JP2008047554A - Manufacturing method of neodymium-based bond magnet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To minimize a decrease in magnetic characteristics, and to efficiently and inexpensively manufacture an Nd-based bond magnet having improved rustproof properties. <P>SOLUTION: Nd-based magnet powder (Nd-Fe-B-based magnet alloy powder) and a binder resin (epoxy resin) are mixed to a prescribed shape, and the forming body is heat-cured in an inert gas atmosphere. The obtained magnet body is heated at a high temperature of 300-500°C for a short time, namely 1 second to 5 minutes, thus performing rustproof treatment for forming an oxide film on the surface of the magnet powder, and then magnetization is performed by an arbitrary method. More preferably, rustproof treatment by short-time heating at high temperature is performed at 350-430°C for 2-5 seconds. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing an Nd-based bonded magnet, and more specifically, relates to a method for producing an Nd-based bonded magnet that forms an oxide film on the surface of a magnet powder by heating at a high temperature for a short time to produce a rust prevention effect. .

  In general, a bonded magnet is manufactured by kneading magnet powder and a thermosetting binder resin, forming the powder into a desired shape using dried and pulverized powder, and then heating to cure the binder resin. Yes. The Nd—Fe—B based bonded magnet is basically manufactured by the same method.

  However, in the case of an Nd—Fe—B based bonded magnet, the magnet alloy powder contains a large amount of active Nd and Fe, and thus has a problem that it is easily rusted. Therefore, in order to protect the magnet powder from external oxidation factors, it is ideal that the binder resin is in a form that covers the magnet powder. Yes.

  However, in order to improve the rust prevention performance by coating the binder resin, it is necessary to considerably increase the resin amount. As a result, when the magnetic powder ratio is lowered, there arises a problem that the magnetic properties are lowered. With recent miniaturization and higher performance of various electronic devices, there is a strong demand to further improve the magnet characteristics, and therefore it is unavoidable to increase the amount of resin more than necessary.

Therefore, various methods for improving the rust prevention property without increasing the resin amount more than necessary have been proposed. For example, Patent Document 1 discloses that an organic binder resin is thermally cured in a CO ₂ , N _2, or CO ₂ + N ₂ mixed gas atmosphere, or magnet powder is a CO ₂ , N _2, or CO ₂ + N ₂ mixed gas. There has been proposed a method of kneading with an organic binder resin after exposure to the above atmosphere. In any case, the exposure to the atmospheric gas is performed by heating to a temperature of 200 ° C. or lower. Although it is presumed that this method forms metal carbides and nitrides on the surface of the magnet powder and suppresses the action of oxygen, the effect of rust prevention is not necessarily remarkable. Patent Document 2 discloses a method using a coating agent resin and a curing agent having a rust prevention function as a coating agent composition liquid for forming a coating layer provided on the magnet surface.

In general, the most reliable method for improving rust prevention is to coat magnetic powder by plating or the like, but such a method is expensive and inferior in productivity, and can be said to be an excessive treatment method as a rust prevention improvement measure. . Therefore, development of a method that is excellent in productivity and that can improve the necessary and sufficient rust prevention property is desired.
Japanese Patent Laid-Open No. 5-267030 JP 2003-261826 A

  The problem to be solved by the present invention is to make it possible to efficiently and inexpensively manufacture an Nd-based bonded magnet with good rust prevention properties while minimizing the deterioration of magnetic properties.

  In the present invention, an Nd-based magnet powder and a binder resin (thermosetting resin) are mixed and molded, and the molded body is subjected to thermosetting treatment in an inert gas atmosphere. Production of an Nd-based bonded magnet characterized in that it is subjected to a rust prevention treatment for forming an oxide film on the surface of the magnet powder by heating at 500 ° C. for 1 second to 5 minutes for a short time, followed by magnetization. Is the method. It is preferable to limit the reduction rate of the coercive force by this high temperature short time heating to 10% or less.

  More preferably, the rust prevention treatment by high-temperature and short-time heating is performed under conditions of a temperature of 350 ° C. to 430 ° C. and a time of 2 seconds to 5 seconds. Under such conditions, the reduction rate of the coercive force due to high-temperature and short-time heating can be reduced to 1% or less.

  Typically, Nd-Fe-B magnet alloy powder is used as the Nd magnet powder, and epoxy resin is used as the binder resin.

  By the way, in the Nd-based bonded magnet, the activity of the magnet powder is high, and the magnetic properties are lowered when exposed at a high temperature, and since the binder resin is used, the resin deteriorates when exposed at a high temperature. For reasons such as going forward, exposure to high temperatures was thought to be against technical common sense. Therefore, even in the thermosetting treatment of the binder resin, extreme care is taken not to oxidize the magnet powder and to prevent the resin from deteriorating, as in the case where the temperature is kept to the minimum necessary and in an inert gas atmosphere. This is the current situation.

