Outdoor box plastic spraying process

Abstract

The invention discloses an outdoor box plastic spraying process, and relates to the technical field of outdoor box surface protection processing, and the outdoor box plastic spraying process comprises the following steps: S1, gradient polishing treatment; s2, double-section ultrasonic cleaning is conducted; s3, carrying out vacuum pre-drying; s4, spraying composite molding powder; and S5, segmented curing and cooling. The molding powder is prepared from the following raw materials in parts by weight: 58-63 parts of a resin base material, 3-5 parts of nano silicon dioxide, 4-6 parts of a compound anti-aging agent, 8-10 parts of titanium dioxide, 5-8 parts of barium sulfate, 1.5-2.5 parts of a flatting agent, 1-2 parts of a coupling agent, 2-3 parts of triglycidyl isocyanurate, 3-5 parts of a multi-element synergistic interaction system and 1-2 parts of amino fluorosilicone oil. According to the process, the adhesive force, the corrosion resistance and the weather resistance are synchronously improved through cooperation of a customized composite molding powder formula and the gradient surface treatment-vacuum drying-segmented curing process.

Description

Technical Field

[0001] This invention relates to the field of outdoor case processing technology, and in particular to a powder coating process for outdoor cases. Background Technology

[0002] Outdoor enclosures, serving as the core carriers for outdoor equipment such as power transmission, communication base stations, and security monitoring systems, are constantly exposed to the natural environment. They must withstand the combined effects of multiple harsh conditions, including high temperatures, freezing temperatures, torrential rain, salt spray corrosion, and ultraviolet radiation. Therefore, the comprehensive performance of the surface protective coating directly determines the structural stability and service life of the outdoor enclosure. Powder coating, with its advantages of good coating density, high construction efficiency, and controllable cost, has become the mainstream technical solution for the surface protection of outdoor enclosures. It achieves the core protective goals of rust prevention, corrosion prevention, and aging resistance by forming a uniform powder coating on the surface of the enclosure's metal substrate.

[0003] The existing outdoor box powder coating process has significant shortcomings in its technical design. The pretreatment stage lacks systematic optimization: the sanding process relies heavily on manual experience to control sandpaper grit and sanding force, resulting in uneven surface roughness. Some areas are excessively rough, causing stress concentration, while others are insufficiently sanded, leaving residual oxide layers and burrs, directly affecting the bonding stability between the subsequent coating and the substrate. Ultrasonic cleaning uses only single-frequency ultrasound and general-purpose cleaning fluid, failing to thoroughly remove stubborn oil and impurities from hidden areas such as gaps and welds. Furthermore, the phosphating reaction is incomplete, resulting in an uneven phosphating film with weak adhesion, failing to provide reliable underlayer support for the coating. This leads to coating failures such as peeling and flaking. The powder coating often uses a single resin base and basic filler combination, with only a small amount of a single type of antioxidant added. It lacks targeted anti-aging and anti-corrosion functional components, causing the coating to easily undergo molecular chain degradation under strong ultraviolet radiation, resulting in chalking and discoloration. In high-salt spray and high-humidity environments, corrosive media can easily penetrate the coating, causing substrate corrosion.

[0004] Therefore, developing an outdoor box powder coating process that can break through existing technological bottlenecks and achieve synergistic improvement of multiple performance aspects has become an urgent technical problem to be solved in the industry. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides an outdoor box powder coating process. By precisely controlling the parameters of each process and optimizing the material formula, it solves the technical problems of weak coating adhesion, insufficient oxidation resistance, poor corrosion resistance, and short service life in existing processes.

[0006] To achieve the above objectives, the present invention provides an outdoor box powder coating process, comprising the following steps: Step S1, Gradient Grinding Process: A two-stage grinding process is adopted. First, 120-150 grit sandpaper is used for coarse grinding to remove the surface oxide layer and burrs. Then, 280-320 grit sandpaper is used for fine grinding to control the surface roughness Ra of the outdoor box body and components to 2.0-3.0μm. Step S2, Dual-stage ultrasonic cleaning: Place the polished workpiece into the first ultrasonic cleaning tank, add phosphating cleaning solution to the tank, control the water temperature to 35±3℃, turn on 28KHz low-frequency ultrasonic waves to soak for 4 minutes, and then transfer it to the second ultrasonic cleaning tank, use 40KHz high-frequency ultrasonic waves in conjunction with deionized water to rinse for 5 minutes to remove residual phosphating solution and impurities. Step S3, Vacuum pre-drying: Place the rinsed workpiece into a vacuum oven, set the vacuum degree to -0.09~-0.08MPa, the temperature to 70-75℃, and pre-dry for 25-30 minutes to remove moisture from the surface of the workpiece and the tiny pores. Step S4, Composite Powder Coating: Fix the pre-baked workpiece with a special anti-dust hanger, and use a silicone heat insulation pad to isolate the contact point between the hanger and the workpiece; put it into the spray booth for powder coating, control the spray booth spraying pressure to 0.5-0.55MPa, the atomizing air pressure to 0.3-0.35MPa, and control the coating thickness to 70-90μm; Step S5, Segmented Curing and Cooling: The powder-coated workpiece is sent into a segmented drying tunnel. The temperature of the first drying tunnel is 160-170℃, and it is kept at this temperature for 10 minutes for pre-melting. The temperature of the second drying tunnel is 190-200℃, and it is kept at this temperature for 15 minutes to achieve complete melting and leveling. The temperature of the third drying tunnel is 180-185℃, and it is kept at this temperature for 8 minutes for post-curing. After exiting the drying tunnel, it is first cooled in a constant temperature cooling zone of 30-40℃ for 20 minutes, and then naturally cooled to room temperature. The finished product is obtained by removing the hanger.

