Preparation method of super-weather-resistant powder coating for aluminum profile

Abstract

The preparation method of the super weather-resistant powder coating for aluminum profiles belongs to the technical field of powder coating, and comprises the following steps: reacting isophorone diisocyanate with 1,2,2,6,6-pentamethyl-4-piperidinol to obtain a hindered amine half-addition product; dissolving a hydroxyl-terminated hyperbranched polyester in butanone, and then adding the addition product, C4C8 perfluoroalkyl isocyanate and a silane ester to obtain a fluorine-containing silicon hyperbranched modifier after removing the solvent by ring-opening of hexahydrophthalic anhydride; uniformly mixing 28 parts of the modifier, 5565 parts of a carboxyl-terminated super weather-resistant polyester resin, 37 parts of a curing agent, 2030 parts of pigments and fillers, 0.8-1.5 parts of a leveling agent and 0.3-0.8 parts of a degassing agent, and then performing melting extrusion, tabletting and crushing to obtain the super weather-resistant powder coating for aluminum profiles; and the powder coating for aluminum profiles has extremely excellent outdoor super weather-resistant performance.

Description

Technical Field

[0001] This invention relates to the field of powder coatings, specifically to a method for preparing ultra-weather-resistant powder coatings for aluminum profiles. Background Technology

[0002] Powder coatings for aluminum profiles are a widely used surface protection and decorative material in fields such as building curtain walls. These coatings possess basic cross-linking networks and physical and mechanical properties, but from the perspective of practical applications of traditional aluminum profile coatings, there are still many shortcomings when used as outdoor protective materials. Under complex climatic conditions such as high UV exposure outdoors, traditional coatings generally suffer from significant technical problems such as severe degradation of weather resistance and loss of adhesion. In addition, conventionally added small molecule light stabilizers or leveling agents are prone to migration and volatilization during long-term use, leading to rapid failure of the coating's protective performance.

[0003] To address the problems of traditional powder coatings, modification through molecular-level spatial configuration design is one of the most effective ways to compensate for defects in polymer coatings. Coating modification mainly involves two methods: physical blending and chemical structure modification. Simple physical blending cannot overcome the inherent limitations of additive migration, while chemical structure modification can construct hyperbranched multifunctional macromolecular modifiers by covalently grafting perfluoroalkyl segments, triethoxysilanes, and hindered amine functional groups onto a hyperbranched polyester backbone. This method utilizes the viscosity-reducing effect of hyperbranched macromolecules to drive the spontaneous enrichment and stratification of low surface energy segments towards the air interface, forming strong aluminosilicate inorganic covalent bonds at the substrate interface. The modification effect is significant and overcomes the technical bottleneck of easy precipitation.

[0004] Currently, the common method for preparing such high-performance modified powder coatings is to premix the base polyester resin, curing agent, macromolecular modifier and pigments and fillers evenly, and then carry out processes such as melt blending and extrusion, tableting and cooling, and crushing and sieving. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing ultra-weather-resistant powder coatings for aluminum profiles, so as to solve the problems mentioned in the background art.

[0006] The technical solution of the present invention includes: reacting isophorone diisocyanate with 1,2,2,6,6-pentamethyl-4-piperidinol in an anhydrous solvent under the protection of anhydrous inert gas to prepare a hindered amine light stabilizer semi-adduct containing isocyanate groups;

[0007] Hydroxyl-terminated hyperbranched polyester was dehydrated under vacuum and dissolved in anhydrous butanone. An organotin catalyst was added, and C4-C8 perfluoroalkyl isocyanate, 3-isocyanate-propyltriethoxysilane and the hindered amine light stabilizer semi-adduct containing isocyanate groups were added dropwise under stirring to carry out urethane esterification reaction.

[0008] Hexahydrophthalic anhydride was then added, and the mixture was heated under the action of a catalyst to carry out a ring-opening half-esterification reaction. After the reaction was completed, the solvent was removed by vacuum distillation to obtain a hyperbranched multifunctional macromolecular modifier containing fluorinated silicon and hindered amine with terminal carboxyl groups.

[0009] The carboxyl-terminated ultra-weather-resistant polyester resin, curing agent, hyperbranched multifunctional macromolecular modifier of carboxyl-terminated fluorinated silicon and hindered amine, pigments, fillers, leveling agent and degassing agent are premixed evenly.

[0010] The premixed material is melt-blended and extruded, then pressed, cooled, crushed and sieved to obtain an ultra-weather-resistant powder coating for aluminum profiles.

[0011] Of which, by weight, the end-carboxyl ultra-weather-resistant polyester resin is 55-65 parts, the curing agent is 3-7 parts, the end-carboxyl fluorinated silicon and hindered amine hyperbranched multifunctional macromolecular modifier is 2-8 parts, the pigments and fillers are 20-30 parts, the leveling agent is 0.8-1.5 parts, and the degassing agent is 0.3-0.8 parts.

