A method for preparing an acrylate rubber based on a wet mixing process

Abstract

The application discloses a preparation method of an acrylate rubber based on a wet mixing process. The preparation method comprises the following steps: performing emulsion polymerization on carboxyl functional group-containing acrylate monomers and other acrylate monomers in water to obtain acrylate rubber latex with active carboxyl groups on the surface; mixing fillers and an epoxy group-containing silane coupling agent in water and performing high-shear dispersion to allow the silane coupling agent to coat the surface of the fillers, thereby obtaining modified filler dispersion liquid; mixing the acrylate rubber latex and the modified filler dispersion liquid and performing wet mixing under alkaline conditions to allow the carboxyl groups in the latex to react with the epoxy groups on the surface of the modified fillers in situ, thereby obtaining in-situ modified mixed latex; and adding a coagulating agent to the in-situ modified mixed latex to perform coagulation, thereby obtaining acrylate rubber mixing rubber. The application realizes chemical bonding between rubber macromolecules and filler interfaces by using liquid-phase in-situ ring-opening reaction, and significantly improves the dispersibility of fillers and the comprehensive performance of rubber.

Description

Technical Field

[0001] This application relates to the field of polymer material synthesis and processing technology, and in particular to a method for preparing acrylate rubber based on a wet mixing process. Background Technology

[0002] Acrylic rubber (ACM) is an elastomer obtained by copolymerization of acrylate as the main monomer. Its main chain is a saturated carbon chain, and the side groups are polar ester groups. Due to this special structure, ACM has excellent heat aging resistance, ozone resistance, ultraviolet resistance, and oil resistance, and is widely used in high-temperature and oil-resistant environments such as automotive seals and oil-resistant pipe fittings.

[0003] In the processing of acrylic rubber, filler mixing is a crucial step. Traditional dry mixing processes, carried out in internal mixers, suffer from high energy consumption, significant dust pollution, and difficulty in uniformly dispersing fillers. This is especially problematic for nanoscale fillers with high specific surface area, where dry mixing easily leads to agglomeration. To address these issues, wet mixing processes have emerged, where rubber latex and filler dispersions are directly mixed in the liquid phase, followed by co-precipitation, effectively improving filler dispersibility.

[0004] However, existing wet compounding processes largely rely on physical adsorption and mechanical shearing, resulting in weak interfacial bonding between rubber macromolecules and filler surfaces. Under external forces or thermal aging, fillers are prone to detachment or secondary agglomeration, making it difficult to achieve ideal mechanical properties and aging resistance. Furthermore, the direct addition of oily or powdered processing aids in traditional wet compounding also presents challenges in achieving uniform dispersion.

[0005] Therefore, there is an urgent need for a wet compounding method for preparing acrylate rubber that requires no complex equipment, can achieve strong chemical bonding between the rubber matrix and the filler interface, and is low in energy consumption and high in performance. Summary of the Invention

[0006] This application provides a method for preparing acrylate rubber based on a wet mixing process, in order to solve the technical problems of weak interfacial bonding and poor dispersibility between fillers and rubber in existing wet mixing processes.

[0007] To solve the above-mentioned technical problems, one technical solution adopted in this application is: to provide a method for preparing acrylate rubber based on a wet mixing process. This method for preparing acrylate rubber based on a wet mixing process includes: S1: Emulsion polymerization of acrylate monomers containing carboxyl functional groups with other acrylate monomers in water to obtain acrylate rubber latex with active carboxyl groups on the surface. S2: The filler and the silane coupling agent containing epoxy groups are mixed in water and dispersed under high shear to coat the surface of the filler with the silane coupling agent, thereby obtaining a modified filler dispersion. S3: The acrylate rubber latex is mixed with the modified filler dispersion and wet-mixed under alkaline conditions at a preset temperature, so that the carboxyl groups in the latex and the epoxy groups on the surface of the modified filler undergo an in-situ ring-opening reaction to obtain an in-situ modified mixed latex. S4: Add a coagulant to the in-situ modified mixed latex to coagulate it, and then wash and dry it to obtain an acrylic rubber compound.

[0008] In some embodiments, the acrylate monomer containing a carboxyl functional group is one or more of acrylic acid, methacrylic acid, itaconic acid, or maleic anhydride; The other acrylate monomers include a main monomer and a comonomer; the main monomer is one or more of ethyl acrylate, butyl acrylate or 2-methoxyethyl acrylate; the comonomer is acrylonitrile or chloroacrylate.

[0009] In some embodiments, the other acrylate monomers further include crosslinking monomers, wherein the crosslinking monomers are one or more of divinylbenzene, triethylene glycol diacrylate, or trimethylolpropane trimethacrylate.

[0010] In some embodiments, the amount of the acrylate monomer containing the carboxyl functional group is 1-5 wt% based on the total weight of the monomers.

[0011] In some embodiments, in step S1, the emulsion polymerization uses an anionic emulsifier and / or a nonionic emulsifier; the anionic emulsifier is sodium dodecyl sulfate, and the nonionic emulsifier is nonylphenol polyoxyethylene ether. The emulsion polymerization uses a thermal decomposition initiator, which is ammonium persulfate or potassium persulfate, with a polymerization temperature of 40-80℃ and a polymerization time of 4-10 hours; or, the emulsion polymerization uses a redox initiator, which is formulated from an organic peroxide oxidant and a reducing agent, wherein the organic peroxide oxidant is one or more of tert-butyl hydroperoxide, benzoyl peroxide, and cumene hydroperoxide, and the reducing agent is one or more of sodium bisulfite, ferrous sulfate, sodium formaldehyde sulfoxylate, and sodium hydrosulfite, with an initiation temperature of 5-30℃, a holding temperature of 60-80℃, and a holding time of 2-6 hours.

[0012] In some embodiments, the epoxy-containing silane coupling agent is one of γ-glycidyl etheroxypropyltrimethoxysilane, β-(3,4-epoxycyclohexyl)ethyltriethoxysilane, or γ-glycidyl etheroxypropylmethyldiethoxysilane.

[0013] In some embodiments, in step S2, the amount of the epoxy group-containing silane coupling agent is 1-8 wt% of the filler weight, and the weight ratio of the filler to water is 1:3 to 1:8. The high-shear dispersion has a shear rate of 2000-5000 rpm, a dispersion time of 15-40 minutes, and a dispersion temperature of 20-30℃.

[0014] In some embodiments, in step S3, wet mixing is carried out under alkaline conditions of 40-60°C and pH 8-9, wherein the stirring speed of wet mixing is 300-1000 rpm and the mixing time is 60-120 minutes. The total solids content of the in-situ modified mixed latex is controlled between 20% and 35%.

[0015] In some embodiments, in step S3, while performing wet mixing, an aqueous processing aid dispersion is also added to the system. The aqueous processing aid dispersion includes one or more of antioxidant aqueous dispersion, plasticizer emulsion, or dispersant aqueous solution. The antioxidant aqueous dispersion contains 2,2,4-trimethyl-1,2-dihydroquinoline polymer or N-phenyl-α-aniline; the plasticizer emulsion contains polyester plasticizer or ether ester plasticizer.

