FILLED POLYARYL ETHER KETONE POWDER, MANUFACTURING METHOD THEREFOR AND USE THEREOF

Abstract

A powder with a volume-weighted particle size distribution, with a median diameter D50 ranging from 40 to 120 micrometers, including at least one polyaryl ether ketone and at least one filler, in which: said at least one polyaryl ether ketone forms a matrix incorporating, at least partly, said at least one filler, and said filler has a Stokes equivalent spherical diameter distribution with a median diameter d′50 of less than or equal to 5 micrometers. Also a powder manufacturing process and the use thereof in a process for the layer-by-layer construction of objects by electromagnetic radiation-mediated sintering.

Claims

1. A powder having a volume-weighted particle size distribution, measured by laser diffraction, according to the standard ISO 13320: 2009, with a median diameter D50 ranging from 40 to 120 micrometers, comprising at least one polyaryl ether ketone (PAEK) and at least one filler, in which: said at least one polyaryl ether ketone forms a matrix incorporating, at least partly, said at least one filler, and said filler has a Stokes equivalent spherical diameter distribution, measured by X-ray with gravitational liquid sedimentation, according to the standard ISO 13317-3: 2001, with a median diameter d′50 of less than or equal to 5 micrometers.

2. The powder as claimed in claim 1, in which said filler has a Stokes equivalent spherical diameter distribution with a median diameter d′50 of less than or equal to 2.5 micrometers.

3. The powder as claimed in claim 1, in which the mass ratio of said filler to said at least one PAEK is from 1:9 to 1:1.

4. The powder as claimed in claim 1, in which said at least one PAEK and said at least one filler together represent at least 60% of the total weight of the powder.

5. The powder as claimed in claim 1, in which said at least one PAEK is a statistical copolymer of polyether ketone ketone (PEKK), consisting essentially of a terephthalic unit and an isophthalic unit, the formula of the terephthalic unit (T) being: ##STR00007## the formula of the isophthalic unit (I) being: ##STR00008##

6. The powder as claimed in claim 5, in which the mass percentage of terephthalic units relative to the sum of the terephthalic and isophthalic units is from 55% to 65%.

7. The powder as claimed in claim 1, in which said at least one PAEK is a copolymer consisting essentially of: unit(s) of formula: -Ph-O-Ph-O-Ph-C(O)—; and unit(s) of formula: -Ph-O-Ph-Ph-O-Ph-C(O)—, in which Ph represents a phenylene group and —C(O)— represents a carbonyl group, each of the phenylenes possibly being, independently, of the ortho, meta or para type.

8. The powder as claimed in claim 1, in which said filler is a mineral filler.

9. The powder as claimed in claim 1, in which said filler has a shape coefficient C of greater than or equal to 2, said shape coefficient C being defined by the following formula: $C=\frac{D^{\prime }50-d^{\prime }50}{d^{\prime }50};$ in which D′50 denotes the volume-weighted median diameter of the filler particles, measured according to the standard ISO 13320: 2009 and in which d′50 denotes the median Stokes equivalent spherical diameter of the filler particles, measured by X-ray with gravitational liquid sedimentation, according to the standard ISO 13317-3: 2001.

10. A powder manufacturing process comprising: supplying at least one polyaryl ether ketone (PAEK) and supplying at least one filler, said at least one filler having a Stokes equivalent spherical diameter distribution, measured by X-ray with gravitational liquid sedimentation, according to the standard ISO 13317-3: 2001, with a median diameter d′50 of less than or equal to 5 micrometers; extrusion-granulation of said at least one polyaryl ether ketone (PAEK) with said at least one filler so as to form granules; and milling of the granules to obtain a powder having a particle size distribution, measured by laser diffraction, according to the standard ISO 13320: 2009, with a median diameter D50 ranging from 40 to 120 micrometers.

11. The process as claimed in claim 10, further comprising: the heat treatment of the granules before the milling step to enable at least partial crystallization of said at least PAEK.

12. A process for the layer-by-layer construction of objects by electromagnetic radiation-mediated sintering, in which a powder as claimed in claim 1 is used.

