Process for recycling used polyamide compositions

Abstract

The present invention relates to a process for recycling a used polyamide composition into a recycled polyamide powder having a single peak melt endotherm and a single melt temperature (Tf1max), the process comprising the steps of: i. Contacting the used polyamide composition with a solvent to obtain a mixture; ii. Heating the mixture so that the polyamide is dissolved in the solvent; iii. Cooling the mixture to a precipitation temperature (Tp) of the polyamide in said solvent, thereby obtaining a precipitated polyamide powder characterized by a non-unimodal heat absorption and more than one melting temperature, Tf1max being the highest melting temperature; and iv. Maintaining the temperature of the mixture at a temperature at most equal to Tp, in particular in the range from Tp-0.1 DEG C to Tp-15 DEG C, until the precipitated polyamide powder is characterized by a single-peak heat absorption by melting and a melting temperature (Tf1max); and v. Recovering the recycled polyamide powder obtained.

Description

Technical Field

[0001] The present invention relates to a method for recycling a used polyamide composition into a polyamide powder having an increased difference between the melting temperature and the crystallization temperature (T f1 -T c ).

[0002] T of polyamide-based powders f1 and T c The large difference between is useful in many applications, in particular in powder agglomeration techniques by melting or sintering induced by radiation such as a laser beam (laser sintering), infrared radiation or UV radiation, or any electromagnetic radiation source that allows powders to melt to make an object.

[0003] The invention also relates to the polyamide powder obtained according to this process.

[0004] Finally, the invention relates to the use of the powder and to articles made therefrom. Background Art

[0005] The technology of agglomerating polyamide powder under a laser beam is used to produce three-dimensional objects such as prototypes and models in various fields.

[0006] A thin layer of polyamide powder is deposited on a horizontal plate held in a chamber which is heated to a temperature at the crystallization temperature T of the polyamide powder. c and melting temperature T f1 The laser condenses the powder particles at different points in the powder layer according to the geometry of the object, for example using a computer that has the shape of the object in its memory and reproduces this shape in the form of slices. Once the temperature of the powder area exposed to the laser has dropped to the crystallization temperature T c The following solidification. Subsequently, the horizontal plate is lowered by a distance corresponding to the thickness of the powder layer, a new powder layer is then deposited, and the laser agglomerates the powder particles according to the geometry corresponding to this new slice of the object, and so on. This process is repeated until the entire object is manufactured. An object surrounded by non-agglomerated powder is obtained inside the chamber. The assembly is then slowly cooled.

[0007] After complete cooling, the objects are separated from the powder, which can be reused for another operation.

[0008] Immediately after the laser beam is applied, the temperature of the exposed area is higher than the crystallization temperature (T c). However, when the temperature drops below this temperature too quickly, for example by applying a new, cooler layer of powder, this causes deformation (a "curling" phenomenon) in the part being printed. Similarly, when the temperature of the powder in the machine is too close to the melting temperature (T f1 ), this leads to solidification around the part (a phenomenon called “caking”), which manifests itself by the formation of powder lumps that affect the print quality.

[0009] In order to avoid these phenomena, it is therefore important to have a powder with a T as far away from the powder as possible. f1 Temperature T c . Differences in powder T f1 -T c The operating temperature window of the device for agglomerating powder particles by radiation-induced melting is determined. The operating window is defined by its upper temperature limit and its lower temperature limit. The upper limit of the operating window corresponds to the temperature at which agglomeration or "caking" occurs. The lower limit of the operating window corresponds to the temperature at which distortion or deformation or "curling" occurs. It is desirable that the operating window is larger than the temperature variation within the 3D printer, which is typically of the order of ±3°C.

[0010] Furthermore, a high melting enthalpy (ΔHf) is advantageous in order to optimize the geometrical definition of the manufactured part. Specifically, if it is too low, the energy supplied by the laser risks sintering, by thermal conduction, the powder particles surrounding the part being constructed, which limits the geometrical precision of the part obtained.

[0011] It is clear that everything explained about the agglomeration of polyamide powders under a laser beam is valid regardless of the electromagnetic radiation that causes the melting and regardless of whether the melting process is selective or non-selective.

[0012] Document US 5932687 discloses a method for preparing a precipitated polyamide powder having a narrow particle distribution and low porosity. The method comprises a first step of cooling a polyamide previously dissolved in an alcohol solvent to a temperature t1 (higher than the precipitation temperature of the polyamide in the solvent) to obtain germination of the polyamide, followed by a second cooling step to obtain supersaturation of the medium and thus obtain precipitation of the polyamide at a temperature t2. The suspension obtained is directly cooled and dried to recover the polyamide powder.

[0013] Document US 2008 / 0166496 discloses a polyamide 11 powder that can be used in a powder agglomeration process, in particular for the preparation of three-dimensional objects. These powders are prepared according to a method comprising the step of cooling a polyamide previously dissolved in ethanol to a temperature at which the polyamide precipitates. The heat generated by the precipitation keeps the medium at this temperature for 25 minutes, then the temperature is slightly reduced and reaches an isotherm of 35 minutes. At the end of this plateau, the mixture is cooled to separate the precipitated polyamide powder.

[0014] However, the inventors have been able to observe that the prior art methods provide polyamide powders whose analysis by differential scanning calorimetry at the first heating shows the presence of two temperature peaks, which are associated with two relatively close but different melting temperatures, revealing the presence of at least two different crystalline phases. For the reasons mentioned above, this inhomogeneity of the thermal characteristics of the powder reduces the working window and can therefore be detrimental to the quality of the objects manufactured according to the powder agglomeration process via electromagnetic radiation mediated melting, and in particular to their definition.

[0015] These methods involve the preparation of virgin polyamide powder.

[0016] As mentioned above, the described technique produces a large amount of powder which is not agglomerated but which has been subjected to a considerable period of time close to T f1 It is advantageous to recycle these powders in order to limit energy and resource consumption. A method for recycling polyamides contained in used compositions, in particular derived from 3D printing waste, has been described.

[0017] Thus, CN110483986 describes a method for recovering residual polyamide 12 powder after selective laser sintering. The method consists in dissolving the powder to be recovered in an acidic solution, then neutralizing and atomizing the solution to obtain the recovered polyamide powder. Therefore, this process (which is specific to the treatment of 3D printing waste) involves a treatment in an acidic medium, which is very aggressive to polyamide. It also does not allow the polyamide to be separated from the other products present in the composition and does not allow the physicochemical characteristics of the recycled polyamide powder to be controlled, in particular its viscosity, particle size or thermal properties. In addition, it requires specific equipment and the management of the acidic solution logistics makes it particularly cumbersome to implement.

[0018] CN109810284 describes a method for dissolving polyamide 12 waste from 3D printing by a complex solvent system comprising a mixture of hydrochloric acid, formic acid and acetic acid. A solid / liquid separation step is carried out at an elevated temperature, followed by precipitation of the polyamide by the addition of water as a non-solvent. However, this dissolution / precipitation process in an acidic medium is very aggressive to the polyamide and does not allow control of the physicochemical characteristics of the circulating powder. In addition, the management of the acid solution logistics also makes this method difficult to implement.

[0019] Therefore, there is a real need to have a process for recycling used polyamide compositions into recycled polyamide powders, which is particularly useful for powder agglomeration technology via electromagnetic radiation mediated melting, allowing to overcome these drawbacks. Summary of the invention

[0020] The inventors have now developed a dissolution / precipitation process which allows recycling of used polyamide compositions and which also effectively increases the T of the recycled polyamide by obtaining a unimodal melting endotherm. f1 -T c difference.

[0021] More specifically, it was found that by introducing a temperature plateau of sufficient duration at the end of the polyamide precipitation stage, a polyamide with a non-unimodal melting endotherm and more than one melting temperature (T f1 ) is converted into a precipitated polyamide powder characterized by a single peak melting endotherm and a temperature equal to (T f1 max ) has a single melting temperature (T f1 ) and thus increase the temperature difference (T f1 -T c ), where (T f1 max ) is the maximum melting temperature. The inventors have been able to demonstrate in particular that this temperature plateau allows crystal refinement to occur and thus a single-crystalline phase to be obtained.

