Multilayer adhesive diffusion source and method of making and use thereof

Abstract

The application discloses a multilayer adhesive diffusion source and a preparation method and application thereof. The preparation steps comprise the following steps: mixing heavy rare earth element powder, an organic polymer solution, a binder and an antioxidant according to proportions to obtain diffusion slurry; 20 wt.%-25 wt.% of polyimide is dissolved in the organic polymer solution; the diffusion slurry is roll-coated on a thermal spraying double-sided adhesive tape and dried to form a multilayer adhesive diffusion source; the thermal spraying double-sided adhesive tape comprises a protective film, a pressure-sensitive adhesive layer A, an adhesive base material and a pressure-sensitive adhesive layer B in sequence, the pressure-sensitive adhesive layer B is used for coating the diffusion slurry, the pressure-sensitive adhesive layer A is used for being attached to a sintered neodymium-iron-boron base body during operation, and a titanate coupling agent is contained in the pressure-sensitive adhesive layer. The multilayer adhesive diffusion source prepared by the method is convenient, safe and reliable to transport and store, is directly attached to a magnet surface during use, is simple to operate and does not need complicated equipment, the magnet obtained through diffusion has good performance consistency, a process flow is easy to control, and the method is suitable for batch production.

Description

Technical Field

[0001] This invention belongs to the field of rare earth permanent magnet material preparation technology, specifically relating to grain boundary diffusion modification technology of sintered NdFeB magnets, and particularly to a multilayer adhesive diffusion source, its preparation method and application. Background Technology

[0002] Sintered NdFeB magnets are widely used in industries such as electric vehicles, wind power generation, and 5G communications due to their excellent magnetic properties. To improve the coercivity and high-temperature stability of sintered NdFeB magnets, a common method is to add large amounts of heavy rare earth elements such as Dy or Tb. However, this method has some significant drawbacks: firstly, heavy rare earth elements exhibit antiferromagnetic coupling with iron atoms, leading to a decrease in the magnet's remanence and maximum energy product; secondly, heavy rare earth elements are limited in abundance and expensive, and adding large quantities significantly increases production costs.

[0003] To overcome these problems, grain boundary diffusion technology has emerged. Grain boundary diffusion forms a diffusion source on the magnet surface and, under high temperature conditions, allows heavy rare earth elements to diffuse along the grain boundaries into the magnet's interior, thereby improving the magnet's coercivity. Currently, the mainstream applications of grain boundary diffusion sources include: powder diffusion, which involves directly laying or coating heavy rare earth powder onto the magnet surface, requiring high temperatures for powder diffusion; slurry spraying / screen printing, which involves coating heavy rare earth slurry onto the magnet surface using spraying or screen printing equipment, requiring masks, specialized equipment (such as spray guns, screen printing machines, and drying equipment), and skilled operators, making the process cumbersome and unsuitable for flexible small-batch production; and vacuum coating, which forms a heavy rare earth thin film on the magnet surface through physical vapor deposition, but with high equipment costs. Furthermore, powder diffusion sources are prone to dust generation and scattering, and the slurry is prone to agglomeration and stratification, resulting in poor stability during transportation and storage, posing safety hazards. Uneven powder placement and fluctuating slurry coating thickness lead to large performance dispersion in the diffused magnet (typically with deviations exceeding ±10%). In summary, these methods generally suffer from low production efficiency, high cost, difficulty in adjusting the diffusion source, and complex equipment and process conditions, limiting their application in large-scale production. To address these issues, some researchers have fabricated diffusion sources in thin film form, attempting to solve the aforementioned technical problems. While this has yielded some improvements, the following technical drawbacks remain: Firstly, existing thin-film diffusion sources suffer from difficulties in achieving both uniformity and stability. The common resin slurry systems used (such as PVB and acrylates) have poor viscosity stability, easily leading to stratification and sedimentation, resulting in large fluctuations in heavy rare earth content and high product performance dispersion. Secondly, there is a contradiction between high-temperature diffusion behavior and interfacial bonding strength. Existing adhesives have wide and difficult-to-control thermal decomposition windows, easily decomposing prematurely and causing rare earth oxidation, or decomposing too late, resulting in high residual carbon levels and contaminating grain boundaries. Furthermore, the diffusion source and magnet surface are mostly physically adsorbed, easily warping and detaching during heating, forming poor local contact and severely affecting the uniformity of diffusion and deep penetration efficiency. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to address the shortcomings of the prior art by providing a multilayer adhesive diffusion source with uniform slurry, suitable decomposition temperature, strong interfacial adhesion, and suitable for convenient and mass production, as well as its preparation method and application.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A method for preparing a multilayer adhesive diffusion source includes the following steps: S1. Mix 40 wt.% to 60 wt.% heavy rare earth element powder, 20 wt.% to 40 wt.% organic polymer solution, 5 wt.% to 15 wt.% binder and 1 wt.% to 5 wt.% antioxidant to obtain a diffusion slurry; The organic polymer solution contains 20 wt.% to 25 wt.% polyimide dissolved in it; S2. The diffusion slurry is roller-coated onto thermally sprayed double-sided adhesive tape and dried to form a multilayer adhesive diffusion source. The thermally sprayed double-sided adhesive tape comprises, in sequence, a protective film, a pressure-sensitive adhesive layer A, an adhesive substrate, and a pressure-sensitive adhesive layer B. The pressure-sensitive adhesive layer B is used to coat the diffusion slurry, and during operation, the pressure-sensitive adhesive layer A is used to bond with the sintered NdFeB substrate. Both the pressure-sensitive adhesive layer A and the pressure-sensitive adhesive layer B contain methyl methacrylate monomer and titanate coupling agent.

