Low temperature fast curing waterborne coating and preparation method thereof

Abstract

The application provides a low-temperature rapid curing water-based paint and a preparation method thereof, relates to the technical field of paint, and the low-temperature rapid curing water-based paint comprises a modified epoxy emulsion, a double curing agent and an additive, the double curing agent comprises a microcapsule accelerator and an ionic liquid modifier, and the additive comprises an ultra-dispersing agent, nano fumed silica, a defoaming agent and a thickening agent. The preparation method of the low-temperature rapid curing water-based paint comprises the following steps: respectively preparing the modified epoxy emulsion and the double curing agent, and dispersing, defoaming and filtering the modified epoxy emulsion and the double curing agent at a high speed together with the additive. The present paint can realize rapid curing at low temperature, the hardness of a coating reaches 2H, has the properties of low-temperature rapid curing, high adhesion and excellent wear resistance, and is suitable for rapid coating of metal and plastic substrates.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of coatings, in particular to a low-temperature rapid-curing water-based paint and a preparation method thereof. BACKGROUND

[0002] Water-based paint has become an important development direction to replace solvent-based paint due to its environmental friendliness and low volatile organic compound emission. However, the curing rate of traditional water-based paint significantly decreases at low temperature, resulting in prolonged film-forming time and reduced construction efficiency, especially in cold regions or winter construction. With the increasing requirements of manufacturing industry for coating efficiency and energy saving, developing a water-based paint system with low-temperature rapid-curing ability and excellent storage stability has become a technical bottleneck that needs to be broken through in the industry. The existing technology generally faces a difficult contradiction: in order to achieve low-temperature rapid curing, the system reactivity must be improved; however, a high-activity system is prone to pre-crosslinking during normal temperature storage or processing, resulting in increased paint viscosity, shortened gel time, or even complete failure. For example, although the use of high-activity amine curing agents can accelerate low-temperature film formation, local curing is caused by mechanical shearing heat generation during production extrusion, resulting in equipment blockage. More seriously, such paint is often discarded due to caking during summer storage and transportation due to the increase in ambient temperature, forcing enterprises to invest additional cold chain costs, which greatly weakens product competitiveness. When the ambient temperature is lower than the conventional film-forming temperature, water-based paint faces double obstacles: on the one hand, the polymer particle movement energy barrier increases, making it difficult for latex particles to fuse, resulting in structural defects such as micropores and cracks in the coating; on the other hand, the water evaporation rate decreases, delaying the phase transition process of the coating film from wet film to dry film. Existing solutions mostly rely on physical heating, which not only increases energy consumption and equipment investment, but also causes surface problems such as sagging and orange peel due to uneven heating on large irregular-shaped components such as wind turbine blades and pipes. The current technical route is often limited to treating the symptoms: in order to improve low-temperature activity, small molecule accelerators are introduced, but due to the inability to precisely control the reaction process, the crosslinking degree of the curing network is insufficient or excessive. The former leads to a sharp decrease in the chemical resistance and mechanical strength of the coating; the latter causes the coating to become brittle and the impact toughness to deteriorate. More importantly, small molecule additives are prone to migration and exudation, and the coating appears yellowing, powdering and other accelerated aging phenomena after long-term exposure. This kind of modification strategy that sacrifices one aspect to improve another aspect cannot meet the stringent requirements of high-end equipment for the comprehensive performance of the coating. During the research and development process, researchers often ignore the fact that the essence of low-temperature rapid curing is the result of multi-scale synergistic action, and only focus on synthesizing high-activity monomers or single-dimensionally regulating particle morphology, relying purely on external field to intensify mass transfer, which can easily lead to deterioration of other dimensions when improving any single dimension. For example, reducing the glass transition temperature of the polymer to improve the low-temperature fusion of the latex particle, but a too low glass transition temperature will deteriorate the storage stability; increasing the hydrophilic group to promote water diffusion may introduce a short board of water resistance of the coating.

[0003] Therefore, there is an urgent need in the market to develop a new low-temperature rapid curing water-based paint and a preparation method thereof. SUMMARY

[0004] The present application provides a low-temperature rapid curing water-based paint and a preparation method thereof to solve the problems in the background art.

