Microbead modified corrosion-resistant dry plating metal powder coating material and preparation method thereof

Abstract

The invention relates to the technical field of coating material preparation, in particular to a microbead modified corrosion-resistant dry plating metal powder coating material and a preparation method thereof, and the material comprises carboxyl polyester resin, epoxy resin, a curing accelerator, a flatting agent, a degassing agent, a pigment filler, brush polymer modified microbeads, a metal pigment, a dry plating binder and a charge adjusting aid. According to the powder coating material, the corrosion resistance and durability are remarkably improved while the metal appearance and the construction stability are maintained, the coating film interface bonding is high, pore channels are few, and foaming, pitting corrosion and corrosion medium permeation along the interface in the salt mist environment can be effectively inhibited; after scratches or micro-cracks are formed, the coating film has micro-crack sealing / self-passivation capability, the corrosion rate extending along the scratches can be reduced, and the service life can be prolonged; and meanwhile, the powder is electrified uniformly, the powdering rate is high, the film thickness distribution is more uniform, the metal dry plating effect is stable, the color difference fluctuation in recycling is small, and the powder coating is suitable for metal base material protective coating with the requirements for appearance and corrosion resistance at the same time.

Description

Technical Field

[0001] This invention relates to the field of coating material preparation technology, specifically to a microsphere-modified corrosion-resistant dry-plated metal powder coating material and its preparation method. Background Technology

[0002] Powder coatings are widely used for the protection and decoration of metal substrates due to their solvent-free nature, low VOC content, dense film formation, and high application efficiency. Dry-plated metallic powder coatings, by dry bonding flake metallic pigments with base powder, can achieve a strong metallic texture and shimmering effect, suitable for applications such as building profiles, home appliances, and industrial equipment. However, this type of system has long faced a trade-off between corrosion resistance and appearance stability: the conductivity and flake morphology of metallic pigments can easily alter the microstructure of the coating and trigger localized electrochemical activation, making it prone to blistering, pitting, and interfacial penetration of corrosive media under salt spray conditions; simultaneously, complex components are susceptible to uneven film thickness due to the Faraday cage effect, further amplifying the corrosion risk at edges and grooves.

[0003] Existing technologies typically improve corrosion resistance by adding rust-inhibiting pigments such as phosphates and molybdates, layered shielding fillers, or modifying inorganic fillers with silane coupling agents. However, in dry plating systems, increased amounts of rust-inhibiting pigments and fillers often weaken the metallic appearance and lead to poor leveling and increased orange peel texture, while offering limited inhibition of defect corrosion caused by scratches / microcracks. Conventional silane coupling layers are mostly small-molecule interfaces, making it difficult to resist filler-matrix debonding caused by thermal cycling and humid aging after curing, thus forming interfacial penetration channels. On the other hand, poor adhesion or uneven composite of metallic pigments can easily cause free and recycled components to drift, resulting in color differences and fluctuations in metallic effects. If functional particles are introduced but their surface properties are mismatched, problems such as agglomeration, uneven charging, decreased powder application rate, and increased local defects may occur, affecting construction stability and durability consistency.

[0004] Therefore, there is an urgent need for a technical solution suitable for dry-plated metal powder systems that can achieve interface densification and penetration channel inhibition while maintaining the appearance of the metal and the stability of the coating, improve salt spray and damp heat resistance, and reduce the corrosion propagation rate at scratches / microcracks, thereby improving the overall durability and application adaptability of the coating. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, the present invention aims to provide a microbead-modified corrosion-resistant dry-plating metal powder coating material and its preparation method. The material includes carboxyl polyester resin, epoxy resin, curing accelerator, leveling agent, degassing agent, pigments and fillers, brush-shaped polymer-modified microbeads, metallic pigments, dry-plating binder, and charge-regulating agent. The powder coating material significantly improves corrosion resistance and durability while maintaining the metallic appearance and application stability: the coating film has strong interfacial bonding and few pore channels, effectively inhibiting blistering, pitting corrosion, and the penetration of corrosive media along the interface in salt spray environments; after scratches or microcracks form, the coating film possesses microcrack sealing / self-passivation capabilities, reducing the rate of corrosion propagation along scratches and extending service life; simultaneously, the powder has uniform charge, high powder application rate, and more uniform film thickness distribution, resulting in stable dry-plating metal effects and minimal color difference fluctuations during recycling, making it suitable for protective coating of metal substrates requiring both appearance and corrosion resistance.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A microsphere-modified corrosion-resistant dry-plating metal powder coating material comprises the following components by weight: 55-65 parts carboxylated polyester resin, 6-14 parts epoxy resin, 0.2-0.8 parts curing accelerator, 0.8-1.5 parts leveling agent, 0.2-0.6 parts degassing agent, 10-20 parts pigments and fillers, 2-8 parts brush-shaped polymer-modified microspheres, 3-10 parts metallic pigment, 0.15-0.6 parts dry-plating binder, and 0.05-0.3 parts charge-regulating agent; The brush-shaped polymer-modified microspheres are composite particles with solid glass microspheres as the core. Their surfaces are anchored to surface initiation sites via silanization, and a polymer brush layer is grown in situ on the surface of the glass microspheres through surface-initiated controlled free radical polymerization. The polymer brush layer comprises at least: A: A resin-loving reaction section containing glycidyl methacrylate structural units; B: Functional segment containing low surface energy monomer structural units and disulfide bond dynamic covalent bond structural units.

