JP2008063649A - Powder for dust core, its production method and method for producing dust core - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a powder for a dust core whose formability can be improved to a standard more excellent than that of the conventional powder for a dust core composed of a phenolic resin-covered metal powder without causing troubles such as the remarkable deterioration in the strength of a formed body as such caused by lubricant addition; to provide its production method; and to provide a method for producing a dust core. <P>SOLUTION: (1) Regarding the powder for a dust core, the surface of a soft magnetic powder is covered with one or more kinds selected from a phenolic resin, an epoxy resin and a silicone resin by the amount of 0.01 to 0.5 mass% to the amount of the soft magnetic powder, and a polyamide resin with the average particle diameter of ≤100 μm is stuck to the surface thereof by the amount of 0.l to 1.0 mass% to the amount of the soft magnetic powder. (2) Regarding the method for producing powder for a dust core from a mixed body comprising a liquid body in which the above resin is dissolved into an organic solvent and a soft magnetic powder, the organic solvent is volatilized, so as to cover the surface of the soft magnetic powder with the above resin, thereafter, a polyamide resin with the average particle diameter of ≤100 μm is added, and mixing is performed. (3) Regarding the method for producing a dust core, when the powder for a dust core is subjected to compression molding, a mold lubrication molding process is used. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention belongs to a technical field relating to a powder for a powder magnetic core, a method for producing the powder, and a method for producing a powder magnetic core.

  Magnetic cores used in AC magnetic fields are required to have low iron loss, especially eddy current loss, and high magnetic flux density, and they do not break during handling or winding to form coils in the manufacturing process. Desired. Further, depending on the use of the magnetic core, a certain level of strength is also required. For example, when it is applied as a core material (magnetic core) such as a rotor of a motor, a centrifugal force is applied.

  In the case of a dust core, eddy current loss can be suppressed by interposing an insulating resin between metal powder particles such as soft magnetic powder, and this resin serves as an adhesive between the metal powder particles. Therefore, it is possible to ensure good mechanical strength and prevent breakage.

  With respect to the powder (powder core powder) used as a raw material for such a dust core, powders for dust core described in JP 2004-319749 A, JP 2003-319749 A, and JP 2003 2003 There are powders for dust cores described in Japanese Patent No. -318014.

  The powder for powder magnetic core described in JP-A-2004-319749 is a powder in which the surface of a metal powder such as soft magnetic powder is coated with a phenol resin having a methylol group in the molecule (phenol resin-coated metal powder). is there.

The powder for a powder magnetic core described in JP-A-2003-318014 contains a soft magnetic powder, a phenol resin powder, and a reactive lubricant.
JP 2004-319749 A JP 2003-318014 A

  The powder for powder magnetic core described in JP-A-2004-319749 (hereinafter also referred to as conventional phenol resin-coated metal powder) further improves the formability when the powder is compression-molded into a powder magnetic core. It is desirable. Lubricant is added as a normal means for improving moldability. However, when a lubricant is added to the powder for powder magnetic core, the moldability is improved, but the strength of the compact (powder magnetic core) is greatly reduced. (It becomes so low that it becomes insufficient).

  The powder for powder magnetic core described in JP-A-2003-318014 contains (adds) a reactive lubricant, so that the moldability is good, but the reactive lubricant and the phenol resin are compatible. Therefore, when the phenol resin is thermally cured, the resin dissolved in the reactive lubricant oozes out from the molded body to the surface of the molded body, contaminates the molded body surface, and may cause a decrease in dimensional accuracy and uneven coating. .

  The present invention has been made paying attention to such circumstances, and its purpose is to produce a significant decrease in the strength of the molded article as in the case of addition of a lubricant (an insufficient decrease), In addition, conventional phenols can be used without causing contamination of the surface of the molded body due to leaching of the resin dissolved in the lubricant to the surface of the molded body as in the case of addition of a reactive lubricant, reduction in dimensional accuracy, and occurrence of coating unevenness. Powder for powder magnetic core capable of improving moldability to a level superior to that of resin-coated metal powder (powder magnetic core powder described in JP-A-2004-319749) An object of the present invention is to provide a method for producing a dust core.

