Highly flexible powder for coatings and process for its production

Abstract

The application provides a high-flexibility powder for paint and a production process thereof, and belongs to the technical field of paint. The high-flexibility powder for paint comprises the following raw materials: high-toughness polyester resin, functionalized composite filler, curing agent HAA, leveling agent and benzoin. The high-toughness polyester resin is prepared by modifying isophorone diisocyanate, polytetrahydrofuran ether diol, terephthalic acid and adipic acid as main modified raw materials. The functionalized composite filler is first introduced with amino groups and silane bonds after silane coupling agent, then is coated with polypropylene glycol diglycidyl ether and polyether amine in sequence, and is mixed with carboxyl-terminated polyester resin, and is prepared by spray drying. The application effectively improves the flexibility and impact resistance of the prepared powder as a whole through the combined action of the interface gradient toughening of the functionalized composite filler and the intrinsic toughening of the high-toughness polyester resin matrix, and the coating after spraying does not have defects such as blistering, cracking, wrinkling or peeling.

Description

Technical Field

[0001] This invention belongs to the field of coating technology, and in particular relates to a high-flexibility powder for coatings and its production process. Background Technology

[0002] Powder coatings, with their numerous advantages such as being environmentally friendly, having high coating efficiency, stable film performance, and safe storage, transportation, and use, have been widely applied in many industrial coating fields, including home appliances, hardware and building materials, precision sheet metal, and outdoor engineering components. Among these, oil-immersed transformer tanks, integrated heat sinks, and assembled plate heat sinks are all low-carbon steel metal components formed by sheet metal stamping, bending, and welding. The mainstream production process in the industry is to first spray protective powder coating, and then perform fin bending, edge shaping, assembly, and welding. The finished components are used outdoors for extended periods, and are subject to significant combined effects of large day-night temperature differences, low winter temperatures, equipment vibration, and wind and sand impacts. Compared to ordinary sheet metal parts, transformer heat dissipation and oil storage components place more stringent requirements on the flexibility, impact resistance, and low-temperature deformation stability of the powder coating. Currently, the base resins used in conventional polyester and epoxy polyester powder coatings on the market have relatively rigid molecular chains and poor glass transition temperature control precision. They are prone to increased brittleness at low temperatures, and after curing, the coatings lack sufficient bending deformation capacity. When subjected to external impact, they cannot effectively dissipate stress, easily leading to defects such as cracking, substrate exposure, and peeling. This makes them unsuitable for subsequent deep processing and complex environmental applications. Existing technologies often improve coating toughness by adding conventional toughening additives and simply adjusting the resin monomer ratio. However, such improvements only achieve single-performance enhancements and have significant limitations. They can easily cause a decrease in the overall physical and chemical properties of the coating, such as hardness, weather resistance, and chemical resistance. Furthermore, poor compatibility between the resin and additives / curing agents can lead to poor melt flow and leveling properties of the powder coating, resulting in wrinkles and defects after spraying and affecting the quality of the finished product. Meanwhile, traditional powder coatings often use unmodified inorganic fillers that are directly blended and added. The interfacial bonding between the filler and the resin matrix is ​​weak, and component agglomeration easily occurs within the powder. Under external forces, stress concentration easily occurs at the filler-matrix interface, failing to effectively disperse and dissipate external impact forces. This significantly limits the improvement in the overall flexibility and impact resistance of the coating. Furthermore, the exposed functional elastic structure is susceptible to failure due to external environmental factors, further reducing the coating's service stability. In addition, existing modified powder coating technologies generally suffer from poor raw material compatibility, complex modification processes, high production costs, and difficulty in continuous mass production, failing to simultaneously meet the multiple demands of high flexibility, high impact resistance, no coating defects, and industrial-scale mass production.

[0003] Patent application CN109749067A discloses a flexible polyester resin for powder coatings and its preparation method, belonging to the field of powder coating chemical technology. The polyester resin uses monomers with good linear structure and employs highly active and flexible diacid glycidyl diacid as a sealing agent, ensuring the comprehensive performance of the final powder coating, including impact resistance and water resistance, while achieving a flexible coating surface. The prepared polyester resin has a good linear structure, low softening point, excellent flexibility, and superior bending resistance, and is compatible with the high-functionality curing agent N,N,N',N'-tetra(β-hydroxyethyl)hexamethylenediamide curing system. This improves the decorative and protective properties of powder coatings, especially exhibiting outstanding flexibility, with a T-bend value reaching up to 1T. The preparation method uses readily available raw materials, is simple to operate, and is suitable for large-scale production, with wide applications in decorative and protective fields such as home appliances, automobiles, and metal furniture. While the patent application significantly improves the flexibility of the powder coating, its excessive pursuit of flexibility leads to a decrease in cross-linking density, which limits the impact resistance threshold under high-speed impact. At the same time, the low softening point design is prone to powder agglomeration at high temperatures, and pinholes are easily generated when the coating is thick. It is difficult to meet the dual requirements of high impact resistance and appearance stability while satisfying high flexibility.

[0004] Based on this, we provide a high-flexibility, high-impact powder for coatings and its production process to overcome the shortcomings of the prior art, which is of great practical significance. Summary of the Invention

[0005] This invention provides a high-flexibility powder for coatings and its production process, which overcomes the problems of insufficient impact resistance and flexibility in the existing technology of coating powders, and effectively improves the impact resistance and flexibility of the powder.

[0006] The technical solution of the present invention is achieved through the following measures:

[0007] The first aspect of this invention provides a highly flexible powder for coatings, comprising the following raw materials in parts by weight: 540-580 parts by weight of high-toughness polyester resin, 386-414 parts by weight of functionalized composite filler, 33.7-36.3 parts by weight of curing agent HAA, 9.6-10.4 parts by weight of leveling agent and 7-8 parts by weight of benzoin; The high-toughness polyester resin is prepared by modification using isophorone diisocyanate, polytetrahydrofuran ether diol, terephthalic acid and adipic acid as modifying raw materials. The functionalized composite filler is first introduced with amino and silane bonds by a silane coupling agent, then coated sequentially with polypropylene glycol diglycidyl ether and polyetheramine, and finally mixed with carboxyl-terminated polyester resin and obtained by spray drying.