13. An object which may be obtained via the process as claimed in claim 12, wherein it has, in at least one direction, a tensile elastic modulus of greater than or equal to 7 GPa, on a specimen of 1BA type, at 23° C., with a travelling speed of 1 mm/minute, according to the standard ISO 527-2: 2012.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0063] FIG. 1 schematically represents a device for performed a process for the layer-by-layer construction of a three-dimensional object by sintering in which the powder according to the invention may be used.

DETAILED DESCRIPTION OF THE INVENTION

[0064] Polyaryl Ether Ketones

[0065] The polyaryl ether ketone(s) (PAEK(s)) of the powders according to the invention include units having the following formulae:

(—Ar—X—) and (—Ar.sub.1—Y—),

[0066] in which: [0067] Ar and Ar.sub.1 each denote a divalent aromatic radical; Ar and Ar.sub.1 may preferably be chosen from 1,3-phenylene, 1,4-phenylene, 4,4′-biphenylene, 1,4-naphthylene, 1,5-naphthylene and 2,6-naphthylene; [0068] X denotes an electron-withdrawing group; it may preferably be chosen from the carbonyl group and the sulfonyl group; [0069] Y denotes a group chosen from an oxygen atom, a sulfur atom or an alkylene group, such as —(CH).sub.2— and isopropylidene.

[0070] In these units X and Y, at least 50%, preferably at least 70% and more particularly at least 80% of the groups X are a carbonyl group, and at least 50%, preferably at least 70% and more particularly at least 80% of the groups Y represent an oxygen atom.

[0071] According to a preferred embodiment, 100% of the groups X denote a carbonyl group and 100% of the groups Y represent an oxygen atom.

[0072] Advantageously, the PAEK(s) of the powders may be chosen from: [0073] a polyether ketone ketone, also known as PEKK; a PEKK comprises one or more units of formula: -Ph-O-Ph-C(O)-Ph-C(O)—; [0074] a polyether ether ketone, also known as PEEK; a PEEK comprises one or more units of formula: -Ph-O-Ph-O-Ph-C(O)—; [0075] a polyether ketone, also known as PEK; a PEK comprises one or more units of formula: -Ph-O-Ph-C(O)—; [0076] a polyether ether ketone ketone, also known as PEEKK; a PEEKK comprises one or more units of formula: -Ph-O-Ph-O-Ph-C(O)-Ph-C(O)—; [0077] a polyether ether ether ketone, also known as PEEEK; a PEEEK comprises one or more units of formula: -Ph-O-Ph-O-Ph-O-Ph-C(O)—; [0078] a polyether diphenyl ether ketone, also known as PEDEK; a PEDEK comprises one or more units of formula: -Ph-O-Ph-Ph-O-Ph-C(O)—; [0079] mixture(s) thereof; and [0080] copolymer(s) thereof.

[0081] In the formulae of the units of the above list, Ph represents a phenylene group and —C(O)— represents a carbonyl group, each of the phenylenes possibly being, independently, of the ortho (1-2), meta (1-3) or para-(1-4) type, preferentially of meta or para type.

[0082] In addition, defects, end groups and/or monomers may be incorporated in very small amount into the polymers as described in the above list, without, however, having an incidence on their performance.

[0083] In certain embodiments, said at least one PAEK is a PEKK. The PEKK may be a copolymer consisting essentially of, preferentially consisting of, “I type” (“isophthalic type”) units, of formula:

##STR00003##

[0084] and “T type” (“terephthalic type”) units, of formula:

##STR00004##

[0085] The mass proportion of T units, relative to the sum of the T and I units of the PEKK(s), may range 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%; or from 85% to 90%; or from 90% to 95%; or from 95% to 100%. The choice of the mass proportion of T units relative to the sum of the T and I units is one of the factors which makes it possible to adjust the melting point and the rate of crystallization at a given temperature of the PEKK. A given mass proportion of T units relative to the sum of the T and I units can be obtained by adjusting the respective concentrations of the reagents during the polymerization, in a manner known per se.