[0007] Preferably, the phosphating cleaning solution in step S2 comprises the following components by weight percentage: 8-10% zinc dihydrogen phosphate, 3-5% surfactant, 2-3% complexing agent, and the balance being water.

[0008] Preferably, the surfactant is a fatty alcohol polyoxyethylene ether; and the complexing agent is trisodium citrate.

[0009] Preferably, the hanging point of the anti-dust special hanger in step S4 is designed with an arc shape, the contact area with the workpiece is ≤0.5cm², and the surface of the hanger is anodized.

[0010] Preferably, the powder used for powder coating in step S4 comprises the following raw materials in parts by weight: 58-63 parts resin base material, 3-5 parts nano silica, 4-6 parts compound anti-aging agent, 8-10 parts titanium dioxide, 5-8 parts barium sulfate, 1.5-2.5 parts leveling agent, 1-2 parts coupling agent, 2-3 parts triglycidyl isocyanate, 3-5 parts multi-component synergistic effect system, and 1-2 parts amino fluorosilicone oil.

[0011] Preferably, the resin substrate is a compound of end-carboxyl hyperbranched polyester HyPer C104 and epoxy modified polyester resin SGR-3340 in a mass ratio of 1:(3-5).

[0012] Preferably, the average particle size of the nano-silica is 20-80 nm; the particle size of the titanium dioxide is 1200-1600 mesh; and the particle size of the barium sulfate is 1500-2000 mesh.

[0013] Preferably, the compound anti-aging agent is composed of UV-327, HALS-944, and antioxidant 168 in a mass ratio of 3:2:1.

[0014] Preferably, the leveling agent is leveling agent BYK-3550; the coupling agent is at least one of silane coupling agent KH550, silane coupling agent KH560, and silane coupling agent KH570.

[0015] Preferably, the multi-component synergistic enhancement system is composed of graphene nanosheets, nano zinc oxide, and organic nano montmorillonite in a mass ratio of 0.3:(0.5-0.8):(3-5).

[0016] Preferably, the graphene nanosheets are XGnP® graphene nanosheets C-300; the average particle size of the nano zinc oxide is 10-60 nm; and the organic nano montmorillonite is Fenghong DK2 nano organic bentonite.

[0017] Preferably, the method for preparing the plastic powder includes the following steps: mixing the raw materials evenly, extruding and granulating them through a twin-screw extruder, crushing them, and passing them through a 180-200 mesh sieve to obtain the plastic powder.

[0018] Preferably, the barrel temperature of the twin-screw extruder is 110-130℃, and the screw speed is 30-40 r / min.

[0019] Preferably, the amino fluorosilicone oil is amino fluorosilicone oil AFS®-O-1300.

[0020] Preferably, the hot air velocity in the segmented drying tunnel in step S5 is 0.8-1.2 m / s, and the hot air circulation method is used to ensure temperature uniformity with a temperature difference ≤ ±2℃.

[0021] Due to the application of the above technical solution, the present invention has the following beneficial effects: (1) The outdoor box powder coating process disclosed in this invention, through the synergistic design of gradient grinding and dual-stage ultrasonic cleaning, enables the surface roughness of the workpiece to be precisely controlled at 2.0-3.0μm. Combined with customized phosphating cleaning solution, a uniform and dense phosphating film is formed. The coating adhesion is significantly improved compared with the existing process, and the problem of coating peeling and falling off caused by incomplete surface treatment in the traditional process is completely solved. The combined effect far exceeds the conventional improvement of single optimization of grinding or cleaning steps, and the interface bonding strengthening effect is achieved.

[0022] (2) The outdoor box powder coating process disclosed in this invention uses a composite substrate of end-carboxyl hyperbranched polyester and epoxy modified polyester resin, combined with a multi-component synergistic system composed of graphene nanofibers, nano zinc oxide and organic nano montmorillonite, to construct a dual barrier of "physical barrier + chemical protection", which significantly extends the neutral salt spray tolerance time of the coating compared with the existing process and significantly improves the aging resistance performance. It breaks through the weather resistance bottleneck of traditional single resin and basic filler formulations and shows unexpected synergistic gains in corrosion resistance and aging resistance.

