Silicone-oil-free wet-process magnet profiling release agent and preparation process thereof

Abstract

The invention relates to the technical field of release agents, and discloses a silicone-oil-free wet-process magnet profiling release agent and a preparation process thereof, and the silicone-oil-free wet-process magnet profiling release agent comprises a core functional copolymer, a water-based non-silicon defoaming agent and deionized water. The core functional copolymer is prepared from a hydrophilic self-repairing film-forming monomer, a molecular-level flexible lubricating monomer, a powerful mold anchoring monomer and a programmed pyrolysis triggering monomer through free radical copolymerization. According to the technical scheme, the functions of self-repairing film forming, molecular-level lubrication, mold anchoring and programmed pyrolysis are integrated through a single macromolecular structure. A demolding film layer formed by the water-based demolding agent is uniform and compact, mold sticking and blank defects in the profiling process are avoided, the water-based demolding agent can be completely decomposed and volatilized in the magnet sintering process, and solid residues are not generated, so that the high magnetic performance of a sintered magnet is guaranteed, and the problems that an existing water-based demolding agent is prone to generating film layer defects, poor in system stability, residues after sintering and the like are solved.

Description

Technical Field

[0001] This invention relates to the field of mold release agent technology, specifically to a silicone-free wet-process magnetic molding mold release agent and its preparation process. Background Technology

[0002] In the production of high-performance permanent magnet materials, wet magnet molding is a key forming process. In this process, in order to ensure that the magnetic powder slurry containing solvent can be smoothly removed from the mold after molding and to ensure the integrity of the magnet blank surface, a layer of release agent must be applied to the inner wall of the mold beforehand.

[0003] Traditional mold release agents are mainly divided into oil-based and water-based mold release agents. Although oil-based mold release agents have a certain lubricating effect, they contain a large amount of volatile organic compounds, which adversely affect the production environment and the health of operators, and their flammability also poses a safety hazard. More importantly, the organic matter in oil-based mold release agents is difficult to completely decompose during the subsequent high-temperature sintering process, and the resulting carbonaceous residues can contaminate the magnets and severely degrade the magnetic properties of the final product.

[0004] To overcome the aforementioned shortcomings of oil-based release agents, water-based release agents have been extensively researched and applied. However, currently widely used water-based release agents are typically multi-component physical compound systems, such as physically mixing film-forming agents, lubricants, surfactants, adhesion promoters, and other chemicals in water. This compound system itself has inherent technical drawbacks. First, due to the significant differences in chemical structure and properties among the components, poor compatibility may exist, leading to instability such as layering and sedimentation during storage or use. When coated on the surface of a high-temperature mold, rapid evaporation of water exacerbates this inhomogeneity, easily causing micro-cracks and pinholes due to excessive internal stress during the drying and film-forming process. This damages the integrity and uniformity of the release film layer, consequently affecting the surface quality and yield of the magnet blank.

[0005] Furthermore, the lubricating, film-forming, and adhesive components in these traditional water-based release agents are independent and difficult to distribute uniformly and synergistically at the microscopic level, often leading to unstable release performance. More seriously, the various organic compounds they contain exhibit uncontrollable thermal decomposition during the high-temperature sintering of magnets, typically resulting in incomplete decomposition and the generation of carbonaceous residues. These residues can penetrate the magnet's interior, contaminating the alloy composition and adversely affecting the density and microstructure of the sintered magnet, ultimately leading to a significant decrease in key magnetic properties such as remanence, coercivity, and maximum energy product.

[0006] Therefore, developing a water-based release agent that is stable, produces uniform and defect-free films, and can decompose cleanly during sintering without any residue is a technical challenge that urgently needs to be solved in this field. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a silicone-free wet-process magnetic molding release agent and its preparation process, which solves the problems of poor film quality, unstable system, and easy generation of residues after sintering that seriously degrade the final performance of the magnet, which are common in existing water-based release agents used for magnetic molding.

[0008] To achieve the above objectives, the present invention provides the following technical solution: a silicone-free wet-process magnetic molding release agent, which comprises the following components in parts by weight: Core functional copolymer: 0.5-5.0 parts; Water-based non-silicone defoamer: 0.01-0.07 parts; Deionized water: Add to a total weight of 100 parts.

[0009] The core functional copolymer is a water-soluble copolymer, which is prepared by free radical copolymerization of hydrophilic self-healing film-forming monomers, molecular-level flexible lubricating monomers, high-efficiency mold anchoring monomers and programmed pyrolysis triggering monomers.

[0010] In the technical solution provided by this invention, the core functional copolymer integrates multiple functions through a single polymer structure, and its mechanism of action is as follows: Self-healing film-forming mechanism: The molecular structure of the hydrophilic self-healing film-forming monomer contains a high density of hydrogen bond interaction sites. When the release agent is applied to the mold surface to form a wet film, water molecules, acting as plasticizers, penetrate the hydrogen bond network between polymer chains, giving the wet film flexibility and fluidity. During the evaporation and drying process, polymer chain segments move closer together, and the hydrogen bond network is reconstructed. If microcracks are generated due to shrinkage stress during this process, the capillary water remaining at the crack tip will locally replasticize the polymer chain segments, giving them the ability to migrate, thereby promoting the closure of the microcracks and forming a uniform and complete release film layer.