[0006] In the preferred embodiment of the above-mentioned method for preparing the multilayer adhesive diffusion source, in step S1, the viscosity of the diffusion slurry is controlled between 10000 mPa·s and 25000 mPa·s, and the thermal decomposition temperature of the diffusion slurry is between 380℃ and 420℃.

[0007] In the preferred method for preparing the above-mentioned multilayer adhesive diffusion source, in step S1, the chemical composition of the heavy rare earth element powder is HRExMy, wherein HRE in HRExMy is at least one of Dy, Tb, and Ho, M is at least one of Al, Cu, Sn, Zr, Ni, Zn, Ti, Ga, In, Nb, O, Fe, Co, and Gd, x is 40 wt.% to 65 wt.%, and x+y is 100 wt.%.

[0008] In the preferred embodiment of the above-mentioned method for preparing the multilayer adhesive diffusion source, in step S1, the solvent used for the organic polymer solution is one or more of ethanol, acetone, and ethyl acetate; the binder is one or more of acrylic resin, polyurethane resin, epoxy resin, polyvinyl acetate, and phenolic resin; and the antioxidant is one or more of stearic acid, tea polyphenols, and phosphite antioxidants.

[0009] The preferred method for preparing the above-mentioned multilayer adhesive diffusion source is as follows: in step S1, the mixing conditions are: stirring at 20℃~50℃ and 300r / min~500r / min for 30min~60min.

[0010] In the preferred embodiment of the above-mentioned method for preparing the multilayer adhesive diffusion source, in step S2, the thickness of the pressure-sensitive adhesive layer A is 10μm to 20μm, and the thickness of the pressure-sensitive adhesive layer B is 10μm to 20μm; the total thickness of the pressure-sensitive adhesive layer A, the adhesive substrate, and the pressure-sensitive adhesive layer B is 40μm to 90μm; the adhesive substrate is a PET film with a thickness of 20μm to 50μm; when adapting to curved magnets, a PP film with a thickness of 25μm to 35μm and a bending radius ≥3mm without cracking is used.

[0011] In step S2, the drying temperature is 60℃~120℃ and the drying time is 10min~30min.

[0012] The preferred method for preparing the above-mentioned multilayer adhesive diffusion source is as follows: the drying is a segmented drying process, which includes first drying at 60℃~80℃ for 5min~10min, and then drying at 100℃~120℃ for 20min~25min.

[0013] As a general inventive concept, the present invention also provides a multilayer adhesive diffusion source prepared by the above-described preparation method.

[0014] The application of the above-mentioned multilayer adhesive diffusion source in the grain boundary diffusion of sintered NdFeB magnets, preferably, includes the following steps: (1) Pretreatment of the surface of the sintered NdFeB matrix; (2) The multilayer adhesive diffusion source is attached and fixed to the surface of the pretreated sintered NdFeB substrate to obtain the magnet to be diffused; (3) The magnet to be diffused is subjected to grain boundary diffusion and secondary tempering heat treatment to obtain sintered NdFeB magnet.

[0015] In the above application, the preferred method is: in step (1), the pretreatment is: first wipe the surface of the sintered NdFeB substrate with alcohol or acetone to remove oil and dust, so that the surface roughness Ra≤0.8μm, and then air dry or bake dry to ensure that the surface is free of moisture.

[0016] In the above application, the preferred method is as follows: In step (2), the bonding and fixing method is as follows: cut the multilayer adhesive diffusion source according to the size of the pretreated sintered NdFeB substrate, so that the multilayer adhesive diffusion source covers the diffusion surface of the sintered NdFeB substrate and leaves a margin of 1mm to 2mm at the edge, peel off the protective film of the multilayer adhesive diffusion source that is away from the diffusion slurry layer, align and press evenly with a pressure of 0.1MPa to 0.3MPa to ensure no air bubbles and no curling edges, and let it stand for 5min to 10min after bonding to allow the pressure-sensitive adhesive layer to fully adhere to the surface of the sintered NdFeB substrate. Multiple multilayer adhesive diffusion sources can be stacked as needed to increase the diffusion amount of heavy rare earth.