[0016] In some embodiments, in step S4, the coagulant is an inorganic salt solution of sodium chloride, calcium chloride, aluminum sulfate or alum, or an inorganic acid solution of hydrochloric acid or sulfuric acid. The coagulation temperature is 50-80℃, the coagulation time is 1-3 hours, and the coagulating agent is added by spraying during coagulation.

[0017] The beneficial effects of this application are as follows: Unlike existing technologies, this application discloses a method for preparing acrylate rubber based on a wet mixing process. The embodiments of this application innovatively introduce carboxyl-containing monomers into the acrylate rubber latex and use epoxy-containing silane coupling agents to coat the fillers. Under the mild liquid-phase conditions of wet mixing, a strong chemical bond is established between the rubber macromolecules and the fillers through the in-situ ring-opening reaction of carboxyl and epoxy groups. This design breaks through the limitations of traditional wet mixing relying solely on physical blending, fundamentally solving the problem of weak interfacial bonding, and significantly improving the dispersibility of the fillers and the mechanical properties and heat aging resistance of the rubber.

[0018] Furthermore, this application ensures the sufficiency of the ring-opening reaction by precisely controlling the ratio of carboxyl-containing monomers and epoxy coupling agents, while avoiding latex gelation or excessive crosslinking caused by excessive functional groups, thus maintaining the good processing performance of the compound. For nano-sized carbon black and silica, high-shear dispersion and coupling agent coating effectively prevent secondary agglomeration in the aqueous dispersion and subsequent mixing processes. The introduction of an aqueous processing aid dispersion during the wet mixing stage solves the problem of uneven dispersion of aids in traditional dry mixing. The uniformity and purity of the coprecipitate are ensured by spraying coagulants, strictly controlling washing conductivity, and employing a suitable vacuum drying process. The heat treatment process after drying further promotes the reaction of residual functional groups and improves the crosslinking network. This preparation method has a reasonable process flow, requires no expensive equipment, and greatly improves the overall performance and production efficiency of acrylate rubber. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort, wherein: Figure 1 This is a schematic flowchart of an embodiment of the method for preparing acrylate rubber based on a wet mixing process provided in this application. Detailed Implementation

[0020] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0021] The terms "first," "second," and "third" used in the embodiments of this application are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first," "second," or "third" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to these processes, methods, products, or devices.

[0022] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0023] To address the problems of weak physical bonding, easy agglomeration of fillers, and uneven dispersion of additives in existing wet mixing processes, this application provides a preparation scheme that utilizes in-situ ring-opening reactions in the liquid phase to achieve interfacial chemical bonding. This scheme introduces specific carboxyl-containing monomers during the emulsion polymerization stage, and introduces silane coupling agents containing epoxy groups to modify the filler surface during the filler dispersion stage. Subsequently, the pH and temperature of the system are controlled during the wet mixing stage, allowing the active carboxyl groups on the rubber macromolecules to undergo in-situ ring-opening reactions with the epoxy groups on the filler surface, thereby constructing strong chemical bonds between the filler and the rubber matrix under mild liquid-phase conditions.

[0024] See Figure 1 , Figure 1 This is a schematic flow chart of an embodiment of the method for preparing acrylate rubber based on a wet mixing process provided in this application. The preparation method includes: Step S1: Emulsion polymerization of acrylate monomers containing carboxyl functional groups with other acrylate monomers in water to obtain acrylate rubber latex with active carboxyl groups on the surface.

[0025] The reactive carboxyl groups are introduced into the acrylic rubber macromolecular chain through copolymerization. By taking advantage of the characteristics of emulsion polymerization, these reactive carboxyl groups are distributed more on the surface or subsurface layer of the latex particles, thus creating space for subsequent contact and reaction with the epoxy groups on the surface of the modified filler in the liquid phase.

[0026] In emulsion polymerization systems, water, as a continuous phase, provides a good heat dissipation medium, enabling the polymerization reaction to proceed smoothly at a mild temperature. This avoids the explosive polymerization or difficulties in mass and heat transfer caused by a sharp increase in viscosity, as seen in bulk polymerization or solution polymerization.

[0027] Furthermore, the acrylate monomers containing carboxyl functional groups are one or more of acrylic acid, methacrylic acid, itaconic acid, or maleic anhydride; these monomers all contain unsaturated double bonds, which can participate in chain growth reactions initiated by free radicals, while the carboxyl groups (or anhydride groups, which will be converted into carboxyl groups in the aqueous phase) in their molecular structure remain inert in the polymer chain, do not participate in the construction of the main chain, but exist as suspended side groups.

[0028] Specifically, acrylic acid (AA) and methacrylic acid (MAA) are commonly used carboxyl-containing monomers. Methacrylic acid, due to the presence of a methyl group on its α-carbon atom, has significant steric hindrance, which slightly reduces the nucleophilicity of its carboxyl group, but its degree of dissociation under alkaline conditions remains high. Itaconic acid (IA) contains two carboxyl groups and a double bond. After polymerization, the double bond enters the main chain, while both carboxyl groups suspend as side groups, effectively introducing double the functionality into a single monomer unit, which is particularly effective when higher reaction densities are required. However, itaconic acid is extremely water-soluble; if used in excessive amounts, it easily undergoes homopolymerization or oligomer formation in the aqueous phase, reducing the efficiency of grafting onto latex particles. Maleic anhydride (MAH) rapidly hydrolyzes to maleic acid in the aqueous phase. Due to the cis configuration of the two carboxyl groups in maleic acid, steric hindrance results in a very low tendency for homopolymerization. It typically only undergoes alternating or random copolymerization with other acrylate monomers, which has a unique advantage in certain implementations requiring precise control of carboxyl group distribution. In practical applications, the choice of acrylic acid or methacrylic acid often achieves the best balance between reactivity and latex stability.

[0029] To ensure sufficient carboxyl reaction sites on the surface of latex particles without compromising latex stability, the amount of acrylate monomers containing carboxyl functional groups should be 1-5 wt% by total monomer weight. If the amount of carboxyl monomers is less than 1 wt%, although the high stability of the latex can be guaranteed, the carboxyl density on the macromolecular chain is too low. In the subsequent in-situ ring-opening reaction, there are few sites that can bond with the epoxy groups on the filler surface. The chemical bonds formed are insufficient to provide strong interfacial bonding forces, and the dispersibility of the filler and the mechanical properties of the composite material cannot be fundamentally improved. Conversely, if the amount of carboxyl-containing monomers exceeds 5 wt%, although there are sufficient reaction sites, the strong hydrophilicity of carboxyl groups will cause a sharp increase in the hydrophilicity of the latex particle surface, resulting in an excessively thick hydration layer of latex particles in the aqueous phase. This can even lead to excessive electrostatic repulsion between latex particles, affecting film formation. More seriously, excessive carboxyl groups can easily trigger cross-linking side reactions during emulsion polymerization (especially when the initiator concentration is high), causing the latex to form micro-gels. This results in an abnormally high Mooney viscosity of the final compound and severely deteriorated processing performance. Therefore, strictly controlling the amount of carboxyl-containing monomers within the range of 1-5 wt% is crucial to balancing latex stability, reactivity, and the processing performance of the final product.

