Extrudable magnetic ink and novel 3D printing method to fabricate bonded magnets of complex shape

1. An extrudable magnetic ink composition for printing a bonded magnet comprising:

magnetic particles having a particle size of at least 500 microns, wherein the magnetic particles are present in the magnetic ink composition in an amount of 35% to 70% by volume;

an epoxy polymer binder;

a latent curing agent comprising an imidazole derivative containing a dicyanimide;

viscosifier; and

a solvent,

wherein the amount of magnetic particles along with viscosifier together impart the extrudable magnetic ink composition with a viscoelastic shear thinning behavior for applying the extrudable magnetic ink composition as a feed material in 3D printing.

2. The magnetic ink composition of claim 1 , wherein the magnetic particles comprise rare earth magnetic particles or ferrite magnetic particles.

3. The magnetic ink composition of claim 1 , wherein the epoxy polymer binder comprises a thermoplastic resin, a thermosetting resin or an elastomer, or combinations thereof.

4. The magnetic ink composition of claim 1 , wherein the viscosifier comprises nanoclay platelets, fumed silica, fumed alumina, polyethylene oxide, or polypropylene oxide.

5. The magnetic ink composition of claim 1 , wherein the solvent comprises acetone, ethanol, methanol, or hexane.

6. The magnetic ink composition of claim 1 , wherein the latent curing agent is 1-ethyl-3-methylimidazolium-dicyanimide.

7. The magnetic ink composition of claim 1 , wherein the magnetic particles comprise rare earth magnetic particles.

8. The magnetic ink composition of claim 1 , wherein the amount of the magnetic particles in the magnetic ink composition is from 45% to 70% by volume.

9. The magnetic ink composition of claim 1 , wherein the viscosifier comprises nanoclay platelets, fumed silica, or fumed alumina.

10. The magnetic ink composition of claim 1 , wherein the viscosifier comprises nanoclay platelets.

11. A method of printing a bonded magnet comprising: extruding a magnetic ink composition according to claim 1 through a nozzle; and depositing one or more continuous filaments comprising the magnetic ink composition on a substrate.

12. The method of claim 11 , further comprising surrounding the nozzle with at least one magnet, wherein the at least one magnet is concentrically assembled around the nozzle.

13. The method of claim 12 , wherein the at least one magnet comprises one or more permanent magnets or one or more electromagnets.

14. The method of claim 11 , wherein the one or more continuous filaments are deposited in a predetermined pattern on the substrate.

15. The method of claim 11 , wherein the magnetic ink composition is extruded through the nozzle at a room temperature.

16. The method of claim 11 , further comprising curing the one or more continuous filaments.

17. The method of claim 16 , wherein curing the one or more continuous filaments is performed at an elevated temperature ranging from 100° C. to 250° C. under an ambient atmosphere.

18. The method of claim 11 , further comprising pre-aligning the magnetic particles under a magnetic field before supplying the magnetic ink composition into the nozzle.

19. The method of claim 11 , wherein the substrate is a mold under a magnetic filed.

20. The method of claim 11 , wherein the magnetic particles comprise rare earth magnetic particles or ferrite magnetic particles.

21. The method of claim 11 , wherein the epoxy polymer binder comprises a thermoplastic resin, a thermosetting resin or an elastomer, or combinations thereof.

22. The method of claim 11 , wherein the viscosifier comprises nanoclay platelets, fumed silica, fumed alumina, polyethylene oxide, or polypropylene oxide.

23. The method of claim 11 , wherein the solvent comprises acetone, ethanol, methanol, or hexane.

24. An extrudable magnetic ink composition for printing a bonded magnet, the composition consisting of:

magnetic particles having a particle size of at least 500 microns;

an epoxy polymer binder present in the extrudable magnetic ink composition in an amount of about 20 vol %;

optionally, a latent curing agent comprising an imidazole derivative containing a dicyanimide present in the extrudable magnetic ink composition in an amount of about 1 pph based on the mass of the epoxy polymer binder;

viscosifier selected from the group consisting of nanoclay platelets and fumed silica and present in the extrudable magnetic ink composition in an amount of about 1 vol %; and

a solvent present in the extrudable magnetic ink composition in an amount of about 0.25 pph based on the mass of the epoxy polymer binder;

wherein the amount of magnetic particles along with viscosifier together impart the extrudable magnetic ink composition with a viscoelastic shear thinning behavior for applying the extrudable magnetic ink composition as a feed material in 3D printing.