Large-particle diaphragm binder and preparation method thereof

Abstract

The invention relates to the technical field of binders, and discloses a large-particle diaphragm binder and a preparation method thereof.The large-particle diaphragm binder is of a core-shell structure, and the large-particle diaphragm binder is prepared by preparing a crosslinking monomer containing a plurality of active hydroxyl groups and active carboxyl groups in the structure and crosslinking an acrylic monomer. A large number of hydroxyl and carboxyl active functional groups are contained in the structure of the binder, the binder and the diaphragm can form strong hydrogen bonds, firm combination of the binder and ceramic particles is achieved through the hydrogen bond action, meanwhile, Li jumps between a lithium carboxylate group and the ceramic surface, a continuous Li transmission interface channel is constructed, the migration resistance of ions at the interface is reduced, and the service life of the diaphragm is prolonged. According to the invention, a traditional'inert 'binder is successfully transformed into an'active' functional material, so that the industrial pain point that the binding performance and the ion conduction performance in a high-energy density battery are difficult to consider at the same time is solved, and the method has extremely high technical advancement and market application value.

Description

Technical Field

[0001] This invention relates to the field of adhesive technology, specifically to a large-particle membrane adhesive and its preparation method. Background Technology

[0002] Currently, in the structure of lithium batteries, the separator, as a key component separating the positive and negative electrodes and allowing lithium ions to pass through, has a connection stability with the positive and negative electrode sheets that is crucial to the overall performance of the battery. The separator binder, as the core material for achieving a firm bond between the separator and the electrode sheets, directly affects the structural integrity and electrochemical performance of the battery under charge-discharge cycles, mechanical vibration, and high and low temperature environments.

[0003] Currently, lithium battery separator binders mainly include polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), sodium carboxymethyl cellulose (CMC), and polyacrylic acid (PAA). Among them, PVDF was widely used in early lithium batteries due to its good chemical stability and bonding strength. However, PVDF has several drawbacks: on the one hand, the fluorine element in its molecular structure leads to higher material costs, increasing the manufacturing cost of power batteries; on the other hand, PVDF has limited affinity with electrolytes, and its bonding strength is easily reduced due to electrolyte swelling during charge and discharge. After long-term cycling, the separator may peel off from the electrode, leading to increased internal resistance and accelerated capacity decay of the battery.

[0004] The composite system of styrene-butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC) is currently the mainstream choice for water-based binders, offering advantages such as lower cost and environmental friendliness. However, the bonding strength of this system is relatively insufficient, especially in high-energy-density batteries. As electrode thickness and active material loading increase, the interfacial bonding force between the separator and the electrode struggles to meet long-term cycling requirements, easily leading to interfacial slippage or delamination, causing fluctuations in battery performance. Furthermore, SBR exhibits poor swelling resistance in electrolytes and may degrade after prolonged immersion, further weakening the bonding effect.

[0005] Polyacrylic acid (PAA) and its derivatives, as novel adhesives, have shown potential in improving adhesive strength due to their good hydrophilicity and coordination ability with metal ions. However, most existing PAA-based adhesives are nano- or submicron-sized particles, which are prone to agglomeration during coating, leading to decreased coating uniformity. Some areas may exhibit adhesive enrichment or deficiency. Enriched areas can clog membrane pores and hinder lithium-ion transport, while deficient areas cannot form effective adhesion, increasing interfacial resistance and the risk of detachment.

[0006] As lithium batteries develop towards higher energy density, longer cycle life, and higher safety, higher requirements are placed on separator binders: they not only need excellent bonding strength to ensure that the separator and electrode do not detach during long-term cycling, but also good electrolyte compatibility, maintaining structural stability without swelling or degradation under electrolyte immersion; simultaneously, the binder particle size needs to be appropriate, both to uniformly cover the separator surface to form a continuous coating and to avoid clogging pores and affecting ion conduction. Currently, existing binders still have significant shortcomings in terms of particle size design, the balance between bonding strength and ion conduction, and cannot fully meet the development needs of high-performance lithium batteries. Summary of the Invention

[0007] In order to solve the problems mentioned in the background art, the purpose of this invention is to provide a large particle membrane adhesive and its preparation method.