[0030] Other acrylate monomers include main monomers and comonomers. The main monomers form the backbone of the acrylate rubber, determining its basic physicochemical properties. The main monomers are one or more of ethyl acrylate, butyl acrylate, or 2-methoxyethyl acrylate. Ethyl acrylate polymers have a glass transition temperature (Tg) of approximately -24°C, exhibiting good cold resistance; butyl acrylate polymers have a Tg of approximately -54°C, imparting excellent low-temperature flexibility; while the introduction of 2-methoxyethyl acrylate significantly improves the rubber's resistance to swelling from polar oils. By compounding these main monomers, the overall performance of the final rubber product can be flexibly adjusted. The comonomers are acrylonitrile or chloroacrylates. The strong polar cyano group of acrylonitrile can significantly improve the oil resistance of the rubber, but its dosage needs to be controlled; excessive use will significantly reduce cold resistance. Chlorinated acrylates provide a halogenated comonomer option, which, in addition to oil resistance, also imparts certain flame-retardant properties to the material.

[0031] Furthermore, other acrylate monomers include crosslinking monomers, such as one or more of divinylbenzene, triethylene glycol diacrylate, or trimethylolpropane trimethacrylate. Introducing multifunctional crosslinking monomers during the emulsion polymerization stage aims to enable the rubber macromolecules to form partially micro-crosslinked structures during polymerization. This micro-crosslinked network can limit excessive flow of polymer chains during subsequent heating, drying, and vulcanization, improving the stiffness of the compound and preventing deformation during processing. Divinylbenzene (DVB) is a strong crosslinking agent, with both vinyl groups on its benzene rings participating in polymerization to form rigid crosslinking nodes; triethylene glycol diacrylate (TEGDA) and trimethylolpropane trimethacrylate (TMPTA) provide crosslinking networks with some degree of flexibility in the spacers. The amount of crosslinking monomers used is usually very small (e.g., 0.5-2 wt% of the total monomers); excessive crosslinking will cause the latex to coagulate and become unusable in the reactor.

[0032] In the implementation process of emulsion polymerization, anionic emulsifiers, nonionic emulsifiers, or a combination thereof are used. The anionic emulsifier is sodium dodecyl sulfate, and the nonionic emulsifier is nonylphenol polyoxyethylene ether. Emulsifiers play a crucial role in emulsion polymerization, determining micelle formation, the number of latex particles, and the stability of the latex. Anionic emulsifiers such as sodium dodecyl sulfate (SDS) dissociate in water to release negatively charged sulfate ester groups, which adsorb onto the surface of latex particles to form an electric double layer, maintaining latex stability through electrostatic repulsion. Nonionic emulsifiers such as nonylphenol polyoxyethylene ether (NP series) stabilize the latex by creating steric hindrance through the hydration of polyoxyethylene segments on the molecular chain in the aqueous phase.

[0033] In practice, anionic and nonionic emulsifiers are often used in combination. This can take advantage of the high nucleation efficiency of anionic emulsifiers and improve the stability of latex to electrolytes by utilizing the steric hindrance effect of nonionic emulsifiers. Especially when the polarity of the system changes after the subsequent addition of carboxyl-containing monomers, the combination of emulsifiers can ensure that the latex does not break down.

[0034] The initiator used in emulsion polymerization is ammonium persulfate or potassium persulfate thermal decomposition initiator. The polymerization temperature is 40-80℃, and the polymerization time is 4-10 hours. Persulfate decomposes in the aqueous phase upon heating, generating sulfate free radicals, which abstract hydrogen atoms from the monomer double bonds, initiating chain growth. The choice of polymerization temperature is closely related to the decomposition half-life of the initiator. 40-80℃ ensures that the initiator decomposes at a moderate rate, maintaining a stable polymerization rate. If the temperature is too low, the polymerization rate is extremely slow, resulting in low production efficiency; if the temperature is too high, free radical generation is too rapid, easily leading to intensified chain termination reactions, a decrease in polymer molecular weight, and high temperatures can easily cause latex particles to aggregate and demulsify. The polymerization time of 4-10 hours is to ensure a high monomer conversion rate and reduce the adverse effects of residual monomers on the odor and performance of the final product.

[0035] The initiator used in emulsion polymerization can also be a redox initiator, which is formulated by an organic peroxide oxidant and a reducing agent. The organic peroxide oxidant is one or more of tert-butyl hydroperoxide, benzoyl peroxide, and cumene hydroperoxide, and the reducing agent is one or more of sodium bisulfite, ferrous sulfate, sodium formaldehyde sulfoxylate, and sodium hydrosulfite. The initiation temperature is 5-30℃, the holding temperature is 60-80℃, and the holding time is 2-6 hours.

[0036] Redox initiation systems generate free radicals through single-electron transfer reactions between oxidants and reductants, with activation energies far lower than those of thermally decomposing initiators. Therefore, when using redox initiators, the initiation temperature can be significantly reduced to room temperature or low temperatures of 5-30°C, and the holding time can be shortened to 2-6 hours. The advantages of low-temperature polymerization are: firstly, it effectively reduces side reactions (such as crosslinking or hydrolysis) that may be caused by high temperatures on carboxyl-containing monomers, improving the linearity and regularity of the polymer; secondly, low temperatures significantly reduce the thermal motion of latex particles, enhancing the kinetic stability of the latex and avoiding the risk of demulsification and coagulation that is easily caused by high temperatures.

[0037] Step S2: The filler and the silane coupling agent containing epoxy groups are mixed in water and dispersed under high shear to coat the surface of the filler with the silane coupling agent, thereby obtaining a modified filler dispersion.

[0038] By combining physical high shear and chemical coating, the problem of inorganic fillers being prone to agglomeration and difficult to disperse uniformly in aqueous phase is solved, and epoxy functional groups that can react with carboxyl groups in rubber latex are given to the filler surface.

[0039] In rubber composites, the reinforcing effect of fillers directly depends on their dispersion state in the rubber matrix and their interfacial interaction with the matrix. For wet compounding, fillers first need to be uniformly dispersed in water.

[0040] The filler is one or more of carbon black, silica, calcium carbonate, talc, or montmorillonite. The surface chemical properties of different fillers vary greatly. Carbon black contains abundant oxygen-containing functional groups (such as carboxyl groups, phenolic hydroxyl groups, quinone groups, etc.), but due to the strong van der Waals forces between particles, nanoscale carbon black easily forms strong secondary aggregates in water. Silica (silicon dioxide) has a surface covered with silanol groups, which not only make it acidic but also readily bond together through hydrogen bonds to form a three-dimensional network structure. Inorganic powders such as calcium carbonate and talc, while having lower costs, have high surface polarity and poor compatibility with hydrophobic rubbers.