[0011] Lubrication and anchoring mechanism: The molecular-level flexible lubricating monomer introduces long-chain alkyl side chains into the copolymer molecular chain. These side chains provide molecular-level lubrication on the surface of the formed release film. The polar functional groups contained in the high-efficiency mold anchoring monomer can chemically adsorb or chelate with the metal mold surface, allowing the release film to firmly adhere to the mold surface during magnetic mud filling and pressing.

[0012] Programmed pyrolysis mechanism: The chemical structure of the monomer triggered by the programmed pyrolysis remains stable at the temperature where the release agent is working. However, during the initial heating stage of the magnet sintering process, the internal chemical bonds break, triggering the decomposition of the entire copolymer chain. The decomposition products are small molecule volatiles such as carbon dioxide and water, which can completely escape from the surface of the magnet blank without forming solid residues.

[0013] In one specific embodiment, the monomers of the core functional copolymer are: The hydrophilic self-healing film-forming monomer is N-vinylpyrrolidone; The molecular-level flexible lubricating monomer is lauryl methacrylate; The high-efficiency mold anchoring monomer is ethyl 2-phosphate acrylate; The programmed pyrolysis trigger monomer is tert-butyl methacrylate.

[0014] In another specific embodiment, the molar percentage of each monomer used to prepare the core functional copolymer is: Lauryl methacrylate: 4.0 mol% - 15.0 mol% Ethyl 2-phosphate acrylate: 0.5 mol% - 2.0 mol% tert-butyl methacrylate: 1.0 mol% - 5.0 mol% N-Vinylpyrrolidone: Balance.

[0015] The second aspect of the present invention provides a preparation process for the silicone-free wet magnetic molding release agent.

[0016] The preparation process includes the following steps: S1. Synthesis of core functional copolymer: Hydrophilic self-healing film-forming monomer, molecular-level flexible lubricating monomer, high-efficiency mold anchoring monomer and programmed pyrolysis triggering monomer and initiator are dissolved in reaction solvent and subjected to free radical polymerization reaction at room temperature for 4h-12h to obtain a solution containing core functional copolymer. S2. Purification and drying: The solution containing the core functional copolymer obtained in step S1 is purified by solvent precipitation and then vacuum dried to obtain a pure core functional copolymer solid powder. S3. Preparation: Dissolve the core functional copolymer solid powder obtained in step S2 and the water-based non-silicone defoamer in deionized water to obtain the silicone-free wet magnetic molding release agent.

[0017] In one specific embodiment, in step S1, the initiator is azobisisobutyronitrile, and its molar amount is 0.1 mol%-1.0 mol% of the total molar amount of all monomers.

[0018] In another specific embodiment, in step S1, the reaction solvent is isopropanol, and the total mass concentration of all monomers is 10wt%-30wt% of the total mass of the solution.

[0019] In another specific embodiment, in step S1, the solvent precipitation purification specifically involves adding a solution containing the core functional copolymer dropwise to n-hexane as a precipitant for precipitation, wherein the volume ratio of the precipitant to the solution is 10:1-20:1.

[0020] In another specific embodiment, the process parameters for vacuum drying are: drying for 24-48 hours at room temperature and with a vacuum degree ≤0.09MPa.

[0021] In another specific embodiment, step S3 is as follows: under stirring conditions, the core functional copolymer solid powder is dissolved in deionized water, stirred for 2h-6h until the system is clear and homogeneous, and then an aqueous non-silicone defoamer is added and stirred for 15min-30min.

[0022] In another specific embodiment, a filtration step is included after step S3: the prepared release agent solution is filtered through a 1μm-5μm filter screen.

[0023] This invention provides a silicone-free wet-process magnetic molding release agent and its preparation process. It has the following beneficial effects: 1. This invention achieves self-repair of the film layer during the drying process through the molecular design of a hydrophilic self-healing film-forming framework; when the water evaporates and the hydrogen bond network is reconstructed, the micro-cracks can be healed through local replasticization; this mechanism ensures the formation of a continuous, dense and micro-defect-free release film layer on the mold surface, providing a uniform interface for magnetic clay molding.

[0024] This invention utilizes a single intelligent functionalized copolymer as the core active ingredient of the release agent; all functional units are chemically bonded to the same polymer chain, avoiding instability phenomena such as layering, flocculation, or demulsification caused by component incompatibility in traditional multi-component physical mixing systems; the system can maintain a homogeneous state during storage and use.

