Polyester resin powder coating with high salt mist corrosion resistance and preparation method thereof

Abstract

The application belongs to the technical field of paint preparation, and provides polyester resin powder paint with high salt mist corrosion resistance and a preparation method thereof.The powder paint is composed of a carboxyl functional polyester resin, a hydroxyalkylamide curing agent and / or trisglycidyl isocyanurate to form a film forming system, and is matched with titanium dioxide, inorganic fillers, acrylate leveling agent, benzoin and wax powder;quaternary ammonium poly-p-vinyl pyridine microgel is introduced into the paint, and double-particle-size microcapsules are added;the microcapsule core layer contains hydroxyl-terminated polydimethylsiloxane, mercaptobenzothiazole corrosion inhibitor components, polycarbodiimide and phthalate plasticizer, the shell layer is a polyurea inner shell and a polydopamine outer shell and contains a disulfide bond structure, an epoxy silane hydrolysis and condensation layer is arranged on the outer layer and loads the microgel.

Description

Technical Field

[0001] This invention belongs to the field of coating preparation technology, and relates to polyester resin powder coatings with high salt spray corrosion resistance and their preparation methods. Background Technology

[0002] Marine engineering equipment and coastal infrastructure are constantly exposed to high humidity, high salt spray, and alternating temperature differences. Coatings not only need to possess conventional adhesion, weather resistance, and abrasion resistance, but also need to maintain shielding integrity under the coupled effects of continuous chloride ion penetration, localized electrochemical corrosion, and the propagation of micro-defects. Polyester resin powder coatings are widely used for the protection of metal substrates due to their advantages such as low volatile emissions, high construction efficiency, dense film, and good decorative appearance. However, in marine environments, coatings inevitably contain pores, pinholes, thin film areas at the edges, and microcracks caused by impact, scratches, or thermal stress. Chloride ions and moisture can penetrate along defect paths and accumulate at the metal / coating interface, leading to blistering, peeling, and rust propagation, thus limiting the coating's durable protective capabilities.

[0003] Existing marine anti-corrosion powder coatings typically improve barrier properties and interfacial stability by increasing crosslinking density, introducing lamellar or layered inorganic fillers, using corrosion-inhibiting pigments, employing silane or phosphate treatment agents, and introducing hydrophobic modifiers. However, in powder coating systems, issues such as the dispersion stability of additives, the thermal shear compatibility of the extrusion process, and the compatibility and interfacial bonding during curing can affect the continuity and long-term performance of the coating film. Some corrosion-inhibiting or functional components exist in the coating film through physical mixing and may gradually be lost due to migration, swelling, or immersion, leading to a decrease in effectiveness. Furthermore, traditional single-size microcapsules or single-functional fillers often struggle to cover and seal defects of different sizes, and the interface between microcapsules and the polyester matrix is ​​primarily physically embedded, easily forming potential penetration channels. On the other hand, many solutions focus on mechanical barrier or single corrosion inhibition mechanisms, lacking synergistic responses to chloride ion intrusion, microcrack initiation and propagation, and interfacial reactions, making it difficult to maintain stable protective effects under long-term salt spray conditions. Summary of the Invention

[0004] In view of the shortcomings of the existing technology, the purpose of this invention is to provide polyester resin powder coating with high salt spray corrosion resistance and its preparation method, so as to meet the needs of actual production.

[0005] To achieve this objective, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides a polyester resin powder coating with high salt spray corrosion resistance, comprising, by weight: 55-70 parts polyester resin, 4-10 parts curing agent, 10-18 parts titanium dioxide, 8-15 parts filler, 0.8-1.3 parts acrylate leveling agent, 0.3-0.8 parts benzoin, 0.2-0.6 parts wax powder, 0.3-1.2 parts quaternized poly(4-vinylpyridine) microgel, and 3-7 parts dual-size microcapsules; wherein the filler is barium sulfate and / or wollastonite; the wax powder is polyethylene wax, polypropylene wax, and / or polytetrafluoroethylene wax; and the dual-size microcapsules are obtained by mixing microcapsules A and B, both loaded with quaternized poly(4-vinylpyridine) microgel, wherein the mass ratio of microcapsule A to microcapsule B is (6-8):(2-4).

[0007] Preferably, the polyester resin is a carboxyl-functionalized polyester resin with an acid value of 25-45 mg KOH / g; the curing agent is N,N,N′,N′-tetra(2-hydroxyethyl)hexamethylenediamide and / or triglycidyl isocyanurate; and the acrylate leveling agent is polybutyl acrylate, poly-2-ethylhexyl acrylate and / or polymethyl acrylate.

[0008] Preferably, the particle size D50 of microcapsule A is 6-15 μm, and microcapsule A is a core-shell structured microcapsule; the core layer of microcapsule A comprises, by weight, 100 parts of hydroxyl-terminated polydimethylsiloxane, 6-10 parts of 2-mercaptobenzothiazole, 1-3 parts of polycarbodiimide, and 0-6 parts of diisononyl phthalate; the number average molecular weight of the hydroxyl-terminated polydimethylsiloxane is 1000-6000.

[0009] Preferably, the particle size D50 of microcapsule B is 20-40 μm, and microcapsule B is a core-shell structured microcapsule; the core layer of microcapsule B comprises, by weight, 100 parts of hydroxyl-terminated polydimethylsiloxane, 3-6 parts of 2-mercaptobenzothiazole, 1-3 parts of polycarbodiimide, and 8-15 parts of diisononyl phthalate.

[0010] Preferably, the shells of microcapsule A and microcapsule B each comprise a polyurea inner shell and a polydopamine outer shell; the polyurea inner shell comprises hexamethylene diisocyanate trimer, diethylenetriamine, ethylenediamine, dopamine hydrochloride, and cystamine dihydrochloride; based on 100 parts by weight of hydroxyl-terminated polydimethylsiloxane, the hexamethylene diisocyanate trimer comprises 10-18 parts by weight, the diethylenetriamine comprises 4-8 parts by weight, the ethylenediamine comprises 1-3 parts by weight, the dopamine hydrochloride comprises 0.3-1.5 parts by weight, and the cystamine dihydrochloride comprises 0.2-2 parts by weight.

[0011] Preferably, the quaternized poly(4-vinylpyridine) microgel is obtained by reacting poly(4-vinylpyridine), 1,4-dibromobutane, benzyl bromide, ethanol and methyl ethyl ketone, followed by precipitation, drying and pulverization; based on 100 parts by weight of poly(4-vinylpyridine), 1-3 parts by weight of 1,4-dibromobutane, 6-15 parts by weight of benzyl bromide, 540-780 parts by weight of ethanol, and 360-520 parts by weight of methyl ethyl ketone.

[0012] Preferably, the quaternized poly(4-vinylpyridine) microgel has a semi-interpenetrating polymer network structure or a graft copolymer structure; its preparation raw materials also include dodecyl bromide, 2-(dimethylamino)ethyl methacrylate and ethylene glycol dimethacrylate; based on 100 parts by weight of poly(4-vinylpyridine), dodecyl bromide is 1-4 parts by weight, 2-(dimethylamino)ethyl methacrylate is 1-10 parts by weight, 2,2′-azobisisobutyronitrile is 0.2 parts by weight, and ethylene glycol dimethacrylate is 0.2-3 parts by weight.