  In order to achieve the above object, the present inventors have intensively studied, and as a result, completed the present invention. According to the present invention, the above object can be achieved.

  The present invention, which has been completed in this way and has achieved the above object, relates to a powder for a dust core, a method for producing the same, and a method for producing a dust core, and the dust according to claim 1 of the claims. A powder for magnetic core (powder for powder magnetic core according to the first invention), a method for producing a powder for powder magnetic core according to claim 2 (a method for producing a powder for powder magnetic core according to the second invention), A method for producing a dust core (a method for producing a dust core according to the third invention), a method for producing a dust core according to claim 4 (a method for producing a dust core according to the fourth invention), The configuration is as follows.

  That is, the powder for a powder magnetic core according to claim 1 is such that at least one of a phenol resin, an epoxy resin, and a silicone resin is present on the surface of the soft magnetic powder in an amount of 0.01 to 0.5 mass% with respect to the amount of the soft magnetic powder. A powder for powder magnetic core, characterized in that a polyamide resin having an average particle diameter of 100 μm or less is coated on the soft magnetic powder in an amount of 0.1 to 1.0% by mass with respect to the soft magnetic powder. There is [the first invention].

  The method for producing a powder for a powder magnetic core according to claim 2 comprises a mixture containing a liquid and soft magnetic powder in which one or more resins selected from a phenol resin, an epoxy resin, and a silicone resin are dissolved in an organic solvent. After the organic solvent is volatilized and the surface of the soft magnetic powder is coated with the resin, a polyamide resin having an average particle diameter of 100 μm or less is added and mixed. Second invention].

  A method for producing a dust core according to claim 3 is a method for producing a dust core comprising a step of compression molding the powder for dust core according to claim 1, wherein a die lubrication molding method is used for the compression molding. This is a method for producing a dust core characterized in that [third invention]. 4. The method for manufacturing a dust core according to claim 4, wherein the ratio of the sliding area of the molded body to the mold and the pressed area of the molded body is 1 or more during the compression molding. It is a manufacturing method of a dust core.

  According to the powder for a powder magnetic core according to the present invention, there is no significant decrease in strength of the molded body (a decrease that is insufficient) as in the case of addition of a lubricant, and in the case of addition of a reactive lubricant. The conventional phenol resin-coated metal powder without causing contamination of the surface of the molded body due to leaching of the resin dissolved in the lubricant onto the surface of the molded body, lowering of dimensional accuracy, and occurrence of coating unevenness Compared with the powder for powder magnetic cores described in Japanese Patent No. 319749, the moldability can be improved to an excellent level.

  According to the method for producing a powder for a powder magnetic core according to the present invention, such a powder for a powder magnetic core according to the present invention can be obtained.

  According to the method for manufacturing a dust core according to the present invention, the strength of the molded body is not significantly reduced as in the case of adding a lubricant, and the powder is dissolved in the lubricant as in the case of adding a reactive lubricant. The molded body (powder magnetic core) can be obtained by compression molding with good moldability without causing contamination of the molded body surface due to seepage of the molded resin surface, deterioration of dimensional accuracy, and occurrence of coating unevenness. it can. In particular, the method of manufacturing a powder magnetic core according to the present invention has a large length (depth) in the compression direction with respect to the area of the pressing surface, which is inherently difficult to perform compression molding. It is suitable for molding a shape in which the ratio of the sliding area to the mold and the pressure area of the molded body is 1 or more.

  As described above, in the powder for a powder magnetic core according to the present invention, at least one of a phenol resin, an epoxy resin, and a silicone resin on the surface of the soft magnetic powder is 0.01 to 0.5% by mass with respect to the amount of the soft magnetic powder. For a powder magnetic core, wherein a polyamide resin having an average particle diameter of 100 μm or less is deposited on the soft magnetic powder in an amount of 0.1 to 1.0% by mass based on the amount of the soft magnetic powder. It is a powder.

  When this powder for powder magnetic core is compression molded into a powder magnetic core, the polyamide resin (polyamide resin adhering to the soft magnetic powder coated with the resin) is excellent in lubricity. Has the effect of improving lubricity. For this reason, the moldability is improved as compared with the conventional phenol resin-coated metal powder (powder magnetic core powder described in JP-A-2004-319749).

