SELECTIVE SUPERPARAMAGNETIC SINTERING AND AN INK SUITABLE THEREFOR

Abstract

Methods can be used for producing three-dimensional objects by powder bed fusion, using inks containing superparamagnetic particles and solvents. Sintering is performed by a magnetic field having a frequency of 50 kHz to 5 GHz.

Claims

1. A method, comprising; fusing a powder bed with an ink, wherein the ink comprises superparamagnetic particles, and at least one solvent.

2. The method according to claim 1, wherein the superparamagnetic particles are core/shell particles having at least one core comprising at least one superparamagnetic substance, and at least one non-magnetic shell.

3. The method according to claim 1, wherein the at least one solvent is an aqueous solvent.

4. The method according to claim 3, wherein the ink further comprises a water-miscible organic solvent.

5. The method according to claim 3, wherein a pH of the ink is 3 to 12.

6. The method according to claim 1, wherein the superparamagnetic particles are selected from the group consisting of a ferromagnetic substance, an antiferromagnetic substance, and a ferrimagnetic substance.

7. The method according to claim 6, wherein the superparamagnetic particles are a substance containing Fe, Co, Ni, Nd, or a mixture thereof.

8. The method according to claim 2, wherein the at least one core has a diameter of 2 nm to 50 .Math.m.

9. The method according to claim 2, wherein a diameter of the core/shell particles is 3 nm to 100 .Math.m.

10. The method according to claim 2, wherein a surface of the at least one non-magnetic shell is functionalized with at least one alkylalkoxysilane or at least one polyether-functional trimethoxysilane.

11. The method according to claim 2, wherein the ink contains: 0.5% to 40% by weight of the core/shell particles, 50% to 75% by weight of the at least one solvent, 0% to 10% by weight of pigments, 0% to 3% by weight of dispersants, 0% to 4% by weight of a thermal conductivity additive, and 0% to 3% by weight of wetting agents, based in each case on a total weight of ink.

12. The method according to claim 1, wherein the ink is applied by an inkjet method.

13. A method for producing a three-dimensional object by powder bed fusion, the method comprising: a. providing a powder in a layer thickness of 30 to 200 .Math.m, b. applying an ink by an inkjet methodto sites in the powder that are to be sintered, c. applying an additional amount of the powder, d. repeating b and c, to obtain a layered arrangement and e. selectively sintering the layered arrangement with a magnetic field having a frequency of 50 kHz - 5 GHz, wherein the ink comprises superparamagnetic particles and at least one solvent.

14. The method according to claim 13, wherein the method is carried out at a temperature of 10° C. to 40° C.

15. The method according to claim 1, wherein the fusing is performed by selective absorbing sintering.

16. The method according to claim 4, wherein the water-miscible organic solvent is a protic solvent.

17. The method according to claim 4, wherein the water-miscible organic solvent is at least one selected from the group consisting of 2-pyrrolidone, ethylene glycol, methoxyisopropanol, polyethylene glycol, and a mixture thereof.

18. The method according to claim 10, wherein the at least one alkylalkoxysilane is selected from the group consisting of hexamethyldisilazane, octyltrimethoxysilane, octyltriethoxysilane, hexadecyltrimethoxysilane, and a mixture thereof.

19. The method according to claim 13, wherein the magnetic field has a frequency of 500 kHz - 10 MHz.

20. The method according to claim 14, wherein the method is carried out at room temperature.

Description

EXAMPLES

Example 1: Sintering of Powder

[0028] Approx. 50 g of PEEK powder (VESTAKEEP 2000 FP) were manually sieved using a sieve with a mesh size of 125 .Math.m. Iron(II/III) oxide (50 - 100 nm), iron(II/III) oxide < 5 .Math.m or superparamagnetic core/shell particles (core: =13 nm, shell: silicon dioxide; MagSilica from Evonik; d.sub.50 particle size = 200 nm) was/were then added to the < 125 .Math.m fraction in the ratio 9:1 (w/w). 10 g of each powder mixture were prepared. The powder mixtures were then finely mixed for approx. 2 h at 40 rpm in a PRM Mini II type drum hoop mixer from J. Engelsmann AG using 12 grinding balls having a diameter of 5 mm. The powder mixtures were then individually filled into silicone moulds and sintered for 10 s at a frequency of 1 MHz under an induction coil (flat geometry; diameter: 5 cm; number of windings N = 4-5) with a spacing of < 3 mm from the powder bed surface.