[0023] (3) The outdoor box powder coating process disclosed in this invention introduces amino fluorosilicone oil and compound anti-aging agent into the powder formulation, and works in conjunction with the segmented curing process. This not only gives the coating excellent stain resistance and self-cleaning ability, but also eliminates the internal stress of the coating through three-stage temperature control, thereby increasing the number of high and low temperature cycle tolerances. This solves the technical contradiction that it is difficult to balance stain resistance and temperature difference resistance in the existing process. The overall performance improvement is far greater than the conventional improvement level in the industry.

[0024] (4) The outdoor box powder coating process disclosed in this invention has a precise matching of process parameters and material formulas throughout the process, which significantly extends the service life of the outdoor box coating compared with existing processes. At the same time, the plastic preparation process is simple and controllable, taking into account the needs of high performance and large-scale production, filling the technical gap between "high performance in the laboratory" and "industrial practical application", and has high economic value and application prospects. Detailed Implementation

[0025] The following description is intended to disclose the invention and enable those skilled in the art to implement it. The preferred embodiments described below are merely examples, and other obvious variations will occur to those skilled in the art.

[0026] Example 1: An outdoor box powder coating process, comprising the following steps: Step S1, Gradient Grinding Process: A two-stage grinding process is adopted. First, 120-grit sandpaper is used for coarse grinding to remove the surface oxide layer and burrs, and then 280-grit sandpaper is used for fine grinding to control the surface roughness Ra of the outdoor box body and components to 2.0μm. Step S2, Dual-stage ultrasonic cleaning: Place the polished workpiece into the first ultrasonic cleaning tank, add phosphating cleaning solution to the tank, control the water temperature to 32℃, turn on 28KHz low-frequency ultrasonic waves to soak for 4 minutes, and then transfer it to the second ultrasonic cleaning tank, use 40KHz high-frequency ultrasonic waves in conjunction with deionized water to rinse for 5 minutes to remove residual phosphating solution and impurities. Step S3, Vacuum pre-drying: Place the rinsed workpiece into a vacuum oven, set the vacuum degree to -0.08MPa and the temperature to 70℃, and pre-dry for 25 minutes to remove moisture from the surface of the workpiece and the tiny pores. Step S4, Composite Powder Coating: Fix the pre-baked workpiece with a special anti-dust hanger, and use a silicone heat insulation pad to isolate the contact point between the hanger and the workpiece; put it into the spray booth for powder coating, control the spray booth spraying pressure to 0.5MPa, the atomizing air pressure to 0.3MPa, and control the coating thickness to 70μm; Step S5, Segmented Curing and Cooling: The powder-coated workpiece is sent into a segmented drying tunnel. The temperature of the first drying tunnel is 160℃, and it is kept at this temperature for 10 minutes for pre-melting. The temperature of the second drying tunnel is 190℃, and it is kept at this temperature for 15 minutes to achieve complete melting and leveling. The temperature of the third drying tunnel is 180℃, and it is kept at this temperature for 8 minutes for post-curing. After exiting the drying tunnel, it is first cooled in a constant temperature cooling zone of 30℃ for 20 minutes, and then naturally cooled to room temperature. The hanger is then removed to obtain the finished product.

[0027] The phosphating cleaning solution in step S2 comprises the following components by weight percentage: 8% zinc dihydrogen phosphate, 3% surfactant, 2% complexing agent, and the balance being water; the surfactant is fatty alcohol polyoxyethylene ether; the complexing agent is trisodium citrate; the hanging point of the anti-dust special hanger in step S4 adopts an arc design, with a contact area with the workpiece ≤0.5cm², and the surface of the hanger is anodized.

[0028] The powder coating used in step S4 comprises the following raw materials in parts by weight: 58 parts resin substrate, 3 parts nano silica, 4 parts compound anti-aging agent, 8 parts titanium dioxide, 5 parts barium sulfate, 1.5 parts leveling agent, 1 part coupling agent, 2 parts triglycidyl isocyanate, 3 parts multi-component synergistic system, and 1 part amino fluorosilicone oil; the resin substrate is a carboxyl-terminated hyperbranched polyester HyPer C104 and epoxy-modified polyester resin SGR-3340 are compounded in a mass ratio of 1:3; the average particle size of the nano-silica is 20nm; the particle size of the titanium dioxide is 1200 mesh; the particle size of the barium sulfate is 1500 mesh; the compounded anti-aging agent is UV-327, HALS-944, and antioxidant 168 compounded in a mass ratio of 3:2:1; the leveling agent is leveling agent BYK-3550; the coupling agent is silane coupling agent KH550 and silane coupling agent KH56. 0. The silane coupling agent KH570 is compounded in a mass ratio of 1:2:1; the multi-component synergistic system is compounded in a mass ratio of 0.3:0.6:3.5 of graphene nanosheets, nano zinc oxide, and organic nano montmorillonite; the graphene nanosheets are XGnP® graphene nanosheets C-300; the average particle size of the nano zinc oxide is 10 nm; the organic nano montmorillonite is Fenghong DK2 nano organic bentonite; and the amino fluorosilicone oil is amino fluorosilicone oil AFS®-O-1300.