[0013] Preferably, the total loading of the quaternized poly(4-vinylpyridine) microgel is 5-20 parts by weight based on the dry solid content of the dual-size microcapsules; the outermost layer of the dual-size microcapsules is a hydrolytic condensation layer of 3-glycidoxypropyltrimethoxysilane, which forms a covalent bond with the polydopamine shell through a hydrolytic condensation reaction; based on 100 parts by weight of the dual-size microcapsule dry powder, 3-glycidoxypropyltrimethoxysilane is 0.2-2.0 parts by weight.

[0014] Secondly, the present invention provides a method for preparing a polyester resin powder coating with high salt spray corrosion resistance, specifically comprising:

[0015] (1) Preparation of quaternized poly(4-vinylpyridine) microgels: Poly(4-vinylpyridine) was dissolved in a mixed solvent of ethanol and methyl ethyl ketone by stirring. 1,4-dibromobutane and benzyl bromide were added to carry out a quaternization reaction. Dodecyl bromide was added to the reaction system. 2-(dimethylamino)ethyl methacrylate and ethylene glycol dimethacrylate were added to the reaction system, and 2,2′-azobisisobutyronitrile was added as an initiator to allow 2-(dimethylamino)ethyl methacrylate to undergo in-situ free radical polymerization and crosslinking in the presence of ethylene glycol dimethacrylate. After the reaction, the reaction system was precipitated, washed, dried and pulverized to obtain quaternized poly(4-vinylpyridine) microgels.

[0016] (2) Preparation of dual-size microcapsules, wherein the preparation steps of the dual-size microcapsules include:

[0017] (a) Hydroxyl-terminated polydimethylsiloxane, 2-mercaptobenzothiazole, polycarbodiimide and diisononyl phthalate were mixed to obtain an oil phase; polyvinyl alcohol was added to deionized water and stirred to dissolve to obtain an aqueous phase; the oil phase was added to the aqueous phase and emulsified under two emulsification conditions to obtain the corresponding core droplet A emulsion system and core droplet B emulsion system.

[0018] (b) Hexamethylene diisocyanate trimer was added to the core droplet A emulsion system and the core droplet B emulsion system, respectively, and diethylenetriamine and ethylenediamine were added to react and form a polyurea inner shell; during the formation of the polyurea inner shell, dopamine hydrochloride and cystamine dihydrochloride were added to participate in the reaction; then the pH of the system was adjusted and dopamine hydrochloride was added to form a polydopamine outer shell on the surface of the microcapsule, and microcapsule A slurry and microcapsule B slurry were obtained respectively.

[0019] (c) After the polydopamine shell is formed, 3-glycidoxypropyltrimethoxysilane is added to microcapsule A slurry and microcapsule B slurry respectively, so that it undergoes hydrolysis and condensation on the surface of the microcapsule to form a silane layer; then, the quaternized poly(4-vinylpyridine) microgel obtained in step (1) is added to load it on the surface of the microcapsule; the obtained microcapsules are subjected to solid-liquid separation, water washing, drying and sieving to obtain microcapsule A dry powder and microcapsule B dry powder respectively, and the microcapsule A dry powder and microcapsule B dry powder are mixed to obtain dual-size microcapsules;

[0020] (3) Polyester resin, curing agent, titanium dioxide, filler, acrylate leveling agent, benzoin, wax powder and quaternized poly(4-vinylpyridine) microgel obtained in step (1) are premixed, the premix is ​​melt-extruded into sheets, cooled and crushed, and the crushed material is pulverized and classified to obtain base powder.

[0021] (4) Add the dual-size microcapsules obtained in step (2) to the base powder obtained in step (3) for cold mixing to obtain polyester resin powder coating.

[0022] Preferably, in step (2), the emulsification speed of nucleus droplet A is 4500-6500 rpm and the emulsification time is 10-15 min, and the emulsification speed of nucleus droplet B is 1200-2200 rpm and the emulsification time is 6-10 min; the reaction temperature for forming the polyurea inner shell in step (2) is 45-55℃; and the pH of the microcapsule system when forming the polydopamine outer shell in step (2) is 8-9.

[0023] In the preparation step of quaternized poly(4-vinylpyridine) microgels, 1,4-dibromobutane and benzyl bromide undergo a nucleophilic substitution quaternization reaction with pyridine nitrogen, transforming the pyridine nitrogen from a neutral Lewis base to a quaternary ammonium salt center, forming fixed positively charged sites on the polymer chain. The addition of dodecyl bromide leads to the quaternization reaction of the bromoalkyl group with pyridine nitrogen, locally introducing hydrophobic alkyl side chains into the chain segments. This alters the swelling equilibrium of the chain segments in the mixed solvent and subsequent aqueous environment, and improves the compatibility of the microgel particles in the organic phase. Subsequently, 2-(dimethylamino)ethyl methacrylate and ethylene glycol dimethacrylate were introduced, and 2,2′-azobisisobutyronitrile was added to initiate the double bond polymerization of methacrylate. Ethylene glycol dimethacrylate provided bifunctional crosslinking sites, forming an interpenetrating or grafted crosslinking network with poly(4-vinylpyridine) as the backbone and containing 2-(dimethylamino)ethyl methacrylate segments. The crosslinking network restricts segment migration, fixing the quaternary ammonium salt sites in a particulate form. After chloride ions in the immersion medium enter the coating film, they tend to form ion associations and ion exchanges with the quaternary ammonium sites, reducing the activity of free chloride ions and weakening the concentration gradient and electromigration driving force required for migration.

