JP5043389B2 - Iron-based soft magnetic powder for dust core, dust core and method for producing dust core - Google Patents

Description

  The present invention relates to a powder for a powder magnetic core made of soft magnetic powder such as iron or iron-based alloy widely used in an alternating magnetic field, which is coated with a resin and a lubricant, and a pressure produced from the powder. The present invention relates to a powder magnetic core and a method for producing a powder magnetic core using the powder.

  Although it has already been put into practical use to produce powder for powder magnetic cores by coating soft magnetic powder with an electrically insulating resin such as phenol, this type of magnetic core used in an alternating magnetic field has a low eddy current. Loss and high magnetic flux density are required. Furthermore, it is also necessary that the mechanical strength is excellent in order to suppress breakage during handling and coiling at the manufacturing site.

  Soft magnetic powder coating with phenol resin can meet the above requirements by giving effective bonding or adhesion to the powder material during compaction molding, but if you try to mold the resin coated powder as it is Since the frictional resistance between the powders and the frictional resistance with the mold are large, the powder may be damaged during molding or may be seized with the mold. In order to prevent such a problem, the soft magnetic powder is usually further mixed with about 0.5 to 1% by mass of a lubricant. However, when the lubricant is added, the above-described problems at the time of molding can be solved, but there is a problem that the strength of the molded body after molding is reduced. In order to prevent such a decrease in strength, in Patent Document 1 below, a lubricant having a high melting point is mixed to prevent the lubricant from being melted during thermosetting of the resin. However, since the lubricant itself remains after molding, it cannot always be said that the strength reduction is sufficiently prevented.

  On the other hand, it is proposed in Patent Document 2 below to try to ensure the strength of the molded body by applying a lubricant to the mold surface instead of mixing the lubricant with powder. However, it is difficult to apply the mold lubrication molding method to a mold for manufacturing a molded body having a complicated shape such as a motor rotor or a stator.

Further, Patent Document 3 below proposes a technique for improving the strength by positively contributing the binding of a lubricant. This is because a phenol resin having many cross-linked methylol groups and a powdered lubricant having a hydroxyl group, an epoxy group or a carboxyl group in the molecule are mixed, thereby causing a reactive bond with the lubricant when the phenol resin is thermally cured. In order to improve the strength, the moldability is not impaired. However, in this method, the resin melted at the time of thermosetting and the lubricant are compatible with each other, and the resin that is compatible with the surface is pushed out. Such surface contamination not only impairs the appearance, but also adversely affects the subsequent surface treatment and dimensional accuracy, so it can be applied to parts that require high dimensional accuracy and parts that require surface treatment, such as motor parts. It was difficult to do.
Japanese Examined Patent Publication No. 4-12605 JP 2001-155914 A JP 2003-318014 A

  In the case of producing a powder magnetic core using soft magnetic powder mixed or coated with a resin as a raw material, the present invention may cause damage at the time of molding due to frictional resistance between powders or between a powder and a mold. It is an object of the present invention to provide a soft magnetic powder for a dust core capable of preventing both of the problem of seizing and preventing the decrease in the strength of the molded body after molding. Furthermore, another object of the present invention is to provide a method for producing a dust core using such a soft magnetic powder for a dust core, and a dust core produced by the production method.

Means to solve the above problems are:
An iron-based soft magnetic powder for a dust core in which a resin and a lubricant are attached to the surface of the iron-based soft magnetic powder, and the lubricant has a boiling point higher than the melting point when the glass transition temperature or melting point of the resin is present. and a low, and the lubricant and the resin, the lubricant or above the melting point, if there is a glass transition temperature or the melting point of the resin all SANYO it is not to compatible at temperatures below the melting point, further wherein The resin adheres at a rate of 0.1 to 5% by mass with respect to the entire iron-based soft magnetic powder for dust core, and the lubricant adheres at a rate of 0.5% by mass or more with respect to the entire iron-based soft magnetic powder for dust core. And the total amount of the resin and the lubricant is 7% by mass or less based on the total amount of the iron-based soft magnetic powder for dust cores. It is.

  The lubricant is preferably an organic substance having a molecular weight of 200 or more and having an OH group and / or a COOH group.

  The resin is 0.1 to 5% by mass with respect to the entire iron-based soft magnetic powder for dust core, and the lubricant is 0.2% by mass or more with respect to the entire iron-based soft magnetic powder for dust core. It is preferable that the resin and the lubricant are adhered in a proportion and 7% by mass or less based on the total amount of the iron-based soft magnetic powder for dust core.

  In producing the dust core, the iron-based soft magnetic powder for dust core is compression molded, and then the compression molded body is heated to a temperature higher than the curing temperature of the resin to cure the resin. A powder magnetic core can be obtained without causing such inconveniences during molding and a decrease in strength of the molded body after molding.

