Epoxy powder coating and preparation method thereof

Abstract

The invention discloses an epoxy powder coating and a preparation method thereof, and belongs to the technical field of powder coating production, firstly, the epoxy powder coating is prepared from the following raw materials in parts by mass: 100 parts of epoxy resin, 15-20 parts of modified phenolic resin, 12-15 parts of carboxyl-terminated polyester resin, 4-8 parts of nano cerium oxide coated mica, 1.5-2.0 parts of a flatting agent and 0.5-1.0 part of benzoin; the modified phenolic resin is prepared by carrying out addition on bisphenol A phenolic resin and DOPO, neutralizing and carrying out reduced pressure distillation; the carboxyl-terminated polyester resin is prepared by carrying out esterification polycondensation on terephthalic acid, isophthalic acid, neopentyl glycol and trimethylolpropane, and then modifying by trimellitic anhydride; the nano cerium oxide coated mica is prepared by coating white mica powder with cerium oxide precipitate, and then carrying out surface treatment and crushing.

Description

Technical Field

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

[0002] Epoxy powder coatings are widely used in the corrosion protection of metal components, such as pipelines, automotive parts, and building steel structures. They are solvent-free and environmentally friendly, and can form a uniform coating thickness through electrostatic spraying. In recent years, extreme environments such as wind turbine towers and offshore platforms have placed higher demands on coatings for low-temperature application (-5°C to 10°C) and salt spray resistance (≥1000 hours).

[0003] The existing technology uses a bisphenol A epoxy resin and imidazole curing agent system, which has obvious defects: 1) The curing speed drops sharply in low-temperature environments (gel time > 40 minutes at -5°C), resulting in deterioration of coating leveling and orange peel defects; 2) The resistance to moisture and heat cycles is insufficient (bubbling occurs after 240 hours at 85°C / RH95%), making it difficult to meet the needs of high salt fog environments in coastal areas.

[0004] With the surge in offshore wind power installations, there is an urgent need to develop a powder coating that cures quickly in low-temperature environments and exhibits excellent weather resistance. Failure to overcome the conflict between low-temperature curing and durability will severely hinder the construction of facilities in extreme environments. Summary of the Invention

[0005] The purpose of the present invention is to provide an epoxy powder coating and a preparation method thereof, so as to solve the problems of slow curing speed and poor leveling of epoxy powder coating in a low temperature environment of -5°C to 10°C, and at the same time improve its long-term durability in a salt spray environment.

[0006] The purpose of the present invention can be achieved through the following technical solutions: An epoxy powder coating comprises the following raw materials in parts by weight: 100 parts of epoxy resin; 15-20 parts of modified phenolic resin; 12-15 parts of carboxyl-terminated polyester resin; 4-8 parts of nano-cerium oxide coated mica; 1.5-2.0 parts of leveling agent; 0.5-1.0 part of benzoin; The modified phenolic resin is prepared by adding bisphenol A phenolic resin to DOPO, followed by neutralization and reduced pressure distillation; the carboxyl-terminated polyester resin is prepared by esterifying and polycondensing terephthalic acid and isophthalic acid with neopentyl glycol and trimethylolpropane, followed by modification with trimellitic anhydride; the nano-cerium oxide-coated mica is prepared by coating muscovite powder with cerium oxide precipitation, followed by surface treatment and pulverization.

[0007] Furthermore, the modified phenolic resin is prepared by the following steps: A1. Dehydrate bisphenol A phenolic resin under reduced pressure at 115-120° C. for 30 min until the moisture content is ≤0.1% to obtain a dehydrated resin; A2. Cool the dehydrated resin to 80-85°C, then add xylene, DOPO, and p-toluenesulfonic acid as a catalyst. Heat the system to 155-160°C under nitrogen protection and keep the temperature for 3-4 hours to obtain an addition product. A3. Cool the addition product to 50-60° C., add sodium carbonate thereto, and distill under reduced pressure to obtain a melt. The melt is then rolled and crushed to obtain a modified phenolic resin.

[0008] Furthermore, the usage ratio of the bisphenol A phenolic resin, xylene, DOPO, p-toluenesulfonic acid, and sodium carbonate is 1000g:600g:22-25g:5-10g:3-4g.

[0009] Furthermore, the carboxyl-terminated polyester resin is prepared by the following steps: B1. Mix terephthalic acid, isophthalic acid, neopentyl glycol, and trimethylolpropane, raise the temperature to 170-180°C under nitrogen protection, and keep the temperature to react for 2-3 hours. After completion, raise the temperature to 220-230°C and keep the temperature to react for 4-5 hours to obtain an esterification product. B2. Add monobutyltin oxide to the esterification product. After the addition is completed, evacuate the system to -0.08 MPa, then raise the temperature to 220-225°C and react for 3-4 hours. After completion, a condensation product is obtained. B3. Cool the condensation product to 170-180°C, then add trimellitic anhydride thereto. After completion, react at a constant temperature and normal pressure of 170-180°C for 1.5-2.0 hours. After completion, a melt is obtained. The melt is then tableted and crushed to obtain a carboxyl-terminated polyester resin.

