FR3146477A1 - Powder mix - Google Patents

Abstract

The invention relates to a dry mixture of powders comprising: a poly-aryl-ether-ketone(s)-based powder having a volume-weighted particle size distribution, measured by laser diffraction, according to ISO 13320:2009, such that the median diameter D50 is such that D50 ≤ 300 µm, and a nucleating filler in powder form, the nucleating filler being selected from a silicate, a carbonaceous material, or their mixture, the nucleating filler representing from 0.1% to 2% by weight, relative to the total weight of poly-aryl-ether-ketone-based powder and nucleating filler. Figure for abstract: Figure 1

Description

Powder mix

The invention relates to the field of poly-aryl-ether-ketone(s) powders.

More particularly, the invention relates to a formulation in powder form based on poly-aryl-ether-ketone(s), which can in particular be used for the layer-by-layer sintering caused by electromagnetic radiation(s) of a three-dimensional object.

Prior art

Poly-aryl-ether-ketones (PAEKs) are well-known high-performance technical polymers. They can be used for applications requiring high temperature and/or mechanical or even chemical constraints. They can also be used for applications requiring excellent fire resistance and low emissions of smoke or toxic gases. Finally, they have good biocompatibility. These polymers are found in fields as varied as aeronautics and space, offshore drilling, automotive, railway, marine, wind, sports, construction, electronics and medical implants.

Notwithstanding these advantageous properties, it is sometimes necessary to formulate polyaryl ether ketones in order to meet specific specifications. Thus, one may seek to formulate a composition making it possible to obtain more ductile objects to accommodate new modes of use, with for example a possibility of greater traction and/or bending, without causing the object to break. One may in particular seek to formulate a composition based on polyaryl ether ketone(s) to increase its deformation at break and/or to increase its stress at break, compared to the same unformulated compositions.

The need to provide such formulated compositions exists in particular for methods of manufacturing articles using compositions in powder form. An example of a method, which is particularly detailed later in the present application, is a method of constructing layer-by-layer objects by sintering caused by electromagnetic radiation(s). Other examples of methods requiring a powder composition are coating, for example metals, from a powder, powder compression molding, powder compression-transfer molding, or even impregnation of fibers with a resin powder for the manufacture of semi-finished products, the powder being able to be used in a fluidized bed or dispersed in an aqueous solution.

It is known that the addition of fillers to a polymer composition influences in particular the crystallization and/or the microstructure of this composition. The nature of the filler as well as the proportion in which the latter is additivated can make it possible to vary certain targeted properties, as shown by several examples below of the prior art.

Application US7790841 discloses for example thermoplastic compositions with nanoparticles, the nanoparticles making it possible to increase the crystallization rate, the crystallinity rate, and the density of the composition. In particular, examples are mixtures obtained by melt mixing of polyetherketoneketone and silica. Example 1a of US7790841 discloses in particular the introduction of 1-2% wt of hydrophilic silica (Aerosil® R150) or hydrophobic silica (Aerosil® R202). This patent application does not disclose a formulation in powder form.

According to another aspect, it is known that the addition of a small amount of hydrophilic silica in dry mixing with a PEKK powder makes it possible to obtain a good compromise between the flowability of the powder and its coalescence at the time of sintering. Application US2016333190 exemplifies in particular a dry mixture of polyetherketoneketone powder and 0.2% by weight of hydrophilic silica (CAB-O-Sil® M-5). However, this application does not study the influence of the hydrophilic silica on the crystallization and/or the microstructure of the sintered object.

Application US20210403652 discloses compositions for laser sintering of powders comprising a polymer and an additive, the additive being a carbon black or a graphite. The objective here is to identify additives that do not modify either the crystallinity or the crystallization of the polymer. In particular, compositions of dry mixtures of polyamide powders and 0.09 wt% of carbon black or graphite are exemplified. The object obtained by sintering from these powder mixtures has spherulites of the same size (see Figures 7 and 8) as those of an object sintered from non-additive powder (see Figure 6), of the order of 20 µm.

Finally, it is known from application WO2021069833 that the compounding of granules of a composition of PAEK and a certain amount of talc makes it possible to make the granules more fragile than granules made of PEKK. These granules can be ground into a powder suitable for a laser sintering process. The objects sintered with the powder thus formulated have the advantage of having a higher elastic modulus than those sintered with a non-formulated powder. Examples include PEKK powders comprising 30% by weight of talc, the PEKK forming a matrix incorporating the talc.

None of the formulations of the prior art meet the aforementioned needs. The present invention thus proposes to provide a formulation in powder form based on poly-aryl-ether-ketone(s), with additives, allowing the manufacture of more ductile objects.

Objective of the invention

The aim of the invention is to provide an additive-containing powder composition for manufacturing objects having a greater elongation at break and/or a greater breaking stress in a process using powders, for example a process for constructing layer-by-layer objects by sintering caused by electromagnetic radiation(s), compared to a non-additive composition.

Another objective, at least according to certain embodiments, is to provide such an additive powder composition having properties similar to a non-additive composition in terms of warping when it is used for the manufacture of an object.

Another objective is, at least according to certain embodiments, to provide an additive powder composition which is easy to implement technically, and preferably having a low additional cost.

The invention relates to a dry powder mixture comprising a poly-aryl-ether-ketone(s)-based powder having a volume-weighted particle size distribution, measured by laser diffraction, according to ISO 13320:2009, such that the median diameter D50 is such that D50 ≤ 300 µm, and a nucleating filler in powder form. The nucleating filler in powder form is selected from a silicate, a carbonaceous material, or a mixture thereof. The nucleating filler represents from 0.1% to 2% by weight, relative to the total weight of poly-aryl-ether-ketone(s)-based powder and nucleating filler.

