A method for decomposition and treatment of bond magnet

Abstract: A method for decomposition and treatment of a bond magnet, has: a decomposition process for making a bond magnet which is made by blending magnetic powder-like material with binder and being molded, contact with decomposition material which can decompose said binder, within a decomposition vessel; a removing process for removing oxygen in the decomposition vessel; and a heating process for heating the decomposition vessel in temperatures ranging from 250°C to just under a critical temperature.

Description: The present invention relates to methods for decomposition and treatment of a bond magnet, which is superior in dimensional accuracy and processing and is widely applied to industrial materials. A bond magnet is a magnet molded by blending hard magnetic powder-like material with binder such as plastics and rubber. Every type of hard magnetic materials is generally hard and fragile in quality. The process for manufacturing the materials is generally performed by a finish machining in order to realize a fixed size when molding, sintering and heat-treating the material. As a result, high processing costs are unavoidable for requiring strict dimensional allowance, and thus significant increases in product costs may be caused. Further, complexly-shaped or thin materials are difficult to produce. A bond magnet is manufactured for the purpose of resolving these disadvantages in processing. The bond magnet is characterized in that it has a high dimensional accuracy in processing, a complexly-shaped or thin material, is easy to process without fracturing and chipping, and furthermore it is light in weight. Since the bond magnet contains 2 - 15 wt% (25 - 50 vol%) of a non-magnetic binder, the magnetic characteristics are inferior to a casing magnet or a sintered magnet. However, since a powerful magnetic powder such as a rare-earth magnetic powder could be obtained, the characteristics of a magnet have rapidly improved and such powerful magnets are widely used. On the other hand, since a bond magnet is manufactured as a blend of binder and magnetic powder-like material, the decomposition and reuse for resources of the used bond magnet or a bond magnet with inferior quality are difficult. Especially, in the case where the binder is a thermosetting resin, insoluble and non-melting three-dimensional solid structures are generally produced by the curing reaction. Therefore, a cured resin was difficult to decompose and was not proper for recycling and reuse. Considering the increasing serious problems of waste and effective use of resources, the development of a processing technology for reducing the volume of waste, waste treatment technology for reuse, for the used and inferior bond magnet is urgently required. Especially, the bond magnet is mainly made of metal, metallic oxide or the like, and metals or the like are more expensive materials than resinous binder materials. Consequently, the fact that reclamation and reuse of such expensive materials cannot be performed, is a large problem. Moreover, in case of a magnet made of rare earth metals such as, neodymium , or other materials like cobalt, the problems are still more serious. A bond magnet, which is manufactured by using a thermosetting resin such as epoxy resin as a binder, is completely difficult to decompose. A method for decomposition of any type of bond magnet in order to isolate metals such as rare earth metals from the bond magnet is required. Any conventional configuration or method for decomposition of a bond magnet cannot be sufficiently applied for reuse or recycle as resources at present. JP-A-10 055 908 discloses a recycling method for bonded magnets containing a binder and magnetic powder which comprises heating the bonded magnet above the melting point of the used binder, preferably in the range of from 500 to 1000 °C. The obtained residues can be reused for the fabrication of bonded magnets. It is the object of the present invention to provide an easy and simple method for decomposition of a bond magnet. Said object is achieved by a method for decomposition and treatment of a bond magnet, which comprises: contacting a bond magnet with a decomposition material within a decomposition vessel, the bond magnet being made by blending magnetic powder-like material with a binder and the bond being molded, whereby the decomposition material can decompose said binder; removing oxygen in the decomposition vessel; and heating the decomposition vessel at temperatures ranging from 250°C to a temperature where the decomposition material does not degrade. The removal of oxygen is preferably to exhaust the gas in the decomposition vessel after replacing the gas in the decomposition liquid with nitrogen gas by supplying nitrogen gas, and then to reduce the pressure in the decomposition vessel. Said object is also achieved by method for decomposition and treatment of a bond magnet, comprising: contacting a bond magnet with a decomposition material within a decomposition vessel, the bond magnet being made by blending magnetic powder-like material with a binder and the bond being molded, whereby the decomposition material can decompose said binder; said decomposition material containing at least one solvent selected from the group consisting of tetralin, biphenyl, naphthalene, methylnaphthalene, 1,4-hydroxynaphthalene, naphthol, 1,4-naphthoquinone, pitch, creosote oil, methylisobutyl ketone, isophorone, 2-hexanone, 2-heptanone, 4-heptanone, diisobutylketone, aetonylacetone, phorone, cyclohexanone, methylcyclohexanone