CN113396178A

CN113396178A - Particles for selective laser sintering, method for producing said particles and their use

Info

Publication number: CN113396178A
Application number: CN201980091999.6A
Authority: CN
Inventors: Y·H·苏; L·谭
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2019-02-15
Filing date: 2019-02-15
Publication date: 2021-09-14
Also published as: WO2020164728A1; DE112019006869T5

Abstract

A method comprising (a) providing a suspension comprising: (a1) at least one polymeric material selected from the group consisting of polypropylene, polypropylene copolymers, and combinations thereof, provided in the form of solid particles suspended in the suspension; (a2) at least one filler; (a3) a first solvent capable of dissolving the at least one polymeric material; and (a4) a second solvent that is miscible with the first solvent. The method may further comprise (b) solubilizing the suspension by heating to dissolve the polymeric material, (c) precipitating and (d) recovering the polymeric composite particles from solution. The recovered particles may be used in a selective laser sintering process for producing sintered objects, for example by i) providing a layer of particles in a bed of particles; ii) applying a laser to the layer to fuse the particles together; and repeating steps i) and ii), thereby providing a sintered object.

Description

Particles for selective laser sintering, method for producing said particles and their use

Technical Field

The present disclosure relates to a method for producing particles for selective laser sintering, particles made by the method and the use of the particles in selective laser sintering.

Background

One of the main limitations of selective laser sintering is the low choice of available materials that can be processed. Currently, the most widely used material is a Polyamide (PA) based polymer, with PA12 constituting about 95% of the selective laser sintering market.

Therefore, there is a need to provide new materials that can be used for selective laser sintering.

SUMMARY

It is therefore an object of the present invention to provide an improved method for producing composite polymer particles for selective laser sintering.

Various embodiments may provide a method of producing a polymer composite particle for selective laser sintering comprising at least one polymeric material and at least one filler. The method can include (a) providing a suspension. The suspension may comprise (a1) at least one polymeric material selected from the group consisting of polypropylene, polypropylene copolymers, and combinations thereof. The at least one polymeric material may be provided in the form of solid particles suspended in the suspension. The suspension may further comprise (a2) at least one filler. The suspension may further comprise (a3) a first solvent capable of dissolving the at least one polymeric material at a first elevated temperature. The suspension may further comprise (a4) a second solvent that is miscible with the first solvent, wherein the at least one polymeric material is insoluble in the second solvent. The method may further comprise (b) solubilizing the suspension by heating the suspension to a temperature equal to or greater than the first elevated temperature to dissolve the polymeric material. The method may further comprise (c) precipitating the polymer composite particles from solution. Precipitation may include cooling. The method may further comprise (d) recovering the formed polymer composite particles.

Various embodiments may provide polymer composite particles suitable for selective laser sintering. The polymer composite particles may be obtained by a method according to various embodiments.

Various embodiments may provide for the use of the particles in a selective laser sintering process for producing sintered objects. The use may comprise i) providing a layer of particles in a bed of particles. The use may further comprise ii) applying a laser to the layer to fuse the particles together. The use may further comprise repeating steps i) and ii), e.g. a plurality of times, thereby providing a sintered object.

Brief Description of Drawings

In the following description, various embodiments of the present disclosure are described with reference to the following drawings, in which:

figure 1 shows a schematic flow diagram of a method 100 according to various embodiments;

figure 2A shows a schematic diagram of a temperature profile including a cooling process according to various embodiments;

figure 2B shows a schematic diagram of a temperature profile including an improved cooling process according to various embodiments;

figure 2C shows a schematic diagram of a temperature profile including a further improved cooling process according to various embodiments;

figure 3 shows two Scanning Electron Microscopy (SEM) images of particles not according to the invention;

fig. 4 shows two SEM images of the particles according to the first embodiment at two different scales;

fig. 5 shows two SEM images of the particles according to the second embodiment at two different scales;

fig. 6 shows a particle size distribution graph 610 and a cumulative distribution graph 624;

fig. 7 shows SEM images of the resulting material according to the first comparative example.