According to certain embodiments, the nucleating charge represents from 0.5% to 1.5% by weight, and preferably from 0.8% to 1.2% by weight, relative to the total weight of powder based on poly-aryl-ether-ketone(s) and nucleating charge.

In some embodiments, the poly-aryl ether ketone(s)-based powder consists essentially of or consists of poly-aryl ether ketone(s).

In some embodiments, the poly-aryl-ether-ketone is a polyetherketoneketone.

In some embodiments, the poly-aryl ether ketone is a polyether ketone ketone consisting essentially of, and preferably consisting of: a terephthalic repeating unit and, where appropriate, an isophthalic repeating unit, the terephthalic repeating unit (“T unit”) having the formula:

(I)

the isophthalic unit (“I unit”) having the formula:

(II)

the mass proportion of T units relative to the sum of the T and I units may vary from 0% to 85%. For use of the powder mixture in a method of constructing layer-by-layer objects by sintering caused by electromagnetic radiation, the mass proportion of T units relative to the sum of the T and I units is preferably from 0% to 25% or from 45% to 75%, more preferably from 0% to 15% or from 55% to 65%, and in particular approximately 0% or approximately 60%.

According to certain embodiments, in particular when the powder mixture according to the invention is used in a method of constructing layer-by-layer objects by sintering caused by electromagnetic radiation, the powder based on poly-aryl-ether-ketone(s) advantageously has a particle size distribution, weighted by volume, measured by laser diffraction, according to the ISO 13320: 2009 standard, such that the median diameter D50 has a value of 40 µm to 80 µm.

According to some embodiments, the nucleating charge is a talc. The volume-weighted particle size, measured by laser diffraction, according to ISO 13320:2009, such that the median diameter d50 may in particular be such that d ₅₀ ≤ 10 µm, and preferably such that d ₅₀ ≤ 5 µm. According to particular embodiments, the median diameter d50 is such that d ₅₀ ≤ 2 µm.

Advantageously, the ratio D ₅₀ /d ₅₀ is between 10 and 500, preferably between 25 and 250, and more preferably between 40 and 150.

According to certain embodiments, the nucleating charge is a carbon material. The carbon material may in particular be chosen from the list consisting of carbon black, carbon nanotubes, graphene, or their mixture. The carbon material advantageously has a BET specific surface area greater than or equal to 200 g/m ² .

According to certain embodiments, in particular when the mixture of powders according to the invention is used in a method of constructing layer-by-layer objects by sintering caused by electromagnetic radiation, the viscosity of the poly-aryl-ether-ketone(s) is chosen in the range from 400 Pa.s to 1000 Pa.s, as measured at 380°C and at 1 Hz in plane/plane geometry.

The present invention also relates to a use of the mixture according to the invention in a method of constructing layer-by-layer objects by sintering caused by electromagnetic radiation(s). Other possible uses are also described.

The present invention also relates to an object manufactured from a method using a mixture of powders according to the invention. The object has spherulites having a maximum spherulite size at least 2 times smaller than that of an object obtained from the same method but using only the powder based on poly-aryl-ether-ketone(s) present in said mixture of powders.

Finally, the present invention also relates to an object manufactured from a process using a mixture of powders according to the invention. The object has an elongation at break greater than at least 5% and/or a breaking stress greater than at least 5%, compared to that(s) of an object obtained from the same process but using only the powder based on poly-aryl-ether-ketone(s) present in said mixture of powders.

Detailed description of the invention

Figures

represents a schematic of a laser sintering installation

schematically represents the thermal profile, temperature as a function of time, observed by the powder composition according to the invention during a laser sintering process.

represents a snapshot of an optical microscope observation of a 3 µm thick microtome section for composition #1c.

Definitions

"Powder" means a fractionated state of matter, generally in the form of particles of very small size, generally of the order of a hundred micrometers or less. "Powdery" means a state of matter, in particular a state of a composition, which is as a whole in the form of a powder.

The particle size distribution of a powder can be measured by laser diffraction according to ISO 13320:2009. The particle size distribution of the polyaryl ether ketone(s) powder can be measured, for example, on a Malvern Insitec® diffractometer. The rules for representing the results of a particle size distribution are given in ISO 9276–parts 1 to 6. “D50” means the value of the particle diameter of the polyaryl ether ketone(s) powder such that the cumulative particle diameter distribution function, weighted by volume, is equal to 50%. Similarly, the terms "D10" and "D90" respectively mean the corresponding diameters so that the cumulative function of the diameters of the particles of powder based on poly-aryl-ether-ketone(s), weighted by volume, is equal to 10%, and respectively, to 90%. "d50" is understood to mean the value of the diameter of the particles of nucleating charge in powder form so that the cumulative function of the distribution of the particle diameters, weighted by volume, is equal to 50%. Similarly, the terms "d10" and "d90" respectively mean the corresponding diameters so that the cumulative function of the diameters of the particles of nucleating charge, weighted by volume, is equal to 10%, and respectively, to 90%.

The term "homopolymer" is understood to mean a polymer consisting of a single repeating unit.

The term "copolymer" refers to a polymer resulting from the copolymerization of at least two types of chemically different monomers, called comonomers. A copolymer is therefore formed of at least two repeating units resulting from different monomers. It can also be formed of three or more repeating units resulting from different monomers.