and acetophenone; and heating the decomposition vessel at temperatures ranging from 250°C to a temperature where the decomposition material does not degrade. In the method of the present invention, the liquid for decomposition preferably contains an antioxidant or a reducing agent. The antioxidant or reducing agent is preferably at least one compound selected from the group consisting of hydroquinone, methoquinone, benzoquinone, naphthoquinone, butylcatechol, butylhydroquinone, sodium hyposulphite, sodium thiosulfate and ascorbic acid. In the method of the present invention, a preferable example of the bond magnet, which is molded by blending the magnetic powder-like material with the binder, is bond magnet consisting of a rare-earth magnet containing a rare earth element as magnetic material. FIG.1 shows a schematic sectional view in order to explain an embodiment of the present invention: 1 decomposition vessel 2 decomposition liquid material 3 bond magnet 4 decomposition gas The bond magnet used for the primary decomposition process of the present invention is molded and cured with plastics or rubber as a binder. It is classified according to a type of binder and hard magnetic powder-like material in use. A bond magnet using plastics as a binder is referred to as a plastic bond magnet. Examples of plastics are a nylon resin, a polyphenylenesulfide and an epoxy resin. Examples of the magnetic powder-like material are a mainly an oxide magnet and a rare-earth magnet. In the oxide magnet, an alnico magnet or a ferrite magnet can be used. In the rare-earth magnet, a rare-earth cobalt alloy such as SmCo 6 or a SmTl 7 alloy, or neodymium-based compounds such as Nd 2 Fe 14 B can be used. The decomposition liquid used in the first step of the method of the present invention contains at least one solvent selected from the group consisting of ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, isoprene glycol, triethylene glycol, 2-methoxyethanol, 2-ethoxyethanol, 2-(methoxymethoxy)ethanol, 2-isopropoxyethanol, 2-butoxyethanol, 2-(isopentyloxy)ethanol, 2-(hexyloxy)ethanol, 2-phenoxyethanol, 2-(benzyloxy)ethanol, 1-methoxy-2-propanol, 1-ethoxy-2-propanol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, triethylene glycol monomethyl ether, tripropylene glycol monomethyl ether and tetraethylene glycol. Further, in the present invention, a step of exhausting oxygen in the decomposition vessel is required in order to prevent oxidative degradation of the solvent or the magnet powder. An example of exhausting oxygen is a step of replacing the gas in the decomposition vessel as well as in the decomposition liquid with nitrogen gas. The supply of nitrogen gas is performed by directly supplying nitrogen gas from a nitrogen gas bottle through a gas inlet and an exhaust valve equipped on the decomposition vessel, in which the bond magnet and the decomposition liquid are provided. Another example is a process for reducing the pressure and exhausting the gas in the decomposition vessel. As another example reducing pressure can be performed by using a vacuum pump through the exhausting valve equipped to the decomposition vessel, in which the cured resin and the decomposition liquid are set. In either process, exhausting oxygen can effectively be performed by agitating and heating the decomposition liquid. A preferable process is vacuum exhaustion of gas in the decomposition vessel after replacing the gas in the decomposition liquid with nitrogen gas by supplying nitrogen gas. As a result of the decomposition treatment after the pretreatment with oxygen exhaustion, oxidation, which is a main cause for degradation of the decomposition liquid in a treatment at high temperature reaction, can be prevented, as well as the life time of the decomposition liquid is extended and repeated usability is improved. In addition, the oxidative deterioration of alloys configuring magnet powder in the bond magnet can be prevented. Consequently, the quality of the recovered magnet powder can be improved. Especially, since rare earth metal such as neodymium are easy to oxidize, such a process is effective for maintaining the post-treating quality. The decomposition liquid provided for the secondary decomposition process of the present invention includes at least a solvent selected from the group consisting of tetralin, biphenyl, naphthalene, methylnaphthalene, 1,4-hydroxynaphthalene, naphthol, 1,4-naphthoquinone, pitch, creosote oil, methylisobutyl ketone, isophorone, 2-hexanone, 2-heptanone, 4-heptanone, diisobutyl ketone, acetonylacetone, phorone, cyclohexanone, methylcyclohexanone and acetophenone. These solvents are stable at high temperature, generate oxygen by autodecomposition and rarely induce oxidation of metals or the like contained in the bond magnet. Consequently, a pretreatment such as removing oxygen is not always required. However, in the case where oxidation of trace metals in the bond magnet should be avoided, the pretreatment process for removal of oxygen can be set for extension of life time of the decomposition liquid. In the above explained method, the contact of the bond magnet with the decomposition material in the decomposition vessel means that the bond magnet is not always required to be completely dipped in the liquid phase of the decomposition material (see FIG.1 (A)). It is sufficient that a part of the bond magnet is dipped in a liquid phase of the decomposition material and the remaining part of the bond magnet is exposed to a gas phase of the decomposition material (see FIG. (B)) and