Corrosion-resistant magnetic article
A magnetic article with a corrosion resistant barrier formed from a poly(tetrafluoro-p-xylene) conformal coating or from a parylene conformal coating having a melting point of at least about 430° C. and a moisture vapor transmission less than about 0.5 g-mm/m 2 /day at 90% RH and 37° C., the conformal coating being covered with a polysulfone thermoplastic overlayer.
1. A magnetic article comprising an NdFeB magnet having thereon a substantially continuous corrosion resistant barrier comprising a fluorinated parylene conformal coating covered with a polysulfone thermoplastic overlayer, wherein the polysulfone melting point is also less than the magnet Curie temperature T c .
2. A magnetic article according to claim 1 wherein the magnet has a Maximum Energy Product BH max of at least 28 Mega Gauss Oersteds, an Intrinsic Coercive Force H ci of at least 10 kiloOersteads and a Curie Temperature T c of at least 300° C.
3. A magnetic article according to claim 1 wherein the magnet has a Maximum Energy Product BH max of at least 32 Mega Gauss Oersteds, an Intrinsic Coercive Force H ci of at least 35 kiloOersteads and a Curie Temperature T c of at least 310° C.
4. A magnetic article according to claim 1 wherein the magnet comprises a bar, rod, ring, partial ring or plate.
5. A magnetic article according to claim 1 wherein the fluorinated parylene has fluoroaliphatic groups.
6. A magnetic article according to claim 1 wherein the conformal coating comprises poly(tetrafluoro-p-xylene).
7. A magnetic article according to claim 1 wherein the fluorinated parylene has fluoroaromatic groups.
8. A magnetic article according to claim 1 wherein the conformal coating comprises parylene VT-4.
9. A magnetic article according to claim 1 wherein the conformal coating has a thickness of 2 to 100 μm.
10. A magnetic article according to claim 1 wherein the overlayer comprises polyethersulfone.
11. A magnetic article according to claim 1 wherein the overlayer comprises sulfonated polyethersulfone or polyphenylsulfone.
12. A magnetic article according to claim 1 wherein the overlayer has an average thickness of 0.5 to 10 mm.
13. A magnetic article according to claim 1 wherein the overlayer has a variable thickness.
14. A magnetic article according to claim 1 wherein the overlayer is an overmolding and is a layer made by injection molding.
15. A magnetic article according to claim 1 wherein the polysulfone melting point is less than the parylene melting point.
16. A magnetic article according to claim 1 wherein the conformal coating has a thickness less than 0.5 mm and the overlayer has an average thickness greater than 0.5 mm.
17. A magnetic article according to claim 1 wherein the magnet or overlayer has a recess or protrusion.
18. A magnetic article according to claim 17 wherein the recess or protrusion comprises a groove, notch, detent, aperture, spline, tab, stop, step, sealing surface, pivot point, axle, bearing surface, indicator to depict direction of fluid flow or magnetization, spring retaining collar, valve or valve actuator.
19. A magnetic article according to claim 1 wherein the magnet does not exhibit visible corrosion after 5 days immersion in 37° C. normal saline solution.
20. A magnetic article according to claim 1 wherein the magnet retains its full magnetic strength without exhibiting visible corrosion after 20 days immersion in 87° C. normal saline solution.
21. A magnetic article comprising an NdFeB magnet having thereon a substantially continuous corrosion resistant barrier comprising a parylene conformal coating having a melting point of at least about 430° C. and a moisture vapor transmission less than about 0.5 g-mm/m 2 /day at 90% RH and 37° C., the parylene conformal coating being covered with a polysulfone thermoplastic overlayer, wherein the polysulfone melting point is also less than the magnet Curie temperature T c .
22. A magnetic article according to claim 21 wherein the conformal coating has a moisture vapor transmission less than about 0.4 g-mm/m 2 /day at 90% RH and 37° C.
23. A magnetic article according to claim 21 wherein the conformal coating has a moisture vapor transmission less than about 0.3 g-mm/m 2 /day at 90% RH and 37° C.
24. A method for making a coated magnetic article, which method comprises vapor depositing upon an NdFeB magnet a layer or layers of a poly(tetrafluoro-p-xylene) conformal coating, and applying molten polysulfone over the poly(tetrafluoro-p-xylene) conformal coating, to provide a substantially continuous corrosion resistant barrier over the magnet, wherein the polysulfone melting point is also less than the magnet Curie temperature T c .
25. A method for making a coated magnetic article, which method comprises vapor depositing upon an NdFeB magnet a layer or layers of a parylene conformal coating having a melting point of at least about 430° C. and a moisture vapor transmission less than about 0.5 g-mm/m 2 /day at 90% RH and 37° C., and applying molten polysulfone over the parylene conformal coating, to provide a substantially continuous corrosion resistant barrier over the magnet, wherein the polysulfone melting point is also less than the magnet Curie temperature T c .
26. An implantable medical device containing a coated magnetic article comprising an NdFeB magnet having thereon a substantially continuous corrosion resistant barrier comprising a poly(tetrafluoro-p-xylene) conformal coating covered with a polysulfone thermoplastic overlayer, wherein the polysulfone melting point is also less than the magnet Curie temperature T c .
27. An implantable medical device containing a coated magnetic article comprising an NdFeB magnet having thereon a substantially continuous corrosion resistant barrier comprising a parylene conformal coating having a melting point of at least about 430° C. and a moisture vapor transmission less than about 0.5 g-mm/m 2 /day at 90% RH and 37° C., covered with a polysulfone thermoplastic overlayer, wherein the polysulfone melting point is also less than the magnet Curie temperature T c .