  The dust core obtained by such a method for producing a dust core is an excellent dust core having high surface strength due to the adhesion of the resin to the surface after molding and having a high compact strength.

  In the present invention, the resin and lubricant to be coated on the soft magnetic powder are appropriately selected from the viewpoint of the curing temperature of the resin, the boiling point of the lubricant, and the compatibility between the resin and the lubricant. In addition to eliminating problems during compression molding, it is possible to increase the strength of the molded article even after the resin is cured.

  The inventors mixed soft magnetic powders uniformly, and repeated various studies in order to achieve both improved mechanical strength and good moldability of the green compact without impairing the appearance after thermosetting. As a result, as a lubricant, the boiling point is lower than the melting point if there is a glass transition temperature or melting point of the resin, and more than the melting point of the lubricant, if there is a glass transition temperature or melting point of the resin at a temperature below the melting point It has been found that the above-mentioned goal can be achieved if a lubricant and a resin that are compatible with each other are selected.

  That is, as for the lubricant applied to the present invention, if the resin coexisting therewith does not have a melting point, the lubricant is selected to be lower than the glass transition temperature of the resin, and if the resin has a melting point Is selected to be lower than its melting point. In addition, if the lubricant and the resin that coexist with each other do not have a melting point, select one that is not compatible with the resin in a temperature range that is higher than the melting point of the lubricant and lower than the glass transition temperature of the resin. If there is a melting point, one that is not compatible in a temperature range above the melting point of the lubricant and below the melting point of the resin is selected.

  In the present invention, the dust core is a resin for imparting electrical insulation and mechanical strength to the surface of the soft magnetic powder, and for reducing friction between the powder and the mold during compression molding. Lubricant is adhered to the resin, and the powder with resin and lubricant adhered is pressure-molded to give a predetermined shape, and then heat-treated (resin curing treatment), mainly used in alternating current It is an electromagnetic component called a magnetic core (core), and refers to a magnetic core used for a power supply component such as a noise filter and a choke coil, as well as a motor rotor and stator. Hereinafter, the present invention will be described in more detail.

  Soft magnetic powder is a ferromagnetic metal powder, and is often pure iron powder or iron-base alloy powder, and is mainly produced by pulverizing a lump obtained by the atomization method or the reduction method. The diameter is usually about 50 to 150 μm. The particle size of the resin or lubricant adhered to such soft magnetic powder needs to be a particle size that can be uniformly mixed with the soft magnetic powder, and therefore is required to be smaller than the average particle size of the soft magnetic powder. It is done. For example, when the average particle size of the soft magnetic powder is about 150 μm, the average particle size of the resin or lubricant is preferably about 100 μm or less. Instead of mixing the resin powder and the soft magnetic powder, the resin is dissolved in a solvent and then attached to the surface of the soft magnetic powder, or the resin is heated and mixed with the soft magnetic powder in a liquid state on the surface of the soft magnetic powder. In such a case, it is not necessary to consider the particle size of the resin, but from the viewpoint of compatibility between the resin and the lubricant, which is one of the characteristics of the present invention, the remaining solvent When the resin is dissolved in a solvent in order to suppress the compatibility with the solvent, it is necessary to pay attention to the selection of the solvent and to select one that does not dissolve the lubricant. In this case, the lubricant is mixed as a powder.

  The dust core formed by mixing soft magnetic powder with a lubricant used in conventional powder metallurgy, such as metal stearate, metal soap, and wax, is used as a release agent. The strength of the powder magnetic core is low to inhibit the force. Further, as described above, a resin obtained by compressing and molding a mixture of a resin in which a resin and a lubricant react with each other and a lubricant and soft magnetic powder are compression-molded, and then thermosetting the resin, as described above. Dirty due to. This is presumed to be due to the following mechanism. That is, almost no resin and lubricant remain on the surface of the molded body after compression molding due to the sliding of the mold and the molded body. Most of the resin and the lubricant are present in the pores (gap between the soft magnetic powders) inside the molded body. When the molded body is heat-treated to cure the resin, the liquid lubricant and resin are compatible in the molded body, and the liquid in which the lubricant and the resin are mixed together has a volume due to capillary action and liquefaction by heat treatment. The surface of the molded body oozes due to an increase in pressure inside the molded body due to the increase. Thereafter, when the temperature is lowered, the oozing liquid is solidified on the surface. If it is only a lubricant, it can be easily wiped off even if it is solidified, but since the exuded liquid contains resin, it cannot be easily wiped off due to the adhesive strength of the resin. Become. In addition, the solidified resin has a color unique to the resin, for example, a brown color in the case of a phenol resin, and surface contamination is conspicuous. In addition, resins used in this field are generally highly viscous, and even if the amount of the resin itself is small, what appears on the surface of the molded body exists in a spherical shape on the surface, and this point also makes the stain noticeable. Cause.