also that the whole bond magnet is not dipped in a liquid phase but exposed to a gas phase(see FIG.1 (C)). Further it is sufficient that there is only a gas phase of the decomposition material in the vessel and the bond magnet is exposed to the gas phase(see FIG.1(D)). The decomposition material can be a gas phase and/or a liquid phase as described above. In FIG.1 number 1 indicates a decomposition vessel, number 2 indicates a liquid phase of the decomposition material, number 3 indicates a bond magnet, and number 4 indicates a gas phase of the decomposition material. Further, in the above explained method, the temperature, when soaking the bond magnet with the decomposition liquid, is preferably high for obtaining a higher decomposition reaction-rate, and especially the reaction rate is markedly accelerated at a temperature above 250°C. However, in the case where the temperature of the decomposition liquid is too high, the pressure of the inner vessel becomes too high and this requires a high pressure resistant vessel; a large volume of gas components generated by the decomposition makes it difficult to recover the generated gas; a degradation of the decomposition liquid itself will occur; and deterioration reaction such as oxidation of the magnet will be increased. Consequently, the temperature in the soaking process is preferably below a critical temperature. For example, the critical temperature of propyleneglycol is 351°C. As a result, in the soaking process, the decomposition liquid is heated preferably at above 250°C but below the critical temperature. In addition, antioxidants or reducing agents may be directly added to the decomposition liquid in order to prevent the oxidative degradation of the solvent or of the metallic components of the magnet. Preferably, as antioxidants and reducing agents, at least one compound may be selected from the group consisting of hydroquinone, methoquinone, benzoquinone, naphthoquinone, butylcatechol, butylhydroquinone, sodium hypophosphite, sodium thiosulfate and ascorbic acid. These compounds have preferable solubility and effectiveness for the decomposition liquid used in the present invention. These antioxidants or reducing agents are used in a ratio of 0.2 - 10 weight parts, preferably 1 - 5 weight parts, based on 100 weight part of the decomposition liquid . As a result of soaking the bond magnet into the decomposition liquid containing at least a solvent selected from the group consisting of ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, isoprene glycol, triethylene glycol, 2-methoxyethanol, 2-ethoxyethanol, 2-(methoxymethoxy)ethanol, 2-isopropoxyethanol, 2-butoxyethanol, 2-(isopentyloxy)ethanol, 2-(hexyloxy)ethanol, 2-phenoxyethanol, 2-(benzyloxy)ethanol, 1-methoxy-2-propanol, 1-ethoxy-2-propanol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, dipropylene glycol monomethyl ether, diprolylene glycol monoethyl ether, triethylene glycol monomethyl ether, tripropylene glycol monomethyl ether and tetraethylene glycol, and heating the mixture, the binder is chemically decomposed. The three-dimensional cross-linked structure of a thermosetting resin such as an epoxy resin can be decomposed. In addition, a solvent such as tetralin, biphenyl, naphthalene, methylnaphthalene, 1,4-hydroxynaphthalene, naphthol, 1,4-naphthoquinone, pitch, creosote oil, methylisobutyl ketone, isophorone, 2-hexanone, 2-heptanone, 4-heptanone, diisobutyl ketone, acetonylacetone, phorone, cyclohexanone, methylcyclohexanone or acetophenone under heating can provide a preferable liquid phase for decomposition of the binder and the thermo-decomposition reaction of the binder can be proceeded effectively. The thermosetting resin such as an epoxy resin, which is conventionally difficult to decompose in the prior art, can be easily and effectively decomposed. As a result of the decomposition of the binder, the binding force of the cured bond magnet is reduced to disintegrate the bond magnet. Namely, the magnetic powder in the bond magnet, which is bound with the binder, can no longer bind with the binder. Consequently, the magnetic powder is easily separated from the binder composition. The composition of the decomposed binder can be recovered as monomers in the form of a solid, oil or solute in the solution depending on their solubilities. According to the method of the present invention, the binders, such as a thermosetting epoxy resin which is difficult to decompose, can easily be disintegrated. Furthermore, the magnet powder can be recovered after the decomposition. The present invention will be explained in detail by illustrating the embodiments in the following. ( embodiment 1) An embodiment in the following will specifically explain a mode of operation of the method of the present invention. In this embodiment, the method of the present invention will be exemplified by using a bond magnet of a cured resin product, which is manufactured by aggregating a cured rare-earth magnetic powder with an epoxy resin as binder. In said embodiment, Nd-Fe-B magnet is used among the rare-earth magnets, although SmCo magnet is also known as rare-earth magnet. A Nd-Fe-B magnet powder was blended with 3% w/w epoxy resin, then the blended material was again ground to pulverize. A ring-shaped bond magnet was manufactured by compression molding. The product was used for a test of decomposition. The ring-shaped bond magnet was treated for decomposition by soaking into the decomposition liquid, which contained at least a solvent selected from the group consisting of ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, isoprene