METHOD FOR RECYCLING METAL AND METHOD FOR MANUFACTURING METAL POWDER-CONTAINING RESIN-MOLDED BODY

Abstract

Provided is a metal regeneration method including a step (S10) for preparing a metal mixture in which multiple types of non-magnetic metal bodies having different shapes from each other are mixed and a step (S20) for pulverizing the metal mixture into metal powder. In the step (S20) for pulverizing, the particle diameters of the entire metal powder are reduced so as to be equal to or less than a first value; first metal powder having the particle diameters that are equal to or less than a second value is removed from the entire metal powder, the second value being less than the first value; and second metal powder having particle diameters that are greater than the second value and equal to or less than the first value is recovered. The above metal regeneration method additionally includes a step (S30) for removing, from the second metal powder, third metal powder having particle diameters that are equal to or greater than a third value and recovering fourth metal powder having particle diameters that are greater than the second value and less than the third value. The third value is greater than the second value and less than the first value.

Description

[Technical Field]

[0001] The present disclosure relates to a method for recycling metals and a method for producing a metal powder-containing resin molded article. [Background technology]

[0002] In recent years, promoting the recycling of components of electrical appliances such as air conditioners, televisions, refrigerators, and washing machines used in ordinary Japanese households has become an important issue, due to legal regulations related to global environmental protection such as the Home Appliance Recycling Law, as well as from the perspective of effective utilization of materials.

[0003] The following methods are known as methods for recovering valuable materials such as plastics and metals from collected electrical appliances.

[0004] First, the components of the collected electrical appliances are sorted by size and material, and then each is roughly crushed into pieces several centimeters to several tens of centimeters square using a crusher.

[0005] Second, magnetic metals such as iron are recovered from the coarsely crushed pieces using a magnetic separator. Third, metals (e.g., non-magnetic metals) such as aluminum (Al), copper (Cu), and stainless steel (SUS) are recovered from the remaining coarse crushed pieces using an eddy current separator.

[0006] Fourth, foams such as urethane, which have a low specific gravity, and metal pieces and metal wires, which have a high specific gravity, are recovered from the remaining coarse crushed pieces by wind sorting.

[0007] The final residue after the above sorting is collected as recycled plastic, with a small percentage of the collected plastic being collected as industrial waste or thermally recycled.

[0008] As a method for recovering metals as valuable resources, a sorting method using a color sorter and a gravity sorter is known. Also, Japanese Patent Laid-Open Publication No. 7-178385 (Patent Document 1) discloses a method for recovering valuable resources from printed circuit boards, which focuses on the properties of the materials and separates metals, which are ductile substances that are difficult to break down, from glass fibers and resins, which are brittle substances that are easily broken down, by crushing and classifying them. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 7-178385 Summary of the Invention [Problem to be solved by the invention]

[0010] Even after metals have been recovered using the magnetic separator and eddy current separator, the recovered plastic still contains up to 5% by weight of various types of valuable metals.

[0011] Furthermore, sorting methods using color or specific gravity have difficulty separating and sorting multiple types of metals that have small differences in color or specific gravity. For example, there is only a small difference in the specific gravity of valuable copper wire and enameled wire, which has a thin polymer film formed around it. Therefore, it is difficult to separate and recover copper wire and enameled wire from recovered plastics using specific gravity sorting methods.

[0012] As such, there is a demand for methods to separate and recycle valuable metals from electrical appliances with a higher recycle rate.

[0013] It should be noted that Patent Document 1 describes a method for separating metals from glass fibers and resins, and does not describe the selective recovery of specific metals from a mixture of metals.

[0014] One object of the present disclosure is to provide a method for regenerating metals that can more efficiently regenerate a specific type of metal from a mixture containing multiple types of metal bodies.

[0015] As described above, the metal recycled by the conventional recycling method contains multiple types of metals, and therefore, in order to produce a metal powder-containing resin molded product containing a specific type of metal powder at high purity, a step of refining the metal recycled by the conventional recycling method is required.

[0016] Another object of the present disclosure is to provide a method for producing a metal powder-containing resin molded body, which can produce a metal powder-containing resin molded body containing a specific type of metal powder at a high purity without refining the metal. [Means for solving the problem]

[0017] A metal recycling method according to one embodiment of the present disclosure includes the steps of preparing a metal mixture containing a mixture of multiple metal bodies having different shapes, and pulverizing the metal mixture into metal powder. In the pulverizing step, the particle sizes of all the metal powders are set to a first value or less, and first metal powders having particle sizes equal to or less than a second value smaller than the first value are removed from all the metal powders, and second metal powders having particle sizes greater than the second value but equal to or less than the first value are recovered. The metal recycling method further includes the steps of removing third metal powders having particle sizes equal to or greater than a third value from the second metal powders, and recovering fourth metal powders having particle sizes greater than the second value but less than the third value. The third value is greater than the second value and less than the first value. [Effects of the Invention]