[0008] The objective of this invention can be achieved through the following technical solutions: A large-particle membrane adhesive, comprising the following raw materials measured in parts by weight: Styrene 30-35 parts, isooctyl acrylate 5-15 parts, initiator one 0.5-1 part, cosolvent 0.05-0.1 part, dispersant 4-8 parts, crosslinking agent 0.2-0.5 parts, emulsifier 0.5-1 part, butyl methacrylate 1-2 parts, methyl methacrylate 1-2 parts, acrylonitrile 0.5-1.5 parts, vinyl acetate 5-10 parts, acrylic acid 0.5-1.5 parts, initiator two 0.02-0.05 parts, deionized water 120-150 parts, alcoholysis agent 20-30 parts.

[0009] As a further embodiment of the present invention, the first initiator is azobisisobutyronitrile or benzoyl peroxide; the cosolvent is hexadecane or hexadecyl alcohol; the dispersant is at least one of polyvinylpyrrolidone, polyvinyl alcohol or polyacrylic acid; the emulsifier is sodium dodecylbenzenesulfonate or sodium dodecylbenzenesulfonate; and the second initiator is at least one of potassium persulfate, sodium persulfate or ammonium persulfate.

[0010] As a further aspect of the present invention, the crosslinking monomer is prepared by the following method: N,N-bis(carboxymethyl)-L-lysine and a functionalizing agent were added to tetrahydrofuran and mechanically stirred until homogeneous. The mixture was then heated to 55-65°C and stirred for 3-6 hours. The solvent was then removed by evaporation, and the crude product was collected and purified to obtain the crosslinking monomer.

[0011] As a further embodiment of the present invention, the functionalizing agent is glycidyl methacrylate or 2,3-epoxypropyl acrylate.

[0012] As a further aspect of the present invention, the molar ratio of N,N-bis(carboxymethyl)-L-lysine to the functionalizing agent is 1:2.

[0013] It should be noted that in the above technical solution, N,N-bis(carboxymethyl)-L-lysine and functionalizing reagents are used as raw materials. The amino groups in their structures can undergo ring-opening addition with the epoxy groups. By controlling the ratio of the two, the crosslinked monomer structure can contain two equivalents of active carboxyl groups, two equivalents of active hydroxyl groups, and two equivalents of unsaturated alkenyl functional groups.

[0014] As a further embodiment of the present invention, the alcoholysis agent is a mixture of lithium hydroxide monohydrate, methanol and deionized water in a mass ratio of 2-3:1.5-2:30-40.

[0015] A method for preparing a large-particle membrane adhesive includes the following steps: Step 1: Weigh and prepare all the raw materials; The second step is to add the dispersant, crosslinking agent and half of the emulsifier to four-fifths of the deionized water, stir and mix evenly to obtain an emulsion; Third, styrene, isooctyl acrylate, acrylic acid, initiator 1 and cosolvent are mixed and stirred evenly to obtain a core layer monomer mixture. Step 4: Add the core layer monomer mixture to the emulsion, and form a micro suspension through high-speed homogenization emulsification. Then, introduce nitrogen gas for protection and raise the temperature to 70-80℃. Stir at a stirring rate of 100-300r / min for 4-8 hours to obtain the core layer polymerization solution. Step 5: Add butyl methacrylate, methyl methacrylate, acrylonitrile, vinyl acetate, acrylic acid, initiator II and the remaining emulsifier to the remaining deionized water, stir and emulsify to form a shell monomer mixture. Step 6: Raise the temperature of the core layer polymerization solution to 80-90℃, then add the shell layer monomer mixture. After the addition is complete, keep it warm and stir for 2-4 hours. Then adjust the temperature to 50-60℃, add the alcoholysis agent dropwise, and after the addition is complete, keep it warm for 40-60 minutes. Then vacuum for 1-2 hours, cool down and discharge the material to obtain the diaphragm binder.

