A double-dynamic reversible crosslinking high-stability weather-resistant water-based acrylic emulsion, a preparation method and application thereof

Abstract

This invention discloses a dual-dynamic reversible crosslinked, highly stable, weather-resistant waterborne acrylic emulsion, its preparation method, and its applications, belonging to the fields of polymer emulsion synthesis and waterborne polymer materials technology. The emulsion uses hard and soft monomers as its basic framework, introduces a rigid alicyclic monomer, dicyclopentadiene acrylate, for main chain modification, and constructs a dual-network system of ketone-hydrazine dynamic reversible crosslinking + imide hydrogen bond dynamic crosslinking using diacetone acrylamide and N-maleimide. It is prepared via a semi-continuous seeded emulsion polymerization process, combined with anionic / nonionic reactive emulsifiers, thermally decomposable initiators, pH buffers, and adipamide hydrazine latent crosslinking agents. The system utilizes two dynamic reversible bonds with different bond energies to achieve wide temperature adaptability of the coating film. At high temperatures, the ketone-hydrazine bonds relax and release pressure to prevent re-adhesion, while at low temperatures, the hydrogen bond network strengthens the structure to prevent brittleness. Simultaneously, dynamic bond reconstruction enables self-repair of micro-scratches and micro-cracks. It is suitable for heavy-duty anti-corrosion and highly weather-resistant waterborne coating systems.

Description

Technical Field

[0001] This invention relates to the fields of polymer emulsion synthesis and waterborne polymer materials technology, specifically to a dual dynamic reversible crosslinking highly stable weather-resistant waterborne acrylic emulsion, its preparation method, and its application. This product is mainly used in the fields of heavy-duty anti-corrosion and high weather-resistant waterborne coatings for metal substrates in automobiles and engineering machinery. Background Technology

[0002] Waterborne acrylic emulsions, with their advantages of being non-toxic and environmentally friendly, having low VOC content, strong adhesion to substrates, wide compatibility with formulations, and simple application processes, are currently the most widely used film-forming resins in industrial anti-corrosion coatings, engineering machinery coatings, and automotive parts coatings. Engineering machinery and outdoor automotive parts operate under complex conditions for extended periods, continuously enduring high and low temperature fluctuations, rain immersion, salt spray corrosion, UV aging, gravel impact, and minor scratches. This places stringent requirements on the film hardness, flexibility, media resistance, temperature stability, and storage stability of acrylic emulsions.

[0003] There are four major technical bottlenecks in the existing waterborne acrylic emulsion technology, and conventional modification methods in the industry cannot completely solve them.

[0004] 1. Single crosslinking system, temperature change contradictions and irreversible damage: Traditional acrylic emulsions are divided into static crosslinking systems and single dynamic crosslinking systems. The chemical bonds in the static crosslinking network are irreversible. Once the paint film develops microcracks or minor scratches, it cannot be repaired. Corrosive media penetrate along the defects, causing the substrate to rust in a short period of time. The single ketone-hydrazine dynamic crosslinking system has only one reversible bond with a single bond energy. It cannot simultaneously achieve high-temperature resistance to tackiness and low-temperature resistance to brittleness. The paint film is prone to brittleness in extremely cold environments of -40°C. In high-temperature environments in summer, the paint film softens and becomes tacky, attracts dust and loses its gloss. Defects expand rapidly under alternating hot and cold conditions.

[0005] 2. The molecular backbone is too flexible, resulting in insufficient weather resistance and corrosion resistance. Conventional acrylic emulsions only use straight-chain alkyl acrylate monomers for copolymerization. The molecular skeleton is highly flexible but lacks rigidity. After film formation, the coating film has poor density, allowing water vapor and salt ions to easily penetrate. It also has weak resistance to salt spray and UV aging, and powdering, blistering, and peeling occur after six months to one year of outdoor use. Existing simple organosilicon modification and core-shell structure modification can only slightly improve individual properties and do not strengthen the rigidity at the molecular skeleton level, thus limiting the effectiveness of technological improvements.

[0006] 3. Migration of small molecule emulsifiers and poor system stability: Most acrylic emulsions on the market use traditional anionic and nonionic small molecule emulsifiers. These substances only adhere to the surface of latex particles through physical adsorption. During long-term storage, the small molecule emulsifiers gradually migrate and precipitate, causing the emulsion to separate, flocculate, and gel. After film formation, the emulsifier accumulates on the surface of the paint film, forming hydrophilic channels, which significantly reduces the water resistance and salt spray resistance of the paint film.

[0007] 4. Homogeneous modification schemes and insufficient creativity: Most of the currently published patents and literature focus on core-shell structures, single organosilicon grafting, and single crosslinking modification. The technical routes are similar, and a multi-synergistic functional system has not been built. The improvement in comprehensive performance is limited, making it difficult to meet the high standards of coatings for high-end engineering machinery and new energy vehicles.

