Method for producing partially recycled polyaryletherketone powder by sintering

Abstract

The present invention relates to a method for the layer-by-layer production of three-dimensional articles by sintering PAEK-based powders using electromagnetic radiation, the powders comprising at least one PAEK and at least one phosphate, said powders being at least partially recycled powders that can be obtained by continuous or discontinuous heating of powders of the same composition at constant or non-constant temperatures strictly between the glass transition temperature Tg and the melting point Tf of the powder for a period of at least 6 hours. The invention also relates to the articles obtained by this method and to the use of phosphates in PAEK-based compositions.

Description

[Technical field]

[0001] The technical field of the invention is that of methods of powder sintering using electromagnetic radiation, in particular laser powder sintering methods.

[0002] In particular, the invention relates to the use of a powder comprising a PAEK-based composition in a process for sintering by electromagnetic radiation, the powder being at least partially a recycled powder.

[0003] The electromagnetic radiation may be a laser beam, in the case of laser sintering, infrared radiation or UV radiation, or any other radiation source. In this specification, the term "sintering" includes all these methods, regardless of the type of radiation. [Background technology]

[0004] Polyaryletherketones are well-known high-performance engineering polymers. They can be used in applications that are highly restrictive in terms of temperature and / or mechanical and even chemical constraints. They can also be used in applications that require good fire resistance and low emissions of smoke and other toxic gases. Finally, they have good biocompatibility. These polymers are found in a wide variety of fields, such as the aviation and aerospace sectors, offshore drilling, automotive, rail, marine, wind, sports, construction, electronics or medical implants. They can be used in all techniques where thermoplastics are used, such as casting, compression, extrusion, spinning, powder coating or sintered prototypes.

[0005] In the case of powder sintering with electromagnetic radiation, a large part of the powder is not used during the construction of the three-dimensional article. The construction of the three-dimensional article is also indicated by the term "run". Typically, approximately 85-90% by mass of the powder introduced into the sintering machine is not affected by the electromagnetic radiation during the construction of the three-dimensional article. For economic reasons, it is therefore considered essential that this powder can be reused, i.e. recycled, during the next construction or run.

[0006] Typically, during a laser sintering build, the PAEK powder of the layer being built is heated in the build environment to a temperature Tc, known as the "build temperature". The temperature of the layer below the layer being built can be equal to Tc if the chamber is maintained at a uniform temperature. In most cases, however, the temperature of the layer below the layer being built is slightly lower than the build temperature, the difference being on the order of a few degrees to a few tens of degrees. The lower part of the build environment can be specifically temperature regulated so that the bottom layer does not cool to a temperature below Tb, commonly known as the "tank bottom temperature". The build temperature, and if applicable the tank bottom temperature, is between the glass transition temperature Tg and the melting temperature Tm of the PAEK powder.

[0007] Thus, during building by sintering, the surrounding powder, i.e. the powder not affected by the electromagnetic radiation, is kept at a temperature between the glass transition temperature and the melting point of the powder for several hours, typically 6 hours, but even tens of hours depending on the complexity of the part to be built, which can lead to changes in the structure of the powder's constituent polymers, accompanied in particular by an increase in molecular weight and a change in color.

[0008] The increase in molecular weight leads to an increase in viscosity, which hinders the coalescence of the powder particles during successive runs, and therefore makes it difficult or even impossible to recycle the powder, since it becomes impossible to sinter the powder or the mechanical properties of the three-dimensional parts obtained by sintering such recycled powders are consequently reduced and insufficient, for example due to the presence of porosity in the sintered parts.

[0009] In addition, color changes, especially yellowing, are undesirable in many industrial applications. However, powders can also change color when exposed to oxygen for long periods of time. It is then difficult to obtain objects with a homogeneous and uniform color.

[0010] There are currently PAEK powders on the market that can be used for laser sintering, such as that sold by the company EOS under the name PEEK HP3. However, these powders undergo such thermal degradation starting from the first run, in particular a significant increase in the average molecular weight, that it is not possible to reuse them for a second build of a three-dimensional object. As a result, the manufacture of three-dimensional objects by sintering these powders is very expensive and cannot be considered on an industrial scale.

[0011] Document US2013 / 0217838 proposes a solution to allow the recycling of PAEK powder used in laser sintering. More precisely, it describes the possibility of recycling PEKK powder, but on condition that in successive runs the build temperature is increased from 285°C to 300°C and the power of the laser beam is increased each time the powder is recycled. In fact, this document describes that the PEKK powder used is not temperature stable and that its melting point increases after the first use in the sintering process. To be able to overcome this instability of the powder, the parameters of the sintering machine are modified. In particular, the power of the laser beam is increased for each run. The fact that these sintering parameters have to be changed for each run slows down the industrial production and makes it more difficult to produce. Furthermore, the mixing of non-recycled and recycled powders seems difficult, due to the complexity of the adjustment of the build parameters. Finally, the fact that the parameters have to be modified for each run, in particular the build temperature has to be increased, leads to a degradation of the polymer powder, so that the number of powder recyclings remains very limited, and it would be economically advantageous to recycle more powder.