[0022] The polyamide powders obtained are therefore particularly advantageous for use in powder agglomeration processes via electromagnetic radiation-mediated melting, in particular in that they allow an increase in the working window and thus an improvement in the quality and / or precision of objects manufactured from these powders.

[0023] According to other advantages, the recycling process according to the invention is easy to carry out and does not require the use of acidic conditions. It also allows the particle size of the powder to be controlled, in particular its span factor, and the polyamide to be separated at least partially from other compounds present in the used composition, such as additives and fillers. Thus, the recycling process allows obtaining a recycled polyamide powder having a high purity and whose thermal characteristics are improved with respect to those of the used polyamide.

[0024] According to a first aspect, the subject of the present invention is therefore to provide a method for recycling a used polyamide composition into a polyamide having a unimodal melting endotherm and a single melting temperature (T f1 max ) of the invention, the method comprising the following steps:

[0025] i. contacting the used polyamide composition with a solvent to obtain a mixture;

[0026] ii. heating the mixture to dissolve the polyamide in the solvent;

[0027] iii. cooling the mixture to the precipitation temperature (T p ), thereby obtaining a precipitated polyamide powder characterized by a non-unimodal melting endotherm and more than one melting temperature, (T f1 max ) is the maximum melting temperature; and

[0028] iv. maintaining the mixture at a temperature at most equal to T p At temperatures above T p -0.1℃ to T p -15°C until the precipitated polyamide powder is characterized by a single-peak melting endotherm and a melting temperature (T f1 max );and

[0029] v. Collecting the obtained recycled polyamide powder.

[0030] Advantageously, the method also has one or more of the following characteristics. Therefore, in certain embodiments, the method according to the present invention is as follows:

[0031] - wherein the solvent contacted with the polyamide is an alcohol, in particular a C1-C4 aliphatic alcohol, preferably ethanol;

[0032] wherein the heating of the mixture is carried out at a temperature of 100°C to 200°C, and preferably 120°C to 160°C; and / or wherein the heating duration of the mixture is 1 to 6 hours, preferably 1 to 3 hours;

[0033] - 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 10°C to 60°C per hour;

[0034] - wherein the polyamide is polyamide 11, polyamide 6, or polyamide 10.10, or polyamide 10.12, or polyamide 6.10;

[0035] - The precipitation temperature of the polyamide is T p Between 80°C and 130°C, especially between 100°C and 120°C;

[0036] - wherein, in step iv), the mixture is kept at a temperature close to the precipitation temperature for a period of at least 2 hours, in particular from 3 to 12 hours, from the start of precipitation of the polyamide;

[0037] - further comprising a step vi) of drying the precipitated polyamide powder recovered in step v) or obtained at the end of step iv) at a temperature between 10° C. and 150° C., more particularly between 50° C. and 100° C.;

[0038] - wherein the drying of the precipitated polyamide powder is carried out at a pressure ranging from 10 mbar to atmospheric pressure;

[0039] - wherein the composition further comprises volatile organic compounds (VOCs);

[0040] - wherein the composition comprises mineral fillers, especially fibers, in particular glass fibers and / or carbon fibers; and / or

[0041] - further comprising a step vii) of separating and recovering the mineral filler which may be present in the precipitated polyamide powder, in particular after step iv), v) or vi).

[0042] According to a second aspect, the present invention also provides a polyamide powder having a unimodal melting endotherm and a single melting temperature (T f1 max ), which can be obtained via the recycling process according to the invention.

[0043] Advantageously, the powder has one or more of the following properties. Thus, in certain embodiments, the powder according to the invention is a polyamide powder:

[0044] - characterized in that its volume average diameter is 10-200 μm, in particular 20-100 μm, preferably 40-80 μm;

[0045] - characterized in that its diameter Dv10 is greater than 5 μm, in particular 10 μm to 70 μm, preferably 20 μm to 60 μm;

[0046] - characterized in that its diameter Dv90 is less than 350 μm, in particular 30 μm to 200 μm, preferably 50 μm to 150 μm;

[0047] - characterized in that its median diameter Dv50 is from 10 to 200 μm, in particular from 20 to 100 μm, preferably from 30 to 90 μm;

[0048] - characterised in that its span factor is between 0.1 and 1.5; preferably between 0.1 and 1.0 and more preferably between 0.5 and 1.0;

[0049] - wherein the polyamide is polyamide 11;

[0050] - It is characterized by its melting temperature (T f1 max ) is 195 to 205°C; and / or

[0051] - wherein the melting temperature (T f1 max ) and the crystallization temperature (T c ) is between 35°C and 45°C.

[0052] According to a third aspect, the present invention relates to a polyamide 11 powder having a unimodal melting endotherm and a single melting temperature (T f1 max ), and at least one of the following characteristics:

[0053] - a volume average diameter of 10-200 μm, in particular 20-100 μm, preferably 40-80 μm;

[0054] a diameter Dv10 greater than 5 μm, in particular between 10 μm and 70 μm and preferably between 20 μm and 60 μm;

[0055] a volume median diameter Dv50 between 10 μm and 200 μm, in particular between 20 μm and 100 μm and preferably between 30 μm and 90 μm;

[0056] a diameter Dv90 of less than 350 μm, in particular between 30 and 200 μm and preferably between 50 and 150 μm;

[0057] - the span factor is between 0.1 and 1.5; preferably between 0.1 and 1, more preferably between 0.5 and 1.0;

[0058] - a melting enthalpy greater than 100 J / g; and preferably between 110 J / g and 160 J / g; and / or

[0059] - Intrinsic viscosity is 0.8-1.8, preferably 1.0-1.5.

[0060] According to a fourth aspect, the subject of the present invention is a composition in powder form for 3D printing, in particular 3D printing by laser sintering, comprising:

[0061] - a polyamide powder according to the invention; and

[0062] - At least one filler or additive.

[0063] According to a fifth aspect, the invention relates to a method for manufacturing a polyamide object by agglomeration of a fused powder mediated by electromagnetic radiation, the powder being as previously defined.

[0064] According to a sixth aspect, the present invention relates to a manufactured article obtained from a powder or composition according to the invention by electromagnetic radiation mediated melting.

[0065] According to a seventh aspect, the subject of the present invention is a method according to the invention for increasing the melting temperature (T f1 ) and crystallization temperature (T c ) f1 -T c )’s purpose.

[0066] According to an eighth aspect, the present invention relates to a recycled mineral filler obtainable by the recycling method according to the present invention.

[0067] According to one embodiment, the recycled mineral filler is pre-coated with a polyamide powder having a unimodal melting endotherm and a single melting temperature, which is obtainable by the recycling process according to the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] Figure 1 Represents an image obtained by scanning electron microscopy (SEM) (magnification x120) of a glass fiber pre-coated with PA11 obtained at the end of the process according to Example 1 of the invention.

[0069] Figure 2 Represents an image obtained by scanning electron microscopy (SEM) (magnification ×240) of carbon fibers pre-coated with PA11 obtained at the end of the process according to Example 2 of the invention. DETAILED DESCRIPTION

[0070] The invention is now described in more detail in a non-limiting manner in the following description.

[0071] definition

[0072] It is to be noted that the expressions “from ... to (to) ...” and “between ... and ...” used in the present specification should be understood to include each endpoint mentioned.

[0073] The term "used polyamide powder composition" means a composition in powder form containing polyamide, optionally in combination with other ingredients, including in particular additives or fillers, resulting from the industrial conversion of a polyamide-based composition, for example by extrusion, molding, typically by injection, or else by 3D printing. It may especially be a composition obtained from a used finished product, or from production waste or waste generated during a process for converting a polyamide-based composition.