[0018] According to the present disclosure, a method for regenerating metals can be provided that can more efficiently regenerate a specific type of metal from a mixture containing multiple types of metal bodies. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a flowchart showing a metal recycling method according to an embodiment of the present invention. [Figure 2]1 is a diagram for explaining a pulverizer used in a metal recycling method according to an embodiment of the present invention. FIG. [Figure 3] 1 is a graph showing the diameter distribution of copper wires contained in a metal mixture fed to a pulverization step in an example. [Figure 4] 1 is a graph showing the diameter distribution of enameled wires contained in a metal mixture fed to a pulverizing step in an example. [Figure 5] 1 is a graph showing the wire diameter distribution of stainless steel wires contained in a metal mixture fed to a pulverization step in an example. [Figure 6] 1 is a graph showing the maximum length distribution of aluminum plates contained in a metal mixture fed to a pulverization step in an example. [Figure 7] 3 is a flowchart showing a method for manufacturing a metal powder-containing resin molded article according to the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. <Metal recycling methods> The metal recycling method according to the present embodiment is a method for recycling a predetermined non-magnetic metal as metal powder from a metal mixture containing multiple types of non-magnetic metal bodies with different shapes. In other words, the metal recycling method according to the present embodiment is a method for producing a predetermined non-magnetic metal as metal powder from a metal mixture containing multiple types of non-magnetic metal bodies with different shapes as a starting material.

[0021] In this specification, non-magnetic metal refers to a metal that does not have ferromagnetic properties and is a concept that includes weakly magnetic metals. A non-magnetic metal body refers to a structure made of a non-magnetic metal and includes non-magnetic metal wires and non-magnetic metal plates. A non-magnetic metal wire is a wire material whose main constituent material is a non-magnetic metal and does not have a plastic coating. A non-magnetic metal plate is a plate material whose main constituent material is a non-magnetic metal and does not have a plastic coating. Examples of non-magnetic metal wires are copper (Cu) wire, stainless steel (SUS) wire, and enameled wire. An example of a non-magnetic metal plate is an aluminum (Al) plate. A copper wire refers to a wire material made only of copper or a copper alloy. An enameled wire refers to a wire material made of a copper wire and an enamel coating that covers the surface of the copper wire. The enamel coating is formed by baking an enamel paint applied to the surface of a core wire.

[0022] The metal powder produced by the metal recycling method according to this embodiment is copper powder. 1, in the metal recycling method according to the present embodiment, first, a metal mixture is prepared in which multiple types of non-magnetic metal bodies with different wire diameter distributions are mixed (step (S10)). The metal mixture can be prepared by any method, but for example, it is produced from recycled plastic by the following method.

[0023] First, various components obtained by dismantling electrical appliances such as refrigerators, washing machines, and air conditioners are roughly crushed into pieces several centimeters to several tens of centimeters square using a crushing device. The various components include large metal parts such as compressors, heat exchangers, and motors, large plastic molded parts such as refrigerator cases and washing machine tubs, control boards, cords, and other components.

[0024] Next, the roughly crushed material fragments are separated by a magnetic separator to remove ferromagnetic metals such as iron, an eddy current separator to remove weakly magnetic metals such as aluminum, copper, and stainless steel, and then air sorting to remove low-density foams such as urethane and high-density metals. The final residue after these sorting processes is collected as recycled plastic. The recycled plastic includes several types of non-magnetic metals, at least one type of coated metal wire, and several types of plastic fragments.

[0025] A coated metal wire is a wire having a core wire made of a non-magnetic metal and a plastic coating covering the surface of the core wire. An example of a coated metal wire is a coated copper wire made of a copper wire and a plastic coating covering the surface of the copper wire. The plastic coating is made of a material such as polyvinyl chloride (PVC).

[0026] The multiple types of non-magnetic metal bodies contained in the recovered plastics include, for example, three types of non-magnetic metal wires: copper wire, enameled wire, and stainless steel, as well as aluminum plates. The at least one type of coated metal wire is, for example, coated copper wire. The copper wire, enameled wire, and coated copper wire are wires that have been used for wiring in electrical appliances, for example. The stainless steel wire includes wires that have been incorporated into plastics as piano wire (spring steel) in electrical appliances. The aluminum plates include aluminum plates that have been used as capacitor electrodes in electrical appliances.

[0027] The wire diameter distributions of the multiple copper wires, multiple enameled wires, and multiple stainless steel wires contained in the recovered plastic are different from one another. The average wire diameter of the multiple copper wires is larger than the average wire diameters of the multiple enameled wires and the average wire diameters of the multiple stainless steel wires. The average maximum length of the multiple aluminum plates contained in the recovered plastic is longer than the average wire diameters of the copper wires, enameled wires, and stainless steel wires. The maximum length of the aluminum plate means the maximum outer dimension of the aluminum plate.

[0028] Next, a first mixture containing multiple types of non-magnetic metal wires and plastic pieces having dimensions within a predetermined range is sorted and recovered from the recovered plastics using a sieve (step (S11)). Preferably, the copper wire, enameled wire, stainless steel wire, aluminum plate, coated copper wire, and plastic pieces sorted and recovered as the first mixture are those separated using a sieve with a mesh size of 3.5 mm or more and less than 15.0 mm. The mesh size conforms to JIS standard (JIS Z 8801-1). If the recovered plastics contain a large amount of non-magnetic metal wires that have been separated by a sieve with a mesh size larger than the upper limit of the above range, it is preferable to coarsely crush the recovered plastics in a crusher as a pre-step of this step (S11) and then feed the crushed recovered plastics into this step (S11), or to coarsely crush the non-magnetic metal wires that have been selected in this step (S11) as having a maximum length larger than the upper limit of the above range in a crusher, and then sieve the crushed non-magnetic metal wires again to separate and recover the first mixture. The sieve used in this step is, for example, an ultrasonic vibration screening machine.