  In order to solve such a problem on the surface of the molded body, it is necessary to prevent the resin inside the molded body from seeping out on the surface. Not a problem). Accordingly, the present inventors first thought that the incompatibility of the lubricant and the resin during the curing heat treatment of the resin would prevent the resin from exuding and consequently solve the surface contamination.

  On the other hand, as described above, the cause of lowering the strength of the molded product after the heat treatment of the resin is the lubricant present in the molded product. In order to improve the strength of the molded body, it is necessary to prevent the lubricant from being present before reaching the temperature necessary for curing the resin during the resin curing heat treatment. In order to prevent the lubricant from being present at such timing, it is necessary that the boiling point of the lubricant evaporates or volatilizes below the curing temperature of the resin.

  Conventionally, as a lubricant in the powder metallurgy field, a metal stearate represented by zinc stearate is used, but the metal stearate does not decompose and evaporate unless it is at a high temperature of 600 ° C. or higher. On the other hand, at a high temperature of 600 ° C. or higher, most of the resin is decomposed and the original functions of the resin such as electrical insulation and imparting mechanical strength are impaired. Therefore, the stearic acid metal salt cannot be used in the present invention.

  The curing temperature of ordinary resins is at most 400 ° C., but organic resins having CO groups and / or COOH groups are typically listed as resins having a boiling point in such a temperature range or lower. Specific examples include dodecyl alcohol, myristyl alcohol, stearyl alcohol, cetyl alcohol, aradecyl alcohol, D-pantenol, sebacic acid, dodecanoic acid, decyl alcohol, tridecanol and the like.

  The molecular weight of the lubricant is preferably 200 to 300. When the molecular weight is less than 200, the melting point becomes near room temperature, and there is a possibility of melting under a normal use environment. If the lubricant is melted before the compression molding process in the mixed powder, the flowability of the powder is remarkably reduced, so that when the mixed powder is filled in the mold for molding, the mold is not filled. Since troubles such as becoming sufficient may occur, the molecular weight is preferably 200 or more so that the lubricant does not melt at room temperature. Further, since the boiling point of the lubricant increases and the volatilization becomes difficult as the molecular weight increases, the molecular weight is preferably 300 or less.

  As for the resin, a desired resin may be appropriately selected from the relationship between the curing temperature and the boiling point of the lubricant, and the compatibility relationship with the lubricant. However, the organic substance having the CO group and / or COOH group described above may be used. When used as a lubricant, it is recommended to use polyimide resin, polyimide amide resin, or PEEK resin from the viewpoint of curing temperature.

The amount of resin and lubricant added is about the same as that of ordinary compounding in the field of powder magnetic cores. Specifically, the resin is pressed to give mechanical strength and electrical insulation between the powders. It is preferable to add 0.1% by mass or more based on the whole iron-based soft magnetic powder for powder magnetic core. Further, since the space factor of the soft magnetic powder in the molded body affects the magnetic flux density of the molded body, the amount of resin added is preferably 5% by mass or less for the purpose of obtaining a sufficient magnetic flux density. The lubricant is added to prevent seizure with the mold during molding, and is 0.2% by mass or more, preferably 0.5% by mass with respect to the entire iron-based soft magnetic powder for the dust core. % Or more is preferably added. On the other hand, for the purpose of ensuring the density of the molded body, it should not be added more than necessary, and the total amount of resin and lubricant is preferably 7% by mass or less.
(Example)
Experiment 1
An experiment was conducted to investigate the compatibility between the resin and the lubricant at the curing temperature of the resin. 25 g of the lubricant is put in a beaker, heated to a temperature equal to or higher than the melting point of the lubricant (a temperature higher by about 30 ° C. than the melting point) and lower than the curing temperature of the resin used in the experiment, and maintained at the temperature for about 10 minutes. As a result, the lubricant was sufficiently melted. Thereafter, 5 g of a resin in a solid powder state was added to the lubricant in a liquid state, and whether or not the resin was dissolved was visually confirmed to confirm the compatibility. The combination of resin and lubricant used in the experiment and the compatibility results are shown in Table 1. The melting point and curing temperature of each resin and the melting point and boiling point of each lubricant are also shown in Table 1. The lubricant used was a reagent manufactured by Wako Pure Chemical Industries, Ltd., and the particle size used was passed through a sieve having an opening of 150 μm. Resin is polyimide resin: PIQ made by Hitachi Chemical DuPont Microsystems (it is a varnish, so it is evaluated by the solidified component after heating and volatilizing the solvent at 75 ° C.), polyamideimide resin: Viromax made by Toyobo (75 because it is varnished) The PEEK resin was 450P (particle size is 20 μm powder) manufactured by Tokyo Belt Co., Ltd.).