[0074] These used compositions are generally characterized by partial degradation of the macromolecular chain of the polyamide, which may be in the form of partial oxidation and may therefore comprise imide and / or alcohol and / or primary amide functionalities not present on the original polyamide (before conversion and optional use). In addition, the polyamide is combined with other ingredients, such as stabilizers, which themselves may have undergone degradation. The recycling process according to the invention advantageously allows the separation of the polyamide from the other ingredients in the used composition and the obtaining of an almost pure polyamide powder.

[0075] The term "powder" is understood to mean a solid material in finely divided form; it is usually provided in the form of particles of very small size, usually of the order of a few hundred micrometers or less.

[0076] Powders are usually characterized by thermograms obtained by differential scanning calorimetry (DSC), according to:

[0077] - a first heating, allowing to characterize the melting phenomena of the polyamide powder;

[0078] - cooling, allowing the characterization of the crystallization phenomena of the polyamide material;

[0079] - A second heating allows characterization of the melting phenomena of the polyamide material itself.

[0080] The following terms related to thermal properties are understood as defined in standard ISO 11357-1:2016:

[0081] - "Peak" refers to a portion of a thermogram obtained by differential scanning calorimetry (DSC) that deviates from the baseline to reach a local maximum or a local minimum and then returns to the baseline. Such a peak may indicate a first order transition (crystallization exotherm or melting endotherm); for the purposes of this specification, a melting peak may include, in particular, several peaks or shoulders before the signal returns to the baseline.

[0082] - "Baseline" means the part of the recorded thermogram without any transitions, in particular in this case without any first order transitions of the melting or crystallization type. In the transition zone, a virtual baseline can be determined: this is an imaginary line drawn through the transition zone, assuming that the heat due to the transition is zero. The virtual baseline can be drawn by interpolating the baseline of the sample with the help of a straight line;

[0083] - "Peak area" means the area bounded by the peak and the interpolated virtual baseline. It is considered the transition enthalpy and is expressed in J / g. The term "melting enthalpy" is understood to mean the amount of heat required to melt the composition, measured according to standard ISO 11357-3:2018, corresponding to the area under the melting peak on the thermogram.

[0084] The term "melting temperature" is understood to mean a representative temperature of the melting phenomenon, during which an at least partially crystallized polyamide powder or polyamide material enters a viscous liquid state, as measured according to standard ISO 11357-3:2018. Unless otherwise indicated, this more particularly corresponds to the temperature of maximum intensity of the melting peak measured by DSC. Therefore, for the purposes of this specification, a melting peak that will comprise several peaks or shoulders will be associated with several melting temperatures, i.e. one melting temperature per peak or shoulder.

[0085] The term "melting temperature of the first and second heating" refers to the melting temperature measured by DSC according to standard ISO11357-3:2018, which is recorded as T of the first heating and T of the second heating, respectively. f1 and the second heating T f2 , and correspond to the maximum signal intensity of the melting peak of the first heating and the second heating, respectively, both at a temperature slope of 20°C / min. Therefore, for the purpose of this specification, if several melting temperatures (T f1 ), then used to calculate the difference (T f1 -T c ) is the melting temperature corresponding to the lowest melting temperature T f1 Temperature, i.e. T f1 min . T f1 max Indicates the maximum melting temperature (T f1 ), and corresponds to the unique melting temperature (T f1 ).

[0086] The term "crystallization temperature", hereinafter referred to as T c , refers to the temperature at which an at least partially crystallized compound passes from a viscous liquid state to a semi-crystalline state, as measured according to standard ISO11357-3:2018 with a temperature slope of -20 ° C / min. The crystallization temperature corresponds more particularly to the temperature measured during the cooling after the first melting (first heating) of the compound and before the second melting (second heating), the first melting allowing the thermal history of the compound to be erased. Unless otherwise specified, this is the temperature of the crystallization peak, corresponding to the maximum intensity of the DSC signal. Therefore, for the purposes of this specification, if several crystallization temperatures are detected during cooling, T ccorresponds to the highest crystallization temperature and must be used to calculate the difference (T f1 -T c ).

[0087] The term "unimodal melting endotherm" of a polyamide powder means the portion of the thermogram obtained by differential scanning calorimetry (DSC) corresponding to the first melting of the polyamide powder and characterized by a single and unique melting temperature T f1 In other words, the melting peak corresponding to the first heating comprises one and only one peak. In contrast, a multimodal melting endotherm is characterized in that the melting peak upon the first heating has several peaks, i.e., several melting peak temperatures. Similarly, a melting endotherm whose melting peak upon the first heating has a shoulder will not be considered a unimodal endotherm for the purposes of this specification.

[0088] The term "precipitation temperature", hereinafter referred to as T p , refers to the temperature at which the mixture formed by the solvent and the polyamide used in the method changes from a homogeneous state to a non-homogeneous state. The precipitation temperature is detected using a temperature sensor (Pt100 type) coupled to a dynamic temperature regulation system (for example, the "petite fleur" system sold by the company Huber). During precipitation, there is a strong spontaneous contribution of thermal energy (exothermicity), which the temperature regulation system may not be able to compensate instantaneously. In this way, the precipitation temperature can be accurately detected by plotting the derivative of the temperature change of the reaction medium over time. The value of this derivative is equal to the cooling rate programmed by the temperature regulation system before and after the precipitation phenomenon: the exothermicity causes a disturbance in the derivative, which allows it to be detected. The temperature corresponding to the beginning of the derivative disturbance is considered to be the precipitation temperature (T p ).

[0089] The term "Dv50" means the median diameter value of the powder particle volume, making the cumulative volume weighted particle size distribution function equal to 50%. Similarly, "Dv10" and "Dv90" are the diameters that make the cumulative volume weighted particle size function equal to 10% and 90% respectively. These values ​​are measured according to standard ISO13319-1:2021, for example, using a Coulter Counter Multisizer3 particle size analyzer. The rules for expressing the particle size distribution results are given by standard ISO9276-Part 1 to Part 6.

[0090] The term "span factor" means a factor characterizing the breadth of the particle size distribution, defined as: span = (Dv90 - Dv10) / Dv50, with diameters "Dv10", "Dv50" and "Dv90" being as defined above.

[0091] The term "mean diameter" means the value of the volume mean diameter of the particles, which corresponds to the volume-weighted arithmetic mean of the particle diameters. This value is measured according to standard ISO 13319-1:2021, for example using a Coulter Counter Multisizer 3 particle size analyzer.

[0092] The term "viscosity" means the intrinsic viscosity measured in an Ubbelohde type viscometer according to standard ISO 307:2019, except that m-cresol is used as solvent and at a temperature of 20° C. The intrinsic viscosity has the dimension of the reciprocal of the concentration and is equal to the natural logarithm of the relative viscosity, all divided by the concentration of the polymer dissolved in the solvent.

[0093] The term “3D printing” denotes technologies involving the production of parts by additive manufacturing, by selective melting of powders mediated by electromagnetic radiation, such as lasers or infrared light.

[0094] The term "VOC" refers to volatile organic compounds, i.e. organic compounds having a vapor pressure of 0.01 kPa or more at a temperature of 293.15 K or having a corresponding volatility under specific conditions of use. The most common are butane, toluene, ethanol (90° alcohol), acetone and benzene.

[0095] Method for recycling used polyamide compositions

[0096] According to a first aspect, the subject of the present invention is therefore to provide a method for recycling a used polyamide composition into a polyamide having a unimodal melting endotherm and a single melting temperature (T f1 max ) of the invention, the method comprising the following steps:

[0097] i. contacting the used polyamide composition with a solvent to obtain a mixture;

[0098] ii. heating the mixture to dissolve the polyamide in the solvent;

[0099] iii. cooling the mixture to the precipitation temperature (T p ), thereby obtaining a precipitated polyamide powder characterized by a non-unimodal melting endotherm and more than one melting temperature, (T f1 max ) is the maximum melting temperature; and

[0100] iv. maintaining the mixture at a temperature at most equal to T p At temperatures above T p -0.1℃ to T p-15°C until the precipitated polyamide powder is characterized by a single-peak melting endotherm and a melting temperature (T f1 max );and

[0101] v. Collecting the obtained recycled polyamide powder.

