COMPOSITE POWDER CONTAINING CALCIUM CARBONATE AND HAVING MICROSTRUCTURED PARTICLES HAVING INHIBITING CALCIUM CARBONATE

Abstract

A composite powder containing microstructured particles having inhibitory calcium carbonate, obtainable by means of a method in which large particles are combined with small particles, wherein the large particles have an average particle diameter within the range from 0.1 μm to 10 mm, the large particles comprise at least one polymer, the small particles are arranged on the surface of the large particles and/or distributed inhomogeneously within the large particles, the small particles comprise calcium carbonate particles, the small particles have an average particle size within the range from 0.01 μm to 1.0 mm,
wherein the small particles are obtainable by means of a method in which calcium carbonate particles are coated with a composition comprising, based on its total weight, at least 0.1% by weight of at least one weak acid.

Preferred application areas of the composite powder encompass its use as additive, especially as polymer additive, as additive substance or starting material for compounding, for the production of components, for applications in medical technology and/or in microtechnology and/or for the production of foamed articles.

The invention therefore also provides components obtainable by selective laser sintering of a composition comprising a composite powder according to the invention, except for implants for uses in the field of neurosurgery, oral surgery, jaw surgery, facial surgery, neck surgery, nose surgery and ear surgery as well as hand surgery, foot surgery, thorax surgery, rib surgery and shoulder surgery.

Claims

1. A composite powder containing microstructured particles having inhibitory calcium carbonate, obtainable by means of a method in which large particles are combined with small particles, wherein the large particles have an average particle diameter within the range from 0.1 μm to 10 mm, the large particles comprise at least one polymer, the small particles are arranged on the surface of the large particles and/or distributed inhomogeneously within the large particles, the small particles comprise calcium carbonate particles, the small particles have an average particle size within the range from 0.01 μm to 1.0 mm, characterized in that the small particles are obtainable by means of a method in which calcium carbonate particles are coated with a composition comprising, based on its total weight, at least 0.1% by weight of at least one weak acid.

2. The composite powder as claimed in claim 1, characterized in that the calcium carbonate particles are coated with a composition comprising, based in each case on its total weight, a mixture of at least 0.1% by weight of at least one calcium complexing agent and/or at least one conjugate base, which is an alkali-metal or calcium salt of a weak acid, together with at least 0.1% by weight of at least one weak acid.

3. The composite powder as claimed in claim 1, characterized in that the weak acid is selected from the group consisting of phosphoric acid, metaphosphoric acid, hexametaphosphoric acid, citric acid, boric acid, sulfurous acid, acetic acid and mixtures thereof.

4. The composite powder as claimed in claim 2, characterized in that the conjugate base is a sodium or calcium salt of a weak acid.

5. The composite powder as claimed in claim 2, characterized in that the conjugate base is sodium hexametaphospate.

6. The composite powder as claimed in claim 2, characterized in that the conjugate base is sodium hexametaphosphate and the weak acid is phosphoric acid.

7. The composite powder as claimed in claim 2, characterized in that the calcium complexing agent is selected from the group consisting of sodium hexametaphosphate and joint polydentate, chelating ligands.

8. The composite powder as claimed in claim 7, characterized in that the joint polydentate, chelating ligands are selected from the group consisting of ethylenediaminetetraacetic acid (EDTA), triethylenetetramine, diethylenetriamine, o-phenanthroline, oxalic acid and mixtures thereof.

9. The composite powder as claimed in claim 2, characterized in that the content of the calcium complexing agent or of the conjugate base is within the range from 0.1 part by weight to 25.0 parts by weight, based on 100 parts by weight of calcium carbonate particles, and the content of the weak acid is within the range from 0.1 part by weight to 30.0 parts by weight, based on 100 parts by weight of calcium carbonate particles.

10. The composite powder as claimed in claim 1, characterized in that the calcium carbonate has an aspect ratio less than 5.

11. The composite powder as claimed in claim 1, characterized in that the calcium carbonate comprises sphere-shaped calcium carbonate.

12. The composite powder as claimed in claim 1, characterized in that the large particles comprise at least one thermoplastic polymer.

13. The composite powder as claimed in claim 1, characterized in that the large particles comprise at least one resorbable polymer.