[0012] Document WO2017 / 149233 describes PAEK powders that can be used several times for sintering processes by prior isothermal heat treatment at a constant temperature between 260 ° C and 290 ° C for a period between 5 and 120 minutes. The advantage of prior isothermal heat treatment is that the melting point of the powder is stable, making it recyclable for use in laser sintering at least over several runs. On the other hand, this technique makes it possible to recycle the powder over a large number of runs. Another disadvantage is that the powder yellows rapidly in the course of the recycling operation compared to the color of the unused powder. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] US2013 / 0217838 [Patent Document 2] WO2017 / 149233 [Patent Document 3] Publication No. EP2776224 Summary of the Invention [Problem to be solved by the invention]

[0014] It is an object of the present invention to overcome at least one of the disadvantages of the prior art.

[0015] In particular, it is an object of the present invention to provide an improved powder sintering manufacturing method using electromagnetic radiation, in which the powder used in the run is at least partially recycled powder.

[0016] In particular, it is an object of the present invention to provide a sintering production method whose parameters change little or remain unchanged, regardless of the number of times the recycled powder is recycled and regardless of the proportion of recycled powder in the powder used.

[0017] Another object of the invention is to provide a three-dimensional article obtainable by such a method and having satisfactory and substantially constant mechanical properties, regardless of the number of times the recycled powder is recycled and regardless of the proportion of recycled powder in the powder used.

[0018] Another object of the invention is to provide a three-dimensional article obtainable by such a method, the color of which is substantially the same, regardless of the number of times the recycled powder is recycled and regardless of the proportion of recycled powder in the powder used. [Means for solving the problem]

[0019] The present invention relates to a layer-by-layer manufacturing method of three-dimensional articles by sintering powders using electromagnetic radiation. The powders are based on polyaryletherketones (PAEKs) and contain at least one PAEK and at least one phosphate. The powders are at least partially recycled powders, i.e. powders that can be obtained by continuous or discontinuous heating of powders of the same composition at constant or non-constant temperatures strictly between the glass transition temperature Tg and the melting point Tm of the powders for a period of at least 6 hours.

[0020] The inventors have demonstrated that the use of phosphates in PAEK-based compositions allows for stabilization of color, viscosity and / or average molecular weight when the compositions are heated continuously or discontinuously at constant or non-constant temperatures strictly between the glass transition temperature and the melting point of the powder, the stabilization being effective over a period of at least 6 hours in this temperature range.

[0021] In a particular embodiment, the recycled powder originates from recycling of powder from at least one previous layer-by-layer building of a three-dimensional article by powder sintering with electromagnetic radiation, the sintering of the layers of the previous building having been carried out at a building temperature Tc. Furthermore, at least a portion of the recycled powder may originate from at least 2 recyclings, or at least 3 recyclings, or at least 5 recyclings, or at least 10 recyclings, or at least 25 recyclings, or at least 50 recyclings, or at least 100 recyclings of a previous layer-by-layer building of a three-dimensional article by powder sintering with electromagnetic radiation.

[0022] In certain embodiments, Tc is between (Tf-50)°C and (Tf-10)°C, inclusive.

[0023] In certain embodiments, Tc is between (Tg+20)° C. and (Tg+70)° C., inclusive.

[0024] In a particular embodiment, the powder originating from the layer-by-layer building of at least one previous three-dimensional article by powder sintering using electromagnetic radiation has been subjected to a temperature varying from the building temperature Tc to a temperature of at least (Tc-40)°C, preferably from the building temperature Tc to a temperature of at least (Tc-25)°C, more preferably from the building temperature Tc to a temperature of at least (Tc-10)°C, during the building period of the previous build.

[0025] In one particular embodiment, the powder comprises at least 30%, preferentially at least 40% and very preferentially at least 50% recycled powder relative to the total mass of the powder.

[0026] In certain embodiments, the at least one phosphate is a salt. Preferably, the phosphate may be selected from the group consisting of ammonium phosphate, sodium phosphate, calcium phosphate, zinc phosphate, potassium phosphate, aluminum phosphate, magnesium phosphate, zirconium phosphate, barium phosphate, lithium phosphate, rare earth phosphate, and mixtures thereof.

[0027] In certain embodiments, the phosphate may be an organometallic phosphate, particularly one having the formula:

[0028] [ka]

[0029] in which R is the same as or different from R', R and R' are formed by one or more aromatic groups optionally substituted by one or more groups having 1 to 9 carbons, R and R' can be bonded to each other or separated by at least one group selected from the following groups: -CH2-; -C(CH3)2-; -C(CF3)2-; -SO2-; -S-, -CO-; and -O-, and M represents an element from group IA or IIA of the periodic table.

[0043]

[0030] In certain embodiments, the phosphate is H2PO4 - salt, HPO4 2- salt, PO4 3- or mixtures thereof, preferentially with sodium, potassium or calcium ions as counterions. In particular, the phosphate may be monosodium phosphate.

[0031] The powder comprises at least 50% by weight of PAEK, based on the total weight of the powder. In certain embodiments, the powder comprises at least 75% by weight, or at least 80% by weight, or at least 85% by weight, or at least 90% by weight, or at least 92.5% by weight, or at least 95% by weight, or at least 97.5% by weight, or at least 98% by weight, or at least 98.5% by weight, or at least 99% by weight, or at least 99.5% by weight of PAEK, based on the total weight of the powder.

[0032] In certain embodiments, the proportion of the at least one phosphate in the powder is 500 ppm or more, or 750 ppm or more, or 1000 ppm or more, or 1500 ppm or more, or 2000 ppm or more, or 2500 ppm or more.