[0102] In the following description, the term "monomer" is to be understood as "repeating unit". The case in which the repeating unit consists of a combination of a diamine and a diacid is special. It is considered that it is the combination of a diamine and a diacid, i.e. a diamine:diacid pair, which corresponds to a monomer. This is explained by the fact that, individually, a diamine or a diacid does not allow an amide-type functional group to be obtained.

[0103] For the purposes of the present invention, the term "polyamide" means the condensation product of a lactam, an amino acid or a diamine: diacid pair. It can be a homopolymer, i.e. a polymer resulting from the condensation of identical repeating units, i.e. the same monomer, or a copolymer resulting from the condensation of at least two repeating units, i.e. two different monomers, called "comonomers", i.e. at least one monomer and at least one comonomer (a monomer different from the first monomer), to form a copolymer, such as a copolyamide (abbreviated CoPA), as defined below.

[0104] The term "copolyamide" (abbreviated as CoPA) refers to the polymerization product of at least two different monomers selected from:

[0105] - monomers of amino acid or aminocarboxylic acid type, and preferably α,ω-aminocarboxylic acid;

[0106] - lactam type monomers;

[0107] - monomer pairs of the "diamine:diacid" type resulting from the reaction between a diamine and a dicarboxylic acid; and

[0108] - mixtures thereof, wherein the monomers contain different carbon numbers in the case of a mixture between monomers of amino acid type and monomers of lactam type.

[0109] These monomers may be linear or branched or substituted where appropriate.

[0110] According to certain embodiments, the polyamide is a homopolymer.

[0111] According to a first type, the polyamides are derived from the condensation of aliphatic, cycloaliphatic or aromatic dicarboxylic acids, especially containing from 4 to 36 carbon atoms, preferably from 6 to 18 carbon atoms, with aliphatic, cycloaliphatic or aromatic diamines, especially containing from 2 to 20 carbon atoms, preferably from 6 to 14 carbon atoms.

[0112] As examples of dicarboxylic acids, mention may be made of 1,4-cyclohexanedicarboxylic acid, succinic acid, adipic acid, azelaic acid, suberic acid, sebacic acid, dodecanedicarboxylic acid, octadecanedicarboxylic acid, terephthalic acid and isophthalic acid, and also dimer fatty acids.

[0113] As examples of diamines, mention may be made of 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), p-aminodicyclohexylmethane (PACM), isophoronediamine (IPDA), 2,6-bis(aminomethyl)norbornane (BAMN) and piperazine (Pip).

[0114] Advantageously, the polyamide is selected from PA4.6, PA4.10, PA4.12, PA4.14, PA4.18, PA6.10, PA6.12, PA6.14, PA6.18, PA9.12, PA10.10, PA10.12, PA10.14 and PA10.18. In the notation PaX.Y, X represents the number of carbon atoms derived from the diamine residue and Y represents the number of carbon atoms derived from the diacid residue, which is conventional.

[0115] In certain embodiments, the polyamide is selected from polyamide 11, polyamide 6, polyamide 10.10, polyamide 10.12 or polyamide 6.10. Preferably, the polyamide is PA11.

[0116] Steps i) and ii)

[0117] The indefinite article "a" or the definite article "the" preceding the term "polyamide" as used in the process according to the invention means in the context of the present specification "at least one polyamide" and "the at least one polyamide", respectively.

[0118] Thus, in a first step i), the used polyamide composition, ie the used composition comprising "at least one" polyamide, is contacted with a solvent to obtain a mixture.

[0119] Preferably, only one polyamide is used in the process.

[0120] However, a mixture of several, in particular two, polyamides may be used. Preferably, this mixture comprises a main polyamide which in particular represents more than 80% by weight of the total weight of the polyamides used in step i), in order to obtain a coprecipitation of the polyamide mixture.

[0121] In certain embodiments, the solvent contacted with the polyamide may be selected from: ethanol, propanol, butanol, isopropanol, heptanol, formic acid, acetic acid, N-methylpyrrolidone, N-butylpyrrolidone, butyrolactam, caprolactam.

[0122] Preferably, the solvent contacted with the polyamide is a C1-C4 aliphatic alcohol, more preferably ethanol, and even more preferably 96% pure technical grade ethanol (containing water and denatured with 2-butanone and propan-2-ol).

[0123] The weight fraction of polyamide in the solvent may be 0.01 to 0.30; and preferably 0.1 to 0.3. In particular, it may have a weight fraction of 0.01 to 0.05, 0.05 to 0.1; or 0.1 to 0.15 or 0.15 to 0.2; or 0.2 to 0.25; or 0.25 to 0.3.

[0124] The mixture obtained is then heated in step ii) in order to dissolve the polyamide, ie until a homogeneous mixture is obtained.

[0125] The heating of the mixture may especially be carried out at a temperature between 100 and 180°C and preferably between 120 and 160°C.

[0126] In certain embodiments, the heating of the mixture can be carried out, for example, 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 170°C to 175°C; or 175°C to 180°C; or 180°C to 185°C; or 185°C to 190°C; or 190°C to 195°C; or 195°C to 200°C.

[0127] In certain embodiments, heating the mixture, especially maintaining the mixture at the dissolution temperature, can have a duration of 1 to 6 hours, and preferably 1 to 3 hours. Thus, the heating of the mixture can last from 1 hour to 1 hour and 30 minutes; or from 1 hour and 30 minutes to 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.

[0128] In certain embodiments, heating comprises at least one step wherein the temperature is increased to reach a maximum temperature of 100°C to 200°C, in particular 120°C to 160°C.

[0129] In certain embodiments, heating comprises at least one step wherein the temperature is kept substantially constant at a value between 100°C and 200°C, in particular between 120°C and 160°C.

[0130] Step iii)

[0131] Next, in step iii), the mixture is cooled in order to precipitate the polyamide in powder form.

[0132] For the same polyamide, the precipitation temperature (T p ) may vary depending on the solvent. Similarly, for the same solvent, it may vary depending on the polyamide. Specifically, the precipitation of the polyamide is accompanied by the release of heat, resulting in a slight increase in the internal temperature. At the end of the precipitation, no more heat is released, and the internal temperature falls back to its nominal temperature.

[0133] The precipitation temperature may be between 80°C and 130°C, in particular between 100°C and 120°C, in particular when the solvent is a C1-C4 aliphatic alcohol.

[0134] The cooling may be performed to a temperature greater than or equal to 50° C. Thus, for example, cooling may be performed to a temperature of 50° C. Thus, for example, cooling may be performed to a temperature in the range of 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 120° C. to 130° C.

[0135] Furthermore, the cooling may be performed at a rate of 1 to 100° C. / hour, preferably 10 to 60° C. / hour, more preferably 20 to 50° C. / hour. For example, cooling can be carried out at a rate of 1 to 5°C / hour; 5 to 10°C / hour; 10 to 15°C / hour; or 15 to 20°C / hour; or 20 to 25°C / hour; or 25 to 30°C / hour; or 30 to 35°C / hour; or 35 to 40°C / hour; or 40 to 45°C / hour; or 45 to 50°C / hour; or 50 to 55°C / hour; or 55 to 60°C / hour; or 60 to 65°C / hour; or 65 to 70°C / hour; or 70 to 75°C / hour; or 75 to 80°C / hour; or 80°C / hour to 85°C / hour; or 85 to 90°C / hour; or 90°C / hour to 95°C / hour; or 95°C / hour to 100°C / hour.

[0136] In certain embodiments, and in order to facilitate precipitation, a certain amount of polyamide may be introduced in step i) of loading the starting material. Preferably, the amount 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 step i). The polyamide may be identical or different from the polyamide dissolved in the solvent, preferably identical. The polyamide may be chosen in particular from polyamide 11, polyamide 6, polyamide 10.10, polyamide 10.12 and polyamide 6.10.