[0086] According to advantageous embodiments, the sum of the terephthalic and isophthalic units in the PEKK is from 55% to 65%; preferentially, the mass percentage of terephthalic units relative to the sum of the terephthalic and isophthalic units is about 60%.

[0087] In certain embodiments, said at least one PAEK is a PEEK-PEDEK copolymer. The PEEK-PEDEK copolymer may consist essentially of, and preferentially may consist of, units of formula:

##STR00005##

and

[0088] units of formula:

##STR00006##

[0089] The molar proportion of units (III), relative to the sum of the units (III) and (IV) of PEEK-PEDEK, may range from 0% to 5%; or from 5% to 10%; or from 10% to 15%; 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%; or from 85% to 90%; or from 90% to 95%; or from 95% to 100%. The choice of the molar proportion of units (III) relative to the sum of the units (III) and (IV) is one of the factors which makes it possible to adjust the melting point and the rate of crystallization at a given temperature of the PEEK-PEDEK copolymer. A given molar proportion of units (III) relative to the sum of the units (III) and (IV) may be obtained by adjusting the respective concentrations of the reagents during the polymerization, in a manner known per se.

[0090] The viscosity index of the PAEK(s), measured as a solution at 25° C. in aqueous sulfuric acid solution at 96% by mass according to the standard ISO 307: 2019, may be from 0.65 dl/g to 1.15 dl/g, preferentially from 0.70 dl/g to 1.05 dl/g and more preferably from 0.70 dl/g to 0.92 dl/g.

[0091] Fillers

[0092] The at least one filler in the powder according to the invention has a Stokes equivalent spherical diameter distribution, measured by X-ray with gravitational liquid sedimentation, according to the standard ISO 13317-3: 2001, with a median diameter d′50 of less than or equal to 5 micrometers.

[0093] The filler may notably have a particle size distribution with a median diameter d′50 of less than or equal to 2.5 micrometers. In certain cases, the filler may have a median diameter d′50 of less than or equal to 2 micrometers, or less than or equal to 1.5 micrometers, or alternatively less than or equal to 1 micrometer. The median diameter d′50 of the filler is generally not less than 0.1 micrometer.

[0094] In certain embodiments, the median diameter d′50 is from 0.1 to 5.0 micrometers, or from 0.25 to 4.0 micrometers, or alternatively from 0.5 to 3.0 micrometers. The median diameter d′50 may notably be from 0.1 to 0.5 micrometer, or from 0.5 to 1.0 micrometer, or from 1.0 to 1.5 micrometers; or from 1.5 to 2.0 micrometers; or from 2.0 to 2.5 micrometers, or from 2.5 to 3.0 micrometers, or from 3.0 to 3.5 micrometers, or from 3.5 to 4.0 micrometers, or from 4.0 to 4.5 micrometers, or alternatively from 4.5 to 5.0 micrometers.

[0095] Advantageously, the filler is a mineral filler.

[0096] Advantageously, the filler is a reinforcing filler, i.e. a filler which can improve the stiffness, notably the tensile elastic modulus and/or the breaking strength of said at least one polyaryl ether ketone (PAEK).

[0097] The filler may comprise a calcium carbonate (calcite).

[0098] The filler may also comprise a silica. The filler may notably be pure silica (SiO.sub.2), a synthetic silica, a quartz or a diatomaceous flour.

[0099] The filler may also comprise a talc.

[0100] The filler may also comprise a wollastonite.

[0101] Finally, the filler may comprise a clay or an aluminosilicate. The filler may notably be a kaolin, a slate flour, vermiculite or a mica.

[0102] The filler is advantageously a talc. Talc has the advantage of having a low cost price and of affording advantageous reinforcing properties for an object obtained from a powder according to the invention.

[0103] The filler is preferentially nonspherical. It may be characterized by its shaped coefficient C, C advantageously being greater than or equal to 2. The shape coefficient C is generally not greater than 20.

[0104] Powder Manufacturing Process

[0105] In the process for manufacturing powders according to the invention, the polyaryl ether ketone(s) and the filler(s) are blended and then extruded.

