High weatherable powder coating and method for its preparation

Abstract

The application provides a kind of high weatherability powder coating and its preparation method, belong to powder coating technical field;The application constructs hyperbranched polyester skeleton by esterification reaction of trimethylolpropane, adipic acid and maleic anhydride, introduces end hydroxyl polyether, pentaerythritol and 2,4-dihydroxybenzophenone to adjust flexibility, thermal stability and anti-uv aging performance, and uses allyl glycidyl ether to improve chemical activity and network stability;Through substitution reaction of hexachlorocyclotriphosphazene and aniline, ethanolamine and subsequent modification, phosphorus-containing heterocyclic-polyazimide oligomer is generated, which gives the coating flame retardance, heat resistance and adhesion;In the preparation of coating, carboxyl polyester resin and curing agent are crosslinked to form a three-dimensional network, combined with barium sulfate, silica powder and bismuth vanadate yellow pigment and other fillers and additives, the mechanical strength, chemical resistance and anti-uv aging performance of the coating film are optimized.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of powder coatings, and relates to a high-weather-resistance powder coating and a preparation method thereof. BACKGROUND

[0002] Powder coatings have superior environmental performance and good physical and chemical properties. Compared with traditional liquid coatings, powder coatings almost do not produce volatile organic compounds during the coating process, thus having significant advantages in reducing environmental pollution and improving workplace safety. In addition, powder coatings have better adhesion and wear resistance, can form a strong and uniform coating, and thus provide higher surface quality and longer service life.

[0003] However, as the market requirements for coatings in weather resistance and performance continue to increase, traditional powder coatings gradually show some deficiencies in these fields. Specifically, many powder coatings in the prior art mainly rely on a simple combination of resin systems and curing agents, and such a single formula often cannot meet the needs of high-strength weather-resistant coatings. Over time, especially in harsh outdoor environments, these coatings are prone to discoloration, peeling and surface deterioration, resulting in a decrease in their use performance.

[0004] In addition, the deficiencies of traditional powder coatings in ultraviolet resistance and mechanical strength make them exhibit poor durability when exposed to sunlight, rain and other natural elements for a long time. This not only affects the aesthetics of the coating, but also can cause corrosion and damage to the substrate, thereby increasing the cost of maintenance and replacement. SUMMARY

[0005] To solve the above problems, the present application aims to provide a high-weather-resistance powder coating and a preparation method thereof. The present application constructs a hyperbranched polyester skeleton through esterification of trimethylolpropane, adipic acid and maleic anhydride, and introduces end-hydroxyl polyether, pentaerythritol and 2,4-dihydroxybenzophenone to adjust flexibility, thermal stability and anti-UV aging performance. At the same time, the use of allyl glycidyl ether gives the material high chemical activity and network stability. The prepared hyperbranched modifier significantly enhances the flexibility, impact resistance and aging performance of the coating. The substitution of hexachlorocyclotriphosphazene with aniline and ethanolamine and the subsequent modification reaction generate a phosphorus-containing heterocyclic-polyazimide oligomer. The stable phosphorus-nitrogen skeleton structure of the oligomer improves the flame retardance, heat resistance and adhesion of the coating. In the preparation of the coating, the carboxyl polyester resin and the curing agent form a three-dimensional network structure through crosslinking, and the synergistic effect of fillers such as precipitated barium sulfate, silicon powder and bismuth vanadate yellow pigment and additives further optimizes the mechanical strength, chemical resistance and anti-UV aging performance of the coating film.

[0006] To achieve this purpose, the present application adopts the following technical solutions:

[0007] In a first aspect, the present application provides a preparation method of high-weather-resistant powder coating, comprising:

[0008] S1: mixing trimethylolpropane, adipic acid, maleic anhydride and p-toluenesulfonic acid to obtain a first reaction liquid, reacting under constant temperature under nitrogen protection to obtain reaction liquid A, heating, adding hydroxyl-terminated polyether and tetrabutyl titanate to obtain reaction liquid B, continuing to react to obtain reaction liquid C, adding pentaerythritol and 2,4-dihydroxybenzophenone in batches to obtain reaction liquid D, cooling, adding allyl glycidyl ether and continuing to stir, cooling, neutralizing, purifying and activating to obtain a hyperbranched modifier;

[0009] S2: dispersing hexachlorotriphosphazene in N-methylpyrrolidone to obtain a mixed liquid, adding aniline and ethanolamine to obtain reaction liquid E, reacting to obtain reaction liquid F, cooling, adding maleic anhydride and 4-dimethylaminopyridine and stirring to react, and obtaining a phosphorus heterocyclic-polyazide oligomer after post-treatment;

[0010] S3: mixing the carboxyl polyester resin and the curing agent uniformly, adding the hyperbranched modifier and the phosphorus heterocyclic-polyazide oligomer to obtain a premixed coating, adding precipitated barium sulfate, silicon powder, pigments, and curing accelerators, leveling agents and defoaming agents uniformly to obtain a pretreated coating, and obtaining the high-weather-resistant powder coating through extrusion, crushing and sieving by a double-screw extruder.

