JPH04337603A - Rare-earth metal and resin composite molded body and production thereof - Google Patents

Abstract

PURPOSE:To provide a rare-earth metal and resin composite molded body which is so superior in heat resistance that the deformation due to swelling may not occur even after it has been used at a high temperature for a long time, and its production method. CONSTITUTION:The swelling of a rare-earth metal and resin composite molded body in the lapse of time is suppressed by combining a rare-earth metal powder, in which an oxide film has been formed in advance on the broken face generated due to the compression molding, with a thermosetting resin. After a solvent is added so as to mix the rare-earth metal powder and the thermosetting resin, the mixed material is press-molded into the specified shape and preheated at 150-200 deg.C for more than 10 minutes in an atmosphere containing 5-90% oxygen to produce the titled body. The preliminary formation of oxide film on the broken face of the rare-earth metal powder can efficiently prevent oxidization from progressing. Therefore, it exhibits an excellent heat resistance without any deformation in the lapse of time even after the final product has been used at a high temperature for a long time.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] This invention is a rare earth metal/resin composite molding that is suitable mainly as a material for plastic magnets and has excellent heat resistance that does not cause deformation due to blistering even when used at high temperatures for a long period of time. The present invention relates to bodies and methods for producing the same.

0002

BACKGROUND OF THE INVENTION Plastic magnets obtained by bonding rare earth metal powders with a thermosetting resin to form rare earth metal/resin composite moldings and magnetizing them are widely used in various industries. For example, the plastic magnet is F
It is particularly suitable as the magnetic pole of small motors in OA-related products, such as spindle motors for DDs (floppy disk drives) and stepping motors for facsimile machines.

Conventional plastic magnets are generally manufactured through the following steps. For example, a thermosetting resin (for example, an epoxy resin) dissolved by adding a methyl ethyl solvent is added to magnetic metal powder made of rare earth elements such as neodymium, iron, and boron, and the mixture is mixed until homogeneous. Fill a mold with the shape of the motor's fixed magnetic poles,
Compression press molding is performed at a pressure of 8 to 10 tons. In the molded mixture, since the thermosetting resin as a binder has not yet hardened, the mixture was charged into a furnace and heated at a temperature of 150°C for about 1 hour under an inert atmosphere of argon gas.
Keep heated for an hour. This causes a hardening process,
A so-called rare earth metal/resin composite molded body is obtained. This rare earth metal/resin composite molded body is subjected to post-processing such as deburring, and then magnetized to produce a plastic magnet in the shape of a motor fixed magnetic pole or the like.

0004

[Problems to be Solved by the Invention] This plastic magnet is generally used at room temperature, but depending on the application, it may be used under severe high temperature conditions. As an example, it is assumed that the magnetic poles of a motor are made of plastic magnets and are used for a long period of time when the outside temperature is high. When used under such high temperatures, the plastic magnet may swell over time and deform, albeit slightly, from its initial shape. For example, if the plastic magnets constitute the fixed magnetic poles of a motor and the motor is used for a long period of time under high temperature conditions, the fixed magnetic poles will be deformed by the influence of heat and come into contact with the rotor, making it impossible for the motor to rotate. This will cause serious inconvenience. A heat blistering test was conducted in which the motor was used for 100 to 200 hours at a maximum operating temperature of 120°C, and the results also confirmed that blistering occurred in the fixed magnetic poles made of the plastic magnets.

[0005] When used under such high temperature conditions,
The reason why plastic magnets swell over time is as follows:
Possible causes are as follows. In other words, during the manufacturing process of plastic magnets, rare earth metal powder mixed with thermosetting resin is press-molded in a mold. Pressure is applied. The metal powders filled in the mold are each wrapped in molten thermosetting resin, but the individual metal powders are crushed by the pressure applied during press molding. This can lead to cracking and breakage. Therefore, the metal powder after applying high pressure has many fractured surfaces when observed microscopically.

