Rare-earth permanent magnet having corrosion-resistant coating, process for producing the same, and treating liquid for forming corrosion-resistant coating
The invention aims to provide a rare earth metal-based permanent magnet which has on the surface an inexpensive corrosion-resistant film combining excellent heat-resistance with excellent adhesiveness; a process for producing the permanent magnet; and a treating liquid for forming the corrosion-resistant film. The invention provides a rare earth metal-based permanent magnet characterized by it has on the surface a corrosion-resistant film containing lithium silicate and a thermoplastic resin as the constituting components, the film containing uniformly dispersed therein the thermoplastic resin at a content of 0.1 wt % to 50 wt %. The treating liquid, which is an excellent liquid for forming the corrosion-resistant film, is characterized by that a soap-free aqueous emulsion of a thermoplastic resin was used and that it contains the thermoplastic resin and lithium silicate in given amounts. The process, which is for producing the rare earth metal-based permanent magnet, is characterized by forming a corrosion-resistant film by using the treating liquid.
1 . A rare earth metal-based permanent magnet characterized by that it has on the surface a corrosion-resistant film containing lithium silicate and a thermoplastic resin as the constituting components, said film containing uniformly dispersed therein the thermoplastic resin at a content of 0.1 wt % to 50 wt %.
2 . The rare earth metal-based permanent magnet as claimed in claim 1 , characterized by that the film further contains sodium silicate as the constituting component.
3 . The rare earth metal-based permanent magnet as claimed in claim 2 , characterized by that the film has sodium content of 10 wt % or less.
4 . The rare earth metal-based permanent magnet as claimed in claim 1 , characterized by that the thermoplastic resin is a soap-free aqueous emulsion of resin.
5 . The rare earth metal-based permanent magnet as claimed in claim 1 , characterized by that the thermoplastic resin is acrylic-styrene resin.
6 . The rare earth metal-based permanent magnet as claimed in claim 1 , characterized by that the magnet has the film at a surface coverage of 0.01 g/m 2 to 5.0 g/m 2 of the magnet.
7 . A process for producing a rare earth metal-based permanent magnet characterized by that it comprises preparing a treating liquid containing from 0.1 wt % to 5 wt % of a thermoplastic resin and from 2 wt % to 30 wt % of lithium silicate by dispersing the thermoplastic resin in the form of a soap-free aqueous emulsion of resin in an aqueous solution of lithium silicate, and after applying the treating liquid to the surface of the magnet, heating and drying it to obtain the corrosion-resistant film.
8 . The production process as claimed in claim 7 , characterized by that the treating liquid further contains sodium silicate.
9 . The production process as claimed in claim 8 , characterized by that the sodium content of the treating liquid is 1 wt % or less.
10 . The production process as claimed in claim 7 , characterized by that the thermoplastic resin is acrylic-styrene resin.
11 . A treating liquid for forming a corrosion-resistant film on the surface of a rare earth metal-based permanent magnet, characterized by that it contains from 0.1 wt % to 5 wt % of a thermoplastic resin in the form of a soap-free aqueous emulsion of resin and from 2 wt % to 30 wt % of lithium silicate.
12 . The treating liquid as claimed in claim 11 , characterized by that the treating liquid further contains sodium silicate.
13 . The treating liquid as claimed in claim 12 , characterized by that the sodium content of the treating liquid is 1 wt % or less.
14 . The treating liquid as claimed in claim 11 , characterized by that the thermoplastic resin is acrylic-styrene resin.