[0017] In the above application, preferably, in step (3), the grain boundary diffusion occurs at 800℃~900℃ and the vacuum degree is less than 1×10⁻⁶. -3 The heat treatment is carried out under conditions of Pa, with a holding time of 2h to 18h; the secondary tempering heat treatment is carried out at 450℃ to 650℃ and a vacuum degree of less than 1×10⁻⁶. -3 The process is carried out under Pa conditions, and the heat preservation time is 2h to 5h.

[0018] Compared with the prior art, the advantages of the present invention are as follows: (1) The preparation method of the multilayer adhesive diffusion source of the present invention introduces polyimide into the slurry system of the multilayer adhesive diffusion source, which greatly increases the viscosity of the diffusion slurry, so that the heavy rare earth powder is stably suspended and uniformly distributed for a long time, avoiding coating sagging and uneven sedimentation of rare earth particles caused by excessively low diffusion slurry viscosity, which leads to uncontrolled macroscopic distribution of the diffusion source. By adjusting the amount of polyimide, the high-temperature decomposition temperature of the slurry is precisely controlled within a certain range, ensuring that the non-metallic part in the diffusion source is decomposed in a timely manner before the rare earth elements begin to diffuse and the residual carbon rate is extremely low, avoiding premature decomposition leading to rare earth oxidation, or decomposition too late, resulting in high residual carbon rate and contamination of the grain boundaries. A titanate coupling agent is introduced into the pressure-sensitive adhesive layer, which enhances the adhesion between the layers in the multilayer adhesive diffusion source by forming chemical bonds, thereby enhancing the bonding force between the diffusion source and the magnet interface and preventing warping and debonding during the high-temperature diffusion process. This invention solves the problems of slurry sedimentation, uneven distribution, rare earth oxidation deactivation, and poor interface adhesion in existing thin film diffusion sources, and ultimately achieves high consistency of magnet performance after diffusion, excellent coercivity enhancement effect, and minimal damage to remanence.

[0019] (2) The preparation method of the present invention uses a pressure-sensitive adhesive layer A and a pressure-sensitive adhesive layer B containing methyl methacrylate monomer and titanate coupling agent to form a thermally sprayed double-sided adhesive tape with an adhesive substrate. This tape has excellent properties such as high temperature resistance, resistance to organic solvent erosion, and stable triple adhesion to the diffusion slurry, the magnet surface, and the adhesive substrate. The present invention utilizes the combined action of the specially made thermally sprayed double-sided adhesive tape and the polyimide and antioxidant in the diffusion slurry to make the multilayer adhesive diffusion source not only have strong interlayer adhesion but also excellent oxidation resistance. Therefore, it has good stability and durability, is easy to transport and store for a long time, and can be directly pasted onto the magnet surface during use. The operation is simple and does not require complicated electroplating, screen printing, and spraying equipment, which greatly improves the convenience of use, simplifies the production process, effectively improves production efficiency, reduces production costs, and is suitable for mass production.

[0020] (3) The preparation method of the present invention forms a multi-layer adhesive diffusion source by coating the diffusion slurry onto the specially made thermal spray double-sided adhesive tape of the present invention. This solves the problem that the diffusion source is difficult to adjust in the prior art, making the thickness and uniformity of the diffusion source easier to control, thereby improving the consistency and stability of the magnet performance.

[0021] (4) The preparation method of the present invention optimizes the formulation design of the slurry and the preparation process parameters, thereby reducing the amount of heavy rare earth elements used while ensuring the magnetic properties of the magnet, and solving the problems of large amount of heavy rare earth elements and high cost in traditional methods.

[0022] (5) Due to the use of polyimide, antioxidant and pressure-sensitive adhesive containing methyl methacrylate monomer and titanate coupling agent, the multilayer adhesive diffusion source of the present invention has multiple excellent properties such as uniform diffusion source distribution, suitable decomposition temperature, strong interlayer adhesion, high temperature resistance, resistance to organic solvent erosion, oxidation resistance and easy decomposition without residue. Attached Figure Description

[0023] Figure 1 This is a process flow diagram of the preparation method of the multilayer adhesive diffusion source in a specific embodiment of the present invention.

[0024] Figure 2 This is a schematic diagram of the structure of the multilayer adhesive diffusion source in a specific embodiment of the present invention.

[0025] Figure 3 This is a process flow diagram illustrating the application of a multilayer adhesive diffusion source in the grain boundary diffusion of sintered NdFeB in a specific embodiment of the present invention. Detailed Implementation

[0026] The present invention will be further described below with reference to the specification and specific preferred embodiments, but this does not limit the scope of protection of the present invention. In the following embodiments of the present invention, unless otherwise specified, the materials and instruments used are commercially available, and the equipment used is conventional equipment. Specifically, the polyimide was purchased from Yantai Xianhua Polymer Materials Co., Ltd., and the coupling agent was a titanate coupling agent produced by Hangzhou Jessica Chemical Co., Ltd.