[0106] According to a first embodiment, the at least one filler and the at least one polyaryl ether ketone are dry-blended and introduced into the main hopper of the extruder. According to a more advantageous second embodiment, the at least one polyaryl ether ketone is introduced into the main hopper whereas the at least one filler is introduced by side feeding and added to the molten polyaryl ether ketone. This has the advantage of preventing the filler(s) from being excessively damaged during their passage through the extruder.

[0107] Any extruder suitable for the extrusion of high-melting polymers may be used. A person skilled in the art is, furthermore, capable of adapting the extrusion conditions as a function of the polymer used. An example of an extruder is a “Labtech” twin-screw extruder with a screw diameter of 26 mm and an L/D ratio of 40.

[0108] The extruded mixture is subdivided so as to form granules.

[0109] The granules are then optionally heat-treated so as to increase the crystallinity of the polyaryl ether ketone(s). The reason for this is that high crystallinity of the granules makes it possible to facilitate the following milling step. Advantageously, the fraction of the PAEK in the powder has a heat of fusion, measured on the first heating and using a heating rate of 20° C./minute according to the standard ISO 11357-2: 2013, ranging from 20 to 50 J/g (PAEK), preferentially ranging from 25 to 40 J/g (PAEK).

[0110] The heat treatment is advantageously performed at a much lower temperature than the melting point of the powder. According to a variant in which the powder is a powder based on PEKK with a mass percentage of terephthalic units relative to the sum of the terephthalic and isophthalic units of from 55% to 65%, the heat treatment may be performed at a temperature of from 180° C. to 220° C.

[0111] The granules are then milled to a powder so as to obtain a powder having a particle size distribution with a median diameter D50 ranging from 40 to 120 micrometers. The granules according to the invention are more brittle than PAEK granules incorporating carbon fibers (for the same volume content of filler): the milling step is thereby facilitated. In addition, the PAEK granules incorporating a filler, advantageously a talc, having a d′50 of less than or equal to 5 micrometers are generally much less abrasive during milling than PAEK granules incorporating carbon fibers.

[0112] The milling may be performed at a temperature below −20° C., preferentially at a temperature below −40° C., by cooling with liquid nitrogen, or liquid carbon dioxide, or cardice, or liquid helium. The mill used is advantageously a pin mill, notably a counter-rotating pin mill, or alternatively an impact mill, such as a hammer mill, or alternatively a vortex mill. The mill may be equipped with a screen onto which the milled particles are sent, the particles passing through the screen having the desired size. The particles retained by the screen may be conveyed back into the mill to undergo longer milling.

[0113] Powders

[0114] The mass ratio of the at least one filler to the at least one PAEK may be from 1:9 to 1:1. For a mass ratio of less than 1:9, the gain in mechanical properties, notably the increase in the elastic modulus value, of an object manufacture from the powder is generally not substantial relative to an object manufactured from unfilled PAEK powder. For a mass ratio of greater than 1:1, the object manufactured from the powder is generally too brittle. The mass ratio of the at least one filler to the at least one PAEK is advantageously from 1:4 to 3:7.

[0115] The mass ratio of the at least one filler to the at least one PAEK may also be from 3:7 to 2:3, or alternatively from 2:3 to 1:1.

[0116] The PAEK(s) and the filler(s) together represent at least 60%, or at least 70%, or at least 80%, or at least 85%, or at least 90%, or at least 92.5%, or at least 95%, or at least 97.5%, or at least 98%, or at least 98.5%, or at least 99% or at least 99.5% or 100% of the total weight of the powder.

[0117] In addition to the PAEK(s) and the filler(s), the powder may comprise another polymer not belonging to the PAEK family, notably other thermoplastic polymers. The powder may also comprise additives. Among the additives, mention may be made of flow agents, stabilizers (light, in particular UV, and heat stabilizers), optical brighteners, dyes, pigments and energy-absorbing additives (including UV absorbers). The additives generally represent less than 5% by weight relative to the total weight of powder, and preferably represent less than 1% by weight relative to the total weight of powder.

[0118] Use of the Powders

[0119] The powders according to the invention may be used in numerous applications, including the nonexhaustive applications below.