Detailed description of the invention

Fig. 1 shows a schematic flow diagram of a method 100 according to various embodiments. The method 100 may include providing a suspension in step 110. The suspension may comprise a first solvent and may comprise the at least one polymeric material. The suspension may further comprise a filler. For example, the filler and solvent may be mixed, e.g., sonicated, in step 110, and the polymeric material may be added thereafter. The filler may comprise or consist of clay. The first solvent may be capable of dissolving the at least one polymeric material at a first elevated temperature. The method may further comprise adding a second solvent to the suspension, the second solvent being miscible with the first solvent, for example, in step 120, wherein the at least one polymeric material is insoluble in the second solvent. The polymeric material may be added to the suspension with the second solvent, e.g., before the second solvent, with the second solvent, or after the second solvent. The method may further include the step 130 of: solubilizing the suspension by heating the suspension to a temperature equal to or greater than the first elevated temperature to dissolve the polymeric material. Solubilization can be carried out under reflux. The method may further comprise the step 140: precipitating the polymer composite particles from the solution, wherein precipitating comprises cooling. The method may further comprise the step 150 of: recovering the formed polymer composite particles.

According to various embodiments, the concentration of the polymeric material in the first solvent may be selected from 1 wt% to 20 wt%, such as 8 wt% to 12 wt%.

According to various embodiments, the method of producing a polymer composite particle may refer to a method of producing a polymer composite particle.

According to the disclosed method, it is possible to obtain polymer composite particles having a uniform size distribution and substantially no sharp edges. The polymer composite particles are mostly single particles, in some cases with binary particles (potato-shaped), but otherwise are substantially free of agglomerates. These particles exhibit good properties for selective laser sintering.

According to various embodiments, the average circularity (Rnd) of the polymer composite particles may be 0.8 or higher. The roundness of the particle can be calculated by the following formula:

wherein A is the area of the measured area of the particle, and

is the maximum length of the particle as a diameter.

According to various embodiments, the at least one polymeric material may be selected from polypropylene (PP), polypropylene copolymers, and combinations thereof. For example, the polypropylene copolymer may be selected from grafted polypropylene, preferably grafted PP (g-PP), such as maleic anhydride grafted polypropylene. For example, the at least one polymeric material may comprise PP and grafted PP, wherein the weight ratio of PP to grafted PP (g-PP) may be selected from 100:1 to 100: 20.

According to various embodiments, the polymeric material may be provided in the form of solid particles, for example in the form of a powder.

According to various embodiments, the first solvent is capable of dissolving the polymeric material. For example, the first solvent and the polymeric material may be selected such that the solvent is capable of dissolving the polymeric material at a first elevated temperature. The first elevated temperature may for example be equal to or higher than 130 ℃ for PP in a p-xylene/1-hexanol mixture and further for example higher than 136 ℃ for PP in a p-xylene/1-hexanol mixture at a pressure of 1 atm.

According to various embodiments, the solvent mixture of the first and second solvents may retain the property of being capable of dissolving the at least one polymeric material at a temperature equal to or higher than the first elevated temperature. The elevated temperature may be above the boiling point of the first solvent, for example above 125 ℃, preferably from 135 ℃ to 155 ℃.

In the present invention and according to various embodiments, the temperature values may include a variation of +/-2 ℃.

According to various embodiments, the first solvent may be selected from para-xylene, meta-xylene, ortho-xylene, toluene, decalin, ethylbenzene, chlorobenzene, or combinations thereof.

According to various embodiments, the second solvent is miscible with the first solvent. The second solvent may be different from the first solvent.

According to various embodiments, the at least one polymeric material may be insoluble in the second solvent.

According to various embodiments, the second solvent may be an alcohol, preferably having a boiling point higher than the boiling point of the first solvent.

According to various embodiments, the alcohol may be selected from: linear primary aliphatic alcohols having 6 or more carbon atoms, linear secondary alcohols having 7 or more carbon atoms, and combinations thereof.

According to various embodiments, the volume ratio of the first solvent to the second solvent may be selected from 1:1 to 1:4, for example it may be selected from 1:2 to 1: 3.

