Process for removing resin applied to the surface of neodymium-iron-boron magnets

Abstract

The present invention relates to a process for removing resin (42) applied to the surface of Neodymium-lron-Boron (NdFeB) magnets (30), comprising the steps of: a) heating the magnets to a resin change-of-state temperature and maintaining said temperature for a predetermined heating time; b) stirring the heated magnets in an aqueous ammonia solution to provoke impacts and / or friction between said magnets, for a predetermined treatment time, wherein the ratio between the volume of the aqueous ammonia solution and the mass of the magnets is comprised between 0.5 1 / kg and 100 1 / kg; c) separating the magnets from the aqueous ammonia solution and rinsing said magnets with washing water to remove any ammonia and / or resin residues from the surface of the magnets. The process of the present invention has the advantage of being capable of completely removing resin applied to the surface of NdFeB magnets.

Description

[0001] Process for removing resin applied to the surface of neodymium-iron-boron magnets

[0002] Field of the invention

[0003] The present invention relates to a process for removing resin applied to the surface of Neodymium-Iron-Boron (NdFeB) magnets.

[0004] Prior art

[0005] The coating of the surface of a magnet with resin, particularly the coating of the surface of a Neodymium-Iron-Boron (NdFeB) magnet with resin, is a widely used practice in various industrial sectors. Coating with resin actually enhances chemical resistance, and especially by preventing oxidation (rust formation) of the thus coated magnets. Moreover, coating with adhesive resin allows the coated magnets to be adhered to various devices, such as for example an electric motor or an electronic device like an HDD (an electromechanical device composed of moving machinery in which data or information is magnetically stored).

[0006] However, when these coated magnets need to be disposed of, for example, recycled through grinding, the presence of surface resin poses a problem. By their nature, resins are chemically rich in carbon (C), therefore due to this high carbon content, if coated magnets were recycled as is, without first undergoing a resin removal process, they would be unusable as secondary raw material for the production of new NdFeB magnets. The high carbon content introduced by the resin particles into the new magnet obtained from recycling the coated magnet would significantly reduce the magnetic properties of the new magnet, rendering it either unusable or poorly performing. For this reason, it is essential to pretreat coated NdFeB magnets to remove the resin from their surface before proceeding with the various recycling process stages.

[0007] As known to the expert in the art, the coating resins used on NdFeB magnets can either be adhesive resins or protective resins.

[0008] The known techniques for removing or reducing the amount of adhesive or protective resin from the surface of NdFeB magnets are two: manual sandblasting and the HPMS process (hydrogen decrepitation of permanent magnet scraps) followed by a sieving phase.

[0009] The sandblasting technique involves manually removing the resin coating with a sandblaster, the resin being removed due to the abrasive action of sand impacting at high speed against the resin. However, this technique requires a large amount of time, making it impractical on a large scale and economically inefficient.

[0010] The HPMS process, followed by sieving, involves treating resin-coated magnets with hydrogen. The hydrogen reacts with the magnets through a hydrogen decrepitation reaction, leading to demagnetization and pulverization of the magnets. Therefore, the reaction between the magnets and hydrogen to occur, the magnetic matrix must be accessible to the hydrogen, which requires the resin coating to be damaged or partially removed to allow hydrogen penetration. Subsequently, the resulting powder is ground using jet milling to further reduce the size of the magnet particles. Being inherently more brittle than the resin coating, the magnet forms smaller particles upon pulverization compared to the coat resin particles. Leveraging this differing physical characteristic, the subsequent sieving phase separates the magnet particles from the resin particles. However, this technique cannot reduce the resin content to levels that yield a high-quality final product. The study "The extraction of NdFeB magnets from automotive scrap rotors using hydrogen " from 2020 describes that the sieved powder contains approximately 1500 ppm of carbon, whereas, as known to the expert in the art, a high-quality final product suitable for use as secondary raw material for new magnet production requires a maximum carbon threshold of 1000 ppm.

[0011] The availability of a process capable of completely removing resin applied to the surface of Neodymium-Iron-Boron (NdFeB) magnets is therefore a pressing market need.

[0012] Summary of the invention

[0013] The object of the present invention is to provide a process capable of completely removing resin applied to the surface of Neodymium-Iron-Boron (NdFeB) magnets. This object is achieved by a process for removing resin applied to the surface of NdFeB magnets as outlined in the appended claims, whose definitions form an integral part of this description.