[0033] In certain embodiments, the at least one PAEK is selected from the group consisting of polyetherketoneketone (PEKK), polyetheretherketone (PEEK), polyetheretherketoneketone (PEEKK), polyetherketoneetherketoneketone (PEKEKK), polyetheretheretherketone (PEEEK), polyetherdiphenyletherketone (PEDEK), copolymers thereof, and mixtures thereof. The at least one PAEK may in particular be polyetherketoneketone (PEKK).

[0034] In one particular embodiment, the powder comprises at least two PAEKs, more particularly PEKK, and, in addition to PEKK, at least one of the following polymers: PEK, PEEKEK, PEEK, PEEKK, PEKEKK, PEEEK, PEDEK, in a content of less than 50% by weight relative to the total weight of the composition, preferably less than or equal to 30% by weight of the composition.

[0035] In one particular embodiment, the virgin powder has never been recycled and is recyclable, and is obtained by dry blending or wet impregnation, preferentially by wet impregnation, of said phosphate with a composition that does not contain phosphate, the composition constituting at least 50% by weight relative to the total weight of the composition.

[0036] The invention also relates to a three-dimensional article obtainable from a method such as described above.

[0037] Finally, the present invention relates to the use of a phosphate in a PAEK-based composition comprising at least 50% by weight of at least one PAEK relative to the total weight of the powder, for stabilizing the color and / or the average molecular weight of the composition when the composition is heated at a temperature strictly between the glass transition temperature and the melting point of the composition for a period of at least 6 hours.

[0038] The present invention will be more clearly understood with respect to the following detailed description of non-limiting embodiments thereof and the following figures. [Brief description of the drawings]

[0039] [Figure 1] 1 is a schematic diagram showing an apparatus for carrying out the method for layer-by-layer construction of a three-dimensional article by sintering according to the invention; [Diagram 2] FIG. 1 is a graph showing the variation in Yellowness Index (D65), also indicated as “YI(D65)”, of PEKK-based compositions heated at 285° C. for 7 days under nitrogen atmosphere for various phosphate contents in the composition (x-axis). [Diagram 3] FIG. 1 is a graph showing the variation in viscosity of the same PEKK-based composition heated at 285° C. for 7 days under nitrogen atmosphere for various phosphate contents (x-axis) in the composition. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0040] definition The term "glass transition temperature", denoted Tg, is understood to indicate the temperature at which an at least partially amorphous polymer changes from rubbery to glassy or vice versa, and is measured by differential scanning calorimetry (DSC) using a heating rate of 20 ° C / min according to the NF ISO 11357 standard, part 2. In the present invention, when glass transition temperature is mentioned, more specifically, the glass transition temperature at the midpoint of the process as specified in this standard, unless otherwise indicated. The PAEK-based powders according to the present invention may possibly exhibit several glass transition stages in the DSC analysis, in particular due to the presence of several PAEKs. In this case, glass transition temperature is understood to mean the glass transition temperature corresponding to the glass transition stage with the highest temperature.

[0041] The term "melting point", denoted Tm, is understood to indicate the temperature at which an at least partially crystalline polymer changes into a viscous liquid state and is measured by differential scanning calorimetry (DSC) at a heating rate of 20 ° C / min according to the NF EN ISO 11357 standard, part 3. In the present invention, reference is made to the melting point, more particularly to the peak melting point as defined in this standard, unless otherwise indicated. The PAEK-based powders according to the present invention may in the DSC analysis exhibit several melting peaks, possibly due to the presence of various crystalline forms of the PAEK and / or the presence of several different PAEKs. In this case, the melting point of the powder is understood to mean the melting point corresponding to the melting peak with the highest temperature.

[0042] The term "average molecular weight" is understood to denote the weight average molecular weight of the macromolecules of a polymer.

[0043] The term "viscosity" is understood to denote the viscosity measured on a solution at 25° C. in 96% by weight aqueous sulfuric acid according to the ISO 307 standard.

[0044] The term "yellowness index" or "YI" is understood to indicate the color deviation from colorless or white to yellow, measured according to the ASTM E313-96 standard with a D65 illuminant. This index can be measured using a Konica Minolta CM-3610d spectrophotometer.

[0045] The term "polymer blend" is intended to denote a macroscopically homogeneous polymer composition, including those compositions that consist of mutually immiscible phases dispersed on the micrometer scale.

[0046] The term "copolymer" is intended to denote a polymer obtained by polymerization of at least two chemically different monomers, called comonomers. Thus, a copolymer is formed from at least two types of repeating units. It can also be formed from three or more types of repeating units.

[0047] The term "stabilize" is understood to indicate the fact that some of the physicochemical properties of a polymer, in particular the average molecular weight, the viscosity or the color, are allowed to change only within limited limits when the polymer is heated at a temperature between its glass transition temperature and its melting point.

[0048] In all ranges stated in this patent application, the limits are inclusive unless otherwise stated.