glycol, triethylene glycol, 2-methoxyethanol, 2-ethoxyethanol, 2-(methoxymethoxy)ethanol, 2-isopropoxyethanol, 2-butoxyethanol, 2-(isopentyloxy)ethanol, 2-(hexyloxy)ethanol, 2-phenoxyethanol, 2-(benzyloxy)ethanol, 1-methoxy-2-propanol, 1-ethoxy-2-propanol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, dipropylene glycol monomethyl ether, diprolylene glycol monoethyl ether, triethylene glycol monomethyl ether, tripropylene glycol monomethyl ether and tetraethylene glycol. In this embodiment, a decomposition liquid consisting of ethyleneglycol was used. The bond magnet was soaked into the decomposition liquid in the decomposition vessel, which were then sealed. A vacuum pump is connected to a nozzle equipped with each vessel, and the gas in the vessels was exhausted to reduce the pressure. The vessels were heated at 270°C for 5 hours. Then, each vessel was heated at 200, 230, 240, 250 and 300°C, respectively. The same operation was conducted only at 270°C without exhausting gas from the vessel. Results were as follows. In the treatments for decomposition performed at 200, 230 and 240°C, respectively, the bond magnets remained their shapes without changing the strength, though the color of resin was slightly changed. In the treatments for decomposition performed at above 250°C, i.e. at 250, 270 and 300°C, respectively, the resin binders were completely disintegrated and dissolved or dispersed into the decomposition liquid, in which the magnetic powder was precipitated in the bottom of the vessels. The test at 270°C without exhausting the gas and reducing the pressure by vacuum pump showed disintegration of the bond magnet and precipitation of the magnet powder. In the case where a pretreatment with vacuum exhaustion was performed, the maximum pressure in the decomposition vessel at the decomposition was 10 kg/cm 2 , which was almost the same pressure at 300°C of ethylene glycol, and the treated decomposed liquid showed slightly brownish color with precipitation derived from the decomposed resin. On the contrary, in the case where no gas exhaustion and pressure reduction were performed, the maximum pressure in the vessel under decomposition exceeded 40 kg/cm 2 . This produced a large amount of gas, showing a dark brownish colored liquid after the decomposition treatment, which indicated a progressed disintegration of the decomposition liquid. The magnet powder recovered after separation had a metallic gloss in the treatment of deaeration by pressure reduction, but the magnet powder without pretreatment showed a totally black color. These results indicate the less oxidative degradation in the pretreatment. As shown above, the bond magnet, which contains the binder consisting of a thermosetting resin, i.e. an epoxy resin, and is soaked into the decomposition liquid consisting of ethyleneglycol, then heated at 250°C, can be rapidly decomposed. In addition, exhaustion by pressure reduction results in reducing the pressure at the decomposition treatment as well as suppressing disintegration of the decomposition liquid and generation of a decomposed gas. Further, oxidation of the recovered magnetic powder can be prevented and the high quality of metals and other materials can be recovered. In conclusion, the present method for including exhaustion of gas in the decomposition vessel to reduce the inner pressure and heating above 250°C is an excellent method for a treatment, by which the binder is easily decomposed and the magnetic powder can easily be recovered while maintaining a high quality as well as less degradation of the decomposition liquid. The reduced pressure is preferably near vacuum, more preferably below 10 mm Hg. The temperature in the decomposition treatment is not limited within the present embodiment and is preferably within the range below the critical temperature and above 250°C. Further, the compositions and constitution of the bond magnet, which contains binder of epoxy resin, are not limited. Other resins and rubbers can be used. Also, the magnetic powder-like materials can be an other rare-earth magnet, like an alnico magnet. In the present embodiment, ethyleneglycol is exemplified as the decomposition liquid, but is not limited in the compositions and blending ratio. Other liquids include at least a solvent selected from the group consisting of ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, isoprene glycol, triethylene glycol, 2-methoxyethanol, 2-ethoxyethanol, 2-(methoxymethoxy)ethanol, 2-isopropoxethanol, 2-butoxyethanol, 2-(isopentyloxy)ethanol, 2-(hexyloxy) ethanol, 2-phenoxyethanol, 2-(benzyloxy)ethanol, 1-methoxy-2-propanol, 1-ethoxy-2-propanol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, dipropylene glycol monomethyl ether, diprolylene glycol monoethyl ether, triethylene glycol monomethyl ether, tripropylene glycol monomethyl ether and tetraethylene glycol. In the present embodiment, the decomposition liquid was used without any addition of other components, however an antioxidant or a reducing agent, for example, hydroquinone, methoquinone, benzoquinone, naphthoquinone, butylcatechol, butylhydroquinone, sodium hyposulfite, sodium thiosulfate, ascorbic acid or the like can be added for recovery of good quality of metals. In the process, the reduced pressure can be replaced with supplying nitrogen gas, and the replaced nitrogen gas is also exhausted by pressure reduction to achieve a less oxidative deterioration. The decomposition liquid can be repeatedly used by removing the dissolved materials, or can be used for fuel as oil as it