[0008] This invention effectively improves the overall flexibility and impact resistance of the powder by combining the interfacial gradient toughening of functionalized composite fillers with the intrinsic toughening of high-toughness polyester resin matrix. Moreover, the coating after spraying is free from defects such as blistering, cracking, wrinkling or peeling.

[0009] In a preferred embodiment of the present invention, the method for preparing the high-toughness polyester resin includes the following steps: Under nitrogen protection, polytetrahydrofuran ether diol was dehydrated, and then isophorone diisocyanate was added dropwise while cooling and stirring to obtain a polyurethane prepolymer. Neopentyl glycol, trimethylolpropane, terephthalic acid, the first part of isophthalic acid, adipic acid, polymerization inhibitor and catalyst are mixed, nitrogen gas is introduced, the mixture is heated and stirred, the mixture is cooled and polyurethane prepolymer is added and stirred, the second part of isophthalic acid is added and stirred again, vacuum is applied, the mixture is discharged, cooled and crushed to obtain high-toughness polyester resin.

[0010] Conventional polyesters have high glass transition temperature (Tg) and exhibit a brittle glassy state at low temperatures. Even with buffering at the filler interface, the matrix itself cannot withstand significant strain. This invention forms a long-chain polyurethane prepolymer by combining isophorone diisocyanate and polytetrahydrofuran ether diol, and then covalently embeds it into the polyester backbone. This results in the presence of compliant segments of long polyether chains between the crosslinking points in the cured network. Consequently, the cured network can undergo segmental conformational transformations to dissipate energy under stress, while maintaining the crosslinking density. This yields a toughened matrix resin, lowers the glass transition temperature, increases the elongation at break, enhances the matrix's resistance to low-temperature brittleness, and imparts excellent resistance to low-temperature deformation to the coating. Furthermore, in the preparation of high-toughness polyester resin, after isophorone diisocyanate reacts with polytetrahydrofuran ether diol to form a prepolymer, terephthalic acid is added to provide rigidity, maintaining the mechanical strength and heat resistance of the resin. Adipic acid is also added as a flexible monomer, whose long carbon chain can increase the flexibility of the molecular chain and reduce the glass transition temperature of the product. At the same time, after block grafting, a second part of isophthalic acid is added. Not only does the carboxyl group of the second part of isophthalic acid react with the hydroxyl group at the chain end to achieve carboxyl end capping and adjust the final acid value, but the newly added isophthalic acid also preferentially reacts at the chain end. Compared with the use of terephthalic acid or adipic acid for end capping, the asymmetric meta-benzene ring structure brought by isophthalic acid can more effectively disrupt the chain segment stacking and form amorphous regions. This helps to adjust the Tg of the final resin, improve the transparency of the resin and the miscibility with curing agents and additives, and improve the melt leveling of powder coatings.

[0011] In a preferred embodiment of the present invention, by weight, the polytetrahydrofuran ether diol is 13-17 parts, isophorone diisocyanate is 6.9-9.1 parts, neopentyl glycol is 21.7-28.3 parts, trimethylolpropane is 0.9-1.3 parts, terephthalic acid is 24.3-31.7 parts, the first part isophthalic acid is 5-6 parts, adipic acid is 5.2-6.8 parts, the polymerization inhibitor is 0.01-0.012 parts, the catalyst is 0.05-0.06 parts, and the second part isophthalic acid is 4-6 parts.

[0012] Furthermore, the polytetrahydrofuran ether diol has an Mn of 1000, the polymerization inhibitor includes hydroquinone monomethyl ether, and the catalyst includes butyltin acid.

[0013] In a preferred embodiment of the present invention, the dehydration is carried out under vacuum at a controlled temperature of 105-110℃ for 1-1.5 hours; the cooling is carried out at a temperature of 70-75℃; the stirring temperature is 70-80℃ for 2-2.5 hours; the heating and stirring is carried out at a temperature of 220-240℃ until the acid value is 2-5 mgKOH / g; the cooling and stirring of the polyurethane prepolymer is carried out at a temperature of 135-140℃ for 1-1.5 hours; the re-stirring is carried out until the acid value is 30-40 mgKOH / g; and the vacuuming is carried out at 130-140℃ to (-0.08)-(-0.095) MPa and maintained for 20-40 minutes.

[0014] In a preferred embodiment of the present invention, the preparation method of the functionalized composite filler includes the following steps: A silane hydrolysate was prepared by dissolving a silane coupling agent and an aqueous ethanol solution, and a polypropylene glycol diglycidyl ether was prepared by dissolving it in deionized water to prepare an aqueous solution of polypropylene glycol diglycidyl ether. A polyether amine was prepared by dissolving it in deionized water to prepare solution A. Titanium dioxide and barium sulfate were mixed at a controlled rate, sprayed into silane hydrolysate and stirred, heated, and dried under negative pressure to obtain an aminated composite filler. Deionized water was added and heated and stirred to obtain slurry A. Part of the polypropylene glycol diglycidyl ether aqueous solution was added dropwise to slurry A and stirred once under controlled temperature. The remaining polypropylene glycol diglycidyl ether aqueous solution was mixed with all of solution A and then added dropwise to slurry A at a uniform rate and stirred twice under controlled temperature. After heating, the temperature was maintained to obtain slurry B. The carboxyl-terminated polyester resin is pulverized and heated for later use; slurry B is preheated and then poured into the prepared carboxyl-terminated polyester resin at a controlled rate for emulsification, then transferred to a spray drying tower for drying and collection to obtain the functionalized composite filler.