[0008] In summary, developing a novel waterborne acrylic emulsion integrating dual dynamic reversible crosslinking, rigid modification of the molecular backbone, and a reactive emulsification system is an inevitable trend for technological upgrading in this field. Summary of the Invention

[0009] To address the shortcomings of existing waterborne acrylic emulsions, such as simple crosslinking structures, poor high and low temperature adaptability, insufficient storage stability, lack of self-healing ability in the coating film, weak weather resistance and corrosion protection, and homogeneous modification technologies, this invention provides a dual-dynamic reversible crosslinked, highly stable, and weather-resistant waterborne acrylic emulsion, its preparation method, and its applications. This invention innovatively constructs a dual-dynamic reversible crosslinking network, combined with rigid alicyclic monomer backbone modification and a bond-type reactive emulsification system, breaking through existing technological barriers from multiple dimensions including molecular structure, microstructure, and film-forming mechanism. The product possesses wide temperature adaptability, self-healing properties, high stability, and high corrosion and weather resistance. The process is simple and controllable, suitable for large-scale industrial production.

[0010] The emulsion of this invention comprises, by weight, the following components: 28-35 parts of hard monomer (methyl methacrylate), 18-24 parts of soft monomer (butyl acrylate), 4-7 parts of rigid alicyclic modified monomer (dicyclopentadiene acrylate), 5-9 parts of dual dynamic crosslinking functional monomer (a compound of diacetone acrylamide and N-maleimide in a weight ratio of 3:2), 1.2-2.0 parts of acidic functional monomer (methacrylic acid), 1.8-2.8 parts of reactive compound emulsifier (sodium allyl hydroxypropyl sulfonate (anionic reactive) + polyoxyethylene allyl ether (nonionic reactive) = 1:1 compound), 0.3-0.6 parts of initiator (ammonium persulfate), 0.1-0.3 parts of buffer (sodium bicarbonate), 40-50 parts of deionized water, and 1.0-2.0 parts of blocked hydrazine crosslinking agent (adipic hydrazide).

[0011] The preparation method includes the following steps.

[0012] This invention employs a semi-continuous seed emulsion polymerization method, which results in a narrow latex particle size distribution, low residual monomer levels, and stable exothermic polymerization, making it suitable for industrial mass production. The specific steps are as follows.

[0013] Preparation of S1 activated seed emulsion (seeds + activation treatment).

[0014] Add 40% of the total mass of deionized water, all of the sodium bicarbonate, and 1 / 3 of the reactive compound emulsifier to the reactor, purge the mixture with nitrogen, and stir at 800 rpm for 5 minutes to dissolve.

[0015] Heat to 81℃ (fixed temperature control, discarding wide temperature range), add 15% of total monomers mixed monomers, and emulsify at 1000r / min for 10min.

[0016] Add 1 / 2 of the ammonium persulfate initiator solution and keep the reaction at a warm temperature for 20 minutes to obtain the basic seed.

[0017] Add a trace amount of initiator (5% of the total initiator mass), and activate at a constant temperature for 5 minutes to activate the active sites on the surface of the seed particles, thus obtaining a highly active activated seed emulsion.

[0018] Preparation of S2 phase stable pre-emulsion (stabilization and synergistic emulsification).

[0019] The remaining deionized water and remaining emulsifier are added to the pre-emulsification kettle, which is then protected with nitrogen.

[0020] Group feeding: First, add hard monomer + soft monomer and stir and disperse for 10 minutes, then add dicyclopentadiene acrylate rigid monomer and stir for 5 minutes, and finally add dual dynamic crosslinking functional monomer + methacrylic acid monomer.

[0021] The composite emulsification mode of "high-speed emulsification + low-frequency ultrasound assistance" was adopted: stirring and emulsifying at 1200r / min for 25min, and simultaneously supplemented with low-frequency ultrasound (20kHz) treatment for 5min, for a total duration of 30min; ultrasound was used to break up monomer agglomerates and improve the dispersion stability of alicyclic monomers and crosslinked monomers in the aqueous phase.

[0022] S3 temperature-controlled zoned synchronous dripping + gradient maturation (variable temperature polymerization + segmented maturation).

[0023] The reactor was kept at a constant temperature of 80-82℃. The pre-emulsion and the remaining initiator aqueous solution were added simultaneously through two channels over a total of 3 hours, with an addition error of ≤±2min.

[0024] After the addition is complete, the product is allowed to mature in two stages.

[0025] 1. First stage: High temperature curing at 80-82℃ for 60 minutes to deeply consume conventional acrylic monomers.

[0026] 2. Second stage: Slowly cool down to 75℃ and maintain the temperature for 30 minutes to adapt to the reactivity of the dual dynamic crosslinking monomer and avoid high-temperature deactivation of the crosslinking groups.

[0027] Nitrogen gas is bubbled throughout the process, isolating oxygen.

[0028] S4 stepped cooling + precise pH control + low-temperature cross-linking curing (stepped process, bound to a dual dynamic cross-linking system).

[0029] 1. Step cooling: First, reduce the temperature from 75℃ to 50℃ (cooling rate 2℃ / min), then reduce it to 42℃ (fixed point temperature).

[0030] 2. Precise pH adjustment: The pH is slowly adjusted to 7.7±0.1 by adding 25% ammonia dropwise (narrow range precise control, adapted to ketone hydrazine / hydrogen bond cross-linking activity).