[0007] Preferably, the solid glass microspheres have a D50 of 10-30 μm.

[0008] Preferably, in the monomer system used to form the polymer brush layer, the mass ratio of glycidyl methacrylate, low surface energy monomer, and disulfide bond-containing monomer is 20-45:5-20:2-10.

[0009] Preferably, the low surface energy monomer is selected from one or more of siloxane acrylates and fluorinated alkyl acrylates; the disulfide bond-containing monomer is selected from one or more of di(2-methacryloyloxyethyl) disulfide, di(2-acryloyloxyethyl) disulfide, cystamine di(meth)acrylate, and cystamine di(meth)acrylamide.

[0010] Preferably, the curing accelerator is selected from one or more of triphenylphosphine, tetraphenylphosphine bromide, 1-methylimidazolium, 2-methylimidazolium, 2-phenylimidazolium, dimethylimidazoline, 2,4,6-tris(dimethylaminomethyl)phenol, and tertiary amine accelerators; the leveling agent is selected from one or more of acrylate leveling agents, polysiloxane-modified leveling agents, and fluorinated leveling agents; the degassing agent is selected from one or more of benzoin, benzoin and its ether derivatives, caprolactam, and benzamide degassing agents; and the charge regulating agent is selected from one or more of quaternary ammonium salts, quaternary phosphine salts, organic sulfonates, organometallic complexes, and polyether-modified / siloxane-modified charge regulating agents.

[0011] Preferably, the pigments and fillers are selected from one or more of titanium dioxide, iron oxide red, phthalocyanine blue, phthalocyanine green, ultramarine, carbon black, chrome green, chromium oxide green, barium sulfate, calcined kaolin, talc, and precipitated silicates; the metallic pigments are selected from one or more of flake aluminum silver powder, coated aluminum silver powder, pearlescent aluminum powder, stainless steel metallic pigments, and nickel-chromium alloy metallic pigments; and the dry plating binder is selected from one or more of polyester binders, acrylic binders, ethylene-vinyl acetate copolymer binders, and polyamide binders.

[0012] A method for preparing a microsphere-modified corrosion-resistant dry-plated metal powder coating material, comprising the following steps: S1. Microsphere surface anchoring: Solid glass microspheres are washed and dried at 80-110℃ for 0.5-2 h; they are dispersed in an alcohol / ester mixed solvent, a silane coupling agent is added, and 0.3-2.0 vol% water relative to the total volume of the solvent is added. The pH of the system is adjusted to 4.0-5.5 using glacial acetic acid, and the reaction is carried out at 50-80℃ for 2-6 h; after the reaction is completed, the mixture is filtered and washed 2-3 times with ethanol, and dried under vacuum at 50-70℃ for 2-6 h to obtain microspheres with anchoring sites on the surface. S2. Surface-Initiated Controlled Polymerization to Grow a Brush Layer: The microspheres obtained in step S1 are dispersed in an ethanol / water mixed solvent, wherein the volume fraction of ethanol is 70-90% and the mass fraction of microspheres is 5-20%; a chain transfer agent and a photocatalyst are added to the suspension system, and a polymer brush layer is grown on the surface of the microspheres by surface-initiated controlled free radical polymerization; the total concentration of the monomer system forming the polymer brush layer is 10-35% by mass fraction of solvent, and a gradient brush layer is constructed by a staged feeding method, that is, first enriching and polymerizing glycidyl methacrylate monomer, and then introducing low surface energy monomers and disulfide bond-containing monomers; the polymerization temperature is 25-75℃, and the reaction time is 2-8 h; after the reaction, the microspheres are separated into solid and liquid, washed with ethanol 2-3 times, and dried under vacuum at 50-70℃ for 4-10 h to obtain brush-shaped polymer-modified microspheres; S3. Preparation of base powder: Accurately weigh carboxylated polyester resin, epoxy resin, curing accelerator, leveling agent, degassing agent, pigments and fillers, and charge regulating agent according to the mass ratio. Dry mix them in a high-speed mixer at 800-1500 rpm for 2-6 min while controlling the discharge temperature to ≤40℃. Feed the dry mixture into a twin-screw extruder for melt mixing and extrusion, where the screw speed is 200-500 rpm and the material residence time is 30-90 s. After the extrudate is pressed into sheets and cooled to <35℃, it is crushed, pulverized, and sieved through a 120-200 mesh to obtain a base powder that does not contain brush-like polymer-modified microspheres or metallic pigments. S4. Low-temperature dry bonding to introduce modified microspheres: The base powder obtained in step S3 is put into a dry plating bonding device, the powder is heated to 30-45℃, and mixed at 600-1500 rpm for 1-2 min. First, a dry plating binder is added to form a capture layer on the surface of the base powder particles. Then, the brush-shaped polymer modified microspheres obtained in step S2 are added in 2-4 batches, with an interval of 30-60 s between each addition. The total mixing time of this step is controlled to be 3-8 min, so that the modified microspheres preferentially adhere to the surface or shallow layer of the base powder particles. Then, the mixture is cooled to below 30℃ within 1-3 min and sieved through a 120-200 mesh sieve. The amount of dry plating binder added is 50-100% of the total amount added in the formula, and the remainder can be added in step S5. S5. Dry plating metal bonding: The powder obtained in step S4 is put into the dry plating bonding equipment and mixed at 35-50℃ and 500-1200rpm for 3-10 minutes. The metal pigment is added in 2-3 batches with an interval of 30-60 seconds. After mixing, the mixture is cooled to below 30℃ and sieved through a 120-200 mesh to obtain the microsphere modified corrosion-resistant dry plating metal powder coating material.

