JP2014199845A - Method of manufacturing composition for metal powder containing resin molded body, preforming body, method of manufacturing metal sintered body, and rare earth sintered magnet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a metal sintered body containing low oxygen and having high density even when metal fine powder containing low oxygen is used.SOLUTION: A method includes the steps of: adjusting atmosphere gas so that oxygen concentration in the atmosphere gas in a kneader before metal fine powder containing low oxygen is injected thereinto is kept to be 200 ppm or less; melting the resin injected into the kneader; and injecting the metal fine powder containing low oxygen into the molten resin and kneading them in the presence of the atmosphere gas whose oxygen concentration is 200 ppm or less.

Description

  The present invention relates to a method for producing a metal powder-containing resin molded body composition, a preform, a method for producing a metal sintered body, and a rare earth sintered magnet.

  In addition to the conventional method of compressing and molding metal powder by the compacting method and sintering the compact to obtain a sintered metal compact, the metal powder and resin are kneaded in order to cope with downsizing and complex shapes. A method is known in which a metal sintered body is obtained by injection molding the kneaded product and degreasing and sintering the obtained molded body. This is called the MIM (Metal Injection Molding) method.

  As an example of the MIM method, Patent Document 1 below discloses a method for manufacturing a rare earth sintered magnet. In this method, a cast ingot mainly composed of rare earth (R), iron (Fe) and boron (B) is pulverized, and the resin is added to the metal powder in the range of 3 to 10% by weight, and then kneaded. A molded product obtained by injection molding a product is degreased and sintered.

  Patent Document 2 describes a method for manufacturing a magnetic anisotropic sintered magnet. In that method, the main component is 20 to 45% by weight of R (R is at least one rare earth element), 0.1 to 3.0% by weight of B, and 52 to 79.9% by weight of Fe or Fe + Co. (However, Co is 1/2 or less of Fe.) A metal powder having an average particle diameter of 1 to 20 μm is used. A mixture of wax, resin and lubricant is added to 100 parts of the metal powder in the range of 6 to 14 parts, and the mixture is kneaded, and the kneaded product is injection molded.

  By the way, in order to improve the characteristics of rare earth sintered magnets, the use of low oxygen metal fine powder as a metal powder has been studied. The conventional metal powder that has been used so far has an oxygen content of 3000 ppm or more, while the low oxygen metal fine powder has an oxygen content of 2000 ppm or less. Recently, a low-oxygen metal fine powder with a smaller oxygen content has been used.

  In the kneading process of kneading conventional metal powder and resin, if the oxygen concentration of the atmosphere gas in the kneading process is about 1000 ppm for conventional metal powder, the characteristics of the magnet obtained by kneading, molding, degreasing, and sintering are as follows: It is sufficient that there is no difference from that obtained by the compacting method. However, when low oxygen metal fine powder is used for the metal powder, the characteristics of the magnet obtained by kneading, molding, degreasing and sintering can be obtained by the compacting method when the oxygen concentration of the atmosphere gas in the kneading process is about 1000 ppm. It is not enough to make it as good as it does. Thus, it has been confirmed by the present inventors that the low oxygen metal fine powder is very easily oxidized and there is a problem that the product characteristics of the magnet deteriorate due to the oxidation.

JP 62-252919 A JP-A-1-150303

  The present invention has been made in view of such a situation, and an object of the present invention is to provide a method for producing a metal sintered body such as a high-performance rare earth sintered magnet even when a low-oxygen metal fine powder and a resin are kneaded and used. Is to provide. Another object of the present invention is to provide a preform for producing such a metal sintered body and a method for producing a metal powder-containing resin molded body composition constituting the preform. is there.

  In order to achieve the above object, the present inventors have made extensive studies, and as a result, have obtained the following new findings. That is, the present inventors, after charging the resin into the kneader, after confirming the oxygen concentration as a low oxygen atmosphere, then melting only the resin, and again confirming the oxygen concentration inside the kneader, It was found that the oxygen concentration of the atmospheric gas was higher than the oxygen concentration of the atmospheric gas before melting the resin. This is probably because the air (oxygen) mixed in the resin is degassed by melting the resin and released into the kneader and diffused to increase the oxygen concentration of the atmospheric gas. Actually, using a closed batch type kneader such as a planetary mixer, charging the resin into the kneader, making the atmosphere inside the kneader into a low oxygen atmosphere with an oxygen concentration of 100 ppm or less, and then heating and melting the resin, kneading The oxygen concentration inside the machine increased to 400 ppm.

