Process for preparing a modified polymer aqueous dispersion

Abstract

This invention discloses a method for preparing modified polymer aqueous dispersions, belonging to the field of polymer material preparation. It provides a method for preparing modified polymer aqueous dispersions through seed emulsion preparation, polymerization to prepare the core phase, polymerization to prepare the intermediate phase, and polymerization to prepare the shell phase. It abandons the traditional single free radical polymerization mechanism and chain transfer agent molecular weight control method, and achieves synergistic optimization of the structure and properties of polymer aqueous dispersions through gradient design of monomer composition, segmented control of initiation system, and in-situ grafting of functional modified monomers.

Description

Technical Field

[0001] This invention relates to the field of polymer material preparation, specifically a method for preparing modified polymer aqueous dispersions through multi-stage non-free radical-initiated aqueous emulsion polymerization. The resulting dispersions can be used as core components of water-based coatings and adhesives, and are particularly suitable for high weather resistance and low VOC building coatings and industrial anti-corrosion coating systems. Background Technology

[0002] Current methods for preparing polymer aqueous dispersions mostly employ free radical emulsion polymerization. In multi-stage polymerization, performance is often improved by controlling the distribution of acidic monomers and the glass transition temperature. However, this method suffers from high dependence on film-forming agents, susceptibility to cracking at high film thicknesses, and poor synergy between water resistance and stain resistance. Furthermore, traditional processes rely on chain transfer agents to control molecular weight, which easily introduces residual impurities. Simultaneously, free radical polymerization tends to produce uneven branching and crosslinking, limiting the storage stability of the dispersion and the mechanical properties of the coating, making it difficult to simultaneously achieve both low film-forming temperature and high weather resistance.

[0003] This invention aims to solve the technical problems in existing polymer aqueous dispersion preparation processes, such as chain transfer agent residue affecting product purity, easy cracking of high-thickness films, inability to synergistically improve water resistance and antifouling properties, as well as low monomer conversion rate and wide particle size distribution of dispersions during polymerization. At the same time, it overcomes the high dependence of traditional free radical polymerization on film-forming aids, achieves low-temperature film formation with no or low film-forming aids, and improves the storage stability of dispersions and the weather resistance and mechanical shock resistance of coatings. Summary of the Invention

[0004] This invention provides a method for preparing modified polymer aqueous dispersions, which abandons the traditional single free radical polymerization mechanism and chain transfer agent molecular weight control method. Through gradient design of monomer composition, segmented control of initiation system, and in-situ grafting of functional modified monomers, the structure and properties of polymer aqueous dispersions are synergistically optimized. The specific process steps are as follows: A method for preparing a modified polymer aqueous dispersion includes the following steps: Step S1, Seed emulsion preparation, includes: adding fatty alcohol polyoxyethylene ether phosphate ammonium salt and polyoxyethylene polyoxypropylene block copolymer to water to form a uniform emulsifier aqueous solution A, blowing nitrogen, adding a mixed monomer of methyl methacrylate and butyl acrylate, adding an initiator, and obtaining a seed emulsion after polymerization; Step S2, monomer pre-emulsion preparation, includes: adding fatty alcohol polyoxyethylene ether phosphate ammonium salt and polyoxyethylene polyoxypropylene block copolymer to water to form a homogeneous emulsifier aqueous solution B; dividing the emulsifier aqueous solution B into three equal parts; adding a pre-mixed homogeneous polymeric first monomer composition dropwise to one part of the emulsifier aqueous solution B to form monomer pre-emulsion B1; adding a pre-mixed homogeneous polymeric second monomer composition dropwise to another part of the emulsifier aqueous solution B to form monomer pre-emulsion B2; and adding a pre-mixed homogeneous polymeric third monomer composition dropwise to the last part of the emulsifier aqueous solution B to form monomer pre-emulsion B3. The polymeric first monomer composition includes a nonionic monomer M1 and a composite acidic functional monomer M2; the polymeric second monomer composition and the polymeric third monomer composition include a nonionic monomer M1, a composite acidic functional monomer M2, and a crosslinking modified monomer M3. Step S3, preparing the core phase by polymerization, includes the following steps: adding the seed latex prepared in step S1 to water, stirring and mixing thoroughly to form a uniform seed dispersion, then raising the temperature to 72.0±0.5℃, purging with nitrogen gas, and simultaneously adding the monomer pre-emulsion B1 prepared in step S2 and the aqueous solution of the redox initiator, and polymerizing to form an aqueous dispersion of the core phase polymer; Step S4, preparing the intermediate phase by polymerization, includes the following steps: the aqueous dispersion of the core-phase polymer prepared in step S3 is heated to 78.5±0.5℃ under stirring and nitrogen purging conditions, while the monomer pre-emulsion B2 prepared in step S2 and the aqueous solution of the coordination initiator are added dropwise to polymerize and form a core-intermediate phase polymer aqueous dispersion; Step S5, preparing the shell phase by polymerization, includes the following steps: the core-intermediate phase polymer aqueous dispersion prepared in step S4 is stirred and purged with nitrogen, and the temperature is adjusted to 75.0±0.5℃. The monomer pre-emulsion B3 prepared in step S2 is added dropwise. After the addition is completed, when the conversion rate is ≥98%, the shell phase polymerization is completed, and a modified polymer aqueous dispersion is formed.

[0005] Further, the nonionic monomer M1 in step S2 is compounded from isooctyl acrylate, isobutyl methacrylate, and cyclohexyl acrylate in a mass ratio of 42.3:35.7:22.0; the composite acidic functional monomer M2 in step S2 is compounded from a mixture of carboxyl monomers and phosphonopropyl methacrylate in a mass ratio of 7.2:1, wherein the carboxyl monomer mixture is composed of acrylic acid and itaconic acid in a mass ratio of 5.1:1; and the crosslinking modified monomer M3 is compounded from γ-methacryloyloxypropyltrimethoxysilane and glycidyl acrylate in a mass ratio of 78.5:21.5.

[0006] Furthermore, based on mass parts, in step S1, for every 1286.5 parts of deionized water, 11.3 parts of fatty alcohol polyoxyethylene ether phosphate ammonium salt and 4.5 parts of polyoxyethylene polyoxypropylene block copolymer are added, along with 450.0 parts of a mixed monomer of methyl methacrylate and butyl acrylate compounded in a mass ratio of 1:1. The initiator is a potassium persulfate initiator aqueous solution, with an addition amount of 18.6 parts and a mass content of 5.2% for the potassium persulfate initiator aqueous solution.

[0007] Furthermore, by mass, in step S2, for every 3876.3 parts of deionized water, 45.2 parts of fatty alcohol polyoxyethylene ether phosphate ammonium salt and 18.1 parts of polyoxyethylene polyoxypropylene block copolymer are added to form a homogeneous emulsifier aqueous solution B. The first monomer composition comprises 4230.8 parts of nonionic monomer M1 and 76.1 parts of composite acidic functional monomer M2; the second monomer composition comprises 435.6 parts of nonionic monomer M1, 88.3 parts of composite acidic functional monomer M2, and 104.0 parts of crosslinking modified monomer M3; the third monomer composition comprises 1435.6 parts of nonionic monomer M1, 88.3 parts of composite acidic functional monomer M2, and 104.0 parts of crosslinking modified monomer M3.

[0008] Furthermore, by mass parts, for every 1890.6 parts of deionized water mentioned in step S3, 176.2 parts of seed latex and 5620.1 parts of the monomer pre-emulsion B1 are added. The redox initiator aqueous solution is a potassium sulfate aqueous solution and a sodium bisulfite aqueous solution, with added amounts of 112.3 parts and 62.4 parts, respectively, and both having a mass concentration of 5.2%.

[0009] Furthermore, by mass fraction, in every 6548.4 parts of the nucleopolymer aqueous dispersion described in step S4, 1941.1 parts of the monomer preemulsion B2 are added. The coordination initiator aqueous solution includes a cobalt acetylacetonate aqueous solution and a trisodium citrate aqueous solution, with added amounts of 36.7 parts and 91.8 parts, respectively, and both having a mass concentration of 3.5%.

[0010] Furthermore, by mass, for every 8304.8 parts of the core-intermediate polymer aqueous dispersion described in step S5, 2941.1 parts of the monomer preemulsion B3 are added.

