High-temperature-resistant powder coating and preparation method thereof

Abstract

The invention discloses a high-temperature-resistant powder coating and a preparation method thereof, and belongs to the technical field of coating production, firstly, the high-temperature-resistant powder coating is prepared from the following raw materials in parts by mass: 50-60 parts of organic silicon resin, 30-35 parts of gradient coating filler, 5-8 parts of PSU-SH modified resin, 1.5-2.0 parts of a titanate coupling agent and 0.5-1.0 part of a flatting agent. Wherein the gradient coating filler is prepared by the following steps: pretreating nano aluminum oxide with a silane coupling agent KH-550 to form hydroxylated nano aluminum oxide, forming an Al2O3-coated SiO2 core-shell structure with fused silicon dioxide, and performing fluidized bed spraying and curing on the Al2O3-coated SiO2 core-shell structure and silicone oil pre-modified white carbon black; wherein the PSU-SH modified resin is prepared by the following steps: dehydrating and activating PSU resin, then carrying out sulfydryl grafting reaction on the dehydrated and activated PSU resin and 3-mercaptopropionic acid under the catalysis of dicyclohexylcarbodiimide and 4-dimethylaminopyridine, and then precipitating and purifying with methanol.

Description

Technical Field

[0001] The invention belongs to the technical field of coating production, and particularly relates to a high-temperature resistant powder coating and a preparation method thereof. Background Art

[0002] With the development of high-end manufacturing, components such as automotive turbochargers and aircraft engine casings are placing increasingly stringent demands on coatings with high temperature resistance. Conventional powder coatings exhibit significant yellowing and chalking at temperatures above 300°C, rendering them ineffective. While mainstream silicone-modified coatings can withstand temperatures of 350°C for short periods, their adhesion drops by more than 50% at 400°C / 24 hours, severely limiting the lifespan of high-temperature equipment.

[0003] Existing technologies mainly improve heat resistance by adding inorganic fillers (such as mica and talc), but there are two major bottlenecks: (1) when the filler content is greater than 25wt%, the coating flexibility drops sharply (impact strength is less than 30kg·cm), and cracking is likely to occur; (2) at high temperatures, microcracks are likely to form at the interface between the resin matrix and the filler, resulting in a salt spray protection performance degradation of more than 80% after aging at 400℃ / 500h.

[0004] The trend toward miniaturization of turbochargers for new energy vehicles has pushed local operating temperatures above 400°C, necessitating the development of coatings that balance high-temperature stability with mechanical strength. Failure to address filler-resin interface degradation will directly lead to increased scrap rates for high-temperature components, severely hindering industrial technological advancement. Summary of the Invention

[0005] Existing high-temperature resistant powder coatings have two major bottlenecks: (1) High filler content leads to deterioration of mechanical properties: when the content of inorganic fillers (such as mica, talc) is greater than 25wt%, the impact strength of the coating is less than 30kg·cm, the flexibility drops sharply, and it is easy to crack; (2) High-temperature interface degradation leads to protection failure: after aging at 400℃ / 500h, microcracks at the resin-filler interface cause the salt spray protection performance to degrade by more than 80%, and the adhesion retention rate is less than 50%.

[0006] The core improvements of this invention are the addition of a self-made gradient-coated filler and a PSU-SH-modified resin to existing powder coatings. For the gradient-coated filler, the present invention superimposes an Al2O3@SiO2 core-shell structure (nanoalumina coated with fused silica) with a silicone oil-modified silica outer layer to form a multilayer buffer interface. For the PSU-SH-modified resin, after thiolation (-SH) of the PSU resin, it forms Si-S bonds with the silicone resin, enhancing interfacial bonding. Synergistically, the gradient-coated filler alleviates thermal stress, while the PSU-SH-modified resin enhances interfacial bonding, jointly resolving the conflict between high-temperature mechanical strength and protective performance. Based on the foregoing, the present invention provides a high-temperature-resistant powder coating and a method for its preparation.

[0007] The purpose of the present invention can be achieved through the following technical solutions: A high-temperature resistant powder coating comprises the following raw materials in parts by weight: 50-60 parts of silicone resin; 30-35 parts of gradient coated filler; 5-8 parts of PSU-SH modified resin; 1.5-2.0 parts of titanate coupling agent; 0.5-1.0 parts of leveling agent; The gradient coated filler is prepared by pre-treating nano-alumina with a silane coupling agent KH-550 to form hydroxylated nano-alumina, then reacting with fused silica to form an Al2O3@SiO2 core-shell structure, and then reacting with silicone oil pre-modified white carbon black through a fluidized bed spraying and aging process; The PSU-SH modified resin is prepared by performing a thiol grafting reaction on a PSU resin after dehydration activation and 3-mercaptopropionic acid under the catalysis of dicyclohexylcarbodiimide and 4-dimethylaminopyridine, and then precipitating and purifying the resin with methanol.

