WO2023067284A1 - Thermoplastic polymer powder for 3d printing by sintering - Google Patents

Abstract

The invention mainly relates to a thermoplastic polymer powder suitable for use in 3D printing by sintering, having: - a volume mean diameter Dv50 of less than 150 μm, a volume mean diameter Dv10 of more than 15 μm and a volume mean diameter Dv90 of less than 300 μm, as measured by laser diffraction according to ISO 13320: 2009, and - a thermal signature characterised by the presence: (i) of two melting peaks Tf1 and Tf2, Tf1 being lower than Tf2, said melting peaks being characterised in that: a. the ratio Formula (I) between the associated enthalpies of fusion, as determined according to NF ISO 11357-3:2018, is less than 0.5; and b. the difference between the two melting peaks (Tf2-Tf1) is less than 40°C; or (ii) of one dissymmetric melt peak, characterised by a ratio σ: Formula (II) in which the extrapolated melting onset temperature Teim, the melting peak temperature Tpm and the extrapolated melting end temperature Tefm are determined on the basis of a DSC thermogram measured with a heating rate of 20°C/min, according to NF EN ISO 11357-3:2018.

Description

Description

Title: Thermoplastic polymer powder for 3D printing by sintering

[Technical area]

This patent application relates to a thermoplastic polymer composition useful for 3D printing by sintering, its method of manufacture and its use in 3D printing by sintering.

[prior technique]

The construction of 3D articles is often used to produce prototypes, models of parts (“rapid prototyping”) or to produce finished parts in small series (“rapid manufacturing”), for example in the fields: automotive, nautical, aeronautics, aerospace, medical (prostheses, hearing systems, cellular tissues...), textiles, clothing, fashion, decoration, boxes for electronics, telephony, home automation, IT, lighting, sport, industrial tools.

Among the techniques for manufacturing 3D articles, the manufacturing process by sintering is particularly interesting. According to this process, a layer of polymer powder is heated and then selectively and briefly irradiated in a chamber by electromagnetic radiation (eg laser beam, infrared radiation, UV radiation), the result being that the particles of powder impacted by the radiation melt. The molten particles coalesce and solidify to lead to the formation of a solid mass. This method can produce, in a simple way, 3D articles by repeatedly irradiating a succession of layers of freshly applied powder.

The quality of the manufactured parts as well as their mechanical properties depend on the characteristics of the polymer powder. Thermoplastic polymers are appreciated for their mechanical properties associated with their thermal and chemical resistance.

A main obstacle to the development of 3D printing by laser sintering is the cost of the powder. This cost of the polymer powder can be reduced substantially if the latter is recyclable, for example by adding a specific quantity of powder already used to a charge of new powder.

The recyclability rate depends in turn on the construction temperature, the temperature to which the powder is exposed during the entire construction process, which can take several hours. Under the effect of temperature, the polymer powder most often evolves, in particular in color and/or in viscosity, thus limiting the interest or even the possibility of its reuse.

However, the construction temperature is also difficult to regulate. Indeed, if the construction temperature is too low, we encounter "curling" phenomena, i.e. a deformation of the part built under the effect of internal stresses appearing when the polymer layers crystallize too quickly. . The appearance of a "curling" most often compromises all the parts built in the enclosure. In addition, one can observe problems of cohesion of the powder bath, necessary for the support of the part under construction, and moreover melting defects which affect the mechanical properties of the printed part. Conversely, when the construction temperature is too high, “caking” phenomena are observed, that is to say agglomeration of the bath of polymer powder under the effect of partial melting of the grains. A powder thus agglomerated cannot be recycled.

It is known to consider the thermal properties of the polymer when developing a powder for 3D printing by sintering. The width of its working window, linked to the gap between the melting peak and the crystallization peak, is of particular importance, particularly in avoiding the problems of “curling” and “caking”. Nevertheless, little interest has been paid until now to the effect of the particular shape of the melting peak and the existence of other peaks apart from the particular cases of polymorphic polymers.

There therefore remains a need to provide a thermoplastic polymer powder having a lower cost while allowing better recyclability.

[Summary of Invention]

The present application is based on the unexpected observation that the use of a polymer powder having a specific thermal signature made it possible to lower the construction temperature. However, reducing the bath temperature makes it possible to limit the aging of the powder, and therefore increases its recyclability. A lower bath temperature also makes it possible to widen the working window for a given polymer, and thus makes it possible to make the printing process more robust, for example with respect to temperature inhomogeneities in the bath, and/or to consider the use of polymers with a low difference between Tf and Te. Also, according to a first aspect, the subject of the invention is a thermoplastic polymer powder suitable for use in p3D printing by sintering, having: an average volume diameter Dv50 of less than 150 μm, an average volume diameter Dv10 greater at 15 μm and an average diameter by volume Dv90 of less than 300 μm, as measured by laser diffraction according to standard ISO 13320: 2009, and a thermal signature characterized by the presence:

(i) two melting peaks Tfi and Tf?, Tfi being less than Tf?, said melting peaks being characterized in that: fi a. the ratio — — between the associated enthalpies of fusion, such as

^Tf2 determined according to standard NF EN ISO 11357-3:2018 is less than 0.5; and B. the difference between the two melting peaks (Tfz-Tfi) is less than 40° C.; Or

(ii) an asymmetrical melting peak, characterized by a ratio o:

(Tefm-Teim) o — - > 2.0

(Tefm-Tpm) where the extrapolated melting onset temperature T _e im, the melting peak temperature T _P m and the extrapolated melting end temperature T _e f _m are determined from a DSC thermogram measured with a heating rate of 20°C/min, according to standard NF EN ISO 11357-3:2018.