[0031] 3. Constant temperature slow-release addition of crosslinking agent: Under low-speed stirring at 400r / min, continuously and uniformly add adipic hydrazide aqueous solution (prepared into a 10% aqueous solution) using a peristaltic pump for 15min.

[0032] 4. Low-temperature curing and complexation: After the addition is complete, the mixture is kept at a constant temperature of 42℃ for 30 minutes to allow the ketone carbonyl and imide groups to fully pre-complex with the hydrazine crosslinking agent and construct a uniform dual dynamic crosslinking network.

[0033] 5. Filtration and discharge: The finished emulsion is obtained by filtering through a 200-mesh filter.

[0034] The above-mentioned method for preparing a dual-dynamic reversible crosslinked highly stable weather-resistant waterborne acrylic emulsion uses methyl methacrylate as a polymerization-grade hard monomer with a purity ≥99.8%, moisture ≤0.05%, color ≤5APHA, and glass transition temperature of 105℃. It is selected from Mitsubishi Chemical and is used to improve the hardness, density, weather resistance, and adhesion to metal substrates of the paint film. If the dosage is less than 28 parts, the paint film is too soft and prone to re-adhesion; if it is more than 35 parts, the paint film is too rigid, the flexibility decreases, and it is prone to cracking.

[0035] The above-mentioned method for preparing a dual-dynamic reversible crosslinked highly stable weather-resistant waterborne acrylic emulsion uses butyl acrylate as a polymerization-grade soft monomer with a purity ≥99.8%, moisture content ≤0.05%, viscosity of 0.72 mPa·s at 20℃, and glass transition temperature of the homopolymer of -54℃. Manufactured by Wanhua Chemical or BASF, it features high copolymerization activity, excellent compatibility, and low residue, providing a foundation for the emulsion film's flexibility, low-temperature crack resistance, substrate wetting adhesion, and application leveling properties.

[0036] The above-mentioned method for preparing a dual-dynamic reversible crosslinked highly stable weather-resistant waterborne acrylic emulsion uses dicyclopentadiene acrylate (DCPA, CAS: 33791-58-1) as a monofunctional high-hardness UV monomer. The molecule contains a bicyclic fused-ring alicyclic structure, which, after copolymerization, is embedded into the acrylic polymer backbone, enhancing the overall rigidity, steric hindrance, and UV aging resistance of the molecular chain, hindering the penetration of corrosive media. It has a purity ≥96%, acid value ≤1mgKOH / g, color ≤5APHA, viscosity at 25℃ 8–18mPa·s, and homopolymer Tg≈100℃. Manufactured by Resonac, it features low viscosity, low shrinkage, high hardness, fast curing, good air-drying properties, and excellent adhesion to difficult-to-bond substrates (PET / PC / ABS), providing a high-heat-resistant, high-wear-resistant, water- and chemical-resistant, and low-deformation skeletal foundation for the photocuring system.

[0037] The above-mentioned method for preparing a dual-dynamic reversible crosslinked highly stable weather-resistant waterborne acrylic emulsion involves using a dual-dynamic crosslinking functional monomer prepared by compounding diacetone acrylamide and N-maleimide in a mass ratio of 3:2. The diacetone acrylamide has a purity ≥99.0%, and the N-maleimide has a purity ≥98.5%. The raw materials are selected from Shanghai Aladdin. The compounding process involves adding the two monomers sequentially to a stirred tank at room temperature according to the specified ratio, controlling the stirring speed at 300–500 r / min, and stirring for 10–15 min until the system is homogeneous and transparent. The compounded product exhibits good copolymer compatibility and stable dynamic crosslinking performance. After participating in emulsion copolymerization, it forms a dual-dynamic reversible crosslinking network, improving the high and low temperature resistance of the paint film and enabling self-repair of micro-scratches.

[0038] (1) Diacetone Acrylamide: The molecule contains a ketone carbonyl group, which undergoes an addition reaction with the later-added adipyl hydrazine to form a dynamic reversible cross-linking bond of ketone hydrazine with low bond energy (low reversible activation energy). Under high temperature conditions, the cross-linking bond relaxes and dissociates, releasing the internal stress of the paint film and avoiding high-temperature re-adhesion and dust accumulation; when the temperature drops, the bond reforms.

[0039] (2) N-maleimide: The molecule contains imide polar groups, and multiple hydrogen bonds form a dynamic cross-linking network between molecules, resulting in higher bond energy and a more stable structure. Under low temperature conditions, the hydrogen bond network locks the coating film structure, inhibits molecular chain movement, and prevents low-temperature brittleness.

[0040] Two cross-linking networks work together to achieve wide temperature range self-adaptation from -40℃ to 90℃; when the paint film develops microcracks or minor scratches, the broken dynamic bonds can be gradually reconstructed at room temperature, achieving in-situ self-repair.