[0008] Furthermore, the gradient coated filler is prepared by the following steps: A1. Add nano-alumina to anhydrous ethanol containing silane coupling agent KH-550, ultrasonically disperse for 20-30 minutes, reflux at 80-90°C for 2-4 hours, and then filter and dry to obtain hydroxylated nano-alumina. A2, add fused silica to isopropanol, ultrasonically disperse for 20 to 30 minutes, and then adjust the pH to 3.8 to 4.2 with acetic acid to obtain a SiO2 dispersion. Then, add hydroxylated nano-alumina to the isopropanol and ultrasonically treat for 20 to 30 minutes to obtain an Al2O3 suspension. Then, add the Al2O3 suspension dropwise to the SiO2 dispersion. At the same time, control the temperature of the system to 58 to 60°C. After the addition is complete, stir for 3 to 4 hours, and then introduce dry nitrogen into the system. Under nitrogen protection, the system is heated to 300°C at 5°C / min and kept warm for 15 to 30 minutes. After completion, the temperature is gradually reduced: from 300°C to 170°C at 5°C / min and kept warm for 20 to 30 minutes, and then cooled to 80°C at 5°C / min and kept warm for 40 to 60 minutes. After completion, the product is obtained, and the product is pulverized by airflow to obtain Al2O3@SiO2 core-shell powder; A3, mixing fumed silica with hydroxy silicone oil, and treating in a high-speed mixer at 80-85° C. for 15-20 min to obtain silicone oil pre-modified silica; A4. Add silicone oil pre-modified silica to anhydrous ethanol and ball mill for 2 hours to obtain a modified silica suspension. Add Al2O3@SiO2 core-shell powder to a fluidized bed and evenly atomize and spray the modified silica suspension therein. The atomization pressure is 0.3-0.5 MPa and the spray gun speed is 2000 rpm. After the modified silica suspension is sprayed, the product is placed at 100-105°C for 1 hour to obtain a gradient coated filler.

[0009] Furthermore, the usage ratio of the nano-alumina, silane coupling agent KH-550, and anhydrous ethanol described in A1 is 55 g:1.0-1.5 g:300 mL.

[0010] Furthermore, the ratio of isopropanol to fused silica in the SiO2 dispersion in A2 is 200 mL:30 g; the ratio of isopropanol to hydroxylated nano-alumina in the Al2O3 suspension is 100 mL:50 g.

[0011] Furthermore, the usage ratio of the fumed silica and the hydroxy silicone oil in A3 is 15g:1.5-2.0g.

[0012] Furthermore, the usage ratio of anhydrous ethanol, silicone oil pre-modified white carbon black, and Al2O3@SiO2 core-shell powder described in A4 is 100mL:10~15g:50g.

[0013] Furthermore, the PSU-SH modified resin is prepared by the following steps: B1. Add NMP solvent to PSU resin, stir and dissolve in an oil bath at 110-120° C. for 1.5-2.0 hours to obtain an activated solution, and dehydrate the activated solution to a water content of ≤100 ppm to obtain a dehydrated activated solution; B2. Add 3-mercaptopropionic acid, dicyclohexylcarbodiimide and 4-dimethylaminopyridine to the dehydrated activation solution. After completion, fill with nitrogen protection, then heat the system to 48-50° C. for pre-reaction for 30 minutes, then heat to 70-74° C. and react at this temperature for 7.5-8.0 hours. After completion of the reaction, obtain a reaction solution. B3. The reaction solution was cooled to 40°C and injected into a precipitation tank containing methanol at 5°C. After dynamic mixing and precipitation, a fibrous precipitate was formed. The fibrous precipitate was centrifuged to collect a fibrous wet cake. The fibrous wet cake was then washed and purified with methanol and deionized water in sequence, and then placed in a vacuum dryer at 80°C for 12 hours. After completion, a PSU-SH modified resin was obtained.

[0014] Furthermore, the usage ratio of the PSU resin, NMP solvent, 3-mercaptopropionic acid, dicyclohexylcarbodiimide, 4-dimethylaminopyridine, and methanol is 100g:300g:20g:0.8-1.0g:0.3-0.5g:800g.

[0015] Furthermore, the preparation method of the high temperature resistant powder coating comprises the following steps: Weigh each raw material according to mass, dry the gradient coated filler at 100-120°C for 2-4h, treat it with the titanate coupling agent in a high-speed mixer at 800rpm for 10-20min, then mix the silicone resin, PSU-SH modified resin and leveling agent and transfer it to a mixing tank, stir it at 25°C for 30min, and after completion, obtain a mixture. The mixture is placed in a twin-screw extruder for segmented temperature-controlled extrusion. The temperature of each zone of the barrel of the twin-screw extruder is set as: 150-160°C for zone 1, 180-190°C for zone 2, and 170-175°C for zone 3. The screw speed of the twin-screw extruder is set to 300rpm. After completion, the extruded material is frozen and crushed by liquid nitrogen, and then passed through a 200-mesh sieve to obtain a high-temperature resistant powder coating.

[0016] Furthermore, the epoxy content of the silicone resin is Dow Corning RSN-0804; the titanate coupling agent is titanate coupling agent NDZ-201; and the leveling agent is leveling agent BYK-361N.

[0017] Beneficial effects of the present invention: By adding a self-made gradient coated filler and PSU-SH modified resin to traditional powder coatings, this invention significantly improves the high-temperature adhesion retention of the powder coatings, while also improving the salt spray protection performance of the powder coatings, while also taking into account the high filler content and excellent mechanical strength of the powder coatings. Specific analysis is as follows: 1. Significantly improve high-temperature adhesion retention rate: Example data: The adhesion retention rate of Examples 7 to 9 after 400°C / 24h reaches 91% to 94%, far exceeding the existing technology.