According to various embodiments, the clay may be an unmodified smectite (smectite), a modified smectite, or a mixture thereof. For example, the clay may comprise or consist of montmorillonite, modified montmorillonite or mixtures thereof.

According to various embodiments, the clay may comprise particles having a size D50 that is less than the size of the polymer composite particles, such as less than 15 microns.

According to various embodiments, the concentration of clay (e.g., OMMT) relative to the polymeric material may be selected from 0.1 wt% to 10 wt%, preferably 0.5 wt% to 2 wt%.

According to various embodiments, the first solvent is capable of dissolving and/or exfoliating and/or dispersing the at least one filler, e.g. the first solvent is capable of exfoliating the at least one filler. This can be done, for example, by means of sonication.

In the present invention and according to various embodiments, the term "suspension" may refer to a mixture of a solvent and at least one of: the at least one polymeric material, the at least one filler, a second solvent. When dissolving (also referred to as solubilizing) the polymeric material in the first solvent, the suspension may be referred to as a solution.

According to various embodiments, a third solvent may be added to the suspension, for example, in the case where the filler is not soluble, exfoliated or dispersed in either of the first or second solvents. The third solvent is capable of exfoliating and/or dispersing the at least one filler prior to providing the suspension. The third solvent is miscible between the first solvent and the second solvent.

According to various embodiments, the method may comprise the step of exfoliating (optionally involving sonication) the at least one filler in the first solvent or in a mixture of the first and second solvents (optionally further comprising a third solvent). For example, the filler may be omt and the first solvent may be para-xylene.

According to various embodiments, the method may comprise adding the at least one polymeric material to a first solvent. At this stage, the suspension may already contain fillers as described above. The method may further comprise adding a second solvent to the suspension, wherein the second solvent is different from the first solvent. For example, the at least one polymeric material may be added to the suspension and the second solvent may be subsequently added to the suspension. Alternatively, the second solvent and the at least one polymeric material may be added to the suspension in reverse order or simultaneously. In one example, the first solvent may be p-xylene and the second solvent may be 1-hexanol.

According to various embodiments, the method may comprise solubilizing the suspension by heating the suspension to a temperature equal to or greater than the first elevated temperature to dissolve the polymeric material, thereby providing the solution. For example, the suspension may be heated to dissolve the polymeric material, e.g., until a clear solution is obtained. The heating may be carried out under reflux, for example to a temperature selected to be 15 ℃ below the boiling point of the second solvent (e.g. 13 ℃ below), which may further be selected to be higher than the boiling point of the first solvent. For example, for a p-xylene/1-hexanol mixture, the temperature may be, for example, above 125 ℃ at ambient pressure, preferably selected from 135 ℃ to 155 ℃. Solubilization can be carried out under reflux. Solubilization can be carried out with stirring. For example, pure PP may be completely dissolved in p-xylene/1-hexanol solution at a temperature equal to or higher than 136 deg.C (with or without filler) when stirred under heating for 30 minutes or more.

According to various embodiments, the method may further comprise precipitating the formed polymer composite particles from the suspension, thereby forming a precipitate. To form a precipitate, the solubilized solution can be cooled during cooling.

According to various embodiments, the cooling process may comprise a first cooling step, wherein the solution is cooled from a temperature equal to or higher than the first elevated temperature T₁Is cooled to a second temperature T₂Said second temperature T₂Below a first elevated temperature T₁And maintained at the second temperature for a first period of time delta_t1. According to various embodiments, the cooling process may further comprise a second cooling step, wherein the solution is cooled to below the second temperature T₂Third temperature T of₃And at a third temperature T₃Lower hold for a second period of time Δ_t2And thereafter the solution may be further cooled to, for example, room temperature. According to various embodiments, in the second cooling step, the solution may be cooled from the second temperature T₂Cooling to below a second temperature T₂First intermediate temperature T of_I1And at a first intermediate temperature T_I1Lower hold first intermediate period Δ_I1. According to various embodiments, the solution may be brought from a first intermediate temperature T_I1Cooling to below the first intermediate temperature T_I1Second intermediate temperature T_I2And at a second intermediate temperature T_I2Lower hold second intermediate period Δ_I2Then cooling the solution to a third temperature T₃。

According to various embodiments, the third temperature may be a precipitation temperature, meaning that a precipitate begins to form at that temperature.