[0029] The method for preparing the plastic powder includes the following steps: after mixing the raw materials evenly, extruding and granulating them through a twin-screw extruder, crushing them, and passing them through a 180-mesh sieve to obtain the plastic powder; the barrel temperature of the twin-screw extruder is 110℃, and the screw speed is 30r / min; the hot air velocity in the segmented drying tunnel in step S5 is 0.8m / s, and the hot air circulation method is used to ensure temperature uniformity, with a temperature difference ≤±2℃.

[0030] Example 2: An outdoor box powder coating process, comprising the following steps: Step S1, Gradient Grinding Process: A two-stage grinding process is adopted. First, 130-grit sandpaper is used for coarse grinding to remove the surface oxide layer and burrs, and then 290-grit sandpaper is used for fine grinding to control the surface roughness Ra of the outdoor box body and components to 2.3μm. Step S2, Dual-stage ultrasonic cleaning: Place the polished workpiece into the first ultrasonic cleaning tank, add phosphating cleaning solution to the tank, control the water temperature to 34℃, turn on 28KHz low-frequency ultrasonic waves to soak for 4 minutes, and then transfer it to the second ultrasonic cleaning tank, use 40KHz high-frequency ultrasonic waves in conjunction with deionized water to rinse for 5 minutes to remove residual phosphating solution and impurities. Step S3, Vacuum pre-drying: Place the rinsed workpiece into a vacuum oven, set the vacuum degree to -0.083MPa and the temperature to 72℃, and pre-dry for 27 minutes to remove moisture from the surface of the workpiece and the tiny pores. Step S4, Composite Powder Coating: Fix the pre-baked workpiece with a special anti-dust hanger, and use a silicone heat insulation pad to isolate the contact point between the hanger and the workpiece; spray the workpiece into the spray booth for powder coating, control the spray booth spraying pressure to 0.52MPa, the atomizing air pressure to 0.32MPa, and control the coating thickness to 75μm; Step S5, Segmented Curing and Cooling: The powder-coated workpiece is sent into a segmented drying tunnel. The temperature of the first drying tunnel is 163℃, and it is kept at this temperature for 10 minutes for pre-melting. The temperature of the second drying tunnel is 193℃, and it is kept at this temperature for 15 minutes to achieve complete melting and leveling. The temperature of the third drying tunnel is 182℃, and it is kept at this temperature for 8 minutes for post-curing. After exiting the drying tunnel, it is first cooled in a constant temperature cooling zone of 33℃ for 20 minutes, and then naturally cooled to room temperature. The hanger is then removed to obtain the finished product.

[0031] The phosphating cleaning solution in step S2 comprises the following components by weight percentage: 8.5% zinc dihydrogen phosphate, 3.5% surfactant, 2.3% complexing agent, and the balance being water; the surfactant is fatty alcohol polyoxyethylene ether; the complexing agent is trisodium citrate; the hanging point of the anti-dust special hanger in step S4 adopts an arc design, with a contact area with the workpiece ≤0.5cm², and the surface of the hanger is anodized.

[0032] The powder coating used in step S4 comprises the following raw materials in parts by weight: 59 parts resin substrate, 3.5 parts nano silica, 4.5 parts compound anti-aging agent, 8.5 parts titanium dioxide, 6 parts barium sulfate, 1.8 parts leveling agent, 1.2 parts coupling agent, 2.3 parts triglycidyl isocyanate, 3.5 parts multi-component synergistic system, and 1.2 parts amino fluorosilicone oil; the resin substrate is a carboxyl-terminated hyperbranched polyester HyPer C104 and epoxy-modified polyester resin SGR-3340 are compounded in a mass ratio of 1:3.5; the average particle size of the nano-silica is 40nm; the particle size of the titanium dioxide is 1300 mesh; the particle size of the barium sulfate is 1600 mesh; the compounded anti-aging agent is UV-327, HALS-944, and antioxidant 168 compounded in a mass ratio of 3:2:1; the leveling agent is leveling agent BYK-3550; the coupling agent is silane. The coupling agent is KH560; the multi-component synergistic system is composed of graphene nanosheets, nano zinc oxide, and organic nano montmorillonite in a mass ratio of 0.3:0.6:3.5; the graphene nanosheets are XGnP® graphene nanosheets C-300; the average particle size of the nano zinc oxide is 30 nm; the organic nano montmorillonite is Fenghong DK2 nano organic bentonite; and the amino fluorosilicone oil is amino fluorosilicone oil AFS®-O-1300.

[0033] The method for preparing the plastic powder includes the following steps: after mixing the raw materials evenly, extruding and granulating them through a twin-screw extruder, crushing them, and passing them through a 185-mesh sieve to obtain the plastic powder; the barrel temperature of the twin-screw extruder is 115℃, and the screw speed is 33r / min.