[0012] Preferably, the reaction of isophorone diisocyanate with 1,2,2,6,6-pentamethyl-4-piperidinol in an anhydrous solvent has a molar ratio of isophorone diisocyanate to 1,2,2,6,6-pentamethyl-4-piperidinol of 1:1.

[0013] The anhydrous solvent is anhydrous dichloromethane;

[0014] The reaction was carried out by slow dropwise addition under an ice-water bath, followed by reaction at room temperature for 3–5 hours.

[0015] Preferably, the hydroxyl-terminated hyperbranched polyester is dehydrated under vacuum at 120°C for 2 hours.

[0016] The organotin catalyst is dibutyltin dilaurate.

[0017] Preferably, the urethane esterification reaction is carried out at a temperature of 50°C to 70°C until the -NCO characteristic peak at 2270 cm⁻¹ in the infrared spectrum completely disappears.

[0018] The total molar amount of the C4-C8 perfluoroalkyl isocyanate, 3-isocyanate-propyltriethoxysilane, and the hindered amine light stabilizer semi-addition compound containing isocyanate groups is 30% to 50% of the total initial molar amount of hydroxyl groups in the hydroxyl-terminated hyperbranched polyester.

[0019] Preferably, the ring-opening semi-esterification reaction is carried out by reflux at 100℃~120℃ for 3~5 hours.

[0020] Preferably, the curing agent is triglycidyl isocyanurate or β-hydroxyalkylamide;

[0021] The pigment and filler are a mixture of rutile titanium dioxide and precipitated barium sulfate.

[0022] Preferably, the melt blending extrusion is carried out in a twin-screw extruder at an extrusion temperature of 100°C to 115°C.

[0023] Preferably, the crushing and sieving is performed using a micro pulverizer and passing the pulverizer through a 180-200 mesh sieve.

[0024] This invention provides an improved method for preparing ultra-weather-resistant powder coatings for aluminum profiles, which, compared with the prior art, has the following improvements and advantages:

[0025] 1. This invention introduces a hyperbranched multifunctional macromolecular modifier containing carboxyl-terminated fluorinated silicon and hindered amine into a carboxyl-terminated ultra-weather-resistant polyester resin system; by combining the special structure of hyperbranched polyester with the characteristics of fluorine and silicon elements in perfluoroalkyl isocyanate and isocyanate-based propyltriethoxysilane, it endows aluminum profile powder coatings with extremely excellent outdoor ultra-weather-resistant performance.

[0026] 2. In this invention, isophorone diisocyanate is first reacted with 1,2,2,6,6-pentamethyl-4-piperidinol to form a semi-addition compound, which is then chemically bonded into the hyperbranched polyester backbone through a carbamate reaction. This design of macromolecularizing the hindered amine light stabilizer effectively avoids the defects of easy volatilization, migration or precipitation of light stabilizers in traditional physical blending, and achieves a long-lasting anti-aging effect.

[0027] 3. After undergoing ring-opening semi-esterification with hexahydrophthalic anhydride, hyperbranched polyester carries a large number of terminal carboxyl groups, which can react efficiently with terminal carboxyl ultra-weather-resistant polyester resin and specific curing agents in the system during curing. This design not only ensures the high compatibility between the modifier and the matrix resin, but also constructs a high-density cross-linking network, improving the comprehensive physical and mechanical properties of the coating film.

[0028] 4. The preparation method of the modifier is rigorous, employing anhydrous inert gas protection and vacuum dehydration pretreatment, and controlling a specific reaction temperature under the action of an organotin catalyst to ensure that multifunctional groups can be grafted onto the hyperbranched framework in an orderly and efficient manner. This not only ensures the smooth progress of the reaction, but also avoids the generation of impurities and unnecessary side reactions.

[0029] 5. The formula scientifically combines rutile titanium dioxide and precipitated barium sulfate as pigments and fillers, and is supplemented with leveling agents and degassing agents; combined with specific twin-screw extrusion temperatures and strict micro-grinding and sieving processes, it ensures uniform dispersion of multi-component materials during melt blending, and the final powder coating film is smooth, has strong hiding power and is free of bubble defects. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0031] Example 1:

[0032] A method for preparing ultra-weather-resistant powder coatings for aluminum profiles includes:

[0033] Under anhydrous inert gas protection, isophorone diisocyanate was reacted with 1,2,2,6,6-pentamethyl-4-piperidinol in an anhydrous solvent to prepare a hindered amine light stabilizer semi-adduct containing isocyanate groups; hydroxyl-terminated hyperbranched polyester was dehydrated under vacuum and dissolved in anhydrous butanone, an organotin catalyst was added, and perfluorobutyl isocyanate, 3-isocyanopropyltriethoxysilane, and the hindered amine light stabilizer semi-adduct containing isocyanate groups were added dropwise under stirring to carry out a carbamate reaction;

[0034] Subsequently, hexahydrophthalic anhydride was added, and the mixture was heated under the action of a catalyst to carry out a ring-opening half-esterification reaction. After the reaction was completed, most of the solvent was removed by vacuum distillation. The concentrated liquid was added dropwise to an excess of ice-cold n-hexane for precipitation. After filtration, the filter cake was washed multiple times with n-hexane and dried at constant weight in a vacuum drying oven to obtain a hyperbranched multifunctional macromolecular modifier with carboxyl-terminated fluorinated silicon and hindered amine. The carboxyl-terminated ultra-weather-resistant polyester resin, curing agent, hyperbranched multifunctional macromolecular modifier with carboxyl-terminated fluorinated silicon and hindered amine, pigments, fillers, leveling agent and degassing agent were premixed evenly. The premixed material was melt-blended and extruded, and after tableting, cooling, pulverizing and sieving, an ultra-weather-resistant powder coating for aluminum profiles was obtained.