[0011] Specifically, S1: mixing trimethylolpropane, adipic acid, maleic anhydride and p-toluenesulfonic acid to obtain a first reaction liquid, reacting under constant temperature under nitrogen protection to obtain reaction liquid A, heating, adding hydroxyl-terminated polyether and tetrabutyl titanate to obtain reaction liquid B, continuing to react to obtain reaction liquid C, adding pentaerythritol and 2,4-dihydroxybenzophenone in batches to obtain reaction liquid D, cooling, adding allyl glycidyl ether and continuing to stir, cooling, neutralizing, purifying and activating to obtain a hyperbranched modifier;

[0012] S2: dispersing hexachlorotriphosphazene in N-methylpyrrolidone to obtain a mixed liquid, adding aniline and ethanolamine to obtain reaction liquid E, reacting to obtain reaction liquid F, cooling, adding maleic anhydride and 4-dimethylaminopyridine and stirring to react, and obtaining a phosphorus heterocyclic-polyazide oligomer after post-treatment;

[0013] S3: mixing the carboxyl polyester resin and the curing agent uniformly, adding the hyperbranched modifier and the phosphorus heterocyclic-polyazide oligomer to obtain a premixed coating, adding precipitated barium sulfate, silicon powder, pigments, and curing accelerators, leveling agents and defoaming agents uniformly to obtain a pretreated coating, and obtaining the high-weather-resistant powder coating through extrusion, crushing and sieving by a double-screw extruder.

[0014] As a preferred technical solution of the present application, in step S1, the mass ratio of trimethylolpropane, adipic acid, maleic anhydride and p-toluenesulfonic acid is (20-25):(15-20):(5-8):(0.5-1).

[0015] In some optional embodiments, the temperature of the first reaction solution under constant temperature reaction under nitrogen protection is 130-140℃, for example, it can be 130℃, 131℃, 132℃, 133℃, 134℃, 135℃, 136℃, 137℃, 138℃, 139℃ or 140℃, but not only limited to such values, and the values not mentioned in the range are also applicable.

[0016] In some optional embodiments, the time of the first reaction solution under constant temperature reaction under nitrogen protection is 2-3h, for example, it can be 2h, 2.1h, 2.2h, 2.3h, 2.4h, 2.5h, 2.6h, 2.7h, 2.8h, 2.9h or 3h, but not only limited to such values, and the values not mentioned in the range are also applicable.

[0017] In some optional embodiments, the reaction solution A is heated to 140-150℃, for example, it can be 140℃, 141℃, 142℃, 143℃, 144℃, 145℃, 146℃, 147℃, 148℃, 149℃ or 150℃, but not only limited to such values, and the values not mentioned in the range are also applicable.

[0018] The mass ratio of trimethylolpropane, hydroxyl-terminated polyether and tetrabutyl titanate is (20-25):(15-20):(0.5-1);

[0019] In some optional embodiments, the reaction solution B continues to react for 1-2h to obtain a reaction solution C, for example, it can be 1h, 1.1h, 1.2h, 1.3h, 1.4h, 1.5h, 1.6h, 1.7h, 1.8h, 1.9h or 2h, but not only limited to such values, and the values not mentioned in the range are also applicable.

[0020] The mass ratio of trimethylolpropane, pentaerythritol and 2,4-dihydroxybenzophenone is (20-25):(3-4):(2-4);

[0021] In some optional embodiments, after the reaction solution C is added with pentaerythritol and 2,4-dihydroxybenzophenone in batches, it continues to react for 1-2h, for example, it can be 1h, 1.1h, 1.2h, 1.3h, 1.4h, 1.5h, 1.6h, 1.7h, 1.8h, 1.9h or 2h, but not only limited to such values, and the values not mentioned in the range are also applicable.

[0022] In some optional embodiments, the reaction liquid D is cooled to 110-120℃ before adding allyl glycidyl ether, for example, it can be 110℃, 111℃, 112℃, 113℃, 114℃, 115℃, 116℃, 117℃, 118℃, 119℃ or 120℃, but not only limited to such values, the values in the range are also applicable.

[0023] The mass ratio of trimethylolpropane to allyl glycidyl ether is (20-25):(2-3);

[0024] In some optional embodiments, after the reaction liquid D is cooled, allyl glycidyl ether is added and stirring is continued for 1-2h, for example, it can be 1h, 1.1h, 1.2h, 1.3h, 1.4h, 1.5h, 1.6h, 1.7h, 1.8h, 1.9h or 2h, but not only limited to such values, the values in the range are also applicable.