The copolymer may have a homogeneous structure, in particular of the statistical, alternating or random type, or a heterogeneous structure, in particular of the block type.

“Consisting essentially of unit(s)” means that the unit(s) represent(s) a molar proportion of 95% to 99.9% relative to the total number of moles of repeating units in the polymer.

“Consisting of unit(s)” means that the unit(s) represent(s) a molar proportion of at least 99.9%, in particular 100%, in the polymer relative to the total number of moles of repeating units in the polymer.

The term “glass transition temperature” means the temperature at which an at least partially amorphous polymer changes from a rubbery state to a glassy state, or vice versa, as measured by differential scanning calorimetry (DSC) according to standard NF EN ISO 11 357-2:2020 in the second heating, using a heating rate of 20°C/min.

• Longueur d’onde : raie principale Kα1 du cuivre (1,54 Angström).
• Puissance du générateur : 50 kV – 0.6 mA.
• Mode d’observation : transmission.
• Temps de comptage : 10 minutes.
• Température : 25°C

The term “crystallinity rate” is understood to mean the crystallinity rate as calculated from wide angle X-ray scattering (WAXS) measurements, on a Nano-inXider® type device with the following conditions:

• Wavelength: main Kα1 line of copper (1.54 Angstroms).
• Generator power: 50 kV – 0.6 mA.
• Observation mode: transmission.
• Counting time: 10 minutes.
• Temperature: 25°C

A spectrum of the scattered intensity is thus obtained as a function of the diffraction angle. This spectrum makes it possible to identify the presence of crystals, when peaks are visible on the spectrum in addition to the amorphous halo. In the spectrum, the area of the crystalline peaks (denoted A) and the area of the amorphous halo (denoted AH) can be measured. The proportion (by mass) in crystalline phase is estimated by the ratio (A)/(A+AH). The crystallinity rates in the present invention are expressed as the mass proportion of crystalline poly-aryl-ether-ketone(s), relative to the total weight of poly-aryl-ether-ketone(s).

The term “spherulite” or “spherolite” means an aggregated formation of needle-shaped crystals with a radiating structure, called fibroradiated. Certain polymers, including poly-aryl-ether-ketones, exhibit this type of crystalline organization when they crystallize. The spherulites in the present invention can be observed under an optical microscope on microtome sections. The size of a spherulite corresponds to the diameter of the smallest circle that can encompass a spherulite thus observed. It is expressed in micrometers. The maximum size of the spherulites corresponds to the maximum size observed on 3 microtome sections of the same sample, each section generally comprising around thirty spherulites. Thus, the maximum size of the spherulites corresponds to the maximum size observed on a distribution of around 90 spherulites.

The term “viscosity” is understood to mean the viscosity as measured at 380°C and 1 Hz under an inert atmosphere (N2), using a TA Instruments ARES G2® oscillatory rheometer, in plane/plane geometry.

The tensile mechanical properties can be determined on type 1BA specimens according to ISO 527-1:2019, at 23°C, with a crosshead speed of 1mm/min, using for example an MTS 810® device, marketed by MTS Systems Corporation, equipped with a mechanical extensometer. A 1BA specimen can be obtained directly by the manufacturing process for which said powder is suitable or, where appropriate, machined from a solid object if the specimen cannot be obtained directly by this process. For example, type 1BA specimens can be manufactured directly by a layer-by-layer object construction process by sintering induced by electromagnetic radiation(s) (no machining is then necessary since this process allows direct manufacture of the specimen).

According to ISO 527-1:2019, “strain”, ε, is taken to mean an increase in length per unit of initial length of the gauge length. It is expressed as a dimensionless ratio or as a percentage (%). In particular, “strain at break” is taken to mean: i) for a brittle material, the strain at the last point recorded before the stress is reduced to a value less than or equal to 10% of the strength when failure occurs before the yield point (which is strictly speaking the “strain at break” according to ISO 527-1:2019), or ii) for a ductile material, the strain at the last point recorded before the stress is reduced to a value less than or equal to 10% of the strength when failure occurs after the yield point (which is the “nominal strain at break” according to ISO 527-1:2019).

According to ISO 527-1:2019, "stress", σ, is taken to mean the force per unit area of the initial cross-section of the gauge length of the specimen. It is expressed in megapascals (MPa). In particular, "fracture stress" is taken to mean the stress at which the specimen breaks.

The term "specific surface area" is used to describe the ratio of the actual surface area of a powder to the amount of material in the powder. It is expressed in m²/g. It can be measured by adsorption of nitrogen gas on the powder and determined using the Brunauer-Emmett-Tellery (BET) equation according to ISO 9277:2022.

The singular forms include, without it being necessary to recall it each time, the embodiments where "un" means "un seul" and "le" means "le seul".

The writing “poly-aryl-ether-ketone(s)”, or its acronym “PAEK(s)”, should be interpreted as meaning one or more poly-aryl-ether-ketones.

In all value ranges stated in this application, the terminals are included unless otherwise stated.

PAEK(s) based powder

A poly-aryl ether ketone (PAEK) has the following formula units:
(−Ar−X−) and (−Ar ₁ −Y−),
in which:
- Ar and Ar ₁ each denote a divalent aromatic radical;
- Ar and Ar ₁ may preferably be selected from 1,3-phenylene, 1,4-phenylene, 1,1'-biphenylene divalent in positions 3,3', 1,1'-biphenyl divalent in positions 3,4', 1,4-naphthylene, 1,5-naphthylene and 2,6-naphthylene;
- X denotes an electron-withdrawing group; it may preferably be chosen from the carbonyl group and the sulfonyl group;
- Y denotes a group selected from an oxygen atom, a sulfur atom, an alkylene group, such as –(CH) ₂ - and isopropylidene.