  As a phenol resin used as a comparative example, Kanebo's Belpearl was used.

Experiment 2
For molded products obtained by compression-molding a mixed powder of iron-based soft magnetic powder (iron powder) mixed with resin and lubricant and then curing the resin, the bending strength of the molded product is measured and molded. An experiment was conducted to visually confirm the presence or absence of dirt on the body surface.

  After adding 0.5% by mass of resin and 0.75% by mass of lubricant to the iron powder, mixing for 30 minutes with a V-type mixer, filling the mixed powder into a 30 mm diameter mold, 8 tons Molded body height: 20 mm with a molding pressure of / cm 2. Thereafter, the resin was cured by being held in an inert gas at a curing temperature (experimental temperature described in Table 2) for 30 minutes, and then slowly cooled to obtain a molded body. The bending strength test was performed according to a test method prescribed in ISO 3325 (sintered metal material bending strength). “AUTOGRAPH AG-5000E” manufactured by Shimadzu Corporation was used as the test apparatus, and the distance between the support points was set to 25 mm. The results are shown in Table 2. In addition, what was displayed as "-" in the column of the experiment temperature of Table 2 was not experimented (because the melting temperature of the phenol resin is lower than the melting point of the lubricant).

  The curing temperature varies depending on the resin, the thermosetting resin is the curing temperature at which curing begins, and in the case of a thermoplastic resin, the glass transition temperature (in order to increase the strength of the powder magnetic core by softening the resin and bringing it into close contact with the soft magnetic powder. The one having no melting point) or a temperature higher than the melting point is set as the curing temperature. In any case, in order to suppress thermal degradation of the resin, it is desirable to keep the temperature 10 to 30 ° C. higher than the curing temperature, glass transition temperature, and melting point.

Experiment 3
The effect of the molecular weight of the resin on the flowability of the mixed powder was confirmed by experiments. In the experiment, 0.65% by mass of a lubricant was added to iron powder, and the powder mixed for 30 minutes with a V-type mixer was evaluated according to Japan Powder Metallurgy Industry Association Standard JPMA P 07-1992 or JIS Z 2502. The results are shown in Table 3. In Table 3, when the flowability is x, the powder did not flow at room temperature, and ◯ means that it flowed.

  From the results of Experiments 1 and 2, according to the present invention, since the resin and the lubricant are not compatible during the heat treatment in the heat treatment process for improving the strength of the molded body, the surface contamination of the molded body due to the resin oozing out. Since the lubricant evaporates at the softening temperature of the resin, it does not remain inside the molded body, and it is possible to suppress a decrease in the strength of the molded body due to the lubricant. It turns out that a powder magnetic core can be obtained.

  Also, in Experiment 3, if a lubricant with a molecular weight of 200 or more whose powder flowability is evaluated as ◯ is used, special lubrication such as mold lubrication molding (the lubricant is applied to the mold by molding powder containing no lubricant) Without using a simple molding method, it is possible to suppress a decrease in strength of the powder magnetic core by ordinary internal lubrication molding (molding of a powder containing a lubricant).

Claims (4)

An iron-based soft magnetic powder for a dust core in which a resin and a lubricant are attached to the surface of the iron-based soft magnetic powder, and the lubricant has a boiling point higher than the melting point when the glass transition temperature or melting point of the resin is present. and a low, and the lubricant and the resin, the lubricant or above the melting point, if there is a glass transition temperature or the melting point of the resin all SANYO it is not to compatible at temperatures below the melting point, further wherein The resin adheres at a rate of 0.1 to 5% by mass with respect to the entire iron-based soft magnetic powder for dust core, and the lubricant adheres at a rate of 0.5% by mass or more with respect to the entire iron-based soft magnetic powder for dust core. And the total amount of the resin and the lubricant is 7% by mass or less based on the total amount of the iron-based soft magnetic powder for dust cores. .   2. The iron-based soft magnetic powder for a dust core according to claim 1, wherein the lubricant is an organic substance having a molecular weight of 200 or more and having an OH group and / or a COOH group. The iron-based soft magnetic powder for a dust core according to claim 1 or 2 is compression-molded, and then the compression-molded body is heated to a melting point or higher if the resin has a glass transition temperature or a melting point. A method for producing a powder magnetic core, characterized by curing.   A dust core obtained by the method for manufacturing a dust core according to claim 3.