[0013] Preferably, in step S1, the alcohol / ester mixed solvent is a mixture of ethanol and ethyl acetate in a volume ratio of 70-90:10-30; the silane coupling agent is selected from one or more of 3-(2-bromoisobutyryloxy)propyltrimethoxysilane, 3-(2-bromoisobutyryloxy)propyltriethoxysilane, 3-(2-chloroisobutyryloxy)propyltrimethoxysilane, and 3-(2-chloroisobutyryloxy)propyltriethoxysilane; the amount of the silane coupling agent added is 1-3 wt% based on the mass of the solid glass microspheres.

[0014] Preferably, in step S2, the surface-initiated controlled radical polymerization is a photoinduced electron transfer reversible addition-fragmentation chain transfer polymerization reaction, using a 405-470 nm light source with an illuminance of 5-30 mW / cm². 2 The chain transfer agent is selected from one or more of trithiocarbonate chain transfer agents and dithiobenzoate chain transfer agents, and its addition amount is 0.2-5.0 wt% based on the total mass of the brush layer monomers; the photocatalyst is selected from one or more of eosin Y and rose red B, and its addition amount is 10-2000 ppm based on the total mass of the brush layer monomers; oxygen is controlled by bubbling with nitrogen for 10-30 min before polymerization; the reaction temperature of reaction stage one is 35-45℃ and the reaction time is 0.5-2 h; in reaction stage two, the functional monomer mixture is continuously added by metering pump within 0.5-2 h and the reaction continues for 1-4 h.

[0015] Preferably, in step S3, the temperatures of each zone of the twin-screw extruder are: zone 1 85-90℃, zone 2 90-95℃, zone 3 95-100℃, zone 4 100-105℃, and zone 5 105-110℃.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention uses solid glass microspheres as the core and constructs a polymer brush layer on their surface in situ, comprising a GMA reaction segment and a low surface energy / disulfide bond functional segment. This transforms the inorganic microspheres from traditional inert fillers into interfacial active units capable of strong interactions with the matrix. During curing, the epoxy groups on the GMA side chains can undergo ring-opening reactions with the carboxyl groups in the carboxylated polyester system and any hydroxyl groups that may be present in the system, forming a stable covalent bond interface (β-hydroxy ester / ether bond). This interface, combined with the physical entanglement of the brush chains during the melt-curing stage, significantly enhances the filler-matrix interfacial bonding strength and anti-debonding ability. This dual interfacial reinforcement of "chemical bonding-physical interpenetration" effectively weakens the formation of interfacial micro-slits and interconnecting channels, thereby reducing water vapor and Cl-. - The probability of rapid migration of corrosive media along the interface is manifested in a significant reduction in the tendency of blistering and pitting corrosion and a delay in penetrating corrosion under salt spray conditions.

[0017] Meanwhile, the surface enrichment effect of low surface energy segments in the brush layer helps reduce the wettability of the coating to water and the stability of the continuous water film, reduces contaminant adhesion, and inhibits the persistence of electrolyte film on the coating surface and at micro-defects, thereby reducing the effective electrolyte environment required for corrosion reaction from the source. The dynamic covalent structural units containing disulfide bonds provide channels for reversible exchange and local segment rearrangement under thermal or stress conditions, thus mitigating stress concentration at microcrack tips and promoting the closure or passivation of microcracks. This reduces the further intrusion rate of corrosive media and the propagation rate of corrosion along scratches after scratches or microcrack formation.

[0018] At the overall system level, modified microspheres and metallic pigments, in synergy with dry plating binders and charge-regulating agents, can participate in spraying and film formation in a composite particle form. This helps reduce uneven charging and film thickness dispersion caused by differences in component electrical properties, thereby improving powder application rate and edge coverage, and mitigating the risk of local film defects caused by the Faraday cage effect. Thus, this coating material maintains the appearance of dry-plated metal and its stability for recycling while achieving synergistic enhancements in interface densification, surface anti-wetting, and defect passivation. It also meets key performance indicators such as salt spray resistance, damp heat resistance, and long-term durability, making it suitable for coating scenarios on metal substrates with high requirements for both decoration and protection. Attached Figure Description