[0018] Mechanism Analysis: The adhesion retention rate of Comparative Example 1 (no silica coating) was only 65%, proving that the silica outer layer of the gradient filler (such as the silicone oil-modified silica in Example 2) dispersed thermal stress and reduced interfacial microcracks. The retention rate of Comparative Example 3 (no PSU-SH) was only 72%, indicating that the thiol bond (-SH) of PSU-SH formed a Si-S covalent bond with the silicone, enhancing interfacial bonding.

[0019] 2. Breakthrough improvement in salt spray protection performance: Example data: After aging at 400°C / 500h, the salt spray corrosion width of Examples 7 to 9 after 500h is only 0.6 to 1.0mm, which is better than the existing technology (the literature value of corrosion width is greater than 2mm and attenuation is greater than 80%).

[0020] Mechanism analysis: In comparative example 1, the rust width reached 2.8 mm. The lack of the silica outer layer led to thermal stress concentration, which accelerated the penetration of the corrosive medium. In comparative example 3, the rust width was 2.2 mm, proving that the Si-S bonds of PSU-SH closed the interface microgaps.

[0021] 3. Balance high filler content with excellent mechanical strength: Example data: Examples 7 to 9 have an impact strength of 55 to 58 kg·cm, and no cracks are observed after bending at 400°C for 24 hours, which completely solves the bottleneck of the prior art that the impact strength is less than 30 kg·cm when the filler content is greater than 25 wt%.

[0022] Mechanism analysis: The impact strength of comparative example 2 (simple filler mixing) is only 26 kg·cm and breaks when bent, proving that the gradient structure (Al2O3@SiO2 core-shell + silica) matches the thermal expansion coefficient and avoids stress concentration. The impact strength of comparative example 1 is 32 kg·cm (lower than the embodiment >55 kg·cm), highlighting the toughening effect of the silica outer layer.

[0023] 4. Verification of synergistic effect: (1) Necessity of gradient filler: Comparative Example 1 (missing silica layer) VS Example 8: Adhesion retention (65% VS 94%), rust width (2.8 mm VS 0.6 mm) and impact strength (32 kg·cm VS 58 kg·cm) are all deteriorated, proving that gradient coating is the core of inhibiting interface degradation; Comparative Example 2 (no core-shell structure) has an impact strength of 26 kg·cm, which is only half of that of the example, verifying the decisive contribution of gradient design to mechanical strength.

[0024] (2) Irreplaceability of PSU-SH: Comparative Example 3 (ordinary PSU) VS Example 8: There is a significant difference in rust width (2.2 mm VS 0.6 mm) and bending performance (obvious cracks VS no cracks), which confirms that thiol grafting improves interfacial chemical bonding.

[0025] In summary, this invention achieves three breakthrough benefits through the synergistic innovation of gradient coated filler (Al2O3@SiO2 core-shell + white carbon black outer layer) and PSU-SH modified resin: (1) High temperature adhesion stability: 400℃ / 24h adhesion retention rate>90%, solving the high temperature powdering problem; (2) Long-term protection performance: salt spray rust width ≤1.0mm after aging at 400℃ / 500h; (3) Balance between mechanical strength and filler content: impact strength > 55 kg·cm, and high flexibility is maintained when the filler content reaches 30-35 wt%. DETAILED DESCRIPTION

[0026] Below in conjunction with the embodiment of the present invention, the technical scheme in the embodiment of the present invention is clearly and completely described, it is obvious that described embodiment is only a part of embodiment of the present invention, rather than whole embodiment. Based on the embodiment in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work premise all fall within the scope of protection of the present invention. Meanwhile, raw materials, reagents or devices used in the following examples, unless otherwise specified, can be obtained from conventional commercial channels, or can be obtained by existing known methods.

[0027] Example 1

[0028] Preparation of gradient coated fillers: A1. Nano-alumina pretreatment: 55 g of nano-alumina (average particle size 30 nm) was added to 300 mL of anhydrous ethanol containing 1.0 g of silane coupling agent KH-550 (Nanjing Shuguang). Ultrasonic dispersion was performed (power 800 W, frequency 25 kHz) for 20 min. The mixture was refluxed at 80°C for 2 h. After completion, the mixture was filtered and the solid component was dried at 100°C for 5 h to obtain hydroxylated nano-alumina. A2. Fused silica coating: 30 g of fused silica (average particle size 200 nm) was added to 200 mL of isopropanol, and ultrasonic dispersion was performed (40 kHz, 800 W) for 20 min. The pH was then adjusted to 3.8 with acetic acid (at which point the SiO2 surface Zeta potential was +35 mV) to obtain a SiO2 dispersion. 50 g of hydroxylated nano-alumina was then added to 100 mL of isopropanol and ultrasonically treated for 20 min to obtain an Al2O3 suspension. The Al2O3 suspension was then added dropwise to the SiO2 dispersion at a rate of 2 mL / min using a constant pressure dropping funnel. The system temperature was controlled at 58°C (to promote the condensation of surface hydroxyl groups). After the dropwise addition was completed, stirring was continued for 3 hours. Dry nitrogen was then introduced into the system. The system was heated to 300°C at a rate of 5°C / min under nitrogen protection and kept warm for 15 minutes. After completion, the system was gradually cooled: from 300°C to 170°C at a rate of 5°C / min and kept warm for 20 minutes, and then cooled to 80°C at a rate of 5°C / min and kept warm for 40 minutes. After completion, the product was obtained, and the product was pulverized by air flow to obtain Al2O3@SiO2 core-shell powder. The Al2O3@SiO2 core-shell powder has fused silica as the core and hydroxylated alumina as the shell. A3. Surface modification of fumed silica: 15 g of fumed silica was mixed with 1.5 g of hydroxy silicone oil (average molecular weight 4000-5000, hydroxyl content 8.5%) and treated in a high-speed mixer (1200 rpm) at 80°C for 15 min to obtain silicone oil pre-modified silica. A4. Gradient coating molding: Add 10g of silicone oil pre-modified silica to 100mL of anhydrous ethanol and ball mill for 2h to obtain a modified silica suspension. Add 50g of Al2O3@SiO2 core-shell powder into a fluidized bed (inlet air temperature 80℃) and evenly atomize and spray the modified silica suspension. The atomization pressure is 0.3MPa and the spray gun speed is 2000rpm. After the modified silica suspension is sprayed, the product is placed at 100℃ for 1h to obtain a gradient coated filler.