14. The composite powder as claimed in claim 13, characterized in that the resorbable polymer has an inherent viscosity, measured in chloroform at 25° C. and 0.1% polymer concentration, within the range from 0.3 dL/g to 8.0 dL/g.

15. The composite powder as claimed in claim 1, characterized in that the large particles comprise poly-D-, poly-L- and/or poly-D,L-lactic acid.

16. The composite powder as claimed in claim 1, characterized in that the large particles comprise at least one resorbable polyester having a number-average molecular weight within the range from 500 g/mol to 1 000 000 g/mol.

17. The composite powder as claimed in claim 1, characterized in that the large particles comprise at least one polyamide.

18. The composite powder as claimed in claim 1, characterized in that the large particles comprise at least one polyurethane.

19. The composite powder as claimed in claim 1, characterized in that the proportion by weight of the calcium carbonate, based on the total weight of the composite powder, is at least 0.1% by weight.

20. The composite powder as claimed in claim 1, characterized in that the composite powder comprise, based on the total weight of the composite powder, 40.0% by weight to 80.0% by weight of PLLA and 20.0% by weight to 60.0% by weight of calcium carbonate particles.

21. A method comprising using composite powder as claimed in claim 1 as additive, especially as polymer additive, as additive substance or starting material for compounding, for the production of components, for applications in medical technology and/or in microtechnology and/or for the production of foamed articles.

22. A component obtainable by selective laser sintering of a composition comprising a composite powder as claimed in claim 1, except for implants for uses in the field of neurosurgery, oral surgery, jaw surgery, facial surgery, neck surgery, nose surgery and ear surgery as well as hand surgery, foot surgery, thorax surgery, rib surgery and shoulder surgery.

23. The composite powder as claimed in claim 1, characterized in that the weak acid is phosphoric acid.

Description

EXAMPLE 1

[0337] At a starting temperature of 10° C., a CO.sub.2 gas mixture containing 20% CO.sub.2 and 80% N.sub.2 was introduced into a 4 L calcium hydroxide suspension having a concentration of 75 g/L CaO. The gas flow rate was 300 L/h. The reaction mixture was stirred at 350 rpm and the reaction heat was dissipated during the reaction. Upon an abrupt drop in the conductance (drop of more than 0.5 mS/cm/min and decrease in the conductance by more than 0.25 mS/cm within 30 seconds), 0.7% aminotris(methylenephosphonic acid), based on CaO (as theoretical reference value), is added to the suspension. The reaction to yield the sphere-shaped calcium carbonate particles was completed when the reaction mixture was quantitatively carbonated to yield sphere-shaped calcium carbonate particles, the reaction mixture having then a pH between 7 and 9. In the present case, the reaction was completed after approximately 2 h and the reaction mixture had a pH of 7 at the end of the reaction.

[0338] The resultant sphere-shaped calcium carbonate particles were separated off and dried by conventional means. They had an average particle diameter of 12 μm. A typical SEM image is presented in FIG. 1.

EXAMPLE 2

Inhibitory Calcium Carbonate Particles; Reactant for Composite Powder According to the Claimed Invention

[0339] 500 mL of demineralized water were initially charged in a 1000 mL beaker. 125 g of sphere-shaped calcium carbonate particles as per Example 1 were added under stirring and the resultant mixture was stirred for 5 min. 37.5 g of a 10% sodium metaphosphate (NaPO.sub.3).sub.n solution were added slowly and the resultant mixture was stirred for 10 min. 75.0 g of 10% phosphoric acid were added slowly and the resultant mixture was stirred for 20 h. The precipitate is separated off and dried overnight at 130° C. in a drying cabinet. The resultant sphere-shaped calcium carbonate particles likewise had an average particle diameter of 12 μm.

[0340] An SEM image of the sphere-shaped calcium carbonate particles is presented in FIG. 2. A thin phosphate layer can be identified on the surface of the sphere-shaped calcium carbonate particles.

EXAMPLE 3

[0341] A composite powder composed of sphere-shaped calcium carbonate particles and a polylactide (PLLA) was produced following the method described in JP 62083029 A, using the instrument NHS-1. Cooling was carried out using 12° C. cold water. A polylactide granulate 1 and the sphere-shaped calcium carbonate particles from Example 1 were used as the mother particles and as the baby particles (filler), respectively.