[0011] Further, in step S1, seed latex preparation, after forming the uniform emulsifier aqueous solution A, the temperature is raised to 75.5±0.5℃, the mixed monomers of methyl methacrylate and butyl acrylate are added and polymerized at a constant temperature for 2.5h, and then naturally cooled to 25±2℃. The temperature in step S2 is controlled at 28±1℃ throughout the entire process; During step S3, when adding the monomer preemulsion B1 and the redox initiator aqueous solution, the temperature, stirring speed, and dropping rate are recorded every 15 minutes. The system temperature is kept stable at 72.0 ± 0.5℃. If the temperature rises by more than 0.8℃, the dropping rate is reduced by 0.1 g / (min). 100g of total monomers), while cooling; if the temperature drops by more than 0.8℃, increase the dropping rate by 0.1g / (min). 100g total monomers), heated simultaneously; During the dropwise addition of monomer preemulsion B2 and coordination initiator aqueous solution in step S4, the temperature and system viscosity were recorded every 10 minutes, maintaining the temperature stable at 78.5±0.5℃ and the system viscosity controlled at 125±10 mPa. s, if the viscosity exceeds 135 mPa s, add deionized water at least 1% of the total water volume; if the viscosity is below 115 mPa The droplet acceleration rate increases by 0.05 g / (min) 100g total monomers); During the dropping process described in step S5, the temperature and system appearance are recorded every 10 minutes, maintaining a stable temperature of 75.0 ± 0.5℃. If gel particles appear in the system, the dropping rate is immediately reduced by 0.08 g / (min). (100g total monomer), increase stirring speed by 10rpm; if the system remains a uniform emulsion, maintain the dropping rate unchanged.

[0012] Furthermore, the quality control indicators of the seed latex mentioned in step S1 are as follows: volume average particle size 32.6±2.0nm, solid content 31.8±0.5wt.%, pH value 3.5~4.0, no gel particles, and no stratification or demulsification during storage. The quality control indicators for the monomer preemulsion described in step S2 are: uniform emulsion without stratification, oil phase content of 49.2±0.3wt.%, and viscosity of 58±5 mPa at 25℃. s; The quality control indicators of the nucleated polymer aqueous dispersion mentioned in step S3 are as follows: After the nucleated polymerization is completed, the quality indicators of the nucleated polymer aqueous dispersion are sampled and tested: the appearance is a uniform milky white emulsion with no gel particles; the volume average particle size is 85.3±3.0nm; the Zeta potential is -38.5±2.0mV; and the theoretical glass transition temperature is -18.7±1.0℃. After the core-intermediate phase polymer aqueous dispersion described in step S4 is completed, samples are taken to test the quality indicators of the core-intermediate phase polymer aqueous dispersion: the appearance is a uniform milky white emulsion, without layering or gelation; the volume average particle size is 108.7±3.5nm; the Zeta potential is -42.3±2.0mV; the theoretical glass transition temperature is 28.3±1.0℃. After all indicators are qualified, proceed to step S5. The quality indicators of the modified polymer aqueous dispersion described in step S5 are as follows: appearance: uniform milky white emulsion, without gel particles; volume average particle size: 128.5~186.3 nm; polydispersity index (PDI): ≤0.045; zeta potential: -45.6±2.0 mV; theoretical glass transition temperature: 56.8±1.0 °C; solid content: 48.5~51.2%.

[0013] Furthermore, after forming the modified polymer aqueous dispersion, the system temperature was raised from 75.0℃ to 85.0±0.5℃ while maintaining a stirring speed of 150 rpm. The heating rate was controlled at 2.0℃ / min. Nitrogen gas was continuously introduced during the heating process at a rate of 0.8 L / min to prevent oxidation of the system. After the temperature stabilized at 85.0±0.5℃, stripping and devolatilization were carried out for 40 min. After the temperature dropped to 45.0±0.5℃, the stirring speed was adjusted to 120 rpm, and 25 wt% of the polymer was added dropwise. Adjust the pH of the system to the range of 8.6-9.2 using % ammonia water. After neutralization, maintain a stirring speed of 120 rpm and a temperature of 45.0±0.5℃, and add polyether-modified silicone defoamer to the system. After completion, maintain a stirring speed of 100 rpm and allow the system to cool naturally to 25±2℃. During the cooling process, continuously introduce nitrogen gas at a rate of 0.5 L / min. After cooling to room temperature, turn off the stirring and nitrogen gas, and filter the dispersion through a 200-mesh nylon screen. After filtration, use a dynamic light scattering instrument to monitor the volume average particle size and polydispersity index of the dispersion in real time. The volume average particle size is in the range of 128.5-186.3 nm, and the PDI is ≤0.045. After the particle size meets the standard, add polyethylene glycol as a stabilizing additive to the dispersion to form a long-term stable modified polymer aqueous dispersion.

[0014] The following are the beneficial effects of implementing the present invention: The modified polymer aqueous dispersion of the present invention has high product purity, thin film, film that is not easy to crack, good water resistance and antifouling performance, as well as high monomer conversion rate during polymerization, narrow particle size distribution of dispersion, low dependence on film-forming aids, low temperature film formation with no / low film-forming aids, and improved storage stability of dispersion and weather resistance and mechanical impact resistance of coating. Detailed Implementation

[0015] Example 1.

[0016] This invention provides a method for preparing modified polymer aqueous dispersions, abandoning the traditional single-radical polymerization mechanism and chain transfer agent molecular weight control method. Through gradient design of monomer compositions, segmented control of the initiation system, and in-situ grafting of functional modified monomers, the method achieves synergistic optimization of the structure and properties of the polymer aqueous dispersion. The specific process steps are as follows: I. Selection of Raw Material System The raw material system for preparing modified polymer aqueous dispersions according to this invention consists of a polymer monomer composition, a composite emulsifier system, a composite initiator system, and deionized water. The type, purity, ratio, and screening criteria of the raw materials in each system are precisely controlled. Traditional thiol chain transfer agents are completely abandoned. The molecular weight and branching degree of the polymer are controlled through the steric hindrance effect of the coordinating monomer. The specific selection requirements and parameters of each raw material system are as follows. All raw materials are of industrial grade purity and are pretreated by dehydration and impurity removal before use to ensure the stability and repeatability of the polymerization reaction.

[0017] (a) Polymer monomer composition The polymer monomer composition is the core reaction raw material, consisting of basic nonionic monomer M1, composite acidic functional monomer M2, and crosslinking modified monomer M3 in a total mass ratio of 92.7:3.5:3.8. The total monomer dosage is precisely calculated based on the final dispersion solid content of 48.5~51.2%. The types, proportions, performance parameters, and selection requirements of each monomer are as follows. All monomers are liquid at 25℃, have good miscibility, and do not exhibit stratification.

[0018] The basic nonionic monomer M1 is a ternary compound system of acrylate and methacrylate, which is composed of isooctyl acrylate, isobutyl methacrylate and cyclohexyl acrylate in a mass ratio of 42.3:35.7:22.0. Under standard conditions of 25°C and 1 bar, the solubility of this compound system in deionized water is 48.6 g / L, which meets the requirement of low water solubility of nonionic monomers. Moreover, the ternary monomers synergistically endow the polymer base with film-forming properties, flexibility and weather resistance. The isooctyl acrylate is selected from industrial-grade products with a purity ≥99.5%, an acid value ≤0.05mgKOH / g, and a moisture content ≤0.03%; isobutyl methacrylate is selected from industrial-grade products with a purity ≥99.4%, an acid value ≤0.06mgKOH / g, and a moisture content ≤0.03%; cyclohexyl acrylate is selected from industrial-grade products with a purity ≥99.3%, an acid value ≤0.04mgKOH / g, and a moisture content ≤0.02%. After blending, the three components exhibit matched reactivity within the polymerization temperature range of 60~85℃, without any uneven polymerization caused by excessive differences in monomer reactivity.

[0019] The composite acidic functional monomer M2 is a binary compound system of carboxyl-containing monomers and phosphonic acid-containing monomers. It is composed of a mixture of carboxyl monomers and phosphonopropyl methacrylate in a mass ratio of 7.2:1, with a total addition amount of 3.5% of the total mass of the polymer monomer composition. This ensures the electrostatic stability of the polymer aqueous dispersion and improves the adhesion of the coating to inorganic substrates such as concrete and metal. Furthermore, the segmented polymerization achieves a gradient distribution of acid groups, avoiding the decrease in water resistance of the coating caused by excessively high local acid concentration. The carboxyl monomer mixture consists of acrylic acid and itaconic acid in a mass ratio of 5.1:1. The acrylic acid is an industrial-grade product with a purity ≥99.8%, a moisture content ≤0.02%, and a polymerization inhibitor content of 200±20ppm. The itaconic acid is an industrial-grade product with a purity ≥99.5%, a moisture content ≤0.03%, and a melting point of 165~168℃. The phosphonopropyl methacrylate is an industrial-grade product with a purity ≥98.5%, a phosphorus content ≥10.2%, a moisture content ≤0.05%, and an acid value of 185~195mgKOH / g. This monomer works synergistically with the carboxyl monomer to improve the storage stability of the dispersion, and the introduction of phosphonic acid groups can enhance the corrosion resistance of the coating.