[0025] As a preferred technical solution of the present application, in step S2, the mass ratio of hexachlorocyclotriphosphazene to N-methylpyrrolidone is (30-35):(15-20);

[0026] The mass ratio of hexachlorocyclotriphosphazene to aniline, ethanolamine is (30-35):(10-15):(3-5);

[0027] In some optional embodiments, the first temperature for the reaction of the reaction liquid E is 80-90℃, for example, it can be 80℃, 81℃, 82℃, 83℃, 84℃, 85℃, 86℃, 87℃, 88℃, 89℃ or 90℃, but not only limited to such values, the values in the range are also applicable.

[0028] In some optional embodiments, the reaction liquid E is reacted at the first temperature for 1-2h, for example, it can be 1h, 1.1h, 1.2h, 1.3h, 1.4h, 1.5h, 1.6h, 1.7h, 1.8h, 1.9h or 2h, but not only limited to such values, the values in the range are also applicable.

[0029] In some optional embodiments, the second temperature for the reaction of the reaction liquid E is 100-105℃, for example, it can be 100℃, 100.5℃, 101℃, 101.5℃, 102℃, 102.5℃, 103℃, 103.5℃, 104℃, 104.5℃ or 105℃, but not only limited to such values, the values in the range are also applicable.

[0030] In some optional embodiments, the reaction solution E is reacted at the second temperature for 50-60 min, for example, it can be 50 min, 51 min, 52 min, 53 min, 54 min, 55 min, 56 min, 57 min, 58 min, 59 min or 60 min, but not only limited to such values, and the values not mentioned in the range are also applicable.

[0031] In some optional embodiments, the reaction solution F is cooled to 60-70℃, and then maleic anhydride and 4-dimethylaminopyridine are added, for example, it can be 60℃, 61℃, 62℃, 63℃, 64℃, 65℃, 66℃, 67℃, 68℃, 69℃ or 70℃, but not only limited to such values, and the values not mentioned in the range are also applicable.

[0032] The mass ratio of the hexachlorotriphosphazene, maleic anhydride and 4-dimethylaminopyridine is (30-35):(8-10):(0.5-1);

[0033] In some optional embodiments, after the reaction solution F is cooled, maleic anhydride, 4-dimethylaminopyridine are added and stirred for 50-60 min, for example, it can be 50 min, 51 min, 52 min, 53 min, 54 min, 55 min, 56 min, 57 min, 58 min, 59 min or 60 min, but not only limited to such values, and the values not mentioned in the range are also applicable.

[0034] As a preferred technical solution of the present application, in step S3, the carboxyl polyester resin is CRYLCOAT2612;

[0035] The curing agent is Araldite® PT-910;

[0036] The pigment is bismuth vanadate yellow;

[0037] The curing accelerator is triphenylphosphine;

[0038] The leveling agent is Modaflow® Powder III;

[0039] The defoaming agent is any one of BYK-066N, BYK-A530;

[0040] The mass ratio of the carboxyl polyester resin, the curing agent, the hyperbranched modifier, the phosphorus-containing heterocyclic-polyazacylimide oligomer, the precipitated barium sulfate, the silicon powder, the pigment, the curing accelerator, the leveling agent and the defoaming agent is (600-650):(60-65):(30-35):(20-25):(50-55):(45-50):(10-20):(3-5):(5-10):(3-4).

[0041] In a second aspect, the present application provides a high weatherability powder coating prepared according to the method for preparing a high weatherability powder coating.

[0042] In the present application, trimethylolpropane is mixed with adipic acid and maleic anhydride to react. Trimethylolpropane is a trifunctional polyol, which forms a branched polyester skeleton through esterification with adipic acid and maleic anhydride, providing a basic framework for the hyperbranched structure. In addition to participating in esterification, the introduction of maleic anhydride can also provide unsaturated double bonds, providing reaction sites for subsequent structural modification.

[0043] The temperature of the first reaction solution is 130-140℃, which can ensure the effective esterification reaction, while avoiding the thermal polymerization of maleic anhydride at too high a temperature.

[0044] The introduction of terminal hydroxyl polyether, which is a flexible molecule with low glass transition temperature characteristics, can adjust the flexibility and thermal stability of the hyperbranched modifier.

[0045] The introduced pentaerythritol is a polyol that can further enhance the branching degree of the hyperbranched structure, improve the crosslinking density between molecules, and improve the mechanical properties of the modifier; the introduced 2,4-dihydroxybenzophenone is an ultraviolet absorber, which is introduced to give the modifier ultraviolet absorption function, enhancing the anti-ultraviolet aging performance of the high weatherability powder coating.

[0046] The introduced allyl glycidyl ether has both epoxy groups and unsaturated allyl groups, which can further crosslink with active groups in the hyperbranched molecule, giving the material higher chemical activity and network structure.

[0047] The prepared hyperbranched modifier can enhance the flexibility and impact resistance of the coating, and improve the anti-ultraviolet aging performance through the introduction of the ultraviolet absorber.