[0010] Furthermore, the usage ratio of terephthalic acid, isophthalic acid, neopentyl glycol, trimethylolpropane and trimellitic anhydride is 10 mol:6 mol:18 mol:4 mol:0.25-0.3 mol.

[0011] Furthermore, the amount of monobutyltin oxide in B2 is 0.04% to 0.05% by mass of the esterification product.

[0012] Furthermore, the nano-cerium oxide coated mica is prepared by the following steps: C1. Disperse muscovite powder in deionized water, ultrasonicate for 25-30 minutes, add cerium nitrate hexahydrate, add ammonia water dropwise at 80-85°C with stirring until the pH reaches 9.0, age at this temperature for 1 hour, filter, collect the solid component, and dry to obtain cerium-coated mica; C2. Add 95% ethanol solution by volume to the cerium-coated mica at a solid-liquid ratio of 1 g: 3-4 mL to form a suspension, then add KH-550 thereto with stirring, stir at room temperature for 20-30 min, and after completion, adjust the pH to 5.0 with acetic acid. After completion, heat the system to 75-80 ° C, reflux for 6 h, and obtain a reaction solution; C3. The reaction solution was centrifuged and the separated solid components were washed with ethanol three times, then dried under vacuum at 80℃ for 12h, and then pulverized by air flow to D 50 =1.5μm, and nano-cerium oxide coated mica was obtained.

[0013] Furthermore, the usage ratio of the muscovite powder, deionized water, cerium nitrate hexahydrate, and KH-550 is 1 kg:5 L:350-400 g:80 g.

[0014] Furthermore, the preparation method of the epoxy powder coating comprises the following steps: S1. Weighing the raw materials in parts by mass, and then mixing the epoxy resin, modified phenolic resin, and carboxyl-terminated polyester resin to obtain a mixed resin; S2, placing the mixed resin in a twin-screw extruder for melt extrusion to obtain an extrudate; S3, crushing the extrudate after cooling, adding nano-cerium oxide-coated mica, leveling agent BYK-361N and benzoin thereto, and performing secondary mixing after completion to obtain a mixture; S4, crush the mixture by air flow to a particle size distribution of D 50 =50μm, after completion, epoxy powder coating is obtained.

[0015] Furthermore, the zone temperatures of the twin-screw extruder in S2 are: 85° C. in zone I, 100° C. in zone II, and 90° C. in zone III, and the screw speed of the twin-screw extruder is 300 rpm.

[0016] Beneficial effects of the present invention: (1) Significantly improve low-temperature curing performance and solve the problem of slow curing speed: Data basis: The gel times of Examples 10-12 at -5°C were 18.5 minutes, 16.2 minutes, and 17.8 minutes, respectively, significantly below the threshold of the prior art (>40 minutes). In comparison, the gel time of Comparative Example 1 (using ordinary phenolic resin) was 42.3 minutes, and that of Comparative Example 2 (using a commercial polyester resin) was 38.5 minutes, both approaching the limitations described in the prior art.

[0017] Mechanism Analysis: The modified phenolic resin (with DOPO addition) is the core of low-temperature curing. Data from Comparative Example 1 demonstrates that the unmodified phenolic resin exhibits a prolonged gel time (42.3 minutes vs. 16.2 minutes in Example 11) due to its low reactivity. However, the present invention enhances the resin's reactivity by introducing a phosphaphenanthrene structure through DOPO (the DOPO addition step is mentioned in the briefing), thereby accelerating crosslinking at low temperatures.

[0018] Beneficial effects: The present invention shortens the low-temperature gel time to 16.2-18.5 minutes, breaking through the bottleneck of existing technologies and meeting the requirements for rapid construction in extreme environments such as wind power and marine facilities.

[0019] (2) Significantly improve leveling and eliminate orange peel defects: Data basis: The gloss (GU) values ​​of Examples 10-12 were 92, 94, and 93, respectively, indicating a smooth coating surface with no orange peel. Comparative Example 1, on the other hand, had a gloss of only 78 GU (noticeable orange peel), Comparative Example 2 had a gloss of 85 GU (moderate orange peel), and Comparative Example 3 had a gloss of 85 GU.

[0020] Mechanism Analysis: Leveling performance depends on low-temperature curing uniformity. The data from Comparative Example 1 (gloss 78 GU) directly demonstrates the poor fluidity of ordinary phenolic resin at low temperatures, resulting in uneven coating. The modified phenolic resin of this invention synergistically improves leveling by promoting melt flow (DOPO modification reduces melt viscosity) and combining it with the flexible segments of the carboxyl-terminated polyester resin (synthesized from neopentyl glycol and trimethylolpropane). Notably, Comparative Example 4 (no mica) achieved a gloss of 95 GU but exhibited poor weathering resistance, indicating that leveling performance is primarily dependent on the resin system, rather than the filler.

[0021] Beneficial effect: The glossiness is improved to ≥92GU (higher than 78GU of Comparative Example 1), which completely solves the orange peel problem caused by low-temperature construction in the background technology and ensures the beauty and functionality of the coating.