[0005] To solve the above technical problems, the present application discloses a low-temperature rapid curing water-based paint, characterized in that it comprises a modified epoxy emulsion, a dual curing agent and an additive.

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

[0007] Further, the modified epoxy emulsion comprises epoxy resin E-44, methyl methacrylate, butyl acrylate, a composite emulsifier, a chain extender polyether amine D230 and deionized water.

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

[0009] Further, the composite emulsifier comprises SDS, OP-10 and COPS-1.

[0010] Further, the microcapsule accelerator takes 2-phenylimidazole as the core material.

[0011] Further, the additive comprises 0.5-1.0 parts by weight of an ultra-dispersant BYK-190, 2.3-2.8 parts by weight of nano-fumed silica, 0.2-0.5 parts by weight of an organic silicon defoaming agent BYK-024 and 0.8-1.4 parts by weight of a thickening agent ASE-60.

[0012] The present application also discloses a preparation method of the low-temperature rapid curing water-based paint, comprising the following steps:

[0013] (1) preparing a modified epoxy emulsion;

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

[0015] (3) mixing and dispersing the modified epoxy emulsion, the dual curing agent and the additive, defoaming and filtering.

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

[0017] a. Stirring and mixing deionized water with composite emulsifier, adding methyl methacrylate, butyl acrylate emulsion;

[0018] b. After warming to 75℃, drop the initiator ammonium persulfate, and the reaction is an acrylate copolymer emulsion;

[0019] c. After cooling to 60℃, add epoxy resin E-44 and chain extender polyetheramine D230 and react for 2 hours.

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

[0021] Further, the spray drying conditions are inlet temperature 150±5℃, outlet temperature 70±3℃, and atomization pressure 0.25MPa.

[0022] Further, vacuum degassing at-0.05MPa for 30min, and filtering through a 200-mesh filter to obtain a low-temperature rapid curing water-based paint.

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

[0024] The mechanism of the above raw material components is as follows: first, the core value of low-temperature rapid curing water-based paint lies in breaking through the curing bottleneck of traditional water-based systems in low-temperature environment, and its innovation comes from the precise synergistic effect between components. This synergy is not a simple superposition, but through molecular level design, a multiple response mechanism is built to enable the coating to achieve efficient crosslinking and structural densification under low temperature conditions. Specifically, the raw material component system develops around three key dimensions: low-temperature activity triggering, reaction depth control, and mechanical strength compensation, which form a dynamic balance. Second, the modified epoxy emulsion serves as the coating skeleton, bearing the dual mission of providing reaction sites and basic film formation. Its core lies in combining traditional rigid epoxy resin and flexible acrylate copolymer through molecular design to form a composite emulsion with a core-shell structure. The outer layer of acrylate segments is rich in polar groups, significantly reducing the kinetic energy barrier of polymer particles at low temperatures, promoting the spreading and fusion of latex particles on the substrate surface; the inner layer of epoxy resin retains a high density of epoxy groups, providing sufficient active sites for subsequent crosslinking reactions. The specially introduced polyetheramine chain extender acts as a bridge, with its long chain structure penetrating into the epoxy network, increasing the flexibility of the molecular chain to resist low-temperature embrittlement, and through the controlled reaction of amine groups and epoxy groups, avoiding the storage instability caused by pre-crosslinking. The compounding strategy of composite emulsifiers is particularly crucial. The synergistic effect of anionic and non-ionic emulsifiers forms a dense interface film, ensuring the spatial stability of the emulsion particles during transportation and storage, and then quickly desorbing after water is encountered during construction, accelerating the particle coalescence process. This dynamic balance design makes the system inert at room temperature, and starts rapid phase transition as soon as it comes into contact with low-temperature moisture. Third, the design concept of dual curing agents stems from the dialectical solution to the contradiction of low-temperature curing. The microcapsule accelerator acts like an internal chemical clock, with its wall material being a hybrid of a moisture-sensitive high molecular pre-polymer and a siloxane material. In a low-temperature environment, it absorbs water through selective permeation, causing the wall material to hydrolyze and thin until it breaks, releasing the encapsulated imidazole catalyst. This triggering mechanism avoids contact between the catalyst and epoxy groups at room temperature, completely solving the problem of pre-reaction during storage. The released imidazole molecules quickly activate the ring-opening of epoxy groups, forming an initial crosslinking network. The ionic liquid modifier, on the other hand, takes on the mission of deep curing. Its unique feature lies in the dissociation of the crystal structure of dicyandiamide, making the amine groups, which normally require high-temperature activation, ionize in the polar microenvironment formed by the ionic liquid, significantly reducing the reaction activation energy. More subtly, the introduction of silane coupling agents enables the ionic liquid to build covalently connected ion channels in the cured network, ensuring reaction uniformity and enhancing the toughness of the coating. These two-stage curing mechanisms form a relay in time sequence: the microcapsule rupture triggers the initial rapid gelation, and the ionic liquid continuously promotes the increase in crosslinking density, ultimately achieving complete curing at low temperature. Fourth, the additive system acts like a precisely functioning synergistic network, ensuring coating performance at multiple scales.The hyperdispersant cooperates with the anchor group through steric hindrance effect to keep the nanoparticles stable dispersion in complex system. The hydrophilic segment in the molecule can also migrate to the interface during film formation to reduce the solidification shrinkage stress. Fumed silica plays a dual role in the system: on the one hand, the surface silicon hydroxyl groups condense to form siloxane crosslinking points under the action of water, compensating for the possible insufficient crosslinking density caused by low temperature curing; on the other hand, the nanoparticles construct a three-dimensional support skeleton in the coating, significantly improving the hardness through crack deflection and energy dissipation mechanisms. The molecular design of the silicone defoamer is highly targeted, and its low surface tension characteristics can quickly penetrate the bubble membrane, while the high molecular weight polysiloxane chain forms an elastic film to inhibit bubble regeneration, especially in low temperature high viscosity systems. The rheological control of the thickener is more sophisticated, and its associated thickening mechanism temporarily dissociates under the action of shear force to reduce the viscosity for construction, and quickly rebuilds the network to prevent sagging after static, this intelligent response characteristic is crucial for vertical surface low temperature construction.