[0024] In the preparation of dual-size microcapsules, hydroxyl-terminated polydimethylsiloxane, 2-mercaptobenzothiazole, polycarbodiimide, and diisononyl phthalate constitute the oil phase. Polyvinyl alcohol forms a protective colloidal layer in the aqueous phase. Under emulsification shear, the oil phase splits into core droplets, which are then adsorbed and stabilized by polyvinyl alcohol, forming a core droplet system with different particle size distributions. After adding hexamethylene diisocyanate trimer, the isocyanate groups undergo addition reactions with the amino groups of diethylenetriamine and ethylenediamine at the interface to form urea bonds. Interfacial polymerization generates a cross-linked polyurea network that coats the core droplets, forming a polyurea inner shell. Dopamine hydrochloride undergoes oxidation under alkaline conditions to form a quinone structure, which further couples and polymerizes to deposit. Polydopamine is deposited on the polyurea surface to form the outer shell. The polydopamine surface retains catechol and amino groups. The catechol groups can undergo coordination adsorption with the metal oxide surface, while the amino groups participate in hydrogen bonding and nucleophilic reaction pathways. Cystamine dihydrochloride introduces a disulfide bond structure. The disulfide bond, through a thiol-disulfide bond exchange and breakage / recombination reaction pathway, allows for bond exchange at microcracks in the shell chain segments. Subsequently, 3-glycidoxypropyltrimethoxysilane is added. The methoxysilane hydrolyzes in the aqueous phase to generate silanols, which condense to form Si-O-Si bonds and deposit a siloxane network on the shell surface. The silanols condense with the hydroxyl groups on the polydopamine surface to form Si-OC bonds, and the epoxy groups can undergo ring-opening addition with the polydopamine amine groups to form CN bonds, thus covalently bonding the silane layer to the shell. After adding the aforementioned quaternized microgel, the counterionic layer of the quaternary ammonium groups on the microgel surface undergoes electrostatic adsorption and hydrogen bonding with the polar groups of the silane and polydopamine layers. The epoxy groups in the silane layer undergo ring-opening reaction pathways with the nucleophilic sites associated with the amine groups in the microgel, forming a chemical anchor. The microgel remains positioned on the microcapsule surface, and chloride ions are initially captured by fixed charge sites around the microcapsules upon penetration. After the microcapsule shell forms an opening, the hydroxyl-terminated polydimethylsiloxane in the core layer wets and spreads along the defect wall. The continuous aqueous phase channel in the defect is occupied by the organosilicon phase, and the effective diffusion cross section of water and chloride ions decreases. Polycarbodiimide undergoes addition with the residual carboxyl groups in the coating to form an N-acylurea structure. After the carboxyl sites are consumed, the local polarity decreases, and the hydrophilic sites required to form a continuous electrolyte water film at the interface are reduced. After 2-mercaptobenzothiazole migrates to the metal interface, it is adsorbed by complexing with metal ions as sulfur atoms. The competitive coordination between chloride ions and metal ions is interfered with by the adsorption site occupancy.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention introduces the synergistic effect of quaternized poly(p-vinylpyridine) microgel and dual-size microcapsules. The microgel provides a fixed positive potential point, which causes ion association and exchange of infiltrated chloride ions, reduces the activity of free chloride ions and weakens the migration driving force. The dual-size microcapsules cover defects of different scales such as micropores and microcracks. After the capsules are broken, the hydroxyl-terminated polydimethylsiloxane in the core layer spreads and seals the defects. The corrosion inhibitor is complexed and adsorbed at the metal interface. Polycarbodiimide undergoes an addition reaction with the residual carboxyl groups and reduces the local polarity. The polyurea and polydopamine shell, together with the silanized outer layer and microgel loading, stabilize the microcapsule interface and inhibit the formation of permeation channels, thereby reducing the risk of blistering, peeling and corrosion propagation under the coating. It is suitable for long-term protection in marine salt spray environments. Attached Figure Description

[0026] Figure 1 This is a SEM image of microcapsule A provided in Embodiment 1 of the present invention. Detailed Implementation

[0027] The technical solutions of the present invention will be described in detail below with reference to specific embodiments and accompanying drawings. The embodiments described herein are specific implementations of the present invention, used to illustrate the concept of the present invention; these descriptions are explanatory and exemplary, and should not be construed as limiting the implementation methods or the scope of protection of the present invention. In addition to the embodiments described herein, those skilled in the art can employ other obvious technical solutions based on the content disclosed in the claims and specification of this application. These technical solutions include those that make any obvious substitutions and modifications to the embodiments described herein.

[0028] The chemical reagents used in the embodiments and comparative examples of this invention are all commercially available products and have not undergone any further purification treatment.

[0029] Example 1

[0030] This embodiment provides a polyester resin powder coating with high salt spray corrosion resistance and its preparation method, which specifically includes, by weight:

[0031] The composition comprises 55 parts polyester resin, 10 parts curing agent, 14 parts titanium dioxide, 12 parts filler, 0.8 parts acrylate leveling agent, 0.8 parts benzoin, 0.2 parts wax powder, 1.2 parts quaternized poly(4-vinylpyridine) microgel, and 7 parts dual-size microcapsules; the filler is barium sulfate; the wax powder is polyethylene wax; the dual-size microcapsules are obtained by mixing microcapsules A and B, both loaded with quaternized poly(4-vinylpyridine) microgel, with a mass ratio of microcapsule A to microcapsule B of 8:2.

[0032] The polyester resin is a carboxyl-functionalized polyester resin with an acid value of 45 mg KOH / g; the curing agent is triglycidyl isocyanurate; and the acrylate leveling agent is polybutyl acrylate.

[0033] The particle size D50 of microcapsule A is 6 μm, and microcapsule A is a core-shell structured microcapsule;

[0034] The core layer of microcapsule A comprises, by weight, 100 parts of hydroxyl-terminated polydimethylsiloxane, 6 parts of 2-mercaptobenzothiazole, and 1 part of polycarbodiimide; the number average molecular weight of the hydroxyl-terminated polydimethylsiloxane is 1000.

[0035] The particle size D50 of microcapsule B is 20 μm, and microcapsule B is a core-shell structured microcapsule;

[0036] The core layer of microcapsule B comprises, by weight, 100 parts of hydroxyl-terminated polydimethylsiloxane, 3 parts of 2-mercaptobenzothiazole, 1 part of polycarbodiimide, and 8 parts of diisononyl phthalate.

[0037] Both microcapsules A and B consist of a polyurea inner shell and a polydopamine outer shell. The polyurea inner shell is formed by reacting hexamethylene diisocyanate trimer, diethylenetriamine, ethylenediamine, dopamine hydrochloride, and cystamine dihydrochloride in an emulsion system. Based on 100 parts by weight of hydroxyl-terminated polydimethylsiloxane, the hexamethylene diisocyanate trimer comprises 18 parts by weight, diethylenetriamine comprises 4 parts by weight, ethylenediamine comprises 3 parts by weight, dopamine hydrochloride comprises 0.3 parts by weight, and cystamine dihydrochloride comprises 2 parts by weight.

[0038] The quaternized poly(4-vinylpyridine) microgel was obtained by reacting poly(4-vinylpyridine), 1,4-dibromobutane, benzyl bromide, ethanol and methyl ethyl ketone, followed by precipitation, drying and pulverization; based on 100 parts by mass of poly(4-vinylpyridine), 3 parts by mass of 1,4-dibromobutane, 6 parts by mass of benzyl bromide, 540 parts by mass of ethanol and 360 parts by mass of methyl ethyl ketone.

[0039] The quaternized poly(4-vinylpyridine) microgel has a semi-interpenetrating polymer network structure or a graft copolymer structure; its preparation raw materials also include dodecyl bromide, 2-(dimethylamino)ethyl methacrylate and ethylene glycol dimethacrylate; based on 100 parts by weight of poly(4-vinylpyridine), dodecyl bromide is 1 part by weight, 2-(dimethylamino)ethyl methacrylate is 10 parts by weight, and ethylene glycol dimethacrylate is 0.2 parts by weight.

[0040] The total loading of the quaternized poly(4-vinylpyridine) microgel is 5 parts by weight based on the dry solid content of the dual-size microcapsules; and the outermost layer of the dual-size microcapsules is a hydrolytic condensation layer of 3-glycidoxypropyltrimethoxysilane, which forms a covalent bond with the polydopamine shell through a hydrolytic condensation reaction; based on 100 parts by weight of the dual-size microcapsule dry powder, 2.0 parts by weight of 3-glycidoxypropyltrimethoxysilane.

[0041] The preparation method includes the following steps:

[0042] (1) Preparation of quaternized poly(4-vinylpyridine) microgels: Poly(4-vinylpyridine) was dissolved in a mixed solvent of ethanol and methyl ethyl ketone by stirring. 1,4-dibromobutane and benzyl bromide were added to carry out a quaternization reaction. Dodecyl bromide was added to the reaction system. 2-(dimethylamino)ethyl methacrylate and ethylene glycol dimethacrylate were added to the reaction system, and 2,2′-azobisisobutyronitrile was added as an initiator to allow 2-(dimethylamino)ethyl methacrylate to undergo in-situ free radical polymerization and crosslinking in the presence of ethylene glycol dimethacrylate. After the reaction, the reaction system was subjected to precipitation separation, washing, drying and pulverization to obtain quaternized poly(4-vinylpyridine) microgel powder.

