Low-temperature fast-curing water-based paint and preparation method thereof

Abstract

The invention provides a low-temperature fast-curing water-based paint and a preparation method thereof, and relates to the technical field of paints.The low-temperature fast-curing water-based paint comprises modified epoxy emulsion, a dual curing agent and auxiliaries, the dual curing agent comprises a microcapsule accelerant and an ionic liquid modifier, the preparation method of the low-temperature fast-curing water-based paint comprises the following steps: respectively preparing the modified epoxy emulsion and the dual curing agent, dispersing the modified epoxy emulsion and the dual curing agent with the auxiliaries at a high speed, and defoaming and filtering the modified epoxy emulsion and the dual curing agent. The paint has the advantages of low-temperature quick curing property, high adhesive force and excellent wear resistance, and is suitable for quick coating of metal and plastic substrates.

Description

Technical Field

[0001] The present application relates to the field of coating technology, and in particular to a low-temperature fast-curing water-based coating and a preparation method thereof. Background Art

[0002] Waterborne coatings, due to their environmental friendliness and low volatile organic compound (VOC) emissions, have become a key alternative to solvent-based coatings. However, the curing rate of traditional waterborne coatings decreases significantly at low temperatures, resulting in prolonged film formation and reduced application efficiency, posing a particular challenge in cold regions or during winter. With the manufacturing industry's increasing demands for coating efficiency and energy conservation, developing waterborne coating systems that combine rapid low-temperature curing with excellent storage stability has become a critical technical bottleneck that the industry urgently needs to overcome. Existing technologies generally face an intractable contradiction: achieving rapid low-temperature curing requires increased system reactivity; however, highly reactive systems are prone to pre-crosslinking during storage or processing at room temperature, resulting in increased viscosity, shortened gel time, or even complete failure. For example, while highly reactive amine curing agents can accelerate low-temperature film formation, they can also cause localized curing during the extrusion stage due to mechanical shear heat generation, leading to equipment blockage. Furthermore, these coatings often clump and become scrapped during summer storage and transportation due to elevated ambient temperatures, forcing companies to incur additional cold chain costs and significantly weakening their product competitiveness. When the ambient temperature falls below the typical film-forming temperature, water-based coatings face two obstacles: First, the energy barrier for polymer particle movement increases, making latex particle fusion difficult, leading to structural defects such as micropores and cracks in the coating. Second, the water evaporation rate decreases dramatically, delaying the phase transition from wet to dry. Existing solutions often rely on physical heating, which not only increases energy consumption and equipment investment but also, on large, irregularly shaped components such as wind turbine blades and pipelines, can cause surface problems such as sagging and orange peel due to uneven heating. Current technical approaches often fall into the limitation of "treating the symptoms but not the root cause." Small molecule accelerators are introduced to enhance low-temperature activity, but the inability to precisely control the reaction process results in insufficient or excessive cross-linking of the cured network. The former leads to a sharp decrease in the coating's chemical resistance and mechanical strength; the latter causes embrittlement and degrades its impact toughness. More critically, small molecule accelerators are prone to migration and exudation, resulting in accelerated aging phenomena such as yellowing and chalking after long-term exposure. This inefficient modification strategy fails to meet the stringent comprehensive performance requirements of high-end equipment. During the R&D process, researchers often overlook a key reality: the essence of low-temperature rapid curing is the synergistic effect of multiple scales. Focusing solely on synthesizing highly reactive monomers, or solely manipulating particle morphology, or relying solely on external field-enhanced mass transfer, can easily lead to improvements in any single dimension leading to performance degradation in other dimensions. For example, improving the low-temperature fusion of latex particles requires lowering the polymer's glass transition temperature, but an excessively low glass transition temperature can worsen storage stability. Adding hydrophilic groups to promote water diffusion can introduce shortcomings in the coating's water resistance.

[0003] In summary, there is an urgent need to develop a new low-temperature fast-curing water-based coating and a preparation method thereof on the market. Summary of the Invention

[0004] The present application provides a low-temperature fast-curing water-based coating and a preparation method thereof, in order to solve the problems raised in the above-mentioned background technology.

[0005] To solve the above technical problems, the present application discloses a low-temperature fast-curing water-based coating, which is characterized by comprising a modified epoxy emulsion, a dual curing agent and an auxiliary agent.

[0006] Furthermore, the dual curing agent includes a microcapsule accelerator and an ionic liquid modifier.

[0007] Furthermore, the modified epoxy emulsion includes: epoxy resin E-44, methyl methacrylate, butyl acrylate, composite emulsifier, chain extender polyetheramine D230 and deionized water.

[0008] Furthermore, the modified epoxy emulsion comprises, by weight, 25-30 parts of epoxy resin E-44, 12-18 parts of methyl methacrylate, 8-12 parts of butyl acrylate, 1.4-1.8 parts of composite emulsifier, 0.3-0.8 parts of chain extender polyetheramine D230 and 30-40 parts of deionized water.