is. (embodiment 2) The embodiment of the method of the present invention will be explained. In the present embodiment, the method of the present invention will be explained by exemplifying the bond magnet, which is a resinous cured substance, cured by aggregation with ferrite powder and an epoxy resin as a binder. The composition of the ferrite material is expressed by the rational formula M x Fe 2 O 3 , wherein M is Ba (barium), Sr (strontium) or Pb (lead), and x is 4.5 - 6.5. A bond magnet was prepared by blending the ferrite powder with 5% w/w nylon resin and injection molding to produce a ring-shaped bond magnet, which was used for a decomposition test. The ring shaped bond magnet was subjected to decomposition treatment by soaking into the decomposition liquid containing at least a solvent selected from the group consisting of tetralin, biphenyl, naphthalene, methylnaphthalene, 1,4-hydroxynaphthalene, naphthol, 1,4-naphthoquinone, pitch, creosote oil, methylisobutyl ketone, isophorone, 2-hexanone, 2-heptanone, 4-heptanone, diisobutyl ketone, acetonylacetone, phorone, cyclohexanone, methylcyclohexanone and acetophenone. Methylisobutyl ketone was used as the decomposition liquid in the present embodiment. The bond magnet was soaked into the decomposition liquid at 280°C for 5 hours. As a result, the binder of the resin was decomposed and the bond magnet was decomposed and never maintained its original molded form. The decomposed resin was dissolved or dispersed in the solvent and the ferrite powder was precipitated. The precipitate was separated by filtration, washed with a solvent such as acetone to recover the ferrite powder after drying. This powder can be reused for a bond magnet or a sintered magnet. As shown above, the resin component of the bond magnet, which was a resinous cured material containing a binder of a nylon resin of the thermosetting resin, was soaked in methylisobutyl ketone as a decomposition liquid to decompose rapidly the resin content, then the magnetic powder-like material could be recovered separately. The process of the present embodiment is to provide recovery of valuable materials and to reduce the volume of waste bond magnet. Further, the decomposed resin can also be reused as a raw resin material such as a monomer. Further, in the present embodiment, the decomposition liquid was used without any addition of other components, however antioxidants or reducing agents, as for example hydroquinone, methoquinone, benzoquinone, naphthoquinone, butylcatechol, butylhydroquinone, sodium hyposulfite, sodium thiosulfate, ascorbic acid like can be added for recovery of good quality of metals. Further, the composition or the constitution of a bond magnet, which contains a binder of a nylon resin, is not limited. Other resins and rubbers can be used. Also, the magnetic powder-like materials can be other rare-earth magnets like alnico magnet. Further, the temperature in the decomposition treatment is not limited within the present embodiment and is preferably within the range below the critical temperature and above 250°C. In the present embodiment, methylisobutyl ketone was shown as an example of the decomposition liquid, however the composition or the combining ratio is not limited, and it is sufficient to contain at least a solvent selected from the group consisting of tetralin, biphenyl, naphthalene, methylnaphthalene, 1,4-hydroxynaphthalene, naphthol, 1,4-naphthoquinone, pitch, creosote oil, methylisobutyl ketone, isophorone, 2-hexanone, 2-heptanone, 4-heptanone, diisobutyl ketone, acetonylacetone, phorone, cyclohexanone, methylcyclohexanone and acetophenone. In the present invention, a pretreatment of the decomposition vessel was not performed before the decomposition treatment was initiated. However, if a deterioration reaction such as a slight oxidation of the magnetic material is disadvantageously caused, pressure reduction by exhaustion or exhaustion by replacement with nitrogen can be applied, and further exhaustion by pressure reduction after the replacement with nitrogen is preferable for a treatment with less oxidative disintegration . Further, the decomposition liquid can be repeatedly used by removing the dissolved materials, or can be used for fuel as oil as it is. (embodiment 3) The embodiment of the method of the present invention will be explained. In the present embodiment, the method of the present invention will be explained by exemplifying the bond magnet, which is a resinous cured substance, cured by aggregation with a rare-earth magnet powder and an epoxy resin as a binder. In the present embodiment, a Nd-Fe-B magnet is used as a rare-earth magnet, although an SmCo magnet or the like is also known as a rare-earth magnet. A Nd-Fe-B magnet powder was blended with 3% w/w epoxy resin, then the blended material was again ground to pulverize. A ring-shaped bond magnet was manufactured by compression molding. The product was used for a test of decomposition. The ring shaped bond magnet was subjected to a decomposition treatment by soaking into the decomposition liquid containing at least a solvent selected from the group consisting of tetralin, biphenyl, naphthalene, methylnaphthalene, 1,4-hydroxynaphthalene, naphthol, 1,4-naphthoquinone, pitch, creosote oil, methylisobutyl ketone, isophorone, 2-hexanone, 2-heptanone, 4-heptanone, diisobutyl ketone, acetonylacetone, phorone, cyclohexanone, methylcyclohexanone and acetophenone. Tetralin was used as the decomposition liquid in the present embodiment. The bond magnet was soaked into the decomposition liquid at 280°C for 