[0043] (2) Preparation of dual-size microcapsules:

[0044] (a) Hydroxyl-terminated polydimethylsiloxane, 2-mercaptobenzothiazole, polycarbodiimide and diisononyl phthalate were mixed to obtain an oil phase; polyvinyl alcohol was added to deionized water and stirred to dissolve to obtain an aqueous phase; the oil phase was added to the aqueous phase and emulsified under two emulsification conditions to obtain the corresponding core droplet A emulsion system and core droplet B emulsion system.

[0045] (b) Hexamethylene diisocyanate trimer was added to the core droplet A emulsion system and the core droplet B emulsion system, respectively, and diethylenetriamine and ethylenediamine were added to react and form a polyurea inner shell; during the formation of the polyurea inner shell, dopamine hydrochloride and cystamine dihydrochloride were added to participate in the reaction; then the pH of the system was adjusted and dopamine hydrochloride was added to form a polydopamine outer shell on the surface of the microcapsule, and microcapsule A slurry and microcapsule B slurry were obtained respectively.

[0046] (c) After the polydopamine shell is formed, 3-glycidoxypropyltrimethoxysilane is added to microcapsule A slurry and microcapsule B slurry respectively, so that it undergoes hydrolysis and condensation on the surface of the microcapsule to form a silane layer; then, the quaternized poly(4-vinylpyridine) microgel obtained in step (1) is added to load it on the surface of the microcapsule; the obtained microcapsules are subjected to solid-liquid separation, water washing, drying and sieving to obtain microcapsule A dry powder and microcapsule B dry powder respectively, and the microcapsule A dry powder and microcapsule B dry powder are mixed to obtain dual-size microcapsules;

[0047] (3) Polyester resin, curing agent, titanium dioxide, filler, acrylate leveling agent, benzoin, wax powder and quaternized poly(4-vinylpyridine) microgel obtained in step (1) are premixed, the premix is ​​melt-extruded into sheets, cooled and crushed, and the crushed material is pulverized and classified to obtain base powder.

[0048] (4) Add the dual-size microcapsules obtained in step (2) to the base powder obtained in step (3) and cold mix to obtain polyester resin powder coating.

[0049] In step (2), the emulsification speed of nucleus droplet A is 6500 rpm and the emulsification time is 10 min, while the emulsification speed of nucleus droplet B is 2200 rpm and the emulsification time is 6 min. The reaction temperature for forming the polyurea inner shell in step (2) is 45℃. The pH of the microcapsule system when forming the polydopamine outer shell in step (2) is 9.

[0050] Figure 1 This is a SEM image of microcapsule A provided in this embodiment.

[0051] Example 2

[0052] This embodiment provides a polyester resin powder coating with high salt spray corrosion resistance and its preparation method, which specifically includes, by weight:

[0053] The composition comprises 70 parts polyester resin, 4 parts curing agent, 10 parts titanium dioxide, 15 parts filler, 1.3 parts acrylate leveling agent, 0.3 parts benzoin, 0.6 parts wax powder, 0.3 parts quaternized poly(4-vinylpyridine) microgel, and 3 parts dual-size microcapsules; the filler is wollastonite; the wax powder is polytetrafluoroethylene wax; the dual-size microcapsules are obtained by mixing microcapsules A and B, both loaded with quaternized poly(4-vinylpyridine) microgel, with a mass ratio of microcapsule A to microcapsule B of 6:4.

[0054] The polyester resin is a carboxyl-functionalized polyester resin with an acid value of 25 mg KOH / g; the curing agent is N,N,N′,N′-tetra(2-hydroxyethyl)hexamethylenediamide; and the acrylate leveling agent is 2-ethylhexyl polyacrylate.

[0055] The particle size D50 of microcapsule A is 15 μm, and microcapsule A is a core-shell structured microcapsule;

[0056] The core layer of microcapsule A comprises, by weight, 100 parts of hydroxyl-terminated polydimethylsiloxane, 10 parts of 2-mercaptobenzothiazole, 3 parts of polycarbodiimide, and 6 parts of diisononyl phthalate; the number average molecular weight of the hydroxyl-terminated polydimethylsiloxane is 6000.

[0057] The particle size D50 of microcapsule B is 40 μm, and microcapsule B is a core-shell structured microcapsule;

[0058] The core layer of microcapsule B comprises, by weight, 100 parts of hydroxyl-terminated polydimethylsiloxane, 6 parts of 2-mercaptobenzothiazole, 3 parts of polycarbodiimide, and 15 parts of diisononyl phthalate.

[0059] Both microcapsules A and B have shells comprising a polyurea inner shell and a polydopamine outer shell. The polyurea inner shell is formed by reacting hexamethylene diisocyanate trimer, diethylenetriamine, ethylenediamine, dopamine hydrochloride, and cystamine dihydrochloride in an emulsion system. Based on 100 parts by weight of hydroxyl-terminated polydimethylsiloxane, the composition is 10 parts by weight of hexamethylene diisocyanate trimer, 8 parts by weight of diethylenetriamine, 1 part by weight of ethylenediamine, 1.5 parts by weight of dopamine hydrochloride, and 0.2 parts by weight of cystamine dihydrochloride.

[0060] The quaternized poly(4-vinylpyridine) microgel was obtained by reacting poly(4-vinylpyridine), 1,4-dibromobutane, benzyl bromide, ethanol and methyl ethyl ketone, followed by precipitation, drying and pulverization; based on 100 parts by mass of poly(4-vinylpyridine), 1 part by mass of 1,4-dibromobutane, 15 parts by mass of benzyl bromide, 780 parts by mass of ethanol and 520 parts by mass of methyl ethyl ketone.

[0061] The quaternized poly(4-vinylpyridine) microgel has a semi-interpenetrating polymer network structure or a graft copolymer structure; its preparation raw materials also include dodecyl bromide, 2-(dimethylamino)ethyl methacrylate and ethylene glycol dimethacrylate; based on 100 parts by mass of poly(4-vinylpyridine), dodecyl bromide is 4 parts by mass, 2-(dimethylamino)ethyl methacrylate is 1 part by mass, and ethylene glycol dimethacrylate is 3 parts by mass.

[0062] The total loading of the quaternized poly(4-vinylpyridine) microgel is 20 parts by weight based on the dry solid content of the dual-size microcapsules; and the outermost layer of the dual-size microcapsules is a hydrolytic condensation layer of 3-glycidoxypropyltrimethoxysilane, which forms a covalent bond with the polydopamine shell through a hydrolytic condensation reaction; based on 100 parts by weight of the dual-size microcapsule dry powder, 3-glycidoxypropyltrimethoxysilane is 0.2 parts by weight.

[0063] The preparation method includes the following steps:

[0064] (1) Preparation of quaternized poly(4-vinylpyridine) microgels: Poly(4-vinylpyridine) was dissolved in a mixed solvent of ethanol and methyl ethyl ketone by stirring. 1,4-dibromobutane and benzyl bromide were added to carry out a quaternization reaction. Dodecyl bromide was added to the reaction system. 2-(dimethylamino)ethyl methacrylate and ethylene glycol dimethacrylate were added to the reaction system, and 2,2′-azobisisobutyronitrile was added as an initiator to allow 2-(dimethylamino)ethyl methacrylate to undergo in-situ free radical polymerization and crosslinking in the presence of ethylene glycol dimethacrylate. After the reaction, the reaction system was subjected to precipitation separation, washing, drying and pulverization to obtain quaternized poly(4-vinylpyridine) microgel powder.