[0015] This invention introduces amino groups to provide sites for the epoxy reaction by forming a covalently linked aminosilane layer on the filler surface using the silane coupling agent KH-550. Then, through a gradient dropwise addition reaction, the epoxy-amine reaction sequence is controlled to construct a cross-linked polyether elastic layer that gradually decreases in cross-linking density from high to low, forming a gradient elastic layer with decreasing modulus from the inside out. This allows the coating to effectively disperse and absorb stress during bending deformation under stress, improving the coating's flexibility. Finally, a carboxyl-terminated polyester resin is coated around the elastic layer to provide a protective shell during extrusion. At relatively high temperatures, the outer shell remains solid or highly viscous, protecting the internal elastic layer and preventing direct exposure. During high-shear extrusion and high-temperature curing, the elastic layer may swell and mix with the matrix resin, causing the gradient to disappear. Furthermore, the outer shell surface is rich in carboxyl groups, which can react with the residual amine / hydroxyl groups in the elastic layer to form covalent anchoring. At the same time, the polyester of the outer shell has a terminal carboxyl structure similar to that of the matrix resin. During subsequent curing, the carboxyl groups of the outer shell can react with the curing agent to form a semi-interpenetrating network with the matrix resin, which not only prevents the outer shell from falling off but also improves the overall bonding strength and enhances the overall stability.

[0016] As a preferred embodiment of the present invention, the specific steps for preparing a silane hydrolysate from a silane coupling agent and an aqueous ethanol solution are as follows: adding the silane coupling agent to the aqueous ethanol solution, adjusting the pH, hydrolyzing, and preparing the silane hydrolysate. The silane coupling agent includes silane coupling agent KH-550, the volume concentration of the ethanol aqueous solution is 10%-15%, the pH is adjusted by adjusting the pH to 4.5-5.5 with acetic acid, and the hydrolysis is performed at room temperature for 20-30 minutes. The ratio of the silane coupling agent to the ethanol aqueous solution is 15-16g:200-230mL; In this invention, silanol generated by KH-550 hydrolysis condenses with hydroxyl groups (-Ti-OH, -Ba-OH) on the surface of the filler to form Si-OM bonds, with -NH2 groups exposed at the outer end, serving as the first-level chemical anchoring point.

[0017] In a preferred embodiment of the present invention, polypropylene glycol diglycidyl ether is dissolved in deionized water to prepare an aqueous solution of polypropylene glycol diglycidyl ether, wherein the ratio of polypropylene glycol diglycidyl ether to deionized water is 30-32g:300-325mL.

[0018] In a preferred embodiment of the present invention, the polyetheramine is dissolved in deionized water to prepare solution A, wherein the polyetheramine is polyetheramine D-400; and the ratio of polyetheramine to deionized water is 18-20g:200-215mL.

[0019] This invention first adds polypropylene glycol diglycidyl ether, and through an epoxy-amine chemical reaction, the epoxy groups react with the -NH2 on the filler surface to form a ring-opening reaction, forming a highly cross-linked inner layer. The polypropylene glycol diglycidyl ether is firmly connected to the surface of the aminated filler through covalent bonds. Then, a solution A containing polyetheramine D-400 is added. D-400 is used as a long-chain diamine, which gradually reduces the cross-linking density of the subsequent network and enhances the mobility of chain segments, thereby forming a gradient elastic layer with decreasing modulus from the inside to the outside. Finally, molten carboxyl-terminated polyester resin is added, emulsified, and then spray-dried. During the spraying process, the molten polyester droplets cool and shrink and solidify on the surface of the elastic layer, forming a reactive outer shell, thus obtaining a gradient-toughened functionalized composite filler.

[0020] In a preferred embodiment of the present invention, during the preparation of slurry A: The titanium dioxide is 590-610 parts by weight, barium sulfate is 345-356 parts by weight, silane hydrolysate is 216-245 parts by weight, and deionized water is 500-550 parts by weight. The controlled mixing speed is 1800-2000 rpm for 10-15 min; the temperature of the silane hydrolysate injection and stirring is 23-25℃ for 30-35 min; the temperature rise is to 75-80℃; the pressure of the negative pressure stirring and drying is (-0.07)-(-0.08) MPa for 1-1.5 h; the heating and stirring is to heat to 55-60℃ and stir for 30-45 min.

[0021] In a preferred embodiment of the present invention, during the preparation of slurry B: The mass of the portion of the polypropylene glycol diglycidyl ether aqueous solution is 38%-40% of the total mass of the polypropylene glycol diglycidyl ether aqueous solution; The temperature for the first temperature-controlled stirring is 55-60℃, and the time is 25-30 min; the temperature for the second temperature-controlled stirring is 55-60℃, and the time is 1-1.5 h; the temperature rise is to 75-80℃; and the holding time is 30-40 min.

[0022] In a preferred embodiment of the present invention, during the preparation of functionalized composite fillers: The carboxyl-terminated polyester resin is 38-42 parts by weight, and the slurry B is 950-1050 parts by weight. The pulverization is performed to a particle size of 100-120 mesh; the heating is performed to a temperature of 115-120°C; the preheating temperature is 75-80°C; the speed control is performed at 2600-3000 rpm; the emulsification time is 10-15 min; the inlet air temperature of the spray drying tower is 185-190°C; and the outlet air temperature is 80-85°C.

[0023] In a preferred embodiment of the present invention, the leveling agent includes CrayvallacFLOW-100 or BYK-361N.

[0024] A second aspect of the present invention provides a production process for a high-flexibility powder for coatings, comprising the following steps: Functionalized composite fillers, high-toughness polyester resin, curing agent HAA, leveling agent and benzoin are premixed and then melt-blended using a twin-screw extruder. After extrusion, tableting, crushing and sieving, a high-flexibility powder product for coatings is obtained.

[0025] This invention utilizes the combined effect of functionalized composite filler interface gradient toughening and the intrinsic toughening of high-toughness polyester resin as the matrix resin. At the microscopic interface, a gradient elastic layer eliminates stress concentration caused by excessive modulus ratio, and interlayer covalent bonds completely block the migration pathways of small molecules. In the macroscopic matrix, flexible polyurethane prepolymer segments are covalently embedded into the polyester backbone through molecular design, giving the cross-linked network high elongation capacity, overcoming the fundamental defect of poor deformability of conventional thermosetting resins, and simultaneously solving the problems of interface stress concentration and low-temperature brittleness of the matrix, effectively improving overall flexibility. Furthermore, the raw materials used in the overall technical solution are readily available, economical, and environmentally friendly, and the overall production process is easy to operate and facilitates continuous production.

[0026] In a preferred embodiment of the present invention, the premixing speed is 1800-2000 rpm and the time is 3-3.5 min; the barrel temperature of the twin-screw extruder is 95-105℃ and the screw speed is 320-350 rpm; the sieving is performed through a 200-250 mesh sieve.