  Thus, since moldability improves, it is not necessary to add a lubricant and it can be used without adding a lubricant. For this reason, it is possible to prevent a significant decrease in the strength of the molded body due to the addition of the lubricant (an insufficient decrease), and a lubricant as a result of the addition of the reactive lubricant. It is possible to prevent the surface of the molded body from being contaminated, the reduction in dimensional accuracy, and the occurrence of coating unevenness due to the resin dissolved in the surface of the molded body.

  As described above, the polyamide resin has an effect of improving lubricity and improving moldability, but has a lower adhesive strength than a phenol resin or the like. However, when compared with lubricants such as zinc stearate and wax, it acts as an adhesive and tends to improve strength. Further, it does not cause contamination of the surface of the molded body due to oozing to the surface of the molded body, reduction in dimensional accuracy, and occurrence of coating unevenness. Furthermore, the moldability is further improved by using mold lubrication molding together.

  Therefore, according to the powder for a powder magnetic core according to the present invention, there is no significant decrease in the strength of the molded body (a decrease that is insufficient) as in the case of addition of a lubricant, and the addition of a reactive lubricant. In the case of the conventional phenol resin-coated metal powder without causing contamination of the surface of the molded body due to leaching of the resin dissolved in the surface of the molded body, lowering of dimensional accuracy and occurrence of coating unevenness The moldability can be improved to an excellent level as compared with the powder for powder magnetic cores described in JP 2004-319749 A.

  In the powder for powder magnetic core according to the present invention, the polyamide resin to be deposited on the soft magnetic powder coated with the resin has an average particle diameter of 100 μm or less. If the average particle size exceeds 100 μm, the particle size of the polyamide resin becomes too large relative to the particle size of the soft magnetic powder, resulting in a decrease in the density of the compact (powder magnetic core), and consequently a decrease in the magnetic flux density. This is because it becomes insufficient.

  The amount of the polyamide resin attached is 0.1 to 1.0% by mass with respect to the amount of the soft magnetic powder. When the amount is less than 0.1% by mass, the degree of improvement in moldability is lowered and insufficient. If the content exceeds 1.0% by mass, there are many nonmagnetic components, the density of the compact (dust core) decreases, and the magnetic flux density decreases and becomes insufficient.

  The amount of the resin coated on the surface of the soft magnetic powder is 0.01 to 0.5% by mass with respect to the amount of the soft magnetic powder. If the amount is less than 0.01% by mass, the coating is insufficient and the compact (dust core) The specific resistance decreases, and as a result, iron loss (especially eddy current loss) increases and becomes insufficient. On the other hand, when it exceeds 0.5% by mass, there are many nonmagnetic components and the density of the compact (dust core) decreases. However, as a result, the magnetic flux density decreases and becomes insufficient.

  In the powder for a powder magnetic core according to the present invention, the surface of the soft magnetic powder is caused by the fact that the lubricity is increased by the polyamide resin and the moldability is improved, and therefore the powder can be used without adding a lubricant. The resin to be coated is not limited to a phenol resin, and an epoxy resin and a silicone resin can be used in addition to a phenol resin, and two or more of a phenol resin, an epoxy resin, and a silicone resin can be used. When two or more of phenol resin, epoxy resin, and silicone resin are used, two or more types are mixed and coated on the surface of the soft magnetic powder, and two or more types are coated on two layers (of soft magnetic powder There is a method in which either one type is coated on the surface, and then the other one type is coated, or the other one type is further coated). Can also be adopted.

  As described above, the method for manufacturing a powder for a powder magnetic core according to the present invention comprises a liquid material in which one or more resins selected from a phenol resin, an epoxy resin, and a silicone resin are dissolved in an organic solvent, and a soft magnetic powder. After the organic solvent is volatilized from the mixture and the surface of the soft magnetic powder is coated with the resin, a polyamide resin having an average particle size of 100 μm or less is added and mixed to produce a powder for a powder magnetic core, Is the method.