[0065] (2) Preparation of dual-size microcapsules:

[0066] (a) Hydroxyl-terminated polydimethylsiloxane, 2-mercaptobenzothiazole, polycarbodiimide and diisononyl phthalate were mixed to obtain an oil phase; polyvinyl alcohol was added to deionized water and stirred to dissolve to obtain an aqueous phase; the oil phase was added to the aqueous phase and emulsified under two emulsification conditions to obtain the corresponding core droplet A emulsion system and core droplet B emulsion system.

[0067] (b) Hexamethylene diisocyanate trimer was added to the core droplet A emulsion system and the core droplet B emulsion system, respectively, and diethylenetriamine and ethylenediamine were added to react and form a polyurea inner shell; during the formation of the polyurea inner shell, dopamine hydrochloride and cystamine dihydrochloride were added to participate in the reaction; then the pH of the system was adjusted and dopamine hydrochloride was added to form a polydopamine outer shell on the surface of the microcapsule, and microcapsule A slurry and microcapsule B slurry were obtained respectively.

[0068] (c) After the polydopamine shell is formed, 3-glycidoxypropyltrimethoxysilane is added to microcapsule A slurry and microcapsule B slurry respectively, so that it undergoes hydrolysis and condensation on the surface of the microcapsule to form a silane layer; then, the quaternized poly(4-vinylpyridine) microgel obtained in step (1) is added to load it on the surface of the microcapsule; the obtained microcapsules are subjected to solid-liquid separation, water washing, drying and sieving to obtain microcapsule A dry powder and microcapsule B dry powder respectively, and the microcapsule A dry powder and microcapsule B dry powder are mixed to obtain dual-size microcapsules;

[0069] (3) Polyester resin, curing agent, titanium dioxide, filler, acrylate leveling agent, benzoin, wax powder and quaternized poly(4-vinylpyridine) microgel obtained in step (1) are premixed, the premix is ​​melt-extruded into sheets, cooled and crushed, and the crushed material is pulverized and classified to obtain base powder.

[0070] (4) Add the dual-size microcapsules obtained in step (2) to the base powder obtained in step (3) and cold mix to obtain polyester resin powder coating.

[0071] In step (2), the emulsification speed of nucleus droplet A is 4500 rpm and the emulsification time is 15 min, while the emulsification speed of nucleus droplet B is 1200 rpm and the emulsification time is 10 min. The reaction temperature for forming the polyurea inner shell in step (2) is 55℃. The pH of the microcapsule system when forming the polydopamine outer shell in step (2) is 8.

[0072] Example 3

[0073] This embodiment provides a polyester resin powder coating with high salt spray corrosion resistance and its preparation method, which specifically includes, by weight:

[0074] The composition comprises 60 parts polyester resin, 7 parts curing agent, 18 parts titanium dioxide, 8 parts filler, 1.0 part acrylate leveling agent, 0.5 parts benzoin, 0.4 parts wax powder, 0.8 parts quaternized poly(4-vinylpyridine) microgel, and 5 parts dual-size microcapsules; the filler is a mixture of barium sulfate and wollastonite; the wax powder is polypropylene wax; the dual-size microcapsules are obtained by mixing microcapsules A and B, both loaded with quaternized poly(4-vinylpyridine) microgel, with a mass ratio of microcapsule A to microcapsule B of 7:3.

[0075] The polyester resin is a carboxyl functional group polyester resin, and the acid value of the carboxyl functional group polyester resin is 35 mg KOH / g; the curing agent is N,N,N′,N′-tetra(2-hydroxyethyl)hexamethylenediamide; and the acrylate leveling agent is polymethyl acrylate.

[0076] The particle size D50 of microcapsule A is 10 μm, and microcapsule A is a core-shell structured microcapsule;

[0077] The core layer of microcapsule A comprises, by weight, 100 parts of hydroxyl-terminated polydimethylsiloxane, 7 parts of 2-mercaptobenzothiazole, 2 parts of polycarbodiimide, and 2 parts of diisononyl phthalate; the number average molecular weight of the hydroxyl-terminated polydimethylsiloxane is 3000.

[0078] The particle size D50 of microcapsule B is 30 μm, and microcapsule B is a core-shell structured microcapsule;

[0079] The core layer of microcapsule B comprises, by weight, 100 parts of hydroxyl-terminated polydimethylsiloxane, 4 parts of 2-mercaptobenzothiazole, 2 parts of polycarbodiimide, and 10 parts of diisononyl phthalate.

[0080] Both microcapsules A and B have shells comprising a polyurea inner shell and a polydopamine outer shell. The polyurea inner shell is formed by reacting hexamethylene diisocyanate trimer, diethylenetriamine, ethylenediamine, dopamine hydrochloride, and cystamine dihydrochloride in an emulsion system. Based on 100 parts by weight of hydroxyl-terminated polydimethylsiloxane, the hexamethylene diisocyanate trimer comprises 14 parts by weight, diethylenetriamine comprises 6 parts by weight, ethylenediamine comprises 2 parts by weight, dopamine hydrochloride comprises 1.0 part by weight, and cystamine dihydrochloride comprises 1.0 part by weight.

[0081] The quaternized poly(4-vinylpyridine) microgel was obtained by reacting poly(4-vinylpyridine), 1,4-dibromobutane, benzyl bromide, ethanol and methyl ethyl ketone, followed by precipitation, drying and pulverization; based on 100 parts by mass of poly(4-vinylpyridine), 2 parts by mass of 1,4-dibromobutane, 10 parts by mass of benzyl bromide, 600 parts by mass of ethanol and 500 parts by mass of methyl ethyl ketone.

[0082] The quaternized poly(4-vinylpyridine) microgel has a semi-interpenetrating polymer network structure or a graft copolymer structure; its preparation raw materials also include dodecyl bromide, 2-(dimethylamino)ethyl methacrylate and ethylene glycol dimethacrylate; based on 100 parts by weight of poly(4-vinylpyridine), dodecyl bromide is 2.5 parts by weight, 2-(dimethylamino)ethyl methacrylate is 5 parts by weight, and ethylene glycol dimethacrylate is 1.5 parts by weight.

[0083] The total loading of the quaternized poly(4-vinylpyridine) microgel is 12 parts by weight based on the dry solid content of the dual-size microcapsules; and the outermost layer of the dual-size microcapsules is a hydrolytic condensation layer of 3-glycidoxypropyltrimethoxysilane, which forms a covalent bond with the polydopamine shell through a hydrolytic condensation reaction; based on 100 parts by weight of the dual-size microcapsule dry powder, 3-glycidoxypropyltrimethoxysilane is 1.0 parts by weight.