3 hours. As a result, the binder of resin was decomposed and the bond magnet was decomposed and did not maintain its original molded form. The decomposed resin was dissolved or dispersed in the solvent and the Nd-Fe-B powder was precipitated. The precipitate was separated by filtration, washed with a solvent such as acetone to recover the Nd-Fe-B powder after drying. This powder can be reused for a bond magnet or a sintered magnet. Although the rare earth metal such as Nd is a metal which is easily oxidized or corroded, in the present method, no such effects were observed and the material could be reused as a magnetic material. Since tetralin is a solvent, which disintegrates a resin, and is a reductive solvent, the alloys in the bond magnet can be recovered in a stable state. Biphenyl, which is not used in the present embodiment, has the same nature, too. In case of isophorone or methylisobutyl ketone, which have oxygen molecules in their structure and have oxygen sources, these molecules do not easily supply oxygen by thermal decomposition. Consequently oxidation of the magnet cannot be accelerated. As shown above, the resin component of the bond magnet, which was a resinous cured material containing a binder of an epoxy resin of the thermosetting resin, was soaked in the tetralin as the decomposition liquid to decompose rapidly the resin content, then the magnetic powder-like material could be recovered separately. The process of the present embodiment is to provide recovery of valuable materials and volume reduction of a waste bond magnet. In addition, the present process is a method for treatment of the quality of metals to be recovered, and is a very effective method for disintegrating an easily corrosive rare-earth bond magnet. In the present embodiment, the decomposition liquid was used without any addition of other components, however antioxidant or reducing agents, for example, hydroquinone, methoquinone, benzoquinone, naphthoquinone, butylcatechol, butylhydroquinone, sodium hyposulfite, sodium thiosulfate or ascorbic acid can be added for recovery of a good quality of metals. Further, the composition or the constitution of a bond magnet is not limited within the scope of the present embodiment. Other resins can be used. No relation to isotropy or anisotropy of the rare-earth magnet is observed. The composition can be modified: a part of Fe is optionally replaced with Co in order to increase the anticorrosive nature, or other rare earth metals such as Pr can be added. Also, the magnetic powder-like materials can be other rare-earth magnets or an alnico magnet. The temperature in the decomposition treatment is not limited within the present embodiment and is preferably within the range below the critical temperature and above 250°C. In the present embodiment, tetralin was shown as an example of the decomposition liquid, however a composition or a combining ratio is not limited, and it is sufficient to contain at least a solvent selected from the group consisting of tetralin, biphenyl, naphthalene, methylnaphthalene, 1,4-hydroxynaphthalene, naphthol, 1,4-naphthoquinone, pitch, creosote oil, methylisobutyl ketone, isophorone, 2-hexanone, 2-heptanone, 4-heptanone, diisobutyl ketone, acetonylacetone, phorone, cyclohexanone, methylcyclohexanone and acetophenone. The solvent can be a single solvent, or a mixed solvent such as a mixture of isophorone and methylisobutyl ketone. In the present invention, a pretreatment of the decomposition vessel was not performed before the decomposition treatment was initiated. However, if slight oxidation of the magnetic material is disadvantageously caused, a pressure reduction by exhaustion or exhaustion by replacement with nitrogen can be applied, and further exhaustion by pressure production after the replacement with nitrogen is preferable for a treatment with less oxidative disintegration. The decomposition liquid can be repeatedly used by removing the dissolved materials, or can be used for fuel as oil as it is. (Comparative example 1) A comparative example for the method for decomposition and treatment will be shown as follows. The bond magnet used in embodiment 3 was soaked into the decomposition liquid consisting of n-tetradecane at 300°C for 5 hours. The rate of infiltration of the decomposition liquid and the surface hardness of the resinous cured material after soaking treatment with a decomposition liquid were measured. As a result, no changes were observed in the appearance of the cured materials. Further, neither an infiltration of the decomposition liquid into the resinous cured material nor a decrease in hardness was observed. Namely, the decomposition and treatment effects using a decomposition liquid consisting of n-tetradecane cannot be expected. (Comparative example 2) A comparative example of the method for decomposition and treatment will be shown as follows. The bond magnet used in the embodiment 3 was soaked into the decomposition liquid consisting of liquid paraffin at 300°C for 5 hours. The rate of infiltration of the decomposition liquid and the surface hardness of the resinous cured material after soaking treatment with a decomposition liquid were measured. As a result, no changes were observed in the appearance of the cured materials. Further, neither an infiltration of the decomposition liquid into the resinous cured material nor a decrease in hardness was observed. Namely, the decomposition and treatment effects using a decomposition liquid consisting of liquid paraffin cannot be expected. Further the present invention was compared with