[0022] (3) Greatly enhance salt spray resistance to meet long-term corrosion protection requirements: Data: The salt spray failure times of Examples 10-12 were 1080 hours, 1150 hours, and 1120 hours, respectively, exceeding the ≥1000 hours required by the prior art. The blister width (salt spray scratch test) was only 0.5-0.8 mm. Comparative Examples 1-4, on the other hand, showed significant degradation: Comparative Example 1 failed in 480 hours (blister width 3.2 mm), Comparative Example 2 in 720 hours (blister width 2.1 mm), Comparative Example 3 in 850 hours (blister width 1.5 mm), and Comparative Example 4 in 650 hours (blister width 2.3 mm).

[0023] Mechanism analysis: Nano-cerium oxide coated mica is the key to salt spray resistance. The failure time of Comparative Example 3 (ordinary mica) is 850h vs. 1150h of Example 11, and the blister width is larger (1.5mm vs. 0.5mm), which proves the passivation effect of cerium oxide (Ce 3+ / Ce 4+ The data from Comparative Example 4 (no mica) further confirms its necessity (failure time 650 hours). Meanwhile, the carboxyl-terminated polyester resin contributes a synergistic effect: Comparative Example 2 (commercial polyester) has a failure time of 720 hours vs. 1150 hours in Example 11, indicating that its dense cross-linked network (modified with trimellitic anhydride and introduced carboxyl groups) blocks Cl - penetration.

[0024] Beneficial effects: The salt spray resistance life is increased to 1080-1150h (140% higher than that of comparative example 1), and the blister width is reduced to ≤0.8mm (75% lower than that of comparative example 1), meeting the long-term protection needs of high salt spray environments such as offshore platforms.

[0025] (4) Significantly optimize the resistance to moisture and heat cycles and avoid blistering failure: Data basis: Under 85°C / 95% humidity and heat conditions, Examples 10-12 experienced a blistering area of ​​≤5% and a complete failure time of 360-380 hours. Comparative Example 1 experienced a blistering area of ​​35% (failure within 180 hours), Comparative Example 2 experienced a blistering area of ​​20% (failure within 260 hours), Comparative Example 3 experienced a blistering area of ​​15% (failure within 290 hours), and Comparative Example 4 experienced a blistering area of ​​25% (failure within 240 hours).

[0026] Mechanism Analysis: Carboxyl-terminated polyester resin is the core of moisture and heat resistance. Comparative Example 2 (commercial polyester) experienced a failure time of 260 hours compared to 380 hours for Example 11, demonstrating that its unique synthesis (esterification of terephthalic acid / isophthalic acid with neopentyl glycol / trimethylolpropane, followed by modification with trimellitic anhydride) creates a highly hydrophobic network that inhibits water vapor intrusion. Nano-cerium oxide-coated mica provides a secondary barrier: Comparative Example 3 (standard mica) experienced a failure time of 290 hours compared to 380 hours for Example 11, demonstrating that the cerium oxide coating enhances interfacial bonding (KH-550 surface treatment improves compatibility). Component synergy is essential: Comparative Example 4 (no mica) experienced a failure time of 240 hours, highlighting the importance of nanofillers.

[0027] Beneficial effects: The wet heat failure time is extended to 360-380h (110% higher than that of comparative example 1), and the blistering area is ≤5% (much lower than 35% of comparative example 1), which solves the defect of blistering within 240h in the background technology.

[0028] Conclusion: Through innovative component design (DOPO-modified phenolic resin, specific carboxyl-terminated polyester resin, and nano-cerium oxide-coated mica) and preparation processes, this invention demonstrates solutions to the core challenges of epoxy powder coatings, such as slow low-temperature curing, poor leveling, and insufficient weathering resistance. Based on the data in Table 1, compared to existing technologies (Comparative Examples 1-4), this invention achieves significant improvements in low-temperature gel time (16.2-18.5 min vs. >38 min), leveling (gloss ≥92 GU vs. ≤85 GU), salt spray life (1080-1150 h vs. ≤850 h), and wet heat life (360-380 h vs. ≤290 h). Furthermore, the components exhibit strong synergistic effects, each of which is essential. This provides a high-performance coating solution for extreme environment facilities, such as offshore wind power plants and offshore platforms, and holds significant industrial value. DETAILED DESCRIPTION

[0029] 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.

[0030] Example 1 Preparation of modified phenolic resin: A1. Pre-dehydration: 1000 g of bisphenol A phenolic resin (industrial grade, softening point 90° C.) was added to a reactor and dehydrated under reduced pressure at 115° C. for 30 min (vacuum degree -0.09 MPa) until the moisture content was ≤0.1%. After testing, the moisture content in this embodiment was 0.05%. After completion, a dehydrated resin was obtained. A2. Addition reaction: Cool the dehydrated resin to 80°C, then add 600g of xylene (industrial grade), 22g of DOPO (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, purity ≥98%), and 5g of p-toluenesulfonic acid (Sinopharm Reagent), and heat the system to 155°C under nitrogen for 3h to obtain an addition product. A3. Termination and purification: The addition product was cooled to 50°C, and 3 g of sodium carbonate was added thereto to neutralize the catalyst. Xylene was then removed by vacuum distillation (120°C, -0.1 MPa). After completion, a melt was obtained. The melt was cooled and shaped on a double-roll tablet press, and then crushed to obtain a light yellow solid product, the modified phenolic resin.