Preferably, the thermoplastic polymer powder has a volume-average diameter Dv50 of between 45 and 130 μm.

— compris entre 0.05 et 0.2 est particulièrement

préférée. A powder with a ratio —

— between 0.05 and 0.2 is particularly

favourite.

According to a preferred embodiment, the thermal signature is characterized by the presence of two peaks Tfi and Tf?, the difference between these melting peaks being spread over a temperature interval ranging from 5 to 30°C. Advantageously, it is characterized by an asymmetrical peak exhibiting a ratio o greater than 2.3.

Advantageously, the melting peak(s) Tfi and Tf? spread over a temperature interval ranging from 2 to 40°C, preferably from 5 to 30°C and very particularly from 10 to 20°C. Preferably, the thermoplastic polymer powder comprises at least two distinct thermoplastic polymers.

According to one embodiment, the thermoplastic polymer powder comprises at least two thermoplastic polymers which are distinct by at least one of their properties, in particular by their viscosity or by their chemical nature.

Advantageously, the thermoplastic polymer powder has an inherent viscosity of 0.65 dl/g to 1.8 dl/g.

According to a preferred embodiment, the thermoplastic polymer powder comprises at least one polymer chosen from polyamides and thermoplastic elastomers, and even more preferred from PA 11, PA 12 and polyetherblock amides.

According to a second aspect, the invention relates to a process for manufacturing such a thermoplastic polymer powder, comprising the steps consisting of:

(i) grinding at least one thermoplastic polymer into a powder having a volume average diameter Dv50 of less than 150 μm, a volume average diameter Dv10 of more than 15 μm and a volume average diameter Dv90 of less than 300 μm, such as measured by laser diffraction according to ISO 13320: 2009, and, where applicable,

(ii) mixing said thermoplastic polymer with another thermoplastic polymer, before, during or after step (i), so that the powder obtained from the process has a thermal signature as defined above.

According to a third aspect, the invention relates to the use of a thermoplastic polymer powder as defined above for 3D printing by sintering, in particular by laser sintering.

[Brief description of figures]

The invention will be better understood with regard to the following description and the figures, which show:

Fig. 1: a 3D printing device by sintering of the SLS type (English acronym for “selective laser sintering”, selective laser sintering); Fig. 2: a thermogram of a polyamide powder according to Example 1, showing the heat flux Q. (in W/g) required to heat the sample at the imposed rate of 20°C/min, as a function of the temperature T;

Fig. 3: a thermogram of a polyamide powder according to example 2 showing the heat flux Q. (in W/g) required to heat the sample at the imposed rate of 20°C/min, as a function of the temperature T; And

Fig. 4: a thermogram of a polyamide powder according to example 3 showing the heat flux Q. (in W/g) required to heat the sample at the imposed rate of 20°C/min, as a function of the temperature T.

[Description of Embodiments]

[Definitions]

The term “powder” is understood to denote a solid material in finely divided form, generally in the form of particles of very small size, generally of the order of a few hundred micrometers or less.

The term “melting temperature” is understood to denote the temperature at which an at least partially crystalline compound changes to the viscous liquid state as measured according to standard NF EN ISO 11357-3:2018. Unless otherwise indicated, it is more particularly the melting peak temperature as defined below.

More specifically, the following terms in relation to melting temperature are understood to mean, as defined in ISO 11357-1:2016:

• a “peak” designates the part of the thermogram obtained by Differential Scanning Calorimetry (DSC, English acronym for “Differential Scanning Calorimetry”) which deviates from the base line of the specimen to reach a maximum or a minimum, then which returns to the baseline of the specimen. Such a peak may indicate a first-order transition;

• an “endothermic peak” designates a peak for which the heat flux provided in the crucible of the test piece is greater than that of the reference crucible. This corresponds to a transition that absorbs heat;

• a “base line” designates the part of the thermogram recorded without any transition, in particular here without any first order transition of fusion type. At a transition zone, a virtual baseline can be determined: it is an imaginary line drawn through the transition zone, assuming that the heat due to the transition is zero. The virtual baseline can be drawn by interpolating the specimen baseline with a straight line;

• a “peak area” designates the area bounded by the peak and the interpolated virtual baseline. It is likened to a transition enthalpy, expressed in J/g;

• an “extrapolated melting start temperature” T _e im designates the point of intersection of the interpolated virtual baseline and the tangent at the level of the point of inflection of the start of the peak;

• a “melting peak temperature” T _pm designates the temperature at which the distance is greatest between the thermogram and the virtual baseline during a peak;

• an “extrapolated end temperature” T _e f _m designates the point of intersection of the virtual baseline and the tangent at the end of peak inflection point.

The term “enthalpy of fusion” means the heat necessary to melt the composition, corresponding to the area under the melting peak(s) on the thermogram, measured according to standard NF EN ISO 11357- 3:2018.

The term “Dv50” is understood to mean the value of the diameter of the powder particles so that the cumulative function of distribution of the diameters of the particles, weighted by volume, is equal to 50%. The “Dv50” value is measured by laser diffraction according to the ISO 13320: 2009 standard, for example on a Malvern Mastersizer 2000® diffra cto meter. Similarly, “Dv10” and “Dv90” are respectively the corresponding diameters so that the cumulative function of the diameters of the particles, weighted by the volume, is equal to 10%, and respectively, to 90%. The rules for representing the results of a particle size distribution are given by the ISO 9276 standard - parts 1 to 6.