  According to this method for producing a powder for a powder magnetic core, the surface of the soft magnetic powder is coated with one or more of a phenol resin, an epoxy resin, and a silicone resin, and a polyamide resin having an average particle diameter of 100 μm or less is coated thereon. An adhering dust core powder is obtained. At this time, the coating amount of the resin can be 0.01 to 0.5% by mass with respect to the amount of the soft magnetic powder. Further, the amount of the polyamide resin adhered can be 0.1 to 1.0% by mass with respect to the amount of the soft magnetic powder. As a result, the surface of the soft magnetic powder is coated with one or more of a phenol resin, an epoxy resin, and a silicone resin in an amount of 0.01 to 0.5% by mass with respect to the amount of the soft magnetic powder. A powder for a powder magnetic core in which a polyamide resin having a particle size of 100 μm or less is attached in an amount of 0.1 to 1.0% by mass with respect to the amount of the soft magnetic powder can be obtained. This powder for powder magnetic core corresponds to the powder for powder magnetic core according to the present invention.

  Therefore, according to the method for manufacturing a powder for a powder magnetic core according to the present invention, the powder for a powder magnetic core according to the present invention can be obtained. As a method for attaching the polyamide resin, as shown in the examples described later, it is most convenient to mix the polyamide resin powder. However, in order to adhere more firmly, the polyamide resin powder is hot-melted, or It is also possible to use a solvent-soluble polyamide resin and once dissolve it in a solvent and adhere it onto the soft magnetic powder.

  A mixture in the method for producing a powder for a powder magnetic core according to the present invention, that is, a mixture of a liquid material in which one or more resins selected from a phenol resin, an epoxy resin, and a silicone resin are dissolved in an organic solvent and a soft magnetic powder is Is obtained as follows. That is, the one or more kinds of resins are dissolved in an organic solvent, and a product (liquid material) obtained thereby is mixed with soft magnetic powder. Alternatively, after mixing the soft magnetic powder and the resin, an organic solvent is mixed therewith to dissolve the resin (to form a liquid). Alternatively, the soft magnetic powder, the resin and the organic solvent are mixed at the same time to dissolve (resin) the resin. Alternatively, after mixing soft magnetic powder and an organic solvent, the resin is mixed therewith and dissolved in the organic solvent (to form a liquid). Any of these methods can be employed.

  As described above, a method for manufacturing a dust core according to the present invention is a method for manufacturing a dust core having a step of compression-molding the powder for a dust core according to claim 1, wherein the lubrication is performed during the compression molding. A method of manufacturing a powder magnetic core using a molding method.

  The powder for a powder magnetic core according to claim 1 corresponds to the powder for a powder magnetic core according to the present invention described above. The powder for powder magnetic core according to the present invention has the above-described effects. In the method of manufacturing a powder magnetic core according to the present invention, such powder for powder magnetic core is compression-molded, so that the strength of the molded body is greatly reduced (decrease is insufficient) as in the case of adding a lubricant. In addition, as in the case of reactive lubricant addition, the surface of the molded body may be contaminated by leaching of the resin dissolved in the lubricant onto the surface of the molded body. In addition, compression molding can be performed with better moldability than conventional phenol resin-coated metal powder (powder magnetic core powder described in JP-A-2004-319749).

  Further, in the method of manufacturing a powder magnetic core according to the present invention, since a mold lubrication molding method is used for compression molding, the lubricity becomes high, and there are complicated shapes and relatively large sizes. It can be molded with good moldability. That is, when molding such a complicated shape or a large size, further lubricity is required, but according to the mold lubrication molding method, further lubricity can be secured. In addition, even when molding a large size, it can be molded with good moldability.

  Therefore, according to the method for producing a dust core according to the present invention, a reactive lubricant is produced without causing a significant decrease in strength of the molded body (a decrease that becomes insufficient) as in the case of adding a lubricant. Molded by good compression molding without causing contamination of the surface of the molded body due to seepage of the resin dissolved in the lubricant, as in the case of addition, deterioration of dimensional accuracy, and generation of uneven coating A compact (powder magnetic core) can be obtained, and a compact (powder magnetic core) can be obtained by compression molding with good moldability even when molding a complex shape or large size. In particular, compression molding, which is difficult to compress, has a large length (depth) in the compression direction relative to the area of the pressing surface, that is, during compression molding, the sliding area of the molded body with the mold and pressurization of the molded body The method for manufacturing a dust core according to the present invention is suitable for forming a shape having a ratio of 1 or more to the area.