[0035] The composition, by weight, includes 55 parts of carboxyl-terminated ultra-weather-resistant polyester resin, 3 parts of curing agent, 2 parts of hyperbranched multifunctional macromolecular modifier containing carboxyl-terminated fluorinated silicon and hindered amine, 20 parts of pigments and fillers, 0.8 parts of leveling agent, and 0.3 parts of degassing agent. Isophorone diisocyanate and 1,2,2,6,6-pentamethyl-4-piperidinol are reacted in an anhydrous solvent at a molar ratio of 1:1. Anhydrous dichloromethane is used as the anhydrous solvent. The reaction is carried out by slow dropwise addition under an ice-water bath, followed by a reaction at room temperature for 3 hours. The hydroxyl-terminated hyperbranched polyester is dehydrated under vacuum at 120°C for 2 hours. The organotin catalyst is dibutyltin dilaurate.

[0036] The carbamate reaction was carried out at 50°C until the characteristic -NCO peak at 2270 cm⁻¹ in the infrared spectrum completely disappeared. The total molar amount of the semi-addition product of perfluorobutyl isocyanate, 3-isocyanopropyltriethoxysilane, and hindered amine light stabilizer containing isocyanate groups was 30% of the total molar amount of initial hydroxyl groups in the hydroxyl-terminated hyperbranched polyester. The ring-opening semi-esterification reaction was carried out by reflux at 100°C for 3 hours. The curing agent was triglycidyl isocyanurate. The pigments and fillers were a mixture of rutile titanium dioxide and precipitated barium sulfate. The melt blending extrusion was carried out in a twin-screw extruder at 100°C. The product was pulverized and sieved using a micro-pulverizer and passed through an 180-mesh sieve.

[0037] This embodiment provides a method for preparing an ultra-weather-resistant powder coating for aluminum profiles, aiming to solve the problems of weather resistance degradation and adhesion loss of traditional aluminum profile coatings under high ultraviolet exposure through molecular-level spatial configuration design; the reaction of isophorone diisocyanate with 1,2,2,6,6-pentamethyl-4-piperidinol in anhydrous dichloromethane constructs a hindered amine light stabilizer semi-addition containing isocyanate groups, which serves as an active precursor for subsequent grafting reactions, and its strict 1:1 stoichiometric ratio ensures the retention of single-terminal isocyanate groups;

[0038] Specifically, under the mild conditions of an ice-water bath, the primary isocyanate group on the aliphatic chain of the isophorone diisocyanate molecule, which has less steric hindrance and higher reactivity, preferentially undergoes an addition reaction with the hydroxyl group of 1,2,2,6,6-pentamethyl-4-piperidinol, while the secondary isocyanate group on the alicyclic ring is retained as an active site for subsequent grafting, thus avoiding cross-linking side reactions caused by double-end capping.

[0039] In this embodiment, the hydroxyl-terminated hyperbranched polyester is a commercially available product; the carboxyl-terminated ultra-weather-resistant polyester resin is a commercially available product; the operation of vacuum dehydration of the hydroxyl-terminated hyperbranched polyester at 120°C for 2 hours effectively removes trace amounts of water in the system and eliminates the side reaction of water molecules consuming isocyanate groups.

[0040] Subsequently, the dehydrated hydroxyl-terminated hyperbranched polyester was dissolved in anhydrous methyl ethyl ketone, and dibutyltin dilaurate (0.05% of the total mass of the reaction system) was added as an organotin catalyst. In the urethane esterification reaction at 50°C, perfluorobutyl isocyanate, 3-isocyanate-propyltriethoxysilane, and a hindered amine light stabilizer semi-adduct containing isocyanate groups were added dropwise at a stirring speed of 280 rpm to covalently graft them onto the hyperbranched framework. The grafting rate was controlled at 30% of the total molar amount of hydroxyl groups, and the molar ratio of perfluorobutyl isocyanate, 3-isocyanate-propyltriethoxysilane, and the hindered amine light stabilizer semi-adduct containing isocyanate groups was controlled at 1:1:1.