The term “viscosity” is understood to denote the inherent viscosity as measured according to standard ISO 307:2007. The term “viscosity” is understood to denote the inherent viscosity as measured in a viscometer of the Ubbelohde type according to standard ISO 307:2019, except when using m-cresol as solvent and at a temperature of 20° C. The inherent viscosity of dimension of the inverse of a concentration and is equal to the natural logarithm of the relative viscosity, all divided by the concentration of polymer dissolved in the solvent.

The term “3D printing by sintering” is understood to refer to a technique aimed at producing parts by additive manufacturing, by selectively melting a powder by means of electromagnetic radiation such as a laser or infrared light.

The term "crystallinity rate" means the crystallinity rate as calculated from wide-angle X-ray scattering measurements (WAXS), on a Nano-inXider® type device with the following conditions:

- Wavelength: main line Kctl of copper (1.54 Angstrom).

- Generator power: 50 kV - 0.6 mA.

- Observation mode: transmission

- Counting time: 10 minutes

A spectrum of the scattered intensity as a function of the diffraction angle is thus obtained. 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, we can measure the area of the crystalline peaks (denoted A) and the area of the amorphous halo (denoted AH). The proportion (mass) of crystalline polymer in the sample is estimated by the ratio (A)/(A+AH).

The thermograms to which reference is made in the present application are obtained by differential scanning calorimetric analysis (DSC) according to standard NF EN ISO 11357-3:2018, in the first heating, of approximately 10 mg of composition to be tested, and in using a temperature ramp of 20°C/min. The initial temperature may in particular be approximately 20°C and the final temperature may be approximately 260°C. The thermograms such as those presented in the figures can be obtained using a Q2000 differential scanning calorimeter, marketed by the company TA Instruments.

The indefinite and definite articles such as "un", "une" or "le" or "la" mean in the context of this presentation by default "at least one", and respectively "said at least one" or " said at least one”.

A. Thermoplastic polymer powder

The thermoplastic polymer powder proposed according to the invention has: a volume-average diameter Dv50 of less than 150 μm, a volume-average diameter Dv10 of greater than 15 μm and a volume-average diameter Dv90 of less than 300 μm, as measured by laser diffraction according to standard ISO 13320: 2009, and a signature thermal characterized by the presence:

— entre les enthalpies de fusion associées, telles que(i) two melting peaks Tfi and Tf?, Tfi being less than Tf?, said melting peaks being characterized in that: a. the ratio -

— between the associated enthalpies of fusion, such as

^Tf2 determined according to standard NF EN ISO 11357-3:2018 is less than 0.5; and B. the difference between the two melting peaks (Tfz-Tfi) is less than 40° C.; Or

(ii) an asymmetrical melting peak, characterized by a ratio o:

(Tefm-Teim) o — - > 2.0

(Tefm-Tpm) where the extrapolated melting onset temperature T _e im, the melting peak temperature T _P m and the extrapolated melting end temperature T _e f _m are determined from a DSC thermogram measured with a heating rate of 20°C/min, according to standard NF EN ISO 11357-3:2018.

The thermoplastic polymers capable of being used in the context of the present invention can in particular be chosen from polyolefins such as polypropylene and polyethylene (the olefin base waxes would not fall outside the scope of the invention), polycarbonate, polymethylmethacrylate ( PMMA), polyamides and thermoplastic elastomers such as polyetherblock amides (PEBA), polyesters and polyether blocks (COPE), thermoplastic polyurethanes (TPU) or mixtures thereof.

Aliphatic polyamides, in particular long chain, that is to say comprising at least 8 carbon atoms per amide group, and in particular PA 11 and PA 12 as well as polyetherblock amides are particularly preferred.

Polyetherblock amides are copolymers comprising polyamide blocks and polyether blocks. Preferably, they are linear (non-crosslinked) copolymers.

PEBA copolymers can result from the polycondensation of polyamide (PA) blocks with reactive ends with polyether (PE) blocks with reactive ends. For example, it may be: polyamide blocks with diamine chain ends polycondensed with polyoxyalkylene blocks with dicarboxylic chain ends; polyamide blocks with dicarboxylic chain ends polycondensed with polyoxyalkylene blocks with diamine chain ends; or of polyamide blocks with dicarboxylic chain ends polycondensed with polyetherdiols, the products obtained being in this case polyetheresteramides. The polyamide blocks with dicarboxylic chain ends come, for example, from the condensation of polyamide precursors in the presence of a chain-limiting dicarboxylic acid. The polyamide blocks with diamine chain ends come, for example, from the condensation of polyamide precursors in the presence of a chain-limiting diamine. These polyamide blocks can be homopolyamides or copolyamides. It may in particular be polyamide blocks PA 11, PA 12, PA 6 or a mixture thereof.

The polyether blocks of PEBA essentially comprise or consist of alkylene oxide units. The polyether blocks can be derived from alkylene glycols such as PEG (polyethylene glycol), PPG (propylene glycol), PO3G (polytrimethylene glycol) or PTMG (polytetramethylene glycol), preferably PTMG. They can also be derived from copolyethers comprising different alkylene oxides distributed in the chain in a regular manner, in particular in blocks, or in a random manner. The polyether blocks can also be obtained by oxyethylation of bisphenols, such as bisphenol A. These products are described in particular in document EP 613919 Al. The polyether blocks can also be ethoxylated primary amines. Finally, the polyether blocks can comprise or consist of polyoxyalkylene blocks with ends of NH2 chains. Such blocks can be obtained by cyanoacetylation of polyetherdiols. Such polyethers are sold by the company Huntsman under the name Jeffamine® or Elastamine® (for example Jeffamine® D400, D2000, ED 2003, XTJ 542).