[0342] 39.5 g of polylactide granulate were mixed with 26.3 g of CaCO.sub.3 powder and filled at 6400 rpm. The rotor speed of the aggregate was adjusted to 6400 rpm (80 m/s) and the metered materials were processed for 10 min. The maximally reached temperature in the grinding space of the NHS-1 was 35° C. Altogether 7 repeats with the same amounts of material and same machine settings were carried out. Altogether 449 g of composite powder were obtained. The composite powder obtained was manually dry-sieved through a 250 μm sieve. The sieve residue (fraction >250 μm) was 0.4%.

[0343] An SEM image of the composite powder obtained is presented in FIG. 3a.

EXAMPLE 5

Composite Powder According to the Claimed Invention and Examples 4, 6 and 7

[0344] Further composite powders were produced analogously to Example 3, though the cooling was carried out at approx. 20° C. in Example 5. 30 g of polylactide granulate were mixed with 20 g of CaCO.sub.3 powder in each case. The maximally reached temperature in the grinding space of the NHS-1 was 33° C. for Example 4, 58° C. for Example 5, 35° C. for Example 6 and 35° C. for Example 7. The products were sieved in order to remove as far as possible the coarse fraction >250 μm (manual dry sieving through a 250 μm sieve). In Examples 4, 6 and 7, the fraction <20 μm was additionally removed as far as possible by flow classification (by means of air classification) or by sieving (by means of an air-jet sieving machine). The materials used, the production procedure with or without sieving/air classification and also the properties of the composite powders obtained are outlined in Table 3 below.

[0345] FIG. 3a, FIG. 3b and FIG. 3c show an SEM image from Example 3 as well as images of various doctor-blade applications (12.5 mm/s) from Example 3 (FIG. 3b: 200 μm doctor blade; FIG. 3c: 500 μm doctor blade).

[0346] The SEM image of the composite powder obtained is presented in FIG. 3a. In contrast to the edged, irregular particle shape typical for cryogenically ground powders, the particles of the composite powder obtained have a round particle shape or high sphericity that is very advantageous for SLM methods. The PLLA surface is sparsely occupied by sphere-shaped calcium carbonate particles and fragments thereof. The sample has a wide particle-size distribution with an increased fine fraction.

[0347] The powder is flowable to a limited extent (FIGS. 3b and 3c). A heap of powder is pushed ahead by the doctor blade. Owing to the limited flow behavior, presumably caused by a relatively high proportion of fine particles, only very thin layers are formed with both doctor blades.

[0348] FIG. 4a, FIG. 4b and FIG. 4c show an SEM image from Example 4 as well as images of various doctor-blade applications (12.5 mm/s) from Example 4 (FIG. 4b: 200 μm doctor blade; FIG. 4c: 500 μm doctor blade).

[0349] The SEM image of the composite powder obtained is presented in FIG. 4a. In contrast to the edged, irregular particle shape typical for cryogenically ground powders, the particles of the composite powder obtained have a round particle shape or high sphericity that is very advantageous for SLM methods. The PLLA surface is sparsely occupied by sphere-shaped calcium carbonate particles and fragments thereof. The sample has a distinctly narrower particle-size distribution with little fine fraction.

[0350] The powder is very highly flowable and blade-coatable (FIGS. 4b and 4c). The thin layers (200 μm) can be blade-coated, too, and are largely free of doctor-blade stripes (grooves). The powder layer blade-coated at 500 μm is homogeneous, densely packed, smooth and free of doctor-blade stripes.

[0351] FIG. 5a, FIG. 5b and FIG. 5c show an SEM image from Example 5 as well as images of various doctor-blade applications (12.5 mm/s) from Example 5 (FIG. 5b: 200 μm doctor blade; FIG. 5c: 500 μm doctor blade). The powder is flowable to a limited extent. A heap of powder is pushed ahead by the doctor blade. Owing to the limited flow behavior, presumably caused by a relatively high proportion of fine particles, only very thin layers are formed with both doctor blades.