[0025] In summary, the interaction of each component involved in the present application constitutes a precise response system, specifically: the emulsion stability maintained by the emulsifier is broken during construction, and the released active component triggers the hydrolysis switch of the microcapsule; after the wall material breaks, the catalyst activates the epoxy group to form a primary network, while the ionic liquid starts to dissociate the curing agent; as the water evaporates, the surface hydroxyl groups of silica condense to reinforce the crosslinking points, while the thickener network gradually dissociates to balance the leveling and sagging. This multi-level response mechanism makes the system operate in an orderly manner like a precision clock under low temperature conditions, and finally forms a dense and hard protective coating.

[0026] The mechanism of the above preparation method is as follows: the preparation process of the coating is essentially a precise process of molecular assembly and structure regulation, each step contains specific physical and chemical principles. The core is to maximize the synergistic effect of each functional unit by step-by-step construction and orderly integration, while avoiding harmful reactions between components. The preparation process can be divided into three key stages: emulsion molecular engineering, micro-nano encapsulation of curing agent, and system synergistic integration, each stage contains fine energy and interface control. The preparation of modified epoxy emulsion uses the strategy of step-by-step reaction to control the phase state. The initial emulsification stage forms an ultra-low interfacial tension environment by compounding emulsifiers, making the acrylate monomer fully dispersed into sub-micron droplets. This process strictly controls the stirring intensity and temperature to avoid excessive emulsification that leads to difficulty in demulsification later. When the initiator is added to initiate polymerization, the reaction is designed as a starvation state feeding mode to ensure that the monomer concentration is always lower than the critical micelle concentration. The acrylate copolymer generated in this way has a narrow distribution of molecular weight, and the carboxyl group is uniformly distributed to form stable micelles. The operation of adding epoxy resin after cooling is very clever. At this time, the system is in a temperature window higher than the softening point of the epoxy resin but lower than its reaction activity, which promotes the epoxy molecules to embed into the micelle core through hydrophobic interaction, and the chain extender polyether amine selectively reacts with the micelle surface carboxyl group. This directional reaction forms core-shell particles with gradient structure: the shell is rich in carboxyl-containing acrylate polymers to provide water dispersibility, the core is reactive epoxy resin, and the transition layer is connected by long-chain flexible polyether amine. The whole reaction process realizes precise control of the phase state through temperature staging: high-temperature polymerization ensures conversion, medium-temperature chain extension avoids premature reaction of epoxy groups, and finally a storage-stable active emulsion system is obtained. The preparation of dual curing agent embodies the wisdom of micro-nano scale encapsulation. The construction of microcapsules promotes the use of interface reaction dominated encapsulation technology, through the synergistic crosslinking of isocyanate prepolymer and siloxane in the wall material solution, a humidity-responsive hybrid wall material is formed. Through precise temperature field control during the spray drying stage, dynamic encapsulation is achieved: high inlet temperature causes the solution to be atomized instantly, and the wall material molecular chains arrange directionally during the solvent evaporation process, with the siloxane groups enriched on the surface to form a dense protective layer; the low outlet temperature ensures the integrity of the core material molecular structure. This thermodynamic controlled phase separation process forms microcapsules with uniform particle size, and the wall thickness and core material ratio are