jet Fusion" (MJF).

[0080] Preferably, the polyamide powder according to the invention is used in a process for manufacturing three-dimensional objects by agglomerating the powder by melting using radiation or a selective sintering process. The term "sintering" in the This text includes all 3D printing processes by powder agglomeration by fusion, regardless of the type of radiation.

[0081] More specifically, the 3D object manufacturing process according to the invention comprises: a. the deposition, preferably in the form of a layer, of the powder according to the invention; and b. sintering the powder, preferably using an electromagnetic radiation beam.

[0082] Preferably, steps a) and b) are repeated so as to form the three-dimensional article.

[0083] The layer deposited in step a) is preferably heated to a temperature called the build temperature. The term "build temperature" (also called "powder bed 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 lower than the melting temperature of polyamide and higher than the crystallization temperature of polyamide and, most preferably, is within the working window of the polyamide powder.

[0084] The 3D object manufacturing process according to the invention may include a step of manufacturing the powder used in step a) according to a process as described above.

[0085] The radiation can be chosen from any radiation well known to those skilled in the art. Examples of radiation include a laser beam (laser sintering), infrared radiation, UV radiation, or any source of electromagnetic radiation that allows the powder to be melted layer by layer to manufacture three-dimensional objects.

[0086] The device used may be any sintering device well known to those skilled in the art. For example, sintering devices marketed by EOS, 3D Systems, Aspect, Trump Precision Machinery, Hewlett Packard, Sinterit, Sintratec, Sharebot, FormLabs, Sonda Sys, Farsoon, Prodways, Ricoh, Wematter3D, VoxelJet, Xaar, etc. EOSINT P396 and Formiga P100 from EOS GmbH are examples of sintering devices.

[0087] According to an advantageous sintering process, a thin layer of powder is deposited on a horizontal plate held in a chamber heated to the construction temperature. Advantageously, electromagnetic radiation subsequently provides the energy necessary to sinter the powder particles at different points in the powder layer according to a geometry corresponding to an object (for example, using a computer that has the shape of an object stored in its memory and reproduces that shape). (in the form of slices). Then, the horizontal plate is lowered by a distance corresponding to the thickness of a powder layer, and a new layer is deposited. Electromagnetic radiation provides the energy needed 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 has been manufactured.

[0088] The layer of powder deposited on a horizontal plate (before sintering) can have a thickness of 20 to 200 µm, preferably 50 to 150 µm. The layer of agglomerated material after sintering can have a thickness of 10 to 150 µm, preferably 30 to 100 µm.

[0089] Preferably, the composition of the invention is used in a selective laser sintering process. The composition can also be used in an MJF type sintering process and HS S high-speed sintering.

[0090] Preferably, the three-dimensional object manufactured by a process according to the invention is chosen from a prototype, a model of a part ("rapidprototyping"), a finished part in small series ("rapid manufacturing"), in particular for the automotive, nautical, aeronautical, aerospace, medical (prostheses, hearing systems, ...), textile, clothing, fashion, decoration, electronics, telephony, home automation, computer, lighting, sports, and industrial tooling sectors.

[0091] The use of the powder according to the invention in additive manufacturing is advantageous because the polyamide powder is recyclable in several successive builds. The polyamide powder can thus be used multiple times, alone or mixed with other powders, whether recycled or not. Indeed, the powder that has not agglomerated can be recovered by sieving, the sieve retaining the 3D objects and allowing the powder to flow through. Preferably, the powder according to the invention is recyclable at least 3 times, preferably at least 5 times, and more preferably at least 10 times.

[0092] Preferably, in each build cycle, or "run", the recycled powder content is at least 50%, preferably at least 60%, and more preferably at least 70% by weight, of the total weight of powder used in the machine in each run. In other words, apart from the first run which uses 100% fresh powder, each subsequent run reuses at least 50%, preferably at least 60%, and preferably at least 70%, by weight of powder from the previous run that has not been sintered, of the total weight of powder used in the machine in each run.

[0093] Before use, the manufactured 3D object can be easily cleaned using any cleaning technique well known to those skilled in the art. For example, the object can be cleaned using a sandblaster.

[0094] The invention also relates to the use of a polyamide powder as described above for the manufacture of a composite, a substrate coating, in particular a metallic substrate (coil-coating), a transfer paper, a liquid or solid ink composition, a liquid or solid paint, a structural adhesive, a cosmetic composition or a pharmaceutical composition. Examples

[0095] The following examples illustrate the invention without limiting it.

[0096] In the examples below, the working windows of different polyamide powders were evaluated.