[0048] In the present application, hexachlorocyclotriphosphazene is reacted with aniline and ethanolamine. Hexachlorocyclotriphosphazene is a phosphorus-containing compound with a cyclic structure that provides multiple active sites. When reacted with aniline and ethanolamine, substitution reaction occurs, with chlorine atoms being replaced by amine groups, forming a phosphorus-containing heterocyclic structure. The introduction of aniline provides a rigid aromatic structure, enhancing the thermal stability of the oligomer; ethanolamine provides additional hydrogen bonding sites, improving the chemical compatibility between molecules.

[0049] In the reaction of reaction solution E, stepwise temperature control is adopted. At the first temperature, aniline and ethanolamine gradually replace the chlorine atoms of hexachlorocyclotriphosphazene to form a primary phosphorus-containing heterocyclic compound; increasing the temperature to the second temperature can promote the further polymerization of the oligomer to form a stable phosphorus-nitrogen skeleton, while inhibiting the formation of by-products.

[0050] Subsequently, maleic anhydride and 4-dimethylaminopyridine are introduced to react.

[0051] The prepared phosphorus-containing heterocyclic-polyazide oligomer can improve the flame retardance and heat resistance of the coating, and the adhesion of the coating is enhanced by the phosphorus element.

[0052] During the preparation of the coating, the carboxyl polyester resin provides the basic film-forming property of the coating, the curing agent added reacts with the carboxyl polyester to form a three-dimensional network structure, and the mechanical strength and chemical resistance of the coating film are ensured.

[0053] The added precipitated barium sulfate serves as a filler to improve the mechanical strength, wear resistance and surface flatness of the coating film; the silicon powder can fill micropores to reduce the water vapor permeability; and the introduced pigment bismuth vanadate yellow can reflect ultraviolet light to enhance the ultraviolet aging resistance of the coating.

[0054] Compared with the prior art, the application has the following beneficial effects:

[0055] The application constructs a hyperbranched polyester skeleton through esterification of trimethylolpropane with adipic acid and maleic anhydride, introduces a hydroxyl-terminated polyether at a suitable temperature to adjust the flexibility and thermal stability, adds pentaerythritol to improve the branching degree and crosslinking density and enhance the mechanical properties; 2,4-dihydroxybenzophenone as an ultraviolet absorber significantly improves the ultraviolet aging resistance; and the multi-functional structure of allyl glycidyl ether endows the material with higher chemical activity and network stability. The finally prepared hyperbranched modifier significantly enhances the flexibility, impact resistance and ultraviolet aging resistance of the coating;

[0056] The application constructs a phosphorus-containing heterocyclic structure through substitution reaction of hexachlorocyclotriphosphazene with aniline and ethanolamine, wherein the aniline introduces a rigid aromatic structure to enhance the thermal stability, and the ethanolamine provides a hydrogen bonding site to improve the chemical compatibility. Under stepwise temperature control, the phosphorus-containing heterocyclic compound is initially generated and further polymerized to form a stable phosphorus-nitrogen skeleton by promoting the temperature rise; subsequently, maleic anhydride and 4-dimethylaminopyridine are introduced to introduce carboxyl groups through catalytic branching reaction and avoid self-polymerization of maleic anhydride; and the finally prepared phosphorus-containing heterocyclic-polyazide oligomer significantly improves the flame retardance, heat resistance and adhesion of the coating;

[0057] In the preparation of the coating, the carboxyl polyester resin provides film-forming properties, the curing agent forms a three-dimensional network structure through cross-linking reaction to improve the mechanical strength and chemical resistance of the coating film; the precipitated barium sulfate as filler enhances the mechanical strength, wear resistance and surface smoothness of the coating film, the silicon powder fills the micropores to reduce the water vapor permeability, and the bismuth vanadate yellow pigment improves the ultraviolet aging resistance of the coating by reflecting ultraviolet light. DETAILED DESCRIPTION

[0058] The technical solutions of the present application will be described in detail below in combination with specific examples. The examples described herein are specific embodiments of the present application, which are used to illustrate the concept of the present application; all the descriptions are explanatory and exemplary, and should not be understood as limiting the embodiments of the present application and the protection scope of the present application. In addition to the examples described herein, those skilled in the art can also employ other technical solutions that are obvious based on the disclosure of the claims and the specification of the present application, which include technical solutions that make any obvious substitutions and modifications to the examples described herein.

[0059] The chemical reagents used in the examples and comparative examples of the present application are all commercially available without further purification or treatment.