[0027] The present invention provides a method for preparing a multilayer adhesive diffusion source, such as... Figure 1 As shown, it includes the following steps: S1. Mix 40 wt.% to 60 wt.% heavy rare earth element powder, 20 wt.% to 40 wt.% organic polymer solution, 5 wt.% to 15 wt.% binder and 1 wt.% to 5 wt.% antioxidant to obtain a diffusion slurry; The organic polymer solution contains 20 wt.% to 25 wt.% polyimide dissolved in it. By controlling the amount of polyimide added, the viscosity of the diffusion slurry is controlled at 10000 mPa·s to 25000 mPa·s (measured at 25°C using a rotational viscometer). This ensures a balance between the slurry's flowability and adhesion during the roller coating process and also controls the thermal decomposition temperature of the diffusion slurry at 380°C to 420°C.

[0028] S2. The diffusion slurry is roller-coated onto a thermally sprayed double-sided adhesive tape and dried to form a multilayer adhesive diffusion source. The thermally sprayed double-sided adhesive tape sequentially comprises a protective film, a pressure-sensitive adhesive layer A, an adhesive substrate, and a pressure-sensitive adhesive layer B. The pressure-sensitive adhesive layer B is used to coat the diffusion slurry, and the pressure-sensitive adhesive layer A is used to bond with the sintered NdFeB substrate. Before bonding with the sintered NdFeB substrate, the pressure-sensitive adhesive layer A is bonded to the protective film (release paper / PE film). Both the pressure-sensitive adhesive layer A and the pressure-sensitive adhesive layer B contain methyl methacrylate monomer and titanate coupling agent.

[0029] Roller coating operation: Inject the diffusion slurry into the feed trough of the roller coating dryer, and adjust the coating thickness (5μm~50μm, which can be adjusted according to diffusion requirements) to make the diffusion slurry evenly coated on the surface of pressure-sensitive adhesive layer B (avoid direct coating on the adhesive substrate to improve adhesion). Drying parameters: Drying temperature 60℃~120℃, drying time 10min~30min (segmented drying: first segment 60℃~80℃, drying for 5min~10min to remove solvent, second segment 100℃~120℃, drying for 20min~25min to cure the adhesive).

[0030] Finished product structure: After drying, it forms a multi-layered adhesive diffusion source consisting of "protective film + pressure-sensitive adhesive layer A + adhesive substrate + pressure-sensitive adhesive layer B + diffusion slurry layer + protective film", such as... Figure 2As shown, it can be rolled into rolls (width 300mm~1000mm, length 50m~200m) or cut into sheets corresponding to the magnet size.

[0031] The multilayer adhesive diffusion sources prepared above are tested, and those that meet the requirements are packaged and stored.

[0032] In this invention, both pressure-sensitive adhesive layer A and pressure-sensitive adhesive layer B include methyl methacrylate monomer and titanate coupling agent, and the adhesive substrate is a PET (polyethylene terephthalate) film or a PP (polypropylene) film. The resulting thermally sprayed double-sided adhesive tape consisting of "pressure-sensitive adhesive layer A, adhesive substrate, and pressure-sensitive adhesive layer B" has the following key performance indicators: Adhesion strength: Adhesion to PET substrate ≥18N / 25mm, adhesion between pressure-sensitive adhesive layer and diffusion slurry layer ≥12N / 25mm, adhesion to sintered NdFeB substrate surface ≥15N / 25mm. Adhesion strength testing was performed using the 180° peel test method, according to GB / T 2792~2014 standard. Samples were bonded at 25℃ and allowed to stand for 10 minutes before testing.

[0033] High temperature resistance: No shrinkage during the drying stage at 60℃~120℃ (dimensional change rate ≤±0.5%), no melting and dripping during the diffusion stage at 800℃~900℃, and decomposition temperature ≥300℃ (to avoid premature failure at low temperatures). Solvent resistance: After immersion in ethanol, acetone or ethyl acetate for 24 hours, the adhesive layer does not swell or peel off (weight change rate ≤ ±2%). Residual adhesive content: The amount of residual adhesive on the magnet surface after diffusion is ≤0.05g / m² (no additional cleaning is required, which meets the requirements of environmental protection and subsequent processing).

[0034] Further improved, in step S1, the chemical composition of the heavy rare earth element powder is HRE. x M y The HRE x M y HRE is at least one of Dy, Tb, and Ho, M is at least one of Al, Cu, Sn, Zr, Ni, Zn, Ti, Ga, In, Nb, O, Fe, Co, and Gd, x is 40 wt.% to 65 wt.%, and x+y is 100 wt.%, with a particle size of 1 μm to 5 μm to ensure diffusion activity.

[0035] In a further improvement, in step S1, the solvent used in the organic polymer solution is one or more of ethanol, acetone, and ethyl acetate, used to adjust the viscosity and high-temperature resistance of the slurry.

[0036] In a further improvement, in step S1, the adhesive is one or more of acrylic resin, polyurethane resin, epoxy resin, polyvinyl acetate and phenolic resin; the adhesive used in this invention can ensure the adhesion between the slurry and the tape and its formability after drying, while also being easily decomposed without residue during subsequent high-temperature diffusion.