[0041] This low grafting ratio design retains sufficient steric hindrance, allowing the three-dimensional spherical conformation of the hyperbranched macromolecules to be maintained. Subsequently, hexahydrophthalic anhydride was added at a molar ratio of 1.05:1 to the remaining hydroxyl groups of the hyperbranched polyester, along with 0.1% N,N-dimethylbenzylamine as a catalyst. The mixture was heated to 100°C for 3 hours to undergo a ring-opening hemiesterification reaction, converting the peripheral remaining hydroxyl groups into terminal carboxyl groups. This not only endows the macromolecular modifier with chemical compatibility with the main polyester resin but also provides reaction sites for multiple chemical anchoring during subsequent curing and film formation. After the reaction, the solvent was removed by vacuum distillation at -0.085 MPa.

[0042] According to gel permeation chromatography (GPC) and titration, the weight-average molecular weight (Mw) of the prepared key intermediate, a hyperbranched multifunctional macromolecular modifier with terminal carboxyl-containing fluorinated silicon and hindered amine, is approximately 3500 g / mol, the polydispersity index (PDI) is 1.8, the acid value is 45 mg KOH / g, and the reaction yield is approximately 95%.

[0043] In the powder coating preparation stage, 55 parts of carboxyl-terminated ultra-weather-resistant polyester resin and 3 parts of triglycidyl isocyanurate curing agent constitute a basic crosslinking network. 2 parts of carboxyl-terminated fluorinated silicon and hindered amine hyperbranched multifunctional macromolecular modifier are uniformly dispersed in the system at an extrusion temperature of 100℃. The extruded material is crushed and passed through a 180-mesh sieve to obtain the finished powder. In the actual spraying and baking process of aluminum profiles for building curtain walls, the hyperbranched skeleton exhibits a melt viscosity reduction effect, which promotes the spontaneous enrichment of low surface energy C4 perfluoroalkyl segments to the air interface, thus constructing an in-situ anti-fouling and anti-UV outer surface layer.

[0044] Meanwhile, the triethoxysilane groups settle to the aluminum substrate interface and undergo alcoholysis condensation with the free hydroxyl groups on the substrate surface to form strong aluminum oxide silicon inorganic covalent bonds. This self-assembly gradient layering mechanism overcomes the technical bottleneck of easy migration and precipitation of conventional small molecule additives. This embodiment verifies the feasibility of the basic reaction kinetics and establishes the process benchmark for the low-temperature processing range.

[0045] Example 2:

[0046] A method for preparing ultra-weather-resistant powder coatings for aluminum profiles includes: adding perfluorohexyl isocyanate, 3-isocyanopropyltriethoxysilane, and a hindered amine light stabilizer semi-adduct containing isocyanate groups dropwise under stirring to carry out an urethane esterification reaction; premixing carboxyl-terminated ultra-weather-resistant polyester resin, curing agent, carboxyl-terminated fluorinated silicon and hindered amine hyperbranched multifunctional macromolecular modifier, pigments and fillers, leveling agent and degassing agent uniformly; and melt-blending and extruding the premixed material.

[0047] The composition, by weight, includes 60 parts of carboxyl-terminated ultra-weather-resistant polyester resin, 5 parts of curing agent, 5 parts of hyperbranched multifunctional macromolecular modifier containing carboxyl-terminated fluorinated silicon and hindered amine, 25 parts of pigments and fillers, 1.2 parts of leveling agent, and 0.5 parts of degassing agent; urethane esterification reaction at a reaction temperature of 60℃; the total molar amount of the semi-addition product of perfluorohexyl isocyanate, 3-isocyanate-propyltriethoxysilane and hindered amine light stabilizer containing isocyanate groups is 40% of the total molar amount of initial hydroxyl groups in the hyperbranched polyester; melt blending extrusion is carried out in a twin-screw extruder at an extrusion temperature of 110℃;

[0048] This embodiment further specifies the parameters of the urethane esterification reaction and extrusion process. The carbon chain length of the perfluoroalkyl isocyanate is increased to C6, the urethane esterification reaction temperature is increased to 60°C, and the grafting rate is increased to 40%. During this process, the molar ratio of perfluorohexyl isocyanate, 3-isocyanate-propyltriethoxysilane, and the hindered amine light stabilizer semi-adduct containing isocyanate groups is controlled at 1.2:1:0.8. This parameter combination aims to enhance the fluorocarbon segment density and steric hindrance effect of the macromolecular modifier.

[0049] The reaction temperature of 60℃ effectively overcomes the steric hindrance caused by the introduction of long-chain perfluoroalkyl groups, accelerating the reaction rate between isocyanate groups and hyperbranched polyester hydroxyl groups. In this embodiment, the terminal hydroxyl hyperbranched polyester is a commercially available product with a weight-average molecular weight of 1400 g / mol and a hydroxyl value of 470 mg KOH / g. The terminal carboxyl ultra-weather-resistant polyester resin is a commercially available product with an acid value of 32 mg KOH / g. In the ring-opening half-esterification reaction, hexahydrophthalic anhydride is added at a molar ratio of 1.1:1 to the remaining hydroxyl groups, and N,N-dimethylbenzylamine is added as a catalyst at 0.15% of the total mass of the system.