[0027] The beneficial effects of this invention are: (1) In the process of preparing high-toughness polyester resin, the present invention first synthesizes polyurethane prepolymer with isophorone diisocyanate and polytetrahydrofuran ether diol and then embeds it into the polyester main chain. When subjected to force, the flexible polyether segment dissipates the external force through conformational transformation, thereby achieving toughening of the matrix resin and lowering Tg, improving the low-temperature brittleness resistance of the matrix and the low-temperature deformation performance of the coating, and improving flexibility. At the same time, the secondary addition of isophthalic acid after block formation introduces an asymmetric meta-benzene ring structure, which can further optimize the resin Tg, improve the compatibility of the resin with curing agent and additives and the melt flowability of powder coating, so that the impact resistance and flexibility of the coating are better and it is not easy to crack after spraying.

[0028] (2) In this invention, an amino group is introduced on the surface of the filler as a site for subsequent epoxy reaction by spraying in a silane hydrolysate prepared with silane coupling agent KH-550. The amino group on the surface of the filler is reacted with an aqueous solution of polypropylene glycol diglycidyl ether. Then, a solution A prepared with polyetheramine D-400 is added to jointly construct a gradient elastic layer with decreasing modulus from the inside to the outside. This allows the gradient elastic layer to effectively disperse and dissipate stress when subjected to external force, thereby improving the flexibility of the coating. On this basis, this invention also adds a carboxyl-terminated polyester resin as a protective shell to protect the inner elastic layer and avoid direct exposure of the elastic layer. At the same time, the outer shell polyester has the same structure as the matrix resin and can form a semi-interpenetrating network with the matrix, which strengthens the stability of the interface between the filler and the matrix and further enhances the flexibility of the finished product.

[0029] (3) This invention effectively improves the overall flexibility and impact resistance of the prepared coating powder through the combined effect of the functionalized composite filler interface gradient toughening and the intrinsic toughening of the high-toughness polyester resin as the matrix resin. Moreover, the coating after spraying is free from defects such as blistering, cracking, wrinkling or peeling. Furthermore, the raw materials used in the overall technical solution of this invention are readily available, economical and environmentally friendly, and the overall production process is easy to operate and facilitates continuous production. Detailed Implementation

[0030] The present invention is not limited to the following embodiments, and the specific implementation can be determined according to the technical solution of the present invention and the actual situation.

[0031] The polypropylene glycol diglycidyl ether used in this invention, model: EPG-207, was purchased from: Yantai Olive Chemical Co., Ltd. The titanium dioxide used was rutile titanium dioxide, type R6600, purchased from Shandong Lubei Chemical Co., Ltd. The barium sulfate used was purchased from Hebei Yudong Coatings Co., Ltd., and its product name was industrial precipitated barium sulfate. The carboxyl-terminated polyester resin used is branded Allnex, model CRYLCOAT® 2440-2, with an acid value of 30-35 mgKOH / g, a softening point of 110-120℃, and a Tg of 63℃. It is manufactured by Allnex Resin (China) Co., Ltd. The above will not be repeated hereafter. The present invention will be further described below with reference to the embodiments: Preparation Example 1 Add 15.2g of silane coupling agent KH-550 to 230mL of 12% ethanol aqueous solution, adjust the pH to 4.7 with acetic acid, and hydrolyze at room temperature for 28min to prepare silane hydrolysate for later use. Dissolve 30.4 g of polypropylene glycol diglycidyl ether in 325 mL of deionized water to prepare an aqueous solution of polypropylene glycol diglycidyl ether for later use. Dissolve 18.4g of polyetheramine D-400 in 203mL of deionized water to prepare solution A, and set aside for later use; 594g of titanium dioxide and 347g of barium sulfate were mixed at 1840rpm for 11min and then sprayed into the prepared silane hydrolysate. The mixture was stirred at 23℃ for 31min, heated to 76℃, and dried under -0.07MPa negative pressure for 1h to obtain an aminated composite filler. 510g of deionized water was added and heated to 56℃ and stirred for 33min to obtain slurry A. Slowly add 38% of the total mass of the prepared polypropylene glycol diglycidyl ether aqueous solution to slurry A and stir at 56°C for 26 minutes. Mix the remaining polypropylene glycol diglycidyl ether aqueous solution with all of solution A and add it to slurry A at a uniform rate. Stir at 56°C for 1 hour and then raise the temperature to 76°C and keep it at that temperature for 32 minutes to obtain slurry B. 38.8g of end-carboxyl polyester resin with an acid value of 32.6mgKOH / g and a softening point of 112℃ was pulverized to 100 mesh and then heated to 116℃ for later use. After preheating slurry B to 76℃, it is slowly poured into the prepared carboxyl-terminated polyester resin at a controlled speed of 2680 rpm and emulsified for 11 minutes. Then, it is transferred to a spray drying tower with an inlet air temperature of 186℃ and an outlet air temperature of 81℃ for drying and collection to obtain the functionalized composite filler.

[0032] Preparation Example 2 Add 15g of silane coupling agent KH-550 to 206mL of 15% ethanol aqueous solution, adjust the pH to 5.5 with acetic acid, and hydrolyze at room temperature for 22min to prepare silane hydrolysate for later use. Dissolve 32g of polypropylene glycol diglycidyl ether in 305mL of deionized water to prepare an aqueous solution of polypropylene glycol diglycidyl ether for later use. Dissolve 19.6g of polyetheramine D-400 in 200mL of deionized water to prepare solution A, and set aside for later use; 590g of titanium dioxide and 354g of barium sulfate were mixed at 1800rpm for 14min and then sprayed into the prepared silane hydrolysate. The mixture was stirred at 23℃ for 34min, heated to 79℃, and dried under -0.07MPa negative pressure for 1.5h to obtain an aminated composite filler. 540g of deionized water was added and heated to 59℃ and stirred for 42min to obtain slurry A. Slowly add 39% of the total mass of the prepared polypropylene glycol diglycidyl ether aqueous solution to slurry A and stir at 55°C for 29 minutes. Mix the remaining polypropylene glycol diglycidyl ether aqueous solution with all of solution A and add it dropwise to slurry A at a uniform rate. Stir at 59°C for 1 hour and then raise the temperature to 79°C and keep it at that temperature for 38 minutes to obtain slurry B. 41.2g of carboxyl-terminated polyester resin with an acid value of 34.4mgKOH / g and a softening point of 118℃ was pulverized to 120 mesh and then heated to 119℃ for later use. After preheating slurry B to 79°C, it is slowly poured into the prepared carboxyl-terminated polyester resin at a controlled speed of 2920 rpm and emulsified for 14 minutes. Then, it is transferred to a spray drying tower with an inlet air temperature of 189°C and an outlet air temperature of 84°C for drying and collection to obtain the functionalized composite filler.

