Magnetic core and process for producing same
The present invention provides a magnetic core which can be produced with improved productivity without increasing a material cost and has required magnetic and mechanical properties and a process for producing the same. The magnetic core is produced by compression molding and thereafter thermally hardening iron-based soft magnetic powder having resin films formed on surfaces of particles thereof. The resin film is an uncured resin film formed by dry mixing the iron-based soft magnetic powder and epoxy resin containing a latent curing agent with each other at a temperature not less than a softening temperature of the epoxy resin and less than a thermal curing starting temperature thereof. The iron-based soft magnetic powder having the resin films formed on the surfaces of the particles thereof is compression molded by using a die to produce a compression molded body. The compression molded body having the resin films formed on the surfaces of the particles thereof is thermally hardened at a temperature not less than the thermal curing starting temperature of the epoxy resin.
1. A magnetic core produced by compression molding iron-based soft magnetic powder having a resin film comprising an epoxy resin formed on surfaces of particles of said iron-based soft magnetic powder and thereafter thermally hardening said epoxy resin in said resin films,
wherein a radial crushing strength of said magnetic core is 90 to 150 MPa,
wherein said iron-based soft magnetic powder passes through a number 100 mesh Tyler sieve, but does not pass through a number 325-mesh Tyler sieve and
wherein said resin film before compression molding is an uncured epoxy resin film formed by dry mixing said iron-based soft magnetic powder and said epoxy resin containing a latent curing agent at a temperature not less than a softening temperature of said epoxy resin containing said latent curing agent and less than a thermal curing starting temperature of said epoxy-resin containing said latent curing agent;
said latent curing agent is dicyandiamide;
said softening temperature of said epoxy resin containing said latent curing agent is 100 to 120° C.;
said iron-based soft magnetic powder having said resin films formed on said surfaces of said particles of said iron-based soft magnetic powder is compression molded by using a die to produce a compression molded body; and
said compression molded body having said epoxy resin film formed on said surfaces of said particles of said magnetic powder is thermally hardened at a temperature not less than said thermal curing starting temperature of said epoxy resin containing said latent curing agent.
2. A magnetic core according to claim 1 , wherein said iron-based soft magnetic powder is reduced iron powder.
3. A magnetic core according to claim 1 , wherein a mixing ratio of said iron-based soft magnetic powder and that of said epoxy resin containing said latent curing agent is 95 to 99 mass % and 1 to 5 mass % respectively for a total amount of said iron-based soft magnetic powder and said epoxy resin containing said latent curing agent.
4. A magnetic core produced by compression molding iron-based soft magnetic powder as defined in claim 1 wherein a radial crushing strength of said magnetic core is 140 to 150 MPa.
5. A process for producing a magnetic core according to claim 1 comprising: a mixing step of dry mixing said iron-based soft magnetic powder and said epoxy resin containing said latent curing agent with each other at a temperature not less than said softening temperature of said epoxy resin and less than said thermal curing starting temperature thereof; a pulverizing step of pulverizing an agglomerated cake generated at said mixing step to obtain composite magnetic powder; a compression molding step of compression molding said composite magnetic powder into a compression molded body by using a die; and a hardening step of thermally hardening said compression molded body at a temperature not less than said thermal curing starting temperature of said epoxy resin.
6. A process for producing a magnetic core according to claim 5 , wherein at said compression molding step, said composite magnetic powder is compression molded at a molding pressure of 200 to 500 MPa.
7. A process for producing a magnetic core according to claim 5 , wherein at said hardening step, said compression molded body is thermally hardened at 170 to 190° C.
8. A process for producing a magnetic core according to claim 7 , wherein at said hardening step, said compression molded body is thermally hardened in a nitrogen atmosphere.