[0060] Example 1

[0061] The present example provides a high-weather-resistant powder coating and a preparation method thereof, and the preparation method of the high-weather-resistant powder coating specifically comprises the following steps:

[0062] S1: 22 g of trimethylolpropane, 18 g of adipic acid, 7 g of maleic anhydride and 0.5 g of p-toluenesulfonic acid are mixed to obtain a first reaction liquid, which is reacted at a constant temperature of 135℃ under nitrogen protection for 2 h to obtain reaction liquid A, which is heated to 148℃, 18 g of hydroxyl-terminated polyether and 0.7 g of tetrabutyl titanate are added to obtain reaction liquid B, which is continuously reacted for 1 h to obtain reaction liquid C, 3.5 g of pentaerythritol and 3 g of 2,4-dihydroxybenzophenone are added in batches and reacted for 1.5 h to obtain reaction liquid D, which is cooled to 118℃, 2.6 g of allyl glycidyl ether is added and stirred for 2 h, and after cooling, neutralization, purification and activation, a hyperbranched modifier is obtained;

[0063] S2: 32 g of hexachlorotriphosphazene is dispersed in 18 g of N-methylpyrrolidone to obtain a mixed liquid, 12 g of aniline and 4.5 g of ethanolamine are added to obtain reaction liquid E, which is reacted at a first temperature of 88℃ for 1 h and then at a second temperature of 102℃ for 50 min to obtain reaction liquid F, which is cooled to 65℃, 9 g of maleic anhydride and 0.5 g of 4-dimethylaminopyridine are added and stirred for 60 min, and then distilled under reduced pressure to obtain a phosphorus heterocyclic-polyazide oligomer;

[0064] S3: 640 g of carboxyl polyester resin CRYLCOAT 2612 was mixed with 64 g of curing agent Araldite® PT-910, 34 g of hyperbranched modifier and 23 g of phosphorus heterocyclic-polyazacylimide oligomer were mixed to obtain a premixed coating, 52 g of precipitated barium sulfate, 48 g of silica powder, 18 g of pigment bismuth vanadate yellow and 4.5 g of curing accelerator triphenylphosphine, 8 g of leveling agent Modaflow® Powder III, 3.8 g of defoaming agent BYK-066N were mixed to obtain a pretreatment coating, which was extruded by a twin-screw extruder, crushed, sieved to obtain a high-weatherability powder coating.

[0065] Example 2

[0066] The present embodiment provides a high-weatherability powder coating and a preparation method thereof, and the preparation method of the high-weatherability powder coating specifically comprises the following steps:

[0067] S1: 24 g of trimethylolpropane, 17 g of adipic acid, 5 g of maleic anhydride and 0.8 g of p-toluenesulfonic acid were mixed to obtain a first reaction solution, which was reacted at a constant temperature of 137°C for 2.5 h under nitrogen protection to obtain reaction solution A, which was heated to 140°C, 16 g of hydroxyl-terminated polyether and 0.5 g of tetrabutyl titanate were added to obtain reaction solution B, which was continuously reacted for 1.5 h to obtain reaction solution C, 3 g of pentaerythritol and 4 g of 2,4-dihydroxybenzophenone were added in batches, and then reacted for 1.8 h to obtain reaction solution D, which was cooled to 110°C, 2 g of allyl glycidyl ether was further added and stirred for 1.8 h, and then cooled, neutralized, purified and activated to obtain a hyperbranched modifier;

[0068] S2: 35 g of hexachlorotriphosphazene was dispersed in 15 g of N-methylpyrrolidone to obtain a mixed solution, 14 g of aniline and 3 g of ethanolamine were added to obtain reaction solution E, which was reacted at a first temperature of 85°C for 1.6 h and then reacted at a second temperature of 100°C for 55 min to obtain reaction solution F, which was cooled to 60°C, 10 g of maleic anhydride and 0.6 g of 4-dimethylaminopyridine were added and stirred for 55 min, and then distilled under reduced pressure to obtain a phosphorus heterocyclic-polyazacylimide oligomer;

[0069] S3: 620 g of carboxyl polyester resin CRYLCOAT 2612 was mixed with 62 g of curing agent Araldite® PT-910, 30 g of hyperbranched modifier and 20 g of phosphorus heterocyclic-polyazacylimide oligomer were mixed to obtain a premixed coating, 54 g of precipitated barium sulfate, 45 g of silica powder, 15 g of pigment bismuth vanadate yellow and 3 g of curing accelerator triphenylphosphine, 5 g of leveling agent Modaflow® Powder III, 3 g of defoaming agent BYK-A530 were mixed to obtain a pretreatment coating, which was extruded by a twin-screw extruder, crushed, sieved to obtain a high-weatherability powder coating.

[0070] Example 3

[0071] This embodiment provides a highly weather-resistant powder coating and a preparation method thereof. The preparation method of the highly weather-resistant powder coating specifically comprises the following steps:

[0072] S1: 20 g of trimethylolpropane, 15 g of adipic acid, 6 g of maleic anhydride, and 1 g of p-toluenesulfonic acid were mixed to obtain a first reaction solution, and the mixture was reacted at a constant temperature of 130° C. for 3 h under nitrogen protection to obtain reaction solution A. The mixture was heated to 145° C., 15 g of hydroxyl-terminated polyether and 0.8 g of tetrabutyl titanate were added to obtain reaction solution B, and the reaction was continued for 1.7 h to obtain reaction solution C. 4 g of pentaerythritol and 2 g of 2,4-dihydroxybenzophenone were added in batches and reacted for 1 h to obtain reaction solution D. The mixture was cooled to 115° C., 3 g of allyl glycidyl ether was added, and stirring was continued for 1 h. After cooling, the mixture was neutralized, purified, and activated to obtain a hyperbranched modifier.