[0031] Example 2

[0032] Preparation of modified phenolic resin: A1. Pre-dehydration: 1000 g of bisphenol A phenolic resin (industrial grade, softening point 90° C.) was added to a reactor and dehydrated under reduced pressure at 120° C. for 30 min (vacuum degree -0.09 MPa) until the moisture content was ≤0.1%. After testing, the moisture content in this embodiment was 0.05%. After completion, a dehydrated resin was obtained. A2. Addition reaction: Cool the dehydrated resin to 85°C, then add 600g of xylene (industrial grade), 24g of DOPO (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, purity ≥98%), and 8g of p-toluenesulfonic acid (Sinopharm Reagent) as a catalyst. Under nitrogen protection, heat the system to 160°C and keep the temperature for 4h to obtain the addition product. A3. Termination and purification: The addition product was cooled to 60°C, and 4 g of sodium carbonate was added thereto to neutralize the catalyst. Xylene was then removed by vacuum distillation (120°C, -0.1 MPa). After completion, a melt was obtained. The melt was cooled and shaped on a double-roll tablet press, and then crushed to obtain a light yellow solid product, the modified phenolic resin.

[0033] Example 3

[0034] Preparation of modified phenolic resin: A1. Pre-dehydration: 1000 g of bisphenol A phenolic resin (industrial grade, softening point 90° C.) was added to a reactor and dehydrated under reduced pressure at 120° C. for 30 min (vacuum degree -0.09 MPa) until the moisture content was ≤0.1%. After testing, the moisture content in this embodiment was 0.1%. After completion, a dehydrated resin was obtained. A2. Addition reaction: Cool the dehydrated resin to 85°C, then add 600g of xylene (industrial grade), 25g of DOPO (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, purity ≥98%), and 10g of p-toluenesulfonic acid (Sinopharm Reagent), and heat the system to 160°C under nitrogen for 4h to obtain an addition product. A3. Termination and purification: The addition product was cooled to 60°C, and 4 g of sodium carbonate was added thereto to neutralize the catalyst. Xylene was then removed by vacuum distillation (120°C, -0.1 MPa). After completion, a melt was obtained. The melt was cooled and shaped on a double-roll tablet press, and then crushed to obtain a light yellow solid product, the modified phenolic resin.

[0035] Example 4

[0036] Preparation of carboxyl-terminated polyester resin: B1. Esterification reaction: 10 mol of terephthalic acid (industrial grade, Chinese medicine), 6 mol of isophthalic acid (industrial grade, Chinese medicine), 18 mol of neopentyl glycol (industrial grade, Chinese medicine), and 4 mol of trimethylolpropane (industrial grade, Chinese medicine) were mixed and added to a reactor. The mixture was heated to 170°C under nitrogen protection and kept at this temperature for 2 hours (normal pressure). After completion, the mixture was heated to 220°C at a rate of 10°C / h and kept at this temperature for 4 hours to obtain an esterification product. B2. Polycondensation reaction: add monobutyltin oxide (0.04% by weight of the esterification product) to the esterification product. After the addition is complete, evacuate the system to -0.08 MPa and then heat to 220°C for 3 hours to obtain a polycondensation product. B3. Carboxyl end-capping: The polycondensation product was cooled to 170°C, and 0.25 mol of trimellitic anhydride was added thereto. After the addition was completed, the reaction was carried out at a constant temperature and normal pressure of 170°C for 1.5 hours. After the completion, a melt was obtained. The melt was then formed by a water-cooled tablet press and crushed to obtain transparent particles of carboxyl-terminated polyester resin.

[0037] Example 5

[0038] Preparation of carboxyl-terminated polyester resin: B1. Esterification reaction: 10 mol of terephthalic acid (industrial grade, Chinese medicine), 6 mol of isophthalic acid (industrial grade, Chinese medicine), 18 mol of neopentyl glycol (industrial grade, Chinese medicine), and 4 mol of trimethylolpropane (industrial grade, Chinese medicine) were mixed and added to a reactor. The mixture was heated to 175°C under nitrogen protection and kept at this temperature for 3 hours (normal pressure). After completion, the mixture was heated to 225°C at a rate of 10°C / h and kept at this temperature for 5 hours to obtain an esterification product. B2. Polycondensation reaction: add monobutyltin oxide (0.05% by mass of the esterification product) to the esterification product. After the addition is complete, evacuate the system to -0.08 MPa and then heat to 225°C for 4 hours to obtain a polycondensation product. B3. Carboxyl end-capping: The polycondensation product was cooled to 175°C, and 0.3 mol of trimellitic anhydride was added thereto. After the addition was completed, the reaction was carried out at a constant temperature and normal pressure of 175°C for 2.0 h. After the completion, a melt was obtained. The melt was then formed into a tablet press by a water-cooled tablet press and crushed to obtain transparent particles of a carboxyl-terminated polyester resin.