[0019] Figure 1 This is a flow chart illustrating the preparation process of the microbead-modified corrosion-resistant dry-plated metal powder coating material described in this invention. Detailed Implementation

[0020] The present invention will now be clearly and completely described in conjunction with embodiments thereof. Obviously, the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0021] Please see Figure 1 The present invention provides a technical solution: Example 1 This embodiment provides a formulation for a microsphere-modified corrosion-resistant dry-plated metal powder coating material. The formulation comprises the following components by weight, as shown in Table 1 (one part by weight is defined as 100g): Table 1. Component ratio of the coating material described in Example 1

[0022] The carboxylated polyester resin is designated as SETAPOLL™ SP282. The epoxy resin is designated as DER® 663U. The curing accelerator is triphenylphosphine; The leveling agent is further specified as an acrylate leveling agent, specifically MODAFLOW® PowderⅢ; The degassing agent is benzoin; The pigment and filler are titanium dioxide; The solid microspheres in the brush-shaped polymer-modified microspheres have a particle size D50 = 20 μm; The metallic pigment is further defined as coated aluminum silver powder, specifically model PCS 1000 from the ECKART STANDART® PCS series; The dry plating adhesive is designated as Röhm DEGALAN® P 24; The charge control agent is further defined as a siloxane-modified charge control agent, specifically ADDITOL® P950; This embodiment also provides a method for preparing a microsphere-modified corrosion-resistant dry-plated metal powder coating material, including the following steps: S1. Microsphere surface anchoring: Solid glass microspheres were washed and dried at 100℃ for 1 h; they were dispersed in an alcohol / ester mixed solvent, a silane coupling agent was added, and 2.0 vol% water relative to the total volume of the solvent was added. The pH of the system was adjusted to 4.5 using glacial acetic acid, and the reaction was carried out at 60℃ for 4 h; after the reaction was completed, the microspheres were filtered and washed three times with ethanol, and dried under vacuum at 70℃ for 4 h to obtain microspheres with anchoring sites on the surface. S2. Surface-Initiated Controlled Polymerization to Grow a Brush Layer: The microspheres obtained in step S1 are dispersed in an ethanol / water mixed solvent, wherein the ethanol volume fraction is 70% and the microsphere mass fraction is 10%; a chain transfer agent and a photocatalyst are added to this suspension system, and a polymer brush layer is grown on the surface of the microspheres using surface-initiated controlled free radical polymerization; the total concentration of the monomer system forming the polymer brush layer is 20% by mass fraction of the solvent, and a gradient brush layer is constructed using a staged feeding method, that is, first enriching and polymerizing the glycidyl methacrylate monomer, and then introducing low surface energy monomers and disulfide bond-containing monomers; the polymerization temperature is 35℃, and the reaction time is 4 h; after the reaction, the mixture is subjected to solid-liquid separation, washed with ethanol 3 times, and dried under vacuum at 70℃ for 6 hours. h, brush-shaped polymer-modified microspheres are obtained. The core reaction of this step is photo-induced controlled free radical polymerization based on anchored initiation sites on the surface of glass microspheres. During the reaction, under 405nm light irradiation, the photocatalyst is excited and undergoes photo-induced electron transfer, generating active species that can continuously initiate free radicals. At the same time, the chain transfer agent dynamically exchanges with the free radicals of the growing chain through a reversible addition-fragmentation process, keeping the free radical concentration at a low level and achieving rapid interconversion of "active / dormant" chains, thereby inhibiting chain termination and homopolymerization side reactions and ensuring the controllability of the polymerization process. Due to the anchored initiation sites on the surface of the microspheres, free radicals are preferentially generated on the surface of the microspheres and induce monomers to be directionally polymerized at the interface, forming a brush-shaped polymer layer that grows "from the solid surface outward". The staged feeding method allows the GMA-dominant chain segments to grow preferentially in the early stage and be enriched near the surface of the microspheres, while the low surface energy monomers and disulfide bond-containing monomers introduced later are enriched on the outside of the brush layer, finally obtaining a gradient brush layer structure that is "rich in GMA inside and rich in functional monomers outside".

[0023] S3. Preparation of base powder: Accurately weigh carboxylated polyester resin, epoxy resin, curing accelerator, leveling agent, degassing agent, pigments and fillers, and charge regulating agent according to the mass fraction. Dry mix them in a high-speed mixer at 1000 rpm for 4 min while controlling the discharge temperature to ≤40℃. Feed the dry mixture into a twin-screw extruder for melt mixing and extrusion, where the screw speed is 300 rpm and the material residence time is 60 s. After the extrudate is pressed into sheets and cooled to <35℃, it is crushed, pulverized, and sieved through a 200-mesh sieve to obtain a base powder that does not contain brush-like polymer-modified microspheres or metallic pigments. S4. Low-temperature dry bonding to introduce modified microspheres: The base powder obtained in step S3 is put into a dry plating bonding device, the powder is heated to 35°C, mixed at 1000 rpm for 2 min, and the dry plating binder is added first to form a capture layer on the surface of the base powder particles; then the brush-shaped polymer modified microspheres obtained in step S2 are added in 4 batches, with an interval of 30 s between each addition, and the total mixing time of this step is controlled to be 6 min, so that the modified microspheres preferentially adhere to the surface or shallow layer of the base powder particles; then the mixture is cooled to below 30°C within 3 min and sieved through a 200-mesh sieve; the amount of the dry plating binder added is 50% of the total amount added in the formula, and the remainder is added in step S5; S5. Dry plating metal bonding: The powder obtained in step S4 is put into the dry plating bonding equipment and mixed for 10 min at 35℃ and 500 rpm. The metal pigment is added in 3 batches with an interval of 30 s. After mixing, the mixture is cooled to below 30℃ and sieved through a 200-mesh sieve to obtain the microsphere modified corrosion-resistant dry plating metal powder coating material.