According to various embodiments, the second temperature T₂May be at a first elevated temperature T₁And a third temperature T₃To select between. In some embodiments, the second temperature T₂Can be selected from T₃+ 10 ℃ and T₃ + 14℃。

According to various embodiments, the first intermediate temperature T_I1Can be at a second temperature T₂And a third temperature T₃To select between. In some embodiments, the first intermediate temperature T_I1Can be selected from T₂-6 ℃ and T₂ - 4℃。

According to various embodiments, the second intermediate temperature T_I2Can be at a first intermediate temperature T_I1And a third temperature T₃To select between. In some embodiments, the second intermediate temperature T_I2Can be selected from T₁-3 ℃ and T₂ - 1℃。

According to various embodiments, the first time period Δ is provided only_t1A second period of time delta_t2A first intermediate period delta_I1A second intermediate period delta_I2Each time period of (a) may be selected from 1 minute to 60 minutes, for example 5 minutes to 60 minutes.

The solution/precipitate mixture may be further cooled to a lower temperature, for example a temperature below 40 ℃, such as 20 ℃ or room temperature, and the precipitate may then be recovered. The cooling rate from the third temperature to a lower temperature (e.g. to room temperature) may for example be adjusted linearly, e.g. such that cooling from the third elevated temperature to the lower temperature takes e.g. 20 minutes to 2 hours.

According to various embodiments, the cooling may be stationary. In other cases, for example, the use of stirring during cooling results in the formation of aggregates, which is not ideal for selective laser sintering of particles.

According to various embodiments, the cooling rate may be selected between 1 ℃/minute and 10 ℃/minute, for example between 1 ℃/minute and 5 ℃/minute. For example, (i) a cooling rate from a first elevated temperature to a second temperature, (ii) in the case where no intermediate temperature is usedAt least one of (i) a cooling rate from the second temperature to the third temperature, (iii) a cooling rate from the second temperature to the first intermediate temperature, (iv) a cooling rate from the first intermediate temperature to the second intermediate temperature, (v) a cooling rate from the second intermediate temperature to the third temperature may be selected between 1 ℃/minute and 10 ℃/minute, for example between 1 ℃/minute and 5 ℃/minute. It was found that by means of the first and second cooling steps it is possible to obtain polymer composite particles having a relatively good morphology, e.g. no sharp edges and a narrow size distribution, suitable for selective laser sintering. Without wishing to be bound by theory, it is believed that nucleation occurs primarily during the first cooling step, while grain growth occurs primarily during the second cooling step. It is believed that particle growth occurs at the third temperature, and at or above the first elevated temperature (T)₁) And a step between the temperature of (a) and the third temperature promotes controlled nucleation of the polymer composite particles.

According to various embodiments, the first cooling step may comprise a temporary heating step, wherein the temperature of the solution may be increased from a temperature equal to or higher than the second temperature to a temporary heating temperature over a period of time, wherein the temporary heating temperature is lower than the highest temperature used during solubilization of the suspension, e.g. the temporary heating temperature may be lower than the first increased temperature. It was found that the incorporation of a temporary heating step improves the homogeneity and size of the polymer composite particles. For example, by including a heating step in the cooling process, it is possible to reduce the formation of potato-shaped particles (binary particles). Furthermore, the particle size distribution obtained is more uniform. For example, for PP in paraxylene containing OMMT, the heating temperature of this heating step may be 122, and the heating duration may be 10 minutes +/-20%. The heating duration may be counted as being included in the cooling duration of the first cooling step, so the total cooling duration of the first cooling step may be 30 minutes +/-20%.