[0097] The crystallization and melting temperatures and the enthalpy of fusion of the powders were measured according to ISO 11357-3:2018 (DSC), the average volume diameter of the powders was determined according to ISO 13319:2007 and the inherent viscosity of the powders was determined according to ISO 307:2019 but at a temperature of 20°C and using m-cresol as the solvent.

[0098] Operating procedure for evaluating the working window

[0099] The operating temperature window was determined in a P100 (EOS) laser sintering machine by operating at constant laser energy and constant shrinkage chamber temperature, so that only the build chamber temperature varied. The laser conditions used for this test are as follows: • Shrinkage chamber temperature: 140°C • Outline • Laser power: 16 W • Speed: 1500 mm / s • Hatching • Power: 18 W • Speed: 3000 mm / s • Radius displacement: 0.20 mm • Energy: 0.3 mJ / mm3

[0100] The build chamber temperature (Tœ) corresponds to the temperature to which the top layer of the powder bed is heated before the laser passes over it. A 3D-printed model of various parts has been developed, according to which: 1. 40 layers of powder are deposited successively, and each one is heated to Tcc before the next layer is deposited (for these 40 layers, the laser is not used to selectively melt the powder); then 2. From the 41st layer onwards, 3D construction by selective laser powder melting begins as soon as the powder layer temperature reaches Tcc, and this is repeated for each layer, in order to build a defined part; then 3. 40 layers of powder are deposited successively, and each one is heated to Tcc before the next layer is deposited (for these 40 layers the laser is not used to selectively melt the powder).

[0101] The part defined in step 2) above is either a type IB pull-up barbell according to ISO 527-2 (15 cm long and 4 mm thick) as shown in [Fig.1], particularly sensitive to curling, or a part having 10 holes of different sizes (4 mm thick) as shown in [Fig.2], particularly sensitive to caking.

[0102] For each of the powders tested, 5 IB type pull-up dumbbells and 2 pieces with 10 holes were manufactured according to the above model construction.

[0103] A two-step protocol based on a temperature scan of the build chamber was then implemented to determine the limits of the powder working window. These two steps are as follows: 1. The model construction described above is first carried out at Tcc = 168°C. It is then reproduced several times, each time increasing the temperature of the construction chamber by 2°C increments until Tcc = 176°C is reached. The machine is then cooled and the 3D objects are retrieved. 2. The model construction described above is again carried out at Tcc = 168°C. It is then reproduced several times, each time decreasing the temperature of the construction chamber by 2°C increments until Tcc = 160°C is reached. The machine is then cooled and the 3D objects are retrieved.

[0104] For each temperature of the construction chamber (Tcc) tested, the following are determined: • the deformation of the dumbbells (reflecting the sensitivity to curling), and • the ease of cleaning 10-hole parts (representative of sensitivity) (at the cake).

[0105] The deformation of the dumbbells was determined by measuring their flatness. The flatter the specimen (dumbbell), the less pronounced the deformation, and therefore the 3D object produced will correspond to the intended geometry. To determine their flatness, each specimen was placed on a flat surface, a 1 kg weight was placed on the left jaw of the dumbbell, and the distance between the end of the right jaw and the flat surface was measured. This measurement was repeated on each of the four longitudinal faces of the dumbbells and the greatest measured distance corresponds to the retained deformation.

[0106] For each construction temperature tested, the deformation was measured for each of the 5 parts built at said construction temperature, and the final deformation is the average of the five measurements taken (this allows for taking into account temperature variations at the surface of the powder bed).

[0107] It has been considered that a distance less than or equal to 2 mm meets the geometric needs of 3D objects and therefore corresponds to a slight curling phenomenon.

[0108] The lower limit of the working window corresponds to the lowest temperature of the construction chamber for which a distance less than or equal to 2 mm was obtained as the final deformation.

[0109] The ease or difficulty of cleaning parts containing 10 holes of varying sizes was evaluated using a compressed air blow gun without sandblasting. The greater the number of holes cleared in the part using the blow gun, the easier the cleaning. A score out of 10 was assigned based on the number of holes cleared. For example, a score of 10 / 10 is assigned to powders for which all 10 holes were cleared, and which will therefore be the easiest to clean. Conversely, a score of 0 / 10 is assigned to powders for which no holes were cleared, and which therefore clump together strongly and will be the most difficult to clean (resulting in a longer cleaning time and potentially leading to damage to some fine and / or fragile elements of the 3D printed parts).

[0110] For each tested build temperature, a score was assigned to each of the two parts built at said build temperature, and the final score is the average of the two scores obtained (this allows for consideration of temperature variations on the surface of the powder bed).