The number-average molar mass (Mn) of the polyamide blocks in the PEBA is preferably from 400 to 1500 g/mol, more preferably from 500 to 1200 g/mol, preferably from 500 to 1000 g/mol. The number-average molar mass (Mn) of the polyether blocks is preferably from 400 to 1500 g/mol, more preferably from 500 to 1200 g/mol, and even more preferably from 500 to 1000 g/mol.

A two-step method for the preparation of PEBA having ester bonds between the PA blocks and the PE blocks is described in the document FR 2846332 Al. of PEBA having amide bonds between the PA blocks and the PE blocks is described in the document EP 1482011 Al. The polyether blocks can also be mixed with polyamide precursors and a diacid chain limiter to prepare PEBAs by a process in one stage.

If the PEBAs generally comprise a polyamide block and a polyether block, they can also comprise two, three, four or even more different blocks.

According to one embodiment, the mass proportion of polyether blocks in the copolymer is at least 50% relative to the total weight of the copolymer. Preferably, the mass proportion of polyether blocks is from 55 to 85% relative to the total weight of the copolymer, and more preferably from 60 to 80% relative to the total weight of the copolymer. The mass proportions of blocks in the copolymer can be determined from the number-average molar masses of the blocks.

The particularly preferred PEBAs are those having an instantaneous hardness (Shore D hardness), as determined according to standard ISO 868:2003, of less than 50 and more preferably between 35 and 45.

Of course, the designation PEBA in the present description of the invention relates both to PEBAX® marketed by Arkema, to Vestamid® marketed by Evonik®, to Grilamid® marketed by EMS, and to Pelestat® type PEBA marketed by Sanyo or any other PEBA from other providers.

According to one embodiment, the thermoplastic polymer powder has an enthalpy of fusion greater than 25 J/g, or from 25 to 30 J/g, or from 30 to 40 J/g, or from 40 to 50 J/g, or 50 to 60 J/g, or 60 to 70 J/g, or 70 to 80 J/g, or 80 to 90 J/g, or 90 to 100 J/g, or 100 to 110 J /g or 110 to 120 J/g or 120 to 130 J/g. Particularly advantageous is a thermoplastic polymer powder having an enthalpy of fusion of between 30 and 110 J/g. More specifically, the enthalpy of fusion varies depending on the polymer being considered. Thus, the enthalpy of fusion for a polyamide may in particular be between 70 and 110 J/g, whereas the enthalpy of fusion for a PEBA will preferably be between 25 and 50 J/g. The thermoplastic polymer powder generally comprises at least 50% by weight of thermoplastic polymer relative to the total weight of powder. According to certain embodiments, the powder comprises at least 75%, 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% by weight of thermoplastic polymer relative to the total weight of the thermoplastic polymer powder of the invention.

According to certain embodiments, the thermoplastic polymer powder can comprise a single thermoplastic polymer, for example only a polyolefin, a polyamide, or even a polyetherblock amide.

Alternatively, the thermoplastic polymer powder may comprise two or more distinct thermoplastic polymers. These polymers can be distinguished in particular by their chemical nature, for example a mixture of polyolefins, polyamides or polyetherblock amides.

According to certain embodiments, the powder according to the invention comprises several polymers, of the same chemical nature or not, distinct by at least one of their properties. These properties may in particular be the viscosity, the crystallinity and the rate of crystallization. Thus, the powder according to the invention may for example comprise a polyamide or polyether block amide and a polyolefin wax.

In order to be suitable for 3D printing by sintering, the thermoplastic polymer powder must meet certain criteria, particularly in terms of particle size.

According to the invention, the thermoplastic polymer powder has a volume-average diameter Dv50 of less than 150 μm. According to certain embodiments, the thermoplastic polymer powder has a volume-average diameter Dv50 of between 45 and 130 μm, in particular between 50 and 120 μm and very particularly between 55 and 100 μm.

In addition to the average diameter alone, the particle size distribution of the thermoplastic polymer powder can also have a significant impact on the performance in 3D printing by sintering.

Thus, according to the invention, the thermoplastic polymer powder has a volume-average diameter Dv10 greater than 15 μm. According to certain embodiments, the thermoplastic polymer powder has a volume-average diameter Dv10 of between 20 and 60 μm, in particular between 25 and 45 μm and very particularly between 30 and 40 μm.

Thus, according to the invention, the thermoplastic polymer powder has a volume-average diameter Dv90 of less than 300 μm. According to certain embodiments, the thermoplastic polymer powder has a volume-average diameter Dv90 of between 100 and 300 μm, in particular between 120 and 250 μm and very particularly between 140 and 200 μm. The polymer powder compositions according to the invention are moreover characterized by a specific thermal signature. This signature is special because the melting peak is not symmetrical and unique as it is conventionally. According to the invention, this thermal signature comprises either two melting peaks, or an asymmetrical melting peak, for example due to the presence of another transition close to the melting point.

This type of thermal signature is observed for example when other phase transitions are located close to the melting point. Usually, such phase transitions are considered as a risk of disturbing or even prohibiting 3D printing by sintering of satisfactory quality.

