JP2704875B2 - Powder compacted magnetic body and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dust-molded magnetic body (for example, a dust core) and a method for producing the same. B. 2. Description of the Related Art As is well known, a magnetic compact formed by compression-molding magnetic powder of various metals and alloys is called a dust core, and is mainly used as a high-frequency core for various electronic device parts. I have. Conventionally, magnetic powders such as iron (carbonyl iron), sendust, and permalloy have been used for these dust cores according to their characteristics and applications. However, the above-mentioned conventional dust cores are not always satisfactory in magnetic properties, and improvements are desired. For example, in a dust core using iron powder, the value of the magnetic permeability μ ′ in an alternating magnetic field is as small as about 70, and the electrical resistivity of the material is small. large. Sendust-based powder magnetic cores have improved permeability μ 'and lowering in a high-frequency range as compared with iron, but the value of permeability μ' is still about 100, which is not sufficient. In the case of Permalloy dust core, the value of permeability μ 'is
With only a slight improvement to 120, this material also has a low electrical resistivity and a large decrease in magnetic permeability μ 'in the high frequency range. C. SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and particularly has a high magnetic permeability μ 'in an alternating magnetic field (10 kHz or less) and a high frequency range (10 kHz to 1 MHz). Permeability μ 'at)
It is an object of the present invention to provide a compacted magnetic body exhibiting excellent magnetic properties with a small decrease in value, and a method for producing the same. D. BACKGROUND OF THE INVENTION Amorphous alloys have attracted attention as various functional materials because of their unique chemical and mechanical properties that are not found in ordinary crystalline alloys. Above all, amorphous alloys such as cobalt-based and nickel-based alloys do not show crystal anisotropy,
It shows very good soft magnetic properties such as very low coercive force and high magnetic permeability. Therefore, a dust core using such an amorphous alloy powder is expected to have excellent magnetic properties not found in conventional dust cores. However, in order to produce a dust core that maintains its excellent magnetic properties after molding using the above amorphous alloy powder,
There are the following difficulties. For example, the first is deterioration of magnetic properties due to residual stress applied to the amorphous alloy during molding. Conventional iron, sendust, permalloy, etc. can be used for heat treatment (usually at 600-700 ° C) to remove the above-mentioned residual stress after powder production or compaction, due to the deterioration of magnetic properties caused by residual stress generated during powder production or compression molding. (Annealing) to recover. An amorphous alloy cannot be heated to a temperature higher than its crystallization temperature in order to maintain the amorphous state and maintain its excellent magnetic properties. The crystallization temperature of an amorphous alloy is generally not higher than 600 ° C. and not high. Therefore, it is difficult to remove stress by heat treatment in a dust core made of an amorphous alloy as in a conventional dust core. The second is a problem of a binder (binder) used for molding. Although related to the problem of the residual stress, in the dust core, an appropriate binder is mixed with the powder when the powder is compression-molded, and the powder is hardened after the molding to secure the mechanical strength of the dust core. Also in this case, internal stress is generated in the powder at the time of solidification and hardening of the binder, and the magnetic characteristics are degraded. In a conventional dust core, the above problem can be solved by using a binder that can withstand the annealing temperature for removing the internal stress. However, in the case of an amorphous alloy dust core, heat treatment for removing stress cannot be performed as described above, so that selection of a binder is important. Third is the difficulty of compression molding due to the extremely high mechanical strength of amorphous alloys. For example, Fe-
Even if the powder of a Co-Si-B soft magnetic amorphous alloy is molded at about 10 t / cm ² which is the molding pressure of a conventional dust core, the molding pressure does not reach the plastic deformation range of the material. However, when the molded body is removed from the mold by removing the pressure after the molding, the springback occurs and it is difficult to maintain the shape. Therefore, it is necessary to harden the binder in the mold so that the dust core has strength, and then remove the core from the mold. The binder hardening process in such a mold can perform the binder hardening process of the conventional powder magnetic core immediately after the pressure molding and from the mold, and can perform the binder hardening process of a large number of the molded products collectively. Obviously, this is a significant economic disadvantage. As