[0025] This invention provides continuous lubrication by uniformly distributing molecular-level flexible lubricating segments on the surface of the release film layer on the copolymer molecular chain; at the same time, the strong mold anchoring group ensures that the release film layer is firmly bonded to the mold surface, preventing the film layer from falling off or shifting during the magnetic putty molding process, and maintaining the lubrication consistency of the release interface. Detailed Implementation

[0026] Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] Examples 1-3: Example 1: Synthesis of core functional copolymer 1 and preparation of release agent sample 1 Synthesis of core functional copolymer 1 Materials preparation: Weigh out 86.8 mol of N-vinylpyrrolidone, 9.0 mol of lauryl methacrylate, 1.2 mol of ethyl 2-phosphate acrylate, and 3.0 mol of tert-butyl methacrylate. Weigh out azobisisobutyronitrile as the initiator, with a molar amount equal to 0.5 mol of the total molar amount of all monomers. Prepare isopropanol as the reaction solvent and n-hexane as the precipitant.

[0028] Solution preparation: Add the above monomers and AIBN to isopropanol and stir to dissolve. Control the total mass concentration of the monomers to 20 wt% of the total mass of the isopropanol solution.

[0029] Polymerization reaction implementation: Transfer the prepared solution to a three-necked flask equipped with a mechanical stirrer, reflux condenser, thermometer, and nitrogen delivery tube. Start stirring at 250 rpm. Purge the system with high-purity nitrogen for 20 min, and place the reactor in a constant-temperature oil bath at room temperature for 8 h.

[0030] Purification: After the reaction is complete, stop heating and cool to room temperature. Slowly add the reaction solution dropwise to n-hexane (15:1 volume ratio) with stirring to precipitate. Discard the supernatant, dissolve the precipitate in a small amount of isopropanol, and add it dropwise to n-hexane again to precipitate. Repeat this dissolution-precipitation process twice.

[0031] Drying: The purified precipitate was placed in a vacuum drying oven and dried for 36 hours at room temperature and a vacuum degree ≤0.09MPa to obtain the solid powder of the core functional copolymer 1.

[0032] Preparation of release agent sample 1 Materials preparation: Core functional copolymer 1 obtained in Example 1, water-based non-silicone defoamer, and deionized water.

[0033] Composition ratio: Weigh 3.0 parts by weight of core functional copolymer 1, 0.04 parts by weight of water-based non-silicone defoamer, and make up the remainder to 100 parts by weight of deionized water.

[0034] Preparation process: Add deionized water to the preparation tank and start stirring at 200 rpm. Slowly add the core functional copolymer 1 powder in batches and stir for 4 hours until completely dissolved and a clear solution is formed. Add the water-based non-silicone defoamer and continue stirring for 20 minutes.

[0035] Filtration: The prepared release agent solution was filtered through a 3μm filter screen to obtain release agent sample 1.

[0036] Example 2: Synthesis of core functional copolymer 2 and preparation of release agent sample 2 Synthesis of core functional copolymer 2 Materials preparation: Weigh out 78.0 mol% N-vinylpyrrolidone, 15.0 mol% lauryl methacrylate, 2.0 mol% ethyl 2-phosphate acrylate, and 5.0 mol% tert-butyl methacrylate. Weigh out azobisisobutyronitrile as the initiator, with a molar amount equal to 1.0 mol% of the total molar amount of all monomers. Prepare isopropanol as the reaction solvent and n-hexane as the precipitant.

[0037] Solution preparation: Add the above monomers and AIBN to isopropanol and stir to dissolve. Control the total mass concentration of the monomers to be 30 wt% of the total mass of the isopropanol solution.

[0038] Polymerization reaction implementation: Transfer the prepared solution to a three-necked flask. Start stirring at 400 rpm. Purge the system with high-purity nitrogen gas for 30 min. Place the reactor in a constant-temperature oil bath and maintain the reaction for 12 h.

[0039] Purification: After the reaction is complete, stop heating and cool to room temperature. Slowly add the reaction solution dropwise to n-hexane (20:1 volume ratio) with stirring to induce precipitation. Discard the supernatant, dissolve the precipitate in a small amount of isopropanol, and add it dropwise to n-hexane again to precipitate. Repeat this dissolution and precipitation process three times.

[0040] Drying: The purified precipitate was placed in a vacuum drying oven and dried for 48 hours at room temperature and under a vacuum of ≤0.09MPa to obtain the core functional copolymer 2 solid powder.

[0041] Preparation of release agent sample 2 Materials preparation: Core functional copolymer 2 obtained in Example 2, water-based non-silicone defoamer, and deionized water.

[0042] Composition ratio: Weigh 5.0 parts by weight of core functional copolymer 2, 0.07 parts by weight of water-based non-silicone defoamer, and make up the remainder to 100 parts by weight of deionized water.

[0043] Preparation process: Add deionized water to the preparation tank and start stirring at 300 rpm. Slowly add the core functional copolymer 2 powder in batches and stir for 6 hours until completely dissolved and a clear solution is formed. Add the water-based non-silicone defoamer and continue stirring for 30 minutes.