  As a result of intensive studies by the present inventors based on the above knowledge, a metal powder-containing resin molded body composition was produced by the method of the present invention shown below, and a preformed body molded using the composition was prepared. It has been found that by sintering, the sintered density is improved, and when the sintered body is a rare earth sintered magnet, Br (residual magnetic flux density) and Hc (coercive force) are improved.

That is, the method for producing a metal powder-containing resin molded body composition according to the present invention,
Adjusting the atmospheric gas inside the kneader so that the oxygen concentration in the atmospheric gas before introducing the low oxygen metal fine powder is maintained at 200 ppm or less;
Melting the resin charged in the kneader;
And a step of charging and kneading the low oxygen metal fine powder into the molten resin in the presence of an atmospheric gas having an oxygen concentration of 200 ppm or less inside the kneader.

  In the method of the present invention, the atmospheric gas inside the kneader is adjusted so that the oxygen concentration in the atmospheric gas existing around the molten resin, that is, the atmospheric gas before introducing the low-oxygen metal fine powder is maintained at 200 ppm or less. To do. Therefore, even if the air (oxygen) contained in the resin before melting diffuses into the atmospheric gas due to melting of the resin, the atmospheric gas inside the kneader is adjusted so that the oxygen concentration is maintained at 200 ppm or less. Yes. Thereafter, the low-oxygen metal fine powder is put into the molten resin and kneaded with the resin. By doing so, the low-oxygen metal fine powder hardly comes into contact with oxygen.

  After kneading, the low-oxygen metal fine powder is in a state of being coated with a resin, and can be exposed to a non-low-oxygen atmosphere in the subsequent process until it is put into the degreasing process. The kneading treatment is preferably performed in an atmosphere having an oxygen concentration of 200 ppm or less. In that case, the low oxygen metal fine powder is less likely to be oxidized during kneading.

  Preferably, the resin is previously introduced into the kneader to adjust the oxygen concentration inside the kneader. According to such a configuration, a large facility for installing the kneader in the low oxygen chamber and a complicated facility for covering the entire kneader with a low oxygen atmosphere are not required, and a simple facility is used. The atmosphere gas before introducing the low oxygen metal fine powder can be maintained in a low oxygen atmosphere. Examples of a method for keeping the inside of the kneader below a predetermined oxygen concentration include a method of evacuating the inside of the kneader and a method of constantly flowing an inert gas inside the kneader.

  In the present invention, the low oxygen metal fine powder is defined as a fine powder having an oxygen content of 2000 ppm or less. The low oxygen metal fine powder used in the present invention is preferably a fine powder having an oxygen content of 1000 ppm or less.

  Preferably, the oxygen concentration inside the kneader is set to 200 ppm or less before introducing the low oxygen metal fine powder. If the oxygen concentration of the atmosphere gas is controlled before the low oxygen metal fine powder is charged, the low oxygen metal fine powder comes into contact with the oxygen of the atmospheric gas after the low oxygen metal fine powder is charged even during kneading. There is very little possibility that fine powder will be oxidized.

  Preferably, before the resin is melted, the oxygen concentration inside the kneader is set to 200 ppm or less. If the oxygen concentration of the atmospheric gas is controlled before the resin is melted, it is easy to control the oxygen concentration of the atmospheric gas to a predetermined value or less immediately after the resin is melted.

  The preform according to the present invention is obtained by molding a composition obtained by the method for producing a metal powder-containing resin molded body composition described above. A method for molding is not particularly limited, but injection molding, compression molding and the like are preferable.

  The method for manufacturing a metal sintered body according to the present invention includes a step of sintering the preform. The rare earth sintered magnet of the present invention is obtained by this method for producing a sintered metal. The rare earth sintered magnet obtained by the manufacturing method has an oxygen content of 2000 ppm or less, a sintering density of 99.0% or more, and excellent magnetic properties.

FIG. 1 is a schematic view of a closed batch kneader used in a method according to an embodiment of the present invention. 2A is a flowchart of a method according to an embodiment of the present invention, and FIG. 2B is a flowchart of a method according to a comparative example of the present invention.