[0016] The beneficial effects of this invention are: (1) This invention prepares a thick-particle membrane binder with a shell-core structure through seed emulsion polymerization. The vinyl acetate added to the shell structure undergoes alcoholysis to remove acetic acid molecules, generating polyvinyl alcohol-like structural units. First, its structure is rich in hydroxyl groups, which are strong polar groups that can form strong hydrogen bonds with the polar groups on the surface of the membrane and electrode active materials, significantly improving the adhesion and cohesion of the binder to the substrate and preventing electrode detachment during battery cycling. Moreover, the alcoholysis-derived shell has good water solubility, ensuring the stability and processability of the binder dispersion, facilitating water-based processing, and is environmentally friendly and low-cost. In addition, the polyvinyl alcohol-like structural units have good film-forming properties and a certain degree of flexibility, which helps to form a continuous, dense, and flexible adhesive network after drying, adapting to the volume changes of the active materials during charging and discharging.

[0017] (2) This invention crosslinks acrylic acid monomers by preparing crosslinking monomers containing multiple active hydroxyl and active carboxyl groups in their structure. The -COO⁻Li⁺ in the binder forms strong hydrogen bonds with the hydroxyl groups (-OH) on the membrane surface. This hydrogen bonding achieves a strong bond between the binder and ceramic particles. Simultaneously, Li⁺ "jumps" between the lithium carboxylate groups and the ceramic surface, constructing continuous Li⁺ transport interface channels and reducing the resistance to ion migration at the interface. After lithiation, lithium carboxylate (-COO⁻Li⁺) is a strong electrolyte and can dissociate into free Li⁺ in the electrolyte. These Li⁺ molecules are directly distributed in the binder network, becoming an additional, uniformly distributed lithium ion source, effectively supplementing lithium ion loss during battery cycling and directly participating in ion conduction at the interface. Lithated hydroxyl groups (-OLi) or unlithiated hydroxyl groups (-OH) undergo weak coordination with Li⁺. This coordination effect is much stronger than the solvation effect but weaker than chemical bonds. Under the influence of an electric field, polymer chain segments continuously coordinate and decoordinate with Li⁺ through dynamic movements (relaxation, rotation, and oscillation). This process, like a relay race, assists Li⁺ in achieving directional hopping migration along the polymer chain. This mechanism significantly reduces the activation energy of Li⁺ migration, making Li⁺ transport at the binder interface layer smoother, thereby greatly improving the battery's fast-charging (high-rate) performance and low-temperature performance.

[0018] (3) This invention successfully transforms traditional “inert” binders into “active” functional materials, solving the industry pain point that it is difficult to balance the bonding performance and ion conduction performance in high energy density batteries. It has extremely high technological advancement and market application value.

[0019] (4) Large particle physical morphology: The microstructure of this binder consists of monodisperse microspheres with a particle size D(50) of 3-8 μm (SPAN value ≤ 1). The large size and narrow distribution ensure that it can form a uniform and porous microstructure on the surface of the diaphragm or electrode during coating, which is beneficial to electrolyte wetting and ion transport. The 3-8 μm particle size binder coating will not clog the pores of the diaphragm, ensuring a gas permeability increase of <30s for the coated diaphragm, while ensuring strong adhesion between the diaphragm and the electrode in the ceramic coating, and better maintaining the stability of the diaphragm / electrode interface.

[0020] Of course, any product implementing this invention does not necessarily need to achieve all of the advantages described above at the same time. Detailed Implementation

[0021] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. 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.

[0022] Example 1 A large-particle membrane adhesive, comprising the following raw materials measured in parts by weight: 30 parts styrene, 5 parts isooctyl acrylate, 0.5 parts azobisisobutyronitrile, 0.05 parts hexadecane, 4 parts polyvinylpyrrolidone, 0.2 parts crosslinking agent, 0.5 parts sodium dodecylbenzenesulfonate, 1 part butyl methacrylate, 1 part methyl methacrylate, 0.5 parts acrylonitrile, 5 parts vinyl acetate, 0.5 parts acrylic acid, 0.02 parts potassium persulfate, 120 parts deionized water, and 20 parts alcoholysis agent.