[0044] Filtration: The prepared release agent solution was filtered through a 5μm filter screen to obtain release agent sample 2.

[0045] Example 3: Synthesis of core functional copolymer 3 and preparation of release agent sample 3 Synthesis of core functional copolymer 3 Materials preparation: Weigh out 94.5 mol of N-vinylpyrrolidone, 4.0 mol of lauryl methacrylate, 0.5 mol of ethyl 2-phosphate acrylate, and 1.0 mol of tert-butyl methacrylate. Weigh out azobisisobutyronitrile as the initiator, with a molar amount equal to 0.1 mol of the total molar amount of all monomers. Prepare isopropanol as the reaction solvent and n-hexane as the precipitant.

[0046] Solution preparation: Add the above monomers and AIBN to isopropanol and stir to dissolve. Control the total mass concentration of monomers to 10 wt% of the total mass of the isopropanol solution.

[0047] Polymerization reaction implementation: Transfer the prepared solution to a three-necked flask. Start stirring at 200 rpm. Purge the system with high-purity nitrogen gas for 15 min. Place the reactor in a constant-temperature oil bath and maintain the reaction for 4 h.

[0048] Purification: After the reaction is complete, stop heating and cool to room temperature. Slowly add the reaction solution dropwise to n-hexane (10:1 volume ratio) with stirring to precipitate. Discard the supernatant, dissolve the precipitate in a small amount of isopropanol, and add it dropwise to n-hexane again to precipitate. Repeat this dissolution and precipitation process twice.

[0049] Drying: The purified precipitate was placed in a vacuum drying oven and dried for 24 hours at room temperature and a vacuum degree ≤0.09MPa to obtain the core functional copolymer 3 solid powder.

[0050] Preparation of release agent sample 3 Materials preparation: Core functional copolymer 3 obtained in Example 3, water-based non-silicone defoamer, and deionized water.

[0051] Composition ratio: Weigh 0.5 parts by weight of core functional copolymer 3, 0.01 parts by weight of water-based non-silicone defoamer, and make up the remainder to 100 parts by weight of deionized water.

[0052] Preparation process: Add deionized water to the preparation tank and start stirring at 100 rpm. Slowly add the core functional copolymer 3 powder in batches and stir for 2 hours until completely dissolved and a clear solution is formed. Add the water-based non-silicone defoamer and continue stirring for 15 minutes.

[0053] Filtration: The prepared release agent solution was filtered through a 1μm filter screen to obtain release agent sample 3.

[0054] Comparative Examples 1-5: Comparative Example 1: Traditional Physically Compounded Water-Based Release Agent Compared to the release agent prepared in the embodiments of this invention, the difference lies in that it does not contain a core functional copolymer, but instead adopts a physical compounding system from the prior art. The specific composition is: 40 parts by weight of polyvinylpyrrolidone, 15 parts by weight of mineral oil emulsion, 10 parts by weight of zinc stearate emulsion, 1 part by weight of isomeric tridecyl alcohol polyoxyethylene ether, 0.05 parts by weight of waterborne non-silicone defoamer, and deionized water to a total of 100 parts by weight. All other preparation processes are carried out under conventional conditions.

[0055] Comparative Example 2: Copolymer release agent without programmed pyrolysis-triggered monomers Compared to the core functional copolymer 1 prepared in Example 1, the difference lies in that tert-butyl methacrylate was not added during the synthesis of the core functional copolymer. The molar percentage of N-vinylpyrrolidone was adjusted to 89.8 mol% to make up the total molar percentage. The molar percentages of all other monomers, the amount of initiator, the reaction conditions, purification, and drying conditions remained the same as in Example 1. When formulating the release agent, this copolymer was used instead of core functional copolymer 1, and the other components and formulation process were the same as in Example 1.

[0056] Comparative Example 3: Copolymer release agent without potent mold-anchoring monomers Compared to the core functional copolymer 1 prepared in Example 1, the difference lies in that ethyl 2-phosphate acrylate is not added during the synthesis of the core functional copolymer. The molar percentage of N-vinylpyrrolidone is adjusted to 88.0 mol% to make up the total molar percentage. The molar percentages of all other monomers, the amount of initiator, the reaction conditions, purification, and drying conditions are the same as in Example 1. When formulating the release agent, this copolymer is used instead of core functional copolymer 1, and the other components and formulation process are the same as in Example 1.

[0057] Comparative Example 4: Copolymer release agent that has not been adequately purified and dried Compared to the core functional copolymer 1 prepared in Example 1, the difference lies in that the solvent precipitation purification process is performed only once in the purification step of the core functional copolymer, and the drying time is shortened to 12 hours. All other monomer molar percentages, initiator dosages, reaction conditions, and the composition and process for preparing the release agent remain the same as in Example 1.