[0037] In a further improvement, in step S1, the antioxidant is one or more of stearic acid, tea polyphenols, and phosphite antioxidants to prevent oxidation of heavy rare earth powder and corrosion of the magnet surface.

[0038] In a further improvement, in step S1, the mixing conditions are: stirring at 20℃~50℃ and 300r / min~500r / min for 30min~60min.

[0039] Further improvements are made in step S2, where the thickness of pressure-sensitive adhesive layer A is 10μm to 20μm, and the thickness of pressure-sensitive adhesive layer B is 10μm to 20μm; the total thickness of pressure-sensitive adhesive layer A, adhesive substrate, and pressure-sensitive adhesive layer B is 40μm to 90μm; the adhesive substrate is a PET (polyethylene terephthalate) film with a thickness of 20μm to 50μm, preferably 30μm to 40μm, balancing flexibility and support to prevent wrinkling or breakage during roller coating; when adapting to curved magnets, a PP (polypropylene) film with a thickness of 25μm to 35μm is used, with a bending radius ≥3mm without cracking; A multilayer adhesive diffusion source prepared by the above preparation method of the present invention.

[0040] The application of the above-mentioned multilayer adhesive diffusion source in the grain boundary diffusion of sintered NdFeB, as described in this invention, is as follows: Figure 3 As shown, the steps include: (1) Pretreatment of the surface of the sintered NdFeB matrix; (2) The multilayer adhesive diffusion source is attached and fixed to the surface of the pretreated sintered NdFeB substrate to obtain the magnet to be diffused; (3) The magnet to be diffused is subjected to grain boundary diffusion and two-stage tempering heat treatment to obtain a sintered NdFeB magnet with high coercivity.

[0041] In step (1), the pretreatment is as follows: first, wipe the surface of the sintered NdFeB substrate with alcohol or acetone to remove oil and dust. No complex treatment such as sandblasting is required. The surface roughness Ra ≤ 0.8 μm is sufficient. Then, air dry or dry at 60℃ for 5 min to ensure that the surface is free of moisture. In step (2), the method of pasting and fixing is as follows: cut the multi-layer adhesive diffusion source according to the size of the pre-treated sintered NdFeB substrate, so that the multi-layer adhesive diffusion source covers the surface of the sintered NdFeB substrate to be diffused and leaves a margin of 1mm to 2mm at the edge. Remove the protective film of the multi-layer adhesive diffusion source that is away from the diffusion slurry layer, align and press evenly with a pressure of 0.1MPa to 0.3MPa to ensure no air bubbles and no curling edges. After pasting, let it stand for 5min to 10min to allow the pressure-sensitive adhesive layer to fully adhere to the surface of the sintered NdFeB substrate. Multiple multi-layer adhesive diffusion sources can be stacked as needed to increase the diffusion amount of heavy rare earth elements. In step (3), the grain boundary diffusion occurs at 800℃~900℃ and a vacuum degree below 1×10⁻⁶. -3 The heat treatment is carried out under conditions of Pa, with a holding time of 2h to 18h; the secondary tempering heat treatment is carried out at 450℃ to 650℃ and a vacuum degree of less than 1×10⁻⁶. -3 The process is carried out under Pa conditions, with a holding time of 2 to 5 hours. After diffusion, the diffusion source automatically carbonizes and decomposes, leaving no residue on the magnet surface, requiring no additional cleaning.

[0042] Example 1 The present invention provides a method for preparing a multilayer adhesive diffusion source, comprising the following steps: S1. Preparation of slurry: Tb 47.5 Al 2.8 Pr 48.4 Ga 1.3 The composition of the slurry consists of 55 wt.% heavy rare earth element powder, 30 wt.% organic polymer solution, 14 wt.% binder, and 1 wt.% antioxidant. The organic polymer solution contains 22.5 wt.% polyimide. These components are added to a mixing tank and stirred for 60 minutes at 30°C and 450 rpm to form a uniformly dispersed, non-agglomerated slurry with a viscosity of 16000 mPa·s (tested using a rotational viscometer at 25°C) and a high-temperature decomposition temperature of 400°C, ensuring a balance between slurry flowability and adhesion during roller coating.

[0043] S2. Roller coating and drying: Inject the slurry into the material tank of the roller coating dryer, adjust the coating thickness to 6μm, so that the slurry is evenly coated on the pressure-sensitive adhesive layer B of the double-sided tape. The drying temperature is 60~120℃ and the drying time is 30 minutes (segmented drying: the first segment is 65℃ for 7.5min to remove the solvent, and the second segment is 112℃ for 22min to cure the adhesive).

[0044] The double-sided tape includes a pressure-sensitive adhesive layer A, an adhesive substrate, and a pressure-sensitive adhesive layer B. Both pressure-sensitive adhesive layer A and pressure-sensitive adhesive layer B contain methyl methacrylate monomer and titanate coupling agent. The adhesive substrate is a PET film.