  Hereinafter, a method of manufacturing a metal sintered body such as a rare earth sintered magnet according to an embodiment of the present invention, a preformed body (an injection molded body as an example) for manufacturing such a metal sintered body, The manufacturing method of the composition for metal powder containing resin moldings which comprises the preform is demonstrated, referring drawings.

  First, a low oxygen metal fine powder and a resin, which are raw materials for the composition according to the present embodiment, are prepared. Although there is no limitation in the kind of low-oxygen metal fine powder, for example, when manufacturing a rare earth sintered magnet, R (rare earth) -TB metal powder is used. In addition, the rare earth R in the main component of the R-T-B-based metal powder (R has a concept including Y. Therefore, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, The ratio of Ho, Er, Tm, Yb, and Lu is selected from one or more.) The ratio is not particularly limited, but is, for example, 20% by mass to 40% by mass, and B is 0.5% by mass to 1.%. The remaining T is composed of one or more elements selected from transition metal elements including Fe or Fe and Co. In addition, the RTB-based metal powder allows the inclusion of other elements. For example, elements such as Al, Cu, Zr, Ti, Bi, Sn, Ga, Nb, Ta, Si, V, Ag, and Ge can be appropriately contained. The particle size of the metal powder is not particularly limited, but preferably the average particle size is 1 μm to 20 μm, more preferably 1 μm to 10 μm.

  As the resin, a thermoplastic resin is preferably used. For example, polypropylene, polystyrene, polyethylene, polyacetal, EVA resin, AS resin, and ABS resin are used, and a resin that does not contain oxygen in the structural formula is particularly preferable. Moreover, you may use additives, such as a wax and a plasticizer, as needed.

  In the present embodiment, the resin is charged into the kneading container 12 of the closed batch kneader 1 shown in FIG. The closed batch kneader 1 is not particularly limited, and examples thereof include a planetary mixer and a pressure kneader.

  A closed batch kneader (hereinafter referred to as “kneader”) 1 shown in FIG. 1 will be described. The kneading machine 1 has a kneading container 12, and a pair of blades 11 are arranged inside the kneading container 12, and the blade 11 rotates to knead the material inside the kneading container. . The kneading container 12 is provided with a charging pot 13, and the low oxygen metal fine powder inside the charging pot 13 can be charged into the kneading container 12 as necessary.

  The kneading vessel 12 is connected with a gas introduction pipe 14, an oxygen concentration meter 16 and a vacuum pump 15. From the gas introduction pipe 14, it is possible to flow an inert gas into the kneading vessel. The vacuum pump 15 can evacuate the inside of the kneading vessel 12 to suck the atmospheric gas in the kneading vessel.

  The oxygen concentration meter 16 can measure the oxygen concentration of the atmospheric gas inside the kneading vessel 12, and the oxygen concentration signal measured there is output to a control device (not shown). In the control device, the flow of the inert gas from the gas introduction tube 14 into the kneading vessel 12 and / or the vacuum pump 15 so that the oxygen concentration inside the kneading vessel 12 is lowered to 200 ppm or less, preferably 100 ppm or less. The pressure inside the kneading container 12 can be controlled.

  In the present embodiment, after the resin is put into the kneading container 12, the resin is heated and melted by stirring the inside of the kneading container 12 using the blade 11. There are no particular limitations on the heating and melting conditions, and the conditions are determined according to the type of resin.

  Moreover, it is preferable to make the inside of the kneading container 12 into a low oxygen atmosphere having an oxygen concentration of 200 ppm or less before heating and melting the resin. The timing of setting the inside of the kneading container 12 to a low oxygen atmosphere may be before or after the resin is put into the kneading container 12. When the inside of the kneading container 12 is put in a low oxygen atmosphere before the resin is charged, a pot for charging the resin may be attached to the kneading container 12 separately from the pot 13 for charging the low oxygen metal fine powder. This eliminates the need to open the kneading container 12 when charging the resin. Although there is no limitation on the method of creating a low oxygen atmosphere, it is preferable to use evacuation by the vacuum pump 15 and an inert gas flow using the gas introduction pipe 14 in combination. Moreover, although there is no limitation in particular also in the kind of inert gas, nitrogen gas, argon gas, helium gas, neon gas etc. are illustrated, for example, Preferably they are nitrogen gas or argon gas.