[0058] Comparative Example 5: Copolymer release agent without molecularly flexible lubricating monomers Compared to the core functional copolymer 1 prepared in Example 1, the difference lies in that lauryl methacrylate is not added during the synthesis of the core functional copolymer. The molar percentage of N-vinylpyrrolidone is adjusted to 95.8 mol% to make up the total molar percentage. The molar percentages of all other monomers, the amount of initiator, the reaction conditions, purification, and drying conditions are all the same as in Example 1. When formulating the release agent, this copolymer is used instead of core functional copolymer 1, and the other components and formulation process are the same as in Example 1.

[0059] Test Example 1: Test on the film uniformity and defects of the release agent Objective: To evaluate the uniformity and defects of the film formed by the release agent on the mold surface.

[0060] Samples to be tested: Release agent sample 1 (prepared according to Example 1), release agent sample 2 (prepared according to Example 2), release agent sample 3 (prepared according to Example 3), Comparative Example 1 (conventional physical compound water-based release agent), Comparative Example 2 (release agent prepared from copolymer release agent without programmed pyrolysis triggering monomer), Comparative Example 3 (release agent prepared from copolymer release agent without strong mold anchoring monomer), Comparative Example 4 (release agent prepared from copolymer release agent without sufficient purification and drying), Comparative Example 5 (release agent prepared from copolymer release agent without molecular-level flexible lubricating monomer).

[0061] Experimental steps: Prepare 8 304 stainless steel plates with dimensions of 100mm x 100mm x 2mm as test molds.

[0062] All test molds were pretreated: their surfaces were wiped with acetone to remove oil, then rinsed with deionized water, and finally dried in an oven at 100°C for 30 minutes.

[0063] The dried test mold plate was placed on a constant temperature heating plate, and its surface temperature was heated and stabilized at 60℃.

[0064] Using precision spraying equipment, each type of release agent to be tested was uniformly sprayed onto the surface of the corresponding test mold. The spraying parameters were uniformly set as follows: the spray gun was 15cm away from the mold surface, the spraying speed was 10cm / s, and the spraying amount was controlled to a wet film thickness of 50μm±5μm.

[0065] Immediately after the coating is completed, the test mold plate is transferred to a constant environment chamber and dried at 25°C and 50% relative humidity for 30 minutes.

[0066] After the film is completely dry, the surface of the release film on each test mold plate is observed visually under a standard white light source. The presence of macroscopically visible pores, cracks, irregular textures, or film peeling is recorded.

[0067] Experimental data: Sample number Macroscopic inhomogeneity of film layer Macroscopic holes macro cracks Film peeling Release agent sample 1 none none none none Release agent sample 2 none none none none Release agent sample 3 none none none none Comparative Example 1 exist exist exist none Comparative Example 2 none none none none Comparative Example 3 none none none exist Comparative Example 4 exist exist none none Comparative Example 5 none none none none Summarize: In the tests of mold release film uniformity and defects, the mold release agents prepared in this invention (samples 1, 2, and 3) all exhibited uniform and continuous film layers after drying, with no macroscopic defects such as pores, cracks, irregular textures, or film peeling observed. This phenomenon is related to the molecular structure of the hydrophilic self-healing film-forming skeleton in the core functional copolymer of this invention. During the wet film coating stage, water molecules, acting as plasticizers, penetrate the hydrogen bond network between polymer chains, giving the film a certain fluidity, enabling it to conform to the mold surface and fill microscopic depressions. As the water evaporates, the polymer chain segments gradually approach and reconstruct the hydrogen bond network, increasing the film strength. Even if microscopic stress may occur during this process, the residual water at the crack tips will trigger local replasticization of the polymer chain segments, causing the cracks to close automatically, ultimately forming a macroscopically defect-free film layer.

[0068] In contrast, the film layer of Comparative Example 1 exhibited macroscopic inhomogeneity, pores, and cracks, indicating that its multi-component system could not effectively overcome internal stress and achieve self-repair of defects during solvent evaporation and drying. The film layer of Comparative Example 3 showed localized peeling, suggesting that the lack of anchoring groups may affect the bonding strength between the film layer and the substrate. The film layer of Comparative Example 4 exhibited macroscopic inhomogeneity and pores, which may be attributed to the interference of incompletely removed low-molecular-weight impurities or incompletely dried solvent on the film formation process. The film layers of Comparative Examples 2 and 5 maintained the same macroscopic uniformity as the embodiments of the present invention; their main differences are expected to be reflected in subsequent demolding performance and residue tests.

[0069] The above results indicate that the present invention integrates a hydrophilic self-healing film-forming framework through molecular design, which can effectively form a uniform release film layer without macroscopic defects.

[0070] Test Example 2: Magnetic Clay Molding Product Qualification Rate Test Objective: To evaluate the product qualification rate of release agents in magnetic molding processes and reflect their release performance in practical applications.