  The soft magnetic powder is a ferromagnetic metal powder. Examples of soft magnetic powder include pure iron powder, iron-base alloy powder (Fe-Al alloy, Fe-Si alloy, Sendust, Permalloy, etc.), amorphous powder, and electrical insulation such as phosphoric acid-based chemical conversion film and oxide film on the surface. There are iron powder etc. which have a film.

  Examples of the present invention and comparative examples will be described below. The present invention is not limited to this embodiment, and can be implemented with appropriate modifications within a range that can be adapted to the gist of the present invention, all of which are within the technical scope of the present invention. include.

(Experiment 1)
Soft magnetic powder (“Atmel 300NH” manufactured by Kobe Steel, Ltd.) (average particle size of about 90 μm) and phenol resin (average particle size of about 30 μm) are mixed for 10 minutes using a high-speed mixer, and then organically mixed therewith. IPA (isopropanol) was added as a solvent and mixed. In this way, a mixture containing a liquid material in which phenol resin was dissolved in IPA and soft magnetic powder was obtained. At this time, the mixing ratio (% by mass) of the phenol resin was changed as shown in Table 1. This mixing ratio (mass%) is the ratio (mass%) of the amount of phenol resin to the amount of soft magnetic powder. In each case, the amount of IPA added was 2 parts per 100 parts of soft magnetic powder.

  Next, the mixture was placed in an open furnace and heated in the atmosphere at 75 ° C. for 30 minutes to volatilize IPA from the mixture. Thereby, the coating layer of the phenol resin was formed on the surface of the soft magnetic powder. In this way, a powder (phenol resin-coated soft magnetic powder) in which the surface of the soft magnetic powder was coated with a phenol resin was obtained.

  A powder for a magnetic core in which a polyamide resin with an average particle size of about 50 μm is added to and mixed with the above phenol resin-coated soft magnetic powder (polyamide resin-attached type phenol resin-coated soft magnetic powder) ) At this time, the mixing ratio (mass%) of the polyamide resin was changed as shown in Table 1. This mixing ratio (mass%) is a ratio (mass%) of the amount of polyamide resin to the amount of soft magnetic powder.

  The powder for magnetic core thus obtained (polyamide resin-attached phenolic resin-coated soft magnetic powder) is filled in a mold, and the temperature is 20 ° C, the pressure is 600 MPa, and the pressurization time is 2 seconds at the maximum load. To obtain a compression molded body. After that, the compression molded body is heated in air at 230 ° C. for 10 minutes, and the phenol resin in the compression molded body is thermally cured to form a powder magnetic core (a cuboid having a length of 31.4 mm, a width of 12.7 mm and a thickness of 5 mm). Obtained.

  At this time, the die lubrication molding method was used for some of the compression moldings (Nos. 7 to 10 in Table 1). In this mold lubrication molding method, a mold in which a lubricant (zinc stearate) dispersed in ethanol was applied to the inner wall surface of the mold with a brush was used. And the metal mold | die after this application | coating was filled with the said powder, and the compression molding was performed on the said conditions. Other than these (Nos. 1 to 6 and 11 in Table 1), the mold lubrication molding method was not used, and no lubricant was added. That is, molding was performed by a normal molding method.

  In order to evaluate compression moldability, the pressure at the time of extraction after compression molding (extraction pressure) was measured. That is, after compression molding, the compression molded body was relatively pushed out from the inside of the mold by pushing up the mold, and the maximum load (punch pressure) applied to the mold at this time was measured. And, when the punching pressure was less than 35 MPa, the moldability: ○ (good), and when the punching pressure was 35 MPa or more, the moldability: x (defective, that is, difficult to mold). However, even if the drawing pressure was less than 35 MPa, if the molded body was scratched, it was evaluated as Δ (acceptable range).