  The inventors of the present invention perform high-temperature and short-time heating (heat treatment at a much higher temperature and in a much shorter time than the conditions during the thermosetting process) on the Nd-based bonded magnet. It has been found that when an extremely thin oxide film is positively formed on the surface of the powder, the rust prevention effect can be remarkably enhanced while minimizing the deterioration of the magnetic properties, and the binder resin is not deteriorated. The present invention has been completed based on the knowledge of such a phenomenon and overturns the conventional technical common sense.

  The manufacturing method of the Nd-based bonded magnet according to the present invention is an inexpensive and simple method of heating at a high temperature and a short time, but can exhibit sufficient rust prevention properties, and does not cause deterioration of the resin. Degradation can be minimized.

  The process of the manufacturing method of the Nd type bonded magnet which concerns on this invention is shown in FIG. Nd—Fe—B magnet alloy powder and epoxy resin are mixed and pulverized to adjust the particle size. Using the powder, it is formed into a desired shape. The molded body is subjected to thermosetting treatment at 200 ° C. for 1 hour in a nitrogen gas atmosphere. Next, the obtained magnet body is subjected to a rust preventive treatment for forming an oxide film on the surface of the magnet powder by performing high-temperature and short-time heating at a temperature of 300 ° C. to 500 ° C. for a time of 1 second to 5 minutes. Finally, magnetization is performed by an arbitrary method.

  The processes up to molding and thermosetting are basically the same as in the prior art. The thermosetting conditions may be changed as appropriate. In the present invention, the conditions for high-temperature and short-time heating are experimentally clarified from the viewpoint of rust prevention. The reason why the heating temperature is set to 300 ° C. to 500 ° C. is that the rust preventive effect is not exhibited unless the heating temperature is 300 ° C. or higher, and the magnetic characteristic deterioration of the magnet alloy powder becomes severe unless the heating temperature is 500 ° C. or lower. The reason why the heating time is set to 1 second to 5 minutes is that the rust preventive effect is not exhibited unless the heating time is 1 second or longer, and the magnetic property deterioration of the magnet alloy powder becomes serious unless the heating time is 5 minutes or shorter. In addition, high temperature short time heating is performed in air | atmosphere. By this high-temperature and short-time heating, an extremely thin oxide film is formed on the surface of the magnet alloy powder, and the inside is protected. Since the oxide film is formed only on the surface of the magnet alloy powder, it is possible to minimize the deterioration of the magnetic properties. In addition, the oxide film only needs to be formed on the magnet alloy powder near the surface of the magnet body (it is not necessary to be formed on the inner magnet alloy powder). There is no need to change the heating conditions.

  Magnetization after high-temperature and short-time heating can be performed using any conventionally known method. A method of magnetizing by a magnetic field generated by an electric current or a method of magnetizing by a magnetic field generated by a permanent magnet may be used. In the magnetization by current, a method of applying a direct current or a method of applying a pulse current may be used. Magnetization may be performed at room temperature or by heating to a temperature lower than the Curie temperature. Alternatively, a method may be used in which the temperature is lowered from a temperature equal to or higher than the Curie point to a temperature lower than the Curie point while the magnetizing magnetic field is continuously applied during that time.

Nd—Fe—B-based magnet alloy powder (particle size: 300 μm or less): 97.5 wt%, epoxy resin: 2.5 wt%, mixed and then pulverized to adjust the particle size to 300 μm or less. The powder was filled in a mold (outer diameter φ2.6 mm / inner diameter φ1.0 mm) and molded at a molding pressure of 3 ton / cm ² . The obtained ring-shaped molded body (length: 3 mm) was subjected to a thermosetting treatment at 200 ° C. for 1 hour in nitrogen gas to produce a magnet body. And about this magnet body, high temperature and short time heating was performed on various conditions.

表１の結果から、従来品は赤錆の出方が甚だしかったが、１秒以上の加熱を行うと防錆性が発現し、２分以上では防錆性が極めて良好で殆ど赤錆の発生は認められなかった。 A sample with a heating temperature of 350 ° C. (constant) and a different heating time was immersed in physiological saline (0.9% NaCl), and the appearance (color) of red rust was visually judged 18 hours later. This is a rustproof test under fairly severe conditions. The results are shown in Table 1. In the order of superior rust prevention as compared to the relative, ◎>○> ×. For comparison, the result of a sample (conventional product) that is not heated for a short time at high temperature is also shown.