[0029] Next, a second mixture containing multiple types of non-magnetic metal bodies and coated metal wires is separated and recovered from the first mixture by centrifugation (step (S12)). Centrifugation is performed, for example, by applying centrifugal force to the first mixture using a water flow, utilizing the difference in specific gravity within the water flow. As a result, plastic pieces with relatively low specific gravity are removed from the first mixture, and copper wire, enameled wire, stainless steel wire, aluminum plate, coated copper wire, and plastic pieces with relatively high specific gravity are separated and recovered as the second mixture.

[0030] For example, the sum of the weight ratios of the copper wire, enameled wire, stainless steel wire, and aluminum plate contained in the second mixture is approximately 5% by weight. The weight ratio of the coated copper wire contained in the second mixture is approximately 35% by weight. The weight ratio of the plastic pieces contained in the second mixture is approximately 60% by weight. The plastic pieces are, for example, plastic flakes mainly composed of polypropylene (PP), polystyrene (PS), acrylonitrile butadiene styrene (ABS) copolymer, polyoxymethylene (POM), polybutylethyleneterephthalate (PBT), polycarbonate (PC), PC / ABS mixed alloy, or PVC.

[0031] Next, the metal mixture containing multiple types of non-magnetic metal wires and non-magnetic metal plates is separated and recovered from the second mixture (step (S13)). In this step (S13), for example, wet gravity separation is first performed, followed by color separation. In wet gravity separation, a solvent with a higher specific gravity than the plastic pieces is used. This removes the plastic pieces contained in the second mixture, and copper wire, enameled wire, stainless steel wire, aluminum plate, and coated copper wire are separated and recovered as a third mixture. The specific gravity of the solvent used in wet gravity separation may be any value that is greater than the specific gravity of each of PP, PS, ABS, POM, PBT, PC, PC / ABS, and PVC, but less than the specific gravity of each of the multiple types of non-magnetic metals, and is, for example, approximately 1.5.

[0032] In color sorting, the coated copper wire is removed from the third mixture, and a metal mixture containing copper wire, enameled wire, stainless steel wire, and aluminum plate is separated and recovered based on the color observed when visible light is irradiated onto the third mixture separated and recovered by wet gravity separation. The color of the plastic coating on the coated metal wire is different from the color (metal color) of the core wire. Therefore, the coated copper wire can be separated from the non-magnetic metal wire based on the color observed when visible light is irradiated onto the mixture containing the non-magnetic metal wire and the coated copper wire.

[0033] The metal mixture contains a metal mass in which copper wire, enameled wire, stainless steel wire, and aluminum plate are entangled with one another. This metal mass is thought to have been formed when centrifugal separation using a water flow was performed in the previous step (S12).

[0034] In the above steps (S11) to (S13), the diameter of each of the multiple types of non-magnetic metal wires does not increase or decrease. Therefore, by the above steps (S11) to (S13), a metal mixture containing multiple types of non-magnetic metal wires with different diameter distributions is prepared. The above steps (S11) and (S12) are effective from the viewpoint of increasing the recovery efficiency of the metal mixture in step (S13). Step (S13) is effective from the viewpoint of increasing the work efficiency in the subsequent step (S20) of pulverizing the metal mixture into metal powder. If the coated copper wires are pulverized in the subsequent step (S20), the plastic coating may generate heat, making it impossible to continue pulverization. One method of pulverizing while cooling with liquid nitrogen or the like to suppress heat generation is conceivable, but if the above step (S13) is not performed, the weight ratio of the coated copper wires in the third mixture is high, resulting in a large amount of heat generation, and the cooling effect is small. Furthermore, if step (S13) is not performed, the weight ratio of coated copper wire in the third mixture will be high, which may reduce the efficiency of copper powder regeneration. Alternatively, instead of step (S13), the third mixture may be heated in a heating furnace at 700°C or higher to carbonize the plastic coating, but this may result in the generation of harmful gases when the plastic burns. Therefore, step (S13) is more advantageous than other methods, even from an environmental perspective.

[0035] In the metal recycling method according to this embodiment, secondly, the metal mixture prepared in the previous step (S10) is pulverized into metal powder (step (S20)). In this step (S20), the metal mixture is pulverized into metal powder using a pulverizer that applies impact and shear forces to the metal mixture. In other words, the pulverization in this step is performed by shortening both the wire diameter and wire length of the non-magnetic metal wire so that the particle size of the metal powder obtained by pulverizing the non-magnetic metal wire is smaller than the wire diameter of the non-magnetic metal wire. Figure 2 shows an example of a pulverizer.

[0036] The pulverizer 10 shown in FIG. 2 includes a supply unit 11, a pulverizing unit 12, and a classifying unit 13. The supply unit 11 is a unit to which a metal mixture is supplied from the outside. The supply unit 11 is configured to vibrate the metal mixture and loosen the metal lumps contained in the metal mixture. The pulverizing unit 12 is configured to apply impact and shear forces to the metal mixture. The pulverizing unit 12 is, for example, a hammer mill, a cutter mill, or a screen mill having a screen on the outlet side (classifying unit 13) of the rotating hammer or cutter blade of the hammer mill or cutter mill. The material constituting the hammer or cutter blade of the pulverizing unit 12 is harder than the non-magnetic metal to be pulverized. The material constituting the hammer or cutter blade of the pulverizing unit 12 is, for example, a cemented carbide. The Vickers hardness of copper is 60 to 120 HV, the Vickers hardness of stainless steel is 200 to 500 HV, and the Vickers hardness of aluminum is 20 to 40 HV. In contrast, the Vickers hardness of cemented carbide is 1700 to 2100 HV. Therefore, the particle size of the metal powder of the non-magnetic metal wire after pulverization is not affected by the hardness of each metal being pulverized, but rather depends on the wire diameter of each metal. The pulverized metal powder has a fractured or sheared surface.