[0045] S3. Detect the diffusion source of the multilayer adhesive. If the test result does not meet the requirements, return to S1. If the test result meets the requirements, proceed to S4. According to the test results, in the multilayer adhesive diffusion source prepared in this embodiment, the adhesion between the pressure-sensitive adhesive layer and the PET substrate is 20 N / 25 mm, the adhesion between the pressure-sensitive adhesive layer and the diffusion slurry layer is 12 N / 25 mm, and the adhesion between the pressure-sensitive adhesive layer and the sintered NdFeB substrate surface is 16 N / 25 mm (tested after standing at 25°C for 10 minutes after pasting).

[0046] S4. Magnet Surface Pretreatment Wipe the surface of the sintered NdFeB substrate with alcohol or acetone to remove oil and dust (no complex treatment such as sandblasting is required; a surface roughness Ra≤0.8μm is sufficient); allow it to air dry naturally or bake it at 60℃ for 5 minutes to ensure that the surface is free of moisture.

[0047] S5, Diffusion source adhesive fixing Cut a multi-layer adhesive diffusion source according to the size of the pretreated sintered NdFeB substrate (covering the surface of the magnet to be diffused, with a 1mm to 2mm margin at the edge); peel off the protective film of the diffusion source away from the slurry layer, align it and press it evenly (pressure 0.1MPa to 0.3MPa) to ensure no air bubbles or curling edges; let it stand for 8 minutes after pasting to allow the pressure-sensitive adhesive to fully adhere.

[0048] S6, Subsequent Diffusion Processing The magnet with the attached diffusion source is fed into a vacuum sintering furnace and sintered at 900°C and a vacuum degree of 8×10⁻⁶. -4 Grain boundary diffusion was carried out under Pa conditions for 15 hours; after diffusion, it was carried out at 550℃ and a vacuum degree of 8×10⁻⁶. -4 Under Pa conditions, the magnets are held at the temperature for 4 hours and then subjected to a two-stage tempering heat treatment to obtain sintered NdFeB magnets with high coercivity.

[0049] Comparative Example 1 A method for preparing a multilayer adhesive diffusion source is basically the same as in Example 1, except that the organic polymer solution is replaced with an organic solvent. The absence of polyimide significantly reduces the viscosity and high-temperature decomposition temperature of the diffusion slurry, resulting in a viscosity of 2000 Pa·s and a high-temperature decomposition temperature of 350℃. This leads to poor slurry flowability and adhesion during roller coating, and the diffusion slurry begins to decompose at a lower temperature, causing premature failure.

[0050] A multilayer adhesive diffusion source prepared by the method described in this comparative example.

[0051] Using the multilayer adhesive diffusion source prepared in this comparative example, sintered NdFeB magnets were prepared according to the steps in Example 1.

[0052] Comparative Example 2 A method for preparing a multilayer adhesive diffusion source is basically the same as that in Example 1, except that neither pressure-sensitive adhesive layer A nor pressure-sensitive adhesive layer B contains a coupling agent. The interlayer adhesion of the prepared multilayer adhesive diffusion source is significantly reduced. The adhesion between the pressure-sensitive adhesive layer and the PET substrate is 3 N / 25 mm, the adhesion between the pressure-sensitive adhesive layer B and the diffusion slurry layer is 2.5 N / 25 mm, and the adhesion between the pressure-sensitive adhesive layer A and the surface of the sintered NdFeB substrate is 2 N / 25 mm (tested after standing at 25°C for 10 minutes after bonding).

[0053] A multilayer adhesive diffusion source prepared by the method described in this comparative example.

[0054] Using the multilayer adhesive diffusion source prepared in this comparative example, sintered NdFeB magnets were prepared according to the steps in Example 1.

[0055] The sintered NdFeB magnets prepared in Example 1, Comparative Example 1, and Comparative Example 2 were subjected to performance tests: the magnet sheet was cut into cylinders with a diameter of 10 mm along the c-axis and the magnetic properties were tested. The results are shown in Table 1.

[0056] Table 1. Performance of the diffused magnets in Example 1 and Comparative Example 1

[0057] Comparative analysis of the magnet performance test data of Example 1 with Comparative Examples 1 and 2 revealed that the magnet prepared in Example 1 of this invention exhibits better coercivity (H). cj It shows a clear advantage in the indicators of coercivity (H) cj The H values ​​of the magnets in the four batches of magnets in Example 1 increased by approximately 8.7% and 5.9%, respectively. cj The average value and the H of the two batches of magnets in Comparative Example 1 cj The average value, H of the two batches of magnets in Comparative Example 2 cj (Average value calculation). Therefore, it can be seen that this invention improves the coercivity of the magnet by adhering and diffusing a multilayer adhesive diffusion source on the surface of the sintered NdFeB substrate, thus preparing a sintered NdFeB magnet with high coercivity.