[0033] Preparation Example 3 Add 15.8g of silane coupling agent KH-550 to 224mL of 10% ethanol aqueous solution, adjust the pH to 5.3 with acetic acid, and hydrolyze at room temperature for 20min to prepare silane hydrolysate for later use. Dissolve 31.6 g of polypropylene glycol diglycidyl ether in 312 mL of deionized water to prepare an aqueous solution of polypropylene glycol diglycidyl ether for later use. Dissolve 19g of polyetheramine D-400 in 212mL of deionized water to prepare solution A, and set aside. 606g of titanium dioxide and 351g of barium sulfate were mixed at a controlled speed of 1960rpm for 10min, then sprayed into the prepared silane hydrolysate and stirred at 24℃ for 30min. The temperature was raised to 80℃ and stirred and dried for 1h under a negative pressure of -0.07MPa to obtain an aminated composite filler. 500g of deionized water was added and heated to 55℃ and stirred for 30min to obtain slurry A. Slowly add 38% of the total mass of the prepared polypropylene glycol diglycidyl ether aqueous solution to slurry A and stir at 60°C for 25 minutes. Mix the remaining polypropylene glycol diglycidyl ether aqueous solution with all of solution A and add it to slurry A at a uniform rate. Stir at 55°C for 1 hour and then raise the temperature to 75°C and keep it at that temperature for 30 minutes to obtain slurry B. 38g of carboxyl-terminated polyester resin with an acid value of 32mgKOH / g and a softening point of 110℃ was pulverized to 100 mesh and then heated to 115℃ for later use. After preheating slurry B to 75°C, it is slowly poured into the prepared carboxyl-terminated polyester resin at a controlled speed of 2600 rpm and emulsified for 10 minutes. Then, it is transferred to a spray drying tower with an inlet air temperature of 185°C and an outlet air temperature of 80°C for drying and collection to obtain the functionalized composite filler.

[0034] Preparation Example 4 Add 16g of silane coupling agent KH-550 to 200mL of 10% ethanol aqueous solution, adjust the pH to 4.5 with acetic acid, and hydrolyze at room temperature for 25min to prepare silane hydrolysate for later use. Dissolve 30g of polypropylene glycol diglycidyl ether in 320mL of deionized water to prepare an aqueous solution of polypropylene glycol diglycidyl ether for later use. Dissolve 18g of polyetheramine D-400 in 215mL of deionized water to prepare solution A, and set aside. 598g of titanium dioxide and 345g of barium sulfate were mixed at 2000rpm for 15min and then sprayed into the prepared silane hydrolysate. The mixture was stirred at 25℃ for 35min, heated to 75℃, and dried under -0.08MPa negative pressure for 1.5h to obtain an aminated composite filler. 550g of deionized water was added and heated to 60℃ and stirred for 45min to obtain slurry A. Slowly add 40% of the total mass of the prepared polypropylene glycol diglycidyl ether aqueous solution to slurry A and stir at 57°C for 30 minutes. Mix the remaining polypropylene glycol diglycidyl ether aqueous solution with all of solution A and add it dropwise to slurry A at a uniform rate. Stir at 60°C for 1.5 hours and then raise the temperature to 80°C and keep it at that temperature for 40 minutes to obtain slurry B. 42g of end-carboxyl polyester resin with an acid value of 35mgKOH / g and a softening point of 120℃ was pulverized to 120 mesh and then heated to 120℃ for later use. After preheating slurry B to 80℃, it is slowly poured into the prepared carboxyl-terminated polyester resin at a controlled speed of 3000 rpm and emulsified for 15 minutes. Then, it is transferred to a spray drying tower with an inlet air temperature of 190℃ and an outlet air temperature of 85℃ for drying and collection to obtain the functionalized composite filler.

[0035] Preparation Example 5 Add 15.5g of silane coupling agent KH-550 to 215mL of 15% ethanol aqueous solution, adjust the pH to 5.0 with acetic acid, and hydrolyze at room temperature for 30min to prepare silane hydrolysate for later use. Dissolve 31g of polypropylene glycol diglycidyl ether in 300mL of deionized water to prepare an aqueous solution of polypropylene glycol diglycidyl ether for later use. Dissolve 20g of polyetheramine D-400 in 208mL of deionized water to prepare solution A, and set aside. 610g of titanium dioxide and 356g of barium sulfate were mixed at 1900rpm for 12min and then sprayed into the prepared silane hydrolysate. The mixture was stirred at 24.5℃ for 32min, heated to 77℃, and dried under -0.08MPa negative pressure for 1h to obtain an aminated composite filler. 525g of deionized water was added and heated to 57℃ and stirred for 38min to obtain slurry A. Slowly add 39% of the total mass of the prepared polypropylene glycol diglycidyl ether aqueous solution to slurry A and stir at 59°C for 27 minutes. Mix the remaining polypropylene glycol diglycidyl ether aqueous solution with all of solution A and add it dropwise to slurry A at a uniform rate. Stir at 57°C for 1.5 hours and then raise the temperature to 77°C and keep it at that temperature for 35 minutes to obtain slurry B. 40g of end-carboxyl polyester resin with an acid value of 33mgKOH / g and a softening point of 115℃ was pulverized to 120 mesh and then heated to 117℃ for later use. After preheating slurry B to 77°C, it is slowly poured into the prepared carboxyl-terminated polyester resin at a controlled speed of 2800 rpm and emulsified for 12 minutes. Then, it is transferred to a spray drying tower with an inlet air temperature of 187°C and an outlet air temperature of 82°C for drying and collection to obtain the functionalized composite filler.