  In the present embodiment, there is no particular limitation as to how the resin is charged into the kneading vessel 12 and can be charged, for example, in the form of resin pellets. Moreover, there is no restriction | limiting in particular about the quantity of resin, However When it is 100 mass% of low oxygen metal fine powder, it is preferable that it is 3 mass%-15 mass%.

  In the present embodiment, while the resin is heated and melted, the atmosphere inside the kneading vessel 12 is evacuated to perform the defoaming process of the resin. There is no particular limitation on the method of defoaming, but the inside of the kneading vessel 12 is decompressed by evacuating with the vacuum pump 15. Further, it is preferable to use an inert gas flow through the gas introduction pipe 14 in the decompressed kneading vessel 12 together. When the inside of the kneading vessel 12 is made into a low oxygen atmosphere after heat melting, the same method as before heat melting may be used to make the low oxygen atmosphere, or a different method may be used to make the low oxygen atmosphere.

  In the present embodiment, the oxygen concentration in the kneading vessel 12 is 200 ppm or less, more preferably 100 ppm or less after heating and melting. The oxygen concentration in the kneading vessel 12 is measured by an oxygen concentration meter 16.

  Subsequently, the low oxygen metal fine powder is put into the kneading vessel 12. Since the low-oxygen metal fine powder is easily oxidized by oxygen contained in the surrounding air, it is preferable to fill the charging pot 13 for the low-oxygen metal fine powder whose interior is previously in a low-oxygen atmosphere. By doing so, it is not necessary to open the kneading container 12 when the low oxygen metal fine powder is charged, and the low oxygen metal fine powder can be charged while keeping the kneading container 12 in a low oxygen atmosphere.

  The oxygen concentration in the charging pot 13 for the low oxygen metal fine powder is 200 ppm or less, more preferably 100 ppm or less. After charging the low-oxygen metal fine powder into the kneading container 12 of the kneading machine 1, the heating inside the kneading container 12 is continued and the blade 11 is used to stir the kneading container 12 together with the molten resin for heating and kneading. To obtain an injection molding composition (metal powder-containing resin molding composition). The heating temperature and the kneading time are not limited, but it is preferable to knead at 100 to 250 ° C. for 5 to 180 minutes, for example.

  Next, the kneaded injection molding composition (metal powder-containing resin molding composition) obtained by the production method of the present embodiment described above was put into an injection molding machine (not shown). A rare earth sintered magnet can be produced by injection molding in an orientation magnetic field, followed by a degreasing (debinding) step and a sintering step. There are no particular limitations on the conditions of the injection molding process, the degreasing process and the sintering process.

  The injection molding step is performed by injecting an injection molding composition (metal powder-containing resin molding composition) while applying an orientation magnetic field to the molding die. By applying an orientation magnetic field, the molded body can have magnetic anisotropy. There are no particular restrictions on the magnetic field strength or application time of the orientation magnetic field in the injection molding process.

  The degreasing step is performed by heating the molded body obtained by injection molding in an atmosphere such as vacuum, inert gas flow, inert gas decompression, or hydrogen flow. There is no restriction | limiting in particular in the heating temperature and heating time in a degreasing process. The oxygen concentration of the atmospheric gas in the degreasing step is preferably 5 ppm or less.

  A sintering process is performed by heating the molded object obtained by the degreasing process in atmosphere, such as a vacuum, an inert gas flow, and inert gas pressure reduction. There is no restriction | limiting in particular in sintering temperature and sintering time, It determines according to the kind etc. of a low oxygen metal fine powder. Thereafter, an aging treatment is performed as necessary.

  By the above method, a rare earth sintered magnet having an oxygen content of 2000 ppm or less, more preferably 1000 ppm or less can be obtained. By setting the oxygen content of the rare earth sintered magnet to 2000 ppm or less, a rare earth sintered magnet having a sintered density of 99.0% or more can be obtained. Furthermore, a rare earth sintered magnet having an oxygen content of 2000 ppm or less and a sintered density of 99.0% or more can have very excellent characteristics.

  In the method of the present embodiment, the atmospheric gas is maintained so that the oxygen concentration in the atmospheric gas existing around the resin melted inside the kneader, that is, the atmospheric gas before introducing the low-oxygen metal fine powder is kept at 200 ppm or less. adjust. Therefore, even if air (oxygen) contained in the resin before melting diffuses into the atmospheric gas due to melting of the resin, the atmospheric gas is adjusted so that the oxygen concentration is maintained at 200 ppm or less. Thereafter, the low-oxygen metal fine powder is put into the kneader and kneaded with the molten resin.