[0041] When the filler is carbon black or silica, its average particle size is 10-50 nm, and its specific surface area is 50-200 m² / g. The nanoscale particle size and high specific surface area mean that the filler has extremely high surface energy, enabling it to generate a wide contact area with rubber macromolecules, thus providing strong physical adsorption and chemical binding sites. However, this is also the root cause of its difficulty in dispersion. If the average particle size of the filler is greater than 50 nm or the specific surface area is too small, its reinforcing effect will be greatly reduced, failing to significantly improve the tensile strength and stress at a given elongation of the rubber; if the particle size is too small (e.g., less than 10 nm), not only is the preparation cost extremely high, but it is also almost impossible to depolymerize it in an aqueous dispersion using conventional mechanical shearing.

[0042] To overcome the aggregation of nanofillers and impart reactivity, this application introduces silane coupling agents containing epoxy groups. The epoxy-containing silane coupling agent is one of γ-glycidyl etheroxypropyltrimethoxysilane, β-(3,4-epoxycyclohexyl)ethyltriethoxysilane, or γ-glycidyl etheroxypropylmethyldiethoxysilane. Silane coupling agents are a class of organosilicon compounds with a bifunctional structure, whose general formula can be represented as YR-Si(OR')3. Here, the (OR') group is a hydrolyzable alkoxy group (such as methoxy or ethoxy), and the Y group is a functional group that reacts with organic polymers (in this application, it is an epoxy group).

[0043] In the aqueous dispersion, the silane coupling agent first undergoes hydrolysis, with alkoxy groups hydrolyzing into silanol groups (Si-OH). Subsequently, these silanol groups undergo condensation reactions with active groups on the filler surface (such as silanol groups on the surface of silica, or oxygen-containing functional groups on the surface of silica), forming strong Si-O-Si or CO-Si covalent bonds, thereby anchoring the coupling agent molecules to the filler surface. Simultaneously, condensation also occurs between silane coupling agent molecules on the filler surface, forming a cross-linked siloxane network coating layer. At this point, the other end of the coupling agent molecule—the epoxy group—faces towards the aqueous phase, transforming the originally polar inorganic filler surface into an organic surface with certain hydrophobicity and high reactivity. The epoxy group is a three-membered ring ether structure; due to ring strain and bond angle strain, its chemical properties are very active, readily undergoing ring-opening reactions under the attack of nucleophiles. This prepares the ground for subsequent in-situ reactions with carboxyl groups in rubber latex.

[0044] The dosage of silane coupling agents containing epoxy groups is 1-8 wt% of the filler weight. If the dosage is less than 1 wt%, the filler surface is not fully coated, leaving a large number of exposed areas that will still aggregate in the aqueous dispersion. Simultaneously, the number of epoxy groups capable of participating in the in-situ reaction is insufficient, failing to form a dense interfacial chemical bond network. If the dosage exceeds 8 wt%, not only does the cost increase significantly, but the excess coupling agent molecules self-condense in water to form free siloxane oligomers. These oligomers, when subsequently mixed with latex, exist as impurities in the system, failing to provide interfacial bonding and instead forming a weak interfacial layer in the rubber matrix, leading to a decrease in the mechanical properties of the composite material. Furthermore, excessive epoxy group aggregation on the filler surface may cause localized over-crosslinking of the rubber macromolecular chains during subsequent reactions, resulting in an abnormally high Mooney viscosity of the compound and making processing difficult.

[0045] In the process parameters for preparing modified filler dispersions, the weight ratio of filler to water is 1:3 to 1:8. This solid-liquid ratio is set to ensure a suitable rheological environment during high-shear dispersion. If the filler-to-water ratio is too high, such as greater than 1:3 (i.e., too little water), the dispersion viscosity will be extremely high, making it difficult for high-shear equipment to operate effectively. Energy input will be converted into heat, leading to a sharp rise in system temperature, which may cause premature cross-linking or failure of the coupling agent. At the same time, excessively high viscosity restricts the Brownian motion of filler particles, which is detrimental to the deagglomeration of aggregates. If the ratio is too low, such as less than 1:8 (i.e., too much water), although the viscosity is low and shearing is easy, the dispersion volume is large. Subsequent mixing with latex requires processing a large amount of low-concentration solution, reducing production efficiency. Furthermore, the probability of filler particles colliding in large amounts of water decreases, and the coating efficiency will also decrease.

[0046] To completely depolymerize the agglomerated nanofillers and achieve uniform coating of the coupling agent, the high-shear dispersion uses a shear rate of 2000-5000 rpm, a dispersion time of 15-40 minutes, and a dispersion temperature of 20-30℃. The high-shear dispersion equipment generates strong mechanical shear forces, liquid friction forces, and impact forces through the high-speed relative motion between the rotor and stator in the narrow gap, forcibly tearing and dispersing the filler agglomerates.

[0047] When the shear rate is below 2000 rpm, the provided mechanical energy is insufficient to overcome the strong binding force between nanoparticles, resulting in poor dispersion. Conversely, when the shear rate exceeds 5000 rpm, not only does the equipment experience severe wear, but the excessively high speed also entrains a large amount of air, generating substantial foam and causing extreme instability in the dispersion system. Furthermore, it may lead to the mechanical degradation of the silane coupling agent. A dispersion time of 15-40 minutes is sufficient to ensure that the filler reaches a dynamic equilibrium between dispersion and coating in the presence of the coupling agent. Maintaining the dispersion temperature at room temperature (20-30℃) is crucial. Excessive temperature accelerates the hydrolysis and condensation rate of the silane coupling agent, potentially causing it to self-aggregate into a gel-like precipitate in the aqueous phase before coating the filler, thus losing its modifying effect. Conversely, excessively low temperatures increase the viscosity of water and increase shear resistance. Through the synergistic control of these process parameters, a highly dispersed, densely coated, and stable modified filler aqueous dispersion can be prepared, laying a solid foundation for the subsequent in-situ wet mixing.

[0048] Step S3: Mix the acrylic rubber latex with the modified filler dispersion and perform wet mixing under alkaline conditions at a preset temperature to allow the carboxyl groups in the latex to undergo an in-situ ring-opening reaction with the epoxy groups on the surface of the modified filler, thereby obtaining an in-situ modified mixed latex.

[0049] By mixing a pre-prepared latex rich in active carboxyl groups with a modified filler dispersion coated with epoxy groups under specific conditions, interfacial collisions and chemical reactions are induced between the two micro-particles that originally existed independently and stably in the liquid phase.

[0050] In this embodiment, the mixture of acrylate rubber latex and modified filler dispersion is wet-mixed under alkaline conditions of 40-60℃ and pH 8-9.

[0051] First, the ring-opening reaction between carboxyl and epoxy groups usually requires certain catalytic conditions. In this example, the alkaline adjuster used to adjust the pH to 8-9 is ammonia, sodium hydroxide solution, or triethylamine aqueous solution. Maintaining the pH of the system at a weakly alkaline level (8-9) is a key process window determined through extensive experimentation. Under weakly alkaline conditions, the carboxyl groups (-COOH) on the surface of latex particles partially dissociate, forming carboxylate anions (-COO₂). - Compared to neutral carboxyl groups, carboxylate anions have stronger nucleophilicity. When a negatively charged carboxylate anion approaches the epoxy ring on the surface of the modified filler, it can act as a nucleophile to attack the less sterically hindered carbon atom on the epoxy ring, causing the CO bond to break and a ring-opening reaction to form a stable ester bond (-COO-).