[0023] The preparation method of the diaphragm adhesive includes the following steps: Step 1: Weigh and prepare all the raw materials; Step 2: Add polyvinylpyrrolidone, crosslinking agent and half of sodium dodecylbenzenesulfonate to four-fifths of deionized water, stir and mix evenly to obtain emulsion; Third, styrene, isooctyl acrylate, acrylic acid, azobisisobutyronitrile and hexadecane are mixed and stirred evenly to obtain a core layer monomer mixture. Step 4: Add the core layer monomer mixture to the emulsion, form a micro suspension through high-speed homogenization emulsification, introduce nitrogen protection, raise the temperature to 75℃, and keep stirring at a stirring rate of 200r / min for 6h to obtain the core layer polymerization solution. Step 5: Add butyl methacrylate, methyl methacrylate, acrylonitrile, vinyl acetate, acrylic acid, potassium persulfate and the remaining sodium dodecylbenzene sulfonate to the remaining deionized water, stir and emulsify to form a shell monomer mixture. Step 6: Raise the temperature of the core layer polymerization solution to 85°C, then slowly add the shell layer monomer mixture over a 1-hour period. After addition, keep the mixture warm and stir for 3 hours. Step 7: Adjust the temperature of the polymer reaction solution obtained in step 6 to 55°C, add the alcoholysis agent dropwise, keep it warm for 40 minutes after the addition is complete, then evacuate for 2 hours, cool down and discharge the material to obtain the diaphragm adhesive.

[0024] The crosslinking monomers were prepared using the following method: 0.6 g of N,N-bis(carboxymethyl)-L-lysine and 0.65 g of glycidyl methacrylate were added to tetrahydrofuran and mechanically stirred until homogeneous. The mixture was then heated to 60 °C and stirred for 4 h. The solvent was removed by evaporation, and the crude product was collected and purified to obtain the crosslinking monomer.

[0025] The alcoholysis agent is a mixture of lithium hydroxide monohydrate, methanol and deionized water in a mass ratio of 2.5:1.5:35.

[0026] Example 2 A large-particle membrane adhesive, comprising the following raw materials measured in parts by weight: 32 parts styrene, 10 parts isooctyl acrylate, 0.6 parts azobisisobutyronitrile, 0.08 parts hexadecane, 6 parts polyvinylpyrrolidone, 0.4 parts crosslinking agent, 0.6 parts sodium dodecylbenzenesulfonate, 1.5 parts butyl methacrylate, 1.5 parts methyl methacrylate, 1 part acrylonitrile, 8 parts vinyl acetate, 1 part acrylic acid, 0.03 parts potassium persulfate, 130 parts deionized water, and 25 parts alcoholysis agent.

[0027] The preparation method of the diaphragm adhesive includes the following steps: Step 1: Weigh and prepare all the raw materials; Step 2: Add polyvinylpyrrolidone, crosslinking agent and half of sodium dodecylbenzenesulfonate to four-fifths of deionized water, stir and mix evenly to obtain emulsion; Third, styrene, isooctyl acrylate, acrylic acid, azobisisobutyronitrile and hexadecane are mixed and stirred evenly to obtain a core layer monomer mixture. Step 4: Add the core layer monomer mixture to the emulsion, form a micro suspension through high-speed homogenization emulsification, introduce nitrogen protection, raise the temperature to 75℃, and keep stirring at a stirring rate of 200r / min for 6h to obtain the core layer polymerization solution. Step 5: Add butyl methacrylate, methyl methacrylate, acrylonitrile, vinyl acetate, acrylic acid, potassium persulfate and the remaining sodium dodecylbenzene sulfonate to the remaining deionized water, stir and emulsify to form a shell monomer mixture. Step 6: Raise the temperature of the core layer polymerization solution to 85°C, then slowly add the shell layer monomer mixture over a 1-hour period. After addition, keep the mixture warm and stir for 3 hours. Step 7: Adjust the temperature of the polymer reaction solution obtained in step 6 to 55°C, add the alcoholysis agent dropwise, keep it warm for 40 minutes after the addition is complete, then evacuate for 2 hours, cool down and discharge the material to obtain the diaphragm adhesive.

[0028] The crosslinking monomer and alcoholysis agent are the same as in Example 1.

[0029] Example 3 A large-particle membrane adhesive, comprising the following raw materials measured in parts by weight: Styrene 35 parts, isooctyl acrylate 15 parts, azobisisobutyronitrile 1 part, hexadecane 0.1 parts, polyvinylpyrrolidone 8 parts, crosslinking agent 0.5 parts, sodium dodecylbenzenesulfonate 1 part, butyl methacrylate 2 parts, methyl methacrylate 2 parts, acrylonitrile 1.5 parts, vinyl acetate 10 parts, acrylic acid 1.5 parts, potassium persulfate 0.05 parts, deionized water 150 parts, alcoholysis agent 30 parts.