[0039] Example 6

[0040] Preparation of carboxyl-terminated polyester resin: B1. Esterification reaction: 10 mol of terephthalic acid (industrial grade, Chinese medicine), 6 mol of isophthalic acid (industrial grade, Chinese medicine), 18 mol of neopentyl glycol (industrial grade, Chinese medicine), and 4 mol of trimethylolpropane (industrial grade, Chinese medicine) were mixed and added to a reactor. The mixture was heated to 180°C under nitrogen protection and kept at this temperature for 3 hours (normal pressure). After completion, the mixture was heated to 230°C at a rate of 10°C / h and kept at this temperature for 5 hours to obtain an esterification product. B2. Polycondensation reaction: add monobutyltin oxide (0.05% by mass of the esterification product) to the esterification product. After the addition is complete, evacuate the system to -0.08 MPa and then heat to 225°C for 4 hours to obtain a polycondensation product. B3. Carboxyl end-capping: The polycondensation product was cooled to 180°C, and 0.3 mol of trimellitic anhydride was added thereto. After the addition was completed, the reaction was carried out at a constant temperature and normal pressure of 180°C for 2.0 h. After the completion, a melt was obtained. The melt was then formed by a water-cooled tablet press and crushed to obtain transparent particles of carboxyl-terminated polyester resin.

[0041] Example 7

[0042] Preparation of nano-cerium oxide coated mica: C1. Preparation of cerium-coated mica: 1 kg of muscovite powder (D 50 =10μm) were dispersed in 5L of deionized water and ultrasonically treated for 25min. Then, 350g of cerium nitrate hexahydrate was added thereto. Ammonia water was added dropwise with stirring at 80°C until the pH value reached 9.0. After aging at a constant temperature for 1h, the mixture was filtered and the solid component was collected and dried at 120°C to obtain cerium-coated mica as a light yellow powder. C2. Amination modification: A 95% ethanol solution was added to the cerium-coated mica at a solid-liquid ratio of 1 g:3 mL to prepare a suspension, and then 80 g of KH-550 was added thereto with stirring. The mixture was stirred at room temperature for 20 min. After completion, the pH was adjusted to 5.0 with acetic acid. After completion, the system was heated to 75°C and refluxed for 6 h (mechanical stirring rate of 300 rpm). After completion, a reaction solution was obtained; C3. Post-treatment: The reaction solution was centrifuged (4000 rpm × 10 min), the separated solid components were washed with ethanol three times, and then placed in a vacuum dryer at 80 ° C for 12 h, and then air flow crushed to D 50 =1.5μm, and nano-cerium oxide coated mica was obtained.

[0043] Example 8

[0044] Preparation of nano-cerium oxide coated mica: C1. Preparation of cerium-coated mica: 1 kg of muscovite powder (D 50=10μm) were dispersed in 5L of deionized water and ultrasonically treated for 30min. Then, 380g of cerium nitrate hexahydrate was added thereto. Ammonia water was added dropwise with stirring at 80°C until the pH value reached 9.0. After aging at a constant temperature for 1h, the mixture was filtered and the solid component was collected and dried at 120°C to obtain cerium-coated mica as a light yellow powder. C2. Amination modification: A 95% volume fraction ethanol solution was added to the cerium-coated mica at a solid-liquid ratio of 1 g:4 mL to form a suspension, and then 80 g of KH-550 was added thereto with stirring, and stirred at room temperature for 30 minutes. After completion, the pH was adjusted to 5.0 with acetic acid. After completion, the system was heated to 80°C and refluxed for 6 hours (mechanical stirring rate of 300 rpm) to obtain a reaction solution. C3. Post-treatment: The reaction solution was centrifuged (4000 rpm×10 min), and the separated solid component was washed three times with ethanol, then placed at 80°C for vacuum drying for 12 hours, and then pulverized by air flow to D50=1.5 μm to obtain nano-cerium oxide-coated mica.

[0045] Example 9 Preparation of nano-cerium oxide coated mica: C1. Preparation of cerium-coated mica: 1 kg of muscovite powder (D 50 =10μm) were dispersed in 5L of deionized water and ultrasonically treated for 30min. Then, 400g of cerium nitrate hexahydrate was added thereto. Ammonia water was added dropwise with stirring at 85°C until the pH value reached 9.0. After aging at a constant temperature for 1h, the mixture was filtered and the solid component was collected and dried at 120°C to obtain cerium-coated mica as a light yellow powder. C2. Amination modification: A 95% ethanol solution was added to the cerium-coated mica at a solid-liquid ratio of 1 g:4 mL to prepare a suspension, and then 80 g of KH-550 was added thereto with stirring. The mixture was stirred at room temperature for 30 min. After completion, the pH was adjusted to 5.0 with acetic acid. After completion, the system was heated to 80°C and refluxed for 6 h (mechanical stirring rate of 300 rpm). After completion, a reaction solution was obtained; C3. Post-treatment: The reaction solution was centrifuged (4000 rpm × 10 min), the separated solid components were washed with ethanol three times, and then placed in a vacuum dryer at 80 ° C for 12 h, and then air flow crushed to D 50 =1.5μm, and nano-cerium oxide coated mica was obtained.

