Coating formulation and application of organic passivation layer onto iron-based rare earth powders

Abstract

The present disclosure relates to coating formulations for neodymium-iron-boron type magnetic powders manufactured from rapid solidification processes for the purpose, inter alia, of corrosion and oxidation resistance when exposed to aggressive environments. The coating formulation preferably contains an epoxy binder, curing agent, an accelerating agent, and a lubricant. By incorporating coupling agents and optionally, other specialty additives with the magnetic powder and the organic epoxy components, additional oxidation and corrosion prevention, enhanced adhesion and dispersion between the filler and matrix phases can be achieved. This disclosure relates to all such rare earth-transition metal-boron (RE-TM-B) powders produced by rapid solidification and encompasses both the bonded magnet products that include combinations of the materials mentioned and the application processes.

1 - 49 . (canceled) 
     
     
         50 . A rapidly solidified rare earth-transition metal-boron magnet material, comprising a coated rare earth-transition metal-boron magnet powder, which comprises a rare-earth transition metal-boron magnet powder and a coating formulation, wherein the coating formulation comprises a combination, in an amount by weight of the coated magnet powder, of about 0.1 weight percent to about 1 weight percent of an organotitanate or organozirconate coupling agent, about 0.18 weight percent to about 4.46 weight percent of an epoxy resin, about 0.01 weight percent to about 0.27 weight percent of an amine-based hardener, an accelerator, and about 0.003 weight percent to about 0.27 weight percent of a lubricant;
 wherein the general form of the coupling agent is
   (RO—) n (Ti or Zr)(—OR′Y) 4−n  
 
   
       where R is a neopentyl(diallyl), dioctyl, or (2,2-diallyloxymethyl)butyl group, Ti or Zr has a coordination number of 4, R′ is a phosphito, pyrophosphato or cyclic pyrophosphato segment, and Y is a dioctyl or ditridecyl end group, with 1≦n≦4. 
     
     
         51 . The rapidly solidified rare earth-transition metal-boron magnet material of  claim 50 , wherein the rare earth-transition metal-boron magnet material comprises the magnet powder in an amount of about 95 weight percent to about 99 weight percent or more of the magnet material. 
     
     
         52 . The rapidly solidified rare earth-transition metal-boron magnet material of  claim 51 , wherein the rare earth-transition metal-boron magnet material is a compression-molded magnetic material. 
     
     
         53 . A rapidly solidified rare earth-transition metal-boron magnet material, comprising a coated rare earth-transition metal-boron magnet powder, which comprises a rare-earth transition metal-boron magnet powder and a coating formulation, wherein the coating formulation comprises a combination, in an amount by weight of the coated magnet powder, of about 0.225 weight percent to about 4.25 weight percent of epichlorohydrin/cresol novolac epoxy resin, about 0.01 weight percent to about 0.26 weight percent of dicyandiamide hardener, an aromatic, tertiary amine accelerator, about 0.004 weight percent to about 0.27 weight percent of zinc stearate lubricant, and about 0.35 weight percent to about 0.75 weight percent of an organotitanate coupling agent of the form
   (RO—)Ti(—OR′Y) 3  
   
       where R is a neopentyl(diallyl) group, Ti has a coordination number of 4, R′ is a pyrophosphato segment, and Y is a dioctyl end group. 
     
     
         54 . The rapidly solidified rare earth-transition metal-boron magnet material of  claim 53 , wherein the rare earth-transition metal-boron magnet material comprises the magnet powder in an amount of about 95 weight percent to about 99 weight percent or more of the magnet material. 
     
     
         55 . The rapidly solidified rare earth-transition metal-boron magnet material of  claim 54 , wherein the rare earth-transition metal-boron magnet material is a compression-molded magnetic material. 
     
     
         56 . A rapidly solidified rare earth-transition metal-boron magnet material, comprising a coated rare earth-transition metal-boron magnet powder, which comprises a rare-earth transition metal-boron magnet powder and a coating formulation, wherein the coating formulation comprises a combination, in an amount by weight of the coated magnet powder, of about 0.1 weight percent to about 1 weight percent of an organotitanate or organozirconate coupling agent, and about 0.18 weight percent to about 4.46 weight percent of an epoxy resin;
 wherein the general form of the coupling agent is
   (RO—) n (Ti or Zr)(—OR′Y) 4−n  
 
   
       where R is a neopentyl(diallyl), dioctyl, or (2,2-diallyloxymethyl)butyl group, Ti or Zr has a coordination number of 4, R′ is a phosphito, pyrophosphato or cyclic pyrophosphato segment, and Y is a dioctyl or ditridecyl end group, with 1≦n≦4. 
     
     
         57 . The rapidly solidified rare earth-transition metal-boron magnet material of  claim 56 , wherein the coating formulation further comprises a hardener. 
     
     
         58 . The rapidly solidified rare earth-transition metal-boron magnet material of  claim 57 , wherein the hardener is an amine-based hardener. 
     
     
         59 . The rapidly solidified rare earth-transition metal-boron magnet material of  claim 57 , wherein the coating formulation comprises about 0.01 weight percent to about 0.27 weight percent of the hardener. 
     
     
         60 . The rapidly solidified rare earth-transition metal-boron magnet material of  claim 56 , wherein the coating formulation further comprises an accelerator. 
     
     
         61 . The rapidly solidified rare earth-transition metal-boron magnet material of  claim 60 , wherein the coating formulation comprises about 0.004 weight percent to about 0.09 weight percent of the accelerator. 
     
     
         62 . The rapidly solidified rare earth-transition metal-boron magnet material of  claim 56 , wherein the coating formulation further comprises a lubricant. 
     
     
         63 . The rapidly solidified rare earth-transition metal-boron magnet material of  claim 62 , wherein the lubricant is zinc stearate. 
     
     
         64 . The rapidly solidified rare earth-transition metal-boron magnet material of  claim 62 , wherein the coating formulation comprises about 0.003 weight percent to about 0.27 weight percent of the lubricant. 
     
     
         65 . The rapidly solidified rare earth-transition metal-boron magnet material of  claim 56 , wherein the rare earth-transition metal-boron magnet material comprises the magnet powder in an amount of about 95 weight percent to about 99 weight percent or more of the magnet material. 
     
     
         66 . The rapidly solidified rare earth-transition metal-boron magnet material of  claim 65 , wherein the rare earth-transition metal-boron magnet material is a compression-molded magnetic material.