Fig. 2A shows a schematic diagram of a temperature profile including a cooling process according to various embodiments. Graph 210 has a vertical axis representing temperature and a horizontal axis representing time. In a first cooling step, the solution is cooled from a temperature equal to or higher than a first elevated temperature T₁Is cooled to below a first elevated temperature T₁Second temperature T₂And at a second temperature T₂Lower hold first period Δ_t1. The cooling process may further comprise a second cooling step wherein the solution is cooled to below the second temperature T₂Third temperature T of₃And at a third temperature T₃Lower hold for a second period of time Δ_t2And thereafter the solution may be further cooled, for example to room temperature. When the temperature is maintained at the second temperature for a first period of time delta_t1The first cooling step may include a temporary heating step 212 as previously described, which lasts for a temporary period of time Δ_tt。

Fig. 2B shows a schematic diagram of a temperature profile including an improved cooling process according to various embodiments. Graph 210 has a vertical axis representing temperature and a horizontal axis representing time. The cooling process may include a first cooling step wherein the solution is cooled from a temperature at or above a first elevated temperature T₁Is cooled to a second temperature T₂Said second temperature T₂Below a first elevated temperature T₁And at a second temperature T₂Lower hold first period Δ_t1. The cooling process may further comprise a second cooling step, wherein the solution may be cooled from a second temperature T₂Cooling to below a second temperature T₂First intermediate temperature T of_I1And at a first intermediate temperature T_I1Lower hold first intermediate period Δ_I1. According to various embodiments, the solution may be brought from a first intermediate temperature T_I1Cooling to below the first intermediate temperature T_I1Second intermediate temperature T_I2And at a second intermediate temperature T_I2Lower hold second intermediate period Δ_I2Then cooling the solution to a third temperature T₃And thereafter the solution may be further cooled, for example to room temperature.

Fig. 2C shows a schematic diagram of a temperature profile including a further improved cooling process according to various embodiments. The cooling process of fig. 2C is the same as the cooling process described in connection with fig. 2B, except that the first cooling step comprises a temporary heating step 212 as described above, which lasts for a temporary period of time Δ_tt。

For example, for PP in paraxylene containing OMMT, the first elevated temperature T₁May be 140 ℃ and a second temperature T₂May be 122 ℃ and a first period of time Δ_t1May be 30 minutes, the first intermediate temperature T_I1May be 116 ℃ and a first intermediate period Δ_I1May be 10 minutes, second intermediate temperature T_I2May be 114 ℃ and a second intermediate period Δ_I2May be 30 minutes, third temperature T₃May be 110 ℃ and a second period of time Δ_t2May be 60 minutes.

According to various embodiments, the recovering step (d) may comprise filtering the suspension obtained in the precipitating step (c), for example a filter may be used to remove solvent and residual dissolved polymeric material from the polymer composite particles. The recovering step (d) may comprise washing the particles obtained by filtration with a fourth solvent, the fourth solvent being miscible with the at least second solvent, and the at least one polymeric material being insoluble in the fourth solvent. Optionally, recovering the precipitate may include sonicating the precipitate prior to filtering the precipitate. The precipitate can be dried, for example, under vacuum.

According to various embodiments, the precipitate comprises polymer composite particles suitable for selective laser sintering. After drying, about 100 wt%, e.g., at least 99 wt%, of the precipitate can be used for selective laser sintering without further treatment. For example, more than 96% by volume of the precipitate may be particles having a size within the desired range. The polymer composite particles are single spherical particles, substantially free of sharp edges and are composites comprising a filler and a polymeric material. The desired range may be from 20 microns to 100 microns, for example from 45 microns to 100 microns. The polymer composite particles may be substantially spherical. The composition of the polymer composite particles may comprise a PP/OMMT composite.

According to various embodiments, the polymer composite particles may be used in a selective laser sintering process for producing sintered objects. The use may comprise i) providing a layer of polymer composite particles in a particle bed (also referred to as a powder bed). The use may further comprise ii) applying a laser to the layer to fuse the polymer composite particles together. Whereby a layer of the sintered object can be provided. The use may further comprise repeating steps i) and ii), thereby providing at least a part of the layer-by-layer manufactured sintered object or a final sintered object. The high roundness of the polymer composite particles (e.g., greater than 0.8) achieved enables good flow of the polymer composite particles in the particle bed, thereby providing good uniformity in the layer. Furthermore, since the polymer composite particles have a narrow size distribution, sintering of the polymer composite particles and control of the sintering is facilitated to allow for better control of the final properties of the sintered object, which is further improved by the homogeneity of the composite material.