  Since the kneading process is performed in an atmosphere having an oxygen concentration of 200 ppm or less, the low oxygen metal fine powder is less likely to be oxidized, and after kneading, the low oxygen metal fine powder is in a state of being coated with a resin, In the subsequent process, it can be exposed to a non-low oxygen atmosphere until it is put into the degreasing process. For example, the low-oxygen metal fine powder can be handled without being oxidized in the air (oxygen-containing atmosphere) for short-time storage or molding.

  In the present embodiment, a resin is previously introduced into the kneading container 12 in the kneader 1 to adjust the oxygen concentration inside the kneading container 12. Therefore, in this embodiment, it does not require a large facility such as installing the kneader in a low oxygen chamber or a complicated facility that covers the entire kneader in a low oxygen atmosphere, using a simple facility, It is possible to maintain the atmosphere gas before introducing the low oxygen metal fine powder in a low oxygen atmosphere.

  Furthermore, in this embodiment, the oxygen concentration inside the kneader is set to 200 ppm or less before the resin is melted. If the oxygen concentration of the atmospheric gas is controlled before the resin is melted, it is easy to control the oxygen concentration of the atmospheric gas to a predetermined value or less immediately after the resin is melted.

  The present invention is not limited to the above-described embodiment, and can be variously modified within the scope of the present invention.

  For example, in the above-described embodiment, the preform before sintering is formed by injection molding in an oriented magnetic field, but the preform before sintering is formed by other methods such as compression molding and extrusion molding. You may do it.

  Hereinafter, although this invention is demonstrated based on a more detailed Example, this invention is not limited to these Examples.

Example 1
The metal powder-containing injection molding composition according to this example was produced by the following method. First, as a low-oxygen metal fine powder, a metal powder having a main component of R (Nd and Dy): 31 mass%, B: 1.0 mass%, the balance being Fe, an average particle diameter of 5 μm, and an oxygen content of 980 ppm is prepared. did. Moreover, polystyrene was prepared as resin.

  Further, as the closed batch kneader, a kneader 1 composed of a planetary mixer as shown in FIG. 1 was used.

  First, polystyrene was put into the kneading container 12 of the planetary mixer. Thereafter, the kneading vessel 12 of the planetary mixer was sealed and evacuated, and then nitrogen gas was flowed as an inert gas to make the inside of the kneading vessel 12 of the planetary mixer have an oxygen concentration of 100 ppm.

  Next, the polystyrene charged in the kneading vessel 12 was heated and melted. Next, after evacuating again, nitrogen gas was flowed as an inert gas, and the heated and melted polystyrene was defoamed at 180 ° C. to 200 ° C. for 10 to 15 minutes. Thereafter, the inside of the kneading vessel 12 of the planetary mixer was adjusted to an oxygen concentration of 100 ppm.

  Subsequently, the low-oxygen metal fine powder filled in the charging pot 13 was charged into the kneading vessel 12, and after charging, heated to 200 ° C. and kneaded for 60 minutes to obtain a metal powder-containing composition for injection molded body. . During the kneading, the oxygen concentration inside the planetary mixer was maintained at the oxygen concentration at which the low oxygen metal fine powder was charged.

  Next, the obtained metal powder-containing composition for resin molded body was put into an injection molding machine, heated to 200 ° C., and injection molded in an orientation magnetic field to obtain 10 preformed bodies. The preform was molded into a rectangular parallelepiped shape of 50 × 10 × 3 mm.

Thereafter, the preform was heated and degreased at 700 ° C. for 10 hours in an inert gas atmosphere. After degreasing, the degreased body was sintered in vacuum (5 × 10 ⁻² Pa) at 1100 ° C. for 4 hours. The obtained sintered body was subjected to an aging treatment at 500 ° C. for 1 hour in an Ar atmosphere.

<Measurement method and criteria>
The amount of oxygen was measured using an oxygen, nitrogen, and hydrogen analyzer (TCH600 manufactured by LECO). Oxygen is measured by reacting oxygen generated from the sample with carbon and in the state of carbon dioxide and carbon monoxide, using a carbon dioxide infrared detector and a carbon monoxide infrared detector. The criterion for determining the amount of oxygen was that the average value of 10 sintered bodies was 2000 ppm or less, and that 1000 ppm or less was particularly good.