[0020] The crosslinking modified monomer M3 is a binary compound system of organosiloxane monomer and epoxy compound monomer. It is composed of γ-methacryloyloxypropyltrimethoxysilane and glycidyl acrylate in a mass ratio of 78.5:21.5, and the total addition amount is 3.8% of the total mass of the polymer monomer composition. This monomer can undergo in-situ grafting and mild crosslinking during the polymerization process, which improves the weather resistance, water resistance and mechanical strength of the polymer. Moreover, the degree of crosslinking is controllable and will not cause a decrease in the film-forming properties of the polymer due to excessive crosslinking. The γ-methacryloxypropyltrimethoxysilane is selected from industrial-grade products with a purity ≥98.0%, silicon content ≥8.5%, moisture content ≤0.05%, and hydrolyzed chlorine content ≤0.01%; the glycidyl acrylate is selected from industrial-grade products with a purity ≥99.0%, epoxy value 0.48~0.50 eq / 100g, acid value ≤0.05mgKOH / g, moisture content ≤0.03%, and polymerization inhibitor content 100±10ppm. The reactivity of the two monomers matches that of the basic nonionic monomer M1, enabling in-situ grafting and avoiding the generation of free crosslinking monomers.

[0021] (II) Composite Emulsifier System The composite emulsifier system is composed of anionic and nonionic emulsifiers, with a total addition amount of 1.7% of the total mass of the polymer monomer composition. When used after compounding at a mass ratio of 2.5:1, it can effectively reduce the surface tension of the polymerization system, stabilize monomer droplets and polymer particles, and avoid the formation of gels or clumps during polymerization. Moreover, the HLB value of the emulsifier is 13.8, which matches the HLB value of the polymer monomer composition, resulting in excellent emulsification effect and uniform particle size distribution of the obtained polymer particles.

[0022] The anionic emulsifier selected is fatty alcohol polyoxyethylene ether phosphate ammonium salt, with an ethylene oxide addition number (EO number) of 12. It is an industrial grade product with an effective content of ≥95.0%, an acid value of 45~55mgKOH / g, a moisture content of ≤0.5%, and a pH value (1% aqueous solution) of 3.0~4.0. This emulsifier has good emulsifying properties and stability, and works synergistically with nonionic emulsifiers to improve the storage stability of polymer aqueous dispersions and avoid stratification and demulsification during long-term storage.

[0023] The nonionic emulsifier is a polyoxyethylene-polyoxypropylene block copolymer with an ethylene oxide to propylene oxide molar ratio (EO / PO) of 3.2:1, a number average molecular weight of 3500~3800 g / mol, and is an industrial grade product with an effective content ≥99.0%, a moisture content ≤0.2%, and a cloud point (1% aqueous solution) of 75~80℃, which matches the polymerization reaction temperature range to avoid emulsifier failure due to excessively low cloud point. In addition, this emulsifier has good wetting properties, which can improve the uniformity of monomer pre-emulsion.

[0024] (III) Composite Initiator System The composite initiator system is a binary system of redox initiators and coordination initiators. The two initiators are used at different stages of polymerization, with a total addition amount of 0.32~0.45% of the total mass of the monomer composition. Both are prepared as aqueous solutions before use to avoid excessive local concentration of solid initiator, which may lead to polymerization bursts. Furthermore, the decomposition temperature of the initiator is matched with the polymerization temperature at each stage, which can achieve precise control of the polymerization rate and ensure monomer conversion rate ≥96%.

[0025] The redox initiator is composed of potassium persulfate and sodium bisulfite in a mass ratio of 1.8:1. Industrial grade products are selected. The potassium persulfate has a purity of ≥99.5%, moisture content ≤0.05%, and iron content ≤0.001%; ​​the sodium bisulfite has a purity of ≥98.5%, moisture content ≤0.1%, and iron content ≤0.002%. Both are prepared into 5.2 wt.% aqueous solutions. They should be prepared and used immediately and stored away from light. The decomposition temperature of this redox initiator is 65~75℃. It is suitable for the first stage of nucleophase polymerization, has high initiation efficiency, and can quickly achieve the preparation of nucleophase polymers.

[0026] The coordination initiator is composed of cobalt acetylacetonate and trisodium citrate in a mass ratio of 1:2.5, using industrial-grade products. The cobalt acetylacetonate has a purity ≥98.0%, moisture content ≤0.5%, and cobalt content ≥20.5%; the trisodium citrate has a purity ≥99.0%, moisture content ≤0.1%, and a pH value (5% aqueous solution) of 7.5~8.5. Both are prepared into 3.5wt.% aqueous solutions and used immediately. The decomposition temperature of this coordination initiator is 75~80℃, which is suitable for the second-stage mesophase polymerization. It can regulate the molecular chain structure of the polymer through coordination, reduce the degree of branching of the polymer, and achieve precise control of molecular weight. Moreover, it can ensure the uniform molecular weight distribution of the polymer without the addition of chain transfer agents.

[0027] (iv) Deionized water Deionized water serves as the continuous phase in the polymerization reaction, acting as both a solvent and dispersion medium throughout the process. Its conductivity is ≤10 μS / cm (25℃), pH value is 6.5~7.5, total hardness (as CaCO3) ≤1 mg / L, chloride ion content ≤0.1 mg / L, sulfate ion content ≤0.1 mg / L, and it is free of mechanical impurities, microorganisms, and organic matter. Before use, it is filtered through a 0.22 μm microporous membrane to prevent impurities from affecting the stability of the polymerization reaction. The total amount of deionized water used is precisely calculated based on the final polymer aqueous dispersion's solid content of 48.5~51.2%. Specifically, 8.5% of the total water is used for seed latex preparation, 32.3% for monomer pre-emulsification, 45.0% for initial loading into the polymerization reactor, and 14.2% for post-treatment replenishment. Precise control of water usage at each stage ensures the solid content and reaction flowability of the polymerization system.

[0028] (v) Monomers for seed latex preparation The seed latex was prepared using methyl methacrylate and butyl acrylate as polymerizable monomers, blended at a 1:1 mass ratio. Both monomers were of industrial-grade purity: methyl methacrylate purity ≥99.5%, acid value ≤0.05 mg KOH / g, and moisture ≤0.03%; butyl acrylate purity ≥99.5%, acid value ≤0.05 mg KOH / g, and moisture ≤0.03%. The polymerization inhibitor content was 200±20 ppm for both monomers. This blended monomers exhibited high reactivity, enabling the rapid preparation of seed latex with uniform particle size. The volume average particle size of the seed latex was controlled at approximately 32.6 nm, with a solid content of 31.8%, providing stable nucleation centers for the subsequent three-stage polymerization and preventing excessively wide particle size distribution during polymerization.

[0029] II. Pretreatment before polymerization The pretreatment before polymerization includes three core steps: seed latex preparation, monomer pre-emulsification, and initiator aqueous solution preparation. Each step is completed in specialized equipment, and the operating parameters, raw material dosage, and reaction conditions are precisely controlled. All operations are carried out in a clean environment at room temperature of 25±2℃, avoiding the introduction of impurities and oxygen throughout the process to ensure the stability and repeatability of the subsequent three-stage polymerization reaction. The specific operating procedures, process parameters, and quality control requirements for each step are as follows.

[0030] (a) Seed latex preparation S11 seed latex preparation was carried out in a 5L jacketed glass reactor. The reactor was equipped with a constant-speed stirrer, nitrogen vent pipe, thermometer, and constant-temperature water bath. The stirrer was a three-bladed propeller type, and the distance between the stirrer and the bottom of the reactor was 1 / 4 of the reactor height. The specific operating procedures and parameters are as follows: Add 1286.5g of deionized water to the reactor, then add 20% of the total amount of the composite emulsifier system (i.e., 11.3g of fatty alcohol polyoxyethylene ether phosphate ammonium salt and 4.5g of polyoxyethylene polyoxypropylene block copolymer), turn on the stirrer, set the stirring speed to 250rpm, and stir for 15min until the emulsifier is completely dissolved and a uniform emulsifier aqueous solution is formed.

[0031] Turn on the constant temperature water bath to raise the temperature of the material in the reactor to 75.5±0.5℃. At the same time, turn on the nitrogen gas inlet pipe to introduce high-purity nitrogen (purity ≥99.99%) into the aqueous solution at a rate of 0.8L / min for 35min to remove dissolved oxygen from the aqueous solution and ensure that the polymerization reaction is carried out in an oxygen-free atmosphere.

[0032] After nitrogen deoxygenation is completed, maintain nitrogen gas flow rate of 0.5 L / min, stirring speed of 250 rpm, and temperature of 75.5 ± 0.5 ℃, and add 450.0 g of a mixture of methyl methacrylate and butyl acrylate monomers (mass ratio of 1:1) at once, and stir for 5 min to allow the monomers and emulsifier aqueous solution to be initially mixed to form a pre-dispersed system.