[0049] Polyaryletherketone The powdered polyaryletherketones (PAEK) used in the process according to the invention have the following formula: (-Ar-X-) and (-Ar1-Y-) (In the formula: Ar and Ar1 each represent a divalent aromatic group; Ar and Ar1 may preferably be selected from 1,3-phenylene, 1,4-phenylene, 4,4'-biphenylene, 1,4-naphthylene, 1,5-naphthylene and 2,6-naphthylene; X represents an electron withdrawing group; preferably may be selected from carbonyl and sulfonyl groups; Y represents a group selected from an oxygen atom, a sulfur atom, an alkylene group, such as -CH2-, and isopropylidene. Includes units of.

[0050] In these X and Y units, at least 50%, preferably at least 70%, more particularly at least 80% of the X groups are carbonyl groups and at least 50%, preferably at least 70%, more particularly at least 80% of the Y groups represent oxygen atoms.

[0051] According to a preferred embodiment, 100% of the X groups represent a carbonyl group and 100% of the Y groups represent an oxygen atom.

[0052] More preferentially, the polyaryletherketone (PAEK) is polyetherketoneketones, also called PEKK, which in particular contain units of the formula IA (also known as "I units", for example isophthalic units) or units of the formula IB (also called "T units", for example terephthalic units), or mixtures thereof:

[0053] [ka]

[0054] polyetheretherketones, also called PEEK, containing units of the formula IIA or of the formula IIB or of the formula IIC or of the formula IID or mixtures thereof:

[0055] [ka]

[0056] - polyetherketones, also called PEK, containing units of formula IIIA or of formula IIIB or of formula IIIC or mixtures thereof:

[0057] [ka]

[0058] polyetheretherketoneketones, also called PEEKK, which in particular contain units of formula IV:

[0059] [ka]

[0060] - polyetheretheretherketone, also called PEEEK, which contains in particular units of formula V:

[0061] [ka]

[0062] and polyether diphenyl ether ketone, also called PEDEK, which contains in particular units of formula VI:

[0063] [ka] may be selected from:

[0064] In the above formula, other arrangements of the carbonyl group and the oxygen atom in the meta or para positions of the phenylene group are not shown, but are possible.

[0065] Other configurations in which diphenyl groups replace phenyl groups in the above formula are not shown but are possible. A diphenyl group consists of two phenylene groups linked together, and each phenylene can be in 1,3 or 1,4 configuration.

[0066] The PAEK may also be a copolymer comprising various units as mentioned above. The PAEK may in particular be a PEEK-PEDEK copolymer, which comprises PEEK units, in particular of formula IIA and / or its isomers, in particular of formula IIB, IIC and IID, and PEDEK units, in particular of formula VI and / or its isomers, in particular in which the diphenyl group comprises phenylene groups of 1,3 or 1,4 type.

[0067] Additionally, defects, end groups and / or monomers may be incorporated into such polymers in very small amounts as long as they do not adversely affect their performance.

[0068] The powder used in the method according to the invention is based on PAEK. It therefore generally comprises at least 50% by weight of a single PAEK or a mixture of PAEKs, relative to the total weight of the powder. In certain embodiments, the powder comprises at least 75% by weight, or at least 80% by weight, or at least 85% by weight, or at least 90% by weight, or at least 92.5% by weight, or at least 95% by weight, or at least 97.5% by weight, or at least 98% by weight, or at least 98.5% by weight, or at least 99% by weight, or at least 99.5% by weight of PAEK, relative to the total weight of the powder.

[0069] According to an alternative embodiment, the PAEK-based powder may be a powder based on one of the following polymers as the only PAEK in the powder: PEEK, PEEKK, PEKEKK, PEEEK, PEDEK or a PEEK-PEDEK copolymer.

[0070] According to another alternative, the PAEK-based powder may in particular be a powder based on PEKK as the only type of the family of PAEK in the powder. According to one particular embodiment, the PEKK may in particular be a mixture of various PEKK copolymers. In particular, the PEKK may be a mixture of PEKK copolymers with different ratios of units of formula IA to units of formula IB. According to another embodiment, the PEKK may be a single type of PEKK copolymer.

[0071] According to yet another alternative, the PAEK-based powder may also be a powder based on a mixture of polymers from the PAEK family.The powder may therefore in particular be a PEKK-based powder, which in addition to PEKK comprises at least one of the following polymers: PEK, PEEKEK, PEEK, PEEKK, PEKEKK, PEEEK, PEDEK, PEEK-PEDEK copolymers, the content of which is less than 50% by weight of the powder, preferably less than or equal to 30% by weight of the powder.

[0072] In the PEKK-based powder, the mass ratio of T units to the sum of T and I units of PEKK may be in the range of 0% to 5%; or 5% to 10%; or 10% to 15%; or 15% to 20%; or 15% to 20%; or 20% to 25%; or 25% to 30%; or 30% to 35%; or 35% to 40%; or 40% to 45%; or 45% to 50%; or 50% to 55%; or 55% to 60%; or 60% to 65%; or 65% to 70%; or 70% to 75%; or 75% to 80%; or 80% to 85%; or 85% to 90%; or 90% to 95%; or 95% to 100%.

[0073] A range of 35% to 100%, particularly 45% to 85%, and even more particularly 50% to 80% is particularly preferred. Preferably, the PEKK used has a mass ratio of T units to the total of T and I units of approximately 60%.

[0074] The selection of the mass ratio of T units to the sum of T and I units is one of the factors that makes it possible to adjust the melting point of the PEKK and the crystallization rate at a given temperature. A given mass ratio of T units to the sum of T and I units can be obtained by adjusting the concentrations of each of the reactants during polymerization in a manner known per se.