[0050] The weight-average molecular weight (Mw) of the hyperbranched multifunctional macromolecular modifier with carboxyl-terminated fluorinated silicon and hindered amine prepared in this embodiment was determined to be approximately 4200 g / mol, with an acid value of 40 mg KOH / g and a reaction yield of approximately 93%. In the coating formulation, the amount of the hyperbranched multifunctional macromolecular modifier with carboxyl-terminated fluorinated silicon and hindered amine was increased to 5 parts, combined with 60 parts of carboxyl-terminated ultra-weather-resistant polyester resin and 5 parts of curing agent, to construct a denser crosslinking network. The extrusion temperature of 110°C is within the critical threshold range where the melt viscosity of the polyester resin decreases sharply. This temperature ensures that the C6 perfluoroalkyl segments are fully extended and uniformly dispersed under the shear force field of the twin-screw extruder, avoiding excessive agglomeration of fluorinated micro-regions. After curing, the thermal hysteresis effect provided by the C6 carbon chain allows the coating to maintain excellent flexibility under a wide temperature range alternating environment. This embodiment demonstrates the compatibility with moderate grafting rate and conventional baking conditions, verifying the robustness of the formulation in conventional industrial mass production.

[0051] Example 3:

[0052] A method for preparing ultra-weather-resistant powder coatings for aluminum profiles includes: adding perfluorooctyl isocyanate dropwise under stirring; adding hexahydrophthalic anhydride; and heating under the action of a catalyst to carry out a ring-opening half-esterification reaction.

[0053] The composition, by weight, includes 65 parts of carboxyl-terminated ultra-weather-resistant polyester resin, 7 parts of curing agent, 8 parts of hyperbranched multifunctional macromolecular modifier containing carboxyl-terminated fluorinated silicon and hindered amine, 30 parts of pigments and fillers, 1.5 parts of leveling agent, and 0.8 parts of degassing agent; a ring-opening semi-esterification reaction is carried out by reflux at 120℃ for 5 hours; the mixture is then pulverized and sieved using a micro-pulverizer and passed through a 200-mesh sieve.

[0054] This embodiment verifies the extreme performance of the ring-opening half-esterification reaction and the high-concentration fluorocarbon modification system. Specifically, in the preparation of the macromolecular modifier, the terminal hydroxyl hyperbranched polyester was dissolved in anhydrous butanone after vacuum dehydration. An organotin catalyst was added, and perfluorooctyl isocyanate, 3-isocyanate-propyltriethoxysilane, and a hindered amine light stabilizer half-adduct containing isocyanate groups were added dropwise under stirring to carry out the carbamate reaction. Perfluorooctyl isocyanate with extremely low surface energy was used as the modifying monomer, and the molar ratio of perfluorooctyl isocyanate, 3-isocyanate-propyltriethoxysilane, and the hindered amine light stabilizer half-adduct containing isocyanate groups was controlled to be 1.5:1:0.5 in this reaction.

[0055] Subsequently, hexahydrophthalic anhydride was added, and the ring-opening half-esterification reaction was carried out under the action of a catalyst. After the reaction, the solvent was removed by vacuum distillation, thereby obtaining a hyperbranched multifunctional macromolecular modifier with terminal carboxyl groups containing fluorinated silicon and hindered amines. The amount of this modifier added was pushed to the upper limit threshold of 8 parts. In order to solve the problem of the conversion of the remaining hydroxyl groups under high steric hindrance, hexahydrophthalic anhydride was added at a molar ratio of hexahydrophthalic anhydride to the remaining hydroxyl groups of 1.2:1, and N,N-dimethylbenzylamine, accounting for 0.2% of the total mass of the system, was added as a catalyst. The ring-opening half-esterification reaction temperature was raised to 120°C and refluxed for 5 hours. This harsh thermodynamic condition ensured that hexahydrophthalic anhydride could fully penetrate into the core voids of the hyperbranched macromolecule and achieve deep conversion of hydroxyl groups to carboxyl groups.

[0056] The parameters of the hydroxyl-terminated hyperbranched polyester and carboxyl-terminated ultra-weather-resistant polyester resin used in this embodiment are the same as in Example 1. The weight-average molecular weight (Mw) of the prepared carboxyl-terminated fluorinated silicon and hindered amine hyperbranched multifunctional macromolecular modifier was determined to be approximately 5100 g / mol, with an acid value of 36 mg KOH / g and a reaction yield of approximately 91%. The high-conversion carboxyl groups formed a highly dense three-dimensional network structure during subsequent crosslinking with 7 parts of curing agent. Increasing the powder mesh size to 200 mesh increased the specific surface area of ​​the powder particles, giving the powder superior charge-carrying ability and deposition efficiency during electrostatic spraying.

[0057] During the baking and melting stage, the high content of C8 perfluorinated segments rapidly migrates to the coating surface under the viscosity reduction drive of the hyperbranched skeleton, constructing a fluorocarbon-like protective layer with extremely strong water and oil repellency. This embodiment endows the aluminum profile coating with the ability to resist corrosion from extreme marine climates by setting limiting parameters.