finely adjusted by solution concentration and atomization parameters. The synthesis of ionic liquid modifier utilizes high-pressure environment to break the energy barrier, in a sealed reactor, the ionic liquid penetrates into the crystal defects of dicyandiamide like a molecular level solvent, and the high-pressure condition promotes the formation of covalent bonds between the alkoxyl group of silane coupling agent and the amine group. It is worth noting that this reaction selectively occurs at the primary amine group of dicyandiamide, leaving the secondary amine group active for curing, and the final product not only retains the low-temperature dissociation characteristics of ionic liquids, but also avoids component migration through chemical bonding. The final mixing process is the key to system synergy. The step-by-step feeding strategy first pre-mixes the dual curing agent with the modified emulsion under moderate shear, at this time the weak interaction between the surface siloxane of the microcapsule and the emulsion particles forms an initial spatial positioning.The subsequently added nanosilica forms a nanoscale dispersion under the action of the hyperdispersant, and the surface silanol groups thereof and the siloxane in the microcapsule wall material undergo a condensation precursor reaction to build physical anchoring 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 the additive molecules on the particle interface, and on the other hand, it destroys local agglomerates through shear thinning. The vacuum defoaming process drives the growth and merging of bubbles through a negative pressure gradient, and in combination with the precise control of the thixotropy of the system, the microbubbles are cut and eliminated by the thickener network during the rising process. The final filtration operation not only removes mechanical impurities, but also re-homogenizes the surface adsorption layer of the particles through the shear flow generated by the screen, thereby improving the storage stability of the system. The energy input and interface regulation of the entire preparation process form a spatiotemporal coupling relationship: the thermodynamic control in the emulsification stage ensures the precision of the molecular structure, the temperature gradient of the spray drying realizes micro-nano encapsulation, and the shear field regulation in the mixing process controls the spatial distribution of the particles. In particular, the choice of the reactor type - the emulsion synthesis adopts a reactor with a wall scraping device to prevent local overheating, the microcapsule preparation chooses a centrifugal spray dryer to ensure uniform particle size, and the mixing process uses a three-axis disperser to realize three-dimensional shearing - these device differences exactly match the mass and heat transfer requirements of each stage. In the final product, the microcapsules are embedded in the epoxy network like time bombs, the ionic liquid modifier is uniformly dispersed in the continuous phase, and the fumed silica forms a reinforcing connection point at the interface. This multi-level ordered structure becomes the material basis for low-temperature rapid curing. It is worth emphasizing that the correlation between process parameters constitutes a self-consistent system: the emulsification temperature determines the micelle size, which affects the subsequent encapsulation rate of the epoxy resin; the temperature difference between the inlet and outlet air of the spray drying controls the crystallinity of the wall material, which is related to the moisture response speed of the microcapsule; the dispersion intensity and time determine the adsorption conformation of the additive at the interface, which finally affects the stress distribution on the coating surface and interface. It is this layer-by-layer progressive and interlocking preparation logic that enables the coating to trigger a series of reactions such as microcapsule hydrolysis, catalyst release, epoxy ring opening, ionic activation, and siloxane condensation in an orderly manner when it encounters low temperature and moisture during construction, and to complete the transformation from a liquid dispersion to a solid protective layer at the molecular scale.