[0352] FIG. 6a, FIG. 6b and FIG. 6c show an SEM image from Example 6 as well as images of various doctor-blade applications (12.5 mm/s) from Example 6 (FIG. 6b: 200 μm doctor blade; FIG. 6c: 500 μm doctor blade). The powder is highly flowable and blade-coatable. The thin layers (200 μm) can be blade-coated, too. Individual doctor-blade stripes presumably due to excessively coarse powder particles are identifiable. The powder layer blade-coated at 500 μm is not quite densely packed, but is free of doctor-blade stripes.

[0353] FIG. 7a, FIG. 7b and FIG. 7c show an SEM image from Example 7 as well as images of various doctor-blade applications (12.5 mm/s) from Example 7 (FIG. 7b: 200 μm doctor blade; FIG. 7c: 500 μm doctor blade). The powder is flowable and blade-coatable. The thin layers (200 μm) can be blade-coated, too. They are not homogeneous and there are more doctor-blade stripes. Somewhat limited flow behavior is presumably caused by excessively coarse powder particles. The powder layer blade-coated at 500 μm is homogeneous and free of doctor-blade stripes.

[0354] Comparison 1 (comparative example)

[0355] Microstructured composite particles composed of sphere-shaped calcium carbonate particles from Example 1 and an amorphous polylactide (PDLLA) were produced following the method described in JP 62083029 A, using the instrument NHS-1. Cooling was carried out using 12° C. cold water. A polylactide granulate 3 and the sphere-shaped calcium carbonate particles from Example 1 were used as the mother particles and as the baby particles, respectively.

[0356] 39.5 g of polylactide granulate were mixed with 10.5 g of CaCO.sub.3 powder and filled at 8000 rpm. The rotor speed of the aggregate was adjusted to 8000 rpm (100 m/s) and the metered materials were processed for 1.5 min. The maximally reached temperature in the grinding space of the NHS-1 was 71° C. Altogether 49 repeats with the same amounts of material and same machine settings were carried out. Altogether 2376 g of structured composite particles were obtained. The structured composite particles obtained were manually dry-sieved through a 800 μm sieve for the measurement of the particle-size distribution. The sieve residue (fraction >800 μm) was 47%.

[0357] The properties of the microstructured composite particles obtained are outlined in Table 3 below.

[0358] FIG. 8a, FIG. 8b and FIG. 8c show an SEM image from Comparison 1 as well as images of various doctor-blade applications (12.5 mm/s) from Comparison 1 (FIG. 8b: 200 μm doctor blade; FIG. 8c: 500 μm doctor blade). The powder is poorly flowable and cannot be blade-coated to form layer thicknesses 200 or 500 μm thin. The excessively coarse, irregular particles become stuck during blade-coating. What arise are inhomogeneous layers with highly frequent and pronounced doctor-blade stripes.

[0359] The SEM analysis shows that the surfaces of the structured composite particles are sparsely occupied by sphere-shaped calcium carbonate particles and fragments thereof. In comparison with Examples 3-7, the particles have a more irregular particle geometry.

EXAMPLE 8

[0360] A composite powder composed of β-tricalcium phosphate particles and a polylactide (PDLLA) was produced following the method described in JP 62083029 A, using the instrument NHS-1. Cooling was carried out using 12° C. cold water. A polylactide granulate 3 and β-tricalcium phosphate (β-TCP; d.sub.20=30 μm; d.sub.50=141 μm; d.sub.90=544 μm) were used as the mother particles and as the baby particles, respectively. The SEM image of the β-TCP used are shown in FIG. 9a and FIG. 9b.

[0361] 30.0 g of polylactide granulate were mixed with 20.0 g of β-TCP powder and filled at 6400 rpm. The rotor speed of the aggregate was adjusted to 6400 rpm (80 m/s) and the metered materials were processed for 10 min. Altogether 5 repeats with the same amounts of material and same machine settings were carried out. Altogether 249 g of composite powder were obtained. The product were sieved in order to remove as far as possible the coarse fraction >250 μm (manual dry sieving through a 250 μm sieve). Thereafter, the fine fraction <20 μm was separated off by means of an air-jet sieving machine via a 20 μm sieve.

EXAMPLE 9

[0362] A composite powder composed of rhombohedral calcium carbonate particles and a polylactide (PDLLA) was produced following the method described in JP 62083029 A, using the instrument NHS-1. Cooling was carried out using 12° C. cold water. A polylactide granulate 3 and rhombohedral calcium carbonate particles (d.sub.20=11 μm; d.sub.50=16 μm; d.sub.90=32 μm) were used as the mother particles and as the baby particles, respectively.

