Heavy-duty anti-corrosion three-proofing powder coating as well as preparation method and construction process thereof

Abstract

The invention relates to a heavy-duty anti-corrosion three-proofing powder coating as well as a preparation method and a construction process thereof, and relates to the technical field of anti-corrosion coatings. The powder coating comprises the following components in parts by weight: 40-60 parts of film-forming resin, 30-50 parts of lamellar composite filler, 10-20 parts of a curing agent, 2-5 parts of a thixotropic agent, 0.5-1.5 parts of a flatting agent and 2-10 parts of pigment. According to the heavy-duty anti-corrosion three-proofing powder coating and the construction process provided by the invention, a coating formed by coating can resist neutral salt mist for more than 3000 hours and damp and heat (40 DEG C, RH is more than or equal to 95%) for more than 5000 hours through detection, the mildew-proof grade reaches 0 grade, a flat and smooth paint film appearance can still be obtained under a thick film condition, the weather resistance, the wear resistance and the impact resistance are excellent, and the service life of the coating is prolonged. The service life is longer than that of traditional paint, and the paint can be suitable for extreme corrosion environments such as C5-M (ocean) and the like.

Description

Technical Field

[0001] This invention relates to the field of anti-corrosion coating technology, and in particular to a heavy-duty anti-corrosion powder coating, its preparation method, and its construction process. Background Technology

[0002] In heavy-duty corrosion protection fields such as marine engineering, bridges, port machinery, and petrochemical pipelines, equipment is exposed to harsh environments with high humidity, high salinity, and strong corrosive media for extended periods. Therefore, the protective performance of the coating (i.e., resistance to damp heat, salt spray, and mold) is extremely demanding. Traditional heavy-duty corrosion protection systems typically employ a liquid coating composite system consisting of a zinc-rich primer, an epoxy intermediate coat, and an aliphatic polyurethane topcoat. While offering acceptable protection, this system suffers from drawbacks such as high VOC emissions, numerous application layers, long application cycles, and limited film thickness per application.

[0003] As an environmentally friendly coating, powder coatings in this field are mostly simple epoxy or pure polyester functional powders. Although they offer good corrosion resistance, they often suffer from poor decorative properties, weather resistance, and impact resistance, poor film leveling, and a rough appearance, making them unsuitable for applications requiring both high protection and high aesthetics. Furthermore, the density of conventional powder coatings is still insufficient to withstand thousands of hours of salt spray corrosion. How to achieve a synergistic effect of physical shielding, chemical corrosion prevention, and electrochemical protection in powder coatings through formulation and process innovation, while maintaining a good film appearance, remains a key technical challenge in this field. Summary of the Invention

[0004] The purpose of this invention is to address the above-mentioned problems by providing a heavy-duty anti-corrosion powder coating, its preparation method, and its construction process.

[0005] The first aspect of this invention provides a heavy-duty anti-corrosion and three-proof powder coating, which adopts the following technical solution:

[0006] A heavy-duty anti-corrosion and three-proof powder coating comprises the following components in parts by weight: 40-60 parts of film-forming resin, 30-50 parts of lamellar composite filler, 10-20 parts of curing agent, 2-5 parts of thixotropic agent, 0.5-1.5 parts of leveling agent, and 2-10 parts of pigment. The film-forming resin includes phenolic resin and bisphenol A type epoxy resin, and the lamellar composite filler includes mica iron oxide, alumina, and lamellar glass powder.

[0007] By adopting the above technical solutions, phenolic resin, with its high molecular weight, high cohesive strength, and good flexibility, can form an extremely dense and tough paint film when mixed with epoxy resin, providing a basic anti-corrosion barrier. The high cross-linking density between the curing agent and the resin can improve chemical resistance. The layered composite filler, composed of mica iron oxide (physical shielding, weather resistance), aluminum hydride (passivation and corrosion prevention, thermal conductivity), and flake glass powder (reinforcing shielding, wear resistance), is arranged in parallel overlapping patterns in the film-forming resin, forming a "maze effect" that greatly extends the penetration path of water, oxygen, and corrosive ions, thereby improving the multi-protective performance of the powder coating. In conjunction with thixotropic agents, leveling agents, and pigments, the decorative performance of the powder coating is improved.