[0030] The preparation method of the diaphragm adhesive includes the following steps: Step 1: Weigh and prepare all the raw materials; Step 2: Add polyvinylpyrrolidone, crosslinking agent and half of sodium dodecylbenzenesulfonate to four-fifths of deionized water, stir and mix evenly to obtain emulsion; Third, styrene, isooctyl acrylate, acrylic acid, azobisisobutyronitrile and hexadecane are mixed and stirred evenly to obtain a core layer monomer mixture. Step 4: Add the core layer monomer mixture to the emulsion, form a micro suspension through high-speed homogenization emulsification, introduce nitrogen protection, raise the temperature to 75℃, and keep stirring at a stirring rate of 200r / min for 6h to obtain the core layer polymerization solution. Step 5: Add butyl methacrylate, methyl methacrylate, acrylonitrile, vinyl acetate, acrylic acid, potassium persulfate and the remaining sodium dodecylbenzene sulfonate to the remaining deionized water, stir and emulsify to form a shell monomer mixture. Step 6: Raise the temperature of the core layer polymerization solution to 85°C, then slowly add the shell layer monomer mixture over a 1-hour period. After addition, keep the mixture warm and stir for 3 hours. Step 7: Adjust the temperature of the polymer reaction solution obtained in step 6 to 55°C, add the alcoholysis agent dropwise, keep it warm for 40 minutes after the addition is complete, then evacuate for 2 hours, cool down and discharge the material to obtain the diaphragm adhesive.

[0031] The crosslinking monomer and alcoholysis agent are the same as in Example 1.

[0032] Comparative Example 1 A large-particle membrane binder differs from Example 2 in that the seventh step of alcoholysis is omitted, and the reaction is directly cooled and discharged after the sixth step of heat preservation.

[0033] Comparative Example 2 A large-particle membrane adhesive differs from Example 2 in that steps five through seven are omitted, and the reaction is carried out directly after the core layer polymerization liquid is obtained in step four and the heat preservation is completed, and the material is discharged by cooling.

[0034] Performance testing A. The particle size of the binder in the examples and comparative examples was measured using a laser particle size analyzer; B. Preparation of coated diaphragm: Take 16.7g of the binder and PVDF from the examples and comparative examples, and mix them with 100g of alumina particles with a particle size of D50 < 1µm, 0.6g of sodium carboxymethyl cellulose, and 150mL of water. Mix at 1000rpm for 5min to obtain a ceramic diaphragm coating slurry. Roll the slurry onto the diaphragm surface, and after drying, obtain a ceramic-coated diaphragm. The diaphragm coating specification is a single-sided surface density of 2-4g / m³. 2 The membrane, used as a test sample, underwent the following performance tests: (1) Peel force test The adhesives used in the examples and comparative examples were coated on the surface of the porous polyolefin membrane substrate and then composited with the positive electrode ternary 622 and the negative electrode graphite electrode, respectively. The pressure composite conditions were 60°C, 5MPa, and 60s, respectively. The membrane after being composited with the positive electrode was then subjected to a 180° peel test. (2) Incremental test of air permeability The air permeability of the base membrane and the coated ceramic diaphragm of each embodiment was tested: air permeability of the coated ceramic diaphragm - air permeability of the base membrane = air permeability increment; (3) Diaphragm ratio and cycle test The coated separators obtained from Implementation Cases 1-3 and Comparative Cases 1-2 were assembled into 3Ah ternary 622 / graphite soft-pack batteries, and their rate performance and cycle performance were tested. The rate performance was tested at 0.5C charge / 0.5C, 1C, 2C, and 5C discharge, and the cycle performance was tested at 1C / 1C charge / discharge.

[0035] The test results are recorded in the table below: Table 1 - Test Results , In summary, the large-particle membrane binder obtained in this invention, by preparing a large-particle core-shell structure and introducing polyvinyl alcohol-like structural units into the shell structure, improves the peel force between the ceramic membrane and the electrode, and reduces the membrane's gas permeability increment. As shown in the table above, the corresponding membrane, rate capability, and cycle performance are all improved.