[0009] Furthermore, the composite emulsifier includes SDS, OP-10 and COPS-1.

[0010] Furthermore, the microcapsule promoter uses 2-phenylimidazole as a core material.

[0011] Furthermore, the auxiliary agent includes, by weight, 0.5-1.0 parts of hyperdispersant BYK-190, 2.3-2.8 parts of nano-fumed silica, 0.2-0.5 parts of organosilicon defoamer BYK-024, and 0.8-1.4 parts of thickener ASE-60.

[0012] The present application also discloses a method for preparing the low-temperature fast-curing water-based coating, comprising the following steps:

[0013] (1) preparing modified epoxy emulsion;

[0014] (2) preparing a dual curing agent;

[0015] (3) Mix and disperse the modified epoxy emulsion, dual curing agent and additives, degas and filter.

[0016] Furthermore, the preparation method of the modified epoxy emulsion comprises:

[0017] a. Stir and mix deionized water and composite emulsifier, add methyl methacrylate and butyl acrylate to emulsify;

[0018] b. After heating to 75°C, the initiator ammonium persulfate was added dropwise to react to obtain an acrylate copolymer emulsion;

[0019] c. Cool to 60°C, add epoxy resin E-44 and chain extender polyetheramine D230 and react for 2 hours.

[0020] Furthermore, the preparation method of the dual curing agent includes mixing 2-phenylimidazole and a wall material solution in a mass ratio of 1:4, spray drying to prepare a microcapsule accelerator; reacting dicyandiamide, an ionic liquid, and a silane coupling agent KH560 at 120°C and 0.8MPa for 3 hours to prepare an ionic liquid modifier; the preparation method of the wall material solution includes dehydrating a polyether or polyester polyol and reacting it with an excess of isocyanate to generate a prepolymer containing an NCO group, and adding KH-560 and TEOS to catalyze the reaction.

[0021] Furthermore, the spray drying conditions are as follows: inlet temperature 150±5°C, outlet temperature 70±3°C, and atomization pressure 0.25 MPa.

[0022] Furthermore, the low-temperature fast-curing water-based coating was obtained by vacuum degassing at -0.05 MPa for 30 minutes and filtering through a 200-mesh filter.

[0023] Furthermore, the SDS in the composite emulsifier is Clariant's HOSTAPON SAS60; the OP-10 in the composite emulsifier is Clariant's GENAPOL X080; and the COPS-1 in the composite emulsifier is Solvay's SIPOMER® COPS-1.