[0073] S2: 33 g of hexachlorocyclotriphosphazene was dispersed in 17 g of N-methylpyrrolidone to obtain a mixed solution, 10 g of aniline and 4 g of ethanolamine were added to obtain a reaction solution E, the mixture was reacted at a first temperature of 80° C. for 1.4 h, and then at a second temperature of 104° C. for 58 min to obtain a reaction solution F, the mixture was cooled to 70° C., 8 g of maleic anhydride and 1 g of 4-dimethylaminopyridine were added, the mixture was stirred and reacted for 50 min, and the mixture was distilled under reduced pressure to obtain a phosphorus-containing heterocyclic-polynitrogen imide oligomer;

[0074] S3: 650g of carboxyl polyester resin CRYLCOAT 2612 and 65g of curing agent Araldite® PT-910 were mixed evenly, and 32g of hyperbranched modifier and 25g of phosphorus-containing heterocyclic-polynitrogen imide oligomer were added to obtain a premixed coating. 50g of precipitated barium sulfate, 50g of silica powder, 10g of pigment bismuth vanadate yellow, 4g of curing accelerator triphenylphosphine, 7g of leveling agent Modaflow® Powder III, and 4g of defoamer BYK-066N were added and mixed evenly to obtain a pretreated coating. The coating was extruded through a twin-screw extruder, crushed, and sieved to obtain a highly weather-resistant powder coating.

[0075] Example 4

[0076] This embodiment provides a highly weather-resistant powder coating and a preparation method thereof. The preparation method of the highly weather-resistant powder coating specifically comprises the following steps:

[0077] S1: 25 g of trimethylolpropane, 20 g of adipic acid, 8 g of maleic anhydride and 0.7 g of p-toluenesulfonic acid were mixed to obtain a first reaction liquid, which was reacted at a constant temperature of 140°C for 2.8 h under nitrogen protection to obtain reaction liquid A, which was heated to 150°C, 20 g of hydroxyl-terminated polyether and 1 g of tetrabutyl titanate were added to obtain reaction liquid B, and the reaction was continued for 2 h to obtain reaction liquid C, 3.7 g of pentaerythritol and 3.4 g of 2,4-dihydroxybenzophenone were added in batches, and the reaction was continued for 2 h to obtain reaction liquid D, which was cooled to 120°C, 2.4 g of allyl glycidyl ether was added and stirring was continued for 1.5 h, and after cooling, neutralization, purification and activation, a hyperbranched modifier was obtained;

[0078] S2: 30 g of hexachlorotriphosphazene was dispersed in 20 g of N-methylpyrrolidone to obtain a mixed liquid, 15 g of aniline and 5 g of ethanolamine were added to obtain reaction liquid E, which was reacted at a first temperature of 90°C for 2 h and then at a second temperature of 105°C for 60 min to obtain reaction liquid F, which was cooled to 68°C, 8.9 g of maleic anhydride and 0.9 g of 4-dimethylaminopyridine were added and stirred for 54 min, and vacuum distillation was performed to obtain a phosphorus heterocyclic-polyimide oligomer;

[0079] S3: 600 g of carboxyl polyester resin CRYLCOAT 2612 was uniformly mixed with 60 g of curing agent Araldite® PT-910, 35 g of hyperbranched modifier and 22 g of phosphorus heterocyclic-polyimide oligomer were added to obtain a premixed coating, and 55 g of precipitated barium sulfate, 46 g of silica powder, 20 g of pigment bismuth vanadate yellow, and 5 g of curing accelerator triphenylphosphine, 10 g of leveling agent Modaflow® Powder III, 3.5 g of defoaming agent BYK-A530 were uniformly mixed to obtain a pretreated coating, which was extruded through a double screw extruder, crushed and sieved to obtain a high-weather-resistant powder coating.

[0080] Comparative Example 1

[0081] This comparative example provides a high-weather-resistant powder coating, which is different from Example 1 in that no hyperbranched modifier is added in S3, and the other operation steps and process parameters are exactly the same as those of Example 1.

[0082] Comparative Example 2

[0083] This comparative example provides a high-weather-resistant powder coating, which is different from Example 1 in that no phosphorus heterocyclic-polyimide oligomer is added in S3, and the other operation steps and process parameters are exactly the same as those of Example 1.

[0084] Comparative Example 3

[0085] The comparative example provides a high-weather-resistant powder coating, which is different from example 1 in that the segmented temperature control in S2 is cancelled, and the reaction is directly carried out at the first temperature for 1h50min, and other operation steps and process parameters are exactly the same as example 1.

[0086] Comparative example 4

[0087] The comparative example provides a high-weather-resistant powder coating, which is different from example 1 in that the phosphorus-containing heterocyclic-polyazacylimide oligomer in S3 is replaced by the phosphate ester flame retardant triphenyl phosphate, and other operation steps and process parameters are exactly the same as example 1.