[0034] In step S5, the hot air velocity in the segmented drying tunnel is 0.9 m / s, and hot air circulation is used to ensure temperature uniformity with a temperature difference of ≤ ±2℃.

[0035] Example 3: An outdoor box powder coating process, comprising the following steps: Step S1, Gradient Grinding Process: A two-stage grinding process is adopted. First, 135-grit sandpaper is used for coarse grinding to remove the surface oxide layer and burrs, and then 300-grit sandpaper is used for fine grinding to control the surface roughness Ra of the outdoor box body and components to 2.5μm. Step S2, Dual-stage ultrasonic cleaning: Place the polished workpiece into the first ultrasonic cleaning tank, add phosphating cleaning solution to the tank, control the water temperature to 35℃, turn on 28KHz low-frequency ultrasonic waves to soak for 4 minutes, and then transfer it to the second ultrasonic cleaning tank, use 40KHz high-frequency ultrasonic waves in conjunction with deionized water to rinse for 5 minutes to remove residual phosphating solution and impurities. Step S3, Vacuum pre-drying: Place the rinsed workpiece into a vacuum oven, set the vacuum degree to -0.085MPa and the temperature to 73℃, and pre-dry for 28 minutes to remove moisture from the surface of the workpiece and the tiny pores. Step S4, Composite Powder Coating: Fix the pre-baked workpiece with a special anti-dust hanger, and use a silicone heat insulation pad to isolate the contact point between the hanger and the workpiece; spray the workpiece into the spray booth for powder coating, control the spray booth spraying pressure to 0.53MPa, the atomizing air pressure to 0.33MPa, and control the coating thickness to 80μm; Step S5, Segmented Curing and Cooling: The powder-coated workpiece is sent into a segmented drying tunnel. The temperature of the first drying tunnel is 165℃, and it is kept at this temperature for 10 minutes for pre-melting. The temperature of the second drying tunnel is 195℃, and it is kept at this temperature for 15 minutes to achieve complete melting and leveling. The temperature of the third drying tunnel is 183℃, and it is kept at this temperature for 8 minutes for post-curing. After exiting the drying tunnel, it is first cooled in a constant temperature cooling zone of 35℃ for 20 minutes, and then naturally cooled to room temperature. The hanger is then removed to obtain the finished product.

[0036] The phosphating cleaning solution in step S2 comprises the following components by weight percentage: 9% zinc dihydrogen phosphate, 4% surfactant, 2.5% complexing agent, and the balance being water; the surfactant is fatty alcohol polyoxyethylene ether; the complexing agent is trisodium citrate; the hanging points of the anti-dust special hanger in step S4 are designed with an arc shape, and the contact area with the workpiece is ≤0.5cm², and the surface of the hanger is anodized; the powder coating for powder coating in step S4 comprises the following raw materials by weight: 61 parts resin substrate, 4 parts nano silica, 5 parts compound anti-aging agent, 9 parts titanium dioxide, 6.5 parts barium sulfate, 2 parts leveling agent, 1.5 parts coupling agent, 2.5 parts triglycidyl isocyanurate, 4 parts multi-component synergistic effect system, and 1.5 parts amino fluorosilicone oil; the resin substrate is end-carboxyl hyperbranched polyester HyPer C104 and epoxy-modified polyester resin SGR-3340 are compounded in a mass ratio of 1:4; the average particle size of the nano-silica is 50nm; the particle size of the titanium dioxide is 1400 mesh; the particle size of the barium sulfate is 1800 mesh; the compounded anti-aging agent is UV-327, HALS-944, and antioxidant 168 compounded in a mass ratio of 3:2:1; the leveling agent is leveling agent BYK-3550; the coupling agent is silane coupling agent KH550 and silane coupling agent KH56. 0. The silane coupling agent KH570 is compounded in a mass ratio of 1:2:1; the multi-component synergistic system is compounded in a mass ratio of 0.3:0.65:4 of graphene nanosheets, nano zinc oxide, and organic nano montmorillonite; the graphene nanosheets are XGnP® graphene nanosheets C-300; the average particle size of the nano zinc oxide is 40nm; the organic nano montmorillonite is Fenghong DK2 nano organic bentonite; and the amino fluorosilicone oil is amino fluorosilicone oil AFS®-O-1300.

[0037] The method for preparing the plastic powder includes the following steps: after mixing the raw materials evenly, extruding and granulating them through a twin-screw extruder, crushing them, and passing them through a 190-mesh sieve to obtain the plastic powder; the barrel temperature of the twin-screw extruder is 120℃, and the screw speed is 35r / min.

[0038] In step S5, the hot air velocity in the segmented drying tunnel is 1 m / s, and a hot air circulation method is used to ensure temperature uniformity with a temperature difference of ≤ ±2℃.