[0008] Preferably, the heavy-duty anti-corrosion and three-proof powder coating comprises the following components in parts by weight: 40 parts film-forming resin, 40 parts lamellar composite filler, 15 parts curing agent, 3 parts thixotropic agent, 1 part leveling agent, and 8 parts pigment. The film-forming resin includes phenolic resin and bisphenol A type epoxy resin, and the lamellar composite filler includes mica iron oxide, alumina, and lamellar glass powder.

[0009] Preferably, the film-forming resin is a mixture of phenolic resin and bisphenol A type epoxy resin in a mass ratio of 1:(1-2).

[0010] Preferably, the number-average molecular weight of the phenolic resin is 15,000 to 30,000, and the epoxy equivalent of the bisphenol A type epoxy resin is 700 to 900.

[0011] Preferably, the mass ratio of mica iron oxide, aluminum oxide and flake glass powder is (15-25):(10-15):(5-10), and the particle size of the flake glass powder is 400-800 mesh.

[0012] Preferably, the mass ratio of mica iron oxide, aluminum oxide and flake glass powder is 5:3:2.

[0013] A second aspect of the present invention provides a method for preparing a heavy-duty anti-corrosion and three-proof powder coating, comprising the following steps:

[0014] S1. Premixing: Add each component raw material into a high-speed mixer according to the proportion and mix at a speed of 800-1200 r / min for 5-10 min to obtain a mixture;

[0015] S2, Melt Extrusion: The mixture from S1 is fed into a twin-screw extruder, the screw speed is controlled at 300-500 rpm, and the barrel temperature from the feed port to the die head is set at 100-115℃ for melt compounding and extrusion.

[0016] S3. Cooling and sieving: The material extruded from S2 is cooled to below room temperature by a cooling steel belt, pressed into thin sheets, coarsely crushed and then sent to a micro powder mill for grinding. The ground powder is then classified by airflow and sieved by vibration to collect the finished powder with a particle size D50 of 25-38μm. The collected powder is the heavy-duty anti-corrosion and three-proof powder coating.

[0017] By adopting the above technical solution, high molecular weight phenolic resin can be fully mixed and dispersed with other components through medium and high temperature melt extrusion, and a powder suitable for electrostatic spraying can be obtained by controlling the differential particle size.

[0018] A third aspect of the present invention provides a construction process for a heavy-duty anti-corrosion and three-proof powder coating, comprising the following steps:

[0019] The first step is to treat the surface of the substrate;

[0020] The second step is to apply a primer to the treated substrate surface, and after the primer is surface dry, apply a heavy-duty anti-corrosion powder coating.

[0021] The third step is to send the workpiece coated with three-proof powder coating into the curing oven and use a stepped temperature rise curing method to heat and cure it. After curing, it is cooled to below 60°C in the oven and then taken out.

[0022] Preferably, the above-mentioned construction technology solution includes the following steps:

[0023] The first step is to sandblast or shot blast the surface of the substrate to achieve a surface cleanliness of Sa2.5 and a roughness of 50-85μm, and then proceed to the next step of construction within 4 hours.

[0024] The second step is to first apply an epoxy zinc-rich / inorganic zinc-rich primer using an airless thermal spraying device, with a dry film thickness of 60-80μm. After the primer is surface dry, use an electrostatic spray gun to spray heavy-duty anti-corrosion and three-proof powder coating on top of the primer, with a target film thickness of 150-250μm.

[0025] The third step is to send the coated workpiece from the second step into the curing oven and use a stepped heating curing method. First, preheat it to 140℃, then raise the temperature to 180-190℃ and hold it for 20-25 minutes. After curing, cool it down to below 60℃ in the oven and remove it from the oven.