[0024] The working mechanisms of these raw material components are as follows: First, the core value of low-temperature, fast-curing waterborne coatings lies in overcoming the curing bottleneck of traditional waterborne systems at low temperatures. Its innovation stems from the precise synergistic interaction between its components. This synergy is not simply a summation of effects, but rather a molecular-level design that constructs multiple response mechanisms, enabling efficient crosslinking and structural densification of the coating even at low temperatures. Specifically, the raw material component system is organized around three key dimensions: low-temperature activation triggering, reaction depth control, and mechanical strength compensation, all nested within each other to form a dynamic equilibrium. Second, the modified epoxy emulsion serves as the coating backbone, fulfilling the dual role of film formation and providing reactive sites. Its core lies in the molecularly designed combination of a traditional rigid epoxy resin and a flexible acrylate copolymer, forming a core-shell composite emulsion. The outer acrylate segments are rich in polar groups, significantly reducing the energy barrier for polymer particle movement at low temperatures and promoting their spreading and fusion on the substrate surface. The inner epoxy resin layer retains a high density of epoxy groups, providing ample reactive sites for subsequent crosslinking reactions. The specially introduced polyetheramine chain extender acts as a bridge, its long chains interwoven within the epoxy network. This not only increases molecular chain flexibility to resist low-temperature embrittlement, but also prevents storage instability caused by pre-crosslinking through controlled reactions between the terminal amine groups and the epoxy groups. The formulation strategy of the composite emulsifier is particularly critical. The synergistic effect of the anionic and nonionic emulsifiers forms a dense interfacial film, ensuring the dimensional stability of the emulsion particles during transportation and storage. It also rapidly desorbs upon contact with water during application, accelerating particle aggregation. This dynamic equilibrium design ensures the system remains inert at room temperature, yet initiates a rapid phase transition upon exposure to low-temperature moisture. Thirdly, the dual-curing agent design concept stems from a dialectical solution to the paradox of low-temperature curing. The microencapsulated accelerator acts as a built-in chemical clock. Its wall material is a moisture-sensitive polymer prepolymer and silicone hybrid. In low-temperature environments, it absorbs moisture through selective permeation, causing the wall material to hydrolyze, thin, and eventually rupture, precisely releasing the encapsulated imidazole catalyst. This triggering mechanism prevents contact between the catalyst and epoxy groups at room temperature, completely resolving the problem of pre-reaction during storage. The released imidazole molecules quickly activate the epoxy ring to open, forming an initial cross-linking network. The ionic liquid modifier takes on the mission of deep curing. Its uniqueness lies in the dissociation of the crystalline structure of dicyandiamide, so that the amino groups that originally required high-temperature activation are ionized in the polar microenvironment formed by the ionic liquid, greatly reducing the activation energy of the reaction. Even more clever is that the introduction of the silane coupling agent enables the ionic liquid to construct covalently linked ion channels in the curing network, which not only ensures the uniformity of the reaction, but also enhances the toughness of the coating through ionic bonds. These two-stage curing mechanisms form a relay in the time series: the rupture of the microcapsules triggers the initial rapid gelation, and the ionic liquid continues to promote the increase in cross-linking density, and finally achieves complete curing at low temperatures. Fourthly, the additive system is like a precisely operated collaborative network, ensuring the performance of the coating from multiple scales.Hyperdispersants, through steric hindrance and synergistically with anchoring groups, maintain stable dispersion of nanoparticles within complex systems. The hydrophilic segments within their molecules also migrate to the interface during film formation, reducing curing shrinkage stress. Fumed silica plays a dual role within the system: on the one hand, its surface silanol groups condense in the presence of water to form siloxane crosslinks, compensating for the insufficient crosslink density that may result from low-temperature curing. On the other hand, the nanoparticles form a three-dimensional support framework within the coating, significantly enhancing hardness through crack deflection and energy dissipation. The molecular design of silicone defoamers is highly targeted. Their low surface tension allows for rapid penetration into the bubble membrane, while the high-molecular-weight polysiloxane chains form an elastic membrane to inhibit bubble regeneration, maintaining effective defoaming capabilities, particularly in low-temperature, high-viscosity systems. Thickeners offer even more sophisticated rheological control. Their associative thickening mechanism temporarily dissociates under shear stress, reducing viscosity for easier application, and then rapidly reconstitutes the network after stagnating to prevent sagging. This intelligent response is crucial for low-temperature application on vertical surfaces.

[0025] In summary, the interactions of the various components involved in this application form a precise response system. Specifically, the emulsion stability maintained by the emulsifier is broken during construction, and the released active components trigger the hydrolysis switch of the microcapsules. After the wall material breaks, the catalyst activates the epoxy groups to form a primary network, and the ionic liquid begins to dissociate the curing agent. As the water evaporates, the hydroxyl groups on the silica surface condense to strengthen the crosslinking points, while the thickener network gradually dissociates to achieve a balance between leveling and anti-sagging. This multi-stage response mechanism enables the system to operate like a precision clock under low-temperature conditions, ultimately forming a dense and hard protective coating.