[0084] The preparation method includes the following steps:

[0085] (1) Preparation of quaternized poly(4-vinylpyridine) microgels: Poly(4-vinylpyridine) was dissolved in a mixed solvent of ethanol and methyl ethyl ketone by stirring. 1,4-dibromobutane and benzyl bromide were added to carry out a quaternization reaction. Dodecyl bromide was added to the reaction system. 2-(dimethylamino)ethyl methacrylate and ethylene glycol dimethacrylate were added to the reaction system, and 2,2′-azobisisobutyronitrile was added as an initiator to allow 2-(dimethylamino)ethyl methacrylate to undergo in-situ free radical polymerization and crosslinking in the presence of ethylene glycol dimethacrylate. After the reaction, the reaction system was subjected to precipitation separation, washing, drying and pulverization to obtain quaternized poly(4-vinylpyridine) microgel powder.

[0086] (2) Preparation of dual-size microcapsules:

[0087] (a) Hydroxyl-terminated polydimethylsiloxane, 2-mercaptobenzothiazole, polycarbodiimide and diisononyl phthalate were mixed to obtain an oil phase; polyvinyl alcohol was added to deionized water and stirred to dissolve to obtain an aqueous phase; the oil phase was added to the aqueous phase and emulsified under two emulsification conditions to obtain the corresponding core droplet A emulsion system and core droplet B emulsion system.

[0088] (b) Hexamethylene diisocyanate trimer was added to the core droplet A emulsion system and the core droplet B emulsion system, respectively, and diethylenetriamine and ethylenediamine were added to react and form a polyurea inner shell; during the formation of the polyurea inner shell, dopamine hydrochloride and cystamine dihydrochloride were added to participate in the reaction; then the pH of the system was adjusted and dopamine hydrochloride was added to form a polydopamine outer shell on the surface of the microcapsule, and microcapsule A slurry and microcapsule B slurry were obtained respectively.

[0089] (c) After the polydopamine shell is formed, 3-glycidoxypropyltrimethoxysilane is added to microcapsule A slurry and microcapsule B slurry respectively, so that it undergoes hydrolysis and condensation on the surface of the microcapsule to form a silane layer; then, the quaternized poly(4-vinylpyridine) microgel obtained in step (1) is added to load it on the surface of the microcapsule; the obtained microcapsules are subjected to solid-liquid separation, water washing, drying and sieving to obtain microcapsule A dry powder and microcapsule B dry powder respectively, and the microcapsule A dry powder and microcapsule B dry powder are mixed to obtain dual-size microcapsules;

[0090] (3) Polyester resin, curing agent, titanium dioxide, filler, acrylate leveling agent, benzoin, wax powder and quaternized poly(4-vinylpyridine) microgel obtained in step (1) are premixed, the premix is ​​melt-extruded into sheets, cooled and crushed, and the crushed material is pulverized and classified to obtain base powder.

[0091] (4) Add the dual-size microcapsules obtained in step (2) to the base powder obtained in step (3) and cold mix to obtain polyester resin powder coating.

[0092] In step (2), the emulsification speed of nucleus droplet A is 5500 rpm and the emulsification time is 12 min, while the emulsification speed of nucleus droplet B is 1700 rpm and the emulsification time is 8 min. The reaction temperature for forming the polyurea inner shell in step (2) is 50℃. The pH of the microcapsule system when forming the polydopamine outer shell in step (2) is 8.5.

[0093] Example 4

[0094] This embodiment provides a polyester resin powder coating with high salt spray corrosion resistance and its preparation method, which specifically includes, by weight:

[0095] The composition comprises 65 parts polyester resin, 6 parts curing agent, 12 parts titanium dioxide, 10 parts filler, 1.1 parts acrylate leveling agent, 0.6 parts benzoin, 0.3 parts wax powder, 0.6 parts quaternized poly(4-vinylpyridine) microgel, and 6 parts dual-size microcapsules; the filler is wollastonite; the wax powder is polyethylene wax and polytetrafluoroethylene wax; the dual-size microcapsules are obtained by mixing microcapsules A and B, both loaded with quaternized poly(4-vinylpyridine) microgel, with a mass ratio of microcapsule A to microcapsule B of 7.5:2.5.

[0096] The polyester resin is a carboxyl functional group polyester resin, and the acid value of the carboxyl functional group polyester resin is 40 mg KOH / g; the curing agent is triglycidyl isocyanurate; the acrylate leveling agent is polybutyl acrylate.

[0097] The particle size D50 of microcapsule A is 8 μm, and microcapsule A is a core-shell structured microcapsule;

[0098] The core layer of microcapsule A comprises, by weight, 100 parts of hydroxyl-terminated polydimethylsiloxane, 9 parts of 2-mercaptobenzothiazole, 2 parts of polycarbodiimide, and 5 parts of diisononyl phthalate; the number average molecular weight of the hydroxyl-terminated polydimethylsiloxane is 4000.

[0099] The particle size D50 of microcapsule B is 25 μm, and microcapsule B is a core-shell structured microcapsule;

[0100] The core layer of microcapsule B comprises, by weight, 100 parts of hydroxyl-terminated polydimethylsiloxane, 5 parts of 2-mercaptobenzothiazole, 3 parts of polycarbodiimide, and 13 parts of diisononyl phthalate.

[0101] Both microcapsules A and B have shells comprising a polyurea inner shell and a polydopamine outer shell. The polyurea inner shell is formed by reacting hexamethylene diisocyanate trimer, diethylenetriamine, ethylenediamine, dopamine hydrochloride, and cystamine dihydrochloride in an emulsion system. Based on 100 parts by weight of hydroxyl-terminated polydimethylsiloxane, the hexamethylene diisocyanate trimer comprises 16 parts by weight, diethylenetriamine comprises 5 parts by weight, ethylenediamine comprises 2.5 parts by weight, dopamine hydrochloride comprises 0.8 parts by weight, and cystamine dihydrochloride comprises 1.5 parts by weight.

[0102] The quaternized poly(4-vinylpyridine) microgel was obtained by reacting poly(4-vinylpyridine), 1,4-dibromobutane, benzyl bromide, ethanol and methyl ethyl ketone, followed by precipitation, drying and pulverization; based on 100 parts by weight of poly(4-vinylpyridine), 1,4-dibromobutane was 2.5 parts by weight, benzyl bromide was 12 parts by weight, ethanol was 650 parts by weight and methyl ethyl ketone was 480 parts by weight.

[0103] The quaternized poly(4-vinylpyridine) microgel has a semi-interpenetrating polymer network structure or a graft copolymer structure; its preparation raw materials also include dodecyl bromide, 2-(dimethylamino)ethyl methacrylate and ethylene glycol dimethacrylate; based on 100 parts by weight of poly(4-vinylpyridine), dodecyl bromide is 3.5 parts by weight, 2-(dimethylamino)ethyl methacrylate is 8 parts by weight, and ethylene glycol dimethacrylate is 2.5 parts by weight.

[0104] The total loading of the quaternized poly(4-vinylpyridine) microgel is 15 parts by weight based on the dry solid content of the dual-size microcapsules; and the outermost layer of the dual-size microcapsules is a hydrolytic condensation layer of 3-glycidoxypropyltrimethoxysilane, which forms a covalent bond with the polydopamine shell through a hydrolytic condensation reaction; based on 100 parts by weight of the dual-size microcapsule dry powder, 3-glycidoxypropyltrimethoxysilane is 1.5 parts by weight.