[0024] In step S1, the alcohol / ester mixed solvent is a mixture of ethanol and ethyl acetate in a volume ratio of 70:30; the silane coupling agent is 3-(2-bromoisobutyryloxy)propyltrimethoxysilane; and the amount of silane coupling agent added is 1.5 wt% based on the mass of the solid glass microspheres. In step S2, the surface-initiated controlled radical polymerization is a photo-induced electron transfer reversible addition-fragmentation chain transfer polymerization reaction, using a 405 nm light source with an illuminance of 20 mW / cm². 2 ; The chain transfer agent is further defined as a trithiocarbonate chain transfer agent, specifically DDMAT (S-dodecyl-S′-(2-methyl-2-propionic acid) trithiocarbonate), and its addition amount is 2.0 wt% based on the total mass of the brush layer monomers; the photocatalyst is eosin Y, and its addition amount is 1000 ppm based on the total mass of the brush layer monomers; In step S2, the mass ratio of glycidyl methacrylate, low surface energy monomer, and disulfide-containing monomer in the monomer system used to form the polymer brush layer is 30:10:6; the product number of the glycidyl methacrylate is Sigma-Aldrich 779342; the low surface energy monomer is further defined as a fluoroalkyl acrylate, specifically 1H,1H-perfluorooctyl methacrylate, with product number Sigma-Aldrich 776491; the disulfide-containing monomer is further defined as di(2-methacryloyloxyethyl) disulfide, with product number Sigma-Aldrich 735094; In step S2, before the photoinduced electron transfer reversible addition-fragmentation chain transfer polymerization reaction occurs, oxygen is controlled by bubbling with nitrogen for 30 min; the reaction temperature of the first stage of the phased reaction is 35℃ and the reaction time is 2 h; in the second stage of the reaction, the functional monomer mixture is continuously added over 0.5 h by a metering pump and the reaction continues for 1.5 h. In step S3, the temperatures of each zone of the twin-screw extruder are: 85°C in the first zone, 90°C in the second zone, 95°C in the third zone, 100°C in the fourth zone, and 110°C in the fifth zone.

[0025] Example 2: This example differs from Example 1 in that, in Example 2, the formula includes the following components by weight, as shown in Table 2 (one part by weight is defined as 100g): Table 2. Component ratio of the coating material described in Example 2

[0026] The remaining steps are exactly the same as in Example 2 and Example 1.

[0027] Example 3: This example differs from Example 1 in that, in Example 3, the formula includes the following components by weight, as shown in Table 3 (one part by weight is defined as 100g): Table 3. Component ratio of the coating material described in Example 3

[0028] The remaining steps are exactly the same as in Example 3 and Example 1.

[0029] Comparative Example Comparative Example 1: The only difference between Comparative Example 1 and Example 1 is that the use of brush-shaped polymer-modified microspheres was omitted in Comparative Example 1 and replaced with ordinary solid glass microspheres of the same mass. The remaining steps are exactly the same in Comparative Example 1 and Example 1.

[0030] Comparative Example 2: Comparative Example 2 differs from Example 1 in that, in step S2 of Comparative Example 2, the modification treatment of solid glass microspheres is partially omitted. In Comparative Example 2, only the solid glass microspheres are subjected to a brushing treatment with glycidyl methacrylate monomer. The remaining steps are exactly the same in Comparative Example 2 and Example 1.

[0031] Comparative Example 3: Comparative Example 3 differs from Example 1 in the following way: In step S2 of Comparative Example 3, the modification treatment of solid glass microspheres is partially omitted. In Comparative Example 3, only the solid glass microspheres are subjected to a brushing treatment with low surface energy monomers and disulfide bond-containing monomers. The remaining steps are exactly the same in Comparative Example 3 and Example 1.