[0026] The mechanism of action of the above-mentioned preparation method is as follows: The preparation process of this coating is essentially a precise process of molecular assembly and structural control, with each step embodying specific physical and chemical principles. Its core lies in maximizing the synergistic effects of various functional units through step-by-step construction and orderly integration, while avoiding harmful reactions between components. The preparation process can be broken down into three key stages: emulsion molecular engineering, curing agent micro-nanoencapsulation, and system synergistic integration, each of which involves sophisticated energy and interface control. The preparation of the modified epoxy emulsion adopts a step-by-step reaction strategy to control phase state. In the initial emulsification stage, an emulsifier is compounded to create an ultra-low interfacial tension environment, allowing the acrylate monomer to be fully dispersed into submicron droplets. During this process, the stirring intensity and temperature are strictly controlled to avoid over-emulsification, which would make it difficult to demulsify later. When the initiator is added dropwise to initiate polymerization, the reaction is designed to adopt a starvation feeding mode to ensure that the monomer concentration is always below the critical micelle concentration. The resulting acrylate copolymer has a narrow molecular weight distribution and its carboxyl groups are uniformly distributed, forming stable micelles. The ingenious addition of the epoxy resin after cooling is employed. This allows the system to enter a temperature window above the epoxy resin's softening point but below its reactivity, encouraging the epoxy molecules to embed into the micelle core through hydrophobic interactions. The chain extender, polyetheramine, then selectively reacts with carboxyl groups on the micelle surface. This directional reaction results in core-shell particles with a gradient structure: the carboxyl-rich acrylate polymer outer shell provides water dispersibility, the epoxy resin core maintains reactivity, and the transition layer is flexibly connected by the long polyetheramine chains. The entire reaction process is precisely controlled by a temperature gradient: high-temperature polymerization ensures conversion, while moderate-temperature chain extension prevents premature reaction of the epoxy groups, ultimately resulting in a storage-stable active emulsion system. The preparation of the dual curing agent embodies the wisdom of micro- and nanoscale encapsulation. The microencapsulation accelerator utilizes an interfacial reaction-driven encapsulation technique, synergistically crosslinking the isocyanate prepolymer and siloxane in the wall material solution to form a humidity-responsive hybrid wall material. Dynamic encapsulation is achieved during the spray drying phase through precise control of the temperature field: high inlet temperatures instantaneously atomize the solution, aligning the wall material molecular chains during solvent evaporation, and siloxane groups concentrate on the surface to form a dense protective layer. Low outlet temperatures ensure the integrity of the core material's molecular structure. This thermodynamically controlled phase separation process results in uniformly sized microcapsules, whose wall thickness and core material ratio are finely tuned by the solution concentration and atomization parameters. The synthesis of the ionic liquid modifier utilizes a high-pressure environment to break down energy barriers. In a closed reactor, the ionic liquid acts as a molecular solvent, penetrating into the defects of the dicyandiamide crystals. High pressure conditions promote covalent bonding between the alkoxy groups in the silane coupling agent and the amine groups. Notably, this reaction occurs selectively at the primary amine groups of the dicyandiamide, preserving the curing activity of the secondary amine groups. The final product maintains the low-temperature dissociation characteristics of the ionic liquid while preventing component migration through chemical bonding. The final mixing process is crucial for the system's synergistic properties. A step-by-step dosing strategy begins by premixing the dual curing agent and the modified latex under moderate shear. Here, weak interactions between the siloxane on the microcapsule surface and the latex particles form initial spatial alignment.The subsequently added nano-silica forms a nanoscale dispersion under the action of the hyperdispersant. The silanol groups on its surface react with the siloxanes in the microcapsule wall material in a condensation precursor reaction, establishing physical anchor points. The mechanical energy applied during the high-speed dispersion stage has a dual effect: on the one hand, it promotes the directional adsorption of additive molecules at the particle interface, and on the other hand, it disrupts localized aggregates through shear thinning. The vacuum degassing process, on the other hand, drives bubble growth and merging through a negative pressure gradient. Combined with precise control of the system's thixotropy, the microbubbles are eliminated by the thickener network during their ascent. The final filtration operation not only removes mechanical impurities, but also generates shear flow through the screen, which re-homogenizes the adsorption layer on the particle surface and improves the storage stability of the system. The energy input and interface control throughout the preparation process form a spatiotemporal coupling relationship: thermodynamic control during the emulsification stage ensures precise molecular structure, the temperature gradient during spray drying achieves micro-nanoencapsulation, and the shear field during the mixing process regulates the spatial distribution of particles. In particular, the choice of reactor type—an autoclave equipped with a scraper to prevent local overheating for emulsion synthesis, a centrifugal spray dryer for microcapsule preparation to ensure uniform particle size, and a triaxial disperser for three-dimensional shearing during mixing—precisely matches the mass and heat transfer requirements of each stage. In the final product, microcapsules are embedded in the epoxy network like time bombs, the ionic liquid modifier is evenly dispersed in the continuous phase, and fumed silica forms reinforcing connection points at the interface. This multi-level, ordered structure forms the material basis for low-temperature, rapid curing. It is worth emphasizing that the correlations between process parameters form a self-consistent system: the emulsification temperature determines the micelle size, affecting the subsequent encapsulation efficiency of the epoxy resin; the inlet and outlet temperature difference of the spray dryer controls the crystallinity of the wall material, which is related to the moisture response speed of the microcapsules; the dispersion intensity and time determine the adsorption conformation of the additive at the interface, ultimately affecting the stress distribution on the coating surface. It is this progressive and interlocking preparation logic that enables the coating to trigger a series of reactions such as microcapsule hydrolysis, catalyst release, epoxy ring opening, ion activation and siloxane condensation in an orderly manner when encountering low temperature and humidity during construction, completing the transformation from liquid dispersion to solid protective layer at the molecular scale.

[0027] Compared with the prior art, this application provides a low-temperature fast-curing water-based coating and a preparation method thereof, which has the following beneficial effects:

[0028] 1. This application involves dual curing. The microcapsule wall material dissolves and releases imidazole under low-temperature water penetration to achieve primary curing. The ionic liquid dissociates the active groups of dicyandiamide to achieve deep curing. Microencapsulated 2-phenylimidazole is used as a trigger. The microcapsule wall material precisely releases imidazole after water penetration, triggering the primary cross-linking of the epoxy resin. This solves the technical bottleneck of low low-temperature curing efficiency of traditional water-based coatings. The fumed silica forms siloxane cross-linking points in the coating to compensate for the loss of strength during low-temperature curing.