[0052] If the pH value is below 8, i.e., neutral or weakly acidic, the degree of dissociation of carboxyl groups is extremely low, and the system mainly exists in the form of the weakly nucleophilic -COOH group. The ring-opening reaction rate is extremely slow, and a sufficient number of chemical bonds cannot be formed within the limited wet mixing time, resulting in insufficient interfacial bonding and a significant reduction in the in-situ modification effect. Conversely, if the pH value is above 9, i.e., strongly alkaline, although the carboxyl groups can completely dissociate and have extremely strong nucleophilicity, the strongly alkaline environment will severely damage the stability of acrylic rubber latex. Emulsifier molecules on the surface of latex particles may undergo structural changes or desorption in a strongly alkaline environment, causing the latex particles to lose electrostatic or steric stability protection, resulting in microscopic or even macroscopic aggregation and demulsification. In addition, strong alkali may also promote uncontrolled hydrolysis side reactions of epoxy groups, generating inactive diols, thus wasting functional groups. Therefore, the weakly alkaline condition of pH 8-9 ensures both sufficient reactivity and maintains the kinetic stability of the latex system.

[0053] Regarding the control of reaction temperature and time, stirring is carried out at 40-60℃ for 60-120 minutes. The chemical reaction rate is closely related to temperature. The temperature range of 40-60℃ provides moderate molecular thermal kinetic energy, increasing the collision frequency between latex particles and filler particles in the liquid phase, while simultaneously improving the activation energy conversion rate of the ring-opening reaction. If the temperature is below 40℃, the reaction rate is too slow, and even with extended stirring time, it is difficult to achieve the ideal grafting rate. If the temperature is above 60℃, although the reaction rate is faster, the high temperature will accelerate the Brownian motion of latex particles, increasing the risk of demulsification due to particle collisions, and may also lead to the decomposition of some heat-sensitive additives or excessively rapid evaporation of water. A stirring time of 60-120 minutes ensures that the reaction can proceed fully while maintaining latex stability. Claim 14 also specifies a stirring speed of 300-1000 rpm. This medium-speed stirring ensures macroscopically uniform mixing, allowing the filler dispersion to be uniformly suspended in the latex, without generating excessive mechanical shear force that could lead to mechanical demulsification of the latex.

[0054] To further optimize the rheological state and reaction efficiency of the reaction system, the total solids content of the in-situ modified mixed latex was limited to 20%-35%. Total solids content represents the mass percentage of non-volatile substances in the dispersion system. If the total solids content is below 20%, it means there is too much water in the system, resulting in excessive distance between latex particles and filler particles, significantly reducing the collision probability, leading to long reaction times, low efficiency, and subsequent coagulation requiring the treatment of large amounts of water, resulting in a sharp increase in energy consumption. If the total solids content is above 35%, the viscosity of the system increases sharply. High viscosity not only hinders the effective operation of the stirrer, leading to uneven mixing, but also restricts the movement of latex and filler particles, further reducing the probability of effective collisions and reactions. Simultaneously, high viscosity easily triggers shear-induced coagulation. Therefore, a total solids content of 20-35% is the optimal balance point for achieving efficient microscopic reaction and good macroscopic flowability.

[0055] In the wet mixing process, this embodiment also introduces the water-based application of processing aids. In step S3, while performing wet mixing, an aqueous processing aid dispersion is added to the system. The aqueous processing aid dispersion includes one or more of the following: an antioxidant aqueous dispersion, a plasticizer emulsion, or an aqueous dispersant solution.

[0056] In traditional dry mixing, powdered antioxidants and oily plasticizers are directly added to the internal mixer. Due to the high viscosity of rubber, this easily leads to uneven dispersion of the additives, resulting in localized enrichment or dead zones. In this embodiment, however, water-based additives are added during the liquid-phase mixing stage. Utilizing the low viscosity and excellent flowability of the liquid phase, the additive molecules can be highly uniformly dispersed in the aqueous phase in the form of nano or micron-sized droplets. Subsequently, as the water evaporates and condenses, they uniformly coat the surface of each rubber particle and filler.

[0057] The antioxidant aqueous dispersion contains 2,2,4-trimethyl-1,2-dihydroquinoline polymer (antioxidant RD) or N-phenyl-α-aniline (antioxidant A); the plasticizer emulsion contains polyester plasticizers or ether ester plasticizers. Antioxidant RD is a typical ketamine antioxidant with excellent protection against thermo-oxidative aging. Its large molecular weight makes it less prone to volatility and blooming. Antioxidant A has a good effect on fatigue aging. Pre-preparing these antioxidants into aqueous dispersions allows for initial molecular-level dispersion in the liquid phase. Polyester or ether ester plasticizers have good compatibility with acrylic rubbers. When added in emulsion form, they can uniformly swell within the rubber network after coagulation, effectively reducing the Mooney viscosity of the compound and improving processing fluidity.

[0058] To precisely control the in-situ reaction process and prevent incomplete or excessive cross-linking, the progress of the in-situ ring-opening reaction is monitored by sampling and titrating the epoxy value until the epoxy value drops to below 10% of the initial value. The epoxy value is typically determined using the hydrochloric acid-dioxane method or perchloric acid titration. During the wet mixing process, samples are taken at regular intervals (e.g., every 20 minutes) to determine the content of remaining epoxy groups in the system. When the epoxy value drops to below 10% of the initial value, it means that more than 90% of the epoxy groups have participated in the ring-opening reaction, forming a dense interfacial chemical bond network. If the reaction continues at this point, the remaining small amount of epoxy groups will be unable to continue reacting due to steric hindrance, resulting in extremely low efficiency; conversely, if the reaction is stopped when the epoxy value is still high, the interfacial bonding force will be insufficient. This quantitative monitoring enables scientific control of the reaction endpoint, ensuring the stability of product quality between batches.

[0059] Step S4: Add a coagulant to the in-situ modified mixed latex to coagulate it, and then wash and dry it to obtain an acrylic rubber compound.

[0060] After the in-situ modification reaction is completed, the system is a stable liquid mixed latex, which needs to be converted into a solid rubber compound.

[0061] Coagulation is a critical process of transition from a liquid phase to a solid phase, and its manner directly affects the distribution of fillers in the final solid rubber. In this embodiment, the coagulant is an inorganic salt solution of sodium chloride, calcium chloride, aluminum sulfate, or alum, or an inorganic acid solution of hydrochloric acid or sulfuric acid. Inorganic salt coagulants reduce the zeta potential by compressing the electric double layer on the surface of latex particles, causing the latex particles to overcome electrostatic repulsion and aggregate; inorganic acids not only compress the electric double layer but also neutralize the negative charge on the latex surface and cause a sharp drop in the pH of the system, leading to rapid demulsification and precipitation of the latex.