[0029] Example 2

[0030] Preparation of gradient coated fillers: A1. Nano-alumina pretreatment: 55 g of nano-alumina (average particle size 30 nm) was added to 300 mL of anhydrous ethanol containing 1.5 g of silane coupling agent KH-550 (Nanjing Shuguang). Ultrasonic dispersion was performed (power 800 W, frequency 25 kHz) for 30 min. The mixture was refluxed at 85°C for 4 h. After completion, the mixture was filtered and the solid component was dried at 110°C for 6 h to obtain hydroxylated nano-alumina. A2. Fused silica coating: 30 g of fused silica (average particle size 200 nm) was added to 200 mL of isopropanol, and ultrasonic dispersion was performed (40 kHz, 800 W) for 30 min. The pH was then adjusted to 4.0 with acetic acid (at which point the SiO2 surface Zeta potential was +35 mV) to obtain a SiO2 dispersion. 50 g of hydroxylated nano-alumina was then added to 100 mL of isopropanol and ultrasonic treatment was performed for 30 min to obtain an Al2O3 suspension. The Al2O3 suspension was then added dropwise to the SiO2 dispersion at a rate of 2 mL / min using a constant pressure dropping funnel. The system temperature was controlled at 60°C (to promote the condensation of surface hydroxyl groups). After the dropwise addition was completed, stirring was continued for 4 hours. Dry nitrogen was then introduced into the system. The system was heated to 300°C at a rate of 5°C / min under nitrogen protection and kept warm for 30 minutes. After completion, the system was gradually cooled: from 300°C to 170°C at a rate of 5°C / min and kept warm for 30 minutes, and then cooled to 80°C at a rate of 5°C / min and kept warm for 60 minutes. After completion, the product was obtained, and the product was pulverized by air flow to obtain Al2O3@SiO2 core-shell powder. The Al2O3@SiO2 core-shell powder has fused silica as the core and hydroxylated alumina as the shell. A3. Surface modification of fumed silica: 15 g of fumed silica was mixed with 1.8 g of hydroxy silicone oil (average molecular weight 4000-5000, hydroxyl content 8.5%) and treated in a high-speed mixer (1200 rpm) at 80°C for 20 min to obtain silicone oil pre-modified silica. A4. Gradient coating molding: Add 12 g of silicone oil pre-modified silica to 100 mL of anhydrous ethanol and ball mill for 2 h to obtain a modified silica suspension. Add 50 g of Al2O3@SiO2 core-shell powder into a fluidized bed (inlet air temperature 80°C) and evenly atomize and spray the modified silica suspension. The atomization pressure is 0.5 MPa and the spray gun speed is 2000 rpm. After the modified silica suspension is sprayed, the product is placed at 105°C for 1 h to obtain a gradient coated filler.

[0031] Example 3

[0032] Preparation of gradient coated fillers: A1. Nano-alumina pretreatment: 55 g of nano-alumina (average particle size 30 nm) was added to 300 mL of anhydrous ethanol containing 1.5 g of silane coupling agent KH-550 (Nanjing Shuguang). Ultrasonic dispersion was performed (power 800 W, frequency 25 kHz) for 30 min. The mixture was refluxed at 90°C for 4 h. After completion, the mixture was filtered and the solid component was dried at 110°C for 6 h to obtain hydroxylated nano-alumina. A2. Fused silica coating: 30 g of fused silica (average particle size 200 nm) was added to 200 mL of isopropanol, and ultrasonic dispersion (40 kHz, 800 W) was performed for 30 min. The pH value was then adjusted to 4.2 with acetic acid (at which point the SiO2 surface Zeta potential was +35 mV) to obtain a SiO2 dispersion. 50 g of hydroxylated nano-alumina was then added to 100 mL of isopropanol and ultrasonic treatment was performed for 30 min to obtain an Al2O3 suspension. The Al2O3 suspension was then added dropwise to the SiO2 dispersion at a rate of 2 mL / min using a constant pressure dropping funnel. The system temperature was controlled at 60°C (to promote the condensation of surface hydroxyl groups). After the dropwise addition was completed, stirring was continued for 4 hours. Dry nitrogen was then introduced into the system. The system was heated to 300°C at a rate of 5°C / min under nitrogen protection and kept warm for 30 minutes. After completion, the system was gradually cooled: from 300°C to 170°C at a rate of 5°C / min and kept warm for 30 minutes, and then cooled to 80°C at a rate of 5°C / min and kept warm for 60 minutes. After completion, the product was obtained, and the product was pulverized by air flow to obtain Al2O3@SiO2 core-shell powder. The Al2O3@SiO2 core-shell powder has fused silica as the core and hydroxylated alumina as the shell. A3. Surface modification of fumed silica: 15 g of fumed silica was mixed with 2.0 g of hydroxy silicone oil (average molecular weight 4000-5000, hydroxyl content 8.5%) and treated in a high-speed mixer (1200 rpm) at 85°C for 20 min to obtain silicone oil pre-modified silica. A4. Gradient coating molding: Add 15g of silicone oil pre-modified silica to 100mL of anhydrous ethanol and ball mill for 2h to obtain a modified silica suspension. Add 50g of Al2O3@SiO2 core-shell powder into a fluidized bed (inlet air temperature 80℃) and evenly atomize and spray the modified silica suspension. The atomization pressure is 0.5MPa and the spray gun speed is 2000rpm. After the modified silica suspension is sprayed, the product is placed at 105℃ for 1h to obtain a gradient coated filler.