[0029] 2. The low-temperature, fast-curing water-based coating involved in this application has deep crosslinking and high strength properties. The ionic liquid modifier dissociates the active group in the late stage of curing to achieve deep construction of the crosslinked network. Combined with the siloxane crosslinking points formed by nano-fumed silica, the coating hardness reaches 2H level and has strong impact strength.

[0030] 3. This application utilizes a multi-scale structure to synergistically optimize coating performance, which is conducive to establishing a dynamic balance between storage stability and reactivity. The microcapsule wall material adopts a polyurethane / SiO2 hybrid prepolymer to isolate the core material activity at room temperature; the modified epoxy emulsion with a core-shell structure provides low-temperature film-forming properties, the dual curing agent triggers cross-linking in stages, and the nano-gas-phase silica filling is enhanced, so that the coating has excellent adhesion and salt spray resistance, and the overall performance is significantly better than that of a single modified system. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a SEM image of the low-temperature fast-curing water-based coating prepared in Example 1 of the present application;

[0032] Figure 2 This is a friction performance diagram of the wear resistance test of the low-temperature fast-curing water-based coating prepared in Example 1 of the present application;

[0033] Figure 3 This is the SEM image of the coating prepared in Comparative Example 1 of this application. DETAILED DESCRIPTION

[0034] The preferred embodiments of the present application are described below in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present application and are not used to limit the present application.

[0035] In addition, in this application, descriptions such as "first" and "second" are only used for descriptive purposes and do not specifically refer to the order or ranking, nor are they used to limit this application. They are only used to distinguish components or operations described with the same technical terms, and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one such feature. In addition, the technical solutions and technical features between the various embodiments can be combined with each other, but this must be based on the ability of ordinary technicians in this field to implement. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by this application.

[0036] Unless otherwise specified, the examples and comparative examples are parallel experiments with the same components, component contents, preparation steps, and preparation parameters. The experimental methods in the following examples are conventional methods unless otherwise specified. The experimental materials used in the following examples are analytical reagents (AR) unless otherwise specified, which were purchased from commercial channels.

[0037] Epoxy resin E-44 is KER-152 from Kukdo Chemical; methyl methacrylate is ELVACITE 2008 from Dow Chemical; butyl acrylate is BUTAFLEX B-100 from BASF; SDS in the composite emulsifier is HOSTAPON SAS60 from Clariant; OP-10 in the composite emulsifier is GENAPOL X080 from Clariant; COPS-1 in the composite emulsifier is SIPOMER® COPS-1 from Solvay; chain extender polyetheramine D230 is JEFFAMINE D-230 from Huntsman; ammonium persulfate initiator is LUROXID AN from Arkema; and 2-phenylimidazole as the microcapsule core material is DYHARD UR from Evonik. 500; dicyandiamide is DICYANEX 1400 produced by Mitsubishi Chemical; silane coupling agent KH560 is SILQUEST A-187 produced by Momentive; hyperdispersant BYK-190 is DISPERBYK-190 produced by BYK; nano-fumed silica is AEROSIL 200 produced by Evonik; silicone defoamer BYK-024 is BYK-024 produced by BYK; and thickener ASE-60 is ACRYSOL ASE-60 produced by Dow Chemical.

[0038] Example 1

[0039] This embodiment discloses a low-temperature, fast-curing water-based coating, comprising a modified epoxy emulsion, a dual curing agent, and additives; the modified epoxy emulsion comprises, by weight, 28 parts of epoxy resin E-44, 15 parts of methyl methacrylate, 10 parts of butyl acrylate, 1.6 parts of a composite emulsifier, 0.6 parts of a chain extender polyetheramine D230, and 35 parts of deionized water; the dual curing agent comprises 0.25 parts of a microcapsule accelerator and 5 parts of an ionic liquid modifier; the additives comprise 0.8 parts of a hyperdispersant BYK-190, 2.5 parts of nano-fumed silica, 0.3 parts of an organosilicon defoamer BYK-024, and 1.2 parts of a thickener ASE-60; and the composite emulsifier comprises 0.5 parts of SDS, 0.8 parts of OP-10, and 0.3 parts of COPS-1.

[0040] The preparation method of the modified epoxy emulsion comprises the following steps: adding 20 parts by weight of deionized water and 1.6 parts of a composite emulsifier to a nitrogen-protected reactor, stirring at 800 rpm for 10 minutes, adding 15 parts of methyl methacrylate and 10 parts of butyl acrylate, emulsifying at 25° C. for 30 minutes, heating to 75° C., dropwise adding 0.4 parts of initiator ammonium persulfate at a dropping rate of 1.0 mL / min, and keeping the temperature for reaction for 1.5 hours to obtain an acrylate copolymer emulsion; and cooling to 60° C., adding 28 parts of epoxy resin E-44 and 0.6 parts of chain extender polyetheramine D230, stirring at 400 rpm for reaction for 2 hours to form an epoxy-acrylic core-shell emulsion.