[0062] To avoid uneven filler encapsulation or impurity embedding caused by localized demulsification, in step S4, the coagulation temperature is 50-80℃, the coagulation time is 1-3 hours, and the coagulant is added by spraying. Traditional methods of directly pouring or rapidly adding the coagulant will create extremely high concentrations of localized demulsification zones upon contact, causing the precipitated rubber macromolecules to rapidly encapsulate a large amount of filler and water, forming dense rubber clumps within. Subsequent washing will struggle to remove the internal salts and emulsifiers.

[0063] In this embodiment, a spray-addition method is used to uniformly disperse the coagulant in the form of tiny droplets throughout the latex system, achieving global synchronous demulsification. A coagulation temperature of 50-80℃ maintains the flexibility of the rubber macromolecular chains, ensuring the precipitated rubber particles have a certain porosity, facilitating the subsequent elution of impurities. A slow coagulation time of 1-3 hours ensures a smooth demulsification process, forming uniform, porous, sponge-like wet rubber particles.

[0064] The coagulated wet particles contain a large amount of residual emulsifiers, unreacted salts, and water-soluble oligomers, requiring thorough washing. In step S4, washing is performed using deionized water at a temperature of 50-70℃ until the conductivity of the washing filtrate is less than 50 μS / cm. Hot water at 50-70℃ accelerates the dissolution and diffusion of impurity molecules, improving washing efficiency. Deionized water avoids the introduction of new metal ion impurities. Conductivity is a direct physical quantity for measuring the thoroughness of washing. When the conductivity drops below 50 μS / cm, it indicates that the vast majority of inorganic salts and ionic emulsifiers in the particles have been removed. If washing is incomplete, residual metal ions (such as Na+) will remain. + Ca 2+ During subsequent high-temperature vulcanization or use, it will become a catalyst for thermo-oxidative aging, accelerating the breakage of rubber molecular chains; residual emulsifiers will form a weak interface layer at the rubber interface, reducing mechanical properties and even causing blooming.

[0065] The washed wet rubber granules contain approximately 30-50% moisture and must be dried. In step S4, drying is performed using either vacuum drying or hot air drying. When vacuum drying is used, the drying temperature is 70-90℃, the vacuum degree is 0.06-0.09 MPa, and the drying time is 8-15 hours. Although acrylic rubber has good heat resistance, prolonged exposure to aerobic and high-temperature conditions still poses a risk of thermo-oxidative crosslinking, leading to increased Mooney viscosity and deteriorated processability. Vacuum drying, under a negative pressure of 0.06-0.09 MPa, significantly lowers the boiling point of water, allowing moisture to rapidly vaporize and dissipate at a mild temperature of 70-90℃. This not only shortens the drying time but, more importantly, isolates oxygen, effectively preventing thermo-oxidative aging of the rubber during the drying stage and ensuring the stability of the Mooney viscosity of the compound.

[0066] Following drying in step S4, a heat treatment step is included, where the dried compound is heat-treated at 120-150℃ for 1-3 hours to further promote the reaction between residual epoxy groups and carboxyl groups. During the liquid-phase wet compounding stage, due to steric hindrance and reaction time, approximately 10% of the epoxy groups fail to participate in the reaction. After the rubber undergoes coagulation and drying to become solid, although the macromolecular chains lose their free movement in the liquid phase, at the high temperature of 120-150℃, the rubber is in a highly elastic state, and the chain segments can undergo a certain degree of creep and rearrangement. This thermal motion allows the residual carboxyl groups and epoxy groups, which were previously unable to contact due to steric hindrance, to approach and react. This "dry-state heat treatment" step acts as a "filling gap," further increasing the interfacial crosslinking density, making the bond between the filler and the rubber stronger, and ultimately improving the physical and mechanical properties of the final product.

[0067] The acrylate rubber compound prepared according to the above process exhibits significantly superior performance compared to products prepared using traditional processes. The Mooney viscosity [ML(1+4)100℃] of the acrylate rubber compound obtained in this application's embodiments is 30-60. Mooney viscosity is an important indicator of rubber processing performance. A Mooney viscosity range of 30-60 indicates that the compound possesses sufficient stiffness to prevent excessive flow and deformation in processing equipment, while also exhibiting good flowability, making it easy to mold in extruders or injection molding machines. This is attributed to the precise control of the in-situ reaction degree in this application's embodiments, avoiding a surge in Mooney viscosity due to excessive crosslinking; simultaneously, the uniform dispersion of the aqueous plasticizer emulsion and antioxidant also provides effective internal lubrication.

[0068] The acrylate rubber compound prepared by the method described in this application, after vulcanization with the addition of a vulcanizing agent, exhibits a 100% tensile stress of not less than 5 MPa and an elongation at break of not less than 250%. In conventional physical blending systems, only weak van der Waals forces exist between the filler and the rubber. Under external tensile stress, the filler particles are prone to slippage or debonding, resulting in a low tensile stress. However, in the system of this application embodiment, the ester bonds formed through the in-situ ring-opening reaction of epoxy-carboxyl groups firmly anchor the filler to the rubber macromolecular network. When the material is subjected to external force, the stress can be uniformly transferred to the filler network through chemical bonds, fully utilizing the reinforcing effect of the filler. Therefore, the 100% tensile stress is significantly improved, reaching not less than 5 MPa. Simultaneously, due to the extremely uniform dispersion of the filler, the absence of stress concentration points caused by large particle agglomeration, and the perfect cross-linking network, the material maintains high strength while possessing good elastic deformation capacity, with an elongation at break of not less than 250%, achieving a good balance between high strength and high elasticity.

[0069] This application's embodiments establish strong chemical bonds between fillers and rubber macromolecules by introducing carboxyl-containing monomers during the emulsion polymerization stage, introducing epoxy-containing silane coupling agents during the filler dispersion stage, and initiating in-situ ring-opening reactions under weakly alkaline conditions during the wet mixing stage. By precisely controlling the ratio of carboxyl-containing monomers (1-5 wt%) and epoxy coupling agents (1-8 wt%), the sufficiency of the ring-opening reaction is ensured, while latex gelation is avoided. For nano-sized carbon black and silica, secondary agglomeration is effectively prevented through high-shear dispersion and coupling agent coating. The introduction of an aqueous processing aid dispersion during the wet mixing stage solves the problem of uneven dispersion of aids in traditional dry mixing. The use of spray-added coagulants, strict control of washing conductivity, and appropriate vacuum drying processes ensures the uniformity and purity of the coprecipitates. The heat treatment process after drying further promotes the reaction of residual functional groups and improves the crosslinking network. The additional technical features of each dependent claim have played an irreplaceable synergistic role in process control, efficiency improvement and performance optimization, and ultimately successfully prepared an acrylic rubber compound with uniform filler dispersion, strong interfacial bonding, and excellent mechanical and aging resistance properties.

[0070] To more intuitively demonstrate the technical solution of this application and its superior effects, a detailed description is provided below with reference to specific embodiments and comparative examples. It should be noted that these embodiments are only used to explain this application and do not constitute a limitation on the scope of protection of this application.