TABLE-US-00001 No. Fe component Fe component particle size m/g Power input relative 1 Fe(II/III) oxide < 5 .Math.m 0.031 1.00 2 Fe(II/III) oxide 50-100 nm 0.065 2.10 3 MagSilica MagSilica 0.206 6.65

[0029] Solids were produced here with different masses as a function of the iron component. If Fe(II/III) oxide < 5 .Math.m was mixed into the PEEK powder as energy-absorbing component, the mass of the molten solid was approx. 30 mg, with smaller particles the mass of the solid was 65 mg, and with MagSilica particles a solid with a mass of 206 mg could be produced in the same time and with the same frequency and field strength. The energy introduction with MagSilica as energy-absorbing component is therefore 6.65 times greater than with Fe(II/III) oxide < 5 .Math.m, assuming that all phase transitions and hence also the profile of the specific heat capacity C are identical in all three samples.

Example 2: Production of a Printed Polyamide 12 Tensile Specimen

[0030] For the production of a printable, aqueous MagSilica ink, a dispersion having a relatively high MagSilica content was first produced.

Production of MagSilica Dispersions

[0031] MagSilica HS (Evonik) was used for the production of the MagSilica dispersions. In order to produce the dispersions, a jacketed dispersing vessel with connected water cooling is charged with 100 g of demineralized water, and to this 45.8 g of MagSilica powder was then added in steps. In this case, dispersion was performed in the range of approx. 900 - 2000 min.sup.-1 using a dissolver disc situated centrally in the vessel. The temperature was held constant at approx. 18° C. After the whole amount of MagSilica had been added and homogeneously dispersed, the disperser disc was removed and replaced with an ultrasonic sonotrode. The sonotrode had a power of approx. 400 W. Dispersion was then performed for 30 minutes by means of ultrasound, with the temperature likewise being held constant at approx. 18° C. by the cooling of the jacket. At the end of dispersion, the sonotrode was removed and the dispersion was characterized. The ignition residue of the dispersion was 33.5%; the viscosity of the dispersion was 72.7 mPas at a shear rate of 100 s.sup.-1 and 493.1 mPas at a shear rate of 10 s.sup.-1 and a temperature of 23° C. (Physica MCR 300, Anton Paar).

Production of MagSilica-Containing Inks

[0032] For the production of a water-based, MagSilica-containing ink, 2.5 g of the above-described stock dispersion were mixed with 10 mg of TegoWet 500 (wetting additive) and 7.49 g of water, the pH was adjusted to 10.5 with a dilute KOH solution, and the mixture was then treated with an ultrasound finger (0.5; 70%, 5 min). The pH of the dispersion was then monitored and readjusted when necessary. Before the ink was printed, it was filtered through cellulose.

Production of a DIN Standard 5A Tensile Specimen

[0033] For the production of a DIN standard 5A tensile specimen, 12 layers of 150 .Math.m Vestosint 1115 alternating with printed layers of the above-described ink were first produced in the appropriate shape (DIN 5A cross section) on a coating substrate made from PVC. All 12 layers were sintered together at a power of 5 kW and a frequency of 980 kHz.

[0034] Ink characterization and test print on a Dimatix: [0035] Droplet speed: 7.1 m/s [0036] Viscosity (30° C., 1000 s-1) 1.84 mPas [0037] Surface tension: 21.4 mN/m [0038] Density: 1.09 g/ml

[0039] The finished tensile specimen was tested in respect of its tensile strength and extensibility by means of tensile testing in accordance with DIN EN ISO 527-1 at room temperature. The tensile strength measured was 23.1 MPs and the corresponding elongation at break was 11%. A test specimen formed in an analogous manner by melting had a comparable tensile strength of 21.3 MPa and a slightly higher elongation at break of 15%.