[0041] The preparation method of the dual curing agent comprises:

[0042] 2-phenylimidazole was used as the core material and mixed with the wall material solution in a mass ratio of 1:4. The spray drying inlet temperature was set at 150±5°C, the outlet temperature was 70±3°C, and the atomization pressure was 0.25 MPa to obtain spherical imidazole microcapsules. 4 parts of dicyandiamide, 1 part of 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid and 0.5 parts of silane coupling agent KH560 were added to a high-pressure reactor by weight, and the mixture was reacted at 120±2°C and 0.8 MPa pressure for 3 hours. After cooling, an ionic liquid modifier was obtained.

[0043] The preparation method of the wall material solution includes: dehydrating a polyether or polyester polyol at 100°C and -0.08MPa vacuum for 2 hours to a moisture content of ≤0.03%, cooling to 60°C, reacting with an excess of isocyanate (NCO:OH molar ratio of 2.5-3:1) at 75°C for 3 hours under the catalysis of 0.05-0.1wt% dibutyltin dilaurate to synthesize a prepolymer containing a terminal NCO group, adding 0.8wt% of a silane coupling agent KH-560, and treating in vacuum at 60°C for 30 minutes; TEOS was purified by vacuum distillation and 0.1 wt% oxalic acid was added to inhibit hydrolysis. Under nitrogen protection, the prepolymer and TEOS were added to a system containing anhydrous ethyl acetate in a mass ratio of 3:1. The mixture was stirred at 500 rpm and heated to 50°C for 1 hour. During this period, 0.02 wt% hydrochloric acid was added dropwise to catalyze the reaction of TEOS ethoxy groups with the prepolymer NCO to form Si-OC hybrid bonds. 0.2 wt% hydroquinone was added as an inhibitor to stabilize the system, and finally a wall material solution with a viscosity of 400 mPa·s at room temperature was obtained.

[0044] A method for preparing a low-temperature fast-curing water-based coating comprises the following steps:

[0045] By weight, 100 parts of modified epoxy emulsion and 13.25 parts of dual curing agent were added to a dispersion kettle at 40°C and dispersed at a high speed of 1200 rpm for 20 minutes. 4 parts of auxiliary agent were added and dispersed at 1800 rpm for 15 minutes. Vacuum degassing was performed at -0.05 MPa for 30 minutes, and the low-temperature fast-curing water-based coating was obtained by filtering through a 200-mesh filter.

[0046] The low-temperature fast-curing water-based paint needs to be sealed and packaged in polyethylene barrels and stored away from light, taking into account both low-temperature construction performance and coating durability. It is suitable for light corrosion protection fields such as automotive primers and metal brackets that require fast curing.

[0047] The low-temperature fast-curing water-based coating prepared in Example 1 was scanned with a scanning electron microscope. The results are as follows: Figure 1 As shown, it can be seen from the image that most of the spherical particles are microcapsule promoters, and the shadows of smaller particles between the spherical main particles are core-shell latex particles. The particles are in a tightly packed state, indicating that the latex particles are fully fused during the film-forming process, and the outer shell acrylic ester of the core-shell structure provides low-temperature deformation ability; the ionic liquid modifier effectively eliminates interface defects and avoids cracking caused by curing shrinkage stress, and the spherical particles have clear boundaries and smooth surfaces, and there are no attachments or holes, which shows that the spray drying process successfully forms dense wall materials, and the polyurethane / SiO2 hybrid layer protects the core material; the preparation method of Example 1 does not destroy the microcapsule structure and has excellent storage stability, thereby ensuring that the imidazole curing agent can be accurately released at low temperatures.

[0048] Example 2

[0049] This embodiment discloses a low-temperature, fast-curing water-based coating, comprising a modified epoxy emulsion, a dual curing agent, and an additive; the modified epoxy emulsion comprises, by weight, 25 parts of epoxy resin E-44, 12 parts of methyl methacrylate, 8 parts of butyl acrylate, 1.4 parts of a composite emulsifier, 0.3 parts of a chain extender polyetheramine D230, and 30 parts of deionized water; the dual curing agent comprises 0.23 parts of a microcapsule accelerator and 3 parts of an ionic liquid modifier; the additive comprises 0.5 parts of a hyperdispersant BYK-190, 2.3 parts of nano-fumed silica, 0.2 parts of an organosilicon defoamer BYK-024, and 0.8 parts of a thickener ASE-60; the composite emulsifier comprises 0.5 parts of SDS, 0.6 parts of OP-10, and 0.3 parts of COPS-1. Other contents are consistent with those in Example 1.