[0026] By adopting the above technical solution, the substrate is cleaned to ensure adhesion. An epoxy zinc-rich / inorganic zinc-rich primer is used as the bottom layer to provide electrochemical protection, forming a synergistic anti-corrosion effect with the three-proof powder top layer. Stepped temperature increase curing is adopted. The softening point of the resin is 102℃. The preheating temperature is increased to 140℃ to ensure that the powder is fully melted and leveled, and to remove residual solvents and air from the primer. Then, the temperature is increased to 180-190℃ to complete full cross-linking and curing. This process ensures that there is no bubbling or cracking in the case of thick film, and that curing is complete. This improves the weather resistance, abrasion resistance, impact resistance, appearance, and gloss of the paint film formed by powder coating.

[0027] Preferably, in the above construction process technology scheme, the third step of the stepped temperature rise curing method is as follows: first, preheat at 140℃ for 10 minutes, then raise the temperature to 185℃ and keep it at that temperature for 25 minutes.

[0028] In summary, this application includes at least one of the following beneficial technical effects:

[0029] 1. The powder coating provided by this invention, through the synergistic effect of the compounded components, such as the high molecular weight, high cohesive strength, and good flexibility of phenolic resin, can form an extremely dense and tough paint film after being mixed with epoxy resin, providing a basic anti-corrosion barrier. The high cross-linking density of the curing agent and resin can improve chemical resistance. The layered composite filler composed of mica iron oxide (physical shielding, weather resistance), aluminum hydride (passivation and corrosion prevention, thermal conductivity), and flake glass powder (reinforcing shielding, wear resistance) is arranged in parallel overlapping arrangement in the film-forming resin to form a "maze effect", which greatly prolongs the penetration path of water, oxygen, and corrosive ions, and improves the multi-protective performance of the powder coating after coating. The thixotropic agent, leveling agent, and pigment are combined to improve the decorative performance of the powder coating after coating.

[0030] 2. The preparation method provided by the present invention ensures that the high molecular weight phenolic resin can be fully mixed and dispersed with other components through medium and high temperature melt extrusion, and obtains a powder suitable for electrostatic spraying by controlling the differential particle size.

[0031] 3. The construction process provided by this invention uses epoxy zinc-rich / inorganic zinc-rich primer as the base layer to provide electrochemical protection, forming a synergistic anti-corrosion effect with the three-proof powder topcoat. Stepped temperature increase curing is adopted. The softening point of the resin is 102℃. The preheating temperature is increased to 140℃ to ensure that the powder is fully melted and leveled, and to remove residual solvents and air from the primer. Then, the temperature is increased to 180-190℃ to complete full cross-linking and curing. This process ensures that there is no bubbling or cracking in the case of thick film, and that curing is complete. This improves the weather resistance, wear resistance, impact resistance, appearance, and gloss of the paint film formed by the powder coating.

[0032] 4. Using the heavy-duty anti-corrosion powder coating and construction process provided by this method, the coating formed can withstand neutral salt spray for more than 3,000 hours, resist damp heat (40℃, RH≥95%) for more than 5,000 hours, and achieve a mildew resistance level of 0. It can still achieve a smooth and even paint film appearance under thick film conditions, and has excellent weather resistance, abrasion resistance and impact resistance. Its service life exceeds that of traditional coatings. It is suitable for extreme corrosive environments such as C5-M (marine). At the same time, it is 100% solid powder with no VOC emissions. A single spray can achieve a film thickness of more than 200μm, and the construction efficiency is high. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Modifications or equivalent substitutions made by those skilled in the art based on their understanding of the technical solutions of this invention, without departing from the spirit and scope of the invention, should be covered within the protection scope of this invention.

[0034] The reagents, instruments, and equipment used in the following examples are commercially available products. Other specific conditions not specified shall be performed according to standard conditions or conditions recommended by the manufacturer.

[0035] In this application:

[0036] The curing agent is a phenolic amine curing agent, and in other feasible embodiments, a modified aromatic amine curing agent may be used instead; the thixotropic agent is fumed silica; the leveling agent is a polyacrylate leveling agent; and the pigment is titanium dioxide.