[0111] It was considered that a score of 8 / 10 or higher allows for a satisfactory ease of cleaning and therefore corresponds to a low caking phenomenon.

[0112] The upper limit of the working window corresponds to the highest temperature of the construction chamber for which a score greater than or equal to 8 / 10 was obtained. Polyamide powder preparation

[0113] The powder preparation processes described below were reproduced until a sufficient quantity of powder was obtained to determine the working window.

[0114] Example 1 (comparative): Preparation of PA 12 powder

[0115] This comparative example is similar to example 4 in document EP 1571173.

[0116] 2800 mL of solvent (a paraffinic hydrocarbon fraction with a boiling range of 145 to 160°C) is introduced into the reactor, which is maintained under nitrogen. This is followed successively by 899 g of dry lauryl lactam, 4.95 g of EBS, and 0.36 g of finely divided and dehydrated silica. After starting the stirring at 300 rpm, the mixture is gradually heated to 110°C. Then, 290 mL of solvent is distilled under vacuum to remove any traces of water that may be present by azeotropy.

[0117] After returning to atmospheric pressure, the anionic catalyst, 1.79 g of 60 wt. pure sodium hydride in oil, is rapidly introduced under nitrogen, and the stirring speed is increased to 400 rpm under nitrogen at 110°C for 30 minutes. Then, the temperature is lowered to 100.5°C and, using a small metering pump, a continuous injection of the stearyl isocyanate activator is carried out into the reaction medium, according to the following program: • 3.6 g of stearyl isocyanate for 60 minutes, then • 5.9 g of stearyl isocyanate for 132 minutes.

[0118] Simultaneously, the temperature is maintained at 100.5°C for the first 60 minutes then raised to 120°C in 30 minutes and maintained at 120°C until 2 hours after the end of the introduction of the stearyl isocyanate.

[0119] The polymerization is then completed, the reaction medium is cooled to 80°C, then the powder is separated by decantation and dried.

[0120] The PA 12 powder particles obtained have a volume average diameter of 55 pm, an inherent viscosity of 1.48 (g / 100 g)1, a melting temperature of 183°C and a crystallization temperature of 135°C.

[0121] The working window was evaluated as indicated above. It is 168°C, as the model construction was only possible at this temperature.

[0122] Example 2 (according to the invention): Preparation of PA 12 powder

[0123] 2800 mL of solvent (paraffinic hydrocarbon fraction with a boiling range of 145 to 160°C) is introduced into the reactor maintained under nitrogen, followed successively by 919 g of lauryllactam (lactam 12), 15.0 g of EBS, and 3.2 g of silica (SIPERNAT 320DS). After starting the stirring at 300 rpm, the mixture is gradually heated to 105°C, and then 360 mL of solvent is distilled under vacuum to remove any traces of water that may be present by azeotropy.

[0124] After returning to atmospheric pressure, the anionic catalyst, 2.4 g of sodium hydride at 60% by weight purity in oil, is then rapidly introduced under nitrogen and the agitation is increased to 550 rpm, under nitrogen at 105°C for 30 minutes.

[0125] Using a small dosing pump, a continuous injection of the chosen activator, namely stearyl isocyanate (27.3 g in 119.7 g of solvent), is carried out into the reaction medium according to the following program: • 12 g / h of stearyl isocyanate solution for 180 minutes, then • 50 g / h of stearyl isocyanate solution for 133 minutes.

[0126] In parallel, the temperature is maintained at 105°C for 313 minutes during the injection, then after the end of the introduction of the isocyanate the reaction medium is heated to 150°C in 30 minutes and maintained at this temperature for 12 hours.

[0127] At the end of polymerization, the polyamide powder is dispersed in the synthesis solvent. The reaction medium is cooled to 80°C to allow the reactor to be drained; after solid / liquid separation, the polyamide powder is placed in an oven at 75°C to dry it from the solvent.

[0128] The PA 12 powder particles obtained have a volume average diameter of 38 pm, an inherent viscosity of 1.32 (g / 100 g)1, a melting temperature of 184°C associated with an enthalpy of fusion of 112 J / g, and a crystallization temperature of 146°C.

[0129] The working window has been evaluated as indicated above. It is 166 to 172°C.