[0036] Example 1 High-flexibility powder for coatings is prepared using the following method: Under dry nitrogen protection, 13g of polytetrahydrofuran ether diol (Mn=1000) was vacuum dehydrated at 105℃ for 1h, cooled to 70℃, and 6.9g of isophorone diisocyanate was slowly added dropwise while stirring at 70℃ for 2.5h to obtain polyurethane prepolymer. 27.1g neopentyl glycol, 1.3g trimethylolpropane, 29.6g terephthalic acid, 5.5g isophthalic acid (first part), 6.3g adipic acid, 0.012g hydroquinone monomethyl ether, and 0.05g butylstannic acid were mixed, heated to 220℃ under nitrogen, and stirred until the acid value was 2mgKOH / g. The mixture was then cooled to 135℃, polyurethane prepolymer was added, and stirred for 1 hour. 4g of isophthalic acid (second part) was added, and the mixture was stirred until the acid value was 30mgKOH / g. The mixture was then vacuumed to -0.08MPa at 130℃ and maintained for 20 minutes. The mixture was then discharged, cooled, and pulverized to obtain a high-toughness polyester resin. 392g of the functionalized composite filler prepared in Example 4, 548g of high-toughness polyester resin, 34.2g of curing agent HAA, 9.8g of CrayvallacFLOW-100 and 7.2g of benzoin were premixed at 1840rpm for 3min. The mixture was then melt-blended using a twin-screw extruder with a barrel temperature of 97℃ and a screw speed of 326rpm. After extrusion, tableting, crushing and passing through a 220-mesh sieve, a high-flexibility powder for coatings was obtained.

[0037] Example 2 High-flexibility powder for coatings is prepared using the following method: Under dry nitrogen protection, 17g of polytetrahydrofuran ether diol (Mn=1000) was vacuum dehydrated at 110℃ for 1.5h, cooled to 75℃, and 7.1g of isophorone diisocyanate was slowly added dropwise while stirring at 80℃ for 2.5h to obtain polyurethane prepolymer. 21.7g neopentyl glycol, 1.1g trimethylolpropane, 24.3g terephthalic acid, 5g isophthalic acid (first part), 6.8g adipic acid, 0.011g hydroquinone monomethyl ether, and 0.06g butylstannic acid were mixed, heated to 240℃ under nitrogen and stirred until the acid value was 5mgKOH / g. The mixture was then cooled to 140℃, polyurethane prepolymer was added, and stirred for 1.5h. 6g of isophthalic acid (second part) was added, and the mixture was stirred until the acid value was 40mgKOH / g. The mixture was then vacuumed to -0.09MPa at 140℃ and maintained for 40min. The mixture was then discharged, cooled, and pulverized to obtain a high-toughness polyester resin. 408g of the functionalized composite filler prepared in Example 2, 572g of high-toughness polyester resin, 35.8g of curing agent HAA, 10.2g of BYK-361N and 7.8g of benzoin were premixed at 1960rpm for 3min. The mixture was then melt-blended using a twin-screw extruder with a barrel temperature of 103℃ and a screw speed of 344rpm. After extrusion, tableting, crushing and passing through a 200-mesh sieve, a high-flexibility powder for coatings was obtained.

[0038] Example 3 High-flexibility powder for coatings is prepared using the following method: Under dry nitrogen protection, 16g of polytetrahydrofuran ether diol (Mn=1000) was vacuum dehydrated at 109℃ for 1h, cooled to 74℃, and 8.3g of isophorone diisocyanate was slowly added dropwise while stirring at 79℃ for 2h to obtain polyurethane prepolymer. 28.3g neopentyl glycol, 0.9g trimethylolpropane, 31.7g terephthalic acid, 5.8g isophthalic acid (first part), 5.5g adipic acid, 0.01g hydroquinone monomethyl ether, and 0.05g butylstannic acid were mixed, heated to 236℃ under nitrogen and stirred until the acid value was 4mgKOH / g. The mixture was then cooled to 139℃, polyurethane prepolymer was added, and stirred for 1.5h. 5.6g isophthalic acid (second part) was added, and the mixture was stirred until the acid value was 38mgKOH / g. The mixture was then vacuumed to -0.09MPa at 138℃ and maintained for 34min. The mixture was then discharged, cooled, and pulverized to obtain a high-toughness polyester resin. 386g of the functionalized composite filler prepared in Example 3, 540g of high-toughness polyester resin, 33.7g of curing agent HAA, 9.6g of CrayvallacFLOW-100 and 7g of benzoin were premixed at 1800rpm for 3.5min. The mixture was then melt-blended using a twin-screw extruder with a barrel temperature of 95℃ and a screw speed of 320rpm. After extrusion, tableting, crushing and passing through a 200-mesh sieve, a high-flexibility powder for coatings was obtained.

[0039] Example 4 High-flexibility powder for coatings is prepared using the following method: Under dry nitrogen protection, 15g of polytetrahydrofuran ether diol (Mn=1000) was vacuum dehydrated at 108℃ for 1h, cooled to 73℃, and 9.1g of isophorone diisocyanate was slowly added dropwise while stirring at 76℃ for 2h to obtain polyurethane prepolymer. 25.5g neopentyl glycol, 1.2g trimethylolpropane, 25.8g terephthalic acid, 6g isophthalic acid (first part), 5.9g adipic acid, 0.01g hydroquinone monomethyl ether, and 0.06g butylstannic acid were mixed, heated to 232℃ under nitrogen, and stirred until the acid value was 3mgKOH / g. The mixture was then cooled to 136℃, polyurethane prepolymer was added, and stirred for 1.5h. 5g of isophthalic acid (second part) was added, and the mixture was stirred until the acid value was 35mgKOH / g. The mixture was then vacuumed to -0.08MPa at 135℃ and maintained for 30min. The mixture was then discharged, cooled, and pulverized to obtain a high-toughness polyester resin. 580g of the functionalized composite filler prepared in Example 5, 414g of high-toughness polyester resin, 36.3g of curing agent HAA, 10.4g of BYK-361N and 8g of benzoin were premixed at 2000rpm for 3.5min. The mixture was then melt-blended using a twin-screw extruder with a barrel temperature of 105℃ and a screw speed of 350rpm. After extrusion, tableting, crushing and passing through a 250-mesh sieve, a high-flexibility powder for coatings was obtained.