[0033] Subsequently, 18.6 g of potassium persulfate initiator aqueous solution (potassium persulfate content of 5.2 wt.%, corresponding to an initiator addition amount of 0.32 wt.% of the seed polymer monomer mass) was added at once. After addition, the reaction conditions were kept unchanged, and polymerization was carried out at a constant temperature for 2.5 h. The state of the system was observed during the polymerization process. When the system changed from a milky white turbid liquid to a semi-transparent emulsion, the seed latex polymerization was completed.

[0034] After polymerization, turn off the constant temperature water bath, keep nitrogen gas flowing and stirring at 250 rpm, and allow the material in the reactor to cool naturally to 25±2℃. Turn off the stirring and nitrogen gas, and transfer the obtained seed latex to a sealed polyethylene container for storage at room temperature away from light.

[0035] The quality control indicators for seed latex are: volume average particle size 32.6±2.0nm, solid content 31.8±0.5wt.%, pH value 3.5~4.0, no visible gel particles, and no stratification or demulsification during storage. If the particle size exceeds the range, the amount of emulsifier or the stirring speed needs to be adjusted and the latex needs to be prepared again.

[0036] (ii) Monomer pre-emulsification Monomer pre-emulsification is carried out in a 10L stainless steel pre-emulsification reactor. The equipment is equipped with a constant-speed anchor stirrer, a constant-pressure dropping funnel, and a thermometer. The gap between the stirring paddle and the reactor wall is ≤5mm to ensure uniform mixing of materials. The temperature inside the reactor is controlled at 28±1℃ throughout the pre-emulsification process. The specific operating procedures and parameters are as follows: Add 3876.3g of deionized water to the pre-emulsification vessel, then add the remaining 80% of the composite emulsifier system (i.e., 45.2g of fatty alcohol polyoxyethylene ether phosphate ammonium salt and 18.1g of polyoxyethylene polyoxypropylene block copolymer). Turn on the stirrer and set the stirring speed to 300rpm. Stir for 20min until the emulsifier is completely dissolved and a homogeneous emulsifier aqueous solution is formed. Monitor the temperature of the aqueous solution. If the temperature deviates from 28±1℃, adjust it by circulating cold or warm water through the jacket.

[0037] Turn on the constant pressure dropping funnel and slowly drop the pre-mixed polymer monomer composition (6489.0g basic nonionic monomer M1, 245.0g composite acidic functional monomer M2, and 266.6g crosslinking modified monomer M3) into the emulsifier aqueous solution. The dropping rate is controlled at 120g / min. During the dropping process, the stirring speed is maintained at 300rpm and the temperature is 28±1℃ to avoid monomer agglomeration and uneven emulsification caused by excessively fast dropping rate.

[0038] After the monomer is added, close the constant pressure dropping funnel, maintain the stirring speed at 300 rpm and the temperature at 28±1℃, and continue stirring for 45 minutes to fully mix the monomer with the emulsifier aqueous solution and form a stable milky white monomer pre-emulsion. During the stirring process, take a sample for observation every 10 minutes. The emulsion should be free of stratification, oil phase floating layer, and solid particles.

[0039] After pre-emulsification, the monomer pre-emulsion is filtered through a 100-mesh nylon screen using positive pressure filtration with a filtration pressure ≤0.1MPa to remove unemulsified monomer particles, trace amounts of gel, and other impurities from the emulsion, thus preventing problems such as uneven particle size and gelation during subsequent polymerization.

[0040] The filtered monomer preemulsion was transferred to a sealed storage tank under nitrogen protection and stored at room temperature away from light for no more than 8 hours to prevent demulsification. A small amount of nitrogen was continuously introduced into the storage tank (at a rate of 0.2 L / min) to isolate it from oxygen.

[0041] The quality control indicators for the monomer preemulsion are: uniform emulsion without stratification, oil phase content 49.2±0.3wt.%, and viscosity (25℃, rotational viscometer) 58±5 mPa. If the emulsion separates into layers or an oil phase floats, add 0.5~1.0g of composite emulsifier and stir again for 30min.

[0042] (III) Preparation of initiator aqueous solution The initiator aqueous solution is divided into a redox initiator aqueous solution and a coordination initiator aqueous solution. Both types of aqueous solutions are prepared separately and used immediately after preparation. They should be used within 30 minutes after preparation to avoid initiator decomposition and inactivation. The preparation process is carried out in brown glass beakers in the dark. The specific preparation process and parameters are as follows: Preparation of redox initiator aqueous solution Take a brown glass beaker (2L), add 865.2g of deionized water, turn on the magnetic stirrer (stirring speed 500rpm), slowly add 45.0g of industrial grade potassium persulfate, stir for 15min until the potassium persulfate is completely dissolved to form a potassium persulfate aqueous solution.

[0043] In a separate brown glass beaker (2L), add 872.6g of deionized water, turn on the magnetic stirrer (stirring speed 500rpm), slowly add 25.0g of industrial grade sodium bisulfite, stir for 10min until the sodium bisulfite is completely dissolved to form an aqueous solution of sodium bisulfite.

[0044] Both aqueous solutions had a mass concentration of 5.2 wt.%. After preparation, they were transferred to brown sealed dropper bottles, stored away from light, and kept for later use. The volume ratio of the two initiator aqueous solutions was 1.8:1, which matched the mass ratio of potassium persulfate and sodium bisulfite.

[0045] Preparation of aqueous solution of coordination initiator Take a brown glass beaker (2L), add 964.8g of deionized water, turn on the magnetic stirrer (stirring speed 500rpm), slowly add 35.0g of industrial grade cobalt acetylacetonate, stir for 20min until the cobalt acetylacetonate is completely dissolved to form an aqueous solution of cobalt acetylacetonate.

[0046] In a separate brown glass beaker (2L), add 951.5g of deionized water, turn on the magnetic stirrer (stirring speed 500rpm), slowly add 87.5g of industrial grade trisodium citrate, stir for 15min until the trisodium citrate is completely dissolved to form a trisodium citrate aqueous solution.

[0047] The mass concentration of both aqueous solutions was 3.5 wt.%. After preparation, they were transferred to brown sealed dropper bottles, stored in the dark, and kept for later use. The volume ratio of the two initiator aqueous solutions was 1:2.5, which matched the mass ratio of cobalt acetylacetonate and trisodium citrate.

[0048] The quality control indicators for the initiator aqueous solution are as follows: the solution is uniform and transparent, without undissolved solid particles, and the pH value meets the requirements (potassium persulfate aqueous solution pH 2.0~3.0, sodium bisulfite aqueous solution pH 4.0~5.0, cobalt acetylacetonate aqueous solution pH 5.5~6.5, trisodium citrate aqueous solution pH 7.5~8.5). If undissolved particles appear, the solution needs to be heated to 30±2℃ and stirred until completely dissolved.

[0049] (iv) Equipment and material preparation requirements for pretreatment processes All equipment involved in the pretreatment (reactors, pre-emulsification vessels, storage tanks, beakers, dropping bottles, etc.) must be cleaned three times with deionized water and then dried with nitrogen to ensure that there are no residual impurities or moisture on the inner walls of the equipment, thus avoiding contamination of the raw materials.

[0050] All raw materials (polymer monomers, emulsifiers, initiators, deionized water, etc.) must be placed in a constant temperature environment of 25±2℃ for 2 hours in advance to ensure that the raw material temperature is consistent with the operating temperature and to avoid uneven mixing and poor dissolution caused by temperature differences.

[0051] All measuring instruments used in the pretreatment process (electronic balance, graduated cylinder, pipette, etc.) must be calibrated with the following accuracy requirements: mass measurement accuracy ±0.01g, volume measurement accuracy ±0.1mL, to ensure the accuracy of raw material addition.

[0052] All pretreated materials (seed latex, monomer preemulsion, initiator aqueous solution) must be properly labeled with the material name, preparation time, concentration / solid content, and stored separately by batch to avoid confusion. The storage environment must be kept clean, dry, and protected from light, with the temperature controlled at 25±2℃.

[0053] III. Three-stage aqueous emulsion polymerization process The three-stage aqueous emulsion polymerization is carried out in a 50L stainless steel jacketed reactor. The reactor is equipped with a constant-speed mechanical stirrer, a dual-channel constant-flow drip pump, a nitrogen vent pipe, a platinum resistance thermometer, a jacketed constant temperature control system, and a tail gas treatment device. The stirrer is an anchor type, with a blade diameter of 70% of the reactor's inner diameter and a blade height of 1 / 5 of the reactor's height from the bottom. A nitrogen atmosphere (purity ≥99.99%) is maintained throughout the process. The total solids content of the polymerization system is controlled at 48.5~51.2%. The monomer addition mass ratio for the three-stage polymerization is 65.2:21.8:13.0. The polymerization of the core phase, mesophase, and shell phase is carried out sequentially in each stage. After each stage of polymerization is completed, a sample is taken and tested to ensure it passes before proceeding to the next stage. The specific operating procedures, process parameters, and quality control requirements are as follows.