[0014] The invention will be better understood from the following detailed description of preferred embodiments, provided by way of example and not limitation, with reference to the accompanying figures, wherein:

[0015] -Figure 1 shows a non-limiting example of a reactor used in the process according to the present invention;

[0016] -Figure 2 shows magnets with adhesive resin, particularly terpenic resin, applied to their surface;

[0017] -Figure 3 shows the magnets of Fig. 2 after heating;

[0018] -Figure 4 shows the magnets of Fig. 3 after being treated with the aqueous ammonia solution, subjected to mechanical action, and rinsed with water;

[0019] -Figure 5 shows magnets with protective resin, particularly epoxy resin, applied to their surface;

[0020] -Figure 6 shows the magnets of Fig. 5 after heating;

[0021] -Figure 7 shows the magnets of Fig. 6 after being treated with the aqueous ammonia solution, and subjected to mechanical action, and rinsed with water.

[0022] In the accompanying figures, identical or similar elements are denoted by the same reference numerals.

[0023] Detailed description of the invention

[0024] A first object of the present invention is a process for removing resin applied to the surface of Neodymium-Iron-Boron (NdFeB) magnets, comprising the steps of: a) heating the magnets to a resin change-of-state temperature and maintaining said temperature for a predetermined heating time; b) stirring the heated magnets in an aqueous ammonia solution in order to provoke impacts and / or friction between said magnets, for a predetermined treatment time, wherein the ratio between the volume of the aqueous ammonia solution and the mass of the magnets is comprised between 0.5 1 / Kg and 1001 / Kg; c) separating the magnets from the aqueous ammonia solution and rinsing said magnets with washing water in order to remove any ammonia and / or resin residues from the surface of the magnets.

[0025] According to a preferred embodiment of the process of the present invention, the resin is preferably an adhesive resin and / or a protective resin. In the context of the present description and the appended claims, the term "adhesive resin" refers to a resin with adhesive properties, i.e., one that enhances the adhesion between two elements. In the context of the present description and the appended claims, the term "protective resin" refers to a resin intended to protect (from external agents) the element (in this case, the magnet) it coats.

[0026] According to a preferred embodiment of the process of the present invention, the step of heating the magnets is preferably carried out using a furnace.

[0027] In the context of the present description and the appended claims, the term "resin change-of- state temperature" refers to a temperature at which the resin undergoes a change of state, for example, transitioning from a solid state to a more liquid state (softening).

[0028] According to a preferred embodiment of the process of the present invention, between step a) and step b), the magnets are preferably allowed to cool to room temperature.

[0029] According to a preferred embodiment of the process of the present invention, the stirring action of step b) is preferably conducted manually by a human operator or mechanically with the aid of a mechanical stirrer, which, in turn, is either operated and controlled by a human operator or by a computerized program.

[0030] According to a preferred embodiment of the process of the present invention, the separation action of step c) is preferably conducted manually by a human operator or mechanically with the aid of a mechanical separator, which, in turn, is either operated and controlled by a human operator or by a computerized program. According to a preferred embodiment of the process of the present invention, the rinsing action of step c) is carried out with running washing water or by cyclically immersing and extracting the magnets from a washing water bath.

[0031] With reference to Figure 1, according to a preferred embodiment of the process of the present invention, step b) is preferably conducted in a reactor 10 (Figure 1 represents a preferred but non-limiting embodiment of the reactor 10) having an inner chamber 12 into which the aqueous ammonia solution is previously poured, wherein the inner chamber 12 is at least partially occupied by a basket 14 permeable to the aqueous ammonia solution, wherein the basket 14 is suitable for receiving said magnets, wherein the basket 14 is a rotating basket and step b) is conducted by rotating said basket 14 in order to provoke collisions between the magnets themselves and / or between the magnets and the walls of the basket 14.

[0032] According to a preferred embodiment of the process of the present invention, the inner chamber 12 preferably has a volume comprised between 100 dm3and 200 dm3, and even more preferably has a volume of 145 dm3.

[0033] According to a preferred embodiment of the process of the present invention, the action of pouring the aqueous ammonia solution into the inner chamber 12 is preferably conducted manually by a human operator or mechanically with the aid of a mechanical device, which, in turn, is either operated and controlled by a human operator or by a computerized program.