[0137] Thus, the amount of polyamide added may represent 0.1% to 1% by mass; or 1% to 2% by mass; or 2% to 3% by mass; or 3% to 4% by mass; or 4% to 5% by mass; or 5% to 8% by mass; or 8% to 12% by mass; or 12% to 16% by mass; or 16% to 20% by mass of polyamide, relative to the total mass of polyamide used in step i).

[0138] Step iii) is advantageously carried out under stirring. For a given stirring system, the stirring speed allows the volume mean diameter of the particles to be controlled. Typically, as the stirring speed increases, the mean diameter of the polyamide particles decreases. On the contrary, as the stirring speed decreases, the mean diameter of the polyamide particles increases.

[0139] Step iv)

[0140] When the precipitation temperature of the polyamide in said solvent is reached during the cooling step, the precipitation phase then begins. The start of this precipitation phase corresponds to the start of step iv) of the process according to the invention.

[0141] In step iv), the mixture is then kept close to the precipitation temperature (T p ), at most equal to the precipitation temperature and in particular in the range of from -0.1°C to -15°C of the precipitation temperature, and kept for a sufficient time to allow the production of a precipitated polyamide powder having a unimodal melting endotherm and an increased melting temperature.

[0142] In other words, the process comprises, in step iv), a temperature plateau during which the temperature remains constant for a duration t. More specifically, the temperature remains constant for the entire duration of the polyamide precipitation phase, ie the time period t1, and then remains constant for an additional duration t2, allowing the crystal lattice of the precipitated polyamide to be refined and thus obtaining a polyamide powder having a unimodal melting endotherm and an elevated melting temperature.

[0143] Typically, the duration t1 is typically much shorter than the duration t2 , so that the total duration t of the temperature plateau is typically very close to t2 .

[0144] The additional duration required to produce a unimodal melting endotherm can be determined by analyzing samples collected at different intervals using differential scanning calorimetry (DSC) according to standard ISO 11357-3.

[0145] By way of example, at the end of the precipitation phase of polyamide 11, i.e. at the end of the time period t1, the inventors were able to observe by DSC the generation of a bimodal melting endotherm, characterized by two different melting temperatures, during the first heating. By keeping the temperature constant for a sufficient additional time period t2 at a temperature close to the precipitation temperature of the polyamide in the solvent, the inventors were able to observe the transformation of the bimodal melting endotherm of the polyamide particles into a unimodal melting endotherm, which is reflected in 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, the temperature plateau of the total time period t1+t2 thus allows T f1 -T c The difference increases and a unimodal melting endotherm is obtained.

[0146] According to certain embodiments, in step iv), the mixture is kept at 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, starting from the end of precipitation of the polyamide. The additional duration after the end of 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.

[0147] In certain embodiments, in step iv), the mixture is kept at 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 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.

[0148] Steps v) and vi)

[0149] At the end of the temperature plateau carried out in step iv), the precipitated polyamide particles are recovered in step v) from the mixture in the form of a powder by conventional solid-liquid separation means.

[0150] This step generally consists in cooling the mixture obtained, making it possible to empty the reactor and thus separate the precipitated polyamide particles obtained from the solvent, in particular by filtration.

[0151] The method for producing a polyamide powder may also comprise a drying step vi) of the polyamide powder obtained in step iv) or recovered in step v). The drying step may be carried out, for example, in a stirring or rotary dryer.

[0152] In certain embodiments, drying may be carried out at a temperature of from 10°C to 150°C, in particular from 50°C to 100°C, preferably from 25°C to 85°C, and more preferably from 70°C to 80°C. Drying may, for example, be carried out at a temperature of from 10°C to 20°C; or from 20°C to 30°C; or from 30°C to 40°C; or from 40°C to 50°C; or 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; or from 130°C to 140°C; or from 140°C to 150°C; or from 150°C to 160°C.

[0153] In certain embodiments, drying can be carried out under vacuum at a pressure of less than 100 mbar, preferably less than 50 mbar. Thus, drying can be carried out at a pressure of 1 to 10 mbar; or 10 to 20 mbar; 20 to 30 mbar; 30 mbar to 40 mbar; 40 to 50 mbar; 50 to 60 mbar; 60 mbar to 70 mbar; 70 to 80 mbar; 80 to 90 mbar; 90 mbar to 100 mbar; 100 to 150 mbar; 150 to 200 mbar; 200 mbar to 250 mbar; or 250 to 300 mbar; or 300 to 500 mbar; or 500 to 700 mbar; or 700 mbar to less than 1 bar (absolute pressure).

[0154] As a variant, drying can be carried out at atmospheric pressure.

[0155] Advantageously, drying of the organic solvent promotes the removal of VOCs that may be present in the initially used composition.

[0156] Step vii)

[0157] The particles recovered in step v), optionally dried in step vi), may optionally undergo a step vii) aimed at separating them from inorganic materials (especially in the form of fillers) that may be present in the used polyamide composition used in step i).

[0158] As examples of mineral fillers that may be present in the used polyamide composition, mention may be made of hollow beads, fibers (for example glass or carbon fibers), talc, carbon black, carbon nanotubes or other nanotubes.

[0159] The mineral filler can be separated from the polyamide by utilizing the density difference. For example, this separation can be carried out by decantation, using a cyclone separator, etc.

[0160] The precipitated polyamide particles can be recovered at the end of step vii), separated from the mineral filler by conventional means such as by decanting the mixture in a suitable liquid, for example a mixture of water and glycerol. They can optionally be dried under conditions similar to those of step v).

[0161] The polyamide powder and mineral fillers can be collected separately and reused.

[0162] Advantageously, the mineral fillers (for example fibres) recovered at the end of step vii) are covered with crystallized polyamide, which makes them particularly compatible with the polymer matrix in order to be used as fillers in subsequent use.

[0163] Thus, according to certain embodiments, the present invention relates to a mineral filler obtainable according to the above-described recycling process, in particular according to steps i) to vii).

[0164] According to other embodiments, the mineral fillers that may be present in the used polyamide composition may be separated and recovered before the precipitation of the polyamide, in particular before step iii). In particular, during step i), the polyamide is generally dissolved in the solvent, while the mineral fillers remain suspended. They may then be separated and recovered by conventional solid-liquid separation techniques, for example by filtration.

[0165] Polyamide powder obtainable according to the recycling process of the invention

[0166] According to a second aspect, the present invention relates to a polyamide powder having a unimodal melting endotherm and a single melting temperature (T f1 max ), the polyamide powder can be obtained via the recycling method as described above.

[0167] In certain embodiments, the polyamide powder has an intrinsic viscosity of from 0.8 to 1.7, and preferably from 1.0 to 1.5. Thus, for example, the powder may have an intrinsic viscosity of from 0.8 to 0.9; or from 0.9 to 1.0; or from 1.0 to 1.1; or from 1.1 to 1.2; or from 1.2 to 1.3; or from 1.3 to 1.4; or from 1.4 to 1.5; or from 1.5 to 1.6; or from 1.6 to 1.7. In the above, the intrinsic viscosity is expressed in (g / 100g) -1 express.

[0168] The intrinsic viscosity is measured using a micro-Ubbelohde tube. The measurement is performed on 75 mg of a powder sample with a concentration of 0.5% (m / m) in m-cresol at 20°C. The intrinsic viscosity is expressed in (g / 100 g) -1 Expressed and calculated according to the following formula:

[0169] Intrinsic viscosity = ln(t s / t0)×1 / C, where C=m / p×100, where t s is the flow time of the solution, t0 is the flow time of the solvent, m is the mass of the sample whose viscosity is measured, and p is the mass of the solvent.