[0041] The above-mentioned method for preparing a dual-dynamic reversible crosslinked highly stable weather-resistant waterborne acrylic emulsion uses methacrylic acid (MAA, CAS: 79-41-4) as a polymerization-grade acidic functional monomer with a purity ≥99.5%, moisture ≤0.05%, acid value ≥645mgKOH / g, viscosity at 20℃ 1.4mPa·s, and homopolymer glass transition temperature 130℃. Manufactured by Dow Chemical, it features high copolymerization activity and excellent emulsification stability, improving the storage stability of the emulsion system, enhancing the interfacial adhesion between the paint film and the metal substrate, increasing the surface hydrophilicity of latex particles, and stabilizing the emulsion system. Simultaneously, it enhances the interfacial adhesion between the paint film and metal substrates such as steel and aluminum alloys. Excessive use will increase the hydrophilicity of the paint film and reduce its water resistance.

[0042] The above-mentioned method for preparing a dual-dynamic reversible crosslinked highly stable weather-resistant waterborne acrylic emulsion, wherein the reactive compound emulsifier is prepared by precisely compounding sodium allyl oxypropyl sulfonate anionic reactive emulsifier and polyoxyethylene allyl ether nonionic reactive emulsifier at a mass ratio of 1:1; wherein the sodium allyl oxypropyl sulfonate has an active content of ≥95%, strong water solubility, and high reactive double bond activity, and the polyoxyethylene allyl ether has a double bond retention rate of ≥98% and a wide emulsion coverage range, and the manufacturer is ADEKA. The compounding process involves adding equal amounts of two reactive emulsifiers sequentially under ambient temperature and pressure, controlling the stirring speed at 400–600 r / min, and stirring at a constant temperature for 10–15 min until the system is uniform, transparent, and free of stratification and flocculation, thus obtaining anionic / nonionic synergistic bonding compound emulsifiers. This compound system combines the electrostatic stabilization effect of anionic emulsification with the steric stabilization effect of nonionic emulsification. During polymerization, it can be completely grafted onto the surface of latex particles without the precipitation of free small molecules, significantly improving the storage stability, salt resistance, and water and weather resistance of the paint film.

[0043] Both contain polymerizable carbon-carbon double bonds. Diacetone acrylamide provides the ketone carbonyl group, which forms a dynamic and reversible crosslinking bond with hydrazine crosslinking agents. N-maleimide provides the imide group, and multiple hydrogen bonds are formed between molecules to form a dynamic crosslinking network with strong copolymerization bonding ability, hydrolysis resistance, no migration, and low foaming. During the polymerization process, it is covalently bonded to the surface of latex particles, eliminating the migration defects of small molecule emulsifiers from the root, and greatly improving the storage stability, water resistance and high humidity construction adaptability of the emulsion.

[0044] The above-mentioned method for preparing a dual-dynamic reversible crosslinked highly stable weather-resistant waterborne acrylic emulsion uses ammonium persulfate (APS, CAS: 7727-54-0) as a polymerization-grade thermally decomposable initiator with a purity ≥99.0%, moisture ≤0.1%, active oxygen ≥6.9%, good water solubility, and moderate decomposition temperature. Manufactured by BASF, it features stable initiation efficiency, low decomposition residue, and low gelation rate, and can stably initiate free radical copolymerization of acrylic monomers, ensuring uniform emulsion particle size, system stability, and high batch repeatability.

[0045] The above-mentioned method for preparing a dual-dynamic reversible crosslinked highly stable weather-resistant waterborne acrylic emulsion uses sodium bicarbonate (baking soda, CAS: 144-55-8) as a polymerization-grade pH buffer with a purity ≥99.0%, good water solubility, and stable buffer zone. Manufactured by Shandong Haihua, it features mild buffering effect, does not affect polymerization activity, and has strong system stability. It stabilizes the pH environment for emulsion polymerization throughout the process, inhibits monomer hydrolysis, avoids polymerization instability, reduces gel formation, and ensures a stable and controllable polymerization process.

[0046] The above-mentioned method for preparing a dual dynamic reversible crosslinked highly stable weather-resistant waterborne acrylic emulsion uses adipamide hydrazine (ADH, CAS: 1071-93-8) as a latent hydrazine crosslinking agent with a purity ≥99.0%, melting point 178~182℃, and excellent water solubility. Manufactured by Jiangsu Runfeng, it features mild reaction, high storage stability, and good low-temperature crosslinking activity. It can form a reversible ketone-hydrazine dynamic crosslinking structure with ketone carbonyl groups, and synergistically enhances the effect with a double hydrogen bond network, achieving self-healing, water and weather resistance, and wide-temperature dimensional stability of the paint film.

[0047] This invention utilizes two types of dynamic reversible bonds with different bond energies to achieve wide temperature adaptability of the coating film. At high temperatures, the ketone-hydrazine bonds relax to release pressure and prevent re-adhesion, while at low temperatures, the hydrogen bond network strengthens the structure to prevent brittleness. Simultaneously, dynamic bond reconstruction enables self-repair of micro-scratches and micro-cracks. The reactive emulsifier is covalently bonded to the surface of the latex particles, completely eliminating the migration problem of free small molecules. The emulsion's stability at room temperature can reach more than 18 months. The emulsion of this invention has a solid content of 48±1%, a particle size of 80 / 120nm, a residual monomer content of <0.1%, and a VOC of <25g / L. After film formation, the coating film has a hardness of 2H, withstands neutral salt spray for ≥1200h, undergoes 120 cycles of high and low temperature (-40℃ / 90℃) without cracking or peeling, and withstands artificial accelerated aging for ≥2200h. The raw materials of this invention are readily available, the process is mature, and it is easy to industrialize and mass-produce. The resulting product has comprehensive performance far exceeding that of traditional acrylic emulsions and is suitable for heavy-duty anti-corrosion and high-weather-resistant waterborne coating systems for automotive chassis, wheel hubs, engineering machinery frames, and body panels.