  The powder core obtained in this way was measured for specific resistance, density and strength as follows.

  The specific resistance was measured by the 4-terminal method. Measurement was performed in a four-terminal resistance measurement mode using “RM-14L” manufactured by Rika Denshi Co., Ltd. as a probe and a digital multimeter “VOAC-7510” manufactured by Iwasaki Tsushin Co., Ltd. as a measuring instrument. The measurement was performed by setting the distance between terminals to 7 mm, pressing the probe against the measurement sample with a stroke of 5.9 mm and a spring load of 10-S. The 10-S specification has a full stroke of 5.9mm and a load of 2/3 stroke is 155g.

  The density was determined by measuring the weight and volume of the dust core and dividing the weight by the volume.

  As for strength, a bending strength was obtained by performing a three-point bending test. That is, the bending strength test was performed according to the test method prescribed in ISO3325 (sintered metal material bending strength). “AUTOGRAPH AG-5000E” manufactured by Shimadzu Corporation was used as the test device, and the distance between fulcrums was set to 25 mm.

The results of the above measurement (test) are shown in Table 1. Here, the specific resistance was evaluated as ○ (good) when the specific resistance was 50 μΩ · m (5000 μΩ · cm) or more, and x (defect) when the specific resistance was less than 50 μΩ · m. The density was evaluated as ○ (good) when the density was 7.1 g / cm ³ or more, and x (bad) when the density was less than 7.1 g / cm ³ . The strength was evaluated as ◯ (good) when the bending strength at room temperature (room temperature) was 40 MPa or more, and X (defect) when the bending strength was less than 40 MPa. Overall, when one or more of specific resistance, density, strength, and formability is x, it is judged as x (defective or insufficient), and when all are not x (when all are Δ or more). Was judged as good (good or sufficient).

  As can be seen from Table 1, in the case of No. 6 (Comparative Example 5), not a polyamide resin-attached phenol resin-coated soft magnetic powder as a powder for powder magnetic core, but a phenol resin-coated soft magnetic powder (phenol resin amount: 0.1) The obtained dust core has a specific resistance: ○ (good), density: ○ (good) and strength: ◎ (level superior to ○), but molded. Properties: x (defective, that is, difficult to mold). Therefore, overall, it is x (defective or insufficient).

  On the other hand, in the case of No. 1 (Example 1 of the present invention), a polyamide resin-attached phenolic resin-coated soft magnetic powder (powder resin amount: 0.1 mass%, polyamide resin amount: 0.7 mass) as a powder magnetic core powder %)), And the obtained powder magnetic core has specific resistance: ○ (good), density: ○ (good), strength: ○ (good), and moldability: ○ (good). is there. Therefore, it is (circle) (good, sufficient) comprehensively. The strength in the case of No. 1 is lower than that in the case of No. 6, but the degree is small, and the strength is greatly reduced as when a lubricant is added (a reduction that is insufficient). is not.

  In the case of No. 1, as in the case of No. 6, the surface of the molded body is contaminated by the leaching of the resin dissolved in the lubricant to the surface of the molded body as in the case of adding a reactive lubricant, the dimensional accuracy is reduced, and The occurrence of coating unevenness was not observed.

  From the above, in the case of No. 1 (Invention Example 1) (powder magnetic core powder: polyamide resin-attached phenol resin-coated soft magnetic powder), the strength of the molded body is greatly reduced as in the case of adding a lubricant ( And the contamination of the molded body surface due to the seepage of the resin dissolved in the lubricant into the molded body surface, as in the case of adding a reactive lubricant, Formability can be improved to a level superior to that of No. 6 (Comparative Example 5) (powder magnetic core powder: phenol resin-coated soft magnetic powder) without causing uneven coating. confirmed.