[0105] The preparation method includes the following steps:

[0106] (1) Preparation of quaternized poly(4-vinylpyridine) microgels: Poly(4-vinylpyridine) was dissolved in a mixed solvent of ethanol and methyl ethyl ketone by stirring. 1,4-dibromobutane and benzyl bromide were added to carry out a quaternization reaction. Dodecyl bromide was added to the reaction system. 2-(dimethylamino)ethyl methacrylate and ethylene glycol dimethacrylate were added to the reaction system, and 2,2′-azobisisobutyronitrile was added as an initiator to allow 2-(dimethylamino)ethyl methacrylate to undergo in-situ free radical polymerization and crosslinking in the presence of ethylene glycol dimethacrylate. After the reaction, the reaction system was subjected to precipitation separation, washing, drying and pulverization to obtain quaternized poly(4-vinylpyridine) microgel powder.

[0107] (2) Preparation of dual-size microcapsules:

[0108] (a) Hydroxyl-terminated polydimethylsiloxane, 2-mercaptobenzothiazole, polycarbodiimide and diisononyl phthalate were mixed to obtain an oil phase; polyvinyl alcohol was added to deionized water and stirred to dissolve to obtain an aqueous phase; the oil phase was added to the aqueous phase and emulsified under two emulsification conditions to obtain the corresponding core droplet A emulsion system and core droplet B emulsion system.

[0109] (b) Hexamethylene diisocyanate trimer was added to the core droplet A emulsion system and the core droplet B emulsion system, respectively, and diethylenetriamine and ethylenediamine were added to react and form a polyurea inner shell; during the formation of the polyurea inner shell, dopamine hydrochloride and cystamine dihydrochloride were added to participate in the reaction; then the pH of the system was adjusted and dopamine hydrochloride was added to form a polydopamine outer shell on the surface of the microcapsule, and microcapsule A slurry and microcapsule B slurry were obtained respectively.

[0110] (c) After the polydopamine shell is formed, 3-glycidoxypropyltrimethoxysilane is added to microcapsule A slurry and microcapsule B slurry respectively, so that it undergoes hydrolysis and condensation on the surface of the microcapsule to form a silane layer; then, the quaternized poly(4-vinylpyridine) microgel obtained in step (1) is added to load it on the surface of the microcapsule; the obtained microcapsules are subjected to solid-liquid separation, water washing, drying and sieving to obtain microcapsule A dry powder and microcapsule B dry powder respectively, and the microcapsule A dry powder and microcapsule B dry powder are mixed to obtain dual-size microcapsules;

[0111] (3) Polyester resin, curing agent, titanium dioxide, filler, acrylate leveling agent, benzoin, wax powder and quaternized poly(4-vinylpyridine) microgel obtained in step (1) are premixed, the premix is ​​melt-extruded into sheets, cooled and crushed, and the crushed material is pulverized and classified to obtain base powder.

[0112] (4) Add the dual-size microcapsules obtained in step (2) to the base powder obtained in step (3) and cold mix to obtain polyester resin powder coating.

[0113] In step (2), the emulsification speed of nucleus droplet A is 6000 rpm and the emulsification time is 13 min, while the emulsification speed of nucleus droplet B is 2000 rpm and the emulsification time is 9 min. The reaction temperature for forming the polyurea inner shell in step (2) is 48℃. The pH of the microcapsule system when forming the polydopamine outer shell in step (2) is 8.2.

[0114] Comparative Example 1

[0115] This embodiment provides a polyester resin powder coating with high salt spray corrosion resistance and its preparation method. The difference between this embodiment and Example 1 is that the mass fraction of the dual-size microcapsules is 0, while the other process parameters and operating conditions are exactly the same as in Example 1.

[0116] Comparative Example 2

[0117] This embodiment provides a polyester resin powder coating with high salt spray corrosion resistance and its preparation method. The difference between this embodiment and Example 1 is that the mass fraction of quaternized poly(4-vinylpyridine) microgel in steps (2) and (3) is 0, while other process parameters and operating conditions are exactly the same as in Example 1.

[0118] Comparative Example 3

[0119] This embodiment provides a polyester resin powder coating with high salt spray corrosion resistance and its preparation method. The difference between this embodiment and Embodiment 1 is that microcapsule B dry powder is removed from the dual-size microcapsules, and only microcapsule A dry powder is contained. Other process parameters and operating conditions are exactly the same as in Embodiment 1.

[0120] Performance testing:

[0121] The neutral salt spray test method is GB / T 10125, and the evaluation index is whether the coating blister / peel after 1000h of salt spray test;

[0122] The electrochemical impedance spectroscopy test method is ISO 16773-2:2016, and the evaluation index is the low-frequency impedance modulus.

[0123] Scribing-salt spray test: The scribing method refers to ISO 17872:2019. An artificial defect is prepared on the coating surface that penetrates the coating until the carbon steel substrate is exposed. Then the scribed sample is tested according to GB / T 10125. The evaluation index is the corrosion spread width at the scribing point. The average value is taken after measuring on both sides of the scribing point according to the caliber of "scibing edge to failure boundary".

[0124] The test results are shown in Table 1.

[0125] Table 1. Test results of polyester resin powder coatings in Examples 1-4 and Comparative Examples 1-3

[0126]

[0127] As shown in Table 1, compared to Example 1, Comparative Example 1 exhibited decreased salt spray resistance, decreased low-frequency impedance modulus, and increased corrosion spread width at the scribing point; Comparative Example 2 also showed decreased salt spray resistance, decreased low-frequency impedance modulus, and increased corrosion spread width at the scribing point; while Comparative Example 1 showed no change in salt spray resistance, decreased low-frequency impedance modulus, and increased corrosion spread width at the scribing point. This is because Comparative Example 1 did not include dual-size microcapsules, causing salt spray water to remain in the interfacial micropores. Chloride ions migrated along the coating / steel interface and induced foaming, leading to increased corrosion spread and decreased impedance. In Comparative Example 2, after removing the quaternized poly(4-vinylpyridine) microgel, the number of fixed cationic pyridine sites in the coating decreased, weakening chloride ion adsorption and charge shielding effects. Salt spray water was more likely to form continuous ion channels, resulting in decreased low-frequency impedance and foaming. Comparative Example 3 retains only microcapsule A. The small particle size makes it easier to disperse into the micropores and release 2-mercaptobenzothiazole earlier. Under the surface salt spray, it is difficult to form large-area bubbling or peeling. However, the content of diisononyl phthalate in the core layer of microcapsule A is low, and the sealing of the scribing defects is insufficient, resulting in an increase in the corrosion spread width and a decrease in low-frequency impedance.

[0128] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A polyester resin powder coating with high resistance to salt spray corrosion, characterized in that, The product comprises, by weight, 55-70 parts polyester resin, 4-10 parts curing agent, 10-18 parts titanium dioxide, 8-15 parts filler, 0.8-1.3 parts acrylate leveling agent, 0.3-0.8 parts benzoin, 0.2-0.6 parts wax powder, 0.3-1.2 parts quaternized poly(4-vinylpyridine) microgel, and 3-7 parts dual-size microcapsules; the filler is barium sulfate and / or wollastonite; the wax powder is polyethylene wax, polypropylene wax, and / or polytetrafluoroethylene wax; the dual-size microcapsules are obtained by mixing microcapsules A and B, both loaded with quaternized poly(4-vinylpyridine) microgel.