[0071] Specifically, in the following examples and comparative examples, all raw materials used were commercially available industrial-grade products. The performance testing methods are as follows: Mooney viscosity: Tested according to GB / T 1232.1, under the conditions of ML(1+4) 100℃.

[0072] 100% tensile stress and elongation at break: The prepared compound is vulcanized with vulcanizing agent (sometimes with accelerator) according to the conventional ACM formula, vulcanized at 180°C for 10 minutes, and then tested according to GB / T 528.

[0073] Filler dispersion: The dispersion of the vulcanized rubber slices was observed using an optical microscope and rated according to ASTM D2663 (grades 1-10, with grade 10 being the best).

[0074] Example 1 S1: Add 200 parts water, 3 parts sodium dodecyl sulfate, 95 parts butyl acrylate, 3 parts acrylonitrile, 2 parts acrylic acid (containing 2 wt% carboxyl monomers of the total monomers), and 0.3 parts potassium persulfate to the reactor. Emulsion polymerization is carried out at 60°C for 8 hours to obtain an acrylic rubber latex with active carboxyl groups on the surface.

[0075] S2: Mix 40 parts of silica (average particle size 30nm, specific surface area 150 m² / g) with 160 parts of water, add 2 parts of γ-glycidyl etheroxypropyltrimethoxysilane (5wt% of filler weight), and disperse under high shear at 3000 rpm for 30 minutes to obtain a modified filler dispersion.

[0076] S3: Mix the latex with the modified filler dispersion, adjust the pH to 8.5 with ammonia, and wet-mix at 50℃ and 500rpm for 90 minutes, resulting in a total solids content of approximately 25%. Titration monitoring showed that the epoxy value of the system decreased to below 5% of the initial value, yielding an in-situ modified mixed latex.

[0077] S4: A 2wt% calcium chloride solution was sprayed into the mixed latex, and coagulated at 70°C for 2 hours. Then, it was washed with deionized water at 60°C until the conductivity of the filtrate was less than 50 μS / cm. Finally, it was dried at 80°C under a vacuum of 0.08 MPa for 10 hours to obtain the acrylic rubber compound.

[0078] Analysis: Due to the introduction of acrylic acid and epoxy silane coupling agents, and the in-situ ring-opening reaction under alkaline conditions, silica particles are chemically bonded to the rubber molecular chains. Microscopic observation shows that the filler dispersion reaches grade 9, with no agglomeration. The vulcanized rubber exhibits a 100% tensile stress of 6.5 MPa, an elongation at break of 320%, and a Mooney viscosity of 45, demonstrating excellent comprehensive performance and proving that chemical bonding significantly improves interfacial strength.

[0079] Example 2 Based on Example 1, in step S1, acrylonitrile was replaced with 2 parts of chloroacrylate, and 1 part of triethylene glycol diacrylate was added as a crosslinking monomer (Right 4). In step S2, the filler was replaced with carbon black (N330, average particle size 40 nm, specific surface area 90 m² / g), and the coupling agent was replaced with β-(3,4-epoxycyclohexyl)ethyltriethoxysilane (Right 10).

[0080] Analysis: The introduction of crosslinking monomers pre-forms a partially micro-crosslinked network during the polymerization stage, which, combined with subsequent in-situ modification, further improves the heat deformation resistance of the rubber. Carbon black, like silica, exhibits extremely high dispersity (grade 9), demonstrating the universality of this process for different nanofillers. The final Mooney viscosity is 48, the 100% tensile stress is 6.8 MPa, and the elongation at break is 300%.

[0081] Example 3 Based on Example 1, in step S2, the weight ratio of silica to water was controlled at 1:5, the shear speed was increased to 4500 rpm, and the dispersion time was 20 minutes. In step S3, the total solids content of the latex after mixing was controlled at 30%, the stirring speed was increased to 800 rpm, and the mixing time was shortened to 70 minutes.

[0082] Analysis: By increasing the shear rate and controlling the material ratio, the coupling agent coating became more uniform and dense. Higher solid content and stirring speed increased the probability of intermolecular collisions, allowing the ring-opening reaction to reach its endpoint in a shorter time. This embodiment significantly improved production efficiency, and the product performance was essentially the same as in Example 1, demonstrating the rationality of the process parameter window design.

[0083] Example 4 In step S3 of Example 1, three parts of an aqueous dispersion containing 2,2,4-trimethyl-1,2-dihydroquinoline polymer (antioxidant RD) were added simultaneously with the start of wet mixing. Meanwhile, the epoxy value was titrated every 20 minutes, and the reaction was stopped when the epoxy value dropped to 8% of its initial value.

[0084] Analysis: The antioxidant, added in the form of an aqueous dispersion, can be uniformly adsorbed onto the surface of latex particles in the liquid phase, avoiding dust dispersion and uneven distribution that occur during dry mixing. In a heat aging test (175℃ × 72h), the tensile strength retention rate of the vulcanizate prepared in this example was 15% higher than that in Example 1, demonstrating that the uniform dispersion of the antioxidant provides excellent resistance to thermo-oxidative aging. Strict monitoring of the epoxy value ensured accurate reaction endpoints, preventing weak interfacial bonding due to insufficient reaction or latex gelation due to over-reaction.

[0085] Example 5 Based on Example 1, triethylamine was used to adjust the pH in S3. In S4, coagulation was achieved using an alum aqueous solution, sprayed at 60°C for 1.5 hours. The washing water temperature was controlled at 70°C, and washing continued until the conductivity was <30 μS / cm. After drying, an additional heat treatment step was added, subjecting the compound to heat treatment at 140°C for 2 hours.

[0086] Technical Effect Analysis: The use of spray-applied coagulant and appropriate warm water washing ensured the purity of the co-precipitated rubber. The heat treatment process allowed residual epoxy groups and carboxyl groups that did not fully react during drying to continue cross-linking under dry conditions. Tests showed that the heat-treated compound exhibited better Mooney viscosity stability, the 100% tensile stress of the vulcanizate increased to 7.2 MPa, and the elongation at break remained at 280%, demonstrating that heat treatment further improved the interfacial cross-linking network between the filler and the rubber matrix.

[0087] Comparative Example 1 Comparative Example 1 did not introduce a carboxyl-containing monomer and did not use an in-situ ring-opening reaction.

[0088] S1: Made with pure butyl acrylate-acrylonitrile copolymer, without acrylic acid.

[0089] S2: Silica is directly dispersed in water (without epoxy silane coupling agent).

[0090] S3: Mix the latex and silica dispersion, adjust the pH to 8.5, and stir for 90 minutes (no ring-opening reaction occurs). The remaining coagulation, washing, and drying are the same as in Example 1.

[0091] Analysis: Comparative Example 1 was only a physical blend. Under the microscope, the silica showed obvious agglomeration, with a dispersion grade of only 5. Due to the lack of chemical bonding, the vulcanizate had a 100% tensile stress of only 4.2 MPa, an elongation at break of 380% (low strength), and a Mooney viscosity of 55. Comparative Example 1 demonstrates that the chemical bonding between carboxyl-containing monomers and epoxy groups is key to improving interfacial bonding and mechanical properties.