[0027] Compared with the prior art, the low-temperature rapid curing water-based paint and the preparation method thereof have the following beneficial effects:

[0028] 1. The present application relates to dual curing, the microcapsule wall material dissolves and releases imidazole to realize primary curing under low-temperature moisture penetration, and the ionic liquid dissociates the active groups of dicyandiamide to realize deep curing. By microencapsulating 2-phenylimidazole as a trigger, the microcapsule wall material precisely releases imidazole upon water penetration, triggering the primary crosslinking of the epoxy resin, thereby solving the technical bottleneck of low-temperature curing efficiency of traditional water-based paints. Fumed silica forms siloxane crosslinking points in the coating to compensate for the loss of low-temperature curing strength.

[0029] 2. The low-temperature rapid curing water-based paint involved in the application has deep cross-linking and high strength performance, the ionic liquid modifier dissociates active groups in the late curing stage to realize deep construction of the cross-linking network, and the siloxane cross-linking points formed by the nano fumed silica make the hardness of the coating reach 2H level and the impact strength be relatively strong.

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

[0031] Figure 1 SEM image of the low-temperature rapid curing water-based paint prepared in Example 1 of the application;

[0032] Figure 2 Friction performance diagram for abrasion resistance test of the low-temperature rapid curing water-based paint prepared in Example 1 of the application;

[0033] Figure 3 SEM image of the paint prepared in Comparative Example 1 of the application. DETAILED DESCRIPTION

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

[0035] In addition, the description of "first", "second" and the like in the application is only for the purpose of description, and does not mean to specially indicate the order or sequence, nor to limit the application, which is only to distinguish the components or operations described by the same technical terms, and cannot be understood as indicating or implying the relative importance of the indicated technical features or implicitly indicating the number of the indicated technical features. Therefore, the features limited by "first" and "second" can explicitly or implicitly include at least one of the features. In addition, the technical solutions and technical features of various embodiments can be combined with each other, but it must be based on the realization of ordinary skilled in the art, when the combination of technical solutions appears contradictory or unachievable, it should be considered that the combination of technical solutions does not exist, nor within the protection scope claimed by the application.

[0036] Unless otherwise specified, the examples and comparative examples are parallel tests 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 test materials used in the following examples are analytical reagents (A.R.) unless otherwise specified, and are all purchased from commercial channels.

[0037] Epoxy resin E-44 is KER-152 from KUKDO; methyl methacrylate is ELVACITE 2008 from Dow; 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 COPS-1 from Solvay; chain extender polyetheramine D230 is JEFFAMINE D-230 from Huntsman; initiator ammonium persulfate is LUROXID AN from Arkema; microcapsule core material 2-phenylimidazole is DYHARD UR 500 from Evonik; dicyandiamide is DICYANEX 1400 from Mitsubishi; silane coupling agent KH560 is SILQUEST A-187 from Momentive; hyperdispersant BYK-190 is DISPERBYK-190 from BYK; nano fumed silica is AEROSIL 200 from Evonik; silicone defoamer BYK-024 is BYK-024 from BYK; thickening agent ASE-60 is ACRYSOL ASE-60 from Dow.

[0038] Example 1

[0039] This example discloses a low-temperature fast-curing water-based paint, which comprises a modified epoxy emulsion, a dual curing agent and an auxiliary agent; the modified epoxy emulsion comprises, by weight parts, 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 auxiliary agent comprises 0.8 parts of a hyperdispersant BYK-190, 2.5 parts of nano fumed silica, 0.3 parts of a silicone defoamer BYK-024 and 1.2 parts of a thickening agent ASE-60; 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 of deionized water and 1.6 parts of a composite emulsifier into a reaction kettle under nitrogen protection, stirring at 800 rpm for 10 min, adding 15 parts of methyl methacrylate and 10 parts of butyl acrylate, emulsifying at 25℃ for 30 min, increasing the temperature to 75℃, adding 0.4 parts of initiator ammonium persulfate dropwise at a speed of 1.0 mL / min, and reacting for 1.5 h to obtain an acrylate copolymer emulsion; cooling to 60℃, adding 28 parts of epoxy resin E-44 and 0.6 parts of chain extender polyetheramine D230, and stirring at 400 rpm for 2 h to form an epoxy-acrylic core-shell emulsion.