[0037] I. Implementation Examples

[0038] Example 1

[0039] A heavy-duty anti-corrosion and three-proof powder coating comprises the following components in parts by weight:

[0040] The film-forming resin consists of 40 parts, the lamellar composite filler consists of 40 parts, the curing agent consists of 15 parts, the thixotropic agent consists of 3 parts, the leveling agent consists of 1 part, and the pigment consists of 8 parts. The film-forming resin includes 20 parts of phenolic resin (number average molecular weight Mn=20000) and 20 parts of bisphenol A type epoxy resin (epoxy equivalent EEW=800). The lamellar composite filler includes 20 parts of mica iron oxide, 12 parts of aluminum hydride, and 8 parts of flake glass powder (600 mesh).

[0041] A method for preparing a heavy-duty anti-corrosion and three-proof powder coating includes the following steps:

[0042] S1. Premixing: Add each component raw material into a high-speed mixer according to the proportion and mix at a speed of 1000 r / min for 8 minutes to obtain a mixture;

[0043] S2, Melt Extrusion: The mixture from S1 is fed into a twin-screw extruder, the screw speed is controlled at 400 rpm, and the barrel temperature from the feed port to the die head is set to 100-115℃ (feed port 100℃, melting section 110℃, extrusion section 108℃) for melt compounding and extrusion.

[0044] S3. Cooling and sieving: The material extruded from S2 is cooled to below room temperature by a cooling steel belt, pressed into thin sheets of 1-2 mm, coarsely crushed and then sent to a micro powder mill for grinding. The ground powder is then sieved through an air classifier and a 400-mesh classifier to collect finished powder with a particle size D50 of 25-38 μm. The collected powder is the heavy-duty anti-corrosion and three-proof powder coating.

[0045] Example 2

[0046] A heavy-duty anti-corrosion and three-proof powder coating comprises the following components in parts by weight:

[0047] The film-forming resin consists of 60 parts, the lamellar composite filler consists of 30 parts, the curing agent consists of 10 parts, the thixotropic agent consists of 2 parts, the leveling agent consists of 0.5 parts, and the pigment consists of 2 parts. The film-forming resin includes 20 parts of phenolic resin (number average molecular weight Mn=15000) and 40 parts of bisphenol A type epoxy resin (epoxy equivalent EEW=700). The lamellar composite filler includes 15 parts of mica iron oxide, 10 parts of aluminum hydride, and 5 parts of flake glass powder (800 mesh).

[0048] A method for preparing a heavy-duty anti-corrosion and three-proof powder coating includes the following steps:

[0049] S1. Premixing: Add each component raw material into a high-speed mixer according to the proportion and mix at a speed of 800 r / min for 10 min to obtain a mixture;

[0050] S2, Melt Extrusion: The mixture from S1 is fed into a twin-screw extruder, the screw speed is controlled at 300 rpm, and the barrel temperature from the feed port to the die head is set to 100-115℃ (feed port 100℃, melting section 110℃, extrusion section 108℃) for melt compounding and extrusion.

[0051] S3. Cooling and sieving: The material extruded from S2 is cooled to below room temperature by a cooling steel belt, pressed into thin sheets of 1-2 mm, coarsely crushed and then sent to a micro powder mill for grinding. The ground powder is then sieved through an air classifier and a 400-mesh classifier to collect finished powder with a particle size D50 of 25-38 μm. The collected powder is the heavy-duty anti-corrosion and three-proof powder coating.

[0052] Example 3

[0053] A heavy-duty anti-corrosion and three-proof powder coating comprises the following components in parts by weight:

[0054] The film-forming resin consists of 50 parts, the lamellar composite filler consists of 50 parts, the curing agent consists of 20 parts, the thixotropic agent consists of 5 parts, the leveling agent consists of 1.5 parts, and the pigment consists of 10 parts. The film-forming resin includes 20 parts of phenolic resin (number average molecular weight Mn=30000) and 30 parts of bisphenol A type epoxy resin (epoxy equivalent EEW=900). The lamellar composite filler includes 25 parts of mica iron oxide, 15 parts of aluminum hydride, and 10 parts of flake glass powder (400 mesh).