[0034] According to an alternative embodiment of the process of the present invention, the inner chamber is preferably entirely occupied by a basket permeable to the aqueous ammonia solution.

[0035] According to a preferred embodiment of the process of the present invention, the action of rotating the basket is preferably conducted manually by a human operator or mechanically with the aid of a mechanical device (even more preferably via a driving shaft), which, in turn, is either operated and controlled by a human operator or by a computerized program.

[0036] According to a preferred embodiment of the process of the present invention, the inner chamber 12 further preferably comprises at least one admission opening 16 at the basket 14; preferably, the reactor 10 also comprises a movable door 18 located at the admission opening 16. The door 18 is preferably attached to the reactor 10 via a hinge 20, which allows the door 18 to move between a closed configuration, in which the door 18 covers the admission opening 16 and isolates the inner chamber 12 from the external environment of the reactor 10, and an open configuration, in which the door 18 does not cover the admission opening 16, allowing the inner chamber 12 to communicate with the external environment of the reactor 10.

[0037] According to a preferred embodiment of the process of the present invention, the basket 14 preferably has a cylindrical shape and also comprises an admission opening at the admission opening 16 of the inner chamber 12. Preferably, the basket 14 is made of a mesh, grate, or membrane permeable to the aqueous ammonia solution.

[0038] According to a preferred embodiment of the process of the present invention, the aqueous ammonia solution fills half of the basket 14, and the basket 14 rotates while partially immersed in the solution. The rotational motion is preferably transmitted to the basket 14 via a driving shaft that transmits the rotation of an electric motor. Preferably, three idler rollers keep the basket 14 in position within the inner chamber 12 and facilitate its rotation of the basket (the three idler rollers are preferably fixed, freely rotating cylinders).

[0039] According to a preferred embodiment of the process of the present invention, the reactor 10 also preferably includes an agitator device arranged in the inner chamber and / or in the basket. Preferably, the agitator device is adapted to increases the number of impacts occurring between the magnets and / or between the magnets and the walls of the basket 14. Non-limiting preferred embodiments of the agitator device include: a mechanical arm, a tilting or rotating platform, or a vibrating element.

[0040] According to a preferred embodiment of the process of the present invention, step b) also preferably includes stirring in the presence of solid bodies, inert to the aqueous ammonia solution, in free motion, to increase the number of impacts occurring between the magnets. Non-limiting preferred embodiments of the solid bodies include: spheres, balls, polygonal solids, or irregular polygonal solids. According to a preferred embodiment, the solid bodies are preferably placed inside the basket 14, and said solid bodies are free to move within the basket during its rotation, increasing the number of impacts occurring between the magnets.

[0041] According to a preferred embodiment of the process of the present invention, the inner surface of the basket preferably has asperities, and / or the surface of the solid bodies preferably has asperities. Preferably, the asperities are protrusions, which are preferably pyramidal, dome-shaped, or trapezoidal in form.

[0042] According to a preferred embodiment of the process of the present invention, step b) is preferably conducted for a predetermined treatment time ranging from 15 minutes to 6 hours, preferably from 15 minutes to 3 hours, and even more preferably from 30 minutes to 75 minutes. Step b) is preferably conducted at a basket 14 rotational speed ranging from 10 rpm to 40 rpm, more preferably from 20 rpm to 30 rpm.

[0043] According to a preferred embodiment of the process of the present invention, in step a), the resin change-of- state temperature is preferably between 300°C and 450°C, more preferably between 370°C and 410°C, and even more preferably 400°C.

[0044] According to a preferred embodiment of the process of the present invention, in step a), the predetermined heating time is preferably between 5 minutes and 60 minutes, and more preferably between 10 minutes and 15 minutes.

[0045] According to a preferred embodiment of the process of the present invention, the resin is preferably an adhesive resin, a protective resin, or mixtures thereof. Wherein preferably, the resin is selected from: epoxy resin, terpenic resin, cyanoacrylate resin, acrylic resin, silicone resin, anaerobic resin, polyurethane resin, or mixtures thereof. Even more preferably, the resin is an epoxy resin or a terpenic resin.