[0006] The mixture press-molded in such a state is subjected to a heat curing treatment in an argon gas atmosphere as described above to form a rare earth metal/resin composite molded body. In this case, the metal powder constituting the rare earth metal/resin composite molded body has many fractured surfaces, but since the heat curing treatment in the furnace is performed in an oxygen-free condition, the fractured surfaces are It will not oxidize. However, when the magnetic poles of a motor are manufactured by magnetizing a rare earth metal/resin composite molded body and the motor is used under high temperature conditions, the fractured surfaces of the individual metal powders that make up the plastic magnet gradually oxidize. However, it is thought that this causes the bulge mentioned above to gradually occur.

[0007]

[Object of the Invention] The present invention has been proposed in order to suitably solve the above-mentioned problems inherent in the case where, for example, the magnetic poles of a motor are constituted by a plastic magnet made of a rare earth metal/resin composite molded body. It is an object of the present invention to provide a rare earth metal/resin composite molded article with excellent heat resistance that does not swell or deform over time even when used at high temperatures for a long period of time, and a method for producing the same. purpose.

[0008]

[Means for Solving the Problems] In order to overcome the above problems and achieve the intended purpose, the rare earth metal/resin composite molded article according to the present invention has an oxide film formed in advance on the fractured surface caused by compression molding. The rare earth metal powder is bonded with a thermosetting resin to suppress swelling over time.

[0009] Similarly, in order to overcome the above-mentioned problems and achieve the intended purpose, there is provided a method for producing a rare earth metal/resin composite molded article according to another invention of the present application, in which a rare earth metal powder and a thermosetting resin are mixed in a solvent. After adding and mixing, this is press-molded into a predetermined shape to form a rare earth metal/resin composite molded body, which is heated with oxygen 5
It is characterized by heating to 150°C to 200°C in an atmosphere of ~90% and holding it for 10 minutes or more.

0010

[Examples] Next, the rare earth metal/resin composite molded article and the method for producing the same according to the present invention will be described below with reference to preferred examples. In view of the fact that the cause of the above-mentioned blistering when a plastic magnet made by magnetizing a rare earth metal/resin composite molded body is used at high temperatures, the inventor has previously analyzed the problem. It has been found that if an oxide film is previously formed on the fracture surface of the metal powder, oxidation will not proceed any further even at high temperatures, and therefore the blistering will not occur. Based on this knowledge, the main content of the examples is how to form an oxide film in advance on the fractured surface of rare earth metal powder after press molding. The process from mixing the rare earth element metal powder and thermosetting resin after adding a solvent to filling a mold and performing press molding is the same as described above.

[0011] In the example, when the thermosetting resin is hardened by heating a mixture containing metal powder that has a fractured surface due to press molding, this is carried out in an oxygen atmosphere, thereby eliminating the fractured surface. An oxide film is formed in advance on the cross section. That is, a rare earth metal/resin composite molded body is obtained by mixing rare earth metal powder and thermosetting resin with the addition of a solvent, and then press-molding this into a predetermined shape. This rare earth metal/resin composite molded body is placed in a furnace, heated under an oxygen atmosphere to a temperature sufficient to volatilize the solvent, and maintained as such for several hours. This allows the solvent contained in the rare earth metal/resin composite molded article to be slowly volatilized, thereby preventing the inconvenience of producing a large number of fine pores.

After volatilizing the solvent in this manner, the rare earth metal/resin composite molded body is heated to 150°C to 200°C in an oxygen atmosphere (5 to 90%) in the same furnace, and Hold for at least 10 minutes, preferably about 1 hour. As a result, an oxide film is formed in advance on the fracture surface of the metal powder. Therefore, the rare earth metal/resin composite molded article obtained in this way contains rare earth metal powder with an oxide film formed on at least the surface of the fractured part.
It is bonded with a thermosetting resin, and once this oxide film is formed, it functions as a protective film and effectively prevents further oxidation.