[0058] In Comparative Example 1, the lack of polyimide reduced the viscosity and high-temperature decomposition temperature of the diffusion slurry, compromising the process stability of the diffusion source and consequently decreasing the coercivity of the grain boundary diffusion magnet. Excessively low slurry viscosity leads to coating sagging and uneven rare earth particle settling, resulting in uncontrolled macroscopic distribution of the diffusion source. Conversely, excessively low decomposition temperatures cause the carrier (components in the diffusion slurry other than heavy rare earth elements) to fail prematurely before high-temperature diffusion, failing to provide effective protection and leading to oxidative deactivation of rare earth particles, potentially introducing residual carbon contamination. This results in a reduction in the effective penetration of heavy rare earth elements, a significant decrease in the coercivity enhancement effect, and exacerbated remanence loss.

[0059] In Comparative Example 2, the lack of a coupling agent in the pressure-sensitive adhesive layer significantly reduced the interlayer adhesion of the multilayer adhesive diffusion source. In this structure, pressure-sensitive adhesive layer A is bonded to the sintered NdFeB substrate, pressure-sensitive adhesive layer B is bonded to the diffusion slurry layer, and the adhesive substrate (PET or PP film) serves as an intermediate support layer. Together, these three layers form a complete multilayer composite system. The interlayer adhesion is crucial for ensuring the diffusion source maintains structural integrity, interface stability, and tight adhesion to the magnet surface during high-temperature diffusion. When no titanate coupling agent is added to the pressure-sensitive adhesive layer, the interlayer adhesion is significantly reduced, primarily manifested in a substantial decrease in the interfacial bonding strength between pressure-sensitive adhesive layer A and the magnet surface, pressure-sensitive adhesive layer B and the diffusion slurry layer, and pressure-sensitive adhesive layer and the substrate. This adhesion failure leads to a weakened effect on the final magnet coercivity enhancement through the following mechanism: interfacial debonding during high-temperature diffusion. Grain boundary diffusion is typically carried out under vacuum conditions at 800℃–900℃. During the heating process, due to the differences in the thermal expansion coefficients of the various layers, insufficient interlayer adhesion can easily lead to localized warping, blistering, or overall delamination. Once a gap or poor contact occurs between the diffusion source and the magnet surface, heavy rare earth elements cannot be effectively transferred from the diffusion source to the magnet surface, resulting in the loss of the diffusion source's "source" function and a significant reduction in heavy rare earth penetration. Diffusion kinetics are hindered. Grain boundary diffusion depends on the continuous supply of heavy rare earth elements in the liquid phase grain boundaries. If the adhesion between the diffusion source and the magnet interface is poor, the transport path of heavy rare earth elements at the interface is blocked, preventing the formation of a stable and continuous diffusion flux. This results in insufficient effective penetration depth, with only a heavy rare earth-rich shell forming in the near-surface region, while the coercivity improvement inside the magnet is limited.

[0060] Example 2 The preparation method of the multilayer adhesive diffusion source of the present invention is basically the same as that in Example 1, except that the heavy rare earth diffusion source component is selected differently. In this example, the heavy rare earth diffusion source component is Tb. 52.1 Al 4.2 Nd 41.1 Ga 2.6 .

[0061] The diffusion magnet prepared in this embodiment was subjected to performance testing: the magnet sheet was cut into cylinders with a diameter of 10 mm along the c-axis and the magnetic properties were tested. The results are shown in Table 2.

[0062] Table 2 Performance of Diffusion Magnet in Example 2

[0063] Comparative analysis of the test data from Example 1 and the control group shows that the magnet prepared in Example 1 of this invention exhibits better coercivity (H). cj The indicators showed a significant improvement, with an increase of approximately 54.7% (based on the H of the four batches of magnets in Example 1 in Table 1). cjAverage value and H of the control group magnet cj (Numerical calculation). Furthermore, by comparing the magnetic performance data of Example 2, compared to the control group, the magnetic performance also showed similar levels of coercivity (H). cj The performance indicators are significantly improved. Therefore, the adhesion and diffusion of the multilayer adhesive diffusion source of this invention on the surface of the sintered NdFeB substrate significantly improves the coercivity of the magnet, resulting in a sintered NdFeB magnet with high coercivity. Furthermore, Examples 1 and 2 respectively list the magnetic performance test results for four batches. The main performance indicators (such as coercivity Hcj, remanence Br, etc.) between batches show small fluctuations and low dispersion, proving that the magnets with adhesion and diffusion of the multilayer adhesive diffusion source of this invention exhibit excellent performance consistency across different batches.

[0064] While the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the invention. Any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention, or modify them into equivalent embodiments, without departing from the spirit and technical essence of the invention. Therefore, any simple modifications, equivalent substitutions, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention, without departing from the content of the present invention, shall still fall within the scope of protection of the present invention.