[0170] In certain embodiments, the precipitated polyamide powder may have a crystallization temperature (Tc) from 100°C to 200°C, and preferably from 130°C to 180°C. c The polyamide powder may in particular have a crystallization temperature of from 100°C to 110°C; or 110°C to 120°C; or 120°C to 130°C; or 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.

[0171] In certain embodiments, the polyamide powder has a melting enthalpy greater than or equal to 60 J / g, preferably greater than or equal to 100 J / g. The melting enthalpy can be, for example, 60 J / g to 80 J / g; or 80 to 100 J / g; or 100 to 110 J / g; or 110 J / g to 120 J / g; or 120 to 130 J / g; or 130 J / g to 140 J / g; or 140 to 150 J / g; or 150 J / g to 160 J / g.

[0172] In certain embodiments, the polyamide powder may have a melting temperature T between 130°C and 260°C, and preferably between 160°C and 210°C. f1 In particular, the polyamide powder may 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 240°C to 250°C; or 250°C to 260°C.

[0173] The melting temperature (T f1 ) is determined during the first heating as explained previously. According to the process 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).

[0174] In certain embodiments, the polyamide powder may have a particle size from 0.1 μm 2 / g to 50m 2 / g, and preferably from 1m 2 / g to 10m 2The precipitated polyamide powder may thus have an apparent specific surface area of ​​0.1 m 2 / g to 1m 2 / g; or 1 to 5 m 2 / g; or 5 to 10m 2 / g; or 10 to 20 m 2 / g; or 20 to 30 m² / g; or 30 to 50 m² / g specific surface area. The apparent specific surface area (SSA) is measured according to the BET (Brunauer-Emmett-Teller) method known to those skilled in the art. It is described in particular 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 area formed by the pores at the surface of the particles.

[0175] According to certain embodiments, the polyamide powder obtained according to the process of the invention is characterized in that it exhibits:

[0176] a volume mean diameter of between 10 μm and 200 μm, in particular between 20 μm and 100 μm and preferably between 40 μm and 80 μm;

[0177] a diameter Dv10 greater than 5 μm, in particular between 10 μm and 70 μm and preferably between 20 μm and 60 μm;

[0178] a volume median diameter Dv50 between 10 μm and 200 μm, in particular between 20 μm and 100 μm and preferably between 30 μm and 90 μm;

[0179] a diameter Dv90 of less than 350 μm, in particular between 30 and 200 μm and preferably between 50 and 150 μm;

[0180] - the span factor is between 0.1 and 1.5; and preferably between 0.5 and 1.0;

[0181] - melting enthalpy greater than 60 J / g; preferably 100 to 160 J / g;

[0182] - The intrinsic viscosity is between 0.5 and 2.0, and preferably between 1.0 and 1.5.

[0183] In a preferred embodiment, the polyolefin having a unimodal melting endotherm and a single melting temperature (T f1 max) is characterized in that it has a span factor between 0.1 and 1.5, preferably between 0.1 and 1.0 and more preferably between 0.5 and 1.0.

[0184] Polyamide 11 powder

[0185] According to another aspect, the invention relates to a polyamide 11 powder, characterized in that it has a unimodal melting endotherm and a temperature T between 195° C. and 205° C., in particular about 200° C. f1 max The single melting temperature T of the first heating f1 , and / or a crystallization temperature T between 150° C. and 165° C., in particular about 158° C. c .

[0186] The polyamide 11 powder is in particular a powder characterized by one or more, preferably all of the following features:

[0187] a volume mean diameter of between 10 μm and 200 μm, in particular between 20 μm and 100 μm and preferably between 40 μm and 80 μm;

[0188] a diameter Dv10 greater than 5 μm, in particular between 10 μm and 70 μm and preferably between 20 μm and 60 μm;

[0189] a volume median diameter Dv50 between 10 μm and 200 μm, in particular between 20 μm and 100 μm and preferably between 30 μm and 90 μm;

[0190] a diameter Dv90 of less than 350 μm, in particular between 30 and 200 μm and preferably between 50 and 150 μm;

[0191] - the span factor is between 0.1 and 1.5; and preferably between 0.5 and 1.0;

[0192] - a melting enthalpy greater than 100 J / g; and preferably between 110 J / g and 160 J / g;

[0193] - Intrinsic viscosity is 0.8-1.8, preferably 1.0-1.5.

[0194] Preferably, the polyamide 11 powder is characterized in that it has a unimodal melting endotherm and a T between 195°C and 205°C. f1 max The single melting temperature T of the first heating f1 , 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.

[0195] Composition in powder form for 3D printing, especially by selective laser sintering.

[0196] According to yet another aspect, the present invention relates to a composition in powder form for 3D printing, in particular 3D printing by selective laser sintering, comprising a polyamide powder as defined above, combined with one or more conventional (i.e. suitable for 3D printing technology) fillers or additives.

[0197] The composition is advantageously ready to use.

[0198] The composition may include additives that help improve the conversion properties of the powder for its use as a function of 3D printing technology.

[0199] The additives generally represent less than 5% by weight relative to the total weight of the composition. Preferably, the additives represent less than 1% by weight relative to the total weight of the composition. Among the additives, mention may be made of flow agents, stabilizers (light, in particular UV, and heat stabilizers), optical brighteners, dyes, pigments and energy absorbing additives (including UV absorbers).

[0200] Among the flow agents, mention may be made, for example, of hydrophilic or hydrophobic silicas. Advantageously, the flow agent represents 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.

[0201] The composition may also comprise one or more fillers, making it possible in particular to improve the mechanical properties (stress at break and elongation at break) of the parts obtained by 3D printing.

[0202] 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, reinforcing fillers are mentioned, especially mineral fillers such as carbon black, talc, carbon or non-carbon nanotubes, fibers (glass, carbon ...), which may or may not be milled.

[0203] The additive or filler can be mixed with the polyamide before the polyamide powder manufacturing process, during the polyamide powder manufacturing process (e.g., before the polyamide is dissolved in step i) or after the precipitation in step iv)), or after the polyamide powder manufacturing process. Preferably, the additive is introduced after the polyamide powder manufacturing process by mixing between the polyamide powder and the additive.

[0204] The composition may contain polyamide, preferably in a weight proportion 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%.

[0205] In certain embodiments, the polyamide included in the composition is polyamide 11.

[0206] In certain embodiments, polyamide 11 has a melting temperature (T) between 185°C and 205°C. f1 ).

[0207] In certain embodiments, the melting temperature (T f1 ) and crystallization temperature (T c ) is between 35°C and 45°C.

[0208] Use of a polyamide powder obtained according to the recycling process of the invention or a composition in powder form comprising polyamide powder in a powder agglomeration process by melting

[0209] A subject of the invention is also a process for manufacturing a polyamide object by agglomeration of a molten powder mediated by electromagnetic radiation, the powder being a polyamide powder as previously defined or a composition in powder form.

[0210] The electromagnetic radiation may be infrared, ultraviolet or visible radiation. Preferably, it is laser radiation (the manufacturing method is then known as "selective laser sintering").

[0211] According to this method, thin layers of powder are deposited on a horizontal plate kept in a chamber heated to a temperature called the build temperature. The term "build temperature" denotes the temperature to which the powder bed constituting the layers of the three-dimensional object being built is heated during the layer-by-layer sintering process of the powder. This temperature is chosen from the difference T of the polyamide powder obtained from the manufacturing process. f1 -T c within, preferably within T f1 -5℃ and T c +5°C, and more preferably between T f1 -10℃ and T c+10° C. The electromagnetic radiation then provides the energy required to sinter the powder particles at different points in the powder layer according to the geometry of the object (for example, using a computer that contains the shape of the object in its memory and reproduces it in the form of slices).

[0212] The horizontal plate is then lowered a distance corresponding to the thickness of the powder layer, and a new layer is deposited. The thickness of the layer is typically between 0.05 mm and 2 mm, and is typically of the order of 0.1 mm. The electromagnetic radiation provides the energy required to sinter the powder particles into the geometry corresponding to this new slice of the object, and so on. The process is repeated until the object is manufactured.