[0032] Performance testing The coating samples were made of cold-rolled steel sheet (SPCC, 100 mm × 150 mm × 1.0 mm), which was degreased, rinsed with deionized water, and then subjected to chromium-free conversion treatment before drying. Each powder formulation was electrostatically sprayed (crown spray gun, voltage 60 kV, spray distance 20 cm, ambient temperature 23 ± 2 ℃, relative humidity 50 ± 10%), with a dry film thickness controlled at 70 ± 5 μm. Curing was performed at a metal temperature of 180℃ for 15 min, followed by cooling and a 24-hour rest period before testing. Adhesion was rated according to the cross-cut test method of GB / T 9286-2021; impact performance was tested according to ASTM D2794-93(2024) and converted to kg·cm; 60° gloss was tested according to GB / T 9754-2025; the electrostatic spraying powder application rate was calculated based on the weight gain of the sample before and after spraying and the amount of powder fed, determining the transfer efficiency; the color difference after recycling was determined according to ASTM D2244-25 after three recycling cycles. Corrosion resistance was tested for 1000 h using neutral salt spray (5% NaCl, 35 ℃) according to GB / T 10125-2021, with a scratch penetrating to the substrate made on the test plate. After salt spray, the blistering grade was evaluated according to GB / T 30789.2-2014, the rusting grade according to GB / T 30789.3-2014, and the peeling / corrosion spread width (mm) on both sides of the scratch was measured according to GB / T 30789.8-2015. The average spread width on both sides is shown. Moisture heat resistance was tested for 240 h using condensation water according to GB / T 1740-2007, and the blistering and adhesion were retested. The blistering grade after condensation was evaluated according to GB / T 30789.2-2014. Surface wettability was determined according to ASTM D7334-08(2022) for the advancing contact angle (dropped to the specified volume / maximum stable volume, averaged at 5 points). The relevant test results are shown in Tables 4 and 5. Table 4. Application and Basic Performance Test Results of Microsphere-Modified Corrosion-Resistant Dry-Glazed Metal Powder Coating Materials

[0033] Table 5. Test results of corrosion resistance and durability of microsphere-modified corrosion-resistant dry-plated metal powder coating materials

[0034] As shown in Tables 4 and 5, the systems of the examples exhibit superior overall performance in both decorative and protective aspects. Taking corrosion resistance as an example, after 1000 h of neutral salt spray, Examples 1–3 showed bubbling levels of 0 (S0), 1 (S1), and 1 (S1), respectively, corresponding to average corrosion spread widths of 0.8, 0.6, and 1.0 mm on both sides of the scratch, with a corrosion grade of Ri0 for all. In contrast, Comparative Example 1 (using ordinary glass microspheres as a substitute) showed a bubbling level of 3 (S3), a spread width of 4.5 mm, and a corrosion grade of Ri3, indicating that the unmodified microspheres were unable to suppress interfacial penetration and defect propagation. Consistent with this, after 240 h of condensate, Examples 1–3 maintained 0 (S0) bubbling and 0-level adhesion, while Comparative Example 1 showed 2 (S2) bubbling and decreased to 2-level adhesion, indicating that the interfacial stability and wet heat durability of the examples were significantly enhanced. Further comparison of Comparative Example 2 and Comparative Example 3 reveals that the improvement provided by a single functional segment has significant limitations: When Comparative Example 2 retains only the GMA brush layer, although the adhesion remains at level 0, the salt spray spread is still 2.2 mm and the corrosion level is Ri1. After condensation, bubbling occurs 2 (S2), and the adhesion drops to level 1. When Comparative Example 3 retains only the low surface energy and disulfide bond brush layer, the forward contact angle is close to that of the Example 1 (103° vs. 104° of Example 1), but the salt spray spread still reaches 3.0 mm and the corrosion level is Ri2. After condensation, bubbling occurs 2 (S2), and the adhesion drops to level 2. This indicates that relying solely on surface wetting control and dynamic bond slow release is insufficient to resist interfacial debonding and the formation of penetration channels. In comparison, the salt spray spread width of the example system was reduced by approximately 55%–73% (0.6–1.0 mm vs 2.2 mm) compared to Comparative Example 2, and by approximately 67%–80% (0.6–1.0 mm vs 3.0 mm) compared to Comparative Example 3, and the corrosion level was steadily increased from Ri1–Ri2 to Ri0, demonstrating the synergistic gain brought about by the coupling of the multifunctional brush layer at the same particle interface.

[0035] The decorative and construction-related indicators also support the above conclusions. The 60° gloss of Examples 1–3 was 56%–64%, on the same order of magnitude as the comparative system (61%–63%), indicating that the improved corrosion resistance did not come at the cost of a significant sacrifice in metallic appearance. Meanwhile, the three-dimensional color difference ΔE*ab of the examples remained at 0.61–0.73, while those of Comparative Examples 1–3 were 1.17, 0.95, and 1.04, respectively, indicating that the combination of modified microspheres and the dry plating system is more effective in suppressing component drift and appearance fluctuations caused by recycling. Regarding the spray transfer efficiency, Examples 1–3 achieved 70%–72%, higher than or close to the comparative example (68%–70%). Combined with the lower propagation and blistering levels shown in Table 5, this indicates that the system achieves higher protective reliability while ensuring powder coating stability.