[0088] Comparative example 5

[0089] The comparative example provides a high-weather-resistant powder coating, which is different from example 1 in that the hyperbranched modifier in S3 is replaced by the linear polyester polyethylene glycol adipate, and other operation steps and process parameters are exactly the same as example 1.

[0090] The high-weather-resistant powder coatings of examples 1-4 and comparative examples 1-5 are tested for performance, and the specific process is as follows:

[0091] The adhesion of the sample is tested according to GB / T 9286;

[0092] The heat resistance of the sample is tested according to GB / T 1735;

[0093] The salt spray resistance of the sample is tested according to GB / T 1771-2007;

[0094] The ultraviolet aging resistance of the sample is tested according to ISO 7724.

[0095] The performance test results are shown in Table 1.

[0096] Table 1 Performance test results of high-weather-resistant powder coatings of examples 1-4 and comparative examples 1-5

[0097] adhesion heat resistance (150°c, 4h) salt spray resistance (500h) ultraviolet light resistance (1000h, delta e < 4) example 1 0 level pass no blistering, no peeling 2.5 example 2 0 level pass no blistering, no peeling 2.6 example 3 1 level pass no blistering, no peeling 2.5 example 4 1 level pass no blistering, no peeling 2.7 comparative example 1 2 level fail (discoloration, blistering) blistering, peeling 4.8 comparative example 2 2 level edge pass (slight discoloration) blistering, peeling 3.2 comparative example 3 2 level fail (partial cracking) blistering, peeling 3.8 comparative example 4 2 level fail (severe discoloration) blistering, peeling 4.1 comparative example 5 2 level fail (partial cracking) blistering, peeling 4.5

[0098] From the test results of example 1 and comparative example 1, it can be seen that after removing the hyperbranched modifier, the three-dimensional crosslinking network structure in the coating is lacking, resulting in loose arrangement of molecular chain segments, decreased compactness, significantly reduced adhesion and heat resistance. The lack of hyperbranched structure reduces the interfacial chemical bonding and shear strength, and the ultraviolet absorption groups are not effectively grafted, the ultraviolet shielding ability is weakened, the photodegradation reaction is intensified, and the weather resistance is deteriorated. In addition, the destruction of the dense crosslinking network leads to increased water and oxygen permeability, and corrosion media more easily invades the substrate, resulting in a significant decrease in salt spray resistance.

[0099] From the test results of Example 1 and Comparative Example 2, after removing the phosphorus-containing heterocyclic-polyazolide oligomer, the phosphorus-nitrogen synergistic flame-retardant mechanism in the coating is destroyed, the thermal decomposition temperature is reduced, the carbon residue rate is reduced, and the heat resistance is marginal. The lack of phosphorus-nitrogen heterocyclic structure leads to insufficient crosslinking density, weakened interfacial bonding ability, and reduced adhesion. At the same time, the ultraviolet reflection function of the phosphorus-nitrogen heterocyclic structure is lost, and only the physical shielding effect of the pigment is relied on, the ultraviolet absorption efficiency is reduced, and the light aging ΔE value is increased. In addition, the passivation effect of phosphorus and nitrogen elements on the metal substrate disappears, the corrosion current density increases, and the salt spray resistance deteriorates.

[0100] From the test results of Example 1 and Comparative Example 3, after canceling the segmented temperature control of S2 step, the phosphazene ring amination reaction is not complete, and residual unreacted phosphorus-chlorine bonds are left. These active chloride ions hydrolyze to generate hydrogen chloride in a humid environment, accelerating the corrosion of the metal substrate, and the salt spray resistance is significantly reduced. At the same time, the structural defects lead to a decrease in the thermal stability of the phosphorus-nitrogen heterocyclic structure, and the coating is prone to decomposition and cracking at high temperatures. The insufficient grafting of maleic anhydride reduces the carboxyl content, the ultraviolet absorption groups are unevenly distributed, the light shielding effect is poor, and the aging resistance is deteriorated. In addition, incomplete amination leads to a decrease in interfacial compatibility and adhesion.

[0101] From the test results of Example 1 and Comparative Example 4, after replacing the phosphorus-nitrogen heterocyclic oligomer with triphenyl phosphate, the compatibility of the flame retardant and the resin matrix is poor, micro-pore defects are formed at the interface, and the adhesion is significantly reduced. The decomposition temperature of triphenyl phosphate is relatively low, and it migrates and separates out at high temperatures, leading to an increase in the porosity of the coating and unqualified heat resistance. The hygroscopicity of the phosphate ester exacerbates moisture penetration, and the lack of nitrogen element synergistic passivation effect increases the corrosion current density, and the salt spray resistance deteriorates. In addition, the ultraviolet absorption band of triphenyl phosphate is relatively narrow, and the shielding effect on long-wave ultraviolet light is poor, and the light aging ΔE value increases.