a result of intensive studies, the present inventor has used powder of a soft magnetic amorphous alloy having a small magnetostriction and molded at a temperature adapted to this alloy, thereby compacting the amorphous alloy to solve the above-mentioned problem. Succeeded in the development of molded magnetic material. E. Constitution of the Invention The first invention of the present invention is a soft magnetic low magnetostrictive amorphous alloy powder composed of plate-like or flaky particles having a length of 10 to 700 μm and an aspect ratio of 2 to 40, which is bonded by a heat-resistant organic binder. To a compacted magnetic material. The second invention of the present invention relates to a method for producing a compacted magnetic material, comprising: (a) a soft magnetic low magnetostrictive amorphous alloy comprising plate-like or scale-like particles having a length of 10 to 700 μm and an aspect ratio of 2 to 40; Mixing the powder and a heat-resistant organic binder, and (b) pressing and molding the mixture at a temperature between the Curie point and the crystallization temperature of the soft magnetic amorphous alloy, The present invention relates to a method for producing a compacted magnetic material according to the first aspect. F. Examples Hereinafter, examples of the present invention will be described. First, the relationship between the composition of the soft magnetic amorphous alloy and the magnetostriction will be described. In order to maintain the excellent magnetic properties of the amorphous alloy, the compacted magnetic body made of the amorphous alloy is induced in the powder at the time of molding pressure received during molding and at the time of hardening of the binder. The composition is preferably such that the influence of stress is reduced. Therefore, in the present invention, a low magnetostrictive (low absolute value of magnetostriction) amorphous alloy powder which is excellent in magnetic properties and has little influence on magnetic properties due to stress is used as a metal component. In particular, it is desirable that the magnetostriction constant λs is −5 × 10 ^{−6 to} 5 × 10 ⁻⁶ . FIG. 2 shows F of (Fe, Co, Ni) ₇₈ Si ₈ B ₁₄ (the number attached to the element symbol represents the atomic% of the element component; the same applies hereinafter).
4 is a graph showing the relationship between the contents of e, Co, and Ni (the relative contents among the three) and the magnetostriction constant λs. As can be seen from the figure, in the Fe-Co-Ni-Si-B based amorphous alloy, a composition having a low magnetostriction constant λs is a composition having a low iron content and a high cobalt and / or nickel content. A composition in which iron is relatively large among iron, cobalt, and nickel is not suitable for a powder compacted magnetic material because the magnetostriction constant λs is large and the magnetic properties are insufficient. Fe-Co-Ni-Si-B
An alloy having a composition in which the magnetostriction constant λs is substantially zero is, for example, Fe _4.5 Co _70.5 S ₁₀ B ₁₅ (Fe: Co = 6: 94).
Therefore, the above composition or a composition in the vicinity thereof is an example of a preferable composition range. In addition to the above compositions, the following Table 1 shows compositions having good magnetic properties and a low absolute value of the magnetostriction constant λs. Next, the size of the particle flakes of the amorphous alloy constituting the powder will be described. If the length of the powder particles is less than 10 μm, the magnetic permeability μ ′ is too low to obtain a good compacted magnetic material. Also, the longer the length is, the higher the magnetic permeability μ 'is, but the magnetic permeability μ' in the high frequency range is reduced. In particular, if the length exceeds 700 μm, the magnetic permeability μ 'in the high frequency range is reduced. Becomes noticeable. Therefore, the length is set to a length in the range of 10 to 700 μm. The amorphous alloy powder made of thin flakes has a higher magnetic permeability μ 'of the powder compacted magnetic material than the granular alloy powder due to the relation of the demagnetizing field coefficient. The aspect ratio of the flaky particles is preferably 2 to 50. Here, the aspect ratio is the ratio of the longest length to the maximum thickness. If the aspect ratio is less than 20, the flakes become close to particles, and it becomes difficult to obtain a compacted magnetic body having high magnetic permeability. On the other hand, when the aspect ratio exceeds 50, handling of the amorphous alloy powder becomes troublesome and productivity is reduced. Amorphous alloy powder composed of flakes having an aspect ratio of 2 to 50 can be obtained by the cavitation method (which has a surface layer having a small leakage property to molten metal) which was previously proposed by the present applicant in Japanese Patent Application Laid-Open No. 58-6907. The molten metal is supplied to the surface of the roll rotating at a high speed, and the molten metal is dispersed into fine molten metal droplets. This method is a desirable method from the viewpoint of productivity. In addition, the amorphous alloy powder produced by this method is a powder composed of