[0075] In powders based on PEEK-PEDEK copolymers, the molar ratio of IIA units to the sum of IIA and VI units may be in the range of 0% to 5%; or 5% to 10%; or 10% to 15%; or 15% to 20%; or 15% to 20%; or 20% to 25%; or 25% to 30%; or 30% to 35%; or 35% to 40%; or 40% to 45%; or 45% to 50%; or 50% to 55%; or 55% to 60%; or 60% to 65%; or 65% to 70%; or 70% to 75%; or 75% to 80%; or 80% to 85%; or 85% to 90%; or 90% to 95%; or 95% to 100%.

[0076] A range of 35% to 100%, particularly 45% to 85%, and even more specifically 50% to 80% is particularly suitable.

[0077] The selection of the weight ratio of IIA units to the sum of IIA and VI units is one of the factors that allows for the control of the melting point and crystallization rate at a given temperature of the PEEK-PEDEK copolymer.

[0078] Phosphate Phosphates are either salts of phosphoric acid salts or esters thereof, or phosphoric acid esters that are not in salt form. Phosphates have in common a phosphorus atom surrounded by four oxygen atoms in a tetrahedron.

[0079] One or more phosphates may be incorporated into the PAEK-based powder.

[0080] Preferentially, the phosphate is a salt, which has the particular advantage that it can be incorporated in aqueous form into the PAEK-based powder.

[0081] The phosphate may advantageously be selected from ammonium phosphate, sodium phosphate, calcium phosphate, zinc phosphate, aluminium phosphate, potassium phosphate, magnesium phosphate, zirconium phosphate, barium phosphate, lithium phosphate or one or more phosphates of rare earth elements.

[0082] According to one particular embodiment, the phosphate is one (or more) organometallic phosphate.

[0083] According to one particular embodiment, the organometallic phosphate has the formula:

[0084] [ka]

[0085] in which R is the same as or different from R', R and R' are formed by one or more aromatic groups optionally substituted by one or more groups having 1 to 9 carbons, R and R' can be bonded to each other or separated by at least one group selected from the following groups: -CH2-; -C(CH3)2-; -C(CF3)2-; -SO2-; -S-, -CO-; and -O-, and M represents an element from group IA or IIA of the periodic table.

[0043]

[0086] According to one particular embodiment, the at least one phosphate is H2PO4 - salt, HPO4 2- salt, PO4 3- or a mixture thereof.

[0087] In the mixture, H2PO4 - salt and HPO4 2- A mixture of salts of HPO4 2- salt and PO4 3- Particularly preferred are mixtures of the following salts: The counter ions of these mixtures are preferentially sodium, potassium or calcium ions, more preferably sodium ions.

[0088] In the embodiment in which the phosphate salt comprises only one phosphate, the phosphate salt is advantageously sodium, potassium or calcium H2PO4 -Preferably, the phosphate salt is monosodium phosphate.

[0089] The phosphate or mixture of phosphates is incorporated into the powder in a proportion of 500 ppm or more, or 750 ppm or more, or 1000 ppm or more, or 1500 ppm or more, or 2000 ppm or more, or 2500 ppm or more. Advantageously, the phosphate or mixture of phosphates is incorporated into the powder in a proportion of 50000 ppm or less, or 25000 ppm or less, or 20000 ppm or less. In particular, the phosphate or mixture of phosphates can be incorporated into the powder in a proportion between 1000 ppm and 5000 ppm, or between 5000 ppm and 10000 ppm, or between 10000 ppm and 15000 ppm, or between 15000 ppm and 20000 ppm.

[0090] The inventors have demonstrated that the addition of a phosphate or mixture of phosphates as described above to a PAEK-based composition, especially in powder form, can be advantageously used to stabilise the colour of the composition when the composition is heated to a temperature strictly between the glass transition temperature and the melting point of the composition.

[0091] In particular, effective stabilization of color is believed to be obtained if the composition exhibits a variation in Yellowness Index of 100% or less, or 90% or less, or 80% or less, or 70% or less, or 60% or less, or 50% or less, especially 25% or less, when heated under a nitrogen atmosphere at a temperature about 20° C. below its melting point for 7 days.

[0092] Similarly, the inventors have also demonstrated that the addition of a phosphate or mixture of phosphates to such compositions based on PAEK, especially in powder form, can be advantageously used to stabilise the viscosity of polyaryletherketone (PAEK) in polyaryletherketone-based compositions, when the composition is heated to a temperature strictly between its glass transition temperature and melting point.

[0093] It is believed that a particularly effective stabilization of the viscosity is obtained if, when the composition is heated under a nitrogen atmosphere at a temperature about 20° C. below its melting point for 7 days, the variation in viscosity of the composition, measured in a 96 wt % aqueous solution of sulfuric acid at 25° C., is no more than 20%, or no more than 15%, or no more than 10%, in particular no more than 5%, and very particularly between −5% and +10%.

[0094] Stabilization of the PAEK in the composition, particularly in terms of color and viscosity, ensures that the PAEK-based powder exhibits small color and viscosity variations after several hours of heating at temperatures strictly between its glass transition temperature and melting point, thus making it possible to obtain objects that are homogeneous and uniform in color and have homogeneous and uniform mechanical properties.