Examples

Fig. 3 shows two SEM images of particles not according to the invention. In both images, the scale bar represents 100 microns. The particles are cryogenically milled and have a typical irregular shape and a rough particle surface. Such particles are not ideal for selective laser sintering, but may be used, for example, as a polymeric material in the methods of the present disclosure.

In a first example, 4.31 mg of OMMT as filler was sonicated in 5 ml of p-xylene (as the first solvent) to help exfoliate the clay layer. 431 mg of pure PP (as a polymeric material) and 10 ml of 1-hexanol (as a second solvent) were then added to the suspension, and the resulting suspension was subsequently heated to 140 ℃ under reflux with stirring until a clear solution was obtained. The solution was held at 140 ℃ (first elevated temperature) for 45 minutes to ensure complete dissolution. The solution was then quiescently cooled to 110 ℃ according to the cooling procedure explained below and kept at this temperature until the precipitation of the polymer composite particles of PP/OMMT was complete. The solution was cooled from a temperature of 140 ℃ to 122 ℃ and held at 122 ℃ for 30 minutes, thereafter cooled to a second temperature of 116 ℃ and held at 116 ℃ for 10 minutes. According to the second cooling step, the solution was cooled to 114 ℃ and held at 114 ℃ for 30 minutes, further cooled to a third temperature of 110 ℃ and held at 110 ℃ for 60 minutes. The suspension was then further cooled to room temperature, sonicated for 15 minutes, and then filtered to yield a powder of PP/OMMT composite particles. The powder was then washed with isopropanol and then dried under vacuum at room temperature to yield polymer composite particles having an average size D50 of 26 microns. The polymer composite particles are spherical or potato-shaped, have smooth surfaces and substantially no sharp angles, and are therefore suitable for selective laser sintering. An SEM image of the resulting polymer composite particle is shown in fig. 4. In the upper graph of fig. 4, the scale bar represents 100 microns. In the lower graph of fig. 4, the scale bar represents 50 microns.

In a second example, polymer composite particles were prepared as in example 1, except that a modified cooling process was used. The solution was cooled from a temperature of 140 ℃ to 122 ℃ and held at 122 ℃ for 15 minutes, after which a temporary heating step was carried out in which the solution was held at 126 ℃ for 10 minutes, then cooled back to 122 ℃ for 5 minutes, and further cooled to a second temperature of 116 ℃ and held at 116 ℃ for 10 minutes. According to the second cooling step, the solution was cooled to 114 ℃ and held at 114 ℃ for 30 minutes, cooled to a third temperature of 110 ℃ and held at 110 ℃ for 60 minutes. The suspension was then further cooled to room temperature, sonicated for 15 minutes, and then filtered to yield a powder of PP/OMMT composite particles. The composite powder was then washed with isopropanol and then dried under vacuum at room temperature to yield polymer composite particles having an average size D50 of 63 microns. The polymer composite particles are spherical and substantially free of potato-shaped particles. The polymer composite particles exhibit smooth surfaces and are substantially free of sharp angles and are therefore suitable for selective laser sintering. An SEM image of the resulting polymer composite particle is shown in fig. 5. In the upper graph of fig. 5, the scale bar represents 200 microns. In the lower graph of fig. 5, the scale bar represents 50 microns.

Fig. 6 shows a graph 610 showing the particle size in microns (horizontal axis 612) of the polymer composite particle size distribution (vertical axis 614) vs, as a volume percentage, of the particles of the second example. The cumulative distribution of the particles of the second embodiment is shown in graph 624 as the particle size in microns (horizontal axis 622) as cumulative volume percent (vertical axis 624) vs. From this plot, a D50 particle size of 63 microns was obtained at the horizontal axis 622 (particle size) where the cumulative volume curve intersects 50% on the vertical axis (point 262D 50).