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

[0042] 2-phenylimidazole is mixed with a wall material solution as a core material at a mass ratio of 1:4, the inlet temperature of the spray drying is set to 150±5℃, the outlet temperature is set to 70±3℃, and the atomization pressure is set to 0.25 MPa, so as to obtain spherical imidazole microcapsules; 4 parts of dicyandiamide, 1 part of 1-butyl-3-methylimidazole tetrafluoroborate ionic liquid, and 0.5 parts of silane coupling agent KH560 are added into a high-pressure reaction kettle, and the reaction is carried out at 120±2℃ and 0.8 MPa for 3 h, and the ionic liquid modifier is obtained after cooling.

[0043] The preparation method of the wall material solution comprises the following steps: polyether or polyester polyol is dehydrated at 100℃ and under a vacuum of-0.08 MPa for 2 hours until the moisture content is less than or equal to 0.03%, and then the temperature is lowered to 60℃, and the pre-polymer containing NCO groups at the end is synthesized by reacting with excess isocyanate (NCO:OH molar ratio 2.5-3:1) at 75℃ for 3 hours under the catalysis of 0.05-0.1 wt% dibutyltin dilaurate, and 0.8 wt% silane coupling agent KH-560 is added and vacuum treated at 60℃ for 30 min; 0.1 wt% oxalic acid is added to inhibit the hydrolysis of TEOS, and the pre-polymer and TEOS are put into a system containing anhydrous ethyl acetate at a mass ratio of 3:1 under nitrogen protection, and stirred at 500 rpm to increase the temperature to 50℃ for 1 hour, during which 002 wt% hydrochloric acid is added to catalyze the reaction of the ethoxy group of TEOS and the NCO group of the pre-polymer to form Si-O-C hybrid bonds, and 0.2 wt% hydroquinone is added as a polymerization inhibitor to stabilize the system, and finally a wall material solution with a viscosity of 400 mPa·s at room temperature is obtained.

[0044] A preparation method of a low-temperature rapid curing water-based paint, comprising the following steps:

[0045] The low-temperature fast-curing water-based paint was obtained by adding 100 parts of modified epoxy emulsion, 13.25 parts of double curing agent, 4 parts of additive, and 0.05 MPa vacuum degassing for 30 min at 40°C, and then filtering through a 200-mesh filter screen.

[0046] The low-temperature fast-curing water-based paint needs to be sealed and packaged in a polyethylene barrel to store in the dark, and has both low-temperature workability and coating durability, and is suitable for the field of light corrosion such as automobile primer and metal support which needs fast curing.

[0047] The low-temperature fast-curing water-based paint prepared in Example 1 was scanned by a scanning electron microscope, and the results are shown in FIG. 1. Figure 1 As can be seen from the image, most of the spherical particles are microcapsule accelerators, there are smaller particles between the spherical main particles, which are core-shell latex particles, the particles are in a close-packed state, which indicates that the latex particles are fully fused during the film forming process, and the shell of the core-shell structure provides low-temperature deformation capability; the ionic liquid modifier effectively eliminates interface defects and avoids cracking caused by curing shrinkage stress, and the spherical particle boundary is clear and the surface is smooth without adhesives or holes, which can be seen that the spray drying process successfully forms a dense wall material, and the polyurethane / SiO2 hybrid layer protects the core material; the preparation method of Example 1 does not damage the microcapsule structure, and has excellent storage stability, so as to ensure that the imidazole curing agent can be accurately released at low temperature.

[0048] Example 2

[0049] The low-temperature fast-curing water-based paint prepared in Example 1 was scanned by a scanning electron microscope, and the results are shown in FIG. 1.