[0037] In the classifying section 13, the metal powder pulverized in the pulverizing section 12 is classified according to its particle size. The classifying section 13 has, for example, an ultrasonic vibration screen.

[0038] In the classification unit 13, the metal powder is classified into metal powder having a particle size equal to or less than the first value A and metal powder having a particle size larger than the first value A. The metal powder having a particle size larger than the first value A is supplied again to the supply unit 11, pulverized again under the same conditions as when it was previously pulverized in the pulverization unit 12, and classified in the classification unit 13. This process is repeated until the particle size of all the metal powders becomes equal to or less than the first value A. As a result, in this step (S20), the particle size of all the metal powders becomes equal to or less than the first value A.

[0039] In this process (S20), first metal powder particles having a particle size equal to or smaller than a second value B that is smaller than the first value A are removed from all metal powder particles having a particle size equal to or smaller than a first value A, and second metal powder particles having a particle size equal to or larger than the second value B and equal to or smaller than the first value A are recovered.

[0040] In this step (S20), the particle size distribution of the metal powder after pulverization differs depending on the wire diameter distribution of the non-magnetic metal wires and the maximum length distribution of the non-magnetic metal plates in the metal mixture before pulverization. As described above, the wire diameter distribution of the non-magnetic metal wires and the maximum length distribution of the non-magnetic metal plates in the metal mixture before pulverization differ depending on the type of non-magnetic metal, and therefore the particle size distribution of the metal powder after pulverization also differs depending on the type of non-magnetic metal.

[0041] Non-magnetic metal wires are easily cut in the wire length direction after the pre-pulverization mass disintegrates, so repeated pulverization gradually shortens the wire length and turns them into powder. It has been confirmed that non-magnetic metal plates gradually become finer and more linear in shape as they are repeatedly pulverized, and that further repeated pulverization gradually shortens the wire length and turns them into powder. Therefore, with regard to the particle size of the metal powder after pulverization, it is thought that the particle size of the metal powder derived from the non-magnetic metal wire depends on the wire diameter before pulverization, and the particle size of the metal powder derived from the non-magnetic metal plate depends on the maximum length before pulverization.

[0042] The first metal powder is a mixture of powders obtained by crushing non-magnetic metal wires with relatively small wire diameters among the multiple types of non-magnetic metal wires contained in the metal mixture. The first metal powder is a mixture of powders obtained by crushing enameled wire and powders obtained by crushing stainless steel wire. The second metal powder is a mixture of powders obtained by crushing non-magnetic metal wires with relatively large wire diameters among the multiple types of non-magnetic metal wires contained in the metal mixture and powders obtained by crushing non-magnetic metal plates with relatively long maximum lengths. The second metal powder is a mixture of powders obtained by crushing copper wire (copper powder) and powders obtained by crushing aluminum plates (aluminum powder).

[0043] In the metal recycling method according to this embodiment, thirdly, third metal powder particles having a particle size equal to or greater than the third value C are removed from the second metal powder formed in the previous step (S20) using a sieve, and fourth metal powder particles having a particle size greater than the second value B but less than the third value C are recovered (step (S30)). The third value C is greater than the second value B and less than the first value A. The sieve used in this step (S30) is, for example, an ultrasonic vibration sieve.

[0044] The third metal powder, which has a relatively large particle size among the second metal powders, is a powder obtained by pulverizing non-magnetic metal plates whose maximum length is longer than the wire diameter of other non-magnetic metal wires among the multiple types of non-magnetic metal bodies contained in the metal mixture. The third metal powder is aluminum powder. The fourth metal powder, which has a relatively small particle size among the second metal powders, is a mixture of powders obtained by pulverizing non-magnetic metal wires whose wire diameter is relatively large among the multiple types of non-magnetic metal wires contained in the metal mixture. The fourth metal powder is copper powder.

[0045] The first value A and second value B used in the above step (S20), and the third value C used in the above step (S30) are set according to the diameter distribution of the non-magnetic metal wires and the maximum length distribution of the non-magnetic metal plates so as to increase the recovery rate of metal powder consisting of a specific type of non-magnetic metal body from multiple types of non-magnetic metal bodies contained in the recycled plastics.

[0046] When the non-magnetic metal bodies contained in the recovered plastics are copper wire, enameled wire, stainless steel wire, or aluminum plate, the first value A is preferably set to 1 mm or less. If the first value A is greater than 1 mm, metal lumps not broken down in the supply unit 11 will be more likely to be discharged to the classifier 13 without being broken down in the crusher 12. Preferably, the first value A is 500 μm or more. If the first value A is less than 500 μm, the total metal powder will be too fine, making classification in the classifier 13 difficult.