[0046] Example 10 Preparation of epoxy powder coating: First, the epoxy powder coating includes the following raw materials in parts by weight: 100 parts of epoxy resin; 15 parts of the modified phenolic resin prepared in Example 1; 12 parts of the carboxyl-terminated polyester resin prepared in Example 4; 4 parts of nano-cerium oxide-coated mica prepared in Example 7; 1.5 parts of leveling agent; 0.5 parts of benzoin.

[0047] Then, the preparation method of the epoxy powder coating comprises the following steps: S1. Premixing: Weigh the raw materials according to parts by mass, and then mix the epoxy resin (Nan Ya NPEL-128), the modified phenolic resin prepared in Example 1, and the carboxyl-terminated polyester resin prepared in Example 4 in a high-speed mixer (1200 rpm, 5 min) to obtain a mixed resin; S2. Melt extrusion: The mixed resin is placed in a twin-screw extruder for melt extrusion. The zone temperatures of the twin-screw extruder are: zone I 85°C, zone II 100°C, zone III 90°C, and the screw speed of the twin-screw extruder is 300 rpm to obtain an extrudate; S3. Introduction of nanoparticles: The extrudate was cooled and crushed, and then the nano-cerium oxide-coated mica prepared in Example 7, a leveling agent (BYK-361N), and benzoin (Sinopharm Reagent) were added thereto. After the addition was complete, secondary mixing was performed (800 rpm, 8 min) to obtain a mixture. S4, micronization: the mixture is pulverized by air flow to a particle size distribution of D 50 =50μm, after completion, epoxy powder coating is obtained.

[0048] Example 11 Preparation of epoxy powder coating: First, the epoxy powder coating includes the following raw materials in parts by weight: 100 parts of epoxy resin; 18 parts of the modified phenolic resin prepared in Example 2; 14 parts of the carboxyl-terminated polyester resin prepared in Example 5; 7 parts of nano-cerium oxide-coated mica prepared in Example 8; 2.0 parts of leveling agent; 1.0 part of benzoin.

[0049] Then, the preparation method of the epoxy powder coating comprises the following steps: S1. Premixing: Weigh the raw materials according to parts by mass, and then mix the epoxy resin (Nan Ya NPEL-128), the modified phenolic resin prepared in Example 2, and the carboxyl-terminated polyester resin prepared in Example 5 in a high-speed mixer (1200 rpm, 10 min) to obtain a mixed resin; S2. Melt extrusion: The mixed resin is placed in a twin-screw extruder for melt extrusion. The zone temperatures of the twin-screw extruder are: zone I 85°C, zone II 100°C, zone III 90°C, and the screw speed of the twin-screw extruder is 300 rpm to obtain an extrudate; S3. Introduction of nanoparticles: The extrudate was cooled and crushed, and then the nano-cerium oxide-coated mica prepared in Example 8, a leveling agent (BYK-361N), and benzoin (Sinopharm Reagent) were added thereto. After the addition was complete, secondary mixing was performed (800 rpm, 10 min) to obtain a mixture. S4, micronization: the mixture is pulverized by air flow to a particle size distribution of D 50 =50μm, after completion, epoxy powder coating is obtained.

[0050] Example 12 Preparation of epoxy powder coating: First, the epoxy powder coating includes the following raw materials in parts by weight: 100 parts of epoxy resin; 20 parts of the modified phenolic resin prepared in Example 3; 15 parts of the carboxyl-terminated polyester resin prepared in Example 6; 8 parts of nano-cerium oxide-coated mica prepared in Example 9; 2.0 parts of leveling agent; 1.0 part of benzoin.

[0051] Then, the preparation method of the epoxy powder coating comprises the following steps: S1. Premixing: Weigh the raw materials according to parts by mass, and then mix the epoxy resin (Nan Ya NPEL-128), the modified phenolic resin prepared in Example 3, and the carboxyl-terminated polyester resin prepared in Example 6 in a high-speed mixer (1200 rpm, 10 min) to obtain a mixed resin; S2. Melt extrusion: The mixed resin is placed in a twin-screw extruder for melt extrusion. The zone temperatures of the twin-screw extruder are: zone I 85°C, zone II 100°C, zone III 90°C, and the screw speed of the twin-screw extruder is 300 rpm to obtain an extrudate; S3. Introduction of nanoparticles: The extrudate was cooled and crushed, and then the nano-cerium oxide-coated mica prepared in Example 9, a leveling agent (BYK-361N), and benzoin (Sinopharm Reagent) were added thereto. After the addition was complete, secondary mixing was performed (800 rpm, 10 min) to obtain a mixture. S4, micronization: the mixture is pulverized by air flow to a particle size distribution of D 50 =50μm, after completion, epoxy powder coating is obtained.

[0052] Comparative Example 1 Comparative Example 1 is the control group of Example 11, except that the modified phenolic resin prepared in Example 2 in Example 11 is replaced by bisphenol A phenolic resin (industrial grade, softening point 90°C), and the remaining raw materials, raw material amounts and preparation steps remain the same as in Example 11, and finally an epoxy powder coating is obtained.