[0213] The powders are used in the agglomeration process by melting or sintering.These powders may have a volume mean diameter ranging from 10 μm to 200 μm and advantageously from 20 to 100 μm.

[0214] Preferably, the volume mean diameter is 40 to 80 μm.

[0215] The invention also relates to a manufactured article, in particular an article manufactured by 3D printing, obtained by electromagnetic radiation mediated sintering of a powder as described previously.

[0216] The article may be chosen from prototypes and models, in particular in the automotive, nautical, aeronautical, aerospace, medical (prostheses, hearing systems, tissue, etc.), textiles, clothing, fashion, decoration, electronics, telephony, home automation, IT and lighting sectors.

[0217] More generally, the present invention also relates to a method for increasing the melting temperature (T f1 ) and crystallization temperature (T c ) f1 -T c )’s purpose.

[0218] Example

[0219] The following examples illustrate embodiments of the present invention but do not limit the invention.

[0220] In all of the following embodiments:

[0221] - The particle size of the powder is characterized by measuring the particle size distribution on a Coulter Counter-Multisizer 3 device (Beckmann Coulter) according to standard ISO 13319-1: 2021. From this, the volume mean diameter and the diameters Dv10, Dv50 and Dv90 are determined. From these volume mean diameters the span value is calculated.

[0222] - The analysis of thermal properties is carried out by DSC according to the standard ISO 11357-3 "Plastics - Differential Scanning Calorimetry (DSC) Part 3: Determination of temperature and enthalpy of melting and crystallization". The temperature of more particular interest in this context is the melting temperature during the first heating (T f1 ) and crystallization temperature (T c ). In particular, in a manner known to those skilled in the art (in the field of manufacturing 3D objects by agglomeration of powders by melting), the difference "T f -T c ” corresponds to T f1 -T c .

[0223] The intrinsic viscosity of the polyamides was measured in an Ubbelohde viscometer according to standard ISO 307:2019, except that m-cresol was used as solvent and at a temperature of 20°C.

[0224] - Acidity (which can be considered as the concentration of COOH chain ends of the polyamide) and basicity (which can be considered as the concentration of NH2 chain ends of the polyamide) are measured potentiometrically. Acidity is measured according to the following method: a sample of the polyamide is dissolved in benzyl alcohol at a concentration of 0.6% by mass; the sample is then analyzed potentiometrically using a 0.02N tetrabutylammonium hydroxide solution. Basicity is measured according to the following method: a sample of the polyamide is dissolved in m-cresol at a concentration of 0.6% by mass; the sample is then analyzed potentiometrically using a 0.02N perchloric acid solution.

[0225] Example 1 according to the invention: Recycling of used polyamide compositions containing glass fibers

[0226] The scrap and cores collected after injection of Rilsan® BZM30 O TLDA grade were first coarsely shredded so that they could be handled more easily. Their composition was as follows: 70 wt% partially oxidized PA11 and 30 wt% glass fibers (and residual antioxidant).

[0227] 85 g of the crushed starting material and 425 g of technical ethanol (96% purity) were charged into a reactor (1 L working volume) and mechanical stirring was performed using an impeller turbine mixer. The agitator was operated at a speed of 500 rpm throughout the test, and the medium was then heated to 160 ° C, followed by an hour of isothermal to dissolve only the used polyamide. Controlled cooling at a rate of -60 ° C / h until 110 ° C was performed to precipitate the polyamide, and then 4 hours of isothermal at the same temperature was performed to achieve crystal refinement. Crystallization exotherm was detected at 115 ° C, and only interfered with thermal regulation for a few minutes. The precipitation temperature was 115 ° C. Then controlled cooling was re-performed until 20 ° C at the same rate of -60 ° C / h, and then the reactor was emptied and the dispersion was dried in an oven at 75 ° C at atmospheric pressure.

[0228] The used PA11 powder can be separated from the glass fibers by decantation using a water / glycerol mixture (45 / 55% by volume). It can then be seen that 61% by mass of the used PA11 is directly precipitated in the form of powder and the remaining 39% by mass allows the coating of the glass fibers (see [ Figure 1 ]). Glass fibers pre-coated with PA11 are easier to incorporate than natural glass fibers and have better compatibility with the polyamide matrix. In addition to being able to be recycled, these glass fibers can now be more easily used in polyamide-based compositions.

[0229] The PA11 powder obtained has the following characteristics: intrinsic viscosity of 1.30, volume mean diameter of 61 μm and also diameters Dv10 = 29 μm, Dv50 = 68 μm and Dv90 = 91 μm, thus span = 0.91. DSC analysis of this PA11 powder shows a unimodal melting endotherm on the first heating, and a single melting temperature of 201° C. associated with a melting enthalpy of 136 J / g, and also a single crystallization temperature T c =158℃. Difference T f1 -T c It is now equal to 43°C.

[0230] Example 2 according to the invention: Recycling of used polyamide compositions containing carbon fibers

[0231] The scrap and cores collected after injection of Rilsan® BSR30 grade were first coarsely shredded so that they could be handled more easily. Their composition was as follows: 70wt% partially oxidized PA11 and 30wt% carbon fibers (and residual antioxidants and carbon black).

[0232] 85 g of the crushed starting material and 425 g of technical ethanol (96% purity) were charged into a reactor (1 L working volume) and mechanical stirring was performed using an impeller turbine mixer. The agitator was operated at a speed of 500 rpm throughout the test, and then the medium was heated to 160 ° C, followed by an hour of isothermal to dissolve only partially oxidized polyamide. Controlled cooling at a rate of -60 ° C / h until 110 ° C was performed to precipitate the polyamide, and then 4 hours of isothermal at the same temperature was performed to achieve crystal refinement. Crystallization exotherm was detected at 115 ° C, and only interfered with thermal regulation for a few minutes. The precipitation temperature was 115 ° C. Then controlled cooling was re-performed until 20 ° C at the same rate of -60 ° C / h, and then the reactor was emptied and the dispersion was dried in an oven at 75 ° C at atmospheric pressure.

[0233] The used PA11 powder can be separated from the carbon fibers by decantation using a water / glycerol mixture (45 / 55% by volume). It can then be seen that 52% by mass of the partially oxidized PA11 is directly precipitated in the form of powder and the remaining 48% by mass allows the coating of the carbon fibers (see [ Figure 2 ]). Carbon fibers pre-coated with PA11 are easier to incorporate than natural carbon fibers and have better compatibility with the polyamide matrix. In addition to being able to be recycled, these fibers can now be more easily used in polyamide-based compositions.

[0234] The PA11 powder obtained has the following characteristics: its color is black (carbon black is not separated out), its intrinsic viscosity is 1.42, its volume mean diameter is 55 μm, and the diameters Dv10=29 μm, Dv50=58 μm and Dv90=77 μm, so the span=0.83. The DSC analysis of this PA11 powder shows a single peak melting endotherm on the first heating, and a single melting temperature of 200° C. associated with a melting enthalpy of 132 J / g, and also a single crystallization temperature T c =159℃. Difference T f1 -T c It is now equal to 42°C.

[0235] Example 3 according to the invention: Recycling of used polyamide compositions contaminated with VOCs

[0236] Used tubes were collected from fuel lines during disassembly of different vehicles. These tubes were originally obtained by extrusion of Rilsan® BESN Black P20 TL. They were coarsely crushed beforehand to make them easier to handle. These used PA11 tubes contained 4% by mass of VOC (mainly petroleum spirit, toluene, xylene and trimethylbenzene). The content was determined by thermogravimetric analysis and the composition was determined by gas chromatography analysis.