[0048] A dual-dynamic reversible crosslinked highly stable weather-resistant waterborne acrylic emulsion and its preparation method are disclosed. Compared with traditional technologies, the beneficial effects of the invention are as follows:

[0049] 1. Core Innovation: Dual dynamic reversible cross-linking network, overcoming the common problem of temperature change in the industry.

[0050] Unlike traditional single static crosslinking and single dynamic crosslinking technologies, this invention is the first to combine low-bond-energy dynamic bonds of ketone-hydrazine with high-bond-energy hydrogen bonds of imide to construct a dual-network adaptive system. At high temperatures, the ketone-hydrazine bonds relax and release pressure, completely solving the problems of paint film stickiness and dust accumulation; at low temperatures, the hydrogen bond network strengthens the structure, preventing brittle cracking and peeling, and widening the operating temperature range to -40℃ to 90℃. Simultaneously, the reversible reconstruction characteristics of the dynamic bonds endow the paint film with self-repair capabilities for micro-damage, blocking the penetration of corrosive media and extending the long-term protective life of the coating.

[0051] 2. Molecular skeleton modification: Rigid alicyclic monomers improve weather resistance and corrosion resistance.

[0052] By introducing a rigid, fused-ring structure of dicyclopentadiene acrylate to modify the polymer backbone, the strength and microstructure of the coating film skeleton are improved. The salt spray resistance and UV aging resistance are more than doubled compared to conventional acrylic emulsions, fully meeting the requirements of engineering machinery and automobiles in outdoor heavy corrosion conditions.

[0053] 3. System innovation: Reactive emulsifiers completely solve the stability problem.

[0054] All emulsifiers used are polymerizable reactive emulsifiers, with emulsifier molecules covalently bonded to the surface of latex particles, preventing the migration of free small molecules. The emulsion can withstand dilution in any proportion of pure water, ethanol, and dilute acids and alkalis without flocculation, and its room temperature storage stability has been improved from the traditional 6 / 12 months to 18 months; there is no whitening, sagging, or loss of gloss in high humidity environments, and the application window has been widened to 40% / 90% relative humidity, making it extremely adaptable to industrial applications. Detailed Implementation

[0055] The present invention will now be described in detail with reference to the embodiments.

[0056] The reactive compound emulsifier is a mixture of sodium allyl oxyhydroxypropyl sulfonate and polyoxyethylene allyl ether in a mass ratio of 1:1.

[0057] The dual dynamic crosslinking functional monomer is composed of diacetone acrylamide and N-maleimide in a mass ratio of 3:2.

[0058] Example groups (4 groups in total, including lower limit, intermediate, upper limit and optimal ratio).

[0059] Example 1 (lower limit ratio).

[0060] Raw material weight parts: methyl methacrylate 28 parts, butyl acrylate 18 parts, dicyclopentadiene acrylate 4 parts, diacetone acrylamide 3 parts, N-maleimide 2 parts, methacrylic acid 1.2 parts, sodium allyl hydroxypropyl sulfonate 0.9 parts, polyoxyethylene allyl ether 0.9 parts, ammonium persulfate 0.3 parts, sodium bicarbonate 0.1 parts, deionized water 40 parts, adipamide hydrazide 1.0 part.

[0061] The preparation method is as follows.

[0062] Preparation of S1 activated seed emulsion (seeds + activation treatment).

[0063] Add 40% of the total mass of deionized water, all of the sodium bicarbonate, and 1 / 3 of the reactive compound emulsifier to the reactor, purge the mixture with nitrogen, and stir at 800 rpm for 5 minutes to dissolve.

[0064] Heat to 80℃ (fixed-point temperature control, discarding wide temperature range), add 15% of total monomer mixed monomer, emulsify at 1000r / min for 10min; the mixed monomer is a mixture of hard monomer, soft monomer, rigid alicyclic modified monomer, dual dynamic crosslinking functional monomer, and acidic functional monomer.

[0065] Add 1 / 2 of the ammonium persulfate solution and keep the reaction at a constant temperature for 20 minutes to obtain the basic seed emulsion; add a trace amount of initiator (5% of the total initiator mass), and activate at a constant temperature for 5 minutes to activate the active sites on the surface of the seed particles to obtain a highly active activated seed emulsion.

[0066] Preparation of S2 phase stable pre-emulsion (stabilization and synergistic emulsification).

[0067] The remaining deionized water and remaining reactive compound emulsifier are added to the pre-emulsification kettle under nitrogen micro-protection.

[0068] Group feeding: First, add hard monomer + soft monomer and stir and disperse for 10 minutes, then add dicyclopentadiene acrylate rigid monomer and stir for 5 minutes, and finally add dual dynamic crosslinking functional monomer + methacrylic acid monomer.