[0039] Example 4: An outdoor box powder coating process, comprising the following steps: Step S1, Gradient Grinding Process: A two-stage grinding process is adopted. First, 140-grit sandpaper is used for coarse grinding to remove the surface oxide layer and burrs, and then 310-grit sandpaper is used for fine grinding to control the surface roughness Ra of the outdoor box body and components to 2.8μm. Step S2, Dual-stage ultrasonic cleaning: Place the polished workpiece into the first ultrasonic cleaning tank, add phosphating cleaning solution to the tank, control the water temperature to 37℃, turn on 28KHz low-frequency ultrasonic waves to soak for 4 minutes, and then transfer it to the second ultrasonic cleaning tank, use 40KHz high-frequency ultrasonic waves in conjunction with deionized water to rinse for 5 minutes to remove residual phosphating solution and impurities. Step S3, Vacuum pre-drying: Place the rinsed workpiece into a vacuum oven, set the vacuum degree to -0.088MPa and the temperature to 74℃, and pre-dry for 29 minutes to remove moisture from the surface of the workpiece and the tiny pores. Step S4, Composite Powder Coating: Fix the pre-baked workpiece with a special anti-dust hanger, and use a silicone heat insulation pad to isolate the contact point between the hanger and the workpiece; spray the workpiece into the spray booth for powder coating, control the spray booth spraying pressure to 0.54MPa, the atomizing air pressure to 0.34MPa, and control the coating thickness to 85μm; Step S5, Segmented Curing and Cooling: The powder-coated workpiece is sent into a segmented drying tunnel. The temperature of the first drying tunnel is 168℃, and it is kept at this temperature for 10 minutes for pre-melting. The temperature of the second drying tunnel is 198℃, and it is kept at this temperature for 15 minutes to achieve complete melting and leveling. The temperature of the third drying tunnel is 184℃, and it is kept at this temperature for 8 minutes for post-curing. After exiting the drying tunnel, it is first cooled in a constant temperature cooling zone of 38℃ for 20 minutes, and then naturally cooled to room temperature. The hanger is then removed to obtain the finished product.

[0040] The phosphating cleaning solution in step S2 comprises the following components by weight percentage: 9.5% zinc dihydrogen phosphate, 4.5% surfactant, 2.8% complexing agent, and the balance being water; the surfactant is fatty alcohol polyoxyethylene ether; the complexing agent is trisodium citrate; the hanging points of the anti-dust special hanger in step S4 are designed with an arc shape, and the contact area with the workpiece is ≤0.5cm², and the surface of the hanger is anodized; the powder coating powder in step S4 comprises the following raw materials by weight: 62 parts resin substrate, 4.5 parts nano silica, 5.5 parts compound anti-aging agent, 9.5 parts titanium dioxide, 7.5 parts barium sulfate, 2.3 parts leveling agent, 1.8 parts coupling agent, 2.8 parts triglycidyl isocyanate, 4.5 parts multi-component synergistic effect system, and 1.8 parts amino fluorosilicone oil; the resin substrate is end-carboxyl hyperbranched polyester HyPer C104 and epoxy-modified polyester resin SGR-3340 are compounded in a mass ratio of 1:4.5; the average particle size of the nano-silica is 70nm; the particle size of the titanium dioxide is 1500 mesh; the particle size of the barium sulfate is 1900 mesh; the compounded anti-aging agent is UV-327, HALS-944, and antioxidant 168 compounded in a mass ratio of 3:2:1; the leveling agent is leveling agent BYK-3550; the coupling agent is silane coupling agent KH550 and silane coupling agent KH56. 0. The silane coupling agent KH570 is compounded in a mass ratio of 1:2:1; the multi-component synergistic system is compounded in a mass ratio of 0.3:0.75:4.5 of graphene nanosheets, nano zinc oxide, and organic nano montmorillonite; the graphene nanosheets are XGnP® graphene nanosheets C-300; the average particle size of the nano zinc oxide is 50nm; the organic nano montmorillonite is Fenghong DK2 nano organic bentonite; and the amino fluorosilicone oil is amino fluorosilicone oil AFS®-O-1300.

[0041] The preparation method of the plastic powder includes the following steps: after the raw materials are mixed evenly, they are extruded and granulated by a twin-screw extruder, crushed, and passed through a 195-mesh sieve to obtain plastic powder; the barrel temperature of the twin-screw extruder is 125℃ and the screw speed is 38r / min; the hot air velocity in the segmented drying tunnel in step S5 is 1.1m / s, and the hot air circulation method is used to ensure temperature uniformity, with a temperature difference ≤±2℃.