However, it turned out unexpectedly that such thermal signatures can, in that they allow the onset of melting at a lower temperature, make it possible to lower the construction temperature and thus reduce the thermal aging of the powder during the construction process and thus increase the possibilities of reuse, thus considerably reducing the cost of the printing material.

According to the invention, the thermal signature of the thermoplastic polymer powder can be characterized by the presence of two melting peaks Tfi and Tf2, which are close together, that is to say not more than 40° C. apart. one another, and characterized by the fact that the melting peak Tfi at lower temperature is significantly smaller than the melting peak Tf? located at higher temperature, so that the ratio between the enthalpy of fusion associated with these peaks AH?' _x

— — is less than 0.5. H

Alternatively, the thermal signature of the thermoplastic polymer powder can be characterized by the presence of an asymmetrical peak. The asymmetry is expressed by the ratio o as follows:

(Tefm-Teim) o — - > 2.0

(Tefm-Tpm) where the extrapolated melting onset temperature T _e im, the melting peak temperature T _pm and the extrapolated melting end temperature T _e f _m are determined from a DSC thermogram measured with a heating rate of 20°C/min, according to standard NF EN ISO 11357-

3:2018. When the thermoplastic polymer powder has several melting peaks, these preferably spread over a temperature range ranging from 2 to 40° C., preferably from 5 to 30° C. and most particularly from 10 to 20° C. .

Indeed, it is generally preferable that the melting peaks are not too far apart. So, for example in 3D printing by laser melting (SLS), a build temperature, lower than the melting temperature Tfi, too far from the temperature of Tf? requires the use of too much laser power or to pass it several times (multiscan). H f

According to the invention, the ratio between the enthalpy of fusion associated with these peaks — — is less than

0.5. Advantageously, this ratio can be between 0.02 and 0.4, and in particular between 0.05 and 0.2.

According to one embodiment, the enthalpy of fusion associated with the melting peak Tfi is greater than 2 J/g, or from 2 to 5 J/g, or from 5 to 10 J/g, or from 10 to 15 J/ g, or 15 to 20 J/g, or 20 to 25 J/g, or 25 to 30 J/g, or 30 to 35 J/g, or 35 to 40 J/g, or 40 at 50 J/g, or from 50 to 60 J/g or from 60 to 70 J/g. Particularly advantageous is a thermoplastic polymer powder having an enthalpy of fusion associated with the melting peak Tfi of between 2 and 40 J/g.

According to another embodiment, the enthalpy of fusion associated with the melting peak Tf? is greater than 15 J/g, or 15 to 20 J/g, or 20 to 30 J/g, or 30 to 40 J/g, or 40 to 50 J/g, or 50 to 60 J /g, or 60 to 70 J/g, or 70 to 80 J/g, or 80 to 100 J/g, or 100 to 120 J/g, or 120 to 130 J/g. Particularly advantageous is a thermoplastic polymer powder exhibiting an enthalpy of fusion associated with the melting peak Tf? between 20 and 130 J/g.

When the thermoplastic polymer powder has an asymmetrical peak, this is characterized by a value of o greater than 2.0, and preferably greater than 2.3. Advantageously, o is between 2.0 and 6.0, in particular between 2.2 and 5.0, and very particularly between 2.3 and 4.0.

According to some embodiments, the thermoplastic polymer powder has an inherent viscosity of 0.65 dl/g to 1.8 dl/g, preferably 0.9 dl/g to 1.4 dl/g, and more preferably 1.0 dl/g to 1.3 dl/g. These powders are particularly advantageous in that they make it possible to obtain a good compromise in order to have both good properties coalescence during sintering (sufficiently low viscosity) and good mechanical properties of the sintered object (sufficiently high viscosity).

The thermoplastic polymer powder may comprise, in addition to the thermoplastic polymer(s), one or more usual additives and fillers.

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

Among the flow agents, mention may be made, for example, of a hydrophilic or hydrophobic silica. Advantageously, the flow agent represents from 0.01 to 0.5% by weight relative to the total weight of composition. Preferably, the thermoplastic polymer powder comprises 0.1 to 0.4% by weight of flow agent.

The thermoplastic polymer powder may also include one or more fillers. The fillers generally represent less than 50% by weight, and preferably less than 40% by weight relative to the total weight of final powder. Among the fillers, mention should be made of reinforcing fillers, in particular mineral fillers such as carbon black, talc, nanotubes, of carbon or not, fibers (glass, carbon, etc.), ground or not.

B. Manufacturing process of thermoplastic polymer powder

The thermoplastic polymer powder can in particular be obtained by grinding thermoplastic polymer in the form of extruded granules or scales, according to conventional techniques.

The grinding can be carried out on equipment known for this purpose, for example by means of a counter-rotating pin mill (pin mill), a hammer mill (hammer mill) or in a whirl mill. When the powder comprises several polymers and/or certain additives and/or certain reinforcing fillers, some or all of them can be incorporated by mixing in the molten state, for example by extrusion (compounding) and granulation followed by grinding of the granules. Alternatively, it is also possible to add other polymers and/or certain additives and/or certain reinforcing fillers by dry blending. Preferably, the flow agent is added by dry mixing. According to one embodiment, and in particular for polyamides, the process for manufacturing the composition of the powder comprises the steps of:

(a) Prepolymerization of the monomer(s) of the thermoplastic polymer and subsequent granulation

(b) Grinding and optional subsequent sieving of the prepolymer powder obtained;

(c) Subjecting the prepolymer powder obtained, optionally screened, to solid phase polycondensation to obtain a polymer powder.