[0054] (a) Initial preparation of the reactor Before polymerization, the reactor should be thoroughly cleaned: first, rinse the reactor body, agitator, and drip pipeline three times with deionized water, then rinse once with anhydrous ethanol in a circulating manner. Turn on the reactor jacket and heat it with steam to raise the temperature inside the reactor to 80°C and maintain it for 30 minutes. Then, cool water should be introduced to cool it down to 25°C. Finally, use nitrogen to blow dry the residual moisture inside the reactor to ensure that there are no impurities, no moisture, and no oil stains inside the reactor.

[0055] Check the equipment operating status: Start the agitator and test that the stirring speed is adjustable and stable within the range of 0~300rpm, with no abnormal noise; calibrate the constant flow drip pump to ensure that the drip rate error is ≤±2%; check the platinum resistance thermometer and calibrate its accuracy to ±0.1℃; confirm that the nitrogen gas inlet pipe and exhaust gas treatment device are unobstructed, and that the jacket constant temperature control system can accurately control the temperature within the range of ±0.5℃.

[0056] (II) First stage polymerization (nuclear phase preparation) Add 1890.6g of deionized water (45.0% of the total water volume) to the pretreated reactor, then add 176.2g of seed latex (calculated as 2.6% of the total monomer mass), turn on the stirrer, set the stirring speed to 180rpm, and stir for 10min to fully mix the seed latex and deionized water to form a uniform seed dispersion.

[0057] Turn on the jacket constant temperature control system to raise the temperature of the material in the reactor to 72.0±0.5℃. At the same time, turn on the nitrogen vent pipe to introduce high-purity nitrogen at a rate of 1.2L / min for 25 minutes to remove dissolved oxygen from the system. During this period, take a sample every 5 minutes to test the dissolved oxygen content of the system. The dissolved oxygen should be ≤0.1mg / L.

[0058] After oxygen removal, maintain a nitrogen gas flow rate of 0.8 L / min, a stirring speed of 180 rpm, and a temperature of 72.0 ± 0.5 °C. Start the dual-channel constant flow drip pump and simultaneously add the first monomer composition and the redox initiator aqueous solution. The first monomer composition consists of 4230.8 g of the basic nonionic monomer M1 and 76.1 g of the composite acidic functional monomer M2 (without crosslinking modified monomer M3), with a dropping rate set to 2.1 g / (min). 100g of total monomers), corresponding to a total dropping time of 158min; the redox initiator aqueous solution was mixed with potassium persulfate aqueous solution and sodium bisulfite aqueous solution in a volume ratio of 1.8:1 and then dropped, with the dropping rate synchronized with the first monomer composition, and the total amount added was 0.45wt.% of the mass of the first monomer, i.e., 112.3g of potassium persulfate aqueous solution and 62.4g of sodium bisulfite aqueous solution.

[0059] The system status was monitored in real time during the dropping process. Temperature, stirring speed, and dropping rate were recorded every 15 minutes. The system temperature was kept stable at 72.0 ± 0.5℃. If the temperature rose by more than 0.8℃, the dropping rate was reduced by 0.1 g / (min). (100g total monomer), while increasing the jacket cooling water flow rate; if the temperature drops by more than 0.8℃, increase the dropping rate by 0.1g / (min). (100g total monomer), appropriately increase the jacket heating temperature.

[0060] After the first monomer composition and the aqueous solution of the redox initiator are added dropwise, the current reaction conditions are kept unchanged, and the polymerization is carried out at a constant temperature for 1.2 hours. During the holding period, samples are taken every 20 minutes, and the monomer conversion rate is determined by mass method. When the conversion rate is ≥96%, the core phase polymerization is considered to be complete.

[0061] After the nucleus-phase polymerization is completed, samples are taken to test the quality indicators of the nucleus-phase polymer aqueous dispersion: the appearance is a uniform milky white emulsion with no gel particles; the volume average particle size is 85.3±3.0nm; the Zeta potential is -38.5±2.0mV; and the theoretical glass transition temperature is -18.7±1.0℃. After all indicators are qualified, the second stage of polymerization begins.

[0062] (III) S3 Second-Stage Polymerization (Mesophase Preparation) After the nucleopolymerization test is passed, maintain a stirring speed of 180 rpm and a nitrogen gas flow rate of 0.8 L / min. Use a jacketed constant temperature control system to raise the temperature inside the reactor to 78.5 ± 0.5℃, with a heating rate controlled at 1.5℃ / min to avoid excessive heating that could lead to system instability. Continuously monitor the system temperature during the heating process to ensure that the temperature fluctuation is ≤ ± 0.3℃.

[0063] After the temperature stabilized at 78.5±0.5℃, the dual-channel constant-flow drip pump was started, simultaneously adding the second monomer composition and the coordination initiator aqueous solution. The second monomer composition consisted of 1435.6g of the basic nonionic monomer M1, 88.3g of the composite acidic functional monomer M2, and 104.0g of the crosslinking modified monomer M3, with a dropping rate set to 2.5g / (min). 100g of total monomers), corresponding to a total dropping time of 68min; the coordination initiator aqueous solution was mixed with cobalt acetylacetonate aqueous solution and trisodium citrate aqueous solution in a volume ratio of 1:2.5 and then dropped, with the dropping rate synchronized with the second monomer composition, and the total amount added was 0.38wt.% of the mass of the second monomer, i.e., 36.7g of cobalt acetylacetonate aqueous solution and 91.8g of trisodium citrate aqueous solution.

[0064] Temperature and system viscosity were recorded every 10 minutes during the dropwise addition process. The temperature was kept stable at 78.5±0.5℃, and the system viscosity (25℃, rotational viscometer) was controlled at 125±10 mPa. If the viscosity is too high, add a small amount of deionized water (each addition ≤ 1% of the total water volume); if the viscosity is too low, appropriately increase the dropping rate by 0.05 g / (min). (100g total monomers).

[0065] After the second monomer composition and the aqueous solution of the coordination initiator are added dropwise, the current reaction conditions are kept unchanged, and the polymerization is carried out at a constant temperature for 1.5 hours. During the holding period, samples are taken every 20 minutes to measure the monomer conversion rate. When the conversion rate is ≥97%, the mesophase polymerization is considered to be complete.

[0066] After the mesophase polymerization is completed, samples are taken to test the quality indicators of the core-mesophase polymer aqueous dispersion: the appearance is a uniform milky white emulsion, without layering or gelation; the volume average particle size is 108.7±3.5nm; the Zeta potential is -42.3±2.0mV; and the theoretical glass transition temperature is 28.3±1.0℃. After all indicators are qualified, the third stage polymerization begins.

[0067] (iv) S4 third-stage polymerization (shell phase preparation) After the mesophase polymerization test is passed, maintain a stirring speed of 180 rpm and a nitrogen gas flow rate of 0.8 L / min. Adjust the temperature inside the reactor to 75.0 ± 0.5℃ using the jacket constant temperature control system. Control the cooling rate at 1.0℃ / min. Continuously stir during the cooling process to avoid localized uneven concentrations in the system.

[0068] After the temperature stabilized at 75.0±0.5℃, a single-channel constant-flow drip pump was started to add the third monomer composition. The third monomer composition consisted of 822.6g of the basic nonionic monomer M1, 50.6g of the composite acidic functional monomer M2, and 38.6g of the crosslinking modified monomer M3. The dropping rate was set to 1.8g / (min). 100g of total monomers), corresponding to a total dropping time of 52min. No additional initiator is required in this stage. The polymerization is completed by self-initiation of the monomers with the free radicals remaining in the previous polymerization system.

[0069] Temperature and system appearance were recorded every 10 minutes during the dropwise addition process, maintaining a stable temperature of 75.0 ± 0.5℃. If slight gel particles appeared in the system, the dropping rate was immediately reduced by 0.08 g / (min). Add 100g of total monomers and increase the stirring speed by 10 rpm. If the system remains a uniform emulsion, the dropping rate can be kept constant.

[0070] After the third monomer composition is added dropwise, keep the current reaction conditions unchanged and maintain the temperature for polymerization for 2.0 h. During the heat preservation period, take samples every 30 min to measure the monomer conversion rate. When the conversion rate is ≥98%, the shell phase polymerization is considered to be complete.

[0071] After the shell-phase polymerization is completed, samples are taken and tested for the quality indicators of the final core-intermediate-shell three-phase polymer aqueous dispersion: appearance is a uniform milky white emulsion with no visible gel particles; volume average particle size is 128.5~186.3nm; polydispersity index (PDI) ≤ 0.045; zeta potential is -45.6±2.0mV; theoretical glass transition temperature is 56.8±1.0℃; solid content is 48.5~51.2%. The polymerization reaction is terminated after all indicators are qualified.