In these X and Y units, at least 50%, preferably at least 70% and more particularly at least 80% of the X groups are a carbonyl group, and at least 50%, preferably at least 70% and more particularly at least 80% of the Y groups represent an oxygen atom.

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

Advantageously, the PAEK(s) may be chosen from:
- a polyether-ketone-ketone, also called PEKK; a PEKK comprises a unit(s) of formula: -Ph-O-Ph-C(O)-Ph-C(O)-;
- a polyether-ether-ketone, also called PEEK; a PEEK comprises a unit(s) of formula: -Ph-O-Ph-O-Ph-C(O)-;
- a polyether ketone, also called PEK; a PEK comprises a unit(s) of formula: -Ph-O-Ph-C(O)-;
- a polyether-ether-ketone-ketone, also called PEEKK; a PEEKK comprises a unit(s) of formula: -Ph-O-Ph-O-Ph-C(O)- Ph-C(O)-;
- a polyether-ether-ether-ketone, also called PEEEK; a PEEEK comprises a unit(s) of formula: -Ph-O-Ph-O-Ph-O- Ph-C(O)-;
- a polyether-diphenyl-ether-ketone also called PEDEK; a PEDEK comprises a unit(s) of the formula: a PEDEK comprises a unit(s) of the formula –Ph-O-Ph-Ph-O-Ph-C(O)-;
- their mixtures; and,
- copolymers comprising at least two of the above-mentioned units,
in which: Ph represents a phenylene group and –C(O)- a carbonyl group, each of the phenylenes being able independently to be of the ortho (1-2), meta (1-3) or para (1-4) type, preferentially being of the meta or para type.

Additionally, defects, end groups and/or monomers may be incorporated in very small amounts into the polymers as described in the above list without affecting their performance.

Preferably, in the embodiments where the poly-aryl-ether-ketone is a copolymer, the latter has a homogeneous structure, in particular of the statistical type.

In some embodiments, the PAEK is a polyetherketoneketone consisting essentially of, and preferably consisting of: a terephthalic repeating unit and, where appropriate, an isophthalic repeating unit, the terephthalic repeating unit (“T unit”) having the formula:

(I)

the isophthalic unit (“I unit”) having the formula:

(II)

The mass proportion of T units relative to the sum of the T and I units may vary from 0% to 85%. The mass proportion of T units relative to the sum of the T and I units may in particular be from 0% to 5%; or from 5% to 10%; or from 10% to 15%; or from 15% to 20%; or from 15% to 20%; or from 20% to 25%; or from 25% to 30%; or from 30% to 35%; or from 35% to 40%; or from 40% to 45%; or from 45% to 50%; or from 50% to 55%; or from 55% to 60%; or from 60% to 65%; or from 65% to 70%, or from 70% to 75%, or from 75% to 80%, or from 80% to 85%. The choice of the molar proportion of T units relative to the sum of T and I units is one of the factors which makes it possible to adjust the crystallization rate properties of polyether-ketone-ketones. A given molar proportion of T units relative to the sum of T and I units can be obtained by adjusting the respective concentrations of the reactants during the polymerization, in a manner known per se.

For use of the powder in a method of constructing layer-by-layer objects by sintering caused by electromagnetic radiation, the mass proportion of T units relative to the sum of the T and I units is preferably from 0% to 25% or from 45% to 75%, and more preferably from 0% to 15% or from 55% to 65%. The mass proportion of T units relative to the sum of the T and I units may in particular be approximately 0% or approximately 60%.

Such poly-aryl-ether-ketones are commercially available under the name Kepstan® from the Arkema company.

In some embodiments, the PAEK may be a homopolymer consisting essentially of, or even consisting of, a repeating unit having the formula:

(III)

Such poly-aryl ether ketones are commercially available under the name KetaSpire® from Solvay, under the name VestaKeep® from Evonik and PEEK Victrex® from Victrex.

In some embodiments, the PAEK may be a copolymer consisting essentially of, or even consisting of, a repeating unit having the formula (III) and a repeating unit having the formula:

(IV)

The molar proportion of unit (III) relative to the sum of units (III) and (IV) can range from 0% to 99%, preferably from 0% to 95%.

In some embodiments, the PAEK may be a copolymer consisting essentially of, or even consisting of, a repeating unit having the formula (III) and a repeating unit having the formula:

(V)

The molar proportion of unit (III) relative to the sum of units (III) and (V) can range from 0% to 99%, preferably from 0% to 95%.

The glass transition temperature of PAEK is preferably between 100 and 250°C, preferably between 120 and 200°C, and most preferably between 140 and 180°C.

Advantageously, the PAEK has a viscosity, measured at 380°C and 1 Hz, greater than 100 Pa s, preferably greater than 200 Pa s and more preferably greater than 300 Pa s. The viscosity of the PAEK is generally not greater than 1500 Pa s. The viscosity of the PAEK may in particular be from 300 Pa s to 600 Pa s, or from 600 Pa s to 800 Pa s, or from 800 Pa s to 1000 Pa s, or from 1000 Pa s to 1200 Pa s, or from 1200 Pa s to 1500 Pa s.