[0102] From the test results of Example 1 and Comparative Example 5, after replacing the hyperbranched modifier with linear polyester polyethylene glycol adipate, the coating loses the three-dimensional branched structure, the molecular chain entanglement density decreases, the compactness decreases, and the adhesion and salt spray resistance are significantly deteriorated. The glass transition temperature of polyethylene glycol adipate is much lower than that of the hyperbranched structure, and the chain segment motion is intensified at high temperatures, the coating softens and deforms, and the heat resistance is unqualified. The ultraviolet absorption groups are not grafted by chemical bonds, but rely on physical dispersion, and are prone to migration and failure under long-term ultraviolet radiation, and the light aging ΔE value increases. In addition, the porosity of the linear structure is relatively high, and the corrosion medium is more easily penetrated to the substrate interface.

[0103] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto, and those skilled in the art should understand that any changes or replacements within the technical scope disclosed by the present application can be easily thought of by those skilled in the art, and all fall within the protection scope and disclosure scope of the present application.

Claims

1. A method for preparing a highly weather-resistant powder coating, characterized in that: The preparation method comprises: S1: trimethylolpropane, adipic acid, maleic anhydride, and p-toluenesulfonic acid are mixed to obtain a first reaction solution, reacted to obtain reaction solution A, heated, added with hydroxyl-terminated polyether and tetrabutyl titanate, and continued to react to obtain reaction solution C, and pentaerythritol and 2,4-dihydroxybenzophenone are added in batches to react to obtain reaction solution D, cooled, added with allyl glycidyl ether, reacted, cooled, and post-treated to obtain a hyperbranched modifier; S2: dispersing hexachlorocyclotriphosphazene in N-methylpyrrolidone to obtain a mixed solution, adding aniline and ethanolamine to obtain a reaction solution E, reacting to obtain a reaction solution F, cooling the solution, adding maleic anhydride and 4-dimethylaminopyridine, stirring and reacting, and post-treating to obtain a phosphorus-containing heterocyclic-polynitrogen imide oligomer; S3: Mixing the carboxyl polyester resin and the curing agent uniformly, adding a hyperbranched modifier and a phosphorus-containing heterocyclic-polynitrogen imide oligomer to obtain a premixed coating, then adding precipitated barium sulfate, silica powder, pigment, as well as a curing accelerator, a leveling agent, and a defoaming agent to obtain a pretreated coating, extruding through a twin-screw extruder, crushing, and sieving to obtain a highly weather-resistant powder coating; The first reaction temperature of the reaction solution E is 80-90°C; The second reaction temperature of the reaction solution E is 100-105°C.

2. The method for preparing a highly weather-resistant powder coating according to claim 1, wherein: In S1: The mass ratio of trimethylolpropane, adipic acid, maleic anhydride and p-toluenesulfonic acid is (20-25): (15-20): (5-8): (0.5-1); The reaction temperature of the first reaction liquid is 130-140°C.

3. The method for preparing a highly weather-resistant powder coating according to claim 1, wherein: In S1: The mass ratio of trimethylolpropane to hydroxyl-terminated polyether and tetrabutyl titanate is (20-25): (15-20): (0.5-1); The mass ratio of trimethylolpropane to pentaerythritol and 2,4-dihydroxybenzophenone is (20-25): (3-4): (2-4).

4. The method for preparing a highly weather-resistant powder coating according to claim 1, wherein: In S1: The mass ratio of trimethylolpropane to allyl glycidyl ether is (20-25): (2-3); The reaction solution D is cooled to 110-120° C. and then allyl glycidyl ether is added for reaction.

5. The method for preparing a highly weather-resistant powder coating according to claim 1, characterized in that: In S2: The mass ratio of the hexachlorocyclotriphosphazene to N-methylpyrrolidone is (30-35): (15-20); The mass ratio of the hexachlorocyclotriphosphazene to aniline and ethanolamine is (30-35): (10-15): (3-5).

6. The method for preparing a highly weather-resistant powder coating according to claim 1, characterized in that: In S2: After the reaction solution F is cooled to 60-70° C., maleic anhydride and 4-dimethylaminopyridine are added; The mass ratio of the hexachlorocyclotriphosphazene to maleic anhydride and 4-dimethylaminopyridine is (30-35): (8-10): (0.5-1).

7. The method for preparing a highly weather-resistant powder coating according to claim 1, characterized in that: In S3: The pigment is bismuth vanadate yellow; The curing accelerator is triphenylphosphine.

8. The method for preparing a highly weather-resistant powder coating according to claim 1, characterized in that: In S3: the mass ratio of the carboxyl polyester resin, curing agent, hyperbranched modifier, phosphorus-containing heterocyclic-polynitrogen imide oligomer, precipitated barium sulfate, silica powder, pigment, curing accelerator, leveling agent, and defoaming agent is (600-650): (60-65): (30-35): (20-25): (50-55): (45-50): (10-20): (3-5): (5-10): (3-4).

9. A highly weather-resistant powder coating prepared according to the preparation method according to any one of claims 1 to 8.