[0046] According to a preferred embodiment of the process of the present invention, the aqueous ammonia solution preferably has a concentration between 2% vol / vol and 30% vol / vol, expressed as a percentage relative to the volume of the aqueous ammonia solution, and more preferably has a concentration between 5% vol / vol and 10% vol / vol.

[0047] A preferred embodiment of the process of the present invention is described below. Preferably, the process according to the present invention comprises the steps of: heating the magnets in a furnace to a temperature between 300°C and 450°C (with an optimal temperature around 400°C) for a time period ranging from 5 minutes to 20 minutes (optimal range: 10-15 minutes), in order to demagnetize the magnets and partially burn the resin they are coated with. An amount of heated magnets, ranging from 5 kg to 50 kg (optimal amount: 30 kg), is placed in the basket 14 of the reactor 10. An aqueous ammonia solution having a concentration between 2% vol / vol and 30% vol / vol (optimal concentration: 5-10% vol / vol) is added to the basket 14. The basket 14 has a volume of 12 dm3, while the reactor has a volume of 145 dm3. Subsequently, the basket 14 (containing the magnets and the aqueous ammonia solution) is rotated to simulate a tumbling process. During this phase, the resin on the surface of the magnets is softened and partially dissolved by the ammonia, and the rotational motion of the basket 14 causes the magnets to slide against one another, creating mechanical friction that helps remove the resin from the surface of the magnets. The detached resin settles at the bottom of the inner chamber 12 of the reactor 10. The treatment times for this phase range from 15 minutes to 3 hours (optimal range: 30-75 minutes). The rotational speed of the reactor ranges from 10 rpm to 40 rpm (optimal range: 20-30 rpm). The process according to the present invention is based on three principles: thermal treatment to soften, bum, or weaken the resin and make it more reactive to the aqueous ammonia solution; a chemical reaction between the aqueous ammonia solution and the resin, this reaction softens the resin, facilitating its removal from the magnets' surface; mechanical action generated by the rotation of the basket 14, causing impacts and friction between the magnets and between the magnets and the walls of the basket 14, this mechanical action allows for the detachment of the resin from the surface of the magnets. At the end of the process, the resin is suspended in the aqueous ammonia solution as coarse particles, partially deposited at the bottom of the inner chamber 12 and partially suspended within the solution, facilitating the removal of these resin particles through filtration. Once filtered, the aqueous ammonia solution can be reused. The magnets are rinsed with water at the end of the process to remove the aqueous ammonia solution and the dissolved resin. Advantageously, the process according to the present invention is practically a liquid-waste- free process, except for very small amounts.

[0048] Advantageously, ammonia (aqueous ammonia solution) is a reagent capable of significantly softening the aforementioned resins, and additionally, it does not react with the magnet. It is a very economical reagent and not extremely toxic or corrosive.

[0049] Advantageously, the process according to the present invention is capable of completely removing resin applied to the surface of Neodymium-Iron-Boron (NdFeB) magnets.

[0050] Examples

[0051] With reference to Figures 2 to 7, the following are some preferred embodiments of the present invention, provided wherein as illustrative and non-limiting examples.

[0052] Example 1 : Process for removing adhesive resin (terpenic resin) applied to the surface of Neodymium-Iron-Boron (NdFeB) magnets.

[0053] 30 kg of magnets coated with adhesive resin (terpenic resin) (Figure 2, reference numeral 30 corresponds to the magnets, while reference numeral 40 corresponds to the adhesive resin) were placed inside a furnace and heated to a temperature of 400°C for a duration of 12 minutes. In Figure 3, the magnets after being heated are shown (reference numeral 30 corresponds to the magnets, while reference numeral 42 corresponds to the adhesive resin after the heating phase). The magnets were allowed to cool and were placed inside the basket 14 of the reactor 10. An aqueous ammonia solution with a concentration of 7% vol / vol was added to the basket 14. The basket 14 has a volume of 12 dm3, while the reactor has a volume of 145 dm3. Subsequently, the basket 14 (containing the magnets and the aqueous ammonia solution) was rotated to simulate a tumbling process. This phase was conducted for 60 minutes. The rotational speed of the reactor was set to 25 rpm. The magnets were extracted from the basket 14, and the aqueous ammonia solution was filtered to remove resin particles. The magnets were rinsed with water to wash off the aqueous ammonia solution and the dissolved resin. In Figure 4, the magnets are shown after being treated with the aqueous ammonia solution and mechanical action and after being rinsed with water (reference numeral 30 corresponds to the magnets).