[0036] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of these embodiments are merely to aid in understanding the method and core ideas of the present invention, including the best mode, and to enable any person skilled in the art to practice the present invention, including manufacturing and using any device or system, and implementing any combined method. It should be noted that those skilled in the art can make various improvements and modifications to the present invention without departing from its principles, and these improvements and modifications also fall within the scope of protection of the claims. The scope of protection of this patent is defined by the claims and may include other embodiments that can be conceived by those skilled in the art. If these other embodiments have structural elements similar to those expressed in the claims, or if they include equivalent structural elements that are not substantially different from those expressed in the claims, then these other embodiments should also be included within the scope of the claims.

[0037] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions will not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A large-particle membrane adhesive, characterized in that, Includes the following raw materials measured in parts by weight: Styrene 30-35 parts, isooctyl acrylate 5-15 parts, initiator one 0.5-1 part, cosolvent 0.05-0.1 part, dispersant 4-8 parts, crosslinking agent 0.2-0.5 parts, emulsifier 0.5-1 part, butyl methacrylate 1-2 parts, methyl methacrylate 1-2 parts, acrylonitrile 0.5-1.5 parts, vinyl acetate 5-10 parts, acrylic acid 0.5-1.5 parts, initiator two 0.02-0.05 parts, deionized water 120-150 parts, alcoholysis agent 20-30 parts.

2. The large-particle membrane adhesive according to claim 1, characterized in that, The first initiator is azobisisobutyronitrile or benzoyl peroxide; the cosolvent is hexadecane or hexadecyl alcohol; the dispersant is at least one of polyvinylpyrrolidone, polyvinyl alcohol or polyacrylic acid; the emulsifier is sodium dodecylbenzenesulfonate or sodium dodecylbenzenesulfonate; the second initiator is at least one of potassium persulfate, sodium persulfate or ammonium persulfate.

3. The large-particle membrane adhesive according to claim 1, characterized in that, The crosslinking monomer is prepared using the following method: N,N-bis(carboxymethyl)-L-lysine and a functionalizing agent were added to tetrahydrofuran and mechanically stirred until homogeneous. The mixture was then heated to 55-65°C and stirred for 3-6 hours. The solvent was then removed by evaporation, and the crude product was collected and purified to obtain the crosslinking monomer.

4. The large-particle membrane adhesive according to claim 3, characterized in that, The functionalizing agent is glycidyl methacrylate or 2,3-epoxypropyl acrylate.

5. The large-particle membrane adhesive according to claim 3, characterized in that, The molar ratio of N,N-bis(carboxymethyl)-L-lysine to the functionalizing agent is 1:

2.

6. The large-particle membrane adhesive according to claim 1, characterized in that, The alcoholysis agent is a mixture of lithium hydroxide monohydrate, methanol, and deionized water in a mass ratio of 2-3:1.5-2:30-40.

7. A method for preparing the large-particle membrane adhesive as described in claim 1, characterized in that, Includes the following steps: Step 1: Weigh and prepare all the raw materials; The second step is to add the dispersant, crosslinking agent and half of the emulsifier to four-fifths of the deionized water, stir and mix evenly to obtain an emulsion; Third, styrene, isooctyl acrylate, acrylic acid, initiator 1 and cosolvent are mixed and stirred evenly to obtain a core layer monomer mixture. Step 4: Add the core layer monomer mixture to the emulsion, and form a micro suspension through high-speed homogenization emulsification. Then, introduce nitrogen gas for protection and raise the temperature to 70-80℃. Stir at a stirring rate of 100-300r / min for 4-8 hours to obtain the core layer polymerization solution. Step 5: Add butyl methacrylate, methyl methacrylate, acrylonitrile, vinyl acetate, acrylic acid, initiator II and the remaining emulsifier to the remaining deionized water, stir and emulsify to form a shell monomer mixture. Step 6: Raise the temperature of the core layer polymerization solution to 80-90℃, then add the shell layer monomer mixture. After the addition is complete, keep it warm and stir for 2-4 hours. Then adjust the temperature to 50-60℃, add the alcoholysis agent dropwise, and after the addition is complete, keep it warm for 40-60 minutes. Then vacuum for 1-2 hours, cool down and discharge the material to obtain the diaphragm binder.