[0033] Example 4

[0034] Preparation of PSU-SH modified resin: B1. PSU activation treatment: 100 g of PSU resin (Udel P-3500) was added to a 500 mL three-necked flask with a condenser, 300 g of NMP solvent (electronic grade) was added thereto, and the mixture was stirred and dissolved in an oil bath at 110° C. (speed 200 rpm) for 1.5 h to obtain a transparent activation solution, which was then dehydrated: the activation solution was connected to a molecular sieve dehydration column (4Å type) and circulated for dehydration at 100° C. for 30 min, with the moisture content being controlled to ≤100 ppm. In this embodiment, the moisture content reached 80 ppm to obtain a dehydrated activation solution; B2. Mercapto grafting reaction: 20 g of 3-mercaptopropionic acid (purity ≥99%), 0.8 g of dicyclohexylcarbodiimide (DCC, reagent grade ≥98%), and 0.3 g of 4-dimethylaminopyridine (DMAP, ≥99%) were added to the dehydrated activated solution in B1. After the addition was completed, nitrogen was introduced into the system for protection. The system was then heated to 48° C. for pre-reaction for 30 min, and then heated to 70° C. for constant temperature reaction for 7.5 h. After completion of the reaction, a reaction solution was obtained. B3. Precipitation and purification: The reaction solution in B2 was cooled to 40°C and injected into a precipitation tank containing 800 g of methanol at 5°C. After dynamic mixing and precipitation (the reaction solution was pumped in at a flow rate of 0.5 L / min, and 5°C methanol was simultaneously pumped in at a flow rate of 1.5 L / min. The two liquids flowed through a tubular static mixer. The turbulence intensity: Reynolds number Re>5000, and the effective precipitation time was about 25 seconds), a fibrous precipitate was formed. The fibrous precipitate was centrifuged to collect a fibrous wet cake. The fibrous wet cake was then washed and purified with methanol and deionized water in sequence, and then dried under vacuum at 80°C (-0.095 MPa) for 12 h. After completion, a PSU-SH modified resin was obtained.

[0035] Example 5

[0036] Preparation of PSU-SH modified resin: B1. PSU activation treatment: 100 g of PSU resin (Udel P-3500) was added to a 500 mL three-necked flask with a condenser, 300 g of NMP solvent (electronic grade) was added thereto, and the mixture was stirred and dissolved in an oil bath at 115° C. (speed 200 rpm) for 2.0 h to obtain a transparent activation solution, which was then dehydrated: the activation solution was connected to a molecular sieve dehydration column (4Å type) and circulated for dehydration at 100° C. for 30 min, with the moisture content being controlled to ≤100 ppm. In this embodiment, the moisture content reached 40 ppm to obtain a dehydrated activation solution; B2. Mercapto grafting reaction: 20 g of 3-mercaptopropionic acid (purity ≥99%), 1.0 g of dicyclohexylcarbodiimide (DCC, reagent grade ≥98%), and 0.4 g of 4-dimethylaminopyridine (DMAP, ≥99%) were added to the dehydrated activated solution in B1. After the addition was complete, nitrogen was introduced into the system for protection. The system was then heated to 50° C. for pre-reaction for 30 min, then heated to 72° C. for constant temperature reaction for 8.0 h. After completion of the reaction, a reaction solution was obtained. B3. Precipitation and purification: The reaction solution in B2 was cooled to 40°C and injected into a precipitation tank containing 800 g of methanol at 5°C. After dynamic mixing and precipitation (the reaction solution was pumped in at a flow rate of 0.5 L / min, and 5°C methanol was simultaneously pumped in at a flow rate of 1.5 L / min. The two liquids flowed through a tubular static mixer. The turbulence intensity: Reynolds number Re>5000, and the effective precipitation time was about 25 seconds), a fibrous precipitate was formed. The fibrous precipitate was centrifuged to collect a fibrous wet cake. The fibrous wet cake was then washed and purified with methanol and deionized water in sequence, and then dried under vacuum at 80°C (-0.095 MPa) for 12 h. After completion, a PSU-SH modified resin was obtained.