From the results in Table 1, the conventional product was very red rust, but when heated for more than 1 second, rust resistance was exhibited, and over 2 minutes the rust resistance was very good and almost no red rust was generated. I was not able to admit.

表２の結果から、従来品は赤錆がかなり発生していたが、３７０℃以上の加熱を行うと防錆性が得られ、４３０℃以上の加熱では防錆性が極めて良好で殆ど赤錆の発生は認められなかった。 Next, a sample with a heating time of 3 seconds (constant) and a different heating temperature was immersed in physiological saline (0.9% NaCl), and the appearance (color) of red rust was visually determined after 9 hours. The results are shown in Table 2. Here, for comparison, the results of a sample (conventional product) that is not heated at a high temperature for a short time are also shown.

From the results shown in Table 2, red rust was considerably generated in the conventional product, but when heated at 370 ° C. or higher, rust prevention was obtained, and when heated at 430 ° C. or higher, rust prevention was extremely good and almost red rust was generated. Was not recognized.

  Therefore, the magnet alloy powder was observed for a sample in which the heating temperature was 350 ° C. (constant) and the heating time was changed. As a result, it was found that a thin film was formed on the surface of the magnet alloy powder, which was an oxide film. FIG. 2 plots the thickness of the oxide film against the heating time. With a heating time of 2 seconds, the oxide film thickness was about 10 nm (TEM: transmission electron microscope), 15 seconds about 60 nm, 120 seconds about 350 nm (both BSE: reflected electron image with scanning electron microscope). It was. It can be seen that the increase in the oxide film thickness corresponds to the improvement in rust prevention.

  From the results of these salt water immersion tests, it was confirmed that high-temperature and short-time heating according to the present invention is extremely effective for improving rust prevention. Next, changes in the resin and magnetic properties due to this high-temperature, short-term heating were examined.

  The crushing strength was measured by changing the heating temperature to 350 ° C. (constant) and variously changing the heating time from 2 seconds to 5 minutes. That is, pressing from the side surface (R surface) determined the maximum load just before the breakage. As a result, the crushing strength was almost constant regardless of the heating time. Since no degradation of the crushing strength is observed, it can be said that there is no resin degradation within the range of the experimental heating conditions. In addition, as a result of comparing the conventional product and the sample heated at 350 ° C. for 5 minutes by analysis by X-ray photoelectron spectroscopy (ESCA), there is no significant difference in the chemical bonding state, and there is no chemical change such as oxidation of the resin. Was confirmed. That is, although the heating of the present invention is a process for a short time although the temperature is considerably high, the resin does not deteriorate and there is no problem in quality.

  Further, the coercive force was measured by changing the heating temperature to 350 ° C. (constant) and variously changing the heating time from 2 seconds to 5 minutes. The results are shown in FIG. The horizontal axis represents the heating time, and the vertical axis represents the ratio of the coercivity of the high-temperature and short-time heating product to the coercivity of the conventional product. It can be seen that if the heating time is within 5 minutes, the coercivity reduction rate can be kept to 10% or less.

  From these things, the high temperature short time heating in this invention is made into the temperature of 300 to 500 degreeC, and time 1 second-5 minutes. Further, from the viewpoint of preventing the deterioration of the magnetic properties as much as possible, it is more preferable to carry out under conditions of a temperature of 350 ° C. to 430 ° C. and a time of 2 seconds to 5 seconds. Under these conditions, the reduction rate of the coercive force can be kept to 1% or less.

The process figure which shows the manufacturing method of the Nd type bonded magnet which concerns on this invention. The graph which shows the relationship of the oxide film thickness with respect to heating time. The graph which shows the relationship of the decreasing rate of coercive force with respect to heating time.

Claims (4)

  After the Nd-based magnet powder and the binder resin are mixed and molded, the molded body is heat-cured in an inert gas atmosphere, and then the obtained magnet body is heated to 300 ° C. to 500 ° C. for 1 second to 5 minutes. A method for producing an Nd-based bonded magnet, which comprises subjecting a surface of a magnet powder to an anticorrosive treatment by heating at a high temperature for a short time, followed by magnetization.   The method for producing an Nd-based bonded magnet according to claim 1, wherein a reduction rate of the coercive force by high-temperature and short-time heating is set to 10% or less.   The method for producing an Nd-based bonded magnet according to claim 1, wherein the rust prevention treatment by high-temperature and short-time heating is performed under conditions of a temperature of 350C to 430C and a time of 2 seconds to 5 seconds. The method for producing an Nd-based bonded magnet according to any one of claims 1 to 3, wherein the Nd-based magnet powder is an Nd-Fe-B-based magnet alloy powder, and the binder resin is an epoxy resin.

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