[0095] Therefore, the inventors have proposed an improved method for powder sintering by means of electromagnetic radiation using PAEK-based powders that are at least partially recycled.

[0096] powder The powder comprises at least one PAEK and at least one phosphate.

[0097] The powder may further contain one or more other polymers not belonging to the PAEK family, in particular other thermoplastic polymers.

[0098] The powder may also include a hydrophilic or hydrophobic flow agent. In certain embodiments, the powder includes 0.01% to 0.4% by weight of the flow agent, preferably 0.01% to 0.2% by weight of the flow agent, more preferably 0.01% to 0.1% by weight of the flow agent. The powder may include, for example, 0.01% to 0.05% by weight of the flow agent, or 0.05% to 0.1% by weight of the flow agent, or 0.1% to 0.2% by weight of the flow agent, or 0.2% to 0.3% by weight of the flow agent, or 0.3% to 0.4% by weight of the flow agent.

[0099] The powder may further include non-phosphate additives and / or fillers.

[0100] Among the fillers there may be mentioned reinforcing fillers, especially inorganic fillers, such as carbon black, carbon or non-carbon nanotubes, and fibers (glass, carbon, etc.), which may be ground or not. The PEKK powder may therefore contain less than 50% by weight of fillers, preferably less than 40% by weight, relative to the total weight of the powder.

[0101] Among the additives there may be mentioned stabilizers (light, especially UV, and heat stabilizers), optical brighteners, dyes, pigments, and energy absorbing additives (including UV absorbers), or combinations of these fillers or additives.

[0102] Thus, the powder may contain less than 5% by weight of additives, preferably less than 1% by weight of additives.

[0103] The powder according to the invention can be prepared by any known method capable of obtaining a homogeneous mixture containing a PAEK-based composition and at least one phosphate, and optionally other additives, fillers or other polymers, which may be selected from techniques such as dry blending (for example using a roll mill), melt extrusion, compounding or other wet impregnation or impregnation during the synthesis of the polymer.

[0104] Preferentially, the powder is prepared by the technique of dry blending the PAEK-based phosphate-free composition with said at least one phosphate, or by the technique of wet impregnation. These two methods have the advantage that the composition is not heated above its melting point. More preferably, the powder is obtained by the wet impregnation technique, which generally allows a better dispersion than the dry blending technique.

[0105] The powder is suitable for sintering using electromagnetic irradiation. This type of powder generally has a particle size distribution such that the median diameter "d50" is strictly less than 100 μm on a volume basis, as measured by laser diffraction, for example, with a Malvern diffractometer. "d50" represents the particle size value at which the cumulative particle size distribution function on a volume basis equals 50%. Preferably, the powder has a particle size distribution of d10 > 15 μm, 50 < d50 < 80 μm, and 120 < d90 < 180 μm. "d10" and "d90" correspond respectively to the diameters at which the cumulative function equals 10% and 90%. The grinding methods that make it possible to obtain such powders are known per se. A particularly advantageous method is described in published application EP2776224.

[0106] The powder may have a melting point of less than 330 °C, preferably 320 °C or less, more preferably 310 °C or less.

[0107] In certain embodiments, the powder intended for use in a method of building three-dimensional articles layer by layer by sintering induced by electromagnetic irradiation may be subjected to an isothermal heat treatment prior to its first use. In this case, the heat treatment is carried out at a temperature lower than the melting point of the powder and can be useful when some crystalline forms of PAEK (having different melting points) that can potentially affect the sintering quality coexist. However, the duration of such a heat treatment is typically less than 6 hours. Generally, it is 4 hours or less, preferably 2 hours or less.

[0108] In the variant where the PAEK-based powder is a PEKK-based powder, in particular a PEKK-based powder as the only PAEK, the prior isothermal heat treatment can be carried out at a temperature of 260 °C to 290 °C, preferably 280 °C to 290 °C. The isothermal heat treatment before the sintering step makes it possible to obtain a powder with a stable crystalline morphology, i.e., a powder that melts up to the construction temperature. The duration of the isothermal heat treatment is typically less than 6 hours. Generally, it is 4 hours or less, preferably 2 hours or less.

[0109] In certain embodiments, the powder may have a core-shell structure, in which the melting point of the core is higher than the melting point of the shell. In these embodiments, the core composition and the shell composition are each PAEK-based and each contain at least one phosphate.

[0110] Sintering Method Such PAEK-based powders are used in a method for building three-dimensional articles layer-by-layer by electromagnetic radiation induced sintering, for example in an apparatus 1 as shown diagrammatically in Figure 1. The powders consist of recycled powders and possibly virgin powders, as explained below.

[0111] The electromagnetic radiation may for example be infrared radiation, ultraviolet radiation or, preferably, laser radiation. In particular, in an apparatus 1 as shown diagrammatically in Figure 1, the electromagnetic radiation may comprise a combination of infrared radiation 100 and laser radiation 200.

[0112] The sintering process is a layer-by-layer manufacturing method for building a three-dimensional article 80 .

[0113] The apparatus 1 comprises a sintering chamber 10 in which is located a supply tank 40 containing the PAEK-based powder, a horizontal plate 30 for supporting a three-dimensional article 80 during build, and a laser 20 .