[0058] Example 4:

[0059] The carbamate reaction was carried out at a temperature of 55°C. The total molar amount of the perfluorobutyl isocyanate, 3-isocyanopropyltriethoxysilane and the hindered amine light stabilizer semi-adduct containing isocyanate groups was 35% of the total molar amount of the initial hydroxyl groups in the hydroxyl-terminated hyperbranched polyester. The ring-opening semi-esterification reaction was carried out by reflux at 105°C for 3.5 hours.

[0060] This embodiment focuses on investigating the synergistic mechanism of urethane esterification and ring-opening hemiesterification under low kinetic conditions. The urethane esterification reaction temperature of 55°C and the grafting rate of 35% were set to find a mild balance between reaction conversion and product molecular weight distribution. The low grafting rate allows the hyperbranched polyester to retain more highly active primary hydroxyl groups on its periphery, which provides a good kinetic match for the subsequent ring-opening hemiesterification reaction at 105°C for 3.5 h.

[0061] Under these conditions, the ring-opening reaction of hexahydrophthalic anhydride exhibits high regioselectivity, preferentially binding to peripheral hydroxyl groups with less steric hindrance, thereby constructing uniformly distributed carboxyl anchoring sites in situ on the surface of the macromolecular modifier. This mild synthesis strategy effectively suppresses the thermal degradation side reaction of the polyester skeleton that may be triggered by high temperature, ensuring the structural uniformity of the macromolecular modifier between batches, and providing a stable rheological basis for viscosity control of coatings during the melt leveling stage.

[0062] Example 5:

[0063] A method for preparing ultra-weather-resistant powder coatings for aluminum profiles includes: pre-mixing carboxyl-terminated ultra-weather-resistant polyester resin, curing agent, carboxyl-terminated fluorinated silicon and hindered amine hyperbranched multifunctional macromolecular modifier, pigments and fillers, leveling agent and degassing agent uniformly; and then performing melt blending extrusion on the uniformly mixed material.

[0064] The composition, by weight, includes 62 parts of carboxyl-terminated ultra-weather-resistant polyester resin, 6 parts of curing agent, 6 parts of hyperbranched multifunctional macromolecular modifier containing carboxyl-terminated fluorinated silicon and hindered amine, 28 parts of pigments and fillers, 1.4 parts of leveling agent, and 0.6 parts of degassing agent; the curing agent is β-hydroxyalkylamide; the melt blending extrusion is carried out in a twin-screw extruder at an extrusion temperature of 115℃;

[0065] This embodiment aims to verify the crosslinking compatibility and interfacial behavior of macromolecular modifiers under an environmentally friendly curing system; β-hydroxyalkylamide is used instead of traditional triglycidyl isocyanurate as a curing agent to respond to the industry trend of detoxification; the esterification and crosslinking reaction of β-hydroxyalkylamide with carboxyl-terminated polyester and macromolecular modifier will release condensation water, which requires the system to have better venting performance.

[0066] To this end, the extrusion temperature was set to 115℃, which enhanced the shearing and mixing effect of the twin-screw extruder while giving the extruded material a lower melt viscosity. Combined with the synergistic effect of 0.6 parts degassing agent and 1.4 parts leveling agent, it ensured that microbubbles escaped rapidly before the coating surface dried. The triethoxysilyl groups in the 6 parts macromolecular modifier underwent deep alcoholysis condensation with the hydroxyl groups on the aluminum substrate surface in the bottom layer of the coating. The resulting inorganic covalent network effectively resisted the inherent defect of the β-hydroxyalkylamide system being susceptible to moisture intrusion, which led to adhesion decay. This embodiment demonstrates that after introducing this hyperbranched multifunctional macromolecular modifier, even in environmentally friendly curing systems that are prone to pinholes and adhesion fluctuations, a dense and flawless coating appearance and strong interfacial anchoring force can still be achieved.

[0067] Comparative Example 1:

[0068] This comparative example provides a method for preparing polyester powder coatings for conventional aluminum profiles. The only difference from Example 2 is that the hyperbranched multifunctional macromolecular modifier with terminal carboxyl-containing fluorinated silicon and hindered amine is not added. Instead, 1.5 parts of small molecule hindered amine light stabilizer and 0.5 parts of commercial fluorocarbon leveling agent with equivalent active ingredient content are directly added during the premixing stage. The other raw material types, ratios, and extrusion and pulverization process parameters are completely consistent with those of Example 2. This comparative example aims to verify the non-obvious advantages of the macromolecular covalent grafting strategy compared to traditional physical blending in resisting additive migration and maintaining long-term weather resistance.

