An Encapsulation Process for Magnetic Metal Powder and Its Application to Powder Core Manufacturing

Abstract

An encapsulation process of magnetic metal particles was investigated for the purpose of manufacturing powder cores for electronic power devices. The following two points were essential in this encapsulation process: the polymer particle attachment to the metal particle surface by static electrification. and the filming process from latex.
A latex contaning 0.5 μm polystyrene particles was mixed with powdery Fe-1%Si alloy (44-74 μm) to obtain a well-dipersed state. This polymer particle-attached powder was h eattreated for 30 min at 180°C to transform the polymer particles into a thin film. The metal particles were thus encapsulated in a uniform film.
The polymer particle-attached powder (Capsule A) and the film-encapsulated powder (Capsule B) were compacted at 600 MPa pressure to yield powder cores(Core A and Core B). Magnetic measurements on these cores indicated that the permeability for Core A decreas ed in higher frequency range. According to SEM observation for core fracture, polymer particles were partially lost from the metal surface by the friction force during compaction. On the other hand, Core B had good frequency characteristic and low iron loss. The reason was that the film, having a high deformation ability and adhesive force to the metal surface, was not exfoliated by the friction force, and remained as a sufficient insulator between metal particles. A magnetic powder core, having a high metal volume fraction, has been thus manufactured.