METHOD FOR PRODUCING SPHERICAL THERMOPLASTIC POLYMER PARTICLES

Abstract

A process for producing particles of a thermoplastic polymer in spherical form involves providing at least one thermoplastic polymer in a molten state and providing an aqueous solution of at least one surface-active substance. The aqueous solution is in a temperature range from 100 to 300° C. The process also involves dispersing the thermoplastic polymer in the aqueous solution to obtain an aqueous solution containing dispersed thermoplastic polymer, which is cooled down to a temperature below the solidification point of the thermoplastic polymer to obtain a suspension containing an aqueous solution and particles of the thermoplastic polymer suspended in a solid state and in spherical form. The particles can be separated from the suspension and, optionally, dried. The particles obtained from the process have a particle size distribution having a d[4,3] value of more than 10 μm and a d.sub.90.3 value of more than 20 μm.

Claims

1: A process for producing particles of a thermoplastic polymer in spherical form, the process comprising: (i) providing at least one thermoplastic polymer in a molten state; (ii) providing an aqueous solution of at least one surface-active substance, wherein the aqueous solution of the at least one surface-active substance is at a temperature in a range from 100 to 300° C.; (iii) dispersing the at least one thermoplastic polymer from (i) in the aqueous solution of the at least one surface-active substance from (ii), to obtain an aqueous solution comprising dispersed thermoplastic polymer; (iv) cooling down the aqueous solution comprising dispersed thermoplastic polymer to a temperature below a solidification point of the at least one thermoplastic polymer, to obtain a suspension comprising an aqueous solution and particles of the at least one thermoplastic polymer suspended therein in a solid state, wherein the particles are in spherical form; (v) separating the particles of the least one thermoplastic polymer in spherical form from the suspension obtained in (iv); and (vi) optionally, drying the particles of the at least one thermoplastic polymer in spherical form that have been separated off in (v); wherein the particles of the at least one thermoplastic polymer in spherical form that have been separated off in (v) and optionally dried in (vi) have a particle size distribution having a d[4,3] value of more than 10 μm and a d.sub.90.3 value of more than 20 μm.

2: The process according to claim 1, wherein (i) comprises: (i.1) providing the at least one thermoplastic polymer in a solid state; and (i.2) melting the at least one thermoplastic polymer to obtain the at least one thermoplastic polymer in the molten state.

3: The process according to claim 1, wherein the at least one thermoplastic polymer in the molten state is dispersed in the aqueous solution of the at least one surface-active substance in (iii) under action of mechanical force, ultrasound, and/or high-pressure homogenization, to obtain the aqueous solution comprising dispersed thermoplastic polymer.

4: The process according to claim 2, wherein the melting in (i.2) is effected in an extruder or by means of extrusion.

5: The process according to claim 1, wherein the dispersing in (iii) is effected at a temperature in range from 100 to 300° C.

6: The process according to claim 1, wherein the cooling in (iv) is effected to a temperature in a range from 20 to 100° C.

7: The process according to claim 1, wherein the particles of the at least one thermoplastic polymer in spherical form that are separated off in (v) and optionally dried in (vi) have a particle size distribution having a d[4,3] value of more than 20 μm.

8: The process according to claim 1, wherein the particles of the at least one thermoplastic polymer in spherical form that are separated off in (v) and optionally dried in (vi) have a particle size distribution having a d.sub.50.3 value of more than 20 μm.

9: The process according to claim 1, wherein the at least one thermoplastic polymer is selected from the group consisting of polyurethane, polyester, polyetherester, polyesterester, polyamide, polypropylene, polyetheramide, polybutadiene-styrene and ethylene-vinyl acetate.

10: The process according to claim 1, wherein the at least one surface-active substance is selected from the group consisting of polyvinylalcohols.

11: The process according to claim 1, wherein the at least one surface-active substance is present in an amount in a range from 0.1% to 20% by weight, based on a total weight of the aqueous solution of the at least one surface-active substance from (ii).

12: The process according to claim 1, wherein the spherical form of the particles of the at least one thermoplastic polymer is a sphere or an ellipsoid.