[0120] The powders according to the invention may be used in processes for the electromagnetic radiation-mediated layer-by-layer sintering construction of objects. An infrared radiation and laser radiation sintering process is illustrated in FIG. 1 and has already been described in the section dealing with the prior art. The powders according to the invention may also be used in processes for coating metal surfaces. Various processes may be used in order finally to obtain a coating on metal parts. Mention may be made of dipping in the fluidized bed for which the metal part is heated and then dipped into the fluidized powder bed. It is also possible to perform electrostatic powder coating (charged powder dusted onto an earthed metal part); in this case, a thermal post-treatment is performed to produce the coating. An alternative is to perform the powder coating on a preheated part, which makes it possible to remove the heat treatment after powder coating. Finally, it is possible to perform flame powder coating; in this case, the powder is melt-sprayed onto an optionally preheated metal part.

[0121] The powders according to the invention may also be used in powder compression processes. These processes are generally used for producing thick parts. In these processes, the powder is first loaded into a mold, compacted and then melted to produce the part. Finally, suitable cooling (usually relatively slow) is performed to eliminate the internal stresses in the part.

[0122] Experimental Data

[0123] The powders of the examples below were manufactured by compounding (extrusion-granulation) of various compositions, heat treatment and then milling. The compounding was performed on a “Labtech” twin-screw extruder having a screw diameter of 26 mm and an L/D ratio of 40, with a flat temperature profile at 350° C. and a screw speed of 400 rpm. Granules with a length equal to about 2 mm were obtained.

[0124] In the case of manufacturing filled powders (carbon fibers or talc), the fillers are introduced during the compounding by side feeding. The granules obtained are termed as being “filled”.

[0125] The granules were subsequently heat treated for 9 hours at 180° C.

[0126] Finally, the heat-treated granules were milled in a Mikropull 2DH® cryogenic hammer mill cooled with liquid nitrogen, the mill furthermore being equipped with a grate with 500-μm round holes.

Example 1 (Comparative)

[0127] The first composition used is a polyether ketone ketone with a mass proportion of T units relative to the sum of the T and I units of 60%, with a viscosity index of 0.75 dl/g at 25° C., in an aqueous sulfuric acid solution at 96% by mass, according to the standard ISO 307: 2019 applied to a PAEK. This polyether ketone ketone is sold by the company Arkema under the name Kepstan®.

[0128] The granules obtained with the composition according to example 1 were able to be milled to obtain a D50, measured using a Malvern Mastersizer 2000® diffractometer, of 500 microns.

Example 2 (Comparative)

[0129] The second composition used consists of the polyether ketone ketone according to example 1 and of carbon fibers, the carbon fibers representing 23% by weight of the composition.

[0130] The carbon fibers used were Tenax®-A fibers, of “HT M100” type, i.e. fibers with fiber lengths of between 60 micrometers and 100 micrometers.

[0131] The granules obtained with the composition according to example 2 were able to be milled to obtain a D50, measured using a Malvern Mastersizer 2000® diffractometer, of 160 microns.

Example 3 (According to the Invention)

[0132] The third composition used consists of the polyether ketone ketone according to example 1 and of Jetfine® 0.7C talc sold by the company Imerys, the talc representing 30% by weight of the composition (so as to ensure a volume proportion of filler equivalent to that of example 2).

[0133] Jetfine® 0.7C talc has a d′50, measured on a Sedigraph III Plus® machine, of 0.7 micron and a D′50, measured on a Malvern Mastersizer 2000® diffractometer, of 2.5 microns, i.e. a shape coefficient C equal to: 2.6.

[0134] The granules obtained with the composition according to example 3 were able to be milled to obtain a D50, measured using a Malvern Mastersizer 2000® diffractometer, of 120 microns.

Example 4 (According to the Invention)

[0135] The third composition used consists of the polyether ketone ketone according to example 1 and of Steaplus® HAR T77 talc sold by the company Imerys, the talc representing 30% by weight of the composition (so as to ensure a volume proportion of filler equivalent to that of example 2).

[0136] Steaplus® HAR T77 talc has a d′50, measured on a Sedigraph III Plus® machine, of 2.2 microns and a D′50, measured on a Malvern Mastersizer 2000® diffractometer, of 10.5 microns, i.e. a shape coefficient C equal to: 3.8.