[0363] 30.0 g of polylactide granulate were mixed with 20.0 g of the rhombohedral calcium carbonate particles and filled at 6400 rpm. The rotor speed of the aggregate was adjusted to 6400 rpm (80 m/s) and the metered materials were processed for 10 min. Altogether 5 repeats with the same amounts of material and same machine settings were carried out. Altogether 232 g of composite powder were obtained. The product were sieved in order to remove as far as possible the coarse fraction >250 μm (manual dry sieving through a 250 μm sieve). Thereafter, the fine fraction <20 μm was separated off by means of an air-jet sieving machine via a 20 μm sieve.

EXAMPLE 10

[0364] A composite powder composed of ground calcium carbonate particles and a polylactide (PDLLA) was produced following the method described in JP 62083029 A, using the instrument NHS-1. Cooling was carried out using 12° C. cold water. A polylactide granulate 3 and ground calcium carbonate (GCC; d.sub.20=15 μm; d.sub.50=46 μm; d.sub.90=146 μm) were used as the mother particles and as the baby particles, respectively.

[0365] 30.0 g of polylactide granulate were mixed with 20.0 g of GCC and filled at 6400 rpm. The rotor speed of the aggregate was adjusted to 6400 rpm (80 m/s) and the metered materials were processed for 10 min. Altogether 5 repeats with the same amounts of material and same machine settings were carried out. Altogether 247 g of composite powder were obtained. The product were sieved in order to remove as far as possible the coarse fraction >250 μm (manual dry sieving through a 250 μm sieve). Thereafter, the fine fraction <20 μm was separated off by means of an air-jet sieving machine via a 20 μm sieve.

TABLE-US-00003 TABLE 3 Example 3 Example 4 Example 5 Example 6 Example 7 Comparison 1 Composition for the production of the composite powder comprising microstructured particles m(Example 1) 40 40 0 40 40 20 [% by weight] m(Example 2) 0 0 40 0 0 0 [% by weight] Polylactide Granulate 1 Granulate 1 Granulate 1 Granulate 2 Granulate 3 Granulate 3 m(Polylactide) 60 60 60 60 60 80 [% by weight] Production of the composite powder comprising microstructured particles Sieving <250 μm <250 μm <250 μm <250 μm <250 μm <800 μm <20 μm (air <20 μm (air- <20 μm (air- (only for classification) jet sieving) jet sieving) measurement of the particle-size distribution) CaCO.sub.3 content 41.0 22.4 35.0 19.5 22.3 22.4 (average [% by weight].sup.1 from 5 measurements) T.sub.P 291 310 341 304 286 319 (average [° C.].sup.1 from 5 measurements) d.sub.50 25 47 26 112 136 228 [μm].sup.1 Fraction <20 μm 43.6 13.7 37.7 0.3 2.3 20.6 [% by volume].sup.1 d.sub.20 9 26 14 69 80 [μm].sup.1 d.sub.90 86 102 70 223 247 [μm].sup.1 d.sub.20/d.sub.50 [%] 36 52 54 62 59 Moisture 0.8 0.6 0.5 0.9 0.9 0.3 [% by weight].sup.1 Inherent 1.0 1.0 0.9 1.9 1.9 1.9 viscosity [dL/g] Three-point 66 68 77 84 67 79 bending strength [MPa] Elastic modulus 4782 3901 4518 3530 3594 3420 [N/mm.sup.2] Flowability 4 1 4 2 3 5 Cytotoxicity test not cytotoxic not cytotoxic not cytotoxic — not cytotoxic not cytotoxic Example 8 Example 9 Example 10 Composition for the production of the composite powder comprising microstructured particles m(Filler) 40 40 40 [% by weight] Polylactide Granulate 3 Granulate 3 Granulate 3 m(Polylactide) 60 60 60 [% by weight] Production of the composite powder comprising microstructured particles Sieving <250 μm <250 μm <250 μm <20 μm Air- <20 μm Air- <20 μm Air- jet sieving jet sieving jet sieving Filler content 24.9 24.2 26.6 [% by weight]* T.sub.P [° C.] 341° C. 303° C. 303° C. d.sub.20 [μm] 85 74 75 d.sub.50 [μm] 131 128 120 d.sub.90 [μm] 226 257 230 Fraction <20 μm 3.0 4.5 1.6 [% by volume] Moisture [% by 0.6 0.6 0.6 weight] Inherent viscosity 1.8 1.8 1.9 [dL/g] .sup.1at least duplicate determination