[0072] (v) Key control points of the polymerization process The nitrogen gas flow rate for the three-stage polymerization process needs to be adjusted according to the stage to ensure that the system is always in an oxygen-free state, thus avoiding polymerization termination or polymer oxidative degradation caused by oxygen.

[0073] The monomer dropping rate at each stage must be strictly matched with the initiator dropping rate to avoid excessive molecular weight due to excessive initiator or incomplete polymerization due to excessive monomer. If a dropping pump malfunctions during the dropping process, dropping must be stopped immediately, the heating system turned off, and the nitrogen gas flow rate increased to 2.0 L / min. After the malfunction is resolved, the dropping pump should be restarted, and the subsequent heat preservation time should be appropriately extended by 30 min.

[0074] During polymerization, the temperature fluctuation of the system needs to be controlled within ±0.5℃. Too high a temperature can easily lead to excessive cross-linking of the polymer, while too low a temperature will reduce the polymerization rate and affect the monomer conversion rate.

[0075] After each polymerization stage is completed, the monomer conversion rate must meet the set requirements: core phase ≥ 96%, meso phase ≥ 97%, shell phase ≥ 98%. If the conversion rate does not meet the requirements, the holding time must be extended, and samples must be taken for testing every 30 minutes until the conversion rate is qualified.

[0076] Throughout the process, a dynamic light scattering instrument is used to monitor the changes in polymer particle size in real time, ensuring that the particle size grows according to the designed gradient at each stage. If the particle size grows too fast, the monomer drop acceleration rate of the corresponding stage needs to be reduced; if the particle size grows too slowly, the amount of emulsifier needs to be appropriately increased (each replenishment amount ≤ 5% of the total emulsifier).

[0077] IV. Post-processing technology The post-processing process involves a series of steps after the three-stage polymerization, including monomer removal, pH neutralization and adjustment, defoaming and filtration, particle size control and stability enhancement of the crude polymer aqueous dispersion. All operations are carried out continuously in the original 50L polymerization reactor and supporting equipment, maintaining a slightly positive nitrogen atmosphere (gauge pressure 0.02~0.03MPa) throughout the process. Parameters such as temperature and stirring speed are precisely controlled to ensure that the purity, stability and application performance of the finished dispersion meet the standards. The specific operation procedures, process parameters and quality control requirements of each step are as follows.

[0078] (a) Monomer removal (stripping and devolatilization) After the three-stage polymerization is completed, maintain the stirring speed of the reactor at 150 rpm, turn on the jacket heating system, and raise the system temperature from 75.0℃ to 85.0±0.5℃. The heating rate is controlled at 2.0℃ / min. Nitrogen gas is continuously introduced during the heating process, and the gas flow rate is maintained at 0.8L / min to avoid oxidation of the system.

[0079] After the temperature stabilizes at 85.0±0.5℃, the steam generator is started to produce saturated steam (pressure 0.1MPa, temperature 100℃). The steam is then uniformly introduced into the system through the gas distributor at the bottom of the reactor at a rate of 0.8L / (h). (kg dispersion), stripping and devolatilization time 40 min, during which water vapor fully contacts the system, carrying away unreacted residual monomers and trace volatile impurities.

[0080] During the stripping process, the tail gas at the top of the reactor is treated by a condensation recovery device, and the condensate is collected in a special container. The monomer content in the condensate is sampled periodically to evaluate the removal effect. At the same time, the residual monomer content in the dispersion is sampled every 10 minutes and determined by gas chromatography. The total residual monomer content is required to be ≤0.1wt.%, of which the residual content of each individual monomer is ≤0.03wt.%.

[0081] If the residual monomer content does not meet the standard after 40 minutes, continue to extend the stripping time by 10 minutes each time until the residual monomer content meets the requirements. The maximum extension time shall not exceed 20 minutes to avoid excessive stripping leading to excessively high dispersion solid content or demulsification.

[0082] After the monomer removal meets the standard, the steam generator is turned off, and the nitrogen gas flow rate is maintained at 0.8 L / min and the stirring speed is 150 rpm. The system temperature is reduced to 45.0 ± 0.5℃ by the jacket cooling water, and the cooling rate is controlled at 1.5℃ / min.

[0083] (ii) Neutralizing and adjusting pH After the system temperature drops to 45.0±0.5℃, adjust the stirring speed to 120rpm to avoid foaming due to excessive stirring. Turn on the constant flow pump and slowly add 25wt.% ammonia water through the drip port at the top of the reactor. The ammonia water should be of industrial grade purity (ammonia content 25±1wt.%, moisture ≤74.5wt.%, impurity content ≤0.5wt.%).

[0084] The ammonia droplet acceleration rate was controlled at 0.5 mL / min. The pH value of the system was monitored in real time during the droplet addition. A pH meter with an accuracy of ±0.01 was used, and the measurement was taken every 2 minutes. During the measurement, the pH meter probe was inserted into the middle of the system to ensure full contact with the dispersion. The reading was recorded after it stabilized.

[0085] When the pH of the system rises to the range of 8.6 to 9.2, stop adding ammonia and continue stirring for 15 minutes to make the pH of the system uniform and stable. Take another sample to measure the pH value. The final pH value fluctuation should be ≤ ±0.2. If the pH value is lower than 8.6, add a small amount of ammonia (≤0.5 mL each time). If the pH value is higher than 9.2, add 0.1 wt.% acrylic acid aqueous solution for fine adjustment (≤1 mL each time).

[0086] During the neutralization process, observe the state of the system. If slight flocculation or stratification occurs, immediately reduce the stirring speed to 100 rpm and slow down the ammonia droplet acceleration rate. If the flocculation continues, add 0.3 wt.% of the composite emulsifier aqueous solution (based on the total mass of the dispersion) and stir for 30 minutes until the system is restored to uniformity.

[0087] (III) Defoaming and Filtration After neutralization, maintain a stirring speed of 120 rpm and a temperature of 45.0 ± 0.5℃, turn on the constant flow pump, and add polyether modified silicone defoamer to the system. The defoamer should be an industrial grade product (active ingredient ≥ 98 wt.%, moisture ≤ 0.5 wt.%), with an addition amount of 0.08 wt.% of the total mass of the dispersion and a dropping rate of 0.3 mL / min. After the addition is complete, continue stirring for 15 min to ensure uniform dispersion of the defoamer and eliminate the foam generated in the system.

[0088] After defoaming is complete, turn off the jacket heating / cooling system, maintain the stirring speed at 100 rpm, and allow the system to cool naturally to 25±2℃. During the cooling process, nitrogen gas is continuously introduced at a rate of 0.5 L / min.

[0089] After the system cools to room temperature, turn off the stirring and nitrogen. Filter the dispersion through a 200-mesh nylon screen. Use positive pressure filtration with the filtration pressure controlled at 0.1~0.15MPa. Ensure uniform filtration speed and avoid excessive pressure that could damage the screen or cause flocculation of the dispersion.

[0090] During the filtration process, the filter residue is collected and weighed. The filter residue content is required to be ≤0.1wt.%. If there is too much filter residue (more than 0.3wt.%), it indicates that the gelation during the polymerization process is serious and the polymerization process parameters need to be re-evaluated. The filtered dispersion is collected into a clean, sealed storage tank. The storage tank is pre-cleaned with deionized water and dried with nitrogen.

[0091] (iv) Particle size control and stability enhancement After the filtered dispersion was transferred to the storage tank, the agitator in the storage tank was turned on and the stirring speed was set to 80 rpm. The volume average particle size and polydispersity index (PDI) of the dispersion were monitored in real time using a dynamic light scattering instrument. During the measurement, the dispersion was diluted with deionized water to 0.01 wt.% and measured at 25°C. Each sample was measured 3 times and the average value was taken.

[0092] If the volume average particle size is within the range of 128.5~186.3nm and the PDI ≤ 0.045, the particle size is considered qualified and no additional adjustment is required. If the particle size is too large (exceeding 186.3nm), add a composite emulsifier aqueous solution (concentration 5wt.%) to the system, the amount added is 0.12wt.% of the total mass of the dispersion, stir for 30min and measure the particle size again until it meets the standard. If the particle size is too small (below 128.5nm), add a small amount of deionized water (the amount added is 2~3% of the total mass of the dispersion), stir for 20min and measure again.

[0093] After the particle size meets the standard, a stabilizing additive is added to the dispersion. Industrial grade polyethylene glycol (number average molecular weight 2000 g / mol, purity ≥99 wt.%, moisture ≤0.5 wt.%) is selected and added at a rate of 0.2 wt.% of the total mass of the dispersion. The dropping rate is 0.2 mL / min. After the addition is completed, stirring is continued for 60 min to ensure uniform dispersion of the additive and improve the long-term storage stability of the dispersion.