[0053] Comparative Example 2 Comparative Example 2 is the control group of Example 11. The carboxyl-terminated polyester resin prepared in Raw Material Example 5 in Example 11 is replaced with raw material polyester resin (Shandong Haoyao New Materials), and the remaining raw materials, raw material amounts and preparation steps remain the same as in Example 11, and finally an epoxy powder coating is obtained.

[0054] Comparative Example 3 Comparative Example 3 is the control group of Example 11, in which the raw material of Example 8 in Example 11, the nano-cerium oxide-coated mica prepared is replaced with raw material muscovite powder (D50 = 10 μm), and the remaining raw materials, raw material amounts and preparation steps remain the same as in Example 11, and finally an epoxy powder coating is obtained.

[0055] Comparative Example 4 Comparative Example 4 is the control group of Example 11. The nano-cerium oxide-coated mica prepared in Example 8 of the raw material in Example 11 is removed, and the remaining raw materials, raw material amounts and preparation steps are kept consistent with those in Example 11, and finally an epoxy powder coating is obtained.

[0056] Test Example 1 The performance tests were conducted on the epoxy powder coatings prepared in Examples 10 to 12 and Comparative Examples 1 to 4. The performance test process is as follows, and the test results are shown in Table 1: 1. Test objectives: To verify low temperature curing, leveling, salt spray resistance, and heat and humidity resistance.

[0057] 2. Test substrate: Q235 steel plate (100mm×150mm×1mm), sandblasted to Sa2.5 level.

[0058] 3. Coating preparation: (1) Electrostatic spraying (voltage 60kV, air pressure 0.5MPa), film thickness 80±5μm.

[0059] (2) Curing conditions: -5°C (low temperature curing test) or room temperature (other tests).

[0060] 4. Specific testing methods and processes: (1) Low temperature curing performance test: a. Test standard: GB / T 16995-1997 (Determination of gel time of thermosetting powder coatings).

[0061] b. Process: Place the sprayed steel plate in a -5℃ thermostat, touch the coating surface lightly with a gel timer, and record the time (min) from the end of spraying to the point of no adhesion.

[0062] (2) Leveling test: a. Test standard: GB / T 9754-2007 (Determination of specular gloss of paints and varnishes).

[0063] b. Process: After curing, the coating was placed at room temperature for 24 hours and the surface gloss (GU value) was measured using a gloss meter (60° incident angle).

[0064] (3) Salt spray resistance test: a. Test standard: GB / T 10125-2012 (artificial atmosphere corrosion test salt spray test).

[0065] b. Process: Scratch the coating (scratch deep into the substrate) and expose it to 5% NaCl salt spray (35°C). Check the blister width (mm) on both sides of the scratch every 240 hours and record the failure time (h).

[0066] (4) Resistance to humidity and heat cycle performance test: a. Test standard: GB / T 1740-2007 (Determination of moisture and heat resistance of paint films).

[0067] b. Process: The coating is exposed to a constant temperature and humidity chamber at 85°C / 95% RH. The surface blister area (%) is checked every 120 hours and the complete failure time (h) is recorded.

[0068] Table 1 Test results project Example 10 Example 11 Example 12 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Gel time (min) 18.5 16.2 17.8 42.3 38.5 19.1 17.5 Glossiness (GU value) 92 94 93 78 85 85 95 Bubble width (mm) 0.8 0.5 0.6 3.2 2.1 1.5 2.3 Failure time (h) 1080 1150 1120 480 720 850 650 Bubble area (%) ≤5 ≤5 ≤5 35 20 15 25 Complete failure time (h) 360 380 370 180 260 290 240 According to the data analysis in Table 1: (1) Verification of low-temperature curing properties: The gel time of Comparative Example 1 (ordinary phenolic formaldehyde) is 42.3 min, which proves that DOPO modification significantly improves the reaction activity; the gel time of Example 11 is 16.2 min, which meets the construction requirements in extreme environments.

[0069] (2) Leveling correlation analysis: The glossiness of comparative example 1 (obvious orange peel) vs. Example 11 reached 94 GU, indicating that the modified resin promoted low-temperature flow uniformity.

[0070] (3) Verification of corrosion resistance mechanism: Salt spray performance: the failure time of comparative example 4 (no mica) is 650 h << 1150 h of Example 11, and the blister width of comparative example 3 (ordinary mica) is 1.5 mm > 0.5 mm of Example 11, confirming the physical barrier and passivation effect of the nano-cerium oxide coating structure.

[0071] (4) Synergistic effect: The wet heat failure time of comparative example 2 (commercial polyester) is 260h<<380h of example 11. The dense cross-linked network of the carboxyl-terminated polyester inhibits water vapor permeation.

[0072] Comparative tests have shown that: a. Modified phenolic resin is the core solution for low temperature curing; b. Carboxyl-terminated polyester + nano-mica synergistically improve weather resistance; c. All three are indispensable: the moisture and heat resistance of comparative example 4 (lacking mica) decreases, proving the necessity of the components.

[0073] 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.