[0055] A method for preparing a heavy-duty anti-corrosion and three-proof powder coating includes the following steps:

[0056] S1. Premixing: Add each component raw material into a high-speed mixer according to the proportion and mix at a speed of 1200 r / min for 5 minutes to obtain a mixture;

[0057] S2, Melt Extrusion: The mixture from S1 is fed into a twin-screw extruder, the screw speed is controlled at 500 rpm, and the barrel temperature from the feed port to the die head is set to 100-115℃ (feed port 100℃, melting section 110℃, extrusion section 108℃) for melt compounding and extrusion.

[0058] S3. Cooling and sieving: The material extruded from S2 is cooled to below room temperature by a cooling steel belt, pressed into thin sheets of 1-2 mm, coarsely crushed and then sent to a micro powder mill for grinding. The ground powder is then sieved through an air classifier and a 400-mesh classifier to collect finished powder with a particle size D50 of 25-38 μm. The collected powder is the heavy-duty anti-corrosion and three-proof powder coating.

[0059] II. Comparative Example

[0060] Comparative Example 1

[0061] A powder coating, which differs from Example 1 in that it does not contain layered composite fillers, but is prepared in the same way as Example 1.

[0062] Comparative Example 2

[0063] A powder coating differs from Example 1 in that the film-forming resin contains only phenolic resin and no bisphenol A type epoxy resin, and the preparation method is the same as that of Example 1.

[0064] Comparative Example 3

[0065] A powder coating differs from Example 1 in that the film-forming resin contains only bisphenol A type epoxy resin and no phenolic resin, and the preparation method is the same as that of Example 1.

[0066] III. Application Examples

[0067] Application Example 1

[0068] A construction process for a heavy-duty anti-corrosion and three-proof powder coating, using the powder coating provided in Example 1, with Q235 steel plate as the substrate, is carried out according to the following steps:

[0069] The first step is to sandblast the substrate surface to achieve a surface cleanliness of Sa2.5 and a roughness of 75μm, and then proceed to the next construction step within 4 hours.

[0070] The second step is to first apply an epoxy zinc-rich / inorganic zinc-rich primer using an airless thermal spraying device, with a dry film thickness of 80μm. After the primer is surface dry, the heavy-duty anti-corrosion powder coating prepared in Example 1 is then sprayed onto the primer using an electrostatic spray gun until the total film thickness is 280μm (i.e., the three-proof powder top layer is 200μm).

[0071] The third step is to send the coated workpiece from the second step into the curing oven and use a stepped heating curing method. First, preheat it to 140℃ for 10 minutes, then raise the temperature to 185℃ and hold for 25 minutes. After curing, cool it down to below 60℃ in the oven and remove it from the oven.

[0072] Application Example 2

[0073] A construction process for a heavy-duty anti-corrosion and three-proof powder coating, using the powder coating provided in Example 2, with Q235 steel plate as the substrate, is carried out according to the following steps:

[0074] The first step is to sandblast the substrate surface to achieve a surface cleanliness of Sa2.5 and a roughness of 50μm, and then proceed to the next construction step within 4 hours.

[0075] The second step is to first apply an epoxy zinc-rich / inorganic zinc-rich primer using an airless thermal spraying device, with a dry film thickness of 60μm. After the primer is surface dry, the heavy-duty anti-corrosion powder coating prepared in Example 2 is then sprayed onto the primer using an electrostatic spray gun until the total film thickness is 310μm (i.e., the three-proof powder top layer is 250μm).

[0076] The third step is to send the coated workpiece from the second step into the curing oven and use a stepped heating curing method. First, preheat it to 140℃ for 10 minutes, then raise the temperature to 180℃ and hold for 25 minutes. After curing, cool it down to below 60℃ in the oven and remove it from the oven.

[0077] Application Example 3

[0078] A construction process for a heavy-duty anti-corrosion and three-proof powder coating, using the powder coating provided in Example 3, with Q235 steel plate as the substrate, is carried out according to the following steps:

[0079] The first step is to sandblast the substrate surface to achieve a surface cleanliness of Sa2.5 and a roughness of 80μm, and then proceed to the next construction step within 4 hours.