[0094] After stability enhancement, the storage stability of the dispersion was tested by sampling and accelerated aging test: the dispersion was sealed and placed in a constant temperature oven at 50℃ for 7 days. After removal, the appearance was observed. The requirements were no layering, no demulsification, no gel particles, particle size change rate ≤5%, and PDI change ≤0.01. If the standard was not met, 0.1wt.% of stability additive was added, and the mixture was stirred for 60 minutes and tested again.

[0095] (v) Finished product quality inspection and packaging preparation After all post-processing steps are completed, a comprehensive quality test is conducted on the finished modified polymer aqueous dispersion. The test items and indicators are as follows: appearance: uniform milky white emulsion, free of visible impurities; volume average particle size: 128.5~186.3nm; PDI ≤ 0.045; solid content: 48.5~51.2% (determined by gravimetric method); pH value: 8.6~9.2; Zeta potential: -45~-50mV; minimum film-forming temperature: ≤ 5℃ (determined according to DIN ISO 2115:2001-04); storage stability: ≥ 12 months (room temperature, protected from light, and sealed).

[0096] After all test items meet the standards, the finished dispersion is transferred to a special packaging container. The packaging container is a high-density polyethylene drum, 20L / drum, which is pre-washed with deionized water three times and dried with nitrogen to ensure that there are no impurities and no moisture residue.

[0097] During the packaging process, maintain a uniform filling speed (1L / min) to avoid foaming. After each packaging barrel is filled, seal it immediately, affix a label indicating the product name, batch number, production date, solid content, pH value, shelf life, and other information, and then store it in a cool, dry, and light-proof warehouse.

[0098] (vi) Key control points of the post-processing process During stripping and devolatilization, the steam introduction rate must be uniform to avoid excessively high local steam concentrations that could cause the dispersion to boil violently or demulsify. The gas distributor must be cleaned regularly to ensure uniform steam distribution.

[0099] When neutralizing and adjusting the pH, the ammonia drop rate should not be too fast, otherwise it will cause a sudden change in local pH value and trigger flocculation of the dispersion. If flocculation occurs, the drop should be stopped immediately, and the ammonia should be added slowly after stirring for 30 minutes.

[0100] During the filtration process, the screen needs to be inspected in advance to ensure that it is undamaged. The filtered dispersion should be transferred to the storage tank as soon as possible to avoid prolonged exposure to air, which could lead to oxidation or contamination.

[0101] When adjusting particle size, the added emulsifier must be the original composite emulsifier system. Other types of emulsifiers should not be used to avoid affecting the stability and performance consistency of the dispersion.

[0102] The operation time for all post-processing steps should be controlled within 4 to 6 hours, from monomer removal to finished product packaging, to avoid performance fluctuations caused by prolonged storage of the dispersion.

[0103] Example 2 All examples follow the original process in terms of raw material system composition, pretreatment process, three-stage polymerization parameters and post-treatment process. The only adjustment is that the mass ratio of basic nonionic monomer (M1), composite acidic functional monomer (M2) and crosslinking modified monomer (M3) in the polymer monomer composition is 94.0:3.0:3.0, which reduces the content of functional monomer and optimizes film formation.

[0104] Example 3 All examples follow the original process in terms of raw material system composition, pretreatment process, three-stage polymerization parameters and post-treatment process. The only adjustment is that the mass ratio of basic nonionic monomer (M1), composite acidic functional monomer (M2) and crosslinking modified monomer (M3) in the polymer monomer composition is 91.0:4.2:4.8, which increases the content of functional monomers and enhances adhesion and weather resistance.

[0105] Example 4 All examples follow the original process in terms of raw material system composition, pretreatment process, three-stage polymerization parameters and post-treatment process. Only the mass ratio of basic nonionic monomer (M1), composite acidic functional monomer (M2) and crosslinking modified monomer (M3) in the polymer monomer composition is adjusted to 93.5:2.8:3.7, and the acidic monomer is finely adjusted to balance stability and water resistance.

[0106] The specific results are shown in the table below:

[0107] Particle size and stability: The volume average particle size of the four examples was within the design range of 128.5~186.3nm, PDI≤0.045, and absolute value of Zeta potential≥44.5mV, indicating that the polymerization system can form a stable core-intermediate-shell three-phase structure under different monomer ratios, and the dispersion has excellent colloidal stability, with no flocculation or demulsification phenomena.

[0108] Film-forming performance: Example 2 has the highest proportion of M1 (94.0%), the lowest minimum film-forming temperature (3.8℃), and the best film-forming continuity; Example 3 has an increased proportion of M3 (4.8%), the degree of crosslinking is increased, and the minimum film-forming temperature is slightly higher (5.0℃), but it still meets the requirements of practical applications (≤5℃).

[0109] Functional performance: In Example 3, by increasing the proportions of M2 (4.2%) and M3 (4.8%), the substrate adhesion reached level 0 (optimal), and the weather resistance color difference ΔE was only 1.5, demonstrating the best adhesion and weather resistance. Although the adhesion (level 2) and weather resistance (ΔE=2.3) of Example 2 were slightly weaker, the water resistance was the best (water absorption rate 4.2%), making it suitable for scenarios with high requirements for film formation.

[0110] Overall performance: The performance of Example 1 (baseline formulation) and Example 4 is at an intermediate level. Example 4, by finely adjusting the proportion of M2 (2.8%), balances film-forming properties, adhesion and water resistance while ensuring stability, and has strong overall applicability.

[0111] The three-stage redox-initiated-coordination composite aqueous emulsion polymerization method proposed in this invention can successfully prepare modified polymer aqueous dispersions with satisfactory performance when the proportions of the polymer monomer composition are adjusted within the range of M1: 91.0%~94.0%, M2: 2.8%~4.2%, and M3: 3.0%~4.8%. This method eliminates the need for traditional thiol chain transfer agents and achieves synergistic optimization of polymer structure and performance through monomer gradient design and segmented initiation control: increasing the proportions of M2 and M3 enhances coating adhesion and weather resistance, while increasing the proportion of M1 optimizes film formation and water resistance. Among them, Example 3 (M1: 91.0%, M2: 4.2%, M3: 4.8%) has the best functional performance, Example 2 (M1: 94.0%, M2: 3.0%, M3: 3.0%) has the best film-forming properties and water resistance, and Examples 1 and 4 have balanced overall performance. The monomer ratio can be flexibly adjusted according to the performance requirements of actual application scenarios, providing diversified choices for coating applications in different fields.

Claims

1. A process for the preparation of a modified polymer aqueous dispersion, characterized in that, Includes the following steps: Step S1, Seed emulsion preparation, includes: adding fatty alcohol polyoxyethylene ether phosphate ammonium salt and polyoxyethylene polyoxypropylene block copolymer to water to form a uniform emulsifier aqueous solution A, blowing nitrogen, adding a mixed monomer of methyl methacrylate and butyl acrylate, adding an initiator, and obtaining a seed emulsion after polymerization; Step S2, monomer pre-emulsion preparation, includes: adding fatty alcohol polyoxyethylene ether phosphate ammonium salt and polyoxyethylene polyoxypropylene block copolymer to water to form a homogeneous emulsifier aqueous solution B; dividing the emulsifier aqueous solution B into three equal parts; adding a pre-mixed homogeneous polymeric first monomer composition dropwise to one part of the emulsifier aqueous solution B to form monomer pre-emulsion B1; adding a pre-mixed homogeneous polymeric second monomer composition dropwise to another part of the emulsifier aqueous solution B to form monomer pre-emulsion B2; and adding a pre-mixed homogeneous polymeric third monomer composition dropwise to the last part of the emulsifier aqueous solution B to form monomer pre-emulsion B3. The polymeric first monomer composition includes a nonionic monomer M1 and a composite acidic functional monomer M2; the polymeric second monomer composition and the polymeric third monomer composition include a nonionic monomer M1, a composite acidic functional monomer M2, and a crosslinking modified monomer M3. Step S3, preparing the core phase by polymerization, includes the following steps: adding the seed latex prepared in step S1 to water, stirring and mixing thoroughly to form a uniform seed dispersion, then raising the temperature to 72.0±0.5℃, purging with nitrogen gas, and simultaneously adding the monomer pre-emulsion B1 prepared in step S2 and the aqueous solution of the redox initiator, and polymerizing to form an aqueous dispersion of the core phase polymer; Step S4, preparing the intermediate phase by polymerization, includes the following steps: the aqueous dispersion of the core-phase polymer prepared in step S3 is heated to 78.5±0.5℃ under stirring and nitrogen purging conditions, while the monomer pre-emulsion B2 prepared in step S2 and the aqueous solution of the coordination initiator are added dropwise to polymerize and form a core-intermediate phase polymer aqueous dispersion; Step S5, preparing the shell phase by polymerization, includes the following steps: the core-intermediate phase polymer aqueous dispersion prepared in step S4 is stirred and purged with nitrogen, and the temperature is adjusted to 75.0±0.5℃. The monomer pre-emulsion B3 prepared in step S2 is added dropwise. After the addition is completed, when the conversion rate is ≥98%, the shell phase polymerization is completed, and a modified polymer aqueous dispersion is formed.