[0042] Example 5: An outdoor box powder coating process, comprising the following steps: Step S1, Gradient Grinding Process: A two-stage grinding process is adopted. First, 150-grit sandpaper is used for coarse grinding to remove the surface oxide layer and burrs, and then 320-grit sandpaper is used for fine grinding to control the surface roughness Ra of the outdoor box body and components to 3.0μm. Step S2, Dual-stage ultrasonic cleaning: Place the polished workpiece into the first ultrasonic cleaning tank, add phosphating cleaning solution to the tank, control the water temperature to 38℃, turn on 28KHz low-frequency ultrasonic waves to soak for 4 minutes, and then transfer it to the second ultrasonic cleaning tank, use 40KHz high-frequency ultrasonic waves in conjunction with deionized water to rinse for 5 minutes to remove residual phosphating solution and impurities. Step S3, Vacuum pre-drying: Place the rinsed workpiece into a vacuum oven, set the vacuum degree to -0.09MPa and the temperature to 75℃, and pre-dry for 30 minutes to remove moisture from the surface of the workpiece and the tiny pores. Step S4, Composite Powder Coating: Fix the pre-baked workpiece with a special anti-dust hanger, and use a silicone heat insulation pad to isolate the contact point between the hanger and the workpiece; put it into the spray booth for powder coating, control the spray booth spraying pressure to 0.55MPa, the atomizing air pressure to 0.35MPa, and control the coating thickness to 90μm; Step S5, Segmented Curing and Cooling: The powder-coated workpiece is sent into a segmented drying tunnel. The temperature of the first drying tunnel is 170℃, and it is kept at this temperature for 10 minutes for pre-melting. The temperature of the second drying tunnel is 200℃, and it is kept at this temperature for 15 minutes to achieve complete melting and leveling. The temperature of the third drying tunnel is 185℃, and it is kept at this temperature for 8 minutes for post-curing. After exiting the drying tunnel, it is first cooled in a constant temperature cooling zone of 40℃ for 20 minutes, and then naturally cooled to room temperature. The hanger is then removed to obtain the finished product.

[0043] The phosphating cleaning solution in step S2 comprises the following components by weight percentage: 10% zinc dihydrogen phosphate, 5% surfactant, 3% complexing agent, and the balance being water; the surfactant is fatty alcohol polyoxyethylene ether; the complexing agent is trisodium citrate; the hanging point of the anti-dust special hanger in step S4 adopts an arc design, with a contact area with the workpiece ≤0.5cm², and the surface of the hanger is anodized.

[0044] The powder coating used in step S4 comprises the following raw materials in parts by weight: 63 parts resin substrate, 5 parts nano silica, 6 parts compounded anti-aging agent, 10 parts titanium dioxide, 8 parts barium sulfate, 2.5 parts leveling agent, 2 parts coupling agent, 3 parts triglycidyl isocyanate, 5 parts multi-component synergistic system, and 2 parts amino fluorosilicone oil; the resin substrate is a compound of carboxyl-terminated hyperbranched polyester HyPer C104 and epoxy-modified polyester resin SGR-3340 in a mass ratio of 1:5; the average particle size of the nano silica is 80 nm; the particle size of the titanium dioxide is 1600 mesh; the particle size of the barium sulfate is 2000 mesh; the compounded anti-aging agent is a compound of UV-327, HALS-944, and antioxidant 168 in a mass ratio of 3:2:1; the leveling agent is leveling agent BYK-3550; and the coupling agent is silane. The coupling agent is KH550; the multi-component synergistic system is composed of graphene nanosheets, nano zinc oxide, and organic nano montmorillonite in a mass ratio of 0.3:0.8:5; the graphene nanosheets are XGnP® graphene nanosheets C-300; the average particle size of the nano zinc oxide is 60nm; the organic nano montmorillonite is Fenghong DK2 nano organic bentonite; and the amino fluorosilicone oil is amino fluorosilicone oil AFS®-O-1300.

[0045] The method for preparing the plastic powder includes the following steps: after mixing the raw materials evenly, extruding and granulating them through a twin-screw extruder, crushing them, and passing them through a 200-mesh sieve to obtain the plastic powder; the barrel temperature of the twin-screw extruder is 130℃, and the screw speed is 40r / min; the hot air velocity in the segmented drying tunnel in step S5 is 1.2m / s, and the hot air circulation method is used to ensure temperature uniformity, with a temperature difference ≤±2℃.

[0046] Comparative Example 1 An outdoor box powder coating process is basically the same as that in Example 5, except that an equal amount of end-carboxyl hyperbranched polyester HyPer C104 is used instead of epoxy-modified polyester resin SGR-3340.

[0047] Comparative Example 2 An outdoor box powder coating process is basically the same as that in Example 5, except that an equal amount of epoxy-modified polyester resin SGR-3340 is used instead of end-carboxyl hyperbranched polyester HyPer C104.

[0048] Comparative Example 3 An outdoor box powder coating process is basically the same as that in Example 5, except that an equal amount of graphene nanosheets are used instead of organic nano-montmorillonite.

[0049] Comparative Example 4 An outdoor box powder coating process is basically the same as that in Example 5, except that an equal amount of organic nano-montmorillonite is used instead of graphene nanosheets.

[0050] Comparative Example 5 An outdoor box powder coating process is basically the same as that in Example 5, except that amino fluorosilicone oil is not added.