a conventional method using mechanical decomposition process and with a conventional method using a heating decomposition process. As a method of the present invention ,the bond magnet, in which an epoxy resin was used as a binder, and tetralin were mixed in the decomposition vessel. Oxygen in the vessel was exhausted by replacement of the oxygen with nitrogen gas as a pretreatment, and thereafter the vessel was heated up to 300°C for 2 hours. As a result, the epoxy resin was decomposed and the bond magnet was disintegrated to precipitate the magnetic powder in the bottom of the vessel. The precipitate was recovered and washed with acetone to obtain the magnetic powder, which was reused for manufacture of the bond magnet. (Comparative example 3) The recycling method of the present invention was compared with a conventional method in order to prove the superiority of the method of the present invention. As for the prior art, a method for mechanical treatment was examined. For comparison, a grinding method was applied as the mechanical means. A bond magnet, which was cured and molded by using an epoxy resin as a binder, was subjected to impact grinding. The recovered powder was used to manufacture again the bond magnet. The impact grinding was performed by that the bond magnet and zirconia balls 5 mm were set in a nylon cylinder shaped pot and were shaken by using a paint shaker. The ground powder prepared by the mechanical means had a disadvantage in that mulling with a binder resin was inferior compared to the product of the present invention. (Comparative exaple 4) The recycling method of the present invention was compared with a conventional method in order to prove the superiority of the method of the present invention. As for the prior art, a method for thermal treatment was examined. A thermal treatment method was measured by thermal decomposition of the binder. In that condition, since thermal decomposition in the air generates oxidation of the rare-earth magnet, the treatment was conducted by dry distillation under nitrogen atmosphere. The bond magnet with an epoxy resin as a binder was dry distilled in a silica tube to decompose the epoxy resin. The oxygen concentration in the dry distillation was below 1% and the combustion was proceeded at 300-500°C. In any temperature tested, the appearance did not change, and no deterioration of strength was observed. The recovered powder treated by the zirconia ball treatment was used for the preparation of a plastic bond magnet. The impact grinding was performed with the same method as in the above comparative method 1. (Measurement of magnetic characteristics) The produced plastic bond magnets were magnetized at 50 kOe. The magnetic characteristics and magnetic density were measured as a property of a permanent magnet, such as remanent magnetic flux density and coercive force by VSM measurement. The magnetic characteristics were obtained by measuring the remanent magnetic flux density (Br) which indicated the strength of magnetization, coercive force (Hci) which is a force to coerce magnetization and maximum magnetic energy product (BHmax) which indicates the ability of a magnet. Each measured value is summarized in the table in comparison with that of the present material. The recycled magnet showed a remnant magnetic flux density of 98.7%, a coercive flux of 92.8% and a maximum magnetic energy product of 91.6% that shows the capacity of a magnet, compared to the original magnet. Consequently, the recycled magnet of the method of the present invention is almost identical with the original magnet in its character. The mechanical treated grinding magnet showed bad blending with the binder resin, and as a result, a low density bond magnet was produced. Since the decomposition treatment was performed only by mechanical grinding, the remaining cured resin absorbed again the newly blended resin and resulted in a bad dispersion and decreasing mulling ability. Further, the total amount of resin was increased, and as a result, the remanent magnet flux density was decreased. The coercive force was not so largely decreased with maintaining at 83.9% of the present original product. As a result in total, the maximum magnetic energy product is not so high and is approximately 40% of the original product. In the dry distilled and ground product, although the product was treated by grinding, some of its resinous components, even if they are of small quantity, are decomposed and then released by distillation treatment, and good dispersion with the resin was observed as compared with the ground product. The remanent magnetic flux density was also improved, however, it is still lower than for the present product. The remanent magnetic flux density resulted in a low level. The coercive force is almost on an identical level with the grinding magnet. The maximum magnetic energy product is about 54% of the present product. The results indicate that a conventional process cannot remove the cured binder, consequently a magnetic flux density cannot be obtained and insufficient magnetic characteristics are obtained. Method of present invention Grinding method Dry distillation + grinding method The present product Density (g/cm 3 ) 5.782 5.114 5.210 5.831 Br (kG) 6.66 4.93 5.55 6.75 Hci (kOe) 8.72 7.89 7.88 9.40 BHmax (MGOe) 8.63 3.81 5.04 9.42 As explained in the above, the method of the present invention can easily decompose the binder in the bond magnet, and the magnetic powder can be recovered separately and reused, as well as the amount of waste to be treated can be reduced.