[0092] Comparative Example 2 Comparative Example 2 introduced a carboxyl-containing monomer, but did not use a coupling agent to coat the filler, meaning no epoxy groups participated in the reaction.

[0093] Based on Example 1, step S2 does not involve the addition of γ-glycidyl etheroxypropyltrimethoxysilane. The remaining steps are the same as in Example 1.

[0094] Analysis: Although the latex contains carboxyl groups, the filler surface lacks epoxy groups, preventing in-situ ring-opening reactions. The silica dispersion is grade 6. The 100% tensile stress is 4.8 MPa. While the performance is slightly better than Comparative Example 1, it is far inferior to Example 1, further demonstrating the necessity of epoxy-carboxyl chemical bonding.

[0095] Unlike existing technologies, this application discloses a method for preparing acrylate rubber based on a wet mixing process. The embodiments of this application innovatively introduce carboxyl-containing monomers into the acrylate rubber latex and use epoxy-containing silane coupling agents to coat fillers. Under the mild liquid-phase conditions of wet mixing, a strong chemical bond is established between the rubber macromolecules and the fillers through the in-situ ring-opening reaction of carboxyl and epoxy groups. This design breaks through the limitations of traditional wet mixing relying solely on physical blending, fundamentally solving the problem of weak interfacial bonding, and significantly improving the dispersibility of fillers and the mechanical properties and heat aging resistance of the rubber.

[0096] Furthermore, this application ensures the sufficiency of the ring-opening reaction by precisely controlling the ratio of carboxyl-containing monomers and epoxy coupling agents, while avoiding latex gelation or excessive crosslinking caused by excessive functional groups, thus maintaining the good processing performance of the compound. For nano-sized carbon black and silica, high-shear dispersion and coupling agent coating effectively prevent secondary agglomeration in the aqueous dispersion and subsequent mixing processes. The introduction of an aqueous processing aid dispersion during the wet mixing stage solves the problem of uneven dispersion of aids in traditional dry mixing. The uniformity and purity of the coprecipitate are ensured by spraying coagulants, strictly controlling washing conductivity, and employing a suitable vacuum drying process. The heat treatment process after drying further promotes the reaction of residual functional groups and improves the crosslinking network. This preparation method has a reasonable process flow, requires no expensive equipment, and greatly improves the overall performance and production efficiency of acrylate rubber.

[0097] The above description is merely an embodiment of this application and does not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

Claims

1. A method for preparing acrylate rubber based on a wet mixing process, characterized in that, include: S1: Emulsion polymerization of acrylate monomers containing carboxyl functional groups with other acrylate monomers in water to obtain acrylate rubber latex with active carboxyl groups on the surface. S2: The filler and the silane coupling agent containing epoxy groups are mixed in water and dispersed under high shear to coat the surface of the filler with the silane coupling agent, thereby obtaining a modified filler dispersion. S3: The acrylate rubber latex is mixed with the modified filler dispersion and wet-mixed under alkaline conditions at a preset temperature, so that the carboxyl groups in the latex and the epoxy groups on the surface of the modified filler undergo an in-situ ring-opening reaction to obtain an in-situ modified mixed latex. S4: Add a coagulant to the in-situ modified mixed latex to coagulate it, and then wash and dry it to obtain an acrylic rubber compound.

2. The preparation method according to claim 1, characterized in that, The acrylate monomer containing a carboxyl functional group is one or more of acrylic acid, methacrylic acid, itaconic acid, or maleic anhydride. The other acrylate monomers include a main monomer and a comonomer; the main monomer is one or more of ethyl acrylate, butyl acrylate or 2-methoxyethyl acrylate; the comonomer is acrylonitrile or chloroacrylate.

3. The preparation method according to claim 2, characterized in that, The other acrylate monomers also include crosslinking monomers, which are one or more of divinylbenzene, triethylene glycol diacrylate, or trimethylolpropane trimethacrylate.

4. The preparation method according to claim 1, characterized in that, The amount of the acrylate monomer containing the carboxyl functional group is 1-5 wt% based on the total weight of the monomers.

5. The preparation method according to claim 1, characterized in that, In step S1, the emulsion polymerization uses an anionic emulsifier and / or a nonionic emulsifier; the anionic emulsifier is sodium dodecyl sulfate, and the nonionic emulsifier is nonylphenol polyoxyethylene ether. The emulsion polymerization uses ammonium persulfate or potassium persulfate thermal decomposition initiator as the initiator, with a polymerization temperature of 40-80℃ and a polymerization time of 4-10 hours; or, the emulsion polymerization uses a redox initiator, which is formulated from an organic peroxide oxidant and a reducing agent, wherein the organic peroxide oxidant is one or more of tert-butyl hydroperoxide, benzoyl peroxide, and cumene hydroperoxide, and the reducing agent is one or more of sodium bisulfite, ferrous sulfate, sodium formaldehyde sulfoxylate, and sodium hydrosulfite, with an initiation temperature of 5-30℃, a holding temperature of 60-80℃, and a holding time of 2-6 hours.

6. The preparation method according to claim 1, characterized in that, The epoxy-containing silane coupling agent is one of γ-glycidyl etheroxypropyltrimethoxysilane, β-(3,4-epoxycyclohexyl)ethyltriethoxysilane, or γ-glycidyl etheroxypropylmethyldiethoxysilane.

7. The preparation method according to claim 1, characterized in that, In step S2, the amount of the silane coupling agent containing epoxy groups is 1-8 wt% of the weight of the filler, and the weight ratio of the filler to water is 1:3 to 1:

8. The high-shear dispersion has a shear rate of 2000-5000 rpm, a dispersion time of 15-40 minutes, and a dispersion temperature of 20-30℃.

8. The preparation method according to claim 1, characterized in that, In step S3, wet mixing is carried out under alkaline conditions of 40-60℃ and pH value of 8-9. The stirring speed of the wet mixing is 300-1000 rpm and the mixing time is 60-120 minutes. The total solids content of the in-situ modified mixed latex is controlled between 20% and 35%.

9. The preparation method according to claim 1, characterized in that, In step S3, while performing wet mixing, an aqueous processing aid dispersion is also added to the system. The aqueous processing aid dispersion includes one or more of the following: an antioxidant aqueous dispersion, a plasticizer emulsion, or an aqueous dispersant solution. The antioxidant aqueous dispersion contains 2,2,4-trimethyl-1,2-dihydroquinoline polymer or N-phenyl-α-aniline; the plasticizer emulsion contains polyester plasticizer or ether ester plasticizer.

10. The preparation method according to claim 1, characterized in that, In step S4, the coagulant is an inorganic salt solution of sodium chloride, calcium chloride, aluminum sulfate or alum, or an inorganic acid solution of hydrochloric acid or sulfuric acid. The coagulation temperature is 50-80℃, the coagulation time is 1-3 hours, and the coagulating agent is added by spraying during coagulation.

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