[0080] The second step is to first apply an epoxy zinc-rich / inorganic zinc-rich primer using an airless thermal spraying device, with a dry film thickness of 80μm. After the primer is surface dry, the heavy-duty anti-corrosion powder coating prepared in Example 3 is then sprayed onto the primer using an electrostatic spray gun until the total film thickness is 230μm (i.e., the three-proof powder top layer is 150μm).

[0081] The third step is to send the coated workpiece from the second step into the curing oven and use a stepped heating curing method. First, preheat it to 140℃ for 10 minutes, then raise the temperature to 190℃ and hold for 20 minutes. After curing, cool it down to below 60℃ in the oven and remove it from the oven.

[0082] Blank application example

[0083] The traditional liquid coating system was used and the construction process provided in Application Example 1 was followed. After the substrate surface was treated, 75 μm of epoxy zinc-rich primer was sprayed. After the primer was surface dry, 100 μm of epoxy micaceous iron oxide intermediate paint was sprayed. After the intermediate paint was surface dry, 50 μm of aliphatic polyurethane topcoat was sprayed. The sprayed workpiece was then placed in a curing oven for curing.

[0084] Comparative Application Example 1

[0085] The powder coating provided in Comparative Example 1 was used, with Q235 steel plate as the substrate, and the construction process provided in Application Example 1 was used for construction.

[0086] Comparative Application Example 2

[0087] The powder coating provided in Comparative Example 2 was used, with Q235 steel plate as the substrate, and the construction process provided in Application Example 1 was used for construction.

[0088] Comparative Application Example 3

[0089] The powder coating provided in Comparative Example 3 was used, with Q235 steel plate as the substrate, and the construction process provided in Application Example 1 was used for construction.

[0090] Comparative Application Example 4

[0091] Using the powder coating provided in Example 1, with Q235 steel plate as the substrate, the construction process differs from that in Example 1 in that the heating and curing in the third step is a one-time heating, raising the temperature to 185°C and holding it at that temperature for 25 minutes.

[0092] IV. Performance Test Experiments and Results

[0093] Performance tests were conducted on the paint films applied for use cases 1-3 and the blank application case, respectively. The test results are shown in the table below:

[0094] Table 1 Performance Test Comparison Table

[0095] Test Project Test Standards Application Example 1 Application Example 2 Application Example 3 Blank application example Resistance to neutral salt spray (3000h) GB / T 1771 Scratching < 2mm, bubbling grade 0 Scratching <2mm, blistering grade 0 Scratching < 2mm, bubbling grade 0 Scratching <3mm, blistering level 1 (S2) Resistant to damp heat (5000h) GB / T 1740 No abnormalities No abnormalities No abnormalities Slight loss of luster, discoloration Mold resistance (28 days) GB / T 1741 Level 0 Level 0 Level 0 Level 1 Adhesion (cross-cut test) GB / T 9286 Level 0 Level 0 Level 0 Level 1 Abrasion resistance (750g / 500r, mg) ASTM D4060 45 43 41 68 Artificial accelerated aging (2000h) GB / T 1865 Gloss loss level 1, chalking level 1 Gloss loss level 1, chalking level 1 Gloss loss level 1, chalking level 1 Gloss loss level 2, chalking level 1 VOC emissions Real-time detection 0 g / L 0 g / L 0 g / L ≈350 g / L

[0096] As shown in Table 1, the coating formed by using the powder coating components provided in this application and the preparation method and construction process provided in this application can withstand neutral salt spray for more than 3000 hours, resist damp heat (40℃, RH≥95%) for more than 5000 hours, and achieve a mildew resistance level of 0. It can still obtain a smooth and flat paint film appearance under thick film conditions, and has excellent weather resistance, wear resistance and impact resistance. Its service life exceeds that of traditional coatings and it can be used in extreme corrosive environments such as C5-M (marine). At the same time, it is 100% solid powder with no VOC emissions. A single spray can achieve a film thickness of more than 200μm, and the construction efficiency is high. It is significantly better than traditional liquid heavy-duty anti-corrosion coating systems in terms of key anti-corrosion performance, mechanical properties and environmental protection. The coating performance obtained in Application Example 1 is the best. Therefore, the component ratio and preparation method provided in Example 1 are the best examples, and the construction process provided in Application Example 1 is the best application example.