[0137] The granules obtained with the composition according to example 4 were able to be milled to obtain a D50, measured using a Malvern Mastersizer 2000® diffractometer, of 110 microns.

[0138] The results for the milling of the powders according to examples 3 and 4 (according to the invention) relative to the results for the milling of the powders according to examples 1 and 2 (comparative examples) show that the milling of PEKK granules incorporating a talc filler with a d′50 of less than or equal to 5 micrometers is facilitated in comparison with unfilled PEKK granules or PEKK granules incorporating carbon fibers with the same volume content of filler.

Example 6 (Comparative)

[0139] Specimens of 1BA type, according to the standard ISO 527-2: 2012, were manufactured by laser sintering of 6002 PL® powder sold by the company Arkema, in an EOS P800® printer sold by the company EOS. The powder has a D50 equal to 50 μm, measured using a Malvern Mastersizer 2000® diffractometer, and a viscosity index of 0.96 dl/g at 25° C., in aqueous sulfuric acid solution at 96% by mass, according to the standard ISO 307: 2019 applied to a PAEK. Specimens of 1BA type were constructed along the X, Y and Z axes at a construction temperature of 290° C. and with a laser sintering energy of 28 mJ/mm.sup.2.

[0140] Irrespective of the construction axis of the specimens in the laser sintering machine, a tensile elastic modulus of 4 GPa was measured at 23° C., with a travelling speed of 1 mm/minute, according to the standard ISO 527-2: 2012, using an MTS 810® machine sold by the company MTS Systems Corporation, equipped with a mechanical extensometer.

Example 7 (According to the Invention)

[0141] Specimens of 1BA type, according to the standard ISO 527-2: 2012, were manufactured by injection of the powder according to example 3, with a feed temperature of 320° C., a screw outlet temperature of 340° C., a mold temperature of 80° C. and a cycle time of not more than 1 minute.

[0142] A tensile elastic modulus of 9 GPa was measured, at 23° C., with a travelling speed of 1 mm/minute, according to the standard ISO 527-2: 2012, using an MTS 810® machine sold by the company MTS Systems Corporation, equipped with a mechanical extensometer.

[0143] It is considered that the elastic modulus value obtained for a specimen manufactured by injection molding is equal to, or even less than, the value that would be determined for a specimen manufactured by laser sintering. Thus, if the specimen had been manufactured by laser sintering, it would necessarily have a tensile elastic modulus of at least 9 GPa.

Example 8 (According to the Invention)

[0144] Specimens of 1BA type, according to the standard ISO 527-2: 2012, were manufactured by injection molding of the powder according to example 4, according to the same protocol as that of example 7.

[0145] A tensile elastic modulus of 9 GPa was also measured, according to the same protocol as that of example 7.

[0146] Similarly, if the specimen had been manufactured by laser sintering, it would necessarily have a tensile elastic modulus of at least 9 GPa.

[0147] The results for the mechanical tests according to examples 7 and 8 (according to the invention) relative to the results for the mechanical tests according to example 6 (comparative example) show that the mechanical properties of objects obtained from PEKK powders incorporating a talc filler with a d′50 of less than or equal to 5 micrometers are higher than those obtained from unfilled PEKK powders.

[0148] The results for the mechanical tests according to examples 7 and 8 furthermore suggest that the mechanical properties of objects obtained from PEKK powders incorporating a talc filler with a d′50 of less than or equal to 5 micrometers would be of the same order as, or even greater than, those of objects obtained for powders filled with the carbon fibers, the comparison being made for the same volume content of filler. Specifically, the specifications sheet for the material HT-23®, sold by the company Advanced Laser Materials, indicates a tensile elastic modulus along X of 6.5 GPa, along Y of 6.4 GPa and along Z of 5.8 GPa, the values being measured according to ASTM D638. HT-23® is a polyether ketone ketone powder incorporating 23% of carbon fibers and intended for laser sintering applications in printers such as the EOS P 500® and EOS P 810® machines sold by the company EOS.