A heat blistering test was conducted on the rare earth metal/resin composite molded article according to this example as follows. That is, the thermosetting resin in the rare earth metal/resin composite molded body was cured by continuing heating at 170° C. for 1 hour in each atmosphere with an oxygen concentration of 5 to 80% in a furnace. In addition, a plurality of rare earth metal/resin composite molded bodies obtained by a conventional manufacturing method, for example, by heating at 150° C. for one hour in an argon gas atmosphere, were separately prepared. 1 of these test pieces
The test specimens were left in the air for 200 hours at a temperature of 20° C., and the heat swelling ratio of each specimen was plotted as shown in FIG. This heat expansion rate is (D-D0)/D0×100(
%). Here, D0 is the diameter of the test piece before the heat blistering test, and D is the diameter of the test piece after the heat blistering test. As is clear from FIG. 1, the rare earth metal/resin composite molded article according to the example has significantly suppressed swelling under high temperature conditions compared to the rare earth metal/resin composite molded article manufactured by the conventional method, and has excellent heat resistance. It can be seen that it is excellent in

In addition, FIG. 2 plots the oxygen content (wt%) including the oxide film formed on the rare earth metal powder for the test piece of the above example, and also shows the test piece prepared by the conventional method. It is. FIG. 3 shows the total oxygen content of each test piece according to the present invention and the conventional method. From these, in the example, it is possible to suppress the oxidation weight after the metal powder is oxidized in advance during molding, but in the conventional method, on the contrary, almost no oxidation occurs during molding, and the subsequent 120 ° C × 2
It is understood that the metal powder is significantly oxidized in the course of 00 hours, causing significant swelling. Therefore, it is preferable to make a plastic magnet by magnetizing the rare earth metal/resin composite molded article according to the example, since it will not undergo deformation due to swelling even when used under high temperature conditions.

[0015]

Effects of the Invention As explained above, according to the rare earth metal/resin composite molded article of the present invention, by forming an oxide film in advance on the fractured surface of the rare earth metal powder constituting the composite, The progress of oxidation can be effectively prevented. Therefore, even after being commercialized as a plastic magnet, such as the fixed magnetic pole of a motor, and used for a long period of time at high temperatures, it will not deform over time and will exhibit excellent heat resistance. It is.

[Brief explanation of drawings]

FIG. 1: Heat resistance of test pieces when a heat blistering test was conducted on a rare earth metal/resin composite molded article according to a preferred embodiment of the present invention and a rare earth metal/resin composite molded article obtained by a conventional manufacturing method. It is a curve diagram plotting swelling ratio.

[Fig. 2] When a heat blistering test was conducted on the rare earth metal/resin composite molded body according to the preferred embodiment of the present invention and the conventional rare earth metal/resin composite molded body, formations in the rare earth metal powder of each test piece were observed. FIG. 3 is a curve diagram plotting the relationship between oxygen content and oxygen content including an oxide film.

[Fig. 3] Total oxygen content in each test piece when a heat swelling test was conducted on the rare earth metal/resin composite molded article according to the preferred embodiment of the present invention and the conventional rare earth metal/resin composite molded article. It is a curve diagram plotting the relationship between .

Claims (4)

[Claims] 1. A rare earth metal characterized by suppressing swelling over time by bonding rare earth metal powder with an oxide film pre-formed on the fractured surface produced by compression molding with a thermosetting resin.・Resin composite molded body. 2. The oxide film formed on the fracture surface of the rare earth metal powder has an oxygen content of about 0.1% by weight or more and 0.5% by weight or less, and the oxygen content of the thermosetting resin The rare earth metal/resin composite molded article according to claim 1, wherein the amount is 1.0% by weight or less. 3. A rare earth metal/resin composite molded body is obtained by mixing a rare earth metal powder and a thermosetting resin with the addition of a solvent, and then press-molding the mixture into a predetermined shape.
1. A method for producing a rare earth metal/resin composite molded article, which comprises heating to 150° C. to 200° C. and holding it for 10 minutes or more in an atmosphere of 4. Prior to heating the rare earth metal/resin composite molded product press-molded into the predetermined shape to 150° C. to 200° C. in an atmosphere containing 5% to 90% oxygen and holding it for 10 minutes or more. 4. The method for producing a rare earth metal/resin composite molded article according to claim 3, further comprising heating to a temperature sufficient to volatilize the solvent and maintaining it for several hours.