[0047] When the non-magnetic metal bodies contained in the recycled plastics are copper wire, enameled wire, stainless steel wire, and aluminum plate, and the first value A is 1 mm, the second value B is preferably set to 45 μm or greater. If the second value B is less than 45 μm, the fourth metal powder having a particle size larger than the second value B will contain a large amount of Cu powder formed by crushing enameled wire and Fe powder formed by crushing stainless steel wire, resulting in a lower weight ratio of Cu powder formed by crushing copper wire in the fourth metal powder. Preferably, the second value B is less than 200 μm. If the second value B is greater than 200 μm, the weight ratio of Cu powder formed by crushing copper wire in the fourth metal powder will increase, but the yield will decrease.

[0048] When the non-magnetic metal bodies contained in the recycled plastics are copper wire, enameled wire, stainless steel wire, and aluminum plate, and the first value A is 1 mm, the third value C is preferably 500 μm or less. When the third value C is greater than 500 μm, a large amount of Al powder formed by crushing aluminum plate is contained in the fourth metal powder having a particle size less than the third value C, resulting in a decrease in the weight ratio of Cu powder formed by crushing copper wire in the fourth metal powder. Preferably, the third value C is 350 μm or greater. When the third value C is less than 350 μm, the weight ratio of Cu powder formed by crushing copper wire in the fourth metal powder increases, but the yield decreases.

[0049] The above-mentioned tendencies regarding the first value A, the second value B, and the third value C are derived from the results of an evaluation test of a copper powder regeneration method, which will be described later.

[0050] As described above, the metal recycling method according to the present embodiment allows a specific type of non-magnetic metal body to be recycled as metal powder from a metal mixture containing multiple types of non-magnetic metal bodies. As an example, the metal recycling method according to the present embodiment allows copper powder to be recycled from a metal mixture containing copper wire, enameled wire, stainless steel wire, and aluminum plate.

[0051] The inventors noticed that the shape distributions (wire diameter distribution and maximum length distribution) of the multiple types of non-magnetic metal wires and non-magnetic metal plates contained in recycled plastics are different from each other, and discovered that the particle size distributions of the powders of each non-magnetic metal obtained by crushing these mixtures are different from each other due to differences in the shape distributions before crushing, and that as a result, metal powders consisting of specific types of non-magnetic metals can be selected and recovered.

[0052] The inventors have confirmed that the recovery rate of metal powder made from a specific type of non-magnetic metal can be increased by appropriately setting the first value A, the second value B, and the third value C according to the diameter distribution of multiple types of non-magnetic metal wires and the maximum length distribution of non-magnetic metal plates contained in recovered plastics. Details will be described later.

[0053] <Evaluation test of copper powder regeneration method> In this evaluation test, the effectiveness of one example of each combination of the first value A, the second value B, and the third value C in the metal recycling method according to this embodiment was evaluated. In this evaluation test, the first value A was 1 mm, the second value B was 45 μm, and the third value C was 500 μm.

[0054] First, a metal mixture containing only copper wire, enameled wire, stainless steel wire, and aluminum plate was prepared through steps (S11) to (S13). The metal mixture was separated using a sieve with a mesh size of 3.5 mm or more and 15.0 mm or less. The mesh size conformed to the JIS standard (JIS Z 8801-1).

[0055] The weight ratios of the copper wire, enameled wire, and stainless steel wire contained in the metal mixture were measured using a digital balance after confirming the composition with an X-ray fluorescence analyzer. As shown in Table 1, the metal mixture contained 80 wt% copper wire, 3 wt% enameled wire, 6 wt% stainless steel wire, and 11 wt% aluminum plate.

[0056] [Table 1]

[0057] The wire diameter distribution of the copper wire, enameled wire, and stainless steel wire contained in the metal mixture, as well as the maximum length distribution of the aluminum plate contained in the metal mixture, were measured using a digital micrometer and vernier calipers. Figures 3 to 6 show the measurement results. The horizontal axis of each of Figures 3 to 5 represents the wire diameter (unit: μm) of the copper wire, enameled wire, and stainless steel wire, and the vertical axis of each of Figures 3 to 5 represents the abundance ratio (frequency) of each wire diameter. The horizontal axis of Figure 6 represents the maximum length (unit: μm) of the aluminum plate, and the vertical axis of Figure 6 represents the abundance ratio (frequency) of each maximum length. The wire diameter of the copper wire contained in the metal mixture was 70 μm or more and 800 μm or less, the wire diameter of the enameled wire was 80 μm or more and 800 μm or less, the wire diameter of the stainless steel wire was 150 μm or more and 900 μm or less, and the maximum length of the aluminum plate was 10,000 μm or more and 25,000 μm or less.

[0058] As shown in Figure 3, the copper wires contained in the metal mixture included one group with a wire diameter of less than 450 μm and one group with a wire diameter of greater than 650 μm. Furthermore, among the copper wires in the group with a wire diameter of less than 450 μm, the wire diameters were distributed relatively uniformly across each class. The average diameter of the copper wires was approximately 320 μm.

[0059] In contrast, the diameter distribution of the enameled wires shown in Figure 4 confirmed that the diameters of the enameled wires were distributed unevenly within a relatively narrow range of 250 μm or less. The average diameter of the enameled wires was approximately 230 μm. The diameter distribution of the stainless steel wires shown in Figure 5 confirmed that the diameters of the stainless steel wires were distributed unevenly within a relatively narrow range of 200 μm or less. The average diameter of the stainless steel wires was approximately 240 μm.

[0060] As shown in FIG. 6, the maximum length of the aluminum plates was distributed widely from less than 12,000 μm to 24,000 μm or less, but the average value of the maximum length of the aluminum plates was approximately 16,000 μm.