[0071] Samples to be tested: Release agent sample 1 (prepared according to Example 1), release agent sample 2 (prepared according to Example 2), release agent sample 3 (prepared according to Example 3), comparative example 1 (conventional physical compound water-based release agent), comparative example 3 (release agent prepared from copolymer release agent without strong mold anchoring monomer), comparative example 5 (release agent prepared from copolymer release agent without molecular-level flexible lubricating monomer).

[0072] Experimental steps: Choose a known NdFeB wet magnet molding production line that includes processes such as mold cleaning, release agent spraying, magnetic putty filling, molding, and blank removal.

[0073] According to the standard operating procedures of the production line, the mold is first thoroughly cleaned to ensure that there are no residues.

[0074] The release agent to be tested is loaded into the spraying system.

[0075] During production line operation, the release agent is evenly sprayed onto the working surface of the molding die using the set spraying parameters.

[0076] Start the magnetic putty filling and molding process, and operate according to the preset molding pressure, holding time and other process parameters of the production line.

[0077] Each release agent to be tested was run continuously for 4 hours. At the end of each hour, 100 pressed magnet blank samples were randomly selected from the production line.

[0078] One hundred magnet blank samples collected every hour undergo visual inspection. The inspection items include: whether there are visible traces of sticking to the mold, missing material on the blank surface, cracks on the sides or feet, and whether there is local peeling at the bottom of the blank.

[0079] Calculate the number of qualified blanks without the aforementioned appearance defects each hour, and use this number to calculate the product qualification rate for that hour. Finally, take the average of the qualification rates over 4 hours as the final product qualification rate for the release agent.

[0080] Experimental data: Sample number 1st Hour Pass Rate (%) 2nd hour pass rate (%) 3rd hour pass rate (%) 4th hour pass rate (%) Average pass rate (%) Release agent sample 1 98 97.5 98.5 97 97.75 Release agent sample 2 99 98.5 98 99.5 98.75 Release agent sample 3 96.5 97 96 95.5 96.25 Comparative Example 1 85 78.5 72 69.5 81.25 Comparative Example 3 82 75 68 60.5 71.38 Comparative Example 5 88.5 83 80 74.5 84 Summarize: In the magnetic putty molding product qualification rate test, the release agent samples 1, 2, and 3 prepared according to the examples all showed high average product qualification rates. This is related to the synergistic effect of the molecular-level flexible lubricating monomer and the high-efficiency mold anchoring monomer in the core functional copolymer of the release agent of this invention. The molecular-level flexible lubricating monomer provides a molecular-level lubricating layer on the surface of the release film by introducing long-chain alkyl side chains. This lubricating layer can effectively reduce the friction coefficient between the magnetic putty and the mold wall during the magnetic putty molding process, reduce the adhesion force, and thus promote the smooth demolding of the magnetic blank.

[0081] Meanwhile, the polar functional groups contained in the high-efficiency mold anchoring monomer establish effective adsorption or chelation with the metal mold surface, ensuring that the release film layer remains firmly attached to the mold surface during magnetic putty filling and high-pressure pressing, preventing displacement or local peeling of the film layer under stress. The stable adhesion of the film layer guarantees the continuity and uniformity of lubrication, avoiding mold sticking and blank defects caused by film layer failure. This integrated lubrication and anchoring mechanism ensures the integrity of the magnet blank during demolding, thereby improving the product yield.

[0082] In contrast, Comparative Example 1 showed a significantly lower product yield, indicating that its multi-component system may have insufficient stability or uncoordinated effects among its components, leading to poor lubrication of the release film or poor adhesion to the mold. Comparative Example 3 showed a further decrease in product yield, with more instances of peeling off the foot of the preform, confirming the importance of the anchoring function for the stability of the film on the mold surface. Comparative Example 5 also had a lower product yield than the example samples, potentially exhibiting more sticking to the mold and surface defects on the preform, reflecting the increased friction between the magnetic putty and the mold due to a lack of effective lubrication.

[0083] Test Example 3: Magnet Sintering Residue Test Objective: To evaluate the residues left after the release agent decomposes and volatilizes during the sintering process of a simulated magnet.

[0084] Samples to be tested: Release agent sample 1 (prepared according to Example 1), release agent sample 2 (prepared according to Example 2), release agent sample 3 (prepared according to Example 3), Comparative Example 1 (traditional physical compound water-based release agent), Comparative Example 2 (release agent prepared from copolymer release agent without programmed pyrolysis trigger monomer).

[0085] Experimental steps: Prepare 5 alumina ceramic substrates with dimensions of 50mm x 50mm x 1mm as carriers.

[0086] Pre-treat all ceramic substrates: wipe their surfaces with anhydrous ethanol to remove stains, then rinse with deionized water, and finally dry in an oven at 120°C for 60 minutes.

[0087] Each release agent to be tested was uniformly coated onto the corresponding ceramic substrate surface using a coating rod. The coating thickness was controlled to be 40 μm ± 5 μm wet film thickness.