[0036] The aforementioned differences can be attributed to the synergistic regulation of the brush-like polymer-modified microspheres along two key pathways: interface structure and defect evolution. First, the GMA reaction segment undergoes a ring-opening reaction with the carboxyl polyester / epoxy network during curing, forming a covalently bonded interface and reducing the tendency for interfacial microcracks and debonding. This effect is absent in Comparative Example 3, leading to significant degradation of adhesion under humid heat and salt spray conditions, accompanied by a larger spread width. Second, low surface energy segments reduce the surface energy of the coating and decrease the stability of the continuous water film, thereby weakening the long-term retention of the electrolyte film. This effect is absent in Comparative Example 2, resulting in good adhesion but still significantly higher blistering and spread rates. Third, the dynamic structure of disulfide bonds provides local segment rearrangement and stress release channels through reversible exchange, which is beneficial for microcrack closure / passivation and delaying corrosion propagation at defects. Comparative Example 2 lacks this slow-release mechanism, resulting in difficulty in further suppressing scratch spread.

[0037] In summary, Examples 1–3 introduce a triple mechanism of “interfacial covalent coupling (GMA) – surface wetting inhibition (low surface energy) – defect passivation (S–S dynamic bond)” on the same particle interface, which enables the coating to simultaneously reduce blistering, corrosion and scratch propagation in salt spray and condensation environments, and significantly improve corrosion resistance and durability while maintaining the appearance of the metal and recycling stability.

[0038] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A microsphere-modified corrosion-resistant dry-plated metal powder coating material, characterized in that, The product comprises the following components by weight: 55-65 parts carboxylated polyester resin, 6-14 parts epoxy resin, 0.2-0.8 parts curing accelerator, 0.8-1.5 parts leveling agent, 0.2-0.6 parts degassing agent, 10-20 parts pigments and fillers, 2-8 parts brushed polymer modified microspheres, 3-10 parts metallic pigments, 0.15-0.6 parts dry plating binder, and 0.05-0.3 parts charge regulating agent; The brush-shaped polymer-modified microspheres are composite particles with solid glass microspheres as the core. Their surfaces are anchored to surface initiation sites via silanization, and a polymer brush layer is grown in situ on the surface of the glass microspheres through surface-initiated controlled free radical polymerization. The polymer brush layer comprises at least: A: A resin-loving reaction section containing glycidyl methacrylate structural units; B: Functional segment containing low surface energy monomer structural units and disulfide bond dynamic covalent bond structural units.

2. The microsphere-modified corrosion-resistant dry-plated metal powder coating material according to claim 1, characterized in that, The solid glass microspheres have a D50 of 10-30 μm.

3. The microsphere-modified corrosion-resistant dry-plated metal powder coating material according to claim 1, characterized in that, In the monomer system used to form the polymer brush layer, the mass ratio of glycidyl methacrylate, low surface energy monomer, and disulfide bond-containing monomer is 20-45:5-20:2-10.

4. The microsphere-modified corrosion-resistant dry-plated metal powder coating material according to claim 3, characterized in that, The low surface energy monomer is selected from one or more of siloxane acrylates and fluorinated alkyl acrylates; the disulfide bond-containing monomer is selected from one or more of di(2-methacryloyloxyethyl) disulfide, di(2-acryloyloxyethyl) disulfide, cystamine di(meth)acrylate, and cystamine di(methacrylamide).

5. The microsphere-modified corrosion-resistant dry-plated metal powder coating material according to claim 1, characterized in that, The curing accelerator is selected from one or more of triphenylphosphine, tetraphenylphosphine bromide, 1-methylimidazolium, 2-methylimidazolium, 2-phenylimidazolium, dimethylimidazoline, 2,4,6-tris(dimethylaminomethyl)phenol, and tertiary amine accelerators; the leveling agent is selected from one or more of acrylate leveling agents, polysiloxane-modified leveling agents, and fluorinated leveling agents; the degassing agent is selected from one or more of benzoin, benzoin and its ether derivatives, caprolactam, and benzamide degassing agents; the charge regulating agent is selected from one or more of quaternary ammonium salts, quaternary phosphine salts, organic sulfonates, organometallic complexes, and polyether-modified / siloxane-modified charge regulating agents.

6. The microsphere-modified corrosion-resistant dry-plated metal powder coating material according to claim 1, characterized in that, The pigments and fillers are selected from one or more of titanium dioxide, iron oxide red, phthalocyanine blue, phthalocyanine green, ultramarine, carbon black, chrome green, chromium oxide green, barium sulfate, calcined kaolin, talc, and precipitated silicates; the metallic pigments are selected from one or more of flake aluminum silver powder, coated aluminum silver powder, pearlescent aluminum powder, stainless steel metallic pigments, and nickel-chromium alloy metallic pigments; the dry plating binder is selected from one or more of polyester binders, acrylic binders, ethylene-vinyl acetate copolymer binders, and polyamide binders.

