SOFT MAGNETIC MATERIAL COMPOSITION AND METHOD OF MOLDING THE SAME

Abstract: Soft magnetic material composition composed of 70 to 95% by weight of powdery soft magnetic material and the balance of a liquid thermosetting resin. A high magnetic permeability molding having a high density and a large initial magnetic permeability and being excellent in strength and dimensional accuracy can be obtained with a good producibility according to the method of this invention.

Description: The present invention relates to a composition having good moldability and permeability which is composed of a soft magnetic material and a liquid thermosetting resin as a binder, and to a molding process therefor. Heretofore, the soft magnetic material used for magnetic cores has been dominated by sintered moldings of spinel ferrite (e.g., Mn-Zn ferrite and Ni-Zn ferrite) which have a low loss at the high-frequency region. Since they are produced by powder metallurgy, they are poor in dimensional accuracy due to shrinkage that takes place at the time of sintering and they cannot be made in complex shape with ease. They have an additional disadvantage of being poor in impact strength which is inherent in sintered products. In order to eliminate these disadvantages, there has been proposed the so-called plastics soft magnetic material formed by bonding a soft magnetic material with a synthetic resin. For example, there is disclosed in Japanese Patent Publication No. 28356/1976 a composition composed of a spinel ferrite having a particle diameter in a specific range and a solid powdery thermosetting resin. The magnetic core formed from such a plastics soft magnetic material is inferior in saturation magnetization and permeability to sintered products, because it contains a synthetic resin as a binder which is a non-magnetic substance. If the magnetic core of the plastics soft magnetic material is to be improved in its magnetic properties, it is necessary to increase the content of the soft magnetic material powder and also to increase the molding pressure, whereby reducing the void ratio and increasing the filling density of the soft magnetic material powder. Increasing the content of the soft magnetic material powder poses the problem that the conventional plastics soft magnetic material is easily damaged and deformed before it is cured and solidified and that the molded item after curing is poor in mechanical strength. Also, increasing the molding pressure to reduce the void ratio breaks the particles of the soft magnetic material, deteriorating the magnetic properties of the magnetic core. In addition, increased molding pressure is liable to cause damage to the mold. In JP-A-50 51 109 a process for the production of a ferrite molded article is described. Magnetic oxide powder is blended with a thermosetting liquid resin and press molded at room temperature and then hardened. In JP-A-50 52 109 a process for the production of a ferrite molded article is described. Magnetic oxide powder is blended with a liquid urethane-modified epoxy resin montan wax and a hardening agent, press molded at room temperature and then hardened. In order to solve the above-mentioned problems, the present inventors carried out a series of researches on the method of increasing the density of the molding, whereby improving the magnetic properties of the molding, while reducing the molding pressure on the mold, and also on the method of increasing the green strength of the molding before curing, whereby preventing the damage and deformation and achieving good dimensional accuracy. The present invention is based on the results of the researches. The invention is given in the claim. The soft magnetic material powder used in this invention includes spinel ferrite such as Mn-Zn ferrite, Ni-Zn ferrite, and Mn-Mg ferrite, formed by sintering at 1100 to 1300°C and subsequent crushing, and also soft magnetic alloy powder such as iron powder, Fe-Ni alloy powder, Fe-Al-Si alloy powder, and amorphous soft magnetic alloy powder. They are used individually or in combination with one another. Preferable among them is spinel ferrite powder which is commercially available. The soft magnetic material powder should have a specific particle size distribution so that it shows good magnetic properties. Examples of the liquid thermosetting resin used in this invention include phenolic resin, epoxy resin, urea resin, melamine resin, furan resin, and unsaturated polyester resin. Preferable among them is phenolic resin, especially resol-type phenolic resin. A liquid thermosetting resin as a binder is superior to a solid powdery resin in miscibility with the soft magnetic material powder. In addition, it provides a compression-molded item having a high green strength and resistance to damage and deformation owing to its adhesive force, and it cures into moldings of high strength. The composition of this invention contains 70 to 95 vol% of soft magnetic material powder, with the balance being a liquid thermosetting resin and 5 to 100 parts by weight of a plasticizer for 100 parts by weight of solids in the liquid thermosetting resin. With the amount of soft magnetic material powder less than 70 vol%, the resulting molding does not show the desired magnetic properties, and with the amount in excess of 95 vol%, the resulting molding is liable to damage and deformation. The above-mentioned liquid thermosetting resin contains a plasticizer. A plasticizer lowers the viscosity of the binder, whereby permitting the uniform distribution of the soft magnetic powder and reducing friction between soft magnetic powders at the time of compression molding. This leads to a high filling density and the improvement in initial permeability. In addition, a binder containing a plasticizer permits the compression molding at a comparatively low pressure without sacrificing the density and initial permeability of the molded product. Thus the mold is relieved from load. The plasticizer used in this invention includes polyester-based plasticizer, phthalic ester-based plasticizer, epoxidized oil-based plasticizer, fatty acid ester-based plasticizer, etc. Their selection depends on the type of liquid thermosetting resin used. Preferred plasticizers for a phenolic resin are polyester of adipic acid, polyester of phthalic acid, dibutyl phthalate, and epoxidized soybean oil. The preferred amount of the plasticizer is 5 to 100 parts by weight for 100 parts by weight of solids in the liquid thermosetting resin. An extreme amount of plasticizer does not produce the desired effect; and an excessive amount of plasticizer more than the amount of solids in the liquid thermosetting resin lowers the mechanical strength of the molding. The composition of this invention may be incorporated with a small amount of coupling agent, slip agent, heat stabilizer, and other additives to improve the properties of the composition. The above-mentioned composition may be molded by compression molding with a hot press or cold press; however, usually a hot press, which needs complex operations, is not necessary, because the liquid binder with a plasticizer provides strong moldings after compression molding. In other words, for good productivity, the composition of this invention should be molded at room temperature and hardened later at a curing temperature of the thermosetting resin. The moldings obtained in this manner have a good dimensional accuracy and good magnetic properties. The compression molding should be performed at a pressure of 2 to 6 t/cm². A pressure lower than 2 t/cm² is not enough to achieve the desired filling density, and a pressure higher than 6 t/cm² does not increase the filling density any more but breaks the soft magnetic material powder, deteriorating the magnetic properties. The invention is now described with reference to the following examples, which are not intended to limit the scope of this invention. The ferrite powder used in Examples and Comparative Examples was prepared by crushing Mn-Zn ferrite sintered product having an initial permeation of 1000 to 3000. The resulting powder was divided into a fraction of particle diameter 0.6 to 0.8 mm and a fraction of particle diameter 0.1 to 0.35 mm. The two fractions were mixed at a ratio of 70 wt% and 30 wt%. Comparative Example 1 and Examples 1 to 6 Ferrite powder (86 vol%) and resol-type phenolic resin (14 vol%) incorporated with a varied amount of plasticizer (polyester of adipic acid) were mixed using a ribbon blender. The amount of the polyester ranged from 0 to 80 parts by weight for 100 parts by weight of solids in the resol-type phenolic resin as shown in Table 1. Each composition thus obtained was molded into a ring shape measuring 30 mm in outside diameter, 20 mm in inside diameter, and 10 mm in height. The resulting molding was easy to handle and free of defects such as chipping and cracking. The molding was cured at 180°C for 2 hours. The cured molding had a good appearance and shape. Table 1 shows the density and initial permeability of the cured molding. Examples 7 and 8 The same procedure as in Example 3 was repeated except that the polyester of adipic acid (plasticizer) was replaced by 60 parts by weight of polyester of phthalic acid or dibutyl phthalate. The resulting ring-shape molding had a good appearance free of chipping and cracking, as shown in Table 1. Comparative Example 2 and Example 9 100 parts by weight of novolak-type phenolic resin and 100 parts by weight of aminosilane coupling agent were reacted with each other at normal temperature in 200 parts by weight of methanol. After removal of methanol by evaporation, there was obtained a modified liquid phenolic resin having the terminal silane. Using the thus obtained modified phenolic resin, the same procedure as in Example 3 was repeated to yield moldings of good appearance. The results are shown in Table 1. Comparative Examples 3 and 4 The same procedure as in Comparative Example 1 was repeated except that the resol-type phenolic resin was replaced by novolak-type phenolic resin powder. In Comparative Example 3, the molding pressure was 2 t/cm² and the resulting molding was too weak to evaluate the magnetic properties. In Comparative Example 4, the molding pressure was 6 t/cm² and the resulting molding was very poor in density and initial permeability. As mentioned above, the present invention provides a molding compound and a process for making the molding compound into molded items of high permeability having a high density, high initial permeability, high strength, high dimensional accuracy, and balanced magnetic properties. The molded items can be used for the accurate correction of current-induced magnetic field.