[0069] Comparative Example 2:

[0070] This comparative example provides a method for preparing powder coatings; the only difference from Example 2 is that, in preparing the macromolecular modifier, a conventional terminal hydroxyl linear polyester with an equivalent amount of hydroxyl content is used to replace the terminal hydroxyl hyperbranched polyester, and a linear macromolecular modifier containing carboxyl-terminated fluorinated silicon and hindered amine is synthesized; the grafting reaction conditions and coating formulation are the same as in Example 2; this comparative example aims to highlight the core synergistic effect of the unique three-dimensional spherical conformation of the hyperbranched polyester skeleton in breaking molecular chain entanglement, reducing melt viscosity, and driving the self-assembly and layering of fluorinated silicon groups.

[0071] Comparative Example 3:

[0072] To verify the significance of the range limits of the core formulation parameters, this invention also independently conducted supplementary comparative experiments with grafting rates deviating from specific ranges. The only difference between this supplementary comparative experiment and Example 2 was that the grafting rate of the urethane esterification reaction was increased to 60%. The test results showed that the ultra-high grafting rate led to a sharp increase in the steric hindrance of the hyperbranched skeleton, which severely hindered the subsequent penetration of hexahydrophthalic anhydride and the ring-opening half-esterification reaction, resulting in a significant decrease in the acid value of the product to 18 mg KOH / g. During coating curing, due to insufficient cross-linking anchoring points, its adhesion deteriorated to level 2 after boiling in water, and the gloss retention rate dropped to 71.2% after 3000 hours.

[0073] Furthermore, excessive steric hindrance disrupts the three-dimensional spherical conformation of hyperbranched macromolecules, hindering the effective enrichment of low surface energy segments to the air interface, resulting in a significant decrease in the enrichment rate of surface fluorine compared to the normal grafting rate system; this confirms the critical necessity of strictly controlling the grafting rate within the range of 30% to 50% to balance the spatial conformation and crosslinking density.

[0074] Verification experiment:

[0075] To comprehensively evaluate the overall performance of the powder coatings prepared in the examples and comparative examples, each group of powder coatings was uniformly sprayed onto the surface of building aluminum alloy profiles that had undergone degreasing and rust removal treatment using an electrostatic spray gun, with the spraying voltage set to 60kV. Subsequently, the sprayed aluminum profiles were placed in an oven at 200°C for curing for 15 minutes, and after being removed and cooled to room temperature, standard test samples were obtained. Each sample was then subjected to rigorous physical and mechanical property and weather resistance tests.

[0076] Testing standards:

[0077] Adhesion testing was conducted strictly according to the GB / T9286 standard using the cross-cut adhesion test; surface leveling was quantitatively measured by visual inspection and a 60° gloss meter; artificial accelerated aging testing was conducted according to the GB / T16422.3 standard, with continuous exposure testing performed in a QUV-B ultraviolet aging test chamber; and surface elemental distribution was analyzed in depth using X-ray photoelectron spectroscopy.

[0078] Specific testing process:

[0079] In the adhesion test, a 1mm×1mm grid was drawn on the coating surface using a special cross-cutting tool. Standard tape was applied and then quickly peeled off to observe the coating peeling in the grid area. The sample was then boiled in boiling water for 2 hours and cooled before the cross-cutting test was repeated to evaluate the wet anchoring force. In the accelerated aging test, the gloss change and color difference value of the sample before and after 3000 hours of exposure were recorded, and the gloss retention rate was calculated. In the surface elemental analysis, the coating was peeled off layer by layer using argon ion etching technology, and the changes in the atomic percentage of fluorine and silicon at different depths from the surface were monitored in real time.

[0080] Table 1 Performance test data of Examples 1-5 and Comparative Examples 1-3

[0081] Standard adhesion level 0 0 0 0 0 1 0 1 Adhesion level after boiling water 0 0 0 0 0 3 1 2 60° gloss % 90 92 93 91 92 85 78 75 3000h light retention rate % 86.5 88.5 91.2 87.0 88.0 45.2 82.1 71.2 3000h color difference ΔE 1.8 1.4 1.1 1.6 1.5 5.8 2.5 3.5 % of surface layer F element 15 18 22 16 17 4 9 10

[0082] Test data show that Examples 1 to 5 exhibited excellent performance in all key indicators; the adhesion of the Example group remained at level 0 after boiling in water, confirming that the aluminum oxysilane inorganic covalent bonds formed by the triethoxysilane groups at the aluminum substrate interface have extremely strong resistance to hydrolytic corrosion; the gloss retention rate and color difference data show that the introduction of macromolecular modifiers solved the migration and volatilization problem of small molecule additives, giving the coating super weather resistance comparable to pure fluorocarbon coatings;

[0083] Compared to Comparative Example 1, the physical blend system rapidly failed under long-term ultraviolet radiation and humid heat alternation, with its gloss retention rate dropping to 45.2%, highlighting the necessity of covalent locking. Comparing Example 2 with Comparative Example 2, it can be seen that the linear polyester skeleton leads to a higher melt viscosity of the system, which not only severely deteriorates the coating gloss but also hinders the effective migration of fluorinated segments to the surface, resulting in a significant decrease in the enrichment rate of fluorine on the surface. In addition, the stepwise adjustment of the amounts of pigments, fillers, leveling agents, and degassing agents in each example is not an isolated and irregular change, but rather a precise match to the system melt viscosity fluctuations caused by macromolecular modifiers with different carbon chain lengths and addition amounts.