7. A method for preparing a microsphere-modified corrosion-resistant dry-plated metal powder coating material, used to prepare the microsphere-modified corrosion-resistant dry-plated metal powder coating material according to any one of claims 1-6, characterized in that, Includes the following steps: S1. Microsphere surface anchoring: Solid glass microspheres are washed and dried at 80-110℃ for 0.5-2 h; they are dispersed in an alcohol / ester mixed solvent, a silane coupling agent is added, and 0.3-2.0 vol% water relative to the total volume of the solvent is added. The pH of the system is adjusted to 4.0-5.5 using glacial acetic acid, and the reaction is carried out at 50-80℃ for 2-6 h; after the reaction is completed, the mixture is filtered and washed 2-3 times with ethanol, and dried under vacuum at 50-70℃ for 2-6 h to obtain microspheres with anchoring sites on the surface. S2. Surface-Initiated Controlled Polymerization to Grow a Brush Layer: The microspheres obtained in step S1 are dispersed in an ethanol / water mixed solvent, wherein the volume fraction of ethanol is 70-90% and the mass fraction of microspheres is 5-20%; a chain transfer agent and a photocatalyst are added to the suspension system, and a polymer brush layer is grown on the surface of the microspheres by surface-initiated controlled free radical polymerization; the total concentration of the monomer system forming the polymer brush layer is 10-35% by mass fraction of solvent, and a gradient brush layer is constructed by a staged feeding method, that is, first enriching and polymerizing glycidyl methacrylate monomer, and then introducing low surface energy monomers and disulfide bond-containing monomers; the polymerization temperature is 25-75℃, and the reaction time is 2-8 h; after the reaction, the microspheres are separated into solid and liquid, washed with ethanol 2-3 times, and dried under vacuum at 50-70℃ for 4-10 h to obtain brush-shaped polymer-modified microspheres; S3. Preparation of base powder: Accurately weigh carboxylated polyester resin, epoxy resin, curing accelerator, leveling agent, degassing agent, pigments and fillers, and charge regulating agent according to the mass parts. Dry mix them in a high-speed mixer at 800-1500 rpm for 2-6 min while controlling the discharge temperature to ≤40℃. Feed the dry mixture into a twin-screw extruder for melt mixing and extrusion, where the screw speed is 200-500 rpm and the material residence time is 30-90 s. After the extrudate is pressed into sheets and cooled to <35℃, it is crushed, pulverized, and sieved through a 120-200 mesh to obtain a base powder that does not contain brush-like polymer-modified microspheres or metallic pigments. S4. Low-temperature dry bonding to introduce modified microspheres: The base powder obtained in step S3 is put into a dry plating bonding device, the powder is heated to 30-45℃, and mixed at 600-1500 rpm for 1-2 min. First, the dry plating binder is added to form a capture layer on the surface of the base powder particles. Then, the brush-shaped polymer modified microspheres obtained in step S2 are added in 2-4 batches, with an interval of 30-60 s between each addition. The total mixing time of this step is controlled to be 3-8 min, so that the modified microspheres preferentially adhere to the surface or shallow layer of the base powder particles. Then, the mixture is cooled to below 30℃ within 1-3 min and sieved through a 120-200 mesh. The amount of the dry plating binder added is 50-100% of the total amount added in the formula, and the remainder can be added in step S5. S5. Dry plating metal bonding: The powder obtained in step S4 is put into the dry plating bonding equipment and mixed for 3-10 min at 35-50℃ and 500-1200 rpm. The metal pigment is added in 2-3 batches with an interval of 30-60 s. After mixing, the mixture is cooled to below 30℃ and sieved through a 120-200 mesh to obtain the microsphere modified corrosion-resistant dry plating metal powder coating material.

8. The method for preparing a microsphere-modified corrosion-resistant dry-plated metal powder coating material according to claim 7, characterized in that, In step S1, the alcohol / ester mixed solvent is a mixture of ethanol and ethyl acetate in a volume ratio of 70-90:10-30; the silane coupling agent is selected from one or more of 3-(2-bromoisobutyryloxy)propyltrimethoxysilane, 3-(2-bromoisobutyryloxy)propyltriethoxysilane, 3-(2-chloroisobutyryloxy)propyltrimethoxysilane, and 3-(2-chloroisobutyryloxy)propyltriethoxysilane; the amount of silane coupling agent added is 1-3 wt% based on the mass of the solid glass microspheres.

9. The method for preparing a microsphere-modified corrosion-resistant dry-plated metal powder coating material according to claim 7, characterized in that, In step S2, the surface-initiated controlled radical polymerization is a photoinduced electron transfer reversible addition-fragmentation chain transfer polymerization reaction, using a 405-470 nm light source with an illuminance of 5-30 mW / cm². 2 The chain transfer agent is selected from one or more of trithiocarbonate chain transfer agents and dithiobenzoate chain transfer agents, and its addition amount is 0.2-5.0 wt% based on the total mass of the brush layer monomers; the photocatalyst is selected from one or more of eosin Y and rose red B, and its addition amount is 10-2000 ppm based on the total mass of the brush layer monomers; oxygen is controlled by bubbling with nitrogen for 10-30 min before polymerization; the reaction temperature of reaction stage one is 35-45℃ and the reaction time is 0.5-2 h; in reaction stage two, the functional monomer mixture is continuously added by metering pump within 0.5-2 h and the reaction continues for 1-4 h.

10. The method for preparing a microsphere-modified corrosion-resistant dry-plated metal powder coating material according to claim 7, characterized in that, In step S3, the temperatures of each zone of the twin-screw extruder are: zone 1 85-90℃, zone 2 90-95℃, zone 3 95-100℃, zone 4 100-105℃, and zone 5 105-110℃.

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