In the first comparative example, particles were prepared as in example 2, but stirring was used during the cooling stage. The resulting material has agglomerates with irregular shape and high porosity, and is therefore not suitable for selective laser sintering. An example of the resulting material of the first comparative example is shown in fig. 7. The scale bar represents 20 microns.

Claims

1. A method of producing a polymer composite particle for selective laser sintering comprising at least one polymeric material and at least one filler, comprising:

(a) providing a suspension comprising:

(a1) at least one polymeric material selected from the group consisting of polypropylene, polypropylene copolymers, and combinations thereof, wherein the at least one polymeric material is provided in the form of solid particles suspended in the suspension;

(a2) at least one filler;

(a3) a first solvent capable of dissolving the at least one polymeric material at a first elevated temperature; and

(a4) a second solvent miscible with the first solvent, wherein the at least one polymeric material is insoluble in the second solvent;

(b) solubilizing the suspension by heating the suspension to a temperature equal to or greater than the first elevated temperature to dissolve the polymeric material;

(c) precipitating the polymer composite particles from the solution, wherein precipitating comprises cooling; and

(d) recovering the formed polymer composite particles.

2. The process according to claim 1, wherein the polypropylene copolymer is selected from grafted polypropylene, preferably maleic anhydride grafted polypropylene.

3. The method according to claim 1 or 2, wherein the suspension further comprises a third solvent that is miscible with the first and second solvents and is capable of effecting dissolution, exfoliation, dispersion, or a combination thereof, of the at least one filler.

4. A process according to any one of claims 1 to 3, wherein the filler is an optionally organically modified inorganic filler, preferably a clay filler, more preferably an Organically Modified Montmorillonite (OMMT).

5. The process according to any one of claims 1 to 4, wherein the first solvent is selected from the group consisting of para-xylene, meta-xylene, ortho-xylene, toluene, decalin, ethylbenzene, chlorobenzene or combinations thereof.

6. A process according to any one of claims 1 to 5, wherein the second solvent is an alcohol, preferably having a boiling point higher than that of the first solvent.

7. The process according to claim 6, wherein the alcohol is selected from the group consisting of a linear primary aliphatic alcohol having 6 or more carbon atoms or a linear secondary aliphatic alcohol having 7 or more carbon atoms.

8. A method according to any one of claims 3 to 7, comprising the step of exfoliating the at least one filler in a first solvent or in a third solvent which is miscible with the first and second solvents and capable of exfoliating and/or dispersing the at least one filler, optionally involving sonication, prior to providing the suspension.

9. A process according to any one of claims 1 to 8, wherein the first elevated temperature is equal to or above the boiling point of the first solvent, preferably above 125 ℃, more preferably from 135 to 155 ℃.

10. The process according to any one of claims 1 to 9, wherein the solubilization step (b) is carried out under reflux.

11. The method according to any one of claims 1 to 10, wherein the precipitation step (c) comprises a cooling process comprising:

-a first cooling step, in which the solution is cooled from equal to or higher thanFirst elevated temperature (T)₁) Is cooled to a second temperature (T)₂) Said second temperature (T)₂) Below a first elevated temperature (T)₁) And maintained at the second temperature for a first period of time (delta)_t1) And are and

-optionally a second cooling step, wherein the solution is cooled to below a second temperature (T)₂) Third temperature (T)₃) And at a third temperature (T)₃) Lower hold for a second period (Δ)_t2)。

12. The process according to any one of claims 1 to 11, wherein the recovery step (d) comprises filtering the suspension obtained in the precipitation step (c), and optionally washing the particles obtained by filtration with a fourth solvent, the fourth solvent being miscible with at least the second solvent, and the at least one polymeric material being insoluble in the fourth solvent.

13. Polymer composite particles for selective laser sintering obtainable by the process according to any one of the preceding claims.

14. Use of the particles according to claim 13 in a selective laser sintering process for producing sintered objects.

15. Use according to claim 14, which comprises:

i) providing a bed of particles in a particle bed;

ii) applying a laser to the layer to fuse the particles together;

repeating steps i) and ii), thereby providing a sintered object.