[0054] Example 2: Process for removing protective resin (epoxy resin) applied to the surface of Neodymium-Iron-Boron (NdFeB) magnets.

[0055] 30 kg of magnets coated with protective resin (epoxy resin) (Figure 5, reference numeral 50 corresponds to the protective resin) were placed inside a furnace and heated to a temperature of 400°C for a duration of 12 minutes. In Figure 6, the magnets after being heated are shown (reference numeral 52 corresponds to the protective resin after the heating phase). The magnets were allowed to cool and were placed inside the basket 14 of the reactor 10. An aqueous ammonia solution with a concentration of 7% vol / vol was added to the basket 14. The basket 14 has a volume of 12 dm3, while the reactor has a volume of 145 dm3. Subsequently, the basket 14 (containing the magnets and the aqueous ammonia solution) was rotated to simulate a tumbling process, this phase was conducted for 60 minutes. The rotational speed of the reactor was set to 25 rpm. The magnets were extracted from the basket 14, and the aqueous ammonia solution was filtered to remove resin particles. The magnets were rinsed with water to wash off the aqueous ammonia solution and the dissolved resin. In Figure 7, the magnets are shown after being treated with the aqueous ammonia solution and mechanical action and after being rinsed with water (reference numeral 30 corresponds to the magnets).

Claims

CLAIMS1. Process for removing resin applied to the surface of Neodymium-Iron-Boron (NdFeB) magnets comprising the steps of: a) heating the magnets to a resin change-of- state temperature and maintaining this temperature for a predetermined heating time; b) stirring the heated magnets in an aqueous ammonia solution in order to provoke impacts and / or friction between said magnets, for a predetermined treatment time, wherein the ratio between the volume of the aqueous ammonia solution and the mass of the magnets is comprised between 0.5 1 / Kg and 1001 / Kg; c) separating the magnets from the aqueous ammonia solution and rinsing said magnets with washing water in order to remove any ammonia and / or resin residue from the surface of the magnets.

2. Process according to claim 1, wherein step b) is conducted in a reactor having an inner chamber into which the aqueous ammonia solution is previously poured, wherein the inner chamber is at least partially occupied by a basket permeable to the aqueous ammonia solution, wherein the basket is suitable for receiving said magnets, wherein the basket is a rotating basket and step b) is conducted by rotating said basket in order to provoke collisions between said magnets and / or collisions between the magnets and the walls of the basket.

3. Process according to claim 2, wherein the reactor further comprises an agitator device arranged in the inner chamber and / or in the basket.

4. Process according to any one of claims 1 to 3, wherein step b) further comprises stirring in the presence of solid bodies, inert to the aqueous ammonia solution, in free motion, so as to increase the number of collisions occurring between the magnets.

5. Process according to claim 2, wherein an inner surface of the basket has asperities; or according to claim 4, wherein the surface of the solid bodies has asperities.

6. Process according to claim 1 or 2, wherein step b) is conducted for a predeterminedtreatment time comprised between 15 minutes and 6 hours, preferably comprised between 15 minutes and 3 hours, even more preferably comprised between 30 minutes and 75 minutes.

7. Process according to any one of claims 1 to 6, wherein in step a) the resin change-of- state temperature is comprised between 300°C and 450°C, preferably is comprised between 370°C and 410°C, and even more preferably is 400°C.

8. Process according to any one of claims 1 to 7, wherein in step a) the predetermined heating time is comprised between 5 minutes and 60 minutes, and preferably is comprised between 10 minutes and 15 minutes.

9. Process according to any one of claims 1 to 8, wherein the resin is an adhesive resin or a protective resin or mixtures thereof, wherein preferably the resin is selected from: epoxy resin, terpenic resin, cyanoacrylate resin, acrylic resin, silicone resin, anaerobic resin, polyurethane resin, or mixtures thereof.

10. Process according to any one of claims 1 to 9, wherein the aqueous ammonia solution has a concentration comprised between 2% vol / vol and 30% vol / vol, the % being expressed relative to the volume of the aqueous ammonia solution, and preferably has a concentration comprised between 5% vol / vol and 10% vol / vol.