[0050] Example 3

[0051] This embodiment discloses a low-temperature, fast-curing water-based coating, comprising a modified epoxy emulsion, a dual curing agent, and an additive; the modified epoxy emulsion comprises, by weight, 30 parts of epoxy resin E-44, 18 parts of methyl methacrylate, 12 parts of butyl acrylate, 1.8 parts of a composite emulsifier, 0.8 parts of a chain extender polyetheramine D230, and 40 parts of deionized water; the dual curing agent comprises 0.28 parts of a microcapsule accelerator and 8 parts of an ionic liquid modifier; the additive comprises 1 part of a hyperdispersant BYK-190, 2.8 parts of nano-fumed silica, 0.5 parts of an organosilicon defoamer BYK-024, and 1.4 parts of a thickener ASE-60; the composite emulsifier comprises 0.6 parts of SDS, 0.7 parts of OP-10, and 0.5 parts of COPS-1. Other contents are consistent with those in Example 1.

[0052] Comparative Example 1

[0053] The difference from Example 1 is that the microcapsule promoter is missing in equal parts by weight, and the other parts are the same.

[0054] The catalyst prepared in Comparative Example 1 was scanned using a scanning electron microscope. Figure 3 As shown in the image, it can be observed that the boundaries of the particles in the image are clear and dispersed, and there are obvious spaces between the particles. The small protrusions on the surface are aggregates of resin that have not completely reacted. The microcapsule accelerator containing 2-phenylimidazole is a key trigger for low-temperature rapid curing. The lack of it will lead to delayed primary curing, that is, the rupture of the microcapsule releases imidazole to promote epoxy cross-linking. After removal, the curing reaction is slow and incomplete. In addition, the particle fusion will fail, and the resin particles cannot melt and cross-link in time and remain independent.

[0055] Comparative Example 2

[0056] The difference from Example 1 is that the ionic liquid modifier is missing in equal parts by weight, and the other parts are the same.

[0057] Comparative Example 3

[0058] The difference from Example 1 is that the chain extender polyetheramine D230 is missing in equal parts by weight, and the other parts are the same.

[0059] Comparative Example 4

[0060] The difference from Example 1 is that the nano-fumed silica is missing in equal parts by weight, and the other parts are the same.

[0061] Performance Testing

[0062] 1. Performance tests were conducted on the Examples and Comparative Examples. Low-temperature curing test: The coating was sprayed onto tinplate (film thickness 50±5μm) and placed in an oven. The surface-dry (no trace when lightly touched with a finger) and through-dry (no indentation when pressed with a pencil) times were recorded according to GB / T 1728-2020. Coating adhesion test: A 1mm×1mm grid was applied according to GB / T 9286-2021. After the tape was peeled off, the area of detachment was observed. Salt spray resistance test: The cross-cut specimen was placed in a salt spray chamber (5% NaCl, 35°C). Rust extension and substrate corrosion at the scratch were evaluated according to GB / T 1771-2021. Impact strength test: The coating was subjected to a free-fall hammer impact according to GB / T 1732-2020, and the crack height was observed. The results are shown in Table 1.

[0063] Table 1

[0064] Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Low temperature curing performance Bake at 100℃ for 15 minutes until completely dry (no sticking) Baking at 100℃ for 2h is not completely dry (sticking) Bake at 100℃ for 1h to dry on the surface, 4h to dry thoroughly Bake at 100℃ for 3h to dry Coating adhesion Level 0 (no shedding after cross-cutting) Level 2 (edge detachment) Level 1 (slight shedding at the intersection of the crosshatch) Level 3 (large area shedding) Salt spray resistance No blistering after 1000 h, rust ≤ level 1 500h The rust expansion at the scratch is >3mm 1000h base material rust spots ≤5% 720h coating bubbling and peeling Impact strength 50 kg·cm without cracks 30kg·cm micro cracks 40kg·cm without cracks 10kg·cm cracking

[0065] As can be seen from Table 1, Example 1 releases imidazole when the microcapsule promoter is heated, triggering rapid crosslinking and curing the fastest. Comparative Example 1 lacks microcapsules, the curing agent is insufficiently active, and it is not completely dry after 2 hours. Comparative Example 2 lacks an ionic liquid modifier, deep crosslinking is delayed, and the actual drying time is extended. Comparative Example 3 lacks a chain extender, and the molecular chain is not flexible enough. Although it is completely dry for 3 hours, the coating is brittle. Example 1 forms a dense network due to dual curing, and the adhesion reaches the highest level. Comparative Example 1 is not fully cured and has weak interface bonding. Comparative Example 3 lacks a chain extender, resulting in excessive rigidity of the molecular chain and the worst adhesion. In Example 1, nano-SiO2 and ionic liquid synergistically enhance density. Comparative Example 1 lacks microcapsules, and curing defects cause corrosion to spread rapidly along scratches. Comparative Example 3 is prone to cracking due to the brittle coating, and bubbling and peeling after salt spray penetration. The chain extender (polyetheramine D230) in Example 1 gives the molecular chain flexibility. Comparative Example 3 has a sudden drop in impact resistance due to excessive segment rigidity. The ionic liquid modifier in Comparative Example 2 is used for deep curing, and its removal mainly leads to insufficient curing depth because the microcapsule accelerator will initially cure the surface layer of the coating, but the deep cross-linking is weak, and microcracks or delamination will appear inside.