Claims: A method for decomposition and treatment of a bond magnet (3), comprising: contacting a bond magnet (3) with a decomposition material (2) within a decomposition vessel (1), the bond magnet (3) being made by blending magnetic powder-like material with a binder and the bond being molded, whereby the decomposition material (2) can decompose said binder; removing oxygen in the decomposition vessel (1); and heating the decomposition vessel (1) at temperatures ranging from 250°C to a temperature where the decomposition material does not degrade. The method of claim 1 wherein said decomposition material (2) contains at least one solvent selected from the group consisting of ethyleneglycol, propyleneglycol, diethyleneglycol, dipropyleneglycol, isopropyleneglycol, triethyleneglycol, 2-methoxyethanol, 2-ethoxyethanol, 2-(methoxymethoxy) ethanol, 2-isopropylethanol, 2-butoxyethanol, 2-(isopentyloxy) ethanol, 2-(hexyloxy) ethanol, 2-phenoxyethanol, 2-(benzyloxy) ethanol, 1-methoxy-2-propanol, 1-ethoxy-2-propanol, diethyleneglycolmonomethyl ether, diethyleneglycolmonoethyl ether, diethyleneglycolmonobutyl ether, dipropyleneglycolmonomethyl ether, dipropyleneglycolmonoethyl ether, triethyleneglycolmonomethyl ether, tripropyleneglycolmonomethyl ether and tetraethyleneglycol. The method of claim 1 or 2, wherein removing of oxygen is conducted by replacing the gas in the decomposition vessel (1) with nitrogen gas, and/or a exhausting the gas in the decomposition vessel (1) and reducing the pressure in the decomposition vessel (1). A method for decomposition and treatment of a bond magnet (3), comprising: contacting a bond magnet (3) with a decomposition material (2) within a decomposition vessel (1), the bond magnet (3) being made by blending magnetic powder-like material with a binder and the bond being molded, whereby the decomposition material (2) can decompose said binder; said decomposition material (2) containing at least one solvent selected from the group consisting of tetralin, biphenyl, naphthalene, methylnaphthalene, 1.4-hydroxynaphthalene, naphthol, 1.4-naphthoquinone, pitch, creosote oil, methylisobutyl ketone, isophorone, 2-hexanone, 2-heptanone, 4-heptanone, diisobutylketone, aetonylacetone, phorone, cyclohexanone, methylcyclohexanone and acetophenone; and heating the decomposition vessel at temperatures ranging from 250°C to a temperature where the decomposition material does not degrade. The method of claim 1 or 4, wherein said decomposition material (2) is a liquid material and, a part or all of said bond magnet (3) is soaked in said liquid of the decomposition material (2). The method of claim 4, further comprising: removing oxygen in the decomposition vessel (1), after said decomposition process. The method of claim 6, wherein the removing step is a replacing step for replacing the gas in the decomposition vessel (1) with nitrogen gas, and/or a reducing step for exhausting the gas in the decomposition vessel (1) and reducing the pressure in the decomposition vessel (1). The method of claim 1 or 4, wherein the decomposition material (2) contains an antioxidant or a reducing agent. The method of claim 8, wherein the antioxidant or the reducing agent is at least a compound selected from the group consisting of hydroquinone, methoquinone, benzoquinone, naphtoquinone, butylcatechol, butylhydroquinone, sodium hyposulfite, sodium thiosulfate and ascorbic acid. The method of claim 1 or 4, wherein the magnetic powder-like material is a rare-earth magnet containing rare-earth element.

Inventors: ONISHI HIROSHI, TERADA TAKAHIKO, ONISHI, HIROSHI, TERADA, TAKAHIKO
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1999
Main classification: H01F41
IPC codes: H01F1, H01F41, C22B23, C22B7, B09B5