[0061] Next, according to the above step (S20), the metal mixture was vibrated using a hopper HLF-30 as the supply section to break up the metal blocks, and then the metal mixture was pulverized using a cutter mill VM-22 equipped with a screen as the pulverization section. The rotary blade was a blunt blade made of cemented carbide. The rotation speed of the rotary blade was 1000 rpm. The clearance between the rotary blade and the inner wall of the pulverization section was 0.5 mm. The opening shape of each hole in the screen was round, and the hole diameter (opening) of the screen was 1 mm.

[0062] While pulverization was performed under the above conditions, the metal powder that passed through the screen was classified using an ultrasonic vibration sieve machine CB50UR-1S as the classification section. Here, the second value B was set to 45 μm. Specifically, of the metal powder that passed through the screen, the first metal powder with a particle size of 45 μm or less was removed. Furthermore, the metal powder that did not pass through the screen and had a particle size of more than 1 mm was returned to the supply section and subjected to the vibration, pulverization, and classification described above in that order. This series of procedures was repeated until all the metal powder had passed through the screen.

[0063] Next, according to the above step (S30), an ultrasonic vibration sieve CB50UR-1S was used to remove the third metal powder having a particle size of 500 μm or more from the second metal powder having a particle size of greater than 45 μm classified as described above, and the fourth metal powder having a particle size of less than 500 μm was sorted and recovered.

[0064] Next, the purities of Cu, Al, and iron (Fe) for each of the first, third, and fourth metal powders obtained as described above were measured using an X-ray fluorescence analyzer. Specifically, 0.5 g of each of the first, third, and fourth metal powders was sampled, and the weight ratios of Cu, Al, and Fe in each sampled metal powder were measured using the X-ray fluorescence analyzer. In addition to Cu, Al, and Fe, each metal powder contained less than 0.1 wt% of manganese (Mn), nickel (Ni), cobalt (Co), zinc (Zn), barium (Ba), tin (Sn), chromium (Cr), titanium (Ti), calcium (Ca), and vanadium (V). However, these elements were ignored, and the weight ratios of Cu, Al, and Fe were calculated assuming the sum of the weights of Cu, Al, and Fe to be 100%.

[0065] Furthermore, using the results of measuring the particle size distribution of the metal powder obtained when copper wire and enameled wire were separately pulverized, the weight ratio of Cu powder attributable to the copper wire and the weight ratio of Cu powder attributable to the enameled wire were estimated from the calculated weight ratio of Cu. Note that the particle size of the metal powder obtained by pulverizing copper wire alone was generally larger than the particle size of the metal powder obtained by pulverizing enameled wire alone. This is thought to be due to the fact that, as mentioned above, the average wire diameter of the copper wire before pulverization was larger than the average wire diameter of the enameled wire before pulverization.

[0066] The calculated weight ratio of Al was taken as the weight ratio of Al powder originating from the aluminum plate, and the calculated weight ratio of Fe was taken as the weight ratio of Fe powder originating from the stainless steel wire.

[0067] The calculation results are shown in Table 2.

[0068] [Table 2]

[0069] As shown in Table 2, the weight ratio of Cu powder estimated to be caused by the copper wire in the fourth metal powder was 92%, which was about 10% higher than the weight ratio of the copper wire in the metal mixture before milling and the weight ratio of Cu powder estimated to be caused by the copper wire in the first metal powder and the third metal powder. Furthermore, Cu powder estimated to be caused by the enameled wire was measured only in the first metal powder, and not in the third metal powder and the fourth metal powder (i.e., the second metal powder).

[0070] Furthermore, as shown in Table 2, Fe powder was measured only in the first metal powder and the third metal powder, but not in the fourth metal powder. Al powder was measured in each of the first metal powder, the third metal powder, and the fourth metal powder, but the weight ratio of Al powder in the fourth metal powder was lower than the weight ratios of Al powder in the first metal powder and the third metal powder.

[0071] From the results shown in Figures 3 to 6 and Tables 1 and 2, it was confirmed that when the metal recycling method of this embodiment is carried out with the first value A set to 1 mm, the second value B set to 45 μm, and the third value C set to 500 μm, the fourth metal powder has the lowest weight ratio of Cu powder estimated to be caused by the enamel wire, Fe powder estimated to be caused by the stainless steel wire, and Al powder estimated to be caused by the aluminum plate, and the highest weight ratio of Cu powder estimated to be caused by the copper wire, compared to the first metal powder and the third metal powder.

[0072] The reasons for the above test results are considered as follows. First, in step (S20), the nonmagnetic metal wires in the metal mixture are pulverized under the same conditions, so that the particle size distribution of the metal powder obtained by pulverizing the nonmagnetic metal wires is approximately the same as the diameter distribution of the nonmagnetic metal wires before pulverization. Therefore, based on the diameter distributions of the nonmagnetic metal wires shown in Figures 3 to 5, the particle size distributions of the Cu powder obtained by pulverizing the enameled wire in step (S20) and the Fe powder obtained by pulverizing the stainless steel wire are biased toward a relatively narrow range, unlike the particle size distribution of the Cu powder obtained by pulverizing the copper wire. In particular, under pulverization conditions where the first value A is 1 mm, the particle size distributions of the Cu powder obtained by pulverizing the enameled wire and the Fe powder obtained by pulverizing the stainless steel wire are biased toward a narrow range of 45 μm or less. As a result, under the crushing conditions where the first value A is 1 mm, by setting the second value B to 45 μm, the weight ratio of Cu powder formed by crushing enameled wire and Fe powder formed by crushing stainless steel wire in the second metal powder (third metal powder and fourth metal powder) recovered as having a particle size larger than the second value B can be sufficiently reduced.