  The sintered density indicates the ratio of the measured density to the theoretical density. The actual density was measured by the Archimedes method. As a criterion for determining the sintered density, an average value of 10 sintered bodies was 99.0% or more.

  Furthermore, the magnetic properties of the sintered body were measured with a vibration test type magnetometer (VSM) manufactured by Toei Industry Co., Ltd. The criterion for determining Br (residual magnetic flux density) was that the average value of 10 sintered bodies was 13.5 kG or higher.

  The criterion of Hc (coercive force) was determined to be good when the average value of 10 sintered bodies was 15.0 kOe or more.

  The physical property value of the sintered body according to Example 1 is such that the average oxygen content of the 10 sintered bodies is 950 ppm, and the sintered density is 99.2%, Br13.7 kG, and Hc15.1 kOe, all good. The value is shown.

Example 2
A sintered body was obtained in the same manner as in Example 1 except that the oxygen content of the low oxygen metal fine powder was changed to 500 ppm. The physical properties of the obtained sintered body were an average of 560 ppm of oxygen for 10 sintered bodies, and all showed good values of sintered density 99.3%, Br13.7 kG, Hc15.2 kOe. It was.

Examples 3-6
As described in Table 1, the kneading temperature and kneading time were changed, and other conditions were the same as in Example 1, and a sintered body was obtained in the same manner as in Example 1. The results are shown in Table 1. In all Examples, the oxygen amount, the sintered density, Br, and Hc all showed good values.

Comparative Example 1
The same low oxygen metal fine powder and resin as those used in Example 1 were used. After the polystyrene is put into the kneading container 12 of the planetary mixer, the inside of the kneading container 12 of the planetary mixer is made to have an oxygen concentration of 1000 ppm, and then the low oxygen metal fine powder is put into the kneading container 12 of the planetary mixer and heated to 200 ° C. The resin was melted and mixed. It knead | mixed for 60 minutes and the composition for metal powder containing resin moldings was obtained. During the melting and kneading of the resin, the oxygen concentration inside the planetary mixer was maintained at 1000 ppm.

  Using the obtained metal powder-containing resin molded body composition, injection molding was performed in the same manner as in Example 1 to obtain a preformed body. The preform was degreased and sintered in the same manner as in Example 1 to obtain a sintered body.

  The obtained sintered body had an average oxygen amount of 6700 ppm as high as 10 sintered bodies, and a sintered density of 96.8%, Br13.0 kG, and Hc11.5 kOe, which were compared with Examples 1-6. Product characteristics deteriorated.

Comparative Example 2
The same low oxygen metal fine powder and resin as in Example 2 were used. After the polystyrene is put into the kneading container 12 of the planetary mixer, the inside of the kneading container 12 of the planetary mixer is made to have an oxygen concentration of 100 ppm, and then the low oxygen metal fine powder is put into the kneading container 12 of the planetary mixer and heated to 200 ° C. The resin was melted and mixed. It knead | mixed for 60 minutes and the composition for metal powder containing resin moldings was obtained. During melting and kneading of the resin, the oxygen concentration inside the planetary mixer was controlled to 100 ppm or less, but temporarily deteriorated to 300 ppm when the resin was dissolved.

  Using the obtained metal powder-containing resin molded body composition, injection molding was performed in the same manner as in Example 1 to obtain a preformed body. The preform was degreased and sintered in the same manner as in Example 1 to obtain a sintered body.

  The obtained sintered body had an average oxygen amount of 2550 ppm as high as 10 sintered bodies, a sintered density of 98.5%, Br13.4 kG, and Hc14.5 kOe, compared with Examples 1-6. Product characteristics deteriorated.

  As shown in FIGS. 2 (A) and 2 (B), the difference in the process between the example and the comparative examples 1 and 2 is that in the example, the oxygen concentration in the atmosphere is reduced after only the resin is heated and melted. Then, while the low oxygen metal fine powder is added and kneaded, in the comparative example, after adding the resin and reducing the oxygen concentration in the atmosphere, the low oxygen metal fine powder is supplied as it is, It is the point which heats and melt | dissolves resin and knead | mixing both of them simultaneously. In Comparative Examples 1 and 2, it is considered that the low-oxygen metal fine powder is oxidized by oxygen generated when the resin is heated and melted, so that the physical property value of the finally obtained sintered body is lowered.