The additives and/or reinforcing fillers can be added to the prepolymer, by melt mixing (compounding) before grinding or by dry mixing. Alternatively, the reinforcing additives and/or fillers can also be added subsequently to the polymer powder, by dry mixing.

C. Use of powder

The described thermoplastic polymer powder is particularly useful in sintering 3D printing processes.

Preferably, the composition of the invention is used in a selective laser sintering process (SLS, Selective Laser Sintering, in English), a sintering process of the MJF (Multi Jet Fusion) type or a sintering process of the HSS type. (High Speed Sintering).

The SLS process is widely known. In this context, particular reference may be made to documents US 6,136,948 and WO 96/06881.

In this type of process, a thin layer of powder is deposited on a horizontal plate held in an enclosure heated to a temperature called the construction temperature. Most often, the heating to the building temperature is carried out by means of IR radiation lamps, for example halogen lamps, which generally have an emission maximum at a wavelength between 750 nm and 1250 nm.

The build temperature refers to the temperature to which the powder bed, of a constituent layer of a three-dimensional article under construction, is heated during the layer-by-layer sintering process of the powder.

Electromagnetic radiation, for example in the form of a laser, then provides the energy needed to sinter the powder particles at different points of the layer of powder according to a geometry corresponding to an object, for example using a computer having in memory the shape of an object and restoring the latter in the form of slices. Then, the horizontal plate is lowered by a height corresponding to the thickness of a layer of powder, and a new layer of powder is spread, heated and then sintered in the same way. The procedure is repeated until the object has been made.

The layer of powder deposited on a horizontal plate can have, before sintering, for example a thickness of 20 to 200 μm, and preferably of 50 to 150 μm. After sintering, the thickness of the layer of agglomerated material is a little lower, and can for example have a thickness of 10 to 150 μm, and preferably of 30 to 100 μm.

For the MJF and HSS process, the entire layer of building material is exposed to radiation, but only a part covered with a melting agent is melted to become a layer of a 3D part. The melting agent is a compound capable of absorbing radiation and converting it into thermal energy, for example black ink. It is applied selectively to the selected region of the building material. The melting agent is able to penetrate the layer of the building material and transmits the absorbed energy to the neighboring building material, thereby causing it to melt or be sintered. By melting, bonding and subsequent hardening of each layer of the building material, the object is formed.

In the particular case of MJF, a detailing agent is additionally added to the edges of the zone to be melted to allow the parts to have a better definition.

Advantageously, the use of the polymer powder composition of the invention in these processes does not require any particular modification. As mentioned above, on the other hand, it makes it possible to obtain parts with lower roughness and better definition.

The polymer powder composition according to the invention can be recycled and reused in several successive constructions. In this case, it can be reused alone or mixed with other powders, whether recycled or not.

By way of example is described below the use of the thermoplastic polymer powder described in a method for constructing a three-dimensional object layer-by-layer by sintering caused by electromagnetic radiation in a device 1, such as that shown schematically in Figure 1. The electromagnetic radiation may for example be infrared radiation, ultraviolet radiation, or preferably laser radiation. In particular, in a device 1 such as that shown schematically in Figure 1, the electromagnetic radiation may comprise a combination of infrared radiation 100 and laser radiation 200. The sintering process is a layer-to-layer manufacturing process for constructing an object three-dimensional 80.

The device 1 comprises a sintering chamber 10 in which are arranged a supply tray 40 containing the thermoplastic polymer powder and a movable horizontal plate 30. The horizontal plate 30 can also act as a support for the three-dimensional object 80 under construction. However, objects made from thermoplastic polymer powder generally do not need additional support and can generally be self-supported by unsintered powder from previous layers.

According to the method, thermoplastic polymer powder is taken from the supply tray 40 and deposited on the horizontal plate 30, forming a thin layer 50 of powder constituting the three-dimensional object 80 under construction. The layer of powder 50 is heated using infrared radiation 100 to reach a substantially uniform temperature equal to the predetermined minimum construction temperature Te.

The energy required to sinter the thermoplastic polymer powder particles at different points of the powder layer 50 is then supplied by laser radiation 200 from the laser 20 moving in the plane (xy), according to a geometry corresponding to that of the object. The molten powder re-solidifies forming a sintered part 55 while the rest of the layer 50 remains in the form of unsintered powder 56. A single passage of a single laser radiation 200 is generally sufficient to ensure the sintering of the powder. Nevertheless, in certain embodiments, it is also possible to envisage several passages at the same place and/or several electromagnetic radiations reaching the same place to ensure the sintering of the powder.

Then, the horizontal plate 30 is lowered along the axis (z) by a distance corresponding to the thickness of a layer of powder, and a new layer is deposited. The laser 20 provides the energy needed to sinter the powder particles according to a geometry corresponding to this new slice of the object and so on. The procedure is repeated until object 80 has been produced. The temperature in the sintering chamber 10 of the layers lower than the layer under construction can be lower than the construction temperature. However, this temperature generally remains above, or even well above, the glass transition temperature of the powder. It is particularly advantageous for the temperature of the bottom of the enclosure to be maintained at a temperature Tb, called "tank bottom temperature", such that Tb is less than Te by less than 40° C., preferably less than 25° C. C and more preferably less than 10°C.

Once the object 80 is finished, it is removed from the horizontal plate 30 and the unsintered powder 56 can be sieved before being returned, at least in part, to the supply bin 40 to serve as recycled powder. The recycling of the powder is made possible by the fact that the construction temperature Te is generally lower than that of traditional construction processes, which makes it possible to attenuate the aging of the powder, unsintered, having undergone the temperature conditions of at least one construction by sintering. The recycled thermoplastic polymer powder can be used as it is or alternatively mixed with a virgin powder.