[0073] Furthermore, aluminum exists in the metal mixture as plates, and its maximum length is significantly larger than the diameter of the nonmagnetic metal wire. Therefore, in the above step (S20), the particle size of the Al powder obtained by pulverizing the aluminum plate is larger than the particle size of the metal powder obtained by pulverizing each nonmagnetic metal wire. In particular, under pulverization conditions in which the first value A is 1 mm, the particle size distribution of the Al powder is biased toward a range greater than 500 μm. As a result, under pulverization conditions in which the first value A is 1 mm, by setting the third value C to 500 μm, the weight ratio of the Al powder obtained by pulverizing the aluminum plate in the fourth metal powder recovered as having a particle size less than the third value C can be sufficiently reduced.

[0074] The purity (weight ratio) of Cu powder in the fourth metal powder regenerated from the metal mixture by the metal regeneration method according to this embodiment is high. Therefore, the metal regeneration method according to this embodiment does not require the copper refining process to increase the purity of copper, which is commonly performed in methods of recovering copper from recycled plastics. Because the copper refining process requires a large amount of energy, when copper powder is regenerated by the metal regeneration method according to this embodiment, energy savings can be achieved compared to conventional recovery methods that involve a copper refining process.

[0075] Furthermore, as described above, the Cu powder in the fourth metal powder recycled from the metal mixture by the metal recycling method according to this embodiment has a high purity (weight ratio) and is composed solely of Cu powder obtained by crushing copper wire, and is separated from Cu powder obtained by crushing enameled wire. Therefore, the Cu powder in the fourth metal powder is suitable as an antibacterial material. In particular, when the fourth metal powder is added as an antibacterial material to a plastic resin to obtain a metal powder-containing resin molded body, the antibacterial activity of the molded body depends on the purity and particle size of the Cu powder in the fourth metal powder. A fourth metal powder containing high-purity, fine Cu powder is suitable as an antibacterial agent.

[0076] The antibacterial activity of Al powder and Fe powder (for example, minimum inhibitory concentration of Salmonella typhi) is about 1 / 100th that of Cu powder made from crushed copper wire. Furthermore, the antibacterial activity of Cu powder made from crushed enameled wire is inferior to that of Cu powder made from crushed copper wire because its surface is coated with an enamel film. A fourth metal powder that contains almost no Al powder, Fe powder, or Cu powder made from crushed enameled wire, but contains high-purity Cu powder made from crushed copper wire, is suitable for use as an antibacterial material.

[0077] In order to enhance the antibacterial activity of the Cu powder, the particle size of the Cu powder is preferably 1 mm or less. Since the particle size of the Cu powder in the fourth metal powder is 500 μm or less, the antibacterial activity of the Cu powder in the fourth metal powder is high.

[0078] <Method of manufacturing metal powder-containing resin molded body> The method for manufacturing a metal powder-containing resin molded body according to this embodiment includes a step of preparing the fourth metal powder recycled and recovered in the above-mentioned step (S30) of the metal recycling method according to this embodiment, and a step (S40) of melting and kneading the fourth metal powder with a thermoplastic resin and then molding the resultant.

[0079] In the molding step (S40), the weight ratio of the fourth metal powder in the kneaded product of the fourth metal powder and the thermoplastic resin may be 30% or more. In this case, the thermoplastic resin is prepared as a powder. The molding method may be any molding method, such as extrusion molding or injection molding.

[0080] In addition, in the molding step (S40), if the weight ratio of the fourth metal powder in the mixture of the fourth metal powder and the thermoplastic resin is 20% or less, the thermoplastic resin can be prepared in any shape such as powder, chips, or pellets.

[0081] The metal powder-containing resin molded article is suitable for an antibacterial member that contains the fourth metal powder as an antibacterial material. (Variation) In the metal recycling method according to the present embodiment, the starting material is a metal mixture containing copper wire, enameled wire, stainless steel wire, and aluminum plate, but the starting material is not limited to the above metal mixture. The metal mixture may contain at least a plurality of first metal wires and a plurality of second metal wires.

[0082] In the diameter distribution of the first metal wires, the maximum diameter D50 of 50% of the first metal wires may be larger than the maximum diameter D75 of 75% of the second metal wires in the diameter distribution of the second metal wires. For example, the first metal wires may be copper wires, and the second metal wires may be enameled wires or stainless steel wires. In the distribution values ​​shown in FIGS. 3 and 4, the maximum diameter D50 of the copper wire (290 μm) is larger than the maximum diameter D75 of the enameled wire (283 μm). In addition, in the distribution values ​​shown in FIGS. 3 and 5, the maximum diameter D50 of the copper wire is larger than the maximum diameter D75 of the stainless steel wire (266 μm).