[0069] The composite emulsification mode of "high-speed emulsification + low-frequency ultrasound assistance" was adopted: stirring and emulsifying at 1200r / min for 25min, and simultaneously supplemented with low-frequency ultrasound (20kHz) treatment for 5min, for a total duration of 30min; ultrasound was used to break up monomer agglomerates and improve the dispersion stability of alicyclic monomers and crosslinked monomers in the aqueous phase, resulting in a pre-emulsion without floating oil and without stratification.

[0070] S3 temperature-controlled zoned synchronous dripping + gradient maturation (variable temperature polymerization + segmented maturation).

[0071] The reactor was kept at a constant temperature of 80°C. The pre-emulsion and the remaining initiator aqueous solution were added simultaneously through two channels over a total of 3 hours, with an addition error of ≤ ±2 min.

[0072] After the addition is complete, the product is allowed to mature in two stages.

[0073] 1. First stage: High temperature curing at 80℃ for 60 minutes to deeply consume conventional acrylic monomers.

[0074] 2. Second stage: Slowly cool down to 75℃ and maintain the temperature for 30 minutes to adapt to the reactivity of the dual dynamic crosslinking monomer and avoid high-temperature deactivation of the crosslinking groups.

[0075] Nitrogen gas is bubbled throughout the process, isolating oxygen.

[0076] S4 stepped cooling + precise pH control + low-temperature cross-linking curing (stepped process, bound to a dual dynamic cross-linking system).

[0077] 1. Step cooling: First, reduce the temperature from 75℃ to 50℃ (cooling rate 2℃ / min), then reduce it to 42℃ (fixed point temperature).

[0078] 2. Precise pH adjustment: The pH is slowly adjusted to 7.5±0.1 by adding 25% ammonia dropwise (narrow range precise control, adapted to ketone hydrazine / hydrogen bond cross-linking activity).

[0079] 3. Constant temperature slow-release addition of crosslinking agent: Under low-speed stirring at 400r / min, continuously and uniformly add adipic hydrazide aqueous solution (prepared into a 10% aqueous solution) using a peristaltic pump for 15min.

[0080] 4. Low-temperature curing and complexation: After the addition is complete, the mixture is kept at a constant temperature of 42℃ for 30 minutes to allow the ketone carbonyl and imide groups to fully pre-complex with the hydrazine crosslinking agent and construct a uniform dual dynamic crosslinking network.

[0081] 5. Filtration and discharge: The finished emulsion is obtained by filtering through a 200-mesh filter.

[0082] Example 2 (intermediate ratio).

[0083] Raw material weight parts: methyl methacrylate 30 parts, butyl acrylate 20 parts, dicyclopentadiene acrylate 5 parts, diacetone acrylamide 4.2 parts, N-maleimide 2.8 parts, methacrylic acid 1.6 parts, sodium allyl hydroxypropyl sulfonate 1.15 parts, polyoxyethylene allyl ether 1.15 parts, ammonium persulfate 0.45 parts, sodium bicarbonate 0.2 parts, deionized water 45 parts, adipic acid hydrazide 1.5 parts.

[0084] Preparation process: Same as in Example 1, except that the polymerization temperature in S3 is 81℃.

[0085] Example 3 (Upper Limit Ratio).

[0086] Raw material weight parts: methyl methacrylate 35 parts, butyl acrylate 24 parts, dicyclopentadiene acrylate 7 parts, diacetone acrylamide 5.4 parts, N-maleimide 3.6 parts, methacrylic acid 2.0 parts, sodium allyl hydroxypropyl sulfonate 1.4 parts, polyoxyethylene allyl ether 1.4 parts, ammonium persulfate 0.6 parts, sodium bicarbonate 0.3 parts, deionized water 50 parts, adipamide hydrazide 2.0 parts.

[0087] Preparation process: Same as in Example 1, except that the polymerization temperature in S3 is 82℃.

[0088] Example 4 (Optimal ratio).

[0089] Raw material weight parts: methyl methacrylate 32 parts, butyl acrylate 21 parts, dicyclopentadiene acrylate 5.5 parts, diacetone acrylamide 4.2 parts, N-maleimide 2.8 parts, methacrylic acid 1.6 parts, sodium allyl hydroxypropyl sulfonate 1.15 parts, polyoxyethylene allyl ether 1.15 parts, ammonium persulfate 0.45 parts, sodium bicarbonate 0.2 parts, deionized water 45 parts, adipic acid hydrazide 1.5 parts.

[0090] Preparation process: Same as in Example 1, except that the polymerization temperature in S3 is 81℃.

[0091] Comparative example group.

[0092] Comparative Example 1 (traditional small molecule emulsifier + ordinary acrylic emulsion, unmodified and uncrosslinked).

[0093] The method used 1.15 parts sodium dodecylbenzenesulfonate and 1.15 parts fatty alcohol polyoxyethylene ether small molecule emulsifier, without adding dual dynamic crosslinking functional monomers, dicyclopentadiene acrylate, or adipyl hydrazide. The amount of other monomers was the same as in Example 4, and the process was consistent.

