Corrosion-resistant R-Fe-B bonded magnet, powder for molding R-Fe-B bonded magnet and methods for manufacture thereof

Abstract

A powder for forming a R—Fe—B bonded magnet, wherein an R compound, such as an R oxide, an R carbide, an R nitride or an R hydride, which is contained in a raw material powder such as a super rapidly cooled powder or a hydrogen treated powder (HDDR powder) and reacts with water vapor to change into R(OH) 3 , has been converted to a R hydroxide R(OH) 3 being stable in the air by subjecting the raw material powder to a heat treatment in an atmosphere of a pressured water vapor. The powder for forming an R—Fe—B bonded magnet is free from the generation of a white powder in the surface of or inside a bonded magnet formed from the powder and accordingly, is free from the occurrence or cracking, chipping, swelling or the like in the bonded magnet caused by volume expansion of a white powder. Thus, the above powder can be used for preparing an R—Fe—B bonded magnet which is free from the white powder which has been observed in a conventional R—Fe—B bonded magnet in the use for a long period of time and is reduced in the occurrence of defects such as cracking, chipping, swelling and the like.

1 . A corrosion-resistant R—Fe—B bonded magnet comprising: 
 a resin; and  
 powder for molding an R—Fe—B bonded magnet containing 10 ppm or less of an R compound capable of becoming a rare earth hydroxide in reaction with water vapor, and 1 ppm to 200 ppm of a rare earth hydroxide.  
 
     
     
         2 . A corrosion-resistant R—Fe—B bonded magnet wherein an organic resin coating layer is formed on the surface of a corrosion-resistant R—Fe—B bonded magnet comprising: 
 a resin; and  
 powder for molding an R—Fe—B bonded magnet containing 10 ppm or less of an R compound capable of becoming a rare earth hydroxide in reaction with water vapor, and 1 ppm to 200 ppm of rare earth hydroxide.  
 
     
     
         3 . The corrosion-resistant R—Fe—B bonded magnet according to  claim 2 , characterized in that said organic resin coating layer consists of 2 wt. % to 70 wt. % of a fluorine resin, and 0.5 wt. % to 50 wt. % of pigment or 0.2 wt. % to 10 wt. % of metal complex dye (provided that the pigment content is 0.2 wt. % to 50 wt. % when a metal complex dye is contained) or the both; and the remainder of at least one kind of an acrylic resin, epoxy resin, phenol resin, or polyester resin.  
     
     
         4 . The corrosion-resistant R—Fe—B bonded magnet according to  claim 2 , characterized in that thickness of said organic resin coating layer is 1 μm to 50 μm.  
     
     
         5 . A method for manufacturing a corrosion-resistant R—Fe—B bonded magnet comprising the steps of: 
 treating raw material powder for R—Fe—B bonded magnets in a water vapor pressure atmosphere and obtaining powder for molding an R—Fe—B bonded magnet containing 10 ppm or less of an R compound capable of becoming a rare earth hydroxide in reacting with water vapor, and 1 ppm to 200 ppm of a rare earth hydroxide; and  
 making that powder for molding an R—Fe—B bonded magnet into a bonded magnet.  
 
     
     
         6 . A method for manufacturing a corrosion-resistant R—Fe—B bonded magnet comprising the steps of: 
 treating raw material powder for R—Fe—B bonded magnets in a water vapor pressure atmosphere and obtaining powder for molding an R—Fe—B bonded magnet containing 10 ppm or less of an R compound capable of becoming a rare earth hydroxide in reacting with water vapor, and 1 ppm to 200 ppm of a rare earth hydroxide;  
 making that powder for molding an R—Fe—B bonded magnet into a bonded magnet; and  
 forming an organic resin coating layer on the surface of the obtained R—Fe—B bonded magnet.  
 
     
     
         7 . The corrosion-resistant R—Fe—B bonded magnet manufacturing method according to claim or  6  characterized in that conditions of treating in said water vapor pressure atmosphere are a water vapor pressure of 15 mmHg to 350 mmHg, and a treatment temperature of −10° C. to 200° C.  
     
     
         8 . The corrosion-resistant R—Fe—B bonded magnet manufacturing method according to  claim 7 , characterized in that said conditions of treating in said water vapor pressure atmosphere are a water vapor pressure of 50 mmHg to 200 mmHg, and a treatment temperature of 30° C. to 80° C.  
     
     
         9 . The corrosion-resistant R—Fe—B bonded magnet manufacturing method according to  claim 6 , characterized in that said organic resin coating layer consists of 2 wt. % to 70 wt. % of a fluorine resin, and 0.5 wt. % to 50 wt. % of pigment or 0.2 wt. % to 10 wt. % of metal complex dye (provided that pigment content is 0.2 wt. % to 50 wt. % when a metal complex dye is contained) or the both; and the remainder of at least one kind of an acrylic resin, epoxy resin, phenol resin, or polyester resin.  
     
     
         10 . The corrosion-resistant R—Fe—B bonded magnet manufacturing method according to  claim 6 , characterized in that thickness of said organic resin coating layer is 1 μm to 50 μm.  
     
     
         11 . The corrosion-resistant R—Fe—B bonded magnet manufacturing method according to  claim 5  or  6 , characterized in that a magnet raw material powder obtained by the rapid quenching method or hydrogenation-treatment method (HDDR method) is used.  
     
     
         12 . Powder for molding an R—Fe—B bonded magnet containing: 
 10 ppm or less of an R compound that reacts with water vapor to become R(OH)3; and 1 ppm to 200 ppm of a rare earth hydroxide.  
 
     
     
         13 . A method for manufacturing powder for molding an R—Fe—B bonded magnet wherein raw material powder for R—Fe—B bonded magnets is treated in a water vapor pressure atmosphere to obtain powder containing 10 ppm or less of an R compound that reacts with water vapor to become R(OH)3, and 1 ppm to 200 ppm of a rare earth hydroxide.  
     
     
         14 . The method for manufacturing powder for molding an R—Fe—B bonded magnet according to  claim 13 , characterized in that said water vapor pressure is 15 mmHg to 350 mmHg, and a treatment temperature is −1° C. to 200° C.  
     
     
         15 . The method for manufacturing powder for molding an R—Fe—B bonded magnet according to  claim 14 , characterized in that said water vapor pressure is 50 mmHg to 200 mmHg, and said treatment temperature is 30° C. to 80° C.  
     
     
         16 . The method for manufacturing powder for molding an R—Fe—B bonded magnet according to  claim 13 , characterized in that a magnet raw material powder obtained by the rapid quenching method or hydrogenation-treatment method (HDDR method) is used.