Claims: A soft magnetic material composition which comprises 70 to 95 vol% of soft magnetic spinel ferrite powder or soft magnetic alloy powder including amorphous soft magnetic alloy powder having a particle size of 0.1 mm to 0.35 mm and 0.6 to 0.8 mm in a ratio of 30 wt% to 70 wt% with the balance being a liquid thermosetting resin, which contains 5 to 100 parts by weight of a plasticizer for 100 parts by weight of solids in the liquid thermosetting resin. A composition as set forth in claim 1, wherein the plasticizer is at least one member selected from polyester-based plasticizers and phthalic ester-based plasticizer. A process for molding a plastics-containing soft magnetic material composition of high permeability, said process comprising compression molding at normal temperature a soft magnetic material composition composed of 70 to 95 vol% of soft magnetic material powder, having a particle size of 0.1 mm to 0.35 mm and 0.6 to 0.8 mm in a ratio of 30 wt% to 70 wt% with the balance being a liquid thermosetting resin containing 5 to 100 parts by weight of a plasticizer for 100 parts by weight of solids in the liquid thermosetting resin, and subsequently solidifying the molding at a curing temperature of the liquid thermosetting resin. A molding process as set forth in claim 3, wherein the compression molding is carried out under a pressure of 2 to 6 t/cm².

Inventors: NAGAI KOICHI, SAKAUCHI TAKASHI, SEZAKI KOJI, NAGAI, KOICHI, SAKAUCHI, TAKASHI, SEZAKI, KOJI
Applicants: KANEGAFUCHI CHEMICAL IND, KANEGAFUCHI KAGAKU KOGYO KABUSHIKI KAISHA
Application year: 1986
Main classification: H01F1
IPC codes: C08K3, H01F1