In particular, in the embodiments where the thermoplastic polymer powder consists of a mixture of a P1 powder and a P2 powder, the construction temperature can be lower than that which would be used for a traditional construction process. using a composition consisting of PI powder (which is not according to the invention). This makes it possible to envisage the improved recycling of unsintered powder composition in a subsequent construction. Advantageously, the mixture of powders to be recycled is mixed with virgin P and/or P2 powder, so as to maintain a construction temperature Te lower than that of traditional construction methods.

The invention will be explained in more detail in the following examples.

[Examples]

In the following examples, several thermoplastic polymer powders with different grain sizes and thermal signatures were examined for their behavior in 3D printing by sintering. EXAMPLE 1

By way of reference, a polyamide 11 powder, formulated for 3D printing, marketed by the company ARKEMA France under the name Rilsan® Invent Natural (RIN) was used.

The thermal signature of the polyamide 11 powder was characterized by differential scanning calorimetry (DSC) carried out on a Q.2000 calorimeter from TA Instruments, in accordance with the ISO 11357-3:2013 standard. In the thermogram shown in Fig. 2, the dotted lines represent the base line and the solid lines the tangents of the flanks of the melting peak at the point of inflection. The temperatures T _e im and T _e f _m are the temperatures at which the baseline is intersected by the tangents of the flanks. The temperature T _pm is that at the minimum of the melting peak. The temperatures T _pm , Teim and T _e f _m were determined from the thermogram illustrated in FIG. 2 and are shown in Table 2 below.

This powder was also characterized by its mean diameter Dv50 of 49 μm, its mean diameter Dv10 of 23 μm and its mean diameter Dv90 of 90 μm, by laser diffraction on a Malvern Insitec diffractometer and RTSizer software, according to the ISO 13320 standard. : 2009 in dry process, by choosing a pressure of 7.5 bars and an air flow of 10 m ³ /h.

EXAMPLE 2

A thermoplastic polymer powder was prepared by dry mixing 90% by weight of polyamide 11 powder marketed by the company ARKEMA France under the name Rilsan® Invent Natural with 10% by weight of heat-treated polyamide 11, obtained according to the process following.

First, a polyamide 11 prepolymer was synthesized from 1.2 kg of amino-ll-undecanoic acid in the presence of 0.5 kg of water, 5 g of hypophosphorous acid and 9.8 g of acid. phosphoric. The mixture was heated to a temperature of 190° C. in 2 hours with stirring as soon as the temperature reached 160° C. or the pressure exceeded 8.5 bars. During the synthesis, the water initially charged with amino-ll-undecanoic acid was eliminated by evaporation at constant pressure (P=10 bars). After having drawn off a quantity of water of 430 g, the molten prepolymer was extruded by means of a twin-screw extruder. The mixture was then cooled using two steel rollers with circulation of cold water to be solidified, cooled and crushed into scales.

The prepolymer recovered is then ground in a hammer mill equipped with an internal selector until a powder having a median diameter by volume Dv50 of 49 μm is obtained. There The powder thus obtained is then subjected to polycondensation in the solid phase in a dryer at 180° C. under vacuum in order to increase the viscosity of the polyamide up to 1.1 dl/g.

The polyamide 11 powder obtained was then sieved through a square mesh of 150 μm.

The powder obtained has a thermal signature characterized by the temperatures T _pm , Teim and Tefm indicated in table 2. These temperatures were determined from a thermogram measured by differential scanning calorimetry (DSC) on a Q.2000 calorimeter of TA Instruments, in accordance with ISO 11357-3:2013. In the thermogram shown in Fig. 3, the dotted lines represent the base line and the solid lines the tangents of the flanks of the melting peak at the point of inflection. The Teim and Tefm temperatures are the temperatures at which the baseline is intersected by the tangents of the flanks. The temperature T _pm is that at the minimum of the peak. The angle of the tangent was adapted to take into account the spreading at low temperature preceding the melting peak.

This powder was also characterized by its mean diameter Dv50 of 49 μm, its mean diameter Dv10 of 23 μm and its mean diameter Dv90 of 90 μm, by laser diffraction according to standard ISO 13320: 2009, on a Malvern Insitec diffra cto meter as explained in Example 1.

EXAMPLE 3

A thermoplastic polymer powder was prepared by dry mixing 90% by weight of polyamide 11 powder marketed by the company ARKEMA France under the name Rilsan® Invent Natural with 10% by weight of polyamide 12 marketed by the company ARKEMA under the name name Orgasol Invent Smooth, exhibiting a Dv10 of 31 µm, a Dv50 of 40 µm and a Dv90 of 50 µm.

The powder obtained has a thermal signature characterized by two melting temperatures Tfi and Tf?, indicated in table 2. These temperatures were determined from the thermogram illustrated in FIG. 4, measured by differential scanning calorimetry (DSC) on a Q.2000 calorimeter from TA Instruments, in accordance with ISO 11357-3:2013. The difference between the two melting peaks Tfi and Tf? is 19°C. The ratio between the enthalpy of Tfi compared to that of Tf? is 0.1.

This powder was also characterized by its mean diameter Dv50 of 49 μm, its mean diameter Dv10 of 23 μm and its mean diameter Dv90 of 90 μm, by laser diffraction according to the ISO 13320: 2009 standard, on a Malvern Mastersizer 2000® diffractometer as explained in example 1.