[0083] In the pulverizing step (S20), the plurality of first metal wires and the plurality of second metal wires are pulverized under the same conditions. If the hardness of the first metal constituting the plurality of first metal wires and the second metal constituting the plurality of second metal wires is softer than the hardness of the hammer or cutter blade used for pulverization, as described above, the particle size of the metal powder obtained by pulverizing each of the plurality of first metal wires and the plurality of second metal wires depends on the wire diameter of each metal wire before pulverization. Therefore, if the maximum wire diameter D50 of the first metal wire is larger than the maximum wire diameter D75 of the second metal wire, by pulverizing the first metal wire and the second metal wire under the same conditions, the maximum particle size d50 of the metal powder obtained by pulverizing the first metal wire will be larger than the maximum particle size d75 of the metal powder obtained by pulverizing the second metal wire.

[0084] As a result, as described above, by appropriately setting the values ​​of the first value A, the second value B, and the third value C according to the wire diameter distribution of each of the first metal wire and the second metal wire, it is possible to efficiently recover metal powder obtained by pulverizing the first metal wire.

[0085] Specifically, the first value A and the third value C are set to values ​​larger than the maximum wire diameter D50 of the first metal wire. The second value B is set to a value larger than the maximum particle size d75 of the metal powder obtained by pulverizing the second metal wire and smaller than the maximum particle size d50 of the metal powder obtained by pulverizing the first metal wire. In this way, as described above, it is possible to regenerate metal powder in which the weight ratio of the metal powder obtained by pulverizing the first metal wire is 90% or more, using a metal mixture including the first metal wire and the second metal wire as a starting material.

[0086] Although the embodiments of the present disclosure have been described above, the above-described embodiments can be modified in various ways. Furthermore, the scope of the present disclosure is not limited to the above-described embodiments. The scope of the present disclosure is defined by the scope of the claims, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0087] 10. Crusher, 11. Feeding section, 12. Crushing section, 13. Classifying section.

Claims

1. A step of preparing a metal mixture including a mixture of multiple types of metal bodies having different shape distributions; milling the metal mixture into metal powder; In the pulverizing step, particle sizes of all the metal powders are set to a first value or less, and first metal powders having particle sizes of a second value or less that is smaller than the first value are removed from all the metal powders, and second metal powders having particle sizes of a second value or more that is larger than the second value and is smaller than the first value are recovered, a step of removing a third metal powder having a particle size equal to or greater than a third value from the second metal powder, and recovering a fourth metal powder having a particle size equal to or greater than the second value and less than the third value, The method for regenerating metals, wherein the third value is greater than the second value and less than the first value.

2. the plurality of types of metal bodies include a first non-magnetic metal wire, a second non-magnetic metal wire, and a third non-magnetic metal plate; the preparing step includes a step of recovering the metal mixture from a mixture including the first non-magnetic metal wire, the second non-magnetic metal wire, the third non-magnetic metal plate, and plastic pieces by centrifugal separation; In the metal mixture, the first non-magnetic metal wire, the second non-magnetic metal wire, and the third non-magnetic metal plate are entangled with each other, In the pulverizing step, the metal mixture is pulverized into the metal powder by a pulverizing unit that applies an impact force and a shear force to the metal mixture, The metal recycling method described in claim 1, wherein the Vickers hardness of each of the material constituting the first non-magnetic metal wire, the material constituting the second non-magnetic metal wire, and the material constituting the third non-magnetic metal plate is lower than the Vickers hardness of the material constituting the crushed portion.

3. the mixture includes a coated metal wire having a core wire made of a non-magnetic metal and a plastic coating covering the surface of the core wire, 3. The method for recycling metals according to claim 2, wherein the preparing step further comprises the step of removing the coated metal wire from the mixture based on a color observed when the mixture is irradiated with visible light.

4. 4. The method for recycling metals according to claim 3, wherein the first value is 1 mm or less and the second value is 45 μm or more.

5. The method for regenerating metals according to claim 4, wherein the third value is 500 μm or less.

6. the plurality of types of metal bodies include a plurality of first metal wires and a plurality of second metal wires; a Vickers hardness of a material constituting the plurality of first metal wires and a material constituting the plurality of second metal wires is lower than a Vickers hardness of a material constituting a pulverizing section used to pulverize the metal mixture in the pulverizing step; a maximum wire diameter D50 that 50% of the first metal wires fall below in the wire diameter distribution of the plurality of first metal wires is larger than a maximum wire diameter D75 that 75% of the second metal wires fall below in the wire diameter distribution of the plurality of second metal wires; The metal recycling method according to claim 1 , wherein in the pulverizing step, each of the plurality of first metal wires and the plurality of second metal wires is pulverized.

7. each of the plurality of first metal wires is a copper wire; each of the plurality of second metal wires is an enameled wire or a stainless steel wire; the first metal powder is a powder obtained by pulverizing at least one of the enameled wire and the stainless steel wire, The metal recycling method according to claim 6 , wherein the fourth metal powder is copper powder obtained by pulverizing the copper wire.

8. the plurality of types of metal bodies include copper wire, enameled wire, stainless steel wire, and aluminum plate; The wire diameter of the copper wire is 70 μm or more and 800 μm or less, The wire diameter of the enameled wire is 80 μm or more and 800 μm or less, The wire diameter of the stainless steel wire is 150 μm or more and 900 μm or less, The maximum length of the aluminum plate is 10,000 μm or more and 25,000 μm or less, The metal recycling method according to any one of claims 1 to 7, wherein the fourth metal powder is copper powder obtained by pulverizing the copper wire.

9. A step of preparing the fourth metal powder recovered in the recovering step of the metal regeneration method according to any one of claims 1 to 8; a step of melting and kneading the fourth metal powder and a thermoplastic resin, and then molding the mixture.

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