[0050] Example 3

[0051] The embodiment discloses a low-temperature rapid curing water-based paint, which comprises a modified epoxy emulsion, a double curing agent and an auxiliary agent; the modified epoxy emulsion comprises 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 polyether amine D230 and 40 parts of deionized water in terms of weight parts; the double curing agent comprises 0.28 parts of a microcapsule accelerator and 8 parts of an ionic liquid modifier; the auxiliary agent comprises 1 part of an ultradispersant BYK-190, 2.8 parts of nano fumed silica, 0.5 parts of an organic silicon defoaming agent BYK-024 and 1.4 parts of a thickening agent ASE-60; the composite emulsifier comprises 0.6 parts of SDS, 0.7 parts of OP-10 and 0.5 parts of COPS-1, and other contents are consistent with those of the embodiment 1.

[0052] Comparative example 1

[0053] The difference from the embodiment 1 is that the same weight parts of the microcapsule accelerator are absent, and other contents are consistent.

[0054] The catalyst prepared in the comparative example 1 is scanned by a scanning electron microscope, and the result is shown in the figure. Figure 3 As can be observed from the image, the particle boundaries in the figure are clear and dispersed, and there is an obvious gap between the particles, wherein the surface small protrusions are resin aggregates that are not completely reacted, and the microcapsule accelerator containing 2-phenylimidazole is a key trigger for low-temperature rapid curing; the absence of the microcapsule accelerator will cause the delay of primary curing, that is, the rupture of the microcapsule to release imidazole to promote the crosslinking of the epoxy resin, and after the removal, the curing reaction is slow and incomplete, and in addition, the particle fusion fails, and the resin particles cannot be fused and crosslinked in time, and remain in an independent state.

[0055] Comparative example 2

[0056] The difference from the embodiment 1 is that the same weight parts of the ionic liquid modifier are absent, and other contents are consistent.

[0057] Comparative example 3

[0058] The difference from the embodiment 1 is that the same weight parts of the chain extender polyether amine D230 are absent, and other contents are consistent.

[0059] Comparative example 4

[0060] The difference from the embodiment 1 is that the same weight parts of the nano fumed silica are absent, and other contents are consistent.

[0061] Performance test

[0062] 1. Performance test of examples and comparative examples, low-temperature curing test: the paint is sprayed on tin plate (film thickness 50±5 μm), and placed in an oven. According to GB / T 1728-2020, the dry touch (finger touch without trace) and dry (pencil pressure without indentation) time are recorded; coating adhesion test: according to GB / T 9286-2021, a grid (1 mm x 1 mm grid) is drawn, and the falling area is observed after the tape is peeled off; salt spray resistance test: the cross-cut sample is placed in a salt spray chamber (5% NaCl, 35℃), and the corrosion expansion at the scratch and the substrate corrosion are evaluated according to GB / T 1771-2021; impact strength test according to GB / T 1732-2020, the coating is impacted by a free-falling weight, and the cracking height is 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 100°C baking 15 min tack free (no blocking) 100°C baking 2 h not tack free (blocking) 100°C baking 1 h skin dry, 4 h tack free 100°C baking 3 h tack free Coating adhesion 0 grade (no peeling in scribe) 2 grade (peeling in edge portion) 1 grade (slight peeling in scribe intersection) 3 grade (large area peeling) Salt spray resistance 1000 h no blistering, rusting < 1 grade 500 h rusting spread > 3 mm in scribe 1000 h rusting spot < 5% on substrate 720 h blistering, peeling of coating Impact resistance 50 kg-cm no cracking 30 kg-cm slight cracking 40 kg-cm no cracking 10 kg-cm cracking

[0065] As can be seen from Table 1, Example 1 releases imidazole due to the release of microcapsule accelerant upon heating, triggering rapid crosslinking, the fastest curing, Comparative Example 1 lacks microcapsules, the curing agent is not active enough, and it is still not dry after 2h, Comparative Example 2 lacks ionic liquid modifier, deep crosslinking is delayed, and the dry time is extended, Comparative Example 3 lacks chain extender, the molecular chain is not flexible enough, although it is dry after 3h, the coating is brittle; Example 1 forms a dense network due to double curing, the adhesion reaches the highest level, Comparative Example 1 is not fully cured, the interface is weakly bonded, and Comparative Example 3 has the worst adhesion due to the lack of chain extender, resulting in excessively rigid molecular chains; the nano-SiO2 in Example 1 synergistically enhances the density with the ionic liquid, Comparative Example 1 has defects in curing due to the lack of microcapsules, resulting in rapid corrosion along the scratch, and Comparative Example 3 has a brittle coating that is prone to cracking, and after salt spray penetration, it bubbles and peels off; the chain extender (polyetheramine D230) in Example 1 imparts flexibility to the molecular chain, and Comparative Example 3 has a sudden drop in impact resistance due to the excessively high rigidity of the chain segment. The ionic liquid modifier in Comparative Example 2 is used for deep curing, and after removal, it mainly leads to insufficient curing depth, and the microcapsule accelerant causes the coating surface to be initially cured, but the deep crosslinking is weak, and internal microcracks or delamination may occur.