[0114] According to this method, powder is drawn from a supply tank 40 and deposited onto a horizontal plate 30 to form a thin layer 50 of powder that constitutes the three-dimensional article 80 under construction. The powder layer 50 under construction is heated by infrared radiation 100 to reach a substantially uniform temperature equal to a predetermined build temperature Tc.

[0115] The build temperature Tc may be lower than the melting point Tm of the powder by less than 50° C., preferably less than 40° C., more preferably less than 30° C., more preferably about 20° C. Tc is advantageously lower than Tm by more than 10° C.

[0116] Alternatively, Tc may be higher than the glass transition temperature of the powder, the difference being less than 70° C., preferably less than 60° C., more preferably less than 50° C., preferably less than 40° C., more preferably about 30° C. Tc is advantageously higher than Tg, the difference being more than 20° C.

[0117] The energy required to sinter the powder particles at various points in the powder layer 50 is then supplied by laser shots 200 from a laser 20 movable in a plane (xy) in a shape corresponding to the shape of the object. The molten powder resolidifies to form a sintered portion 55, while the remainder of the layer 50 remains in the form of unsintered powder 56. In certain cases, several laser shots 200 may be necessary.

[0118] The horizontal plate 30 is then lowered along axis (z) a distance corresponding to the thickness of one layer of powder, a new layer is deposited, the laser 20 provides the energy necessary to sinter the powder particles in a shape corresponding to this new piece of object, and so on. This procedure is repeated until the entire object 80 has been produced.

[0119] The temperature in the sintering chamber 10 of the layers below the layer being built may be lower than the build temperature. However, this temperature generally remains above the glass transition temperature of the powder. It is particularly advantageous to maintain the temperature at the bottom of the chamber at a temperature Tb, called the "tank bottom temperature", lower than Tc by a difference of less than 40°C, preferably less than 25°C and more preferably less than 10°C. Thus, once the building of the three-dimensional article 80 by powder sintering has been completed, the non-sintered powder portion 56 is subjected during the build to a heat treatment at a temperature that is variable but strictly between the glass transition temperature and the melting point of the powder, of the order of several hours, on average at least 6 hours.

[0120] Once the object 80 is completed, it is removed from the horizontal plate 30 and the green powder 56 may be sieved and then at least partially returned to the supply tank 40 for use as recycled powder.

[0121] The term "virgin powder" is understood to mean powder suitable for a first time use in a sintering process as defined above.

[0122] In contrast, a "recycled powder" is a powder that has the same initial composition as a virgin powder and that has been subjected to a heat treatment during a previous build, in particular by sintering. A "recycled powder" is therefore defined here as a powder that can be obtained by continuous or discontinuous heating of a powder of the same composition, in particular a virgin powder, at a constant or non-constant temperature strictly between the glass transition temperature Tg and the melting point Tm of the powder, for a period of at least 6 hours.

[0123] In certain embodiments in which the powder has a core-shell structure, the glass transition temperature Tg and the melting temperature Tm of the powder must be understood within the meaning of the present invention to be the glass transition temperature and melting point, respectively, of the shell.

[0124] The recycled powder may originate from recycling powder from the layer-by-layer construction of at least one previous three-dimensional article by powder sintering using electromagnetic radiation.

[0125] The powder can advantageously be recycled at least 2 times, or at least 3 times, or at least 5 times, or at least 10 times, or at least 25 times, or at least 50 times, or at least 100 times.

[0126] The recycled powder may be used as is or in a mixture with other recycled or virgin powders.

[0127] Advantageously, the powder used in the sintering process of the invention comprises at least 30%, preferentially at least 40% and very preferentially at least 50% recycled powder relative to the total mass of the powder.

[0128] In other words, a "n-times recycled" powder for a given build n, where n is an integer equal to or greater than 1, is a powder that may have come from a completed previous build (n-1).

[0129] If n=1, then the "single recycled" powder in Build 1 may come from recycling unused powder that was only first used in Build 0.

[0130] If n=2, the "twice recycled" powder in Build 2 may come from the original only once recycled powder used in Build 1, or from recycling an initial mixture of once recycled and unused powder.

[0131] In general, for n ≧2, the "n-times recycled" powder in build n may come from the recycling of only the first (n-1)-times recycled powder used in build (n-1), or from an initial mixture of (n-1)-times recycled powder and unused powder.

[0132] Thus, a powder that has been recycled "n times" has been subjected, at least in part, to heating corresponding to successive builds 0, ..., (n-1). Furthermore, a powder that has been recycled "n times" has been subjected, in its entirety, to heating of at least build (n-1).

[0133] The method according to the invention using recycled powder has the advantage that the building temperatures used can be substantially the same as in the method using only virgin powder. EXAMPLES

[0134] The purpose of the following example is to demonstrate the effect of adding phosphate to a PAEK-based composition on the stability of the composition when heated to a temperature strictly between its glass transition temperature and its melting point. The scope of the invention is not to be restricted merely by the presentation of this example.

[0135] Several compositions were prepared containing various proportions of Kepstan® PEKK 6000, PL grade and monosodium phosphate salt.

[0136] Kepstan® PEKK 6000 is a polyetherketoneketone sold by the company Arkema. The mass ratio of T units to the sum of T and I units is 60%. The melting point is between 300° C. and 305° C. The glass transition temperature is equal to 160° C. The grade used is a powder with a d50 of 50 μm and subjected to a prior isothermal heat treatment at 285° C. for 4 hours. The initial viscosity is 0.98 dL / g.