  In the case of No. 11 (Invention Example 6), the powder for the powder magnetic core is a polyamide resin-attached soft magnetic powder of the same type as that of No. 1, but No. 1 is the amount of phenol resin and polyamide Resin amount is different. However, these amounts all satisfy the amounts defined in the present invention (phenol resin amount: 0.01 to 0.5 mass%, polyamide resin: 0.1 to 1.0 mass%). In the case of No.11, the formability is △ (allowable range), which is lower than that of No.1, but can be improved to a level superior to that of No.6. It is in. In addition, since the moldability is Δ, the specific resistance is ◯ (good), the density is ◯ (good), and the strength is ◯ (good), the overall result is ◯ (good or sufficient).

  In the case of No. 2 to 5 (Comparative Examples 1 to 4), the powder for the powder magnetic core is a polyamide resin-attached phenolic resin-coated soft magnetic powder of the same type as No. 1 and No. 11, but No. 1 The amount of phenol resin and / or polyamide resin is different from No. 11 and the amount of phenol resin and / or polyamide resin does not satisfy the amount specified in the present invention. In the case of these Nos. 2 to 5, since any one of the specific resistance, density, strength, and formability is x, overall, it is x (defective or insufficient).

  In the case of No. 7 to 10 (Invention Examples 2 to 5), a die lubrication molding method is used for compression molding. In any case, the obtained powder magnetic core has specific resistance: ○ (good), density: ○ (good), strength: ○ (good), and moldability: ○ (good). Is o (good or sufficient). In all of these, the amount of phenol resin and the amount of polyamide resin satisfy the amounts specified in the present invention. Among these, in the case of No. 7 and 10, the amount of polyamide resin is less than in the case of No. 11 (Example 6 of the present invention), but the moldability is ○, which is better than the case of No. 11 (△). ing. This is because the mold lubrication molding method is used.

(Experiment 2)
Various samples (Nos. 12 to 17) shown in Table 2 were prepared under the same conditions as in Experiment 1 except that the shape of the compression molded body was changed. The shape of the compression-molded body is all cylindrical, and the sliding area of the molded body with the mold (side surface of the cylinder) is changed by variously changing the height of the cylinder with respect to the size of the pressure surface (circular) (about 10 mm). ) And the pressed area of the molded body was changed to 1-10. The compression moldability of these samples was evaluated in the same manner as in Experiment 1. The results are shown in Table 2. In Table 2, “ratio” indicates the value of the sliding area of the molded body with the mold / pressed area of the molded body.

  As apparent from Table 2, when the mold lubrication molding method is employed using the powder for a powder magnetic core of the present invention, the sliding area of the molded body with the mold and the pressed area of the molded body Even a compression molded product having a ratio of 1 or more exhibits excellent moldability.

  According to the powder for a powder magnetic core according to the present invention, there is no significant decrease in strength of the molded body (a decrease that is insufficient) as in the case of addition of a lubricant, and in the case of addition of a reactive lubricant. Compared with the conventional phenol resin-coated metal powder without causing contamination of the surface of the molded body due to seepage of the resin dissolved in the lubricant to the surface of the molded body, lowering of dimensional accuracy, and occurrence of coating unevenness. Therefore, the moldability can be improved to an excellent level, so that it can be suitably used as a powder for a dust core and is useful.

Claims (4)

  The surface of the soft magnetic powder is coated with one or more of a phenol resin, an epoxy resin, and a silicone resin in an amount of 0.01 to 0.5% by mass with respect to the amount of the soft magnetic powder, and an average particle diameter of 100 μm or less is further formed thereon. A powder for a powder magnetic core, wherein the polyamide resin is adhered in an amount of 0.1 to 1.0% by mass relative to the amount of the soft magnetic powder.   An organic solvent is volatilized from a mixture including a liquid material in which one or more resins selected from a phenol resin, an epoxy resin, and a silicone resin are dissolved in an organic solvent, and the soft magnetic powder, and the resin is formed on the surface of the soft magnetic powder. A method for producing a powder for a powder magnetic core, comprising: adding a polyamide resin having an average particle size of 100 μm or less after mixing and mixing.   A method for producing a dust core comprising a step of compression-molding the powder for a dust core according to claim 1, wherein a mold lubrication molding method is used for the compression molding.   The method for manufacturing a dust core according to claim 3, wherein a ratio of a sliding area of the molded body to the mold and a pressed area of the molded body is 1 or more during the compression molding.