[0088] The coated ceramic substrate was placed in a forced-air drying oven and dried at 80°C for 30 minutes to ensure that the film was completely dry.

[0089] The dried substrate was placed in a tube sintering furnace. The atmosphere of the sintering furnace was set to a vacuum of 0.01 Pa. The sintering temperature program was set as follows: the temperature was increased from room temperature to 300°C at a rate of 5°C / min and held for 2 hours; then increased to 1150°C at a rate of 10°C / min and held for 4 hours; finally, the temperature was cooled to room temperature at a rate of 10°C / min.

[0090] After sintering, the cooled ceramic substrate is removed.

[0091] Visually inspect each substrate surface for any visible solid residues, carbonization marks, or discoloration.

[0092] Record the observations.

[0093] Experimental data: Sample number Surface solid residue carbonization traces Discoloration of substrate surface Release agent sample 1 none none none Release agent sample 2 none none none Release agent sample 3 none none none Comparative Example 1 exist exist Slight yellowing in some areas Comparative Example 2 exist exist There are localized blackenings. Summarize: In the magnet sintering residue test, samples 1, 2, and 3 of the release agent prepared in this invention, after being treated with a simulated sintering temperature program, showed no visible solid residue, carbonization marks, or discoloration on the ceramic substrate surface after coating. This directly reflects the clean decomposition characteristics of the core functional copolymer in the release agent of this invention during the high-temperature sintering stage. The programmed pyrolysis trigger monomer introduced into the core functional copolymer breaks its chemical bonds during the initial heating stage of the magnet sintering process, triggering the pyrolysis of the entire polymer chain. The pyrolysis products are small molecule volatiles such as carbon dioxide and water, which can completely escape from the substrate surface under a vacuum sintering atmosphere, thus leaving no solid traces after cooling.

[0094] In contrast, after sintering, Comparative Example 1 showed obvious solid residues and carbonization marks on the substrate surface, accompanied by slight local discoloration. This indicates that the organic or inorganic components in traditional release agents cannot be completely decomposed or volatilized at high temperatures, forming solid residues that are difficult to remove. Comparative Example 2 also showed significant solid residues and carbonization marks, and localized blackening appeared on the substrate surface. This result confirms the crucial role of programmed pyrolysis triggering monomers in achieving clean decomposition of core functional copolymers. Without this specific monomer, even high molecular weight polymers may still undergo incomplete pyrolysis at high temperatures, forming carbonaceous residues.

[0095] The above results confirm that the core functional copolymer of the release agent of this invention can achieve complete and clean decomposition during the magnet sintering process through a programmed pyrolysis mechanism, ensuring that there is no residual contamination on the surface of the magnet product. This characteristic has a direct impact on ensuring the purity and subsequent performance of the sintered magnet.

[0096] Test Example 4: Magnetic Properties Test of Sintered Magnets Objective: To evaluate the effect of release agent on the final magnetic properties of the magnet after compression molding and sintering.

[0097] Test samples: Magnet samples that have undergone magnetic mud molding and sintering treatment, wherein during molding, release agent sample 1 (prepared according to Example 1), release agent sample 2 (prepared according to Example 2), release agent sample 3 (prepared according to Example 3), comparative example 1 (traditional physical compound water-based release agent), and comparative example 2 (release agent prepared from copolymer release agent without programmed pyrolysis trigger monomer) were used respectively.

[0098] Experimental steps: Five sintered magnet samples of the same size were randomly selected from each batch of magnets that were molded by each release agent to be tested and treated by the same sintering process.

[0099] All selected sintered magnet samples underwent surface cleaning to remove any surface dust that may be present.

[0100] The magnetic field strength on the surface of each sample was measured using a gaussmeter.

[0101] The magnetic properties of each sample were tested using a hysteresis loop tester. The test parameters included remanence, coercivity, and maximum energy product.

[0102] Record the measurement results for each sample and calculate the average value of 5 samples within the same batch.

[0103] Experimental data: Sample number remanence Coercivity Maximum magnetic energy product Release agent sample 1 1.45 1025 368 Release agent sample 2 1.48 1030 375 Release agent sample 3 1.43 1010 360 Comparative Example 1 1.32 880 310 Comparative Example 2 1.35 915 325 Summarize: In the magnetic performance testing of sintered magnets, the magnets sintered by compression molding using the release agent samples 1, 2, and 3 prepared according to this invention exhibited higher remanence, coercivity, and maximum energy product than the comparative samples. This is directly related to the clean decomposition mechanism achieved by the programmed pyrolysis-triggered monomer in the core functional copolymer of the release agent of this invention. This ensures that during the magnet sintering process, the copolymer can be completely decomposed into volatile small molecules and completely escape from the magnet blank, leaving no solid residue.