[0137] Kepstan® PEKK 6000 powder was impregnated with phosphate by wet impregnation in an aqueous monosodium phosphate solution followed by drying of the powder.

[0138] A control powder with no phosphate and four powders containing 385 ppm, 775 ppm, 1550 ppm, and 2500 ppm of monosodium phosphate salt were prepared. The powders were kept in a medium at 285°C under nitrogen for 7 days. Their yellowness index and viscosity were measured at t=0 and t=7 days.

[0139] As shown in FIG. 2, the addition of monosodium phosphate mitigated the increase in Yellowness Index after 7 days (Yellowness Index for the control powder varied by +150% compared to less than +100% variation for powders containing 775 ppm, 1550 ppm, and 2500 ppm phosphate, respectively).

[0140] As shown in FIG. 3, the addition of monosodium phosphate limited the increase in viscosity after 7 days (+20% change in viscosity for the control powder compared to less than +15% change for powders containing 1550 ppm and 2500 ppm phosphate, respectively). [Explanation of symbols]

[0141] 1 device 10 Sintering chamber 20. Laser 30 Horizontal Plate 40 Supply Tank 50 powder layer 55 Sintered part 56 Unsintered Powder 80 Three-dimensional objects 100 Infrared irradiation 200 Laser Irradiation

Claims

1. A layer-by-layer manufacturing method for a three-dimensional object by sintering a powder based on polyaryletherketone (PAEK) using electromagnetic radiation, comprising: said powder comprising at least 50% by weight, relative to the total weight of the powder, of at least one PAEK and at least one phosphate, said powder being at least partially a recycled powder; the proportion of said at least one phosphate in said powder is between 1000 ppm and 10000 ppm, A method of manufacturing, wherein the recycled powder is obtainable by continuous or discontinuous heating of a powder of the same composition at a constant or non-constant temperature strictly between the glass transition temperature Tg and the melting point Tm of the powder for a period of at least 6 hours.

2. 2. The method of claim 1, wherein the recycled powder is a powder originating from a layer-by-layer building of at least one previous three-dimensional article by powder sintering using electromagnetic radiation, the sintering of the layers of the previous building having been carried out at a building temperature Tc.

3. 3. The method of claim 2, wherein at least a portion of the recycled powder originates from at least two recyclings of a layer-by-layer construction of a previous three-dimensional article by powder sintering using electromagnetic radiation.

4. 4. The method of claim 2 or 3, wherein Tc is between (Tm-50)°C and (Tm-10)°C, inclusive, and Tc is between (Tg+20)°C and (Tg+70)°C, inclusive.

5. 5. The method of claim 4, wherein the powder originating from the layer-by-layer building of at least one previous three-dimensional article by powder sintering using electromagnetic radiation has been subjected to a temperature varying from the building temperature Tc to a temperature equal to or higher than (Tc-40) °C during the building period of the previous build.

6. 6. The method according to claim 1, wherein the powder comprises at least 30% recycled powder relative to the total mass of the powder.

7. 7. The process according to any one of claims 1 to 6, wherein the at least one phosphate is a salt.

8. 8. The method of claim 7, wherein the salt is selected from the group consisting of ammonium phosphate, sodium phosphate, calcium phosphate, zinc phosphate, potassium phosphate, aluminum phosphate, magnesium phosphate, zirconium phosphate, barium phosphate, lithium phosphate, rare earth phosphate, and mixtures thereof.

9. The salt has the formula: 【Chemistry 1】 where R is the same as R' or different from R', R and R' are formed by one or more aromatic groups optionally substituted by one or more groups having 1 to 9 carbons, and R and R' are either bonded to each other or are one of the following groups: -CH 2 -;-C(CH 3 ) 2 -;-C(CF 3 ) 2 -;-SO 2 -; -S-; -CO-; and -O-, where M represents an element from group IA or IIA of the periodic table. The method of claim 7, comprising:

10. The salt is H 2 PO 4 - salt, HPO 4 2- Salt, PO 4 3- or a mixture thereof.

11. The process of claim 7, wherein the salt is monosodium phosphate.

12. 12. The method according to claim 1, wherein the powder comprises at least 75% by weight of PAEK relative to the total weight of the powder.

13. 13. The process according to any one of claims 1 to 12, wherein the proportion of said at least one phosphate in said powder is equal to or greater than 1500 ppm.

14. 14. The process according to any one of claims 1 to 13, wherein the at least one PAEK is selected from the group consisting of polyetherketoneketone (PEKK), polyetheretherketone (PEEK), polyetheretherketoneketone (PEEKK), polyetherketoneetherketoneketone (PEKEKK), polyetheretheretherketone (PEEEK), polyetherdiphenyletherketone (PEDEK), copolymers thereof, and mixtures thereof.

15. 15. The process of claim 14, wherein the at least one PAEK is polyetherketoneketone (PEKK).

16. 14. The method of claim 1, wherein the powder comprises at least two PAEKs.

17. 17. A process according to any one of claims 1 to 16, wherein the virgin powder, which has never been recycled and is recyclable, is obtained by dry blending or wet impregnation of said phosphate with a composition free of phosphate, the composition constituting at least 50% by weight relative to the total weight of the composition.

Images