13: Particles of a thermoplastic polymer in spherical form, obtained or obtainable by the process according to claim 1.

14: Particles of a thermoplastic polymer in spherical form, wherein the particles have a particle size distribution having a d[4,3] value of more than 10 μm and a d.sub.90.3 value of more than 20 μm.

15: A method, comprising: performing an additive manufacturing method or a powder coating method, with particles of a thermoplastic polymer in spherical form having a particle site distribution having a d[4,3] value of more than 10 μm and a d.sub.90.3 value of more than 20 μm.

16: The process according to claim 7, wherein the particles of the at least one thermoplastic polymer in spherical form that are separated off in (v) and optionally dried in (vi) have a particle size distribution having a d.sub.90.3 value of more than 50 μm.

17: The process according to claim 9, wherein the at least one thermoplastic polymer comprises a thermoplastic polyurethane (TPU).

18: The process according to claim 10, wherein the at least one surface-active substance is selected from the group consisting of at least partly hydrolysed polyvinylacetates.

19: The method according to claim 15, wherein the particles of the thermoplastic polymer are in a form of a powder.

20: The method according to claim 15, wherein the additive manufacturing method is selected from the group consisting of powder bed fusion, high-speed sintering, and multi-jet fusion; and wherein the powder coating method is selected from the group consisting of powder sintering, powder slush, and slush molding.

Description

EXAMPLES

1. Chemicals

[0080]

TABLE-US-00001 Name Chemical name Polymer 1 Aliphatic thermoplastic polyester-based polyurethane elastomer having a Shore A hardness of 88 (Elastollan A C 88 A 12 001; BASF Polyurethanes GmbH, Lemförde) Surface-active Party hydrolyzed polyvinylacetate substance 1 Hydrolysis level 78-81 mol %; is used as a 4% by weight aqueous solution (viscosity 37-45 mPa .Math. s at 20° C. determined to DIN 53015/JIS K 6726) DM water Demineralized water Antifoam 1 Aqueous polydimethylsiloxane emulsion having a solids content of 33% by weight and a viscosity at 25° C. of 150 mPa s (pH 7)

2. Reference Example 1: Production of Spherical Particles of a Thermoplastic Polymer

[0081] The thermoplastic polymer to be emulsified was metered continuously into an extruder (Collin E16T extruder) by means of a differential metering screw in the form of a pelletized material that was solid at room temperature (23° C.), and it was melted therein at a temperature above Tg, preferably above Tm. The molten thermoplastic polymer was conveyed continuously into a dispersing apparatus with the aid of the extruder. At the same time, a continuous phase that contained at least one interface-active substance (emulsifier) in water was metered continuously into the dispersing apparatus with the aid of a pump via a heat exchanger. In the heat exchanger, the aqueous emulsifier solution was heated to a temperature in the range from 150 to 250° C.

[0082] In the dispersing apparatus, the polymer melt was emulsified in the continuous phase as a disperse phase at a temperature in the range from 150 to 250° C. preferably in the range from 170 to 220° C., so as to result in small melt droplets of the thermoplastic polymer that are stabilized against coalescence in the solution by the at least one interface-active substance. Downstream of the dispersing apparatus, the emulsion with the droplets of the thermoplastic polymer present therein was cooled down with the aid of a cooling apparatus to a temperature below the solidification point Tg of the thermoplastic polymer, solidifying the droplets of the thermoplastic polymer. What was thus obtained was a suspension with finely distributed, spherical thermoplastic polymer particles in the continuous phase.

3. Example 1: Production of Spherical TPU Particles

[0083] Polymer 1 was melted at a temperature of 220° C. according to the method from reference example 1 and processed further according to the method from reference example 1: surface-active substance 1 was used in a concentration of 2.7% by weight, and the continuous phase thus had the following composition: [0084] 2.7% by weight of emulsifier 1 [0085] 0.1% by weight of defoamer 1 [0086] 97.2% by weight of DM water

[0087] In the heat exchanger, the aqueous emulsifier solution was heated to a temperature in the region of about 170° C.