[0104] If traditional release agents do not decompose completely during sintering, their residues, such as carbonaceous matter or inorganic oxides, can form non-magnetic inclusions or defects inside or on the surface of the sintered magnet. These non-magnetic inclusions hinder the movement of domain walls, affecting the formation of domain structures and thus reducing the magnet's remanence, i.e., the effective magnetic flux density per unit volume. Simultaneously, these defects may also become regions for reverse domain nucleation, leading to a decrease in coercivity, i.e., a weakening of the magnet's resistance to demagnetization. The maximum energy product, a combined manifestation of remanence and coercivity, will also decrease as a result.

[0105] The clean decomposition characteristics of the release agent in this invention ensure the uniformity and purity of the magnet's microstructure by avoiding the introduction of non-magnetic impurities or defects into the sintered magnet. This residue-free characteristic allows for thorough sintering between magnetic powder particles, forming a dense grain structure and maintaining the magnet's inherent magnetic properties. Therefore, this invention eliminates the negative impact of traditional release agent residues on magnetic properties through a programmed pyrolysis mechanism, ultimately resulting in sintered magnets with high remanence, high coercivity, and a high maximum energy product.

Claims

1. A silicone-free wet-process magnetic molding release agent, characterized in that, It is composed of the following components in parts by weight: Core functional copolymer: 0.5-5.0 parts; Water-based non-silicone defoamer: 0.01-0.07 parts; Deionized water: Add to a total weight of 100 parts; The core functional copolymer is a water-soluble copolymer prepared by free radical copolymerization of hydrophilic self-healing film-forming monomers, molecular-level flexible lubricating monomers, high-efficiency mold anchoring monomers, and programmed pyrolysis triggering monomers.

2. The silicone-free wet-process magnetic molding release agent according to claim 1, characterized in that, The core functional copolymer is specifically: The hydrophilic self-healing film-forming monomer is N-vinylpyrrolidone; The molecular-level flexible lubricating monomer is lauryl methacrylate; The high-efficiency mold anchoring monomer is ethyl 2-phosphate acrylate; The programmed pyrolysis trigger monomer is tert-butyl methacrylate.

3. The silicone-free wet-process magnetic molding release agent according to claim 2, characterized in that, The molar percentage of each monomer in the core functional copolymer is as follows: Lauryl methacrylate: 4.0 mol% - 15.0 mol% Ethyl 2-phosphate acrylate: 0.5 mol% - 2.0 mol% tert-butyl methacrylate: 1.0 mol% - 5.0 mol% N-Vinylpyrrolidone: Balance.

4. The preparation process of a silicone-free wet-process magnetic molding release agent according to any one of claims 1-3, characterized in that, Includes the following steps: S1. Synthesis of core functional copolymer: Hydrophilic self-healing film-forming monomer, molecular-level flexible lubricating monomer, high-efficiency mold anchoring monomer and programmed pyrolysis triggering monomer and initiator are dissolved in reaction solvent and subjected to free radical polymerization reaction at room temperature for 4h-12h to obtain a solution containing core functional copolymer. S2. Purification and drying: The solution containing the core functional copolymer obtained in step S1 is purified by solvent precipitation and then vacuum dried to obtain a pure core functional copolymer solid powder. S3. Preparation: Dissolve the core functional copolymer solid powder obtained in step S2 and the water-based non-silicone defoamer in deionized water to obtain the silicone-free wet magnetic molding release agent.

5. The preparation process of a silicone-free wet-process magnetic molding release agent according to claim 4, characterized in that, In step S1, the initiator is azobisisobutyronitrile, and its molar amount is 0.1 mol%-1.0 mol% of the total molar amount of all monomers.

6. The preparation process of a silicone-free wet-process magnetic molding release agent according to claim 1, characterized in that, In step S1, the reaction solvent is isopropanol, and the total mass concentration of all monomers is 10wt%-30wt% of the total mass of the solution.

7. The preparation process of a silicone-free wet-process magnetic molding release agent according to claim 4, characterized in that, In step S2, the solvent precipitation purification specifically involves adding a solution containing the core functional copolymer dropwise to n-hexane as a precipitant for precipitation, wherein the volume ratio of the precipitant to the solution is 10:1-20:

1.

8. The preparation process of a silicone-free wet-process magnetic molding release agent according to claim 7, characterized in that, The process parameters for vacuum drying are as follows: drying is carried out at room temperature and under a vacuum degree ≤0.09MPa for 24h-48h.

9. The preparation process of a silicone-free wet-process magnetic molding release agent according to claim 4, characterized in that, Step S3 specifically involves dissolving the core functional copolymer solid powder in deionized water under stirring conditions, stirring for 2-6 hours until the system is clear and homogeneous, then adding an aqueous non-silicone defoamer and continuing to stir for 15-30 minutes.

10. The preparation process of a silicone-free wet-process magnetic molding release agent according to claim 9, characterized in that, The process after step S3 includes a filtration step: filtering the prepared release agent solution through a 1μm-5μm filter.