[0097] The performance of the coatings applied in Application Example 1 and Comparative Application Examples 1-4 was further tested, and the test results are as follows:

[0098] Compared to Application Example 1, the coating in Application Example 1 provides significantly shorter protection time for the substrate, exhibits higher embrittlement, and is more prone to cracking under temperature changes or stress. Its hardness and abrasion resistance decrease, and thick coatings exhibit sagging during application, making it difficult to achieve the designed film thickness. However, its surface is smoother due to the absence of lamellar filler. Lamellar filler effectively severs the continuous resin phase, reduces curing shrinkage and internal stress, and prevents microcrack propagation, resulting in a lower physical barrier, a denser coating, and higher internal stress. Consequently, it is highly susceptible to cracking, which easily becomes the initiation point for corrosion, thus exhibiting poor corrosion resistance.

[0099] Compared to Application Example 1, the coating in Comparative Application Example 2, lacking epoxy resin, exhibits a curing mechanism that changes from thermosetting to thermoplastic. Upon heating, the coating softens, swells in strong solvents, exhibits moderate alkali resistance, and has poor acid and chemical resistance. In strong acid environments, it softens and dissolves, resulting in poor corrosion resistance and heat resistance. Furthermore, its abrasion resistance and tensile strength decrease, making it more susceptible to scratches and wear, and prone to peeling off the substrate. Adhesion retention is poor; surface drying is fast, but complete drying is slow, and a "sandwich" phenomenon is likely to occur during use.

[0100] Compared to Application Example 1, the coating in Application Example 3 is without phenolic resin, i.e. lacking a polymer toughening agent. Due to the lack of the long-chain structure of phenolic resin to cut the continuous phase of epoxy resin, the internal stress cannot be released, so it is prone to cracking and peeling. At the same time, the adhesion is reduced, but its hardness and wear resistance are extremely high, while its chemical resistance is average.

[0101] The coating obtained in Application Example 1 has no bubbles, no pinholes, good leveling properties, and no sagging. Its internal stress and curing degree are also good. In contrast, the coating obtained in Application Example 4, due to different construction processes, lacks a stepped heating step, resulting in an excessively thick coating. This causes the additives to not evaporate in a short time. When exposed to high temperatures, the additive solvents evaporate, resulting in a large number of bubbles and pinholes on the coating surface. Furthermore, the coating is applied in one thick coat, with thinner paint films at the edges and corners and thicker films in flat areas. Before curing, the coating shows obvious tear-like sagging due to gravity, reducing or even eliminating its decorative properties. During the curing of the thick coating, the uneven curing shrinkage and temperature between the internal and external layers, as well as the upper and lower layers, generate huge internal stress. The large gradient of solvent evaporation from the inside to the outside also generates shrinkage stress, resulting in mud-crack-like network cracks after cooling. Similarly, due to the thick coating, the heat conduction time is insufficient, and the one-time heating causes the outer layer to harden while the inner layer remains in an under-cured state. The overall hardness, chemical resistance, and mechanical strength do not meet the design specifications, and the bottom layer softens, leading to reduced adhesion.

[0102] In summary, the coating formed by applying the specific component ratio, preparation method, and construction process of this application has been tested and found to withstand neutral salt spray for over 3000 hours, resist damp heat (40℃, RH≥95%) for over 5000 hours, achieve a mildew resistance rating of 0, and still achieve a smooth and even film appearance even under thick film conditions. It also exhibits excellent weather resistance, abrasion resistance, and impact resistance, with a service life exceeding that of traditional coatings. It is suitable for extreme corrosive environments such as C5-M (marine). Furthermore, it is 100% solid powder with no VOC emissions, and a single spray can achieve a film thickness of over 200μm, resulting in high construction efficiency.

