JPH0224303B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a soft magnetic material that has good magnetic properties and can be injection molded. Conventionally, it is known that a soft magnetic material is made by compression molding metal powder such as iron with a suitable binder and applying an external magnetic field before or after the compression molding to form a powder magnetic core. . Even if injection molding is attempted using the materials used in the production of conventional powder magnetic cores, it is impossible to mold the materials due to the fluidity of the material and other molding conditions. Therefore, as mentioned above, all of these processes have been carried out by methods such as compression molding. However, when compression molding is used, it has been impossible to accurately mold relatively complex shapes or small molded products. For example, it is difficult to make a small gear-like item by compression molding using this material, and even if it could be made, it would not be possible to accurately make the shape and size of extremely small teeth. The object of the present invention is to mix needle-like metal (for example iron) and ferrite powder with a thermoplastic synthetic resin as a binder, thereby increasing the total amount of metal and ferrite. Another object of the present invention is to provide an injection-moldable magnetic material that maintains sufficient fluidity during molding and thus can be injection-molded and has good magnetic properties. The magnetic material of the present invention is a mixture of a filler made of a mixture of acicular metal (metal fiber) and ferrite powder and a thermoplastic resin, and the thermoplastic resin as a binder is in the range of 40 to 60% by volume. It consists of the amount of Generally, when the viscosity of a material increases, its fluidity when heated and melted decreases, making injection molding impossible. Further, when a needle-like metal is mixed into a thermoplastic resin material, the viscosity when heated and melted increases as the degree of mixing of the needle-like metal increases. Therefore, in order to carry out injection molding using a thermoplastic resin material mixed with acicular metal, there is a certain limit to the degree of incorporation of acicular metal, and if this limit is exceeded, injection molding becomes impossible. Therefore, injection molding using a material containing acicular metal is possible only when the acicular metal content is within about 30% by volume. Furthermore, when injection molding is performed using a material with a high blending ratio, sintering occurs between the metals, making molding impossible. For this reason, the limit on the mixing rate of needle metal that can actually be injection molded is even lower, and injection molding is only possible if the mixing rate is extremely low, for example, 20% by volume or less. Although injection molding is possible with such a material with a low metal content, it is difficult to obtain a material with good magnetic properties. Furthermore, when ferrite powder is mixed into the thermoplastic resin material, injection molding is possible even if the amount of ferrite powder mixed is considerably larger than when needle-like metal is mixed. However, products molded from thermoplastic resin materials mixed with ferrite powder do not have very good magnetic properties, and even if a large amount of this is mixed in to the moldable limit, very good magnetic properties cannot be obtained. The present invention provides that when needle metal and ferrite powder are mixed into a thermoplastic resin material, the total amount of needle metal and ferrite that can be mixed in by injection molding is larger than the limit amount when only needle metal is mixed. This was done with the focus on the fact that it can increase the width and also improve the magnetic properties. By blending the filler and the binder (thermoplastic resin) within the above-mentioned range, a magnetic material that can be injection molded and has good magnetic properties can be obtained. It is considered desirable that the acicular metal of the filler should be in the range of 10 to 40 percent by volume of the total, and that the ferrite powder should be in the range of 10 to 40 percent by volume of the total. Examples of the magnetic material of the present invention described above will be described. Example: Iron fiber (acicular iron): 25ν% Ferrite powder: 25ν% Nylon: 50ν% A comparison between the embodiment having the above structure and the conventional example is as shown in the following table.

[Table] In the above table, (1) is iron powder 50ν%, nylon 50ν%
(2) When the same material is oriented, (3) is 50ν% iron fiber and 50ν% nylon.
% of the material is non-oriented, (4) is the same material as (3) and is oriented, (5) is the same material as (3) and is non-oriented, (6) is the same as (5). This is the case when they are oriented using the same material. Further, the characteristics of each of the above examples are shown in FIGS. 1 to 6, respectively. As is clear from the above table and drawings, the properties of the material of the present invention are better than those of other iron and nylon materials. In particular, the oriented material of the present invention has good properties. It also has excellent processability by injection molding. It is believed that the influence of orientation on magnetic properties is related to the length of the needle-shaped iron, particularly the aspect ratio, which is the value obtained by dividing the length by the diameter. That is, the larger the aspect ratio, the better the magnetic properties. However, the smaller the aspect ratio, the easier the orientation becomes. Therefore, it is desirable to maximize the magnetic properties due to orientation by selecting iron with an appropriate aspect ratio. In the present invention, by mixing needle-shaped iron with other ferrite powder, needle-shaped iron has a relatively large aspect ratio and is well oriented. Therefore, the effect of orientation can be obtained more effectively, and as a result, particularly good magnetic properties can be obtained when the materials are oriented as shown in the table. As explained above, the magnetic material of the present invention can be injection molded and has better magnetic properties than conventional materials.

[Brief explanation of drawings]

1 to 4 are diagrams showing the magnetic properties of the conventional example, and FIGS. 5 and 6 are diagrams showing the magnetic properties of the material of the present invention.

Claims (1)

[Claims] 1. A soft magnetic material that can be injection molded, which is a mixture of a filling made of needle metal and ferrite powder and a thermoplastic resin, the thermoplastic resin being 40 to 60% by volume.