[0088] The dispersing apparatus used was a DLM/S-007 dynamic flow mixer from INDAG, Borsfleet, Germany. In the dispersing apparatus, the polymer melt was emulsified in the continuous phase as a disperse phase at a temperature in the range from 170 to 220° C., with the following conditions in the dispersing apparatus:

[0089] Dispersing apparatus speed: 211 rpm

[0090] Continuous phase temperature (aqueous emulsifier solution): 180° C.

[0091] Continuous phase throughput: 4 kg/h

[0092] Melt feed temperature: 220° C.

[0093] Throughput of polymer 1 melt: 0.4 kg/h

[0094] Suspension temperature downstream of the cooling apparatus: 70° C.

[0095] The particle size distribution of the dispersed thermoplastic polymer in the suspension was measured with a Malvern Mastersizer 3000 laser diffraction spectrometer. The particle sizes at 90, 50 and 10 percent throughput of the cumulative volume distribution and the weighted average d[4,3] were as follows:

[0096] d.sub.90.3=155 μm

[0097] d.sub.50.3=56 μm

[0098] d.sub.90.3=11 μm

[0099] d[4,3]=74 μm

[0100] The particle size distribution and cumulative volume distribution are shown in the form of graphs in FIG. 1. FIG. 2 shows an image of the spherical TPU particles created by means of scanning electron microscopy. It is clearly apparent from FIG. 2 in particular that the spherical particles obtained, no matter what size, have a spherical shape and do not show any surface unevenness.

4. Example 2: Production of Spherical TPU Particles with Carbon Black Additization

[0101] A melt consisting of 62% by weight of polymer 1 and 38% by weight of carbon black was dispersed in an aqueous continuous phase consisting of 97.27% by weight of demineralized water, 2.7% by weight of surface-active substance 1 and 0.03% by weight of defoamer 1, and then cooled.

[0102] The dispersing apparatus used was a DLM/S-007 dynamic flow mixer from INDAG, Borsfleet, Germany. The polymer melt was fed to the dispersing apparatus at a temperature of 225° C. and dispersed in the continuous phase, with the following conditions in the dispersing apparatus:

[0103] Dispersing apparatus speed: 356 rpm

[0104] Continuous phase temperature: 180° C.

[0105] Continuous phase throughput: 4 kg/h

[0106] Melt feed temperature: 225° C.

[0107] Polymer melt throughput: 0.4 kg/h

[0108] Suspension temperature downstream of the cooling apparatus: 70° C.

[0109] The suspension obtained after the cooling was sieved through a sieve having a square mesh size of 400 μm and then dried under reduced pressure at a temperature of 70° C.

[0110] The particle size distribution of the dispersed thermoplastic polymer in the suspension was measured with a Malvern Mastersizer 3000 laser diffraction spectrometer. The particle sizes at 90, 50 and 10 percent throughput of the cumulative volume distribution and the weighted average d[4,3] were as follows:

[0111] d.sub.90.3=262 μm

[0112] d.sub.50.3=83 μm

[0113] d.sub.10.3=32 μm

[0114] d[4,3]=118 μm

DESCRIPTION OF THE FIGURES

[0115] FIG. 1 shows the density distribution and the cumulative volume distribution of the spherical TPU particles produced according to example 1;

[0116] FIG. 2 shows a scanning electron micrograph of the spherical TPU particles produced according to example 1;

[0117] FIG. 3 shows the density distribution and the cumulative volume distribution of the spherical TPU particles produced according to example 2;

[0118] FIG. 4 shows a light micrograph of the spherical TPU particles produced according to example 2.

CITED LITERATURE

[0119] U.S. Pat. No. 8,604,101 B2 [0120] J. Schmidt, M. Sachs, S. Fanselow, M. Zhao, S. Romeis. D. Drummer, K.-E. Wirth, W. Peukert, Chemical Engineering Science 156 (2016), 1-10 [0121] “Kunststoffhandbuch, 7, Polyurethane”, Carl Hanser Verlag, 3rd edition 1993, section 3.1 [0122] “Kunststoffhandbuch”; 7, “Polyurethane”, Carl Hanser Verlag, 1st edition 1966, pages 103-113