[0130] Example 3 (according to the invention): Preparation of PA 12 / 6 powder

[0131] 2800 mL of solvent (paraffinic hydrocarbon fraction with a boiling range of 145 to 160°C) is introduced into the reactor maintained under nitrogen, followed successively by 919 g of lauryllactam (lactam 12), 4.6 g of caprolactam (lactam 6), 14.0 g of EBS, and 4.2 g of Orgasol® 2001 UD Nat 1 (PA 12 powder). After starting the stirring at 300 rpm, the mixture is gradually heated to 105°C, and then 360 mL of solvent is distilled under vacuum to remove any traces of water that may be present by azeotropy.

[0132] After returning to atmospheric pressure, the anionic catalyst, 3.9 g of sodium hydride at 60% by weight purity in oil, is then rapidly introduced under nitrogen and the agitation is increased to 550 rpm, under nitrogen at 105°C for 30 minutes.

[0133] Using a small dosing pump, a continuous injection of the chosen activator, namely stearyl isocyanate (25.3 g in 185.1 g of solvent), is carried out into the reaction medium according to the following program: • 12 g / h of stearyl isocyanate solution for 180 minutes, then • 50 g / h of stearyl isocyanate solution for 210 minutes.

[0134] In parallel, the temperature is maintained at 105°C for 390 minutes during the injection, then raised to 150°C in 30 minutes and maintained at this temperature for 12 hours after the end of the introduction of the isocyanate.

[0135] At the end of polymerization, the polyamide powder is dispersed in the synthesis solvent. The reaction medium is cooled to 80°C to allow the reactor to be drained; after solid / liquid separation, the polyamide powder is placed in an oven at 75°C to dry it from the solvent.

[0136] The PA 12 / 6 powder particles obtained have a volume average diameter of 39 pm, an inherent viscosity of 1.34 (g / 100 g), a melting temperature of 183°C associated with an enthalpy of fusion of 109 J / g, and a crystallization temperature of 145°C.

[0137] The working window has been evaluated as indicated above. It is 164 to 172°C.

[0138] Example 4 (comparative): Preparation of PA 12 powder with subsequent heat treatment

[0139] The PA 12 powder particles of Orgasol® 2002 ES4 Nat 3 have a volume mean diameter of 41 pm, an inherent viscosity of 1.02 (g / 100 g)', a melting point of 177°C associated with an enthalpy of fusion of 112 J / g, and a crystallization temperature of 150°C.

[0140] The working window was evaluated as indicated above. The powder does not exhibit any working window.

[0141] An 88h heat treatment at 167°C was carried out on this PA 12 powder in a stirred reactor under nitrogen purging, as described in document WO 2013 / 090174. The powder particles after heat treatment have a volume average diameter of 41 pm, an inherent viscosity of 1.02 (g / 100 g)', a melting temperature of 182°C (with a marked shoulder at 180°C on the DSC curve) associated with an enthalpy of fusion of 118 J / g, and a crystallization temperature of 150°C.

[0142] The working window was evaluated as indicated above. It is 168°C, as the model construction was only possible at this temperature.

[0143] Example 5 (according to the invention): Preparation of PA 12 / 6 powder

[0144] 2800 mL of solvent (paraffinic hydrocarbon fraction with a boiling range of 145 to 160°C) is introduced into the reactor maintained under nitrogen, followed successively by 919 g of lauryllactam (lactam 12), 4.6 g of caprolactam (lactam 6), 14.0 g of EBS, and 3.0 g of Orgasol® 2001 UD Nat 1 (PA 12 powder). After starting the stirring at 300 rpm, the mixture is gradually heated to 105°C, and then 360 mL of solvent is distilled under vacuum to remove any traces of water that may be present by azeotropy.

[0145] After returning to atmospheric pressure, the anionic catalyst, 3.9 g of sodium hydride at 60% by weight purity in oil, is then rapidly introduced under nitrogen and the agitation is increased to 550 rpm, under nitrogen at 105°C for 30 minutes.

[0146] Using a small dosing pump, a continuous injection of the chosen activator, namely stearyl isocyanate (25.3 g in 185.1 g of solvent), is carried out into the reaction medium according to the following program: • 50 g / h of stearyl isocyanate solution for 253 minutes.

[0147] In parallel, the temperature is maintained at 105°C for 253 minutes during the injection, then raised to 150°C in 30 minutes and maintained at this temperature for 6 hours after the end of the introduction of the isocyanate.

[0148] At the end of polymerization, the polyamide powder is dispersed in the synthesis solvent. The reaction medium is cooled to 80°C to allow the reactor to be drained; after solid / liquid separation, the polyamide powder is placed in an oven at 75°C to dry it from the solvent.