flake-like particles having a thickness of 50 μm or less, usually 20 to 30 μm, and is obtained from a ribbon-shaped amorphous alloy by a mechanical method. Compared to the powdered one, no processing stress is applied during powder production, which is very advantageous for the purpose of the present invention. When the surface of the amorphous alloy powder particles is subjected to a surface treatment to form a thin insulating film, it is possible to increase the magnetic permeability μ ′ of the obtained compacted magnetic body and further reduce the frequency dependence thereof. it can. Next, molding will be described. When a soft magnetic amorphous alloy powder is pressed into a powder compacted magnetic material, it is necessary to use a molding method that minimizes the influence of stress on the amorphous alloy powder. Specifically, the molding temperature is set to a temperature equal to or higher than the Curie point of the amorphous alloy powder to be used and equal to or lower than the crystallization temperature.
For example, Co _68.8 Fe _4.2 Si _17.5 B which is a low magnetostrictive amorphous alloy
_{In the case} of the amorphous alloy of _9.5 , the Curie point is 310 ° C. and the crystallization temperature is 515 ° C., so that the pressure is formed at a temperature in the range between the two. By molding at a temperature equal to or higher than the Curie point, the amorphous alloy powder becomes non-magnetic at the time of molding, and the resulting compacted magnetic material has no magnetic anisotropy, which is extremely advantageous. As a binder used for molding, a binder that is solidified or cured at a temperature lower than the molding temperature (a temperature equal to or lower than the Curie point) and has heat resistance is used. For example, even if an epoxy resin or a nylon resin is used and molded at a low temperature adapted to these resins, good results cannot be obtained. Therefore, approximately 30
Use a thermoplastic or thermosetting organic binder that can be used at a temperature of 0 ° C to 500 ° C. Molding at a temperature as high as possible within the allowable range from the heat resistance of the binder (but lower than the crystallization temperature) gives better results. As the organic binder, polyimide, polybenzimidazole, polyimide amide, and polydiphenyl ether can be used. The binder not only maintains the mechanical strength of the compacted magnetic material, but also covers the surface of the particle flakes of the amorphous alloy powder to insulate them from each other, and in the high frequency range of the compacted magnetic material. This contributes to preventing a decrease in the magnetic permeability μ ′. Using powder consisting of amorphous flakes of Co _68.8 Fe _4.2 Si _17.5 B _9.5 , the type of binder and the corresponding compaction temperature and the magnetic permeability μ ′ at 10 kHz of the compacted magnetic material were determined. Several examples of the relationship are shown in Table 2 below. As can be seen from the table, a heat-resistant polyimide is used for the binder, and the temperature between the Curie point and the crystallization temperature is 470 ° C.
The powder compacted magnetic material molded by the above method has a much higher magnetic permeability μ ′ than that molded under other conditions. This excellent result is due to the fact that the amorphous alloy powder is molded using a heat-resistant resin as a binder at a temperature at which it becomes non-magnetic, in combination with the low magnetostriction of the amorphous alloy powder. This is considered to be caused by minimizing the stress applied to the amorphous alloy powder during the pressing and suppressing the occurrence of induced magnetic anisotropy during the pressing. Hereinafter, specific examples of the present invention will be described. Co _68.8 Fe _4.2 Si _17.5 by the cavitation method
To prepare an amorphous alloy powder B _9.5. This amorphous alloy powder has a magnetostriction of zero, a saturation magnetic flux density of 7000 G, and a magnetic permeability of 10,000. Further, the length of the particles constituting the powder, 74-149μm, 149-297μm, 2 by classification using a sieve
There were three types of 97 to 500 μm. These amorphous alloy powders were molded under the conditions shown in Table 3 below to obtain four types of dust cores. The results of measuring the magnetic permeability μ ′ and iron loss w / cm ³ (B = 1000 G, 10 kHz) of these dust cores (Examples 1 to 4) are as shown in Table 4 below. For comparison, two types of dust cores using Sendust powder (Comparative Examples 1 and 2), a powder core of molybdenum-permalloy (Comparative Example 3), and two types of dust cores of carbonyl iron are shown for comparison. (Comparative Example 4,
5) and the results of the same measurement performed on a wound magnetic core (Comparative Example 6) formed by spirally winding an amorphous alloy ribbon having the same composition as in the above-described example. Further, for some of the above Examples and Comparative Examples, magnetic permeability μ ′ according to frequency
1 is shown in FIG. As can be seen from Table 4 and FIG. 1, all of the examples have a magnetic permeability μ ′ of 10 kHz and 1 MHz as compared with Comparative Examples 1 to 5.