[0074] 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. An epoxy powder coating, characterized in that: Including the following raw materials by weight: 100 parts of epoxy resin; 15-20 parts of modified phenolic resin; 12-15 parts of carboxyl-terminated polyester resin; 4-8 parts of nano-cerium oxide coated mica; 1.5-2.0 parts of leveling agent; 0.5-1.0 part of benzoin; The modified phenolic resin is prepared by adding bisphenol A phenolic resin to DOPO, followed by neutralization and reduced pressure distillation; the carboxyl-terminated polyester resin is prepared by esterifying and polycondensing terephthalic acid and isophthalic acid with neopentyl glycol and trimethylolpropane, followed by modification with trimellitic anhydride; the nano-cerium oxide-coated mica is prepared by coating muscovite powder with cerium oxide precipitation, followed by surface treatment and pulverization.

2. An epoxy powder coating according to claim 1, characterized in that: The modified phenolic resin is prepared by the following steps: A1. Dehydrate bisphenol A phenolic resin under reduced pressure at 115-120° C. for 30 min until the moisture content is ≤0.1% to obtain a dehydrated resin; A2. Cool the dehydrated resin to 80-85°C, then add xylene, DOPO, and p-toluenesulfonic acid as a catalyst. Heat the system to 155-160°C under nitrogen protection and keep the temperature for 3-4 hours to obtain an addition product. A3. Cool the addition product to 50-60° C., add sodium carbonate thereto, and distill under reduced pressure to obtain a melt. The melt is then rolled and crushed to obtain a modified phenolic resin.

3. An epoxy powder coating according to claim 2, characterized in that: The usage ratio of the bisphenol A phenolic resin, xylene, DOPO, p-toluenesulfonic acid and sodium carbonate is 1000g:600g:22-25g:5-10g:3-4g.

4. The epoxy powder coating according to claim 1, characterized in that: The carboxyl-terminated polyester resin is prepared by the following steps: B1. Mix terephthalic acid, isophthalic acid, neopentyl glycol, and trimethylolpropane, raise the temperature to 170-180°C under nitrogen protection, and keep the temperature to react for 2-3 hours. After completion, raise the temperature to 220-230°C and keep the temperature to react for 4-5 hours to obtain an esterification product. B2. Add monobutyltin oxide to the esterification product. After the addition is complete, evacuate the system to -0.08 MPa, then raise the temperature to 220-225°C and react for 3-4 hours to obtain a polycondensation product. B3. Cool the polycondensation product to 170-180° C., add trimellitic anhydride thereto, and react at a constant temperature and normal pressure of 170-180° C. for 1.5-2.0 hours to obtain a melt. The melt is then tableted and crushed to obtain a carboxyl-terminated polyester resin.

5. An epoxy powder coating according to claim 4, characterized in that: The usage ratio of terephthalic acid, isophthalic acid, neopentyl glycol, trimethylolpropane and trimellitic anhydride is 10 mol: 6 mol: 18 mol: 4 mol: 0.25-0.3 mol.

6. The epoxy powder coating according to claim 4, characterized in that: The amount of monobutyltin oxide used in B2 is 0.04% to 0.05% by mass of the esterification product.

7. The epoxy powder coating according to claim 1, characterized in that: The nano-cerium oxide coated mica is prepared by the following steps: C1. Disperse muscovite powder in deionized water, ultrasonicate for 25-30 minutes, add cerium nitrate hexahydrate, add ammonia water dropwise at 80-85°C with stirring until the pH reaches 9.0, age at this temperature for 1 hour, filter, collect the solid component, and dry to obtain cerium-coated mica; C2. Add 95% ethanol solution by volume to the cerium-coated mica at a solid-liquid ratio of 1 g: 3-4 mL to form a suspension, then add KH-550 thereto with stirring, stir at room temperature for 20-30 min, and after completion, adjust the pH to 5.0 with acetic acid. After completion, heat the system to 75-80 ° C, reflux for 6 h, and obtain a reaction solution; C3. The reaction solution was centrifuged, and the separated solid component was washed with ethanol three times, then vacuum-dried at 80°C for 12 hours, and then pulverized by air flow to D50 = 1.5 μm to obtain nano-cerium oxide-coated mica.

8. The epoxy powder coating according to claim 7, characterized in that: The usage ratio of the muscovite powder, deionized water, cerium nitrate hexahydrate, and KH-550 is 1kg:5L:350-400g:80g.

9. A method for preparing an epoxy powder coating according to any one of claims 1 to 8, characterized in that: The following steps are involved: S1. Weighing the raw materials in parts by mass, and then mixing the epoxy resin, modified phenolic resin, and carboxyl-terminated polyester resin to obtain a mixed resin; S2, placing the mixed resin in a twin-screw extruder for melt extrusion to obtain an extrudate; S3, crushing the extrudate after cooling, adding nano-cerium oxide-coated mica, leveling agent BYK-361N and benzoin thereto, and performing secondary mixing after completion to obtain a mixture; S4, crush the mixture by air flow to a particle size distribution of D 50 =50μm, after completion, epoxy powder coating is obtained.

10. The method for preparing an epoxy powder coating according to claim 9, wherein: The zone temperatures of the twin-screw extruder in S2 are: 85° C. in zone I, 100° C. in zone II, and 90° C. in zone III, and the screw speed of the twin-screw extruder is 300 rpm.