[0066] 2. Abrasion resistance test of examples and comparative examples, according to GB / T 23988-2009, the paint is sprayed on a 120 mm x 50 mm tin plate substrate that has been polished and cleaned, the dry film thickness is 50 μm, it is sprayed twice with 10 min flash drying in between, and treated in a 100℃ oven for 15 minutes; a Taber abrasion tester (configured with CS-10 grinding wheel, 500g constant load) is used to test the cured coating for 1800 seconds of continuous friction, the real-time change data of the friction coefficient is recorded simultaneously, a high sampling rate recording system is used to directly output the COF-time curve, the results are shown in Figure 2 .

[0067] From Figure 2It can be seen that Example 1 has a very low friction coefficient and excellent friction stability due to the microcapsule accelerator ensuring fast and complete curing at low temperature, and the nano-SiO2 enhancing the density of the coating; Comparative Example 1 has a high and continuously rising friction coefficient due to the lack of microcapsules leading to delayed crosslinking and a loose coating; Comparative Example 4 has a significant curve fluctuation, indicating that the wear resistance is weaker than Example 1 but stronger than Comparative Example 1, and the curing mechanism is complete compared to Comparative Example 1. Through 1800 seconds of continuous monitoring, the synergistic effect of the 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 can make various modifications and variations to the present application without departing from the spirit and scope of the present application. If these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application also intends to include these modifications and variations.

Claims

1. A low temperature fast curing waterborne coating, characterized in that, The modified epoxy emulsion, the dual curing agent and the auxiliary agent are included. The dual curing agent includes a microcapsule accelerator and an ionic liquid modifier. The preparation method of the modified epoxy emulsion includes: a. Stir and mix deionized water with a composite emulsifier, add methyl methacrylate and butyl acrylate emulsion; b. After warming up to 75℃, drop the initiator ammonium persulfate, and the acrylic ester copolymer emulsion is obtained by reaction; c. Cool down to 60℃, add epoxy resin E-44 and chain extender polyetheramine D230 and react for 2 hours; The preparation method of the dual curing agent includes mixing 2-phenylimidazole with a wall material solution in a mass ratio of 1:4, spray drying to prepare a microcapsule accelerator; reacting dicyandiamide, ionic liquid and silane coupling agent KH560 at 120℃ and 0.8MPa for 3 hours to prepare an ionic liquid modifier; the preparation method of the wall material solution includes dehydrating polyether or polyester polyol, then reacting with excess isocyanate to generate a pre-polymer containing NCO groups, and adding KH-560 and TEOS for reaction; The auxiliary agent includes nano fumed silica.

2. The coating of claim 1, wherein, The modified epoxy emulsion includes, by weight fraction, 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 a composite emulsifier, 0.3-0.8 parts of a chain extender polyetheramine D230 and 30-40 parts of deionized water.

3. The coating of claim 1, wherein, The composite emulsifier includes SDS, OP-10 and COPS-1.

4. The coating of claim 1, wherein, The auxiliary agent includes, by weight fraction, 0.5-1.0 parts of an ultra-dispersant BYK-190, 2.3-2.8 parts of nano fumed silica, 0.2-0.5 parts of a silicone defoaming agent BYK-024 and 0.8-1.4 parts of a thickening agent ASE-60.

5. A process for the preparation of a low temperature fast curing waterborne coating as claimed in any one of claims 1 to 4, characterized in that, The method includes the following steps: (1) preparing a modified epoxy emulsion; (2) preparing a dual curing agent; (3) mixing and dispersing the modified epoxy emulsion, the dual curing agent and the auxiliary agent, defoaming and filtering.

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