2. The polyester resin powder coating with high salt spray corrosion resistance according to claim 1, characterized in that, The polyester resin is a carboxyl-functionalized polyester resin with an acid value of 25-45 mg KOH / g; the curing agent is N,N,N′,N′-tetra(2-hydroxyethyl)hexamethylenediamide and / or triglycidyl isocyanurate; the acrylate leveling agent is polybutyl acrylate, poly-2-ethylhexyl acrylate and / or polymethyl acrylate.

3. The polyester resin powder coating with high salt spray corrosion resistance according to claim 1, characterized in that, The mass ratio of microcapsule A to microcapsule B is (6-8):(2-4).

4. The polyester resin powder coating with high salt spray corrosion resistance according to claim 3, characterized in that, The particle size D50 of microcapsule A is 6-15 μm, and microcapsule A is a core-shell structured microcapsule; The core layer of microcapsule A comprises, by weight, 100 parts of hydroxyl-terminated polydimethylsiloxane, 6-10 parts of 2-mercaptobenzothiazole, 1-3 parts of polycarbodiimide, and 0-6 parts of diisononyl phthalate; wherein the number average molecular weight of the hydroxyl-terminated polydimethylsiloxane is 1000-6000.

5. The polyester resin powder coating with high salt spray corrosion resistance according to claim 4, characterized in that, The particle size D50 of microcapsule B is 20-40 μm, and microcapsule B is a core-shell structured microcapsule; The core layer of microcapsule B comprises, by weight, 100 parts of hydroxyl-terminated polydimethylsiloxane, 3-6 parts of 2-mercaptobenzothiazole, 1-3 parts of polycarbodiimide, and 8-15 parts of diisononyl phthalate.

6. The polyester resin powder coating with high salt spray corrosion resistance according to claim 5, characterized in that, Both microcapsules A and B have shells comprising a polyurea inner shell and a polydopamine outer shell; the polyurea inner shell comprises hexamethylene diisocyanate trimer, diethylenetriamine, ethylenediamine, dopamine hydrochloride, and cystamine dihydrochloride; based on 100 parts by weight of hydroxyl-terminated polydimethylsiloxane, the hexamethylene diisocyanate trimer comprises 10-18 parts by weight, the diethylenetriamine comprises 4-8 parts by weight, the ethylenediamine comprises 1-3 parts by weight, the dopamine hydrochloride comprises 0.3-1.5 parts by weight, and the cystamine dihydrochloride comprises 0.2-2 parts by weight.

7. The polyester resin powder coating with high salt spray corrosion resistance according to claim 1, characterized in that, The quaternized poly(4-vinylpyridine) microgel is obtained by reacting poly(4-vinylpyridine), 1,4-dibromobutane, benzyl bromide, ethanol, and methyl ethyl ketone, followed by precipitation, drying, and pulverization. The raw materials also include dodecyl bromide, 2-(dimethylamino)ethyl methacrylate, 2,2′-azobisisobutyronitrile, and ethylene glycol dimethacrylate. Based on 100 parts by weight of poly(4-vinylpyridine), 1,4-dibromobutane comprises 1-3 parts by weight, benzyl bromide 6-15 parts by weight, ethanol 540-780 parts by weight, methyl ethyl ketone 360-520 parts by weight, dodecyl bromide 1-4 parts by weight, 2-(dimethylamino)ethyl methacrylate 1-10 parts by weight, 2,2′-azobisisobutyronitrile 0.2 parts by weight, and ethylene glycol dimethacrylate 0.2-3 parts by weight.

8. The polyester resin powder coating with high salt spray corrosion resistance according to claim 1, characterized in that, The total loading of the quaternized poly(4-vinylpyridine) microgel is 5-20 parts by weight based on the dry solid content of the dual-size microcapsules; the outermost layer of the dual-size microcapsules is a hydrolytic condensation layer of 3-glycidoxypropyltrimethoxysilane, and the amount of 3-glycidoxypropyltrimethoxysilane is 0.2-2.0 parts by weight based on 100 parts by weight of the dry powder of the dual-size microcapsules.

9. A method for preparing a polyester resin powder coating with high salt spray corrosion resistance as described in any one of claims 1-8, characterized in that, Includes the following steps: (1) Poly(4-vinylpyridine) was dissolved in a mixed solvent of ethanol and methyl ethyl ketone by stirring. 1,4-dibromobutane and benzyl bromide were added to carry out a quaternization reaction. Dodecyl bromide was added to the reaction system. 2-(dimethylamino)ethyl methacrylate and ethylene glycol dimethacrylate were added to the reaction system, and 2,2′-azobisisobutyronitrile was added as an initiator to allow 2-(dimethylamino)ethyl methacrylate to undergo in-situ free radical polymerization and crosslinking in the presence of ethylene glycol dimethacrylate. After the reaction was completed, the reaction system was precipitated, washed, dried and pulverized to obtain quaternized poly(4-vinylpyridine) microgels. (2) Preparation of dual-size microcapsules, wherein the preparation steps of the dual-size microcapsules include: (a) Hydroxyl-terminated polydimethylsiloxane, 2-mercaptobenzothiazole, polycarbodiimide and diisononyl phthalate were mixed to obtain an oil phase; polyvinyl alcohol was added to deionized water and stirred to dissolve to obtain an aqueous phase; the oil phase was added to the aqueous phase and emulsified under two emulsification conditions to obtain the corresponding core droplet A emulsion system and core droplet B emulsion system. (b) Hexamethylene diisocyanate trimer was added to the core droplet A emulsion system and the core droplet B emulsion system, respectively, and diethylenetriamine and ethylenediamine were added to react and form a polyurea inner shell; during the formation of the polyurea inner shell, dopamine hydrochloride and cystamine dihydrochloride were added to participate in the reaction; then the pH of the system was adjusted and dopamine hydrochloride was added to form a polydopamine outer shell on the surface of the microcapsule, and microcapsule A slurry and microcapsule B slurry were obtained respectively. (c) After the polydopamine shell is formed, 3-glycidoxypropyltrimethoxysilane is added to microcapsule A slurry and microcapsule B slurry respectively, so that it undergoes hydrolysis and condensation on the surface of the microcapsule to form a silane layer; then, the quaternized poly(4-vinylpyridine) microgel obtained in step (1) is added to load it on the surface of the microcapsule; the obtained microcapsules are subjected to solid-liquid separation, water washing, drying and sieving to obtain microcapsule A dry powder and microcapsule B dry powder respectively, and the microcapsule A dry powder and microcapsule B dry powder are mixed to obtain dual-size microcapsules; (3) Polyester resin, curing agent, titanium dioxide, filler, acrylate leveling agent, benzoin, wax powder and quaternized poly(4-vinylpyridine) microgel obtained in step (1) are premixed, the premix is ​​melt-extruded into sheets, cooled and crushed, and the crushed material is pulverized and classified to obtain base powder. (4) Add the dual-size microcapsules obtained in step (2) to the base powder obtained in step (3) for cold mixing to obtain polyester resin powder coating.

10. The method for preparing a polyester resin powder coating with high salt spray corrosion resistance according to claim 9, characterized in that, In step (2), the emulsification speed of nucleus droplet A is 4500-6500 rpm and the emulsification time is 10-15 min, while the emulsification speed of nucleus droplet B is 1200-2200 rpm and the emulsification time is 6-10 min. The reaction temperature for forming the polyurea inner shell in step (2) is 45-55℃. The pH of the microcapsule system when forming the polydopamine outer shell in step (2) is 8-9.

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