[0084] For example, in embodiments with higher amounts of pigments, fillers, and macromolecular modifiers, the simultaneous increase in the amount of leveling agent and degassing agent effectively ensured the escape of microbubbles and surface smoothness of the high-filler system during the melt leveling stage. This was fully demonstrated in the stable and excellent 60° gloss performance of each embodiment, eliminating the interference of conventional additive changes on the core modification effect. In summary, this invention successfully achieved a simultaneous leap in the weather resistance, adhesion, and leveling properties of aluminum profile coatings through the viscosity reduction and enhancement effect of the hyperbranched skeleton and the self-assembly gradient layering of fluorinated silicon groups.

[0085] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing ultra-weather-resistant powder coatings for aluminum profiles, characterized in that, include: Under anhydrous inert gas protection, isophorone diisocyanate was reacted with 1,2,2,6,6-pentamethyl-4-piperidinol in an anhydrous solvent to prepare a hindered amine light stabilizer semi-adduct containing isocyanate groups. Hydroxyl-terminated hyperbranched polyester was dehydrated under vacuum and dissolved in anhydrous butanone. An organotin catalyst was added, and C4~C8 perfluoroalkyl isocyanate, 3-isocyanate-propyltriethoxysilane and the hindered amine light stabilizer semi-adduct containing isocyanate groups were added dropwise under stirring to carry out urethane esterification reaction. Hexahydrophthalic anhydride was then added, and the mixture was heated under the action of a catalyst to carry out a ring-opening half-esterification reaction. After the reaction was completed, the solvent was removed by vacuum distillation to obtain a hyperbranched multifunctional macromolecular modifier containing fluorinated silicon and hindered amine with terminal carboxyl groups. The carboxyl-terminated ultra-weather-resistant polyester resin, curing agent, hyperbranched multifunctional macromolecular modifier of carboxyl-terminated fluorinated silicon and hindered amine, pigments, fillers, leveling agent and degassing agent are premixed evenly. The premixed material is melt-blended and extruded, then pressed, cooled, crushed and sieved to obtain an ultra-weather-resistant powder coating for aluminum profiles. Of which, by weight, the end-carboxyl ultra-weather-resistant polyester resin is 55-65 parts, the curing agent is 3-7 parts, the end-carboxyl fluorinated silicon and hindered amine hyperbranched multifunctional macromolecular modifier is 2-8 parts, the pigments and fillers are 20-30 parts, the leveling agent is 0.8-1.5 parts, and the degassing agent is 0.3-0.8 parts.

2. The preparation method of the ultra-weather-resistant powder coating for aluminum profiles as described in claim 1, characterized in that: The reaction of isophorone diisocyanate with 1,2,2,6,6-pentamethyl-4-piperidinol in an anhydrous solvent, wherein the molar ratio of isophorone diisocyanate to 1,2,2,6,6-pentamethyl-4-piperidinol is 1:1; The anhydrous solvent is anhydrous dichloromethane; The reaction was carried out by slow dropwise addition under an ice-water bath, followed by reaction at room temperature for 3–5 hours.

3. The preparation method of the ultra-weather-resistant powder coating for aluminum profiles as described in claim 1, characterized in that: The hydroxyl-terminated hyperbranched polyester was dehydrated under vacuum at 120°C for 2 hours. The organotin catalyst is dibutyltin dilaurate.

4. The preparation method of the ultra-weather-resistant powder coating for aluminum profiles as described in claim 1, characterized in that: The urethane esterification reaction is carried out at a temperature of 50℃~70℃ until the -NCO characteristic peak at 2270cm⁻¹ in the infrared spectrum completely disappears. The total molar amount of the C4~C8 perfluoroalkyl isocyanate, 3-isocyanate-propyltriethoxysilane, and the hindered amine light stabilizer semi-addition containing isocyanate groups is 30% to 50% of the total initial molar amount of hydroxyl groups in the hydroxyl-terminated hyperbranched polyester.

5. The preparation method of the ultra-weather-resistant powder coating for aluminum profiles as described in claim 1, characterized in that: The ring-opening semi-esterification reaction is carried out by reflux at 100℃~120℃ for 3~5h.

6. The preparation method of the ultra-weather-resistant powder coating for aluminum profiles as described in claim 1, characterized in that: The curing agent is triglycidyl isocyanurate or β-hydroxyalkylamide; The pigment and filler are a mixture of rutile titanium dioxide and precipitated barium sulfate.

7. The preparation method of the ultra-weather-resistant powder coating for aluminum profiles as described in claim 1, characterized in that: The melt blending extrusion is carried out in a twin-screw extruder at an extrusion temperature of 100℃~115℃.

8. The method for preparing ultra-weather-resistant powder coating for aluminum profiles as described in claim 1, characterized in that: The crushing and sieving process involves using a micro pulverizer to crush the material and then passing it through a 180-200 mesh sieve.