According to certain embodiments, in particular for powder mixtures intended to be used in a sintering process, the viscosity of the PAEK(s), measured at 380°C and 1 Hz, is chosen in the range from 400 Pa.s to 1000 Pa.s.

According to certain embodiments, the PAEK-based powder comprises at least two PAEKs. The powder may in particular comprise at least 50% by weight of a PEKK, relative to the total weight of PAEKs, and at least one other PAEK different from said PEKK.

In some embodiments, the at least two PAEKs may be PAEKs having different repeat units. For example, a PEKK and a PEEK may be cited.

According to certain embodiments, these at least two PAEKs can be copolymers having the same repeating units but with a different ratio. For example, two PEKKs can be mentioned having a different proportion of T:I units.

In some embodiments, the powder comprises a single PAEK. In some embodiments, this PAEK may be a PEKK. For use of the PEKK-based powder in a method of constructing layer-by-layer objects by sintering induced by electromagnetic radiation, the mass proportion of T units relative to the sum of the T and I units is preferably from 0% to 25% or from 45% to 75%, and more preferably from 0% to 15% or from 55% to 65%. The mass proportion of T units relative to the sum of the T and I units may in particular be approximately 0% or approximately 60%.

The PAEK(s)-based powder comprises at least 60% by weight of PAEK(s), relative to the total weight of said powder. The powder may comprise at least 70%, or at least 80%, or at least 90%, or at least 95%, or at least 98%, or at least 99%, or at least 99.5% by weight of PAEK(s), relative to the total weight of said powder.

The PAEK(s)-based powder may comprise, in addition to the PAEK(s), a thermoplastic polymer other than the PAEK(s) and/or additives.

The PAEK(s)-based powder may comprise from 0% to 40% by weight of another thermoplastic polymer, relative to the weight of said powder. As another thermoplastic polymer, mention may be made of a poly(etherimide). A poly(etherimide) is known to be an amorphous polymer miscible with PAEK(s). It may be used to adjust the crystallization kinetics and/or crystallinity of the composition of the powder mixture according to the invention. According to certain embodiments, the PAEK(s)-based powder may comprise from 5% to 30% by weight of another thermoplastic polymer than the PAEK(s), in particular a polyetherimide.

The PAEK(s)-based powder may also comprise one or more additives. The additives generally represent less than 5% by weight relative to the total weight of the powder mixture. Preferably, the additives represent less than 1% by weight relative to the total weight of the powder mixture. Among the additives, mention may be made of flow agents, stabilizers (to light, in particular UV, thermal), optical brighteners, dyes, pigments and energy-absorbing additives (including UV absorbers).

In some embodiments, the PAEK(s)-based powder does not include a flow agent. The PAEK(s)-based powder notably does not include hydrophilic silica.

According to certain embodiments, the PAEK(s)-based powder may comprise a phosphate as a thermal stabilizer. The phosphate may in particular be a phosphate salt, such as a salt of H ₂ PO ₄ ^- , HPO ₄ ^2- , PO ₄ ^3- , or a mixture thereof, preferably having a sodium ion, a potassium ion or a calcium ion, and more preferably a sodium ion, as a counterion. Advantageously, the phosphate is incorporated into the PAEK(s)-based powder in a proportion greater than or equal to 500 ppm, or greater than or equal to 750 ppm, or greater than or equal to 1000 ppm, or greater than or equal to 1500 ppm, or greater than or equal to 2000 ppm, or greater than or equal to 2500 ppm, relative to the total weight of PAEK.

According to certain embodiments, the PAEK(s)-based powder may consist of at least 60% by weight of PAEK(s), from 0% to 40% by weight of another thermoplastic polymer and from 0% to 5% by weight of an additive, relative to the total weight of said powder.

According to certain embodiments, the PAEK(s)-based powder may consist of at least 95% by weight of PAEK(s) and from 0% to 5% by weight of an additive, relative to the total weight of said powder.

In some embodiments, the PAEK(s)-based powder may consist essentially of PAEK(s).

The poly-aryl-ether-ketone(s) based powder advantageously has a particle size distribution, as measured by laser diffraction according to ISO 13320:2009, with a median diameter D ₅₀ such that: D50 ≤ 300 µm,

In some embodiments, D50 ≤ 200 µm, or D50 ≤ 150 µm, or D50 ≤ 120 µm, or D50 ≤ 100 µm, or D50 ≤ 80 µm.

According to certain embodiments, in particular for powder mixtures intended to be used in a sintering process, D50 is advantageously such that: 40 µm ≤ D50 ≤ 80 µm. In these embodiments, the particle size distribution is preferentially such that D ₁₀ ≥ 15 µm, 40 µm ≤ D50 ≤ 80 µm and D90 ≤ 240 µm. In particular, it is possible to have D90 ≤ 220 µm or even d90 ≤ 200 µm.

Nucleating charge

The nucleating charge is in powder form. It is chosen from a silicate, a carbon material, or their mixture. A proportion of 0.1% to 2% by weight of nucleating charge relative to the total weight of poly-aryl-ether-ketone powder and nucleating charge has proven to be optimal for enabling the reduction of the size of spherulites during the construction of objects by making it possible to improve certain mechanical properties (elongation at break/breaking stress), without modifying other properties targeted for the application (including the crystallinity rate).

Preferably, the nucleating charge represents from 0.5% to 1.5% by weight, relative to the total weight of powder based on poly-aryl-ether-ketone and nucleating charge.

Preferably again, the nucleating charge represents from 0.8% to 1.2% by weight, relative to the total weight of powder based on poly-aryl-ether-ketone and nucleating charge.