[Table 1]

Composition of the powders, relative to the weight of the composition

[Table 2]

Thermal characteristics

Behavior of powders in 3D printing

The polymer powders obtained were then used to manufacture by 3D printing by laser sintering, a 1BA XY test piece (1BA test piece according to ISO 527-1BA standard, called "XY" because printed in the horizontal plane of the printer) on a P100 machine (marketed by the company EOS) by adjusting the thickness of the layer of powder to 100 μm. The printing parameters used are as follows: Laser power: 24W Laser speed: 3000mm/s Distance between 2 laser passes: 0.25mm

It was found on the one hand that the powder of example 2 could be sintered at a construction temperature of 9° C. below the temperature of powder 1 (183° C. for powder 1 vs. 174° C. for powder 1). powder of example 2). The specimens obtained from powders 1 and 2 nevertheless possessed comparable mechanical properties. However, a drop in the construction temperature makes it possible to reuse the powder 2 more widely, which has undergone less thermal aging during the construction process, and therefore to substantially reduce the cost of the material for 3D printing.

It was also observed that the powder of Example 3 also made it possible to obtain good quality specimens at a construction temperature below the temperature of powder 1. Thus, it is therefore possible to take advantage the presence of several melting peaks when they are not too far apart.

These examples show that a powder having a specific particle size associated with a complex thermal signature, characterized either by the presence of two melting peaks separated by less than 40° C. and having a ratio between the associated enthalpies of fusion AHfi and AHf2 < 0.5 or by an asymmetrical melting peak characterized by a ratio o > 2.0, can make it possible to lower the construction temperature during 3D printing, thus limiting thermal aging and therefore the cost of the material.

[List of cited documents]

[US 6,136,948]

[WO 96/06881]

Claims

CLAIMS Thermoplastic polymer powder suitable for use in 3D printing by sintering, having: a volume average diameter Dv50 of less than 150 μm, a volume average diameter Dv10 of more than 15 μm and a volume average diameter Dv90 of less than 300 pm, as measured by laser diffraction according to ISO 13320: 2009, and a thermal signature characterized by the presence: (i) two melting peaks Tfi and Tf?, Tfi being lower than Tf?, said melting peaks being characterized in that: ATYj’ f a. the ratio — — between the associated enthalpies of fusion, such as ^Tf2 determined according to standard NF EN ISO 11357-3:2018 is less than 0.5; and B. the difference between the two melting peaks (Tfz-Tfi) is less than 40° C.; Or (ii) an asymmetrical melting peak, characterized by a ratio o: _Q > (Tefm-Teim)^ _Q (Tefm-Tpm) where the extrapolated melting onset temperature T _e im, the melting peak temperature T _P m and the extrapolated melting end temperature T _e f _m are determined from a DSC thermogram measured with a heating rate of 20°C/min, according to standard NF EN ISO 11357-3:2018. Thermoplastic polymer powder according to Claim 1, characterized in that it has a volume-average diameter Dv50 of between 45 and 130 μm. Thermoplastic polymer powder according to claim 1 or 2, wherein the ah?' ratio — — is between 0.05 and 0.2. H Thermoplastic polymer powder according to one of Claims 1 to 3, in which the thermal signature is characterized by the presence of two peaks Tfi and Tf?, the difference between these melting peaks being spread over a temperature interval ranging from 5 to 30°C. 5. Thermoplastic polymer powder according to one of claims 1 to 4, characterized in that the thermal signature is characterized by an asymmetrical peak having a ratio o greater than 2.3. 6. Thermoplastic polymer powder according to one of claims 1 to 5, in which the melting peak(s) Tfi and Tf? spread over a temperature range ranging from 2 to 40°C, preferably from 5 to 30°C and very particularly from 10 to 20°C. 7. Thermoplastic polymer powder according to one of claims 1 to 6, comprising at least two distinct thermoplastic polymers. 8. Thermoplastic polymer powder according to one of claims 1 to 7, comprising at least two distinct thermoplastic polymers by at least one of their properties, in particular by their viscosity. 9. Thermoplastic polymer powder according to one of claims 1 to 7, comprising at least two distinct thermoplastic polymers differing in their chemical nature. 10. Thermoplastic polymer powder according to one of claims 1 to 9, having an inherent viscosity of 0.65 dl / g to 1.8 dl / g as measured in an Ubbelohde type viscometer according to ISO 307: 2019, except to use m-cresol as solvent and a temperature of 20°C. 11. Thermoplastic polymer powder according to one of claims 1 to 10, comprising at least one polymer chosen from polyamides and thermoplastic elastomers. 12. Thermoplastic polymer powder according to claim 11, comprising at least one polymer chosen from PA 11, PA 12 and polyetherblock amides. 13. A method of manufacturing a thermoplastic polymer powder according to one of claims 1 to 12, comprising the steps consisting of: a. Grinding of at least one thermoplastic polymer into a powder having a volume average diameter Dv50 less than 150 μm, a volume average diameter Dv10 greater than 15 μm and a volume average diameter Dv90 less than 300 μm, as measured by diffraction laser according to ISO 13320: 2009, and, if applicable, b. mixing said thermoplastic polymer with another thermoplastic polymer, before, during or after step (i), so that the powder obtained from the process has a thermal signature as defined in claim 1. 14. Use of a powder according to one of claims 1 to 13 for 3D printing by sintering. 15. Use according to claim 14, for 3D printing by laser sintering.