[0040] Example 5 High-flexibility powder for coatings is prepared using the following method: Under dry nitrogen protection, 14g of polytetrahydrofuran ether diol (Mn=1000) was vacuum dehydrated at 107℃ for 1.5h, cooled to 72℃, and 7.7g of isophorone diisocyanate was slowly added dropwise while stirring at 73℃ for 2h to obtain polyurethane prepolymer. 24.3g neopentyl glycol, 1g trimethylolpropane, 27g terephthalic acid, 5.2g isophthalic acid (first part), 5.2g adipic acid, 0.011g hydroquinone monomethyl ether, and 0.05g butylstannic acid were mixed, heated to 228℃ under nitrogen and stirred until the acid value was 3mgKOH / g. The mixture was then cooled to 137℃, polyurethane prepolymer was added, and stirred for 1 hour. 4.4g of isophthalic acid (second part) was added, and the mixture was stirred until the acid value was 32mgKOH / g. The mixture was then vacuumed to -0.08MPa at 132℃ and maintained for 26 minutes. The mixture was then discharged, cooled, and pulverized to obtain a high-toughness polyester resin. 400g of the functionalized composite filler prepared in Example 1, 560g of high-toughness polyester resin, 35g of curing agent HAA, 10g of CrayvallacFLOW-100 and 7.5g of benzoin were premixed at 1900rpm for 3min. The mixture was then melt-blended using a twin-screw extruder with a barrel temperature of 100℃ and a screw speed of 335rpm. After extrusion, tableting, crushing and passing through a 220-mesh sieve, a high-flexibility powder for coatings was obtained.

[0041] Comparative Example 1 Compared with Example 5, the difference is that no polyurethane prepolymer is added, while the other operation steps and parameters remain unchanged.

[0042] Comparative Example 2 Compared with Example 5, the difference is that no second part of isophthalic acid is added, while the other operation steps and parameters remain unchanged.

[0043] Comparative Example 3 Compared with Example 5, the difference is that the functionalized composite filler prepared in Preparation Example 1 of Example 5 is replaced with a functionalized composite filler that does not spray in silane hydrolysate, while the other operation steps and parameters remain unchanged.

[0044] Comparative Example 4 Compared with Example 5, the difference is that the functionalized composite filler prepared in Example 1 of Example 5 is replaced with a functionalized composite filler that does not contain an aqueous solution of polypropylene glycol diglycidyl ether, while the other operation steps and parameters remain unchanged.

[0045] Comparative Example 5 Compared with Example 5, the difference is that the functionalized composite filler prepared in Preparation Example 1 was replaced with a functionalized composite filler without the addition of solution A, while the other operation steps and parameters remained unchanged.

[0046] Comparative Example 6 Compared with Example 5, the difference is that the functionalized composite filler prepared in Example 1 of Example 5 is replaced with a functionalized composite filler without added carboxyl-terminated polyester resin, while the other operation steps and parameters remain unchanged.

[0047] Experimental testing: Preparation of test samples: Under the same spraying pressure, the high-flexibility powder coatings prepared in Examples 1-5 and Comparative Examples 1-6 were sprayed onto preheated galvanized tinplate by high-pressure electrostatic spraying. The thickness of the galvanized tinplate was 0.2 mm, the coating thickness was 60 μm, the curing temperature was 200 °C, and the curing time was 5 min. Thus, the test samples prepared from the high-flexibility powder coatings prepared in Examples 1-5 and Comparative Examples 1-6 were obtained. (1) Coating appearance test: Observe whether the test sample prepared above has any of the following phenomena: blistering, cracking, wrinkling and peeling. The final results are shown in Table 1. (2) Flexibility test: At room temperature: T-bend tests were performed on the test samples prepared in Examples 1-5 and Comparative Examples 1-6, in accordance with GB / T 30791-2014. At low temperatures: After the test samples prepared in Examples 1-5 and Comparative Examples 1-6 are kept at -30°C for 2 hours, T-bend tests are immediately performed in accordance with GB / T30791-2014. The flexibility was evaluated using the T-level, with higher T-levels indicating poorer flexibility. The final results are shown in Table 1. (3) Impact resistance test: In accordance with GB / T 1732-2020, the impact resistance test was carried out on the test samples prepared by Examples 1-5 and Comparative Examples 1-6. A 4x magnifying glass was used to observe whether there were cracks, wrinkles and peeling. The maximum drop height of the hammer was recorded when no cracks, wrinkles and peeling were observed in the three tests. The greater the maximum drop height of the hammer, the better the impact resistance of the paint film. The final results are shown in Table 1.

[0048] Table 1

[0049] As can be seen from the appearance of the paint film in Table 1, Examples 1-5 all exhibited excellent coating integrity, with no defects such as blistering, cracking, wrinkling or peeling. This indicates that the high-flexibility powder coating product prepared by the formulation of the present invention has a stable and smooth appearance after film formation.

[0050] As can be seen from the flexibility and impact resistance data in Table 1, the T-bend rating of Examples 1-5 of the present invention does not exceed 1T at room temperature and does not exceed 2T at low temperature, and the maximum height of the hammer drop can reach 75-80cm. Compared with Comparative Examples 1-6, they all have lower T-bend ratings and greater maximum hammer drop heights, indicating that the present invention can significantly improve the flexibility and impact resistance of powder coatings after film formation by using high-toughness polyester resin in combination with functionalized composite fillers.

[0051] Of course, the present invention may have other various embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications according to the present invention, but these corresponding changes and modifications should all fall within the protection scope of the present invention.