[0037] Example 6

[0038] Preparation of PSU-SH modified resin: B1. PSU activation treatment: 100 g of PSU resin (Udel P-3500) was added to a 500 mL three-necked flask with a condenser, 300 g of NMP solvent (electronic grade) was added thereto, and the mixture was stirred and dissolved in an oil bath at 120° C. (speed 200 rpm) for 2.0 h to obtain a transparent activation solution, which was then dehydrated: the activation solution was connected to a molecular sieve dehydration column (4Å type) and circulated for dehydration at 100° C. for 30 min, with the moisture content being controlled to ≤100 ppm. In this embodiment, the moisture content reached 100 ppm to obtain a dehydrated activation solution; B2. Mercapto grafting reaction: 20 g of 3-mercaptopropionic acid (purity ≥99%), 1.0 g of dicyclohexylcarbodiimide (DCC, reagent grade ≥98%), and 0.5 g of 4-dimethylaminopyridine (DMAP, ≥99%) were added to the dehydrated activated solution in B1. After the addition was completed, nitrogen was introduced into the system for protection. The system was then heated to 50° C. for pre-reaction for 30 min, and then heated to 74° C. for constant temperature reaction for 8.0 h. After completion of the reaction, a reaction solution was obtained. B3. Precipitation and purification: The reaction solution in B2 was cooled to 40°C and injected into a precipitation tank containing 800 g of methanol at 5°C. After dynamic mixing and precipitation (the reaction solution was pumped in at a flow rate of 0.5 L / min, and 5°C methanol was simultaneously pumped in at a flow rate of 1.5 L / min. The two liquids flowed through a tubular static mixer. The turbulence intensity: Reynolds number Re>5000, and the effective precipitation time was about 25 seconds), a fibrous precipitate was formed. The fibrous precipitate was centrifuged to collect a fibrous wet cake. The fibrous wet cake was then washed and purified with methanol and deionized water in sequence, and then dried under vacuum at 80°C (-0.095 MPa) for 12 h. After completion, a PSU-SH modified resin was obtained.

[0039] Example 7

[0040] Preparation of high temperature resistant powder coatings: First, the high temperature resistant powder coating includes the following raw materials in parts by weight: Silicone resin (Dow Corning RSN-0804) 50 parts; 30 parts of the gradient coated filler prepared in Example 1; 5 parts of the PSU-SH modified resin prepared in Example 4; Titanate coupling agent (NDZ-201) 1.5 parts; Leveling agent (BYK-361N) 0.5 parts.

[0041] Then, the preparation method of the high temperature resistant powder coating comprises the following steps: The raw materials were weighed according to their mass parts. The gradient coated filler prepared in Example 1 was dried at 100° C. for 2 h, treated with a titanate coupling agent in a high-speed mixer (800 rpm) for 10 min, and then mixed with the silicone resin, the PSU-SH modified resin prepared in Example 4, and the leveling agent, and transferred to a mixing tank. The mixture was stirred at 25° C. for 30 min (speed 200 rpm). After completion, a mixture was obtained, which was placed in a twin-screw extruder for segmented temperature-controlled extrusion. The temperature of each zone of the barrel of the twin-screw extruder was set as follows: 150° C. for zone 1, 180° C. for zone 2, and 170° C. for zone 3. The screw speed of the twin-screw extruder was set to 300 rpm. After completion, the extruded material was frozen and crushed by liquid nitrogen, and then passed through a 200-mesh sieve to obtain a high-temperature resistant powder coating.

[0042] Example 8

[0043] Preparation of high temperature resistant powder coatings: First, the high temperature resistant powder coating includes the following raw materials in parts by weight: Silicone resin (Dow Corning RSN-0804) 55 parts; 32 parts of the gradient coated filler prepared in Example 2; 7.5 parts of the PSU-SH modified resin prepared in Example 5; Titanate coupling agent (NDZ-201) 1.8 parts; Leveling agent (BYK-361N) 0.7 parts.

[0044] Then, the preparation method of the high temperature resistant powder coating comprises the following steps: Each raw material was weighed according to mass parts, the gradient coated filler prepared in Example 2 was dried at 110°C for 4h, treated with a titanate coupling agent in a high-speed mixer (800rpm) for 20min, and then mixed with the silicone resin, the PSU-SH modified resin prepared in Example 5 and the leveling agent and transferred to a mixing tank. The mixture was stirred at 25°C for 30min (speed 200rpm). After completion, a mixture was obtained, which was placed in a twin-screw extruder for segmented temperature-controlled extrusion. The temperature of each zone of the barrel of the twin-screw extruder was set as: 155°C in zone 1, 185°C in zone 2, and 175°C in zone 3. The screw speed of the twin-screw extruder was set to 300rpm. After completion, the extruded material was frozen and crushed by liquid nitrogen and then passed through a 200-mesh sieve to obtain a high-temperature resistant powder coating.

[0045] Example 9

[0046] Preparation of high temperature resistant powder coatings: First, the high temperature resistant powder coating includes the following raw materials in parts by weight: Silicone resin (Dow Corning RSN-0804) 60 parts; 35 parts of the gradient coated filler prepared in Example 3; 8 parts of the PSU-SH modified resin prepared in Example 6; Titanate coupling agent (NDZ-201) 2.0 parts; Leveling agent (BYK-361N) 1.0 part

[0047] Then, the preparation method of the high temperature resistant powder coating comprises the following steps: The raw materials were weighed according to their mass parts. The gradient coated filler prepared in Example 3 was dried at 120° C. for 4 h, treated with a titanate coupling agent in a high-speed mixer (800 rpm) for 20 min, and then mixed with the silicone resin, the PSU-SH modified resin prepared in Example 6, and the leveling agent, and transferred to a mixing tank. The mixture was stirred at 25° C. for 30 min (speed 200 rpm). After completion, a mixture was obtained, which was placed in a twin-screw extruder for segmented temperature-controlled extrusion. The temperature of each zone of the barrel of the twin-screw extruder was set as follows: 160° C. for zone 1, 190° C. for zone 2, and 175° C. for zone 3. The screw speed of the twin-screw extruder was set to 300 rpm. After completion, the extruded material was frozen and crushed by liquid nitrogen, and then passed through a 200-mesh sieve to obtain a high-temperature resistant powder coating.