[0094] Comparative Example 2 (single ketone-hydrazine crosslinked emulsion, without hydrogen bond crosslinking and without rigid monomer).

[0095] N-maleimide and dicyclopentadiene acrylate were removed, and only the diacetone acrylamide + adipamide hydrazide single ketone hydrazide crosslinking system was retained. 2.3 parts of reactive compound emulsifier were used, and the weight parts of the remaining raw materials and the process were the same as in Example 4.

[0096] Comparative Example 3 (single hydrogen bond crosslinking, no ketone hydrazine crosslinking, no rigid monomer).

[0097] Diacetone acrylamide, adipamide hydrazide, and dicyclopentadiene acrylate were removed, leaving only 2.3 parts of the N-maleimide hydrogen bond crosslinking system. The remaining raw materials and processes were the same as in Example 4.

[0098] Comparative Example 4 (Dual dynamic crosslinking + small molecule emulsifier, no rigid monomer).

[0099] The dual dynamic crosslinking functional monomer and adipamide hydrazide were retained and replaced with 2.3 parts of traditional small molecule emulsifier (sodium dodecylbenzenesulfonate and fatty alcohol polyoxyethylene ether were compounded at a mass ratio of 1:1). Dicyclopentadiene acrylate was removed, and the remaining raw material weight parts and processes were the same as in Example 4.

[0100] Comparative Example 5 (Dual dynamic crosslinking + rigid monomer + small molecule emulsifier).

[0101] The dual dynamic crosslinking functional monomer and rigid alicyclic monomer are retained. 2.30 parts of traditional small molecule emulsifier (sodium dodecylbenzenesulfonate and fatty alcohol polyoxyethylene ether are compounded at a mass ratio of 1:1) are used. The weight parts of the remaining raw materials and the process are the same as in Example 4.

[0102] Methods for coating film preparation and performance testing.

[0103] Substrate: Q235 cold-rolled steel sheet, size 150mm×70mm×1mm. The substrate is treated with degreasing, rust removal and grinding, with a surface roughness of 30~50μm.

[0104] Coating method: air spraying, dry film thickness controlled at 50±5μm.

[0105] Maintenance conditions: normal temperature (25℃), relative humidity 50%, test after 7 days of maintenance.

[0106] Execution standards: Adhesion (cross-cut test): GB / T9286-1998; Pencil hardness: GB / T6739-2006; Resistance to pure water immersion: GB / T1733-1993; Resistance to neutral salt spray: GB / T10125-2021; High and low temperature cycling: -40℃ (2h) ↔ 90℃ (2h) is one cycle; Artificial accelerated weathering: GB / T1865-2009; Self-healing test: Prepare 50μm wide micro-scratches with standard needles, and observe the repair status at room temperature.

[0107] Specific testing technical indicators are shown in Table 1.

[0108] Table 1. Performance comparison of the embodiments and comparative examples.

[0109]

[0110] Examples 1 to 4 of the present invention all exhibited excellent comprehensive performance within the defined formula range, with Example 4 (optimal ratio) reaching peak performance in all indicators.

[0111] Comparative Example 1 (traditional emulsion) lagged behind in all aspects of performance, proving that a single copolymer system cannot meet the requirements of high-end working conditions.

[0112] Comparative Examples 2 and 3, which only use a single dynamic crosslinking system, cannot simultaneously solve the problems of high-temperature re-adhesion and low-temperature cracking, and have no self-healing effect, thus verifying the synergistic creativity of the dual dynamic crosslinking network.

[0113] When comparative examples 4 and 5 were replaced with small molecule emulsifiers, the storage stability and water resistance of the emulsions decreased significantly, verifying the technical contribution of the reactive emulsification system.

[0114] All comparative examples showed no complete self-healing effect, further demonstrating that the dual dynamic reversible cross-linking structure of the present invention possesses non-obviousness and inventiveness.

[0115] Example 5.

[0116] Using the dual-dynamic reversible crosslinked highly stable weather-resistant waterborne acrylic emulsion obtained in Example 4 of this invention as the main film-forming resin, an automotive waterborne coating was formulated according to a conventional formula. The coating comprised the following components by weight: 30 parts of the dual-dynamic reversible crosslinked highly stable weather-resistant waterborne acrylic emulsion obtained in Example 4, 20 parts of calcium carbonate, 16 parts of mica powder, 4 parts of graphite powder, 8 parts of zinc phosphate anti-rust pigment, 6 parts of talc filler, 3 parts of film-forming aid, 1 part of wetting and dispersing agent, 0.3 parts of defoamer, and 11.7 parts of deionized water. Application process: Automotive frame substrate → degreasing and rust removal → spraying automotive waterborne coating (wet film 2mm) → air drying at room temperature.

[0117] Outdoor field test: Placed in the natural environment of an open-air factory area, it has been in continuous service for 18 months. The paint film showed no chalking, no blistering, no rust, and no peeling. Minor scratches caused by human intervention were repaired on their own within 3 to 4 hours, fully meeting the requirements for long-term outdoor protection.