Claims

1. A heavy-duty anti-corrosion and three-proof powder coating, characterized in that: It comprises the following components by weight: 40-60 parts of film-forming resin, 30-50 parts of lamellar composite filler, 10-20 parts of curing agent, 2-5 parts of thixotropic agent, 0.5-1.5 parts of leveling agent, and 2-10 parts of pigment. The film-forming resin includes phenolic resin and bisphenol A type epoxy resin, and the lamellar composite filler includes mica iron oxide, alumina, and lamellar glass powder.

2. The powder coating according to claim 1, characterized in that: It comprises the following components by weight: 40 parts film-forming resin, 40 parts lamellar composite filler, 15 parts curing agent, 3 parts thixotropic agent, 1 part leveling agent, and 8 parts pigment. The film-forming resin includes phenolic resin and bisphenol A type epoxy resin, and the lamellar composite filler includes mica iron oxide, alumina, and lamellar glass powder.

3. The powder coating according to claim 1 or 2, characterized in that: The film-forming resin is a mixture of phenolic resin and bisphenol A type epoxy resin in a mass ratio of 1:(1-2).

4. The powder coating according to claim 3, characterized in that: The number-average molecular weight of the phenolic resin is 15,000 to 30,000, and the epoxy equivalent of the bisphenol A type epoxy resin is 700 to 900.

5. The powder coating according to claim 1 or 2, characterized in that: The mass ratio of mica iron oxide, aluminum oxide and flake glass powder is (15-25):(10-15):(5-10), and the particle size of the flake glass powder is 400-800 mesh.

6. The powder coating according to claim 5, characterized in that: The mass ratio of mica iron oxide, aluminum oxide and flake glass powder is 5:3:

2.

7. The method for preparing heavy-duty anti-corrosion and three-proof powder coating according to any one of claims 1-6, characterized in that: Includes the following steps: S1. Premixing: Add each component raw material into a high-speed mixer according to the proportion and mix at a speed of 800-1200 r / min for 5-10 min to obtain a mixture; S2, Melt Extrusion: The mixture from S1 is fed into a twin-screw extruder, the screw speed is controlled at 300-500 rpm, and the barrel temperature from the feed port to the die head is set at 100-115℃ for melt compounding and extrusion. S3. Cooling and sieving: The material extruded from S2 is cooled to below room temperature by a cooling steel belt, pressed into thin sheets, coarsely crushed and then sent to a micro powder mill for grinding. The ground powder is then classified by airflow and sieved by vibration to collect the finished powder with a particle size D50 of 25-38μm. The collected powder is the heavy-duty anti-corrosion and three-proof powder coating.

8. The construction process of the heavy-duty anti-corrosion and three-proof powder coating according to any one of claims 1-6, characterized in that: Includes the following steps: The first step is to treat the surface of the substrate; The second step is to apply a primer to the treated substrate surface, and after the primer is surface dry, apply a heavy-duty anti-corrosion powder coating. The third step is to send the workpiece coated with three-proof powder coating into the curing oven and use a stepped temperature rise curing method to heat and cure it. After curing, it is cooled to below 60°C in the oven and then taken out.

9. The construction process according to claim 8, characterized in that: Includes the following steps: The first step is to sandblast or shot blast the surface of the substrate to achieve a surface cleanliness of Sa2.5 and a roughness of 50-85μm, and then proceed to the next step of construction within 4 hours. The second step is to first apply an epoxy zinc-rich / inorganic zinc-rich primer using an airless thermal spraying device, with a dry film thickness of 60-80μm. After the primer is surface dry, use an electrostatic spray gun to spray heavy-duty anti-corrosion and three-proof powder coating on top of the primer, with a target film thickness of 150-250μm. The third step is to send the coated workpiece from the second step into the curing oven and use a stepped heating curing method. First, preheat it to 140℃, then raise the temperature to 180-190℃ and hold it for 20-25 minutes. After curing, cool it down to below 60℃ in the oven and remove it from the oven.

10. The construction process according to claim 9, characterized in that: In the third step, the steps of the stepped temperature curing method are as follows: first, preheat at 140℃ for 10 minutes, then raise the temperature to 185℃ and hold for 25 minutes.