Claims

1. A highly flexible powder for coatings, characterized in that, Including the following parts by weight of raw materials: 540-580 parts by weight of high-toughness polyester resin, 386-414 parts by weight of functionalized composite filler, 33.7-36.3 parts by weight of curing agent HAA, 9.6-10.4 parts by weight of leveling agent and 7-8 parts by weight of benzoin; The preparation method of the high-toughness polyester resin includes the following steps: under nitrogen protection, polytetrahydrofuran ether glycol is dehydrated, and then isophorone diisocyanate is added dropwise while cooling and stirring to obtain a polyurethane prepolymer; neopentyl glycol, trimethylolpropane, terephthalic acid, a first part of isophthalic acid, adipic acid, polymerization inhibitor and catalyst are mixed, nitrogen is introduced, the mixture is heated and stirred, the polyurethane prepolymer is added while cooling and stirring, a second part of isophthalic acid is added and stirred again, vacuum is applied, the mixture is discharged, cooled and pulverized to obtain the high-toughness polyester resin; The functionalized composite filler is first introduced with amino and silane bonds by a silane coupling agent, then coated sequentially with polypropylene glycol diglycidyl ether and polyetheramine, and finally mixed with carboxyl-terminated polyester resin and obtained by spray drying.

2. The high-flexibility powder for coatings according to claim 1, characterized in that, The composition is as follows: polytetrahydrofuran ether diol 13-17 parts, isophorone diisocyanate 6.9-9.1 parts, neopentyl glycol 21.7-28.3 parts, trimethylolpropane 0.9-1.3 parts, terephthalic acid 24.3-31.7 parts, first part isophthalic acid 5-6 parts, adipic acid 5.2-6.8 parts, polymerization inhibitor 0.01-0.012 parts, catalyst 0.05-0.06 parts, second part isophthalic acid 4-6 parts; The polymerization inhibitor includes hydroquinone monomethyl ether, and the catalyst includes butyltin acid.

3. The high-flexibility powder for coatings according to claim 1, characterized in that, The dehydration is carried out under vacuum at a controlled temperature of 105-110℃ for 1-1.5 hours; the cooling is carried out at 70-75℃; the stirring is carried out at 70-80℃ for 2-2.5 hours; the heating and stirring is carried out at 220-240℃ until the acid value is 2-5 mgKOH / g; the cooling and stirring of polyurethane prepolymer is carried out at 135-140℃ for 1-1.5 hours; the re-stirring is carried out until the acid value is 30-40 mgKOH / g; the vacuuming is carried out at 130-140℃ to (-0.08)-(-0.095) MPa and maintained for 20-40 minutes.

4. The high-flexibility powder for coatings according to claim 1, characterized in that, The preparation method of the functionalized composite filler includes the following steps: A silane hydrolysate was prepared by dissolving a silane coupling agent and an aqueous ethanol solution, a polypropylene glycol diglycidyl ether was dissolved in deionized water to prepare an aqueous solution of polypropylene glycol diglycidyl ether, and a polyether amine was dissolved in deionized water to prepare solution A. Titanium dioxide and barium sulfate were mixed at a controlled rate, sprayed into silane hydrolysate and stirred, heated, and dried under negative pressure to obtain an aminated composite filler. Deionized water was added and heated and stirred to obtain slurry A. Part of the polypropylene glycol diglycidyl ether aqueous solution was added dropwise to slurry A and stirred once under controlled temperature. The remaining polypropylene glycol diglycidyl ether aqueous solution was mixed with all of solution A and then added dropwise to slurry A at a uniform rate and stirred twice under controlled temperature. After heating, the temperature was maintained to obtain slurry B. The carboxyl-terminated polyester resin is pulverized and heated for later use; slurry B is preheated and then poured into the prepared carboxyl-terminated polyester resin at a controlled rate for emulsification, then transferred to a spray drying tower for drying and collection to obtain the functionalized composite filler.

5. The high-flexibility powder for coatings according to claim 4, characterized in that, The ratio of the silane coupling agent to the ethanol aqueous solution is 15-16g:200-230mL; the ratio of the polypropylene glycol diglycidyl ether to deionized water is 30-32g:300-325mL; and the ratio of the polyether amine to deionized water is 18-20g:200-215mL. In the preparation of slurry A: the titanium dioxide is 590-610 parts by weight, the barium sulfate is 345-356 parts by weight, the silane hydrolysate is 216-245 parts by weight, and the deionized water is 500-550 parts by weight. The controlled mixing speed is 1800-2000 rpm for 10-15 min; the temperature of the silane hydrolysate injection and stirring is 23-25℃ for 30-35 min; the temperature rise is to 75-80℃; the pressure of the negative pressure stirring and drying is (-0.07)-(-0.08) MPa for 1-1.5 h; the heating and stirring is to heat to 55-60℃ and stir for 30-45 min.

6. The high-flexibility powder for coatings according to claim 4, characterized in that, In the process of preparing slurry B: The mass of the portion of the polypropylene glycol diglycidyl ether aqueous solution is 38%-40% of the total mass of the polypropylene glycol diglycidyl ether aqueous solution; The temperature for the first temperature-controlled stirring is 55-60℃, and the time is 25-30 min; the temperature for the second temperature-controlled stirring is 55-60℃, and the time is 1-1.5 h; the temperature rise is to 75-80℃; and the holding time is 30-40 min.

7. The high-flexibility powder for coatings according to claim 4, characterized in that, In the process of preparing functionalized composite fillers: The carboxyl-terminated polyester resin is 38-42 parts by weight, and the slurry B is 950-1050 parts by weight. The pulverization is performed to a particle size of 100-120 mesh; the heating is performed to a temperature of 115-120°C; the preheating temperature is 75-80°C; the speed control is performed at 2600-3000 rpm; the emulsification time is 10-15 min; the inlet air temperature of the spray drying tower is 185-190°C; and the outlet air temperature is 80-85°C.

8. A production process for a high-flexibility powder for coatings as described in any one of claims 1-7, characterized in that, Includes the following steps: Functionalized composite fillers, high-toughness polyester resin, curing agent HAA, leveling agent and benzoin are premixed and then melt-blended using a twin-screw extruder. After extrusion, tableting, crushing and sieving, a high-flexibility powder product for coatings is obtained.

9. The production process of high-flexibility powder for coatings according to claim 8, characterized in that, The premixing speed is 1800-2000 rpm, and the time is 3-3.5 min; the barrel temperature of the twin-screw extruder is 95-105℃, and the screw speed is 320-350 rpm; the sieving is through a 200-250 mesh sieve.

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