2. The method for preparing a modified polymer aqueous dispersion according to claim 1, characterized in that, The nonionic monomer M1 in step S2 is compounded from isooctyl acrylate, isobutyl methacrylate, and cyclohexyl acrylate in a mass ratio of 42.3:35.7:22.0; the composite acidic functional monomer M2 in step S2 is compounded from a mixture of carboxyl monomers and phosphonopropyl methacrylate in a mass ratio of 7.2:1, wherein the carboxyl monomer mixture is composed of acrylic acid and itaconic acid in a mass ratio of 5.1:1; the crosslinking modified monomer M3 is compounded from γ-methacryloyloxypropyltrimethoxysilane and glycidyl acrylate in a mass ratio of 78.5:21.

5.

3. The method for preparing a modified polymer aqueous dispersion according to claim 1, characterized in that, By mass fraction, in step S1, for every 1286.5 parts of deionized water, 11.3 parts of fatty alcohol polyoxyethylene ether phosphate ammonium salt and 4.5 parts of polyoxyethylene polyoxypropylene block copolymer are added, along with 450.0 parts of a mixed monomer of methyl methacrylate and butyl acrylate in a mass ratio of 1:

1. The initiator is an aqueous solution of potassium persulfate initiator, with an addition amount of 18.6 parts and a mass content of 5.2% for the aqueous solution of potassium persulfate initiator.

4. The method for preparing a modified polymer aqueous dispersion according to claim 3, characterized in that, In step S2, for every 3876.3 parts of deionized water, 45.2 parts of fatty alcohol polyoxyethylene ether phosphate ammonium salt and 18.1 parts of polyoxyethylene polyoxypropylene block copolymer are added to form a homogeneous emulsifier aqueous solution B. The first monomer composition comprises 4230.8 parts of nonionic monomer M1 and 76.1 parts of composite acidic functional monomer M2; the second monomer composition comprises 435.6 parts of nonionic monomer M1, 88.3 parts of composite acidic functional monomer M2, and 104.0 parts of crosslinking modified monomer M3; the third monomer composition comprises 1435.6 parts of nonionic monomer M1, 88.3 parts of composite acidic functional monomer M2, and 104.0 parts of crosslinking modified monomer M3.

5. The method for preparing a modified polymer aqueous dispersion according to claim 4, characterized in that, By mass fraction, for every 1890.6 parts of deionized water mentioned in step S3, 176.2 parts of seed latex and 5620.1 parts of the monomer pre-emulsion B1 are added. The redox initiator aqueous solution is potassium sulfate aqueous solution and sodium bisulfite aqueous solution, with added amounts of 112.3 parts and 62.4 parts, respectively, and both having a mass concentration of 5.2%.

6. The method for preparing a modified polymer aqueous dispersion according to claim 5, characterized in that, By mass fraction, in step S4, 1941.1 parts of the monomer preemulsion B2 are added to every 6548.4 parts of the core phase polymer aqueous dispersion. The coordination initiator aqueous solution includes cobalt acetylacetonate aqueous solution and trisodium citrate aqueous solution, with added amounts of 36.7 parts and 91.8 parts, respectively, and both having a mass concentration of 3.5%.

7. The method for preparing a modified polymer aqueous dispersion according to claim 6, characterized in that, By mass fraction, for every 8304.8 parts of the core-intermediate polymer aqueous dispersion described in step S5, 2941.1 parts of the monomer preemulsion B3 are added.

8. A method for preparing a modified polymer aqueous dispersion according to any one of claims 1-7, characterized in that, Step S1 Seed latex preparation: After forming the uniform emulsifier aqueous solution A, the temperature is initially raised to 75.5±0.5℃, the mixed monomers of methyl methacrylate and butyl acrylate are added and polymerized at a constant temperature for 2.5h, and then naturally cooled to 25±2℃. The temperature in step S2 is controlled at 28±1℃ throughout the entire process; During the step S3 of the dropwise addition of the monomer pre-emulsion B1 and the aqueous solution of the redox initiator, the temperature, the stirring speed, and the dropwise addition rate are recorded every 15 min, the system temperature is kept stable at 72.0±0.5°C, and if the temperature increases by more than 0.8°C, the dropwise addition rate is reduced by 0.1 g / (min 100 g total monomers) while cooling; If the temperature decreases more than 0.8 °C, increase the drop rate by 0.1 g / (min 100 g total monomers) while heating; During the dropwise addition of monomer preemulsion B2 and coordination initiator aqueous solution in step S4, the temperature and system viscosity were recorded every 10 minutes, maintaining the temperature stable at 78.5±0.5℃ and the system viscosity controlled at 125±10 mPa. s, if the viscosity exceeds 135 mPa s, add deionized water at least 1% of the total water volume; if the viscosity is below 115 mPa The droplet acceleration rate increases by 0.05 g / (min) 100g total monomers); During the dropping process described in step S5, the temperature and system appearance are recorded every 10 minutes, maintaining a stable temperature of 75.0 ± 0.5℃. If gel particles appear in the system, the dropping rate is immediately reduced by 0.08 g / (min). (100g total monomer), increase stirring speed by 10rpm; if the system remains a uniform emulsion, maintain the dropping rate unchanged.

9. A method for preparing a modified polymer aqueous dispersion according to any one of claims 1-7, characterized in that, The quality control indicators for the seed latex described in step S1 are: volume average particle size 32.6±2.0nm, solid content 31.8±0.5wt.%, pH value 3.5~4.0, no gel particles, and no stratification or demulsification during storage. The quality control indicators for the monomer preemulsion described in step S2 are: uniform emulsion without stratification, oil phase content of 49.2±0.3wt.%, and viscosity of 58±5 mPa at 25℃. s; The quality control indicators of the nucleated polymer aqueous dispersion mentioned in step S3 are as follows: After the nucleated polymerization is completed, the quality indicators of the nucleated polymer aqueous dispersion are sampled and tested: the appearance is a uniform milky white emulsion with no gel particles; the volume average particle size is 85.3±3.0nm; the Zeta potential is -38.5±2.0mV; and the theoretical glass transition temperature is -18.7±1.0℃. After the core-intermediate phase polymer aqueous dispersion described in step S4 is completed, samples are taken to test the quality indicators of the core-intermediate phase polymer aqueous dispersion: the appearance is a uniform milky white emulsion, without layering or gelation; the volume average particle size is 108.7±3.5nm; the Zeta potential is -42.3±2.0mV; the theoretical glass transition temperature is 28.3±1.0℃. After all indicators are qualified, proceed to step S5. The quality indicators of the modified polymer aqueous dispersion described in step S5 are as follows: appearance: uniform milky white emulsion, without gel particles; volume average particle size: 128.5~186.3 nm; polydispersity index (PDI): ≤0.045; zeta potential: -45.6±2.0 mV; theoretical glass transition temperature: 56.8±1.0 °C; solid content: 48.5~51.2%.

10. A method for preparing a modified polymer aqueous dispersion according to any one of claims 1-7, characterized in that, After forming the modified polymer aqueous dispersion, the system temperature was raised from 75.0℃ to 85.0±0.5℃ while maintaining a stirring speed of 150 rpm. The heating rate was controlled at 2.0℃ / min. Nitrogen gas was continuously introduced during the heating process at a rate of 0.8 L / min to prevent oxidation of the system. After the temperature stabilized at 85.0±0.5℃, stripping and devolatilization were performed for 40 min. After the temperature dropped to 45.0±0.5℃, the stirring speed was adjusted to 120 rpm, and 25 wt% of the modified polymer was added dropwise. Adjust the pH of the system to the range of 8.6-9.2 using % ammonia water. After neutralization, maintain a stirring speed of 120 rpm and a temperature of 45.0±0.5℃, and add polyether-modified silicone defoamer to the system. After completion, maintain a stirring speed of 100 rpm and allow the system to cool naturally to 25±2℃. During the cooling process, continuously introduce nitrogen gas at a rate of 0.5 L / min. After cooling to room temperature, turn off the stirring and nitrogen gas, and filter the dispersion through a 200-mesh nylon screen. After filtration, use a dynamic light scattering instrument to monitor the volume average particle size and polydispersity index of the dispersion in real time. The volume average particle size is in the range of 128.5-186.3 nm, and the PDI is ≤0.

045. After the particle size meets the standard, add polyethylene glycol as a stabilizing additive to the dispersion to form a long-term stable modified polymer aqueous dispersion.

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