[0366] Comparison 2, Example 11, Example 12 (composite powder according to the claimed invention), Example 13, Example 14 (composite powder according to the claimed invention) and Example 15

[0367] PLA pellets were mixed and melted as pure pellets and with 4 different fillers (25% by weight) using a Brabender Plasti-Corder. The chamber temperature was 190° C. at a rotational speed of 50 rpm. Pellets and filler powder were mixed for 5 minutes; thereafter, approx. 16 g of the mixture were pressed in a hydraulic press at a pressure of 0.96-1.2 MPa for 5 minutes.

[0368] In all the examples, the polymer used was PLA (NatureWorks Ingeo TM Biopolymer 3251 D). In Comparison 2, no calcium carbonate particles were added. In Example 11, calcium carbonate particles according to Example 1 were added. In Example 12, calcium carbonate particles according to Example 2 were added. In Example 13, calcium carbonate particles were added, the particles having been produced analogously to Example 2 but without addition of phosphoric acid. In Example 14, calcium carbonate particles were added, the particles having been produced analogously to Example 2 but without addition of sodium metaphosphate (NaPO.sub.3).sub.n). In Example 15, stearic acid-coated calcium carbonate particles obtained by conventional means were added.

[0369] Characterization of the PLA composites of Comparison 2 and Example 11-15

[0370] a) Mechanical Properties

[0371] The mechanical properties of PLA and of the composites were tested using the universal testing machine UTM 1445 from Zwick/Roell. The tensile strength, the elastic modulus and the stretch of the materials were determined here. The test speed was 10 mm/min at a measurement length of 50 mm.

[0372] b) Thermal Properties

[0373] The thermal stability of the samples was determined by means of thermogravimetry. The thermogravimetric measurements were carried out using an STA 6000 from Perkin Elmer under nitrogen within the range from 40° C. to 1000° C. at a heating rate of 20° C./min.

[0374] c) Optical assessment of the samples (**grades of 1-3)

[0375] 1=transparent pure polymer; no identifiable discoloration due to thermal degradation

[0376] 2=white polymer compound; change in color to white due to addition of the filler; no identifiable discoloration due to thermal degradation

[0377] 3=brown color due to thermal degradation of the compound

[0378] The addition of the CaCO.sub.3 particles to the PLA matrix led to a change in color from transparent pure PLA to white composites for all the fillers except for Example 15. In the case of the sample with stearic acid-coated calcium carbonate particles, the color changed to a light brown, indicating polymer degradation. All the other samples show no signs of degradation at all. he observed properties are outlined in Table 4.

TABLE-US-00004 TABLE 4 Comparison 2 Example 11 Example 12 Example 13 Example 14 Example 15 CaCO.sub.3 particles Example 1 Example 2 Example 2 Example 2 Coated with without without stearic acid addition of addition of (1.0%) phosphoric sodium acid meta- phosphate pH .sup.1) 10.0/10.0 6.1/6.2 8.9/9.0 7.0/7.0 — (immediately/24 h) Moisture 0.1 0.1 0.1 0.1 0.1 [%] d.sub.50 12.1 12.2 12.0 14.3 14.2 [μm] Spec. surface area 1.1 0.2 0.6 0.9 4.9 [m.sup.2/g] P.sub.2O.sub.5 content 0.3 3.1 0.4 6.8 — [%] Qualitative phase analysis Calcite Calcite Calcite Calcite + brushite Tensile strength [MPa] 47.99 44.57 40.56 40.20 37.95 41.39 Elastic modulus [MPa] 1345.0 1680.4 1718.9 1601.9 1625.8 1627.1 Onset temperature 348.8 326.1 360.3 337.4 358.4 322.9 (TGA) [° C.] Peak temperature 377.6 356.5 380.3 368.1 380.8 354.5 (TGA) [° C.] Grading of test pieces** 1 2 2 2 2 3