A silicate is a mineral containing in its structure one or more anions of chemical formula: SiO _4-X ^{(4-2 X)-} , where 0 ≤ x < 2. The counterion(s) can be mainly aluminum, potassium, magnesium, sodium, calcium, iron, or a mixture of these elements. The silicate can be present in hydroxylated form.

The nucleating charge can in particular be chosen from: a talc, a mica, a kaolin, or their mixture.

According to particular embodiments, the nucleating charge is a talc.

The nucleating charge, particularly when it is a silicate, advantageously has a particle size distribution such that d ₅₀ ≤ 10 µm, and preferably such that d ₅₀ ≤ 5 µm.

According to some preferred embodiments, ₅₀ ≤ 2 µm is preferred.

Furthermore, according to certain embodiments, the ratio D ₅₀ /d ₅₀ ranges from 10 to 500, preferably from 25 to 250, and more preferably from 40 to 150.

In embodiments where the nucleating charge is a carbon material, it may in particular be chosen from carbon black, graphene, carbon nanotubes, or their mixture.

The BET specific surface area of the nucleating charge being a carbon material is advantageously greater than or equal to 200 g/m ² . It may in particular be greater than or equal to 500 g/m ² , or greater than or equal to 600 g/m ² , or greater than or equal to 700 g/m ² , or greater than or equal to 800 g/m ² , or greater than or equal to 900 g/m ² , or greater than or equal to 1000 g/m ² .

Dry mix of powders

The dry - blending process consists of mixing the poly-aryl-ether-ketone(s)-based powder and the nucleating charge in their solid form, dry. It makes it possible to obtain a dry blend of powders ( dry-blend ) . The mixing speed and/or the mixing duration are chosen by the person skilled in the art to obtain a homogeneous mixture in a manner known per se.

A dry mixing process comprises at least the following steps:
(i) supply of the powder based on poly-aryl-ether-ketone(s),
(ii) providing the nucleating charge in powder form, and
(iii) at least one step of dry mixing at least a portion of said poly-aryl-ether-ketone(s)-based powder with at least a portion of said nucleating charge in powder form.

In a preferred embodiment, the dry mixing process is carried out by means of a single step of mixing the poly-aryl-ether-ketone(s)-based powder with the nucleating charge in powder form, in the desired final proportions of the powder mixture according to the invention.

According to other embodiments, the dry mixing method is implemented by means of a plurality of steps of mixing the polyaryl ether ketone(s)-based powder with the nucleating charge in powder form. In particular, a powder mixture in which the nucleating charge is in a greater proportion than in the final powder mixture can initially be prepared ( master batch ). This master batch can then be mixed one or more times with polyaryl ether ketone(s)-based powder in order to obtain the desired proportion of nucleating charge.

According to preferred embodiments, the dry mixture of powders according to the invention is essentially constituted, or constituted of said powder based on polyaryletherketone(s) and said nucleating charge in powder form.

Uses

The powders according to the invention can be used in several manufacturing processes, including the manufacturing processes listed non-exhaustively below.

The processes for constructing layer-by-layer objects by sintering caused by electromagnetic radiation(s), in particular by infrared radiation and laser radiation, are well known to those skilled in the art. With reference to the , the laser sintering device 1 comprises a sintering enclosure 10 in which are arranged a feed tank 40 containing the powder composition (dry mixture of powders according to the invention) to be sintered, a horizontal plate 30 for supporting the three-dimensional object 80 under construction and a laser 20. The powder composition is taken from the feed tank 40 and deposited on the horizontal plate 30, forming a thin layer 50 of powder composition constituting the three-dimensional object 80 under construction. A compactor/scraper roller (not shown) ensures good uniformity of the layer 50 of powder composition. The layer 50 of powder composition, under construction, is heated using infrared radiation 100 to reach a substantially uniform temperature equal to a predetermined construction temperature Tc. In traditional construction processes for sintering PAEK(s)-based powders, Tc is generally about 20°C lower than the melting temperature of the powder, as measured by DSC in the first heating with a temperature ramp equal to 20°C/min. In some cases Tc can even be lower. The energy required to sinter the PAEK(s)-based powder particles at different points of the layer 50 of powder composition is then provided by laser radiation 200 from the laser 20 movable in the (xy) plane, according to a geometry corresponding to that of the object. The molten powder incorporates the nucleating charge, then re-solidifies forming a sintered part 55 while the rest of the layer 50 of powder composition remains in the form of unsintered powder composition 56. Several passes of laser radiation 200 may be necessary in some cases. Then, the horizontal plate 30 is lowered along the (z) axis by a distance corresponding to the thickness of a layer of powder composition, and a new layer is deposited. The laser 20 provides the energy necessary to sinter the PAEK(s)-based powder particles according to a geometry corresponding to this new slice of the object and so on. The procedure is repeated until the object 80 has been manufactured. Once the object 80 is finished, it is removed from the horizontal plate 30 and the unsintered powder composition 56 can be sieved before being returned, if necessary, to the feed bin 40 to serve as recycled powder.

The dry powder mixtures according to the invention can also be used in surface coating processes, in particular for metal surfaces. Different processes can be used to obtain a coating on a metal part. Examples include dipping in a fluidized bed, for which the metal part is heated and then dipped in the fluidized powder bed. It is also possible to carry out so-called electrostatic powdering (electrically charged powder powdered on a metal part connected to the ground), in which case a post-heat treatment is carried out to produce the coating. An alternative is to carry out the powdering on a previously heated part, which makes it possible to eliminate the heat treatment after powdering. Finally, it is possible to carry out flame powdering, in which case the powder is sprayed molten onto a possibly preheated metal part.