Claims

1. A dual-dynamic reversible crosslinking highly stable weather-resistant waterborne acrylic emulsion, characterized in that, By weight, the following raw materials are included: 28-35 parts hard monomer, 18-24 parts soft monomer, 4-7 parts rigid alicyclic modified monomer, 5-9 parts dual dynamic crosslinking functional monomer, 1.2-2.0 parts acidic functional monomer, 1.8-2.8 parts reactive compound emulsifier, 0.3-0.6 parts initiator, 0.1-0.3 parts buffer, 40-50 parts deionized water, and 1.0-2.0 parts blocked hydrazine crosslinking agent.

2. The dual-dynamic reversible crosslinking highly stable weather-resistant waterborne acrylic emulsion according to claim 1, characterized in that, The raw materials include: 32 parts hard monomer, 21 parts soft monomer, 5.5 parts rigid alicyclic modified monomer, 7 parts dual dynamic crosslinking functional monomer, 1.6 parts acidic functional monomer, 2.3 parts reactive compound emulsifier, 0.45 parts initiator, 0.2 parts buffer, 45 parts deionized water, and 1.5 parts blocked hydrazine crosslinking agent.

3. A dual-dynamic reversible crosslinking highly stable weather-resistant waterborne acrylic emulsion according to claim 1 or 2, characterized in that, The dual dynamic crosslinking functional monomer is composed of diacetone acrylamide and N-maleimide in a mass ratio of 3:

2.

4. A dual-dynamic reversible crosslinking highly stable weather-resistant waterborne acrylic emulsion according to claim 1 or 2, characterized in that, The rigid alicyclic modified monomer is dicyclopentadiene acrylate.

5. A dual-dynamic reversible crosslinking highly stable weather-resistant waterborne acrylic emulsion according to claim 1 or 2, characterized in that, The reactive compound emulsifier is prepared by compounding sodium allyl oxyhydroxypropyl sulfonate and polyoxyethylene allyl ether in a mass ratio of 1:

1.

6. A dual-dynamic reversible crosslinking highly stable weather-resistant waterborne acrylic emulsion according to claim 1 or 2, characterized in that, The hard monomer is methyl methacrylate, the soft monomer is butyl acrylate, the acidic functional monomer is methacrylic acid; the initiator is ammonium persulfate, the buffer is sodium bicarbonate, and the blocked hydrazine crosslinking agent is adipic acid hydrazine.

7. A method for preparing the dual-dynamic reversible crosslinked highly stable weather-resistant waterborne acrylic emulsion as described in claim 1 or 2, characterized in that, The process includes the following steps: S1. Preparation of seed emulsion: Add 40% by weight of deionized water, all buffer, and 1 / 3 by weight of reactive compound emulsifier to a reaction vessel, stir evenly, and heat; add 15% by weight of mixed monomers, emulsify, then add 1 / 2 by weight of initiator aqueous solution, maintain the temperature for reaction, add 5% initiator, and activate at a constant temperature to obtain a highly active activated seed emulsion. The mixed monomers are a mixture of hard monomers, soft monomers, rigid alicyclic modified monomers, dual dynamic crosslinking functional monomers, and acidic functional monomers; S2. Preparation of pre-emulsion: Mix the remaining deionized water and the remaining reactive compound emulsifier. Nitrogen gas was introduced, and the remaining hard monomer, soft monomer, rigid alicyclic modified monomer, dual dynamic crosslinking functional monomer, and acidic functional monomer were added sequentially. The mixture was emulsified under ultrasonic conditions with high-speed stirring to obtain a pre-emulsion without floating oil or stratification. S3 Gradient dropwise polymerization: The pre-emulsion and the remaining initiator aqueous solution were simultaneously and uniformly added dropwise in the reactor for 3 hours. After the addition was completed, the mixture was kept at a constant temperature for curing. S4 Post-treatment and discharge: The reactor was cooled and the pH of the system was adjusted to weakly alkaline. A blocked hydrazine crosslinking agent was added under low-speed stirring, and the mixture was kept at a constant temperature and stirred. After filtration, a dual dynamic reversible crosslinked highly stable weather-resistant waterborne acrylic emulsion was obtained.

8. The method for preparing a dual-dynamic reversible crosslinked highly stable weather-resistant waterborne acrylic emulsion according to claim 7, characterized in that, In step S1, the temperature increase is to raise the temperature to 80-82°C.

9. The method for preparing a dual-dynamic reversible crosslinked highly stable weather-resistant waterborne acrylic emulsion according to claim 7, characterized in that, In step S3, the temperature inside the reactor is 80-82℃. The pre-emulsion and the initiator aqueous solution are added simultaneously via dual-path flow, with an addition error not exceeding ±5 min. The aging temperature is 75-82℃, and the aging time is 90 min. In step S4, the cooling is to lower the temperature to 40-50℃. The pH of the system is adjusted to a slightly alkaline state by using 25% ammonia water to adjust the pH to 7.5-8.

0. The low-speed stirring is to stir at 400 r / min for 30 min.

10. The application of the dual dynamic reversible crosslinking highly stable weather-resistant waterborne acrylic emulsion as described in claim 1 or 2 in metal anti-corrosion and weather-resistant coatings.

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