[0149] The PA12 / 6 powder particles obtained have a volume average diameter of 42 pm, an inherent viscosity of 1.16 (g / 100 g)1, a melting temperature of 182°C associated with an enthalpy of fusion of 122 J / g, and a crystallization temperature of 149°C.

[0150] The working window was evaluated as indicated above. It is 168 to 172°C. Results

[0151] It is observed that the powders prepared according to the invention have a relatively wide working temperature window for 3D printing, of at least 4°C when the curing step lasts 6 hours at 150°C and of at least 6°C when it lasts 12 hours at 150°C. Furthermore, it is noted that the PA 12 powder according to the invention prepared according to Example 2 has a much wider working temperature window compared to the PA 12 powder prepared according to comparative Example 1, in which the curing step is carried out at 120°C for a duration of 2 hours.

[0152] Furthermore, when heat treatment is applied to the powder afterward (comparative example 4), the working window is not widened even though the Tf-Te difference has increased. According to the inherent viscosity results before and after heat treatment, no change in molar mass is observed. This demonstrates that the baking step must take place on the compounds under polymerization conditions in order to obtain a widening of the working window.

Claims

Demands

1. A process for manufacturing a polyamide powder by anionic polymerization in a solvent, comprising the following steps: a) the formation of a reaction medium comprising: • the introduction of at least one lactam monomer into said solvent; • the introduction of at least one catalyst into said solvent; and • the introduction of at least one activator into said solvent at a given temperature; b) the polymerization of the lactam monomer into polyamide in the reaction medium; c) the precipitation of the polyamide in powder form in the reaction medium; and d) heating, after step a), of the reaction medium to a temperature higher than the temperature of the introduction of at least one activator and of 145 to 200°C, for a period greater than or equal to 5h.

2. A method according to claim 1, wherein the heating in step d) is carried out for a period of 8 to 15 hours, preferably 10 to 12 hours.

3. A method according to claim 1 or 2, wherein step a) further comprises the introduction of at least one filler into the solvent, the at least one filler preferably being a mineral filler, preferably silica, and / or an organic filler, preferably a polyamide powder.

4. A method according to any one of claims 1 to 3, wherein step a) further comprises the introduction of at least one amide into the solvent, the at least one amide preferably being an N,N'-alkylene bisamide, more preferably N,N'-Ethylene bis-stearamide and / or N,N'-Ethylene bis-oleamide.

5. A method according to any one of claims 1 to 4, wherein at least one lactam monomer is selected from the group consisting of 2-pyrrolidone, caprolactam, 2-azacyclononanone, lauryllactam and mixtures thereof.

6. A method according to any one of claims 1 to 5, wherein at least one catalyst is selected from the group consisting of sodium, potassium, alkali metal hydrides and hydroxides, alkali metal alkoxides, and mixtures thereof, preferably from the group consisting of sodium hydride, potassium hydride, sodium, sodium methylate, sodium ethoxide, and mixtures thereof.

7. A method according to any one of claims 1 to 6, wherein at least one activator is selected from the group consisting of N-carboxyanilide lactams, (mono)isocyanates, polyisocyanates, carbodiimides, cyanamides, acyllactams and acylcarbamates, triazines, ureas, N-substituted imides, esters, phosphorus trichloride and mixtures thereof.

8. A process according to any one of claims 1 to 7, wherein the solvent is a cut of paraffinic hydrocarbons having a boiling temperature range of 120 to 170°C.

9. A method according to any one of claims 1 to 8, wherein the heating temperature at step d) is from 145 to 160°C, preferably still from 145 to 155°C.

10. A method according to any one of claims 1 to 9, wherein the temperature of introduction of at least one activator is from 50 to 150°C, preferably from 60 to 135°C.

11. A method according to any one of claims 1 to 10, further comprising a step of introducing into the solvent one or more additives selected from the group consisting of pigments, dyes, carbon black, carbon nanotubes, antioxidants, anti-UV agents and plasticizers.

12. Polyamide powder obtained by a manufacturing process according to any one of claims 1 to 11.

13. Use of a powder according to claim 12, for the construction of a three-dimensional article, preferably layer by layer, more preferably by sintering, even more preferably by sintering caused by electromagnetic radiation.

14. Use of a powder according to claim 12, for the manufacture of a composite, a substrate coating, a transfer paper, a liquid or solid ink composition, a liquid or solid paint, structural adhesive, cosmetic composition or pharmaceutical composition.

15. A method for manufacturing a three-dimensional article comprising the following steps: • manufacturing a powder by a method according to any one of claims 1 to 11; • deposition, preferably in the form of a layer, of said powder; and • sintering the powder, preferably by means of electromagnetic radiation.

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