Examples 7-10
The same low oxygen metal fine powder and resin as those used in Example 1 were used. As described in Table 1, a sintered body was obtained in the same manner as in Example 1 except that the oxygen concentration before melting the resin and the oxygen concentration after melting the resin were changed. When the oxygen concentration after melting the resin was 200 ppm or less, a sintered body with an oxygen content of 1000 ppm or less was obtained regardless of the oxygen concentration before resin melting, and various physical property values were also in the good range.

Comparative Example 3
The same low oxygen metal fine powder and resin as those used in Example 1 were used. However, the oxygen concentration before the resin was melted was 100 ppm, but after that vacuuming and the flow of inert gas were stopped. As a result, the oxygen concentration after melting the resin was 400 ppm. In this state, low-oxygen metal fine powder was added, and thereafter, a sintered body was obtained in the same manner as in Example 1. The results are shown in Table 1.

  As described in Table 1, in the sintered body of Comparative Example 3, the amount of oxygen in the sintered body was high, and various physical property values were out of the good range.

  From the above, even when the low oxygen metal fine powder is added after the resin is melted, if the oxygen concentration after the resin melt exceeds 200 ppm, it has preferable physical properties even if the oxygen concentration in the kneading container before the resin melt is low. A sintered body cannot be obtained. Conversely, if the oxygen concentration after resin melting is 200 ppm or less, a sintered body having various physical property values within a good range can be obtained even if the oxygen concentration in the kneading container before resin melting is high.

Example 11
The steps until obtaining the metal powder-containing resin molded body composition were performed in the same manner as in Example 1, and then compression molding was performed instead of injection molding. The metal powder-containing resin molded body composition was heated to 180 ° C. and compression molded to obtain a 20 × 10 × 3 mm rectangular parallelepiped preform. The preform was degreased and sintered to obtain a sintered body. The results are shown in Table 1.

  As shown in Table 1, even in the case of compression molding, a sintered body with a small amount of oxygen was obtained as in the case of injection molding, and various physical property values of the sintered body were also within a good range.

Example 12
The same test as in Example 1 was performed by changing the low oxygen metal fine powder to a fine powder having an oxygen content of 2000 ppm. The results are shown in Table 1. The amount of oxygen in the sintered body was 2000 ppm or less, and various physical property values were also in a good range.

Examples 13 and 14
The same test as in Example 1 was performed by changing the type of resin. The results are shown in Table 2. In any of the examples, the amount of oxygen in the sintered body was 1000 ppm or less, and various physical property values were within a good range.

DESCRIPTION OF SYMBOLS 1 ... Sealed batch type kneader 11 ... Blade 12 ... Kneading container 13 ... Pot for injection 14 ... Gas introduction pipe 15 ... Vacuum pump 16 ... Oxygen concentration meter

Claims (7)

Adjusting the atmospheric gas so that the oxygen concentration in the atmospheric gas inside the kneader is maintained at 200 ppm or less;
Introducing a resin into the kneader;
Melting the resin charged into the kneader;
A step of charging and kneading the low-oxygen metal fine powder inside the kneader,
The step of adding and kneading the low-oxygen metal fine powder is a method for producing a composition for a metal powder-containing resin molded body, which is performed in the presence of an atmospheric gas having an oxygen concentration of 200 ppm or less.   The method for producing a composition for a metal powder-containing resin molded article according to claim 1, wherein the resin is previously introduced into the kneader and the oxygen concentration inside the kneader is adjusted.   The method for producing a metal powder-containing resin molded body composition according to claim 1 or 2, wherein an oxygen concentration in an atmospheric gas inside the kneader is set to 200 ppm or less before the resin is melted.   The method for producing a metal powder-containing resin molded body composition according to any one of claims 1 to 3, wherein after the resin is melted, an oxygen concentration in an atmospheric gas inside the kneader is set to 200 ppm or less.   The preform formed by the composition obtained by the manufacturing method of the composition for metal powder containing resin moldings of any one of Claims 1-4.   The manufacturing method of the metal sintered compact which has the process of sintering the preforming body of Claim 5.   A rare earth sintered magnet having an oxygen content of 2000 ppm or less and a sintered density of 99.0% or more obtained by the method for producing a metal sintered body according to claim 6.

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