Claims

1. A method for preparing a multilayer adhesive diffusion source, characterized in that, Includes the following steps: S1. Mix 40 wt.% to 60 wt.% heavy rare earth element powder, 20 wt.% to 40 wt.% organic polymer solution, 5 wt.% to 15 wt.% binder and 1 wt.% to 5 wt.% antioxidant to obtain a diffusion slurry; The organic polymer solution contains 20 wt.% to 25 wt.% polyimide dissolved in it; S2. The diffusion slurry is roller-coated onto a thermally sprayed double-sided adhesive tape and dried to form a multilayer adhesive diffusion source. The thermally sprayed double-sided adhesive tape comprises, in sequence, a protective film, a pressure-sensitive adhesive layer A, an adhesive substrate, and a pressure-sensitive adhesive layer B. The pressure-sensitive adhesive layer B is used to coat the diffusion slurry, and during operation, the pressure-sensitive adhesive layer A is used to bond with the sintered NdFeB substrate. Both the pressure-sensitive adhesive layer A and the pressure-sensitive adhesive layer B contain methyl methacrylate monomer and titanate coupling agent.

2. The method for preparing the multilayer adhesive diffusion source according to claim 1, characterized in that: In step S1, the viscosity of the diffusion slurry is controlled between 10000 mPa·s and 25000 mPa·s, and the thermal decomposition temperature of the diffusion slurry is between 380℃ and 420℃.

3. The method for preparing the multilayer adhesive diffusion source according to claim 1, characterized in that: In step S1, the chemical composition of the heavy rare earth element powder is HRE. x M y The HRE x M y HRE is at least one of Dy, Tb, and Ho, M is at least one of Al, Cu, Sn, Zr, Ni, Zn, Ti, Ga, In, Nb, O, Fe, Co, and Gd, x is 40 wt.% to 65 wt.%, and x+y is 100 wt.%.

4. The method for preparing the multilayer adhesive diffusion source according to claim 1, characterized in that: In step S1, the solvent used in the organic polymer solution is one or more of ethanol, acetone, and ethyl acetate; the binder is one or more of acrylic resin, polyurethane resin, epoxy resin, polyvinyl acetate, and phenolic resin; and the antioxidant is one or more of stearic acid, tea polyphenols, and phosphite antioxidants.

5. The method for preparing the multilayer adhesive diffusion source according to claim 1, characterized in that: In step S1, the mixing conditions are: stirring at 20℃~50℃ and 300r / min~500r / min for 30min~60min.

6. The method for preparing the multilayer adhesive diffusion source according to any one of claims 1 to 5, characterized in that: In step S2, the thickness of pressure-sensitive adhesive layer A is 10μm to 20μm, and the thickness of pressure-sensitive adhesive layer B is 10μm to 20μm; the total thickness of pressure-sensitive adhesive layer A, adhesive substrate, and pressure-sensitive adhesive layer B is 40μm to 90μm; the adhesive substrate is a PET film with a thickness of 20μm to 50μm; when adapting to curved magnets, a PP film with a thickness of 25μm to 35μm is used, with a bending radius ≥3mm and no cracking. In step S2, the drying temperature is 60℃~120℃ and the drying time is 10min~30min.

7. The method for preparing the multilayer adhesive diffusion source according to claim 6, characterized in that: The drying process is a segmented drying process, which includes first drying at 60℃~80℃ for 5min~10min, and then drying at 100℃~120℃ for 20min~25min.

8. A multilayer adhesive diffusion source prepared by the preparation method according to any one of claims 1 to 7.

9. The application of the multilayer adhesive diffusion source as described in claim 8 in the grain boundary diffusion of sintered NdFeB, characterized in that, The application steps include: (1) Pretreatment of the surface of the sintered NdFeB matrix; (2) The multilayer adhesive diffusion source is attached and fixed to the surface of the pretreated sintered NdFeB substrate to obtain the magnet to be diffused; (3) The magnet to be diffused is subjected to grain boundary diffusion and secondary tempering heat treatment to obtain sintered NdFeB magnet.

10. The application according to claim 9, characterized in that: In step (1), the pretreatment is as follows: first, wipe the surface of the sintered NdFeB substrate with alcohol or acetone to remove oil and dust, so that the surface roughness Ra≤0.8μm, and then air dry or bake dry to ensure that the surface is free of moisture; In step (2), the method of pasting and fixing is as follows: cut the multi-layer adhesive diffusion source according to the size of the pre-treated sintered NdFeB substrate, so that the multi-layer adhesive diffusion source covers the surface of the sintered NdFeB substrate to be diffused and leaves a margin of 1mm to 2mm at the edge. Remove the protective film of the multi-layer adhesive diffusion source that is away from the diffusion slurry layer, align and press evenly with a pressure of 0.1MPa to 0.3MPa to ensure no air bubbles and no curling edges. After pasting, let it stand for 5min to 10min to allow the pressure-sensitive adhesive layer to fully adhere to the surface of the sintered NdFeB substrate. Multiple multi-layer adhesive diffusion sources can be stacked as needed to increase the diffusion amount of heavy rare earth elements. In step (3), the grain boundary diffusion occurs at 800℃~900℃ and a vacuum degree below 1×10⁻⁶. -3 The heat treatment is carried out under conditions of Pa, with a holding time of 2h to 18h; the secondary tempering heat treatment is carried out at 450℃ to 650℃ and a vacuum degree of less than 1×10⁻⁶. -3 The process is carried out under Pa conditions, and the heat preservation time is 2h to 5h.

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