[0048] Comparative Example 1 Comparative Example 1 is the control group of Example 8, and the gradient coated filler prepared in Example 2 of the raw materials in Example 8 is replaced by the Al2O3@SiO2 core-shell powder prepared in step A2 of Example 2, and the remaining raw materials, raw material amounts and preparation methods remain the same as in Example 8, and finally a high-temperature resistant powder coating is obtained.

[0049] Comparative Example 2 Comparative Example 2 is the control group of Example 8, except that the gradient coated filler prepared in Example 2 of the raw materials in Example 8 is replaced with fused silica (average particle size 200 nm) and the hydroxylated nano-alumina prepared in step A1 of Example 2 are simply mixed in a mass ratio of 3:5. The remaining raw materials, raw material amounts and preparation methods remain the same as in Example 8, and a high-temperature resistant powder coating is finally obtained.

[0050] Comparative Example 3 Comparative Example 3 is the control group of Example 8, in which the PSU-SH modified resin prepared in Example 5 of Example 8 is replaced with the raw material PSU resin (Udel P-3500), and the remaining raw materials, raw material amounts and preparation methods remain the same as in Example 8, and finally a high temperature resistant powder coating is obtained.

[0051] The performance test of the high temperature resistant powder coatings prepared in Examples 7 to 9 and Comparative Examples 1 to 3 was carried out. The performance test process is as follows, and the test results are shown in Table 1: (1) High-temperature adhesion retention rate: Refer to the test process in GB / T 9286-1998 "Scratch test for paint and varnish films" to test the initial adhesion (grade). The paint coating is then baked at 400℃ for 24h, cooled to 25℃, and the adhesion retention rate (%) after 400℃ / 24h is tested.

[0052] (2) Salt spray protection performance attenuation rate: Refer to the test process in GB / T 1771-2007 "Determination of resistance of paints and varnishes to neutral salt spray", place them in 400℃ / 500h aging, then conduct salt spray test for 500h, and finally measure the single-side rust width (mm) of the paint coating.

[0053] (3) Impact strength: Determine the impact strength (kg·cm) of the paint film at 25°C according to the test procedure in GB / T 1732-1993 “Determination of impact resistance of paint films”.

[0054] (4) High temperature flexibility: Refer to the test process in GB / T 6742-2007 "Bending test for paints and varnishes (cylindrical axis)" to measure the bending performance around a 5mm diameter axis after 400℃ / 24h.

[0055] Table 1 Test results project Example 7 Example 8 Example 9 Comparative Example 1 Comparative Example 2 Comparative Example 3 Initial adhesion (level) 0 0 0 0 0 0 400℃ / 24h adhesion retention rate 92% 94% 91% 65% 48% 72% 500h salt spray corrosion width (mm) 0.9 0.6 1.0 2.8 4.5 2.2 Impact strength (kg·cm) 56 58 55 32 26 45 400℃ / 24h bending performance No cracks No cracks No cracks microcracks fracture Obvious cracks According to the data analysis in Table 1: (1) Comparative Example 1 (without silica coating): 400℃ / 24h adhesion retention (65%) / 500h salt spray rust width (2.8mm) significantly deteriorated, proving that: without the outer buffer layer of fumed silica, thermal stress cannot be dispersed, and interface microcracks are aggravated.

[0056] (2) Comparative Example 2 (non-gradient structure): impact strength (26 kg·cm) plummeted, bending fracture, Proof: The thermal expansion coefficients of simple mixed fillers do not match, and stress concentration leads to the collapse of mechanical properties.

[0057] (3) Comparative Example 3 (without PSU-SH modified resin): The 500h salt spray corrosion width (2.2mm) is significantly higher than that of the embodiment (≤1mm), proving that ordinary PSU cannot form Si-S bonds, the interface bonding strength is insufficient, and the corrosive medium is easy to penetrate.

[0058] It should be noted that, in this document, terms such as "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or apparatus that includes a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements that are inherent to such process, method, article or apparatus.

[0059] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A high temperature resistant powder coating, characterized in that: Including the following raw materials by weight: 50-60 parts of silicone resin; 30-35 parts of gradient coated filler; 5-8 parts of PSU-SH modified resin; 1.5-2.0 parts of titanate coupling agent; 0.5-1.0 parts of leveling agent; The gradient coated filler is prepared by pre-treating nano-alumina with a silane coupling agent KH-550 to form hydroxylated nano-alumina, then reacting with fused silica to form an Al2O3@SiO2 core-shell structure, and then reacting with silica pre-modified with silicone oil through a fluidized bed spraying and aging process. The PSU-SH modified resin is prepared by dehydrating and activating PSU resin, then reacting it with 3-mercaptopropionic acid under the catalysis of dicyclohexylcarbodiimide and 4-dimethylaminopyridine for a thiol grafting reaction, and then purifying it through methanol precipitation.