The dry powder mixes according to the invention can also be used in powder compression processes. These processes are generally used to produce thick parts. In these processes, the powder is first loaded into a mold, then compacted and finally melted to produce the part. Finally, suitable cooling, often quite slow, is carried out in order to limit the presence of internal stresses in the part.

Finally, the dry powder mixtures according to the invention can also be used for impregnating fibers with a resin powder for the manufacture of semi-finished products, the powder being able to be used in a fluidized bed or dispersed in an aqueous solution.

Characterization of manufactured objects

• une taille maximale de sphérulite au moins 2 fois inférieure, à celle d’un objet obtenu selon le même procédé utilisant une composition non additivée (poudre à base de PAEK(s) uniquement) ;
• un taux de cristallinité comparable à celui d’un objet obtenu selon le même procédé utilisant une composition non additivée (poudre à base de PAEK(s) uniquement) ;
• un allongement à la rupture supérieur d’au moins 5%, par rapport à celui d’un objet obtenu selon le même procédé utilisant une composition non additivée (poudre à base de PAEK(s) uniquement) ;
• une contrainte à la rupture supérieure d’au moins 5%, par rapport à celle d’un objet obtenu selon le même procédé utilisant une composition non additivée (poudre à base de PAEK(s) uniquement) ;

The objects manufactured from one of the aforementioned manufacturing processes, for example a process for constructing layer-by-layer objects by sintering caused by electromagnetic radiation(s), using the mixture of powders according to the invention (additive composition) have at least one, and according to certain embodiments all, of the following properties:

• a maximum spherulite size at least 2 times smaller than that of an object obtained by the same process using a non-additive composition (powder based on PAEK(s) only);
• a crystallinity rate comparable to that of an object obtained using the same process using a non-additive composition (powder based on PAEK(s) only);
• an elongation at break greater than at least 5%, compared to that of an object obtained according to the same process using a non-additive composition (powder based on PAEK(s) only);
• a breaking stress at least 5% higher than that of an object obtained by the same process using a non-additive composition (powder based on PAEK(s) only);

• un taux de cristallinité supérieur ou égal à 10%, ou supérieur ou égal à 12%, ou supérieur ou égal à 14%, tel que mesuré par diffusion des rayons X aux grands angles (WAXS) ;
• un allongement à la rupture d’au moins 2,5% et/ou une contrainte à la rupture d’au moins 90 MPa, tels que mesurés éprouvettes de type 1BA selon la norme ISO 527-1 :2019, à 23°C, avec une vitesse de traverse de 1mm/min.
• une taille maximale de sphérulites inférieure à 10 µm.

Objects manufactured by a process for building layer-by-layer objects by sintering induced by electromagnetic radiation(s) from a mixture of powders in which the poly-aryl-ether-ketone is a PEKK, in particular a copolymer essentially consisting of or consisting of isophthalic and terephthalic repeating units, and preferably having a T:I ratio of 55:45 to 65:35, advantageously have the following properties:

• a crystallinity rate greater than or equal to 10%, or greater than or equal to 12%, or greater than or equal to 14%, as measured by wide-angle X-ray scattering (WAXS);
• an elongation at break of at least 2.5% and/or a stress at break of at least 90 MPa, as measured by type 1BA specimens according to ISO 527-1:2019, at 23°C, with a crosshead speed of 1mm/min.
• a maximum spherulite size of less than 10 µm.

Examples

Raw materials:

• Polyetherketoneketone with a T/I ratio of 60/40: KEPSTAN®, grade PEKK 6000, marketed by Arkema. The polyetherketoneketone used has a viscosity of 820 Pa.s, at 380°C and at 1Hz in plane-plane geometry. The polyetherketoneketone used is in the form of a powder with a particle size distribution such that D ₁₀ = 23 microns, D ₅₀ = 53 microns and D ₉₀ = 113 microns, the latter being suitable for a laser sintering process.
• Talc 1: Jetfine® 1A talc, marketed by Imerys. This talc has a particle size distribution such that d ₅₀ = 3.5 µm and d ₉₅ = 7 µm;
• Talc 2: Jetfine® 07 talc, marketed by Imerys. This talc has a particle size distribution such that d ₅₀ = 2.5 µm and d ₉₅ = 5.2 µm;
• Talc 3: Talc Nano-ace® D1000, marketed by the company Nippon Talc. This talc has a particle size distribution such that d ₅₀ = 1.0 µm.
• Talc 4: Talc SG2000®, marketed by the company Nippon Talc. This talc has a particle size distribution such that d ₅₀ = 0.85 µm.
• Talc 5: Talc Nano-ace® D600, marketed by the company Nippon Talc. This talc has a particle size distribution such that d ₅₀ = 0.60 µm.
• NC: Ketjenblack® EC-600JD carbon black marketed by the company Nouryon. This carbon black has aggregates of approximately 0.1 µm to 1 µm in size. It also has a BET of 1400 m ² /g.
• Silica 1: Hydrophilic pyrogenic silica Aerosil® R150, marketed by the company Evonik. This silica has aggregates of size of the order of 0.1 µm. It has a BET of 135-165 m ² /g.

Compositions:

Dry-blends of polyetherketoneketone powder and a nucleating charge were prepared using a Magimix mixer, with a mixing time of 100 s.