[0066] 2. Abrasion resistance test was conducted on the examples and comparative examples. The coating was sprayed onto a 120 mm × 50 mm tinplate substrate that had been polished and cleaned according to GB / T 23988-2009. The dry film thickness was 50 μm. The coating was sprayed twice, flash-dried after 10 minutes, and then oven-treated at 100°C for 15 minutes. A Taber abrasion tester (equipped with a CS-10 grinding wheel and a 500 g constant load) was used to perform a continuous 1800-second friction test on the cured coating. The real-time change data of the friction coefficient was recorded simultaneously. A high sampling rate recording system was used to directly output the COF-time curve. The results are shown in Table 2. Figure 2 .

[0067] from Figure 2It can be seen that in Example 1, the microcapsule accelerator ensures rapid and complete curing at low temperature, and the nano-SiO2 enhances the density of the coating, so the friction coefficient remains at an extremely low level throughout the process, and it has an extremely low friction coefficient and excellent friction stability; the comparative example 1 lacks microcapsules, resulting in delayed cross-linking and loose coating, so the friction coefficient is high and continues to rise; the comparative example 4 lacks nano-SiO2 and the curve fluctuates significantly, indicating that the wear resistance is weaker than that of Example 1 but stronger than that of comparative example 1, and the curing mechanism of comparative example 1 is more complete. Through 1800 seconds of continuous monitoring, the synergistic effect of microcapsule accelerator and nano-SiO2 on reducing the friction coefficient and improving the durability of the coating is verified.

[0068] Obviously, those skilled in the art may make various changes and modifications to this application without departing from the spirit and scope of this application. If these modifications and variations of this application fall within the scope of the claims of this application and their equivalents, this application is intended to include these modifications and variations.

Claims

1. A low-temperature fast-curing water-based paint, characterized in that: Including modified epoxy emulsion, dual curing agent and additives.

2. The coating according to claim 1, characterized in that The dual curing agent includes a microcapsule accelerator and an ionic liquid modifier.

3. The coating according to claim 1, characterized in that The modified epoxy emulsion comprises: epoxy resin E-44, methyl methacrylate, butyl acrylate, composite emulsifier, chain extender polyetheramine D230 and deionized water.

4. The coating according to claim 1, characterized in that The modified epoxy emulsion comprises, by weight, 25-30 parts of epoxy resin E-44, 12-18 parts of methyl methacrylate, 8-12 parts of butyl acrylate, 1.4-1.8 parts of composite emulsifier, 0.3-0.8 parts of chain extender polyetheramine D230 and 30-40 parts of deionized water.

5. The coating according to claim 1, characterized in that The composite emulsifier includes SDS, OP-10 and COPS-1.

6. The coating according to claim 2, characterized in that The microcapsule promoter uses 2-phenylimidazole as a core material.

7. The coating according to claim 1, characterized in that The auxiliary agent comprises, by weight, 0.5-1.0 parts of hyperdispersant BYK-190, 2.3-2.8 parts of nano-fumed silica, 0.2-0.5 parts of organosilicon defoamer BYK-024, and 0.8-1.4 parts of thickener ASE-60.

8. A method for preparing a low-temperature fast-curing water-based coating according to any one of claims 1 to 7, characterized in that: The following steps are involved: (1) preparing modified epoxy emulsion; (2) preparing a dual curing agent; (3) Mix and disperse the modified epoxy emulsion, dual curing agent and additives, degas and filter.

9. The preparation method according to claim 8, characterized in that The preparation method of the modified epoxy emulsion comprises: a. Stir and mix deionized water and composite emulsifier, add methyl methacrylate and butyl acrylate to emulsify; b. After heating to 75°C, the initiator ammonium persulfate was added dropwise to react to obtain an acrylate copolymer emulsion; c. Cool to 60°C, add epoxy resin E-44 and chain extender polyetheramine D230 and react for 2 hours.

10. The preparation method according to claim 8, characterized in that The preparation method of the dual curing agent includes mixing 2-phenylimidazole and a wall material solution in a mass ratio of 1:4, spray drying to prepare a microcapsule accelerator; reacting dicyandiamide, an ionic liquid, and a silane coupling agent KH560 at 120° C. and 0.8 MPa for 3 hours to prepare an ionic liquid modifier; and the preparation method of the wall material solution includes dehydrating a polyether or polyester polyol, reacting the resulting mixture with an excess of isocyanate to form a prepolymer containing an NCO group, and adding KH-560 and TEOS to react.

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