Both are extremely high and have a small decrease in permeability μ 'due to an increase in frequency, exhibit excellent magnetic properties in the high frequency range, and can be applied to various electronic components such as choke coils and inductors for noise filters as cores for harmonics. Very suitable. Comparative Example 6, which is composed of an amorphous alloy ribbon having the same composition as the example, has extremely high values of magnetic permeability μ ′ of 7500 at 10 kHz and 1000 at 1 MHz, but has extremely low iron loss. In particular, as a magnetic core for a noise filter used in a high-frequency range, one that shows an appropriate iron loss in order to reduce noise energy in a circuit into the magnetic core is appropriate. Therefore, a magnetic core having extremely small iron loss as in Comparative Example 6 is not suitable as a magnetic core for a nozzle filter. On the other hand, all of the examples have a high magnetic permeability μ ′ and a moderate iron loss of the order of 10 ^{−1, and} can be expected to have a very characteristic application when applied to inductors and the like of noise filters. The difference in iron loss as described above is caused by the shape of the material constituting the magnetic core, and is considered to be related to the aspect ratio. Permeability μ '
It is also known that the use of a powder composed of granular particles can reduce the ratio to one-tenth or less. G. Effect of the Invention As described above, the compacted magnetic body according to the present invention has a soft magnetic amorphous alloy powder composed of plate-like or flaky particles having a length of 10 to 700 μm as a metal component, and thus has a high magnetic permeability. And excellent magnetic properties such that the magnetic permeability is high and the decrease in magnetic permeability in a high frequency range is small. The soft magnetic amorphous alloy powder is of low magnetostriction, and is pressed and molded at a temperature between the Curie point and the crystallization temperature of the soft magnetic amorphous alloy powder using a heat-resistant organic binder. As a result, in addition to being firmly formed, the magnetic anisotropy is effectively suppressed. As a result of the above, it is extremely useful for use in various elements of a high-frequency circuit.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows an embodiment of the present invention. FIG. 1 is a graph showing the relationship between frequency and magnetic permeability μ ′, and FIG. Fe alloy _{Co · Ni) 78 Si 8 B} 14, C
6 is a graph showing the relationship between the relative contents of o and Ni and the magnetostriction constant λs.

   ────────────────────────────────────────────────── ─── Continuation of front page    (72) Inventor Kenzo Suzuki               810 Kumagaya, Kumagaya-shi, Saitama               Kumagaya Office                (56) References JP-A-62-226603 (JP, A)                 JP-A-61-154014 (JP, A)

Claims (1)

(57) [Claims] A compacted magnetic material in which a soft magnetic low magnetostrictive amorphous alloy powder composed of plate-like or flaky particles having a length of 10 to 700 µm and an aspect ratio of 2 to 40 is bound by a heat-resistant organic binder. 2. In producing the compacted magnetic body, (a) a soft magnetic low magnetostrictive amorphous alloy powder consisting of plate-like or flaky particles having a length of 10 to 700 μm and an aspect ratio of 2 to 40,
And (b) pressing and molding the mixture at a temperature between the Curie point and the crystallization temperature of the soft magnetic amorphous alloy. Manufacturing method of magnetic material.