2. A high temperature resistant powder coating according to claim 1, characterized in that: The gradient coated filler is prepared by the following steps: A1. Add nano-alumina to anhydrous ethanol containing silane coupling agent KH-550, ultrasonically disperse for 20-30 minutes, reflux at 80-90°C for 2-4 hours, and then filter and dry to obtain hydroxylated nano-alumina. A2, add fused silica to isopropanol, ultrasonically disperse for 20 to 30 minutes, and then adjust the pH to 3.8 to 4.2 with acetic acid to obtain a SiO2 dispersion. Then, add hydroxylated nano-alumina to the isopropanol and ultrasonically treat for 20 to 30 minutes to obtain an Al2O3 suspension. Then, add the Al2O3 suspension dropwise to the SiO2 dispersion. At the same time, control the temperature of the system to 58 to 60°C. After the addition is complete, stir for 3 to 4 hours, and then introduce dry nitrogen into the system. Under nitrogen protection, the system is heated to 300°C at 5°C / min and kept warm for 15 to 30 minutes. After completion, the temperature is gradually reduced: from 300°C to 170°C at 5°C / min and kept warm for 20 to 30 minutes, and then cooled to 80°C at 5°C / min and kept warm for 40 to 60 minutes. After completion, the product is obtained, and the product is pulverized by airflow to obtain Al2O3@SiO2 core-shell powder; A3, mixing fumed silica with hydroxy silicone oil, and treating in a high-speed mixer at 80-85° C. for 15-20 min to obtain silicone oil pre-modified silica; A4. Add silicone oil pre-modified silica to anhydrous ethanol and ball mill for 2 hours to obtain a modified silica suspension. Add Al2O3@SiO2 core-shell powder to a fluidized bed and evenly atomize and spray the modified silica suspension therein. The atomization pressure is 0.3-0.5 MPa and the spray gun speed is 2000 rpm. After the modified silica suspension is sprayed, the product is placed at 100-105°C for 1 hour to obtain a gradient coated filler.

3. A high temperature resistant powder coating according to claim 2, characterized in that: The usage ratio of the nano-alumina, silane coupling agent KH-550, and anhydrous ethanol described in A1 is 55g:1.0-1.5g:300mL.

4. A high temperature resistant powder coating according to claim 2, characterized in that: The amount ratio of isopropanol and fused silica in the SiO2 dispersion in A2 is 200mL:30g; the amount ratio of isopropanol and hydroxylated nano-alumina in the Al2O3 suspension is 100mL:50g.

5. The high temperature resistant powder coating according to claim 2, characterized in that: The usage ratio of the fumed silica and the hydroxy silicone oil in A3 is 15g:1.5-2.0g.

6. A high temperature resistant powder coating according to claim 2, characterized in that: The usage ratio of anhydrous ethanol, silicone oil pre-modified white carbon black, and Al2O3@SiO2 core-shell powder described in A4 is 100mL:10~15g:50g.

7. The high temperature resistant powder coating according to claim 1, characterized in that: The PSU-SH modified resin is prepared by the following steps: B1. Add NMP solvent to PSU resin, stir and dissolve in an oil bath at 110-120°C for 1.5-2.0 hours to obtain an activated solution, and dehydrate the activated solution to a water content of ≤100 ppm to obtain a dehydrated activated solution; B2. Add 3-mercaptopropionic acid, dicyclohexylcarbodiimide and 4-dimethylaminopyridine to the dehydrated activation solution. After completion, fill with nitrogen protection, then heat the system to 48-50° C. for pre-reaction for 30 minutes, then heat to 70-74° C. and react at this temperature for 7.5-8.0 hours. After completion of the reaction, obtain a reaction solution. B3. The reaction solution was cooled to 40°C and injected into a precipitation tank containing methanol at 5°C. After dynamic mixing and precipitation, a fibrous precipitate was formed. The fibrous precipitate was centrifuged to collect a fibrous wet cake. The fibrous wet cake was then washed and purified with methanol and deionized water in sequence, and then placed in a vacuum dryer at 80°C for 12 hours. After completion, a PSU-SH modified resin was obtained.

8. The high temperature resistant powder coating according to claim 7, characterized in that: The usage ratio of the PSU resin, NMP solvent, 3-mercaptopropionic acid, dicyclohexylcarbodiimide, 4-dimethylaminopyridine and methanol is 100g:300g:20g:0.8-1.0g:0.3-0.5g:800g.

9. A method for preparing a high temperature resistant powder coating according to any one of claims 1 to 8, characterized in that: The following steps are involved: Weigh each raw material according to mass, dry the gradient coated filler at 100-120°C for 2-4h, treat it with the titanate coupling agent in a high-speed mixer at 800rpm for 10-20min, then mix the silicone resin, PSU-SH modified resin and leveling agent and transfer it to a mixing tank, stir it at 25°C for 30min, and after completion, obtain a mixture. The mixture is placed in a twin-screw extruder for segmented temperature-controlled extrusion. The temperature of each zone of the barrel of the twin-screw extruder is set as: 150-160°C for zone 1, 180-190°C for zone 2, and 170-175°C for zone 3. The screw speed of the twin-screw extruder is set to 300rpm. After completion, the extruded material is frozen and crushed by liquid nitrogen, and then passed through a 200-mesh sieve to obtain a high-temperature resistant powder coating.

10. The method for preparing a high temperature resistant powder coating according to claim 9, characterized in that: The epoxy content of the silicone resin is Dow Corning RSN-0804; the titanate coupling agent is titanate coupling agent NDZ-201; and the leveling agent is leveling agent BYK-361N.