The composition of the different mixtures (#2 - #10, #11c) is presented in Table 1.

Nucleant %wt #1c - - #2 Talc 1 0.5 #3 Talc 1 1 #4 Talc 2 0.5 #5 Talc 3 0.5 #6 Talc 3 1 #7 Talc 4 0.5 #8 Talc 5 1 #9 NC 0.5 #10 NC 1 #11c Silica 1 1

Composition #1c corresponds to the non-additive powder, composed only of polyetherketoneketone.

Estimation of the size of the spherulites:

A simulation of a laser sintering process of powders was implemented by placing each mixture in an ARES G2 rheometer, marketed by the company TA Instrument. More precisely, the compositions were heated to 380°C to melt the PEKK (simulating laser heating), then rapidly cooled to 285°C (simulating re-solidification), and finally cooled at a ramp of 0.5°C/min to a temperature of 165°C (simulating slow cooling to the bath temperature) (see temperature profile as a function of time at ).

The objects resulting from the simulation of a sintering process were observed under an optical microscope on microtome sections of 3 µm thickness. The maximum size of the spherulites was measured. The crystallinity of these objects was also measured, by WAXS.

The results are presented in Table 2

Maximum spherulite size (µm) Crystallinity (%) #1c 20 18 #2 10 18 #3 9 18 #4 9 18 #5 7 18 #6 3 18 #7 8 18 #8 5 18 #9 7 18 #10 5 18 #11c 13 18

There represents the optical microscope view of a microtome section of the object resulting from the simulation of the sintering process with composition #1c. The maximum spherulite size is 20 µm (circle surrounding this spherulite shown).

ISO 527/1BA type specimens are printed in the xy plane using a P810® printer, marketed by EOS. The construction temperature is set at 285°C and the laser energy at 29 mJ/mm ² .

The breaking stress for a non-additive PEKK powder (composition #1c) is 85 MPa and the elongation at break is 2.3%.

In comparison, the breaking stress of a mixture of PEKK powder and 1% by weight of talc (notably composition #6) is greater than 90 MPa. Its elongation at break is greater than 2.5%.

Claims (15)

Dry mixture of powders comprising:

• a powder based on poly-aryl-ether-ketone(s) having a volume-weighted particle size distribution, measured by laser diffraction, according to ISO 13320:2009, such that the median diameter D50 is such that D50 ≤ 300 µm, and
• a nucleating charge in powder form, the nucleating charge being chosen from a silicate, a carbon material, or their mixture, the nucleating charge representing from 0.1% to 2% by weight, relative to the total weight of powder based on poly-aryl-ether-ketone(s) and nucleating charge.

Powder mixture according to claim 1, in which said nucleating charge represents from 0.5% to 1.5% by weight, and preferably from 0.8% to 1.2% by weight, relative to the total weight of powder based on poly-aryl-ether-ketone(s) and nucleating charge. A powder mixture according to any one of claims 1 and 2, wherein the poly-aryl-ether-ketone(s) based powder consists essentially of or consists of poly-aryl-ether-ketone(s). A powder mixture according to any one of claims 1 to 3, wherein the poly-aryl-ether-ketone is a polyetherketoneketone. A powder mixture according to any one of claims 1 to 4, wherein the poly-aryl-ether-ketone(s) based powder has a volume-weighted particle size distribution, measured by laser diffraction, according to ISO 13320:2009, such that the median diameter D50 has a value of 40 µm to 80 µm. A powder mixture according to any one of claims 1 to 5, wherein the nucleating filler is a talc. A powder mixture according to any preceding claim, wherein the nucleating charge has a volume-weighted particle size distribution, measured by laser diffraction, according to ISO 13320:2009, such that the median diameter d50 is such that d ₅₀ ≤ 10 µm, and preferably such that d ₅₀ ≤ 5 µm. A powder mixture according to any preceding claim, wherein the nucleating agent has a volume-weighted particle size distribution, measured by laser diffraction, according to ISO 13320:2009, such that the median diameter d50 is such that d ₅₀ ≤ 2 µm. Powder mixture according to any one of claims 7 and 8, in which the ratio D ₅₀ /d ₅₀ is between 10 and 500, preferably between 25 and 250, and more preferably between 40 and 150. A powder mixture according to any preceding claim, wherein the nucleating charge is a carbonaceous material having a BET specific surface area greater than or equal to 200 g/m ² . A powder mixture according to any preceding claim, wherein the nucleating agent is a carbon material selected from the list consisting of carbon black, carbon nanotubes, graphene, or a mixture thereof. A powder mixture according to any preceding claim, wherein the viscosity of the polyaryl ether ketone(s) of the polyaryl ether ketone(s) powder is selected from the range of 400 Pa.s to 1000 Pa.s, as measured at 380°C and 1 Hz in plane/plane geometry. Use of a mixture of powders according to any one of claims 1 to 12, in a process for constructing layer-by-layer objects by sintering caused by electromagnetic radiation(s). Object manufactured from a process using a mixture of powders according to any one of claims 1 to 12, said object having a maximum spherulite size at least 2 times smaller than that of an object obtained from the same process but using only the powder based on poly-aryl-ether-ketone(s) present in said mixture of powders. An object manufactured from a process using a mixture of powders according to any one of claims 1 to 12, said object having an elongation at break greater than at least 5% and/or a stress at break greater than at least 5%, compared to that(s) of an object obtained from the same process but using only the powder based on poly-aryl-ether-ketone(s) present in said mixture of powders.