[0237] 85 g of the crushed starting material and 425 g of technical ethanol (96% purity) were charged into a reactor (1 L working volume) and mechanical stirring was performed using an impeller turbine mixer. The agitator was operated at a speed of 500 rpm throughout the test, and the medium was then heated to 160 ° C, followed by an hour of isothermal to dissolve only partially oxidized polyamide. Controlled cooling at a rate of -60 ° C / h until 115 ° C was performed to precipitate the polyamide, and then 4 hours of isothermal at the same temperature was performed to achieve crystal refinement. Crystallization exotherm was detected at 120 ° C, and only interfered with thermal regulation for a few minutes. The precipitation temperature was 120 ° C. Then controlled cooling was re-performed until 20 ° C at the same rate of -60 ° C / h, and then the reactor was emptied and the dispersion was dried at 90 ° C under vacuum (50 mbar) for 6 hours.

[0238] The VOC content of the PA11 powder is now 0.35 mass% (consisting mainly of ethanol, with trace contaminants <0.1 mass%). Therefore, the dissolution in / precipitation from ethanol approach appears to be able to extract the contaminants from the PA11 and then eliminate them by entrainment during vacuum drying.

[0239] The PA11 powder obtained has the following characteristics: its color is black (carbon black is not separated out), its intrinsic viscosity is 1.45, its volume mean diameter is 51 μm, and the diameters Dv10=25 μm, Dv50=49 μm and Dv90=62 μm, so the span=0.76. The DSC analysis of this PA11 powder shows a single peak melting endotherm on the first heating, and a single melting temperature of 199° C. associated with a melting enthalpy of 136 J / g, and also a single crystallization temperature T c =159℃. Difference T f1 -T c It is now equal to 40℃.

[0240] Example 3a (Comparative): Removal of VOCs from a Used Composition by Drying

[0241] The same pulverized starting material as in Example 3 was placed directly in a dryer in order to extract the VOCs from the PA11. After drying for 12 hours at 90°C under a vacuum of 50 mbar, only 0.5% by mass of these VOCs could be removed. The dryer had to be heated at 150°C under a vacuum of 50 mbar for a further 12 hours in order to remove 3.5% by mass of the VOCs. The pulverized PA11 powder thus obtained still contained a residual VOC content of 0.5% by mass. Furthermore, its particle size made it unsuitable for 3D printing.

[0242] In addition to recovering powder that can be used directly for 3D printing, drying according to Example 3 of the present invention advantageously requires less energy to eliminate VOCs.

[0243] According to Example 4 of US 2008 / 0166496 (Comparative)

[0244] The diamine-terminated PA11 was prepared by polymerizing 250 g of 11-aminoundecanoic acid in the presence of 1.25 g of 4,4'-diaminocyclohexylmethane (PACM, mixture of isomers). The polyamide 11 obtained had an intrinsic viscosity of 1.42, combined with a concentration of chain-end COOH groups equal to 19 mmol / kg and a concentration of chain-end NH2 groups equal to 67 mmol / kg.

[0245] 85g of this diamine-terminated PA11 and 425g of technical-grade ethanol (purity 96%) were loaded into a reactor (1L working volume) and mechanically stirred using an impeller turbine mixer. The agitator was operated at a speed of 500rpm throughout the test. The medium was heated to 152°C and then isothermally maintained at this temperature for one hour. The medium was then cooled to 112°C at a rate of 25°C / h and then maintained at this temperature for one hour. During this cooling phase, when the internal temperature reached 125°C, the jacket temperature must be 2 to 3°C lower than the internal temperature. Crystallization exothermicity was detected and only interfered with controlled cooling for a few minutes. After 1 hour at this temperature, the medium was cooled to room temperature. The reactor was then emptied and ethanol was distilled in a stirred dryer at 70°C / 400 mbar, and the powder was then dried at 84°C / 20 mbar.

[0246] The PA11 powder obtained has the following particle size characteristics: volume mean diameter of 89 μm, and diameters Dv10 = 65 μm, Dv50 = 93 μm and Dv90 = 123 μm, so span = 0.62. DSC analysis of this PA11 powder shows a bimodal melting endotherm on the first heating, with a shoulder at 193°C and a peak at 202°C, which is associated with a melting enthalpy of 140 J / g, and also a single crystallization temperature T c = 162°C. The lower of the two melting temperatures is used to calculate the difference T f1 -T c , which is therefore equal to 29°C.

Claims

1. For recycling used polyamide compositions into polyamide compositions having a single peak melting endotherm and a single melting temperature (T f1 max ) of the invention, the method comprising the following steps: i. contacting the used polyamide composition with a solvent to obtain a mixture; ii. heating the mixture to dissolve the polyamide in the solvent; iii. cooling the mixture to the precipitation temperature (T p ), thereby obtaining a precipitated polyamide powder characterized by a non-unimodal melting endotherm and more than one melting temperature, (T f1 max ) is the maximum melting temperature; and iv. maintaining the mixture at a temperature at most equal to T p At temperatures above T p -0.1℃ to T p -15°C until the precipitated polyamide powder is characterized by a single-peak melting endotherm and a melting temperature (T f1 max );and v. Collecting the obtained recycled polyamide powder.

2. The process according to claim 1, wherein the solvent contacted with the polyamide is an alcohol, in particular a C1-C4 aliphatic alcohol, preferably ethanol.

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

10.

4. The method according to any one of the preceding claims, wherein in step iv), the mixture is kept at a temperature for a duration of at least 2 hours, in particular 3 hours to 12 hours, from the end of the precipitation of the polyamide.

5. The method according to any one of the preceding claims, wherein the composition further comprises volatile organic compounds (VOCs).

6. The method according to any one of the preceding claims, wherein the composition comprises mineral fillers, in particular fibers, in particular glass fibers and / or carbon fibers.

7. The method according to claim 6, further comprising the step vii) of separating and recovering the mineral filler which may be present in the precipitated polyamide powder, in particular after step iv), v) or vi).

8. Has a single melting endotherm and a single melting temperature (T f1 max ) which can be obtained by the recycling method as claimed in any one of claims 1 to 7.

9. The polyamide powder according to claim 8, characterized in that The polyamide powder has a span factor between 0.1 and 1.5, preferably between 0.1 and 1.0, and more preferably between 0.5 and 1.

0.

10. The powder according to any one of claims 8 and 9, wherein the polyamide is polyamide 11.

11. A powder according to any one of claims 9 and 10, wherein the melting temperature (T f1 max ) and the crystallization temperature (T c ) is between 35°C and 45°C.

12. The polyamide 11 powder according to any one of claims 8 to 11, having a unimodal melting endotherm and a single melting temperature (T f1 max ), and also has at least one of the following characteristics: a volume mean diameter of between 10 μm and 200 μm, in particular between 20 μm and 100 μm and preferably between 40 μm and 80 μm; a diameter Dv10 greater than 5 μm, in particular between 10 μm and 70 μm and preferably between 20 μm and 60 μm; a volume median diameter Dv50 between 10 μm and 200 μm, in particular between 20 μm and 100 μm and preferably between 30 μm and 90 μm; a diameter Dv90 of less than 350 μm, in particular between 30 and 200 μm and preferably between 50 and 150 μm; - the span factor is between 0.1 and 1.5; preferably between 0.1 and 1, and more preferably between 0.5 and 1.0; - a melting enthalpy greater than 100 J / g; and preferably between 110 J / g and 160 J / g; and / or - The intrinsic viscosity is from 0.8 to 1.8, preferably from 1.0 to 1.

5.

13. A composition in powder form for 3D printing, in particular 3D printing by laser sintering, comprising: - a polyamide powder according to any one of claims 8 to 12; and - At least one filler or additive.

14. Process for manufacturing a polyamide object by agglomeration of a powder via fusion mediated by electromagnetic radiation, the powder being as defined in any one of claims 8 to 13.

15. Article obtained by electromagnetic radiation mediated melting of a powder according to any one of claims 8 to 12 or a composition according to claim 13.

16. Mineral filler obtainable by the recycling process according to claim 6 or 7.

17. The mineral filler according to claim 16, pre-coated with a polyamide powder having a unimodal melting endotherm and a single melting temperature.

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