[0051] To further illustrate the beneficial technical effects of the embodiments of the present invention, outdoor boxes of the same material (Q235 cold-rolled steel plate) and specifications were selected. Relevant performance tests were conducted on the coatings produced by the powder coating process of the outdoor boxes in Example 5 and Comparative Examples 1-5. The test results are shown in Table 1. The test methods referred to GB / T9286-2021, GB / T 10125-2021, and GB / T 1735-2009, as detailed below: (1) Coating adhesion test: A single-blade cutting tool was used to make a 6×6 grid with a spacing of 1 mm on the coating surface (total area 1 cm²). 2 Cut to the substrate depth, brush lightly 5 times along the diagonal of the grid with a soft brush, then apply 3M 610 pressure-sensitive tape. Press the tape firmly with an eraser to ensure complete adhesion to the coating. After standing for 90 seconds, quickly peel off the tape at a 180° angle and observe the coating peeling at the grid intersections and edges. Determine the adhesion level according to the standard.

[0052] (2) Neutral salt spray tolerance test: Place the sample in a salt spray test chamber, set the test solution to 5% (mass fraction) sodium chloride aqueous solution, pH value 7.0, test temperature 35℃, salt spray deposition amount 1.5mL / (80cm²·h), spray continuously without interruption, observe the corrosion of the sample coating periodically, and record the time when rust spots first appear or coating blistering and peeling occurs.

[0053] (3) Weather resistance (high and low temperature cycle) test: Place the sample in a high and low temperature test chamber and perform a cycle test continuously at -40℃ (4 hours of heat preservation) → room temperature (1 hour of transition) → 85℃ (4 hours of heat preservation) → room temperature (1 hour of transition). After each cycle, observe whether the coating has defects such as cracking, discoloration, or chalking, and record the maximum number of cycles that the coating can maintain its integrity.

[0054] Table 1. Test results of coating performance of outdoor boxes made by powder coating process project Coating adhesion Neutral salt spray test tolerance time Weather resistance unit class h Second-rate Example 5 0 2520 400 Comparative Example 1 2 1150 180 Comparative Example 2 1 1680 250 Comparative Example 3 1 1560 220 Comparative Example 4 1 1420 280 Comparative Example 5 0 2050 350

[0055] As shown in Table 1, Example 5, using a resin substrate composed of end-carboxyl hyperbranched polyester HyPer C104 and epoxy-modified polyester resin SGR-3340, a multi-component synergistic system of graphene nanosheets-nano zinc oxide-organic nano-montmorillonite, and amino fluorosilicone oil, combined with precise process parameters throughout the entire process, achieved a coating adhesion grade of 0, a neutral salt spray tolerance time of 2520 hours, and a high and low temperature cycle tolerance of 400 times. These results are significantly better than those of the comparative examples (single resin substrate, single synergistic component replacement or absence of amino fluorosilicone oil). This fully demonstrates that the present invention achieves simultaneous optimization of multiple coating properties through the synergistic effect of each component in the formulation and process adaptation, with technical effects far exceeding those of conventional schemes that improve single components.

[0056] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention. The scope of protection claimed by the appended claims and their equivalents is defined.

Claims

1. A powder coating process for outdoor boxes, characterized in that, Includes the following steps: Step S1, Gradient Grinding Process: A two-stage grinding process is adopted. First, 120-150 grit sandpaper is used for coarse grinding to remove the surface oxide layer and burrs. Then, 280-320 grit sandpaper is used for fine grinding to control the surface roughness Ra of the outdoor box body and components to 2.0-3.0μm. Step S2, Dual-stage ultrasonic cleaning: Place the polished workpiece into the first ultrasonic cleaning tank, add phosphating cleaning solution to the tank, control the water temperature to 35±3℃, turn on 28KHz low-frequency ultrasonic waves to soak for 4 minutes, and then transfer it to the second ultrasonic cleaning tank, use 40KHz high-frequency ultrasonic waves in conjunction with deionized water to rinse for 5 minutes to remove residual phosphating solution and impurities. Step S3, Vacuum pre-drying: Place the rinsed workpiece into a vacuum oven, set the vacuum degree to -0.09~-0.08MPa, the temperature to 70-75℃, and pre-dry for 25-30 minutes to remove moisture from the surface of the workpiece and the tiny pores. Step S4, Composite Powder Coating: Fix the pre-baked workpiece with a special anti-dust hanger, and use a silicone heat insulation pad to isolate the contact point between the hanger and the workpiece; put it into the spray booth for powder coating, control the spray booth spraying pressure to 0.5-0.55MPa, the atomizing air pressure to 0.3-0.35MPa, and control the coating thickness to 70-90μm; Step S5, Segmented Curing and Cooling: The powder-coated workpiece is sent into a segmented drying tunnel. The temperature of the first drying tunnel is 160-170℃, and it is kept at this temperature for 10 minutes for pre-melting. The temperature of the second drying tunnel is 190-200℃, and it is kept at this temperature for 15 minutes to achieve complete melting and leveling. The temperature of the third drying tunnel is 180-185℃, and it is kept at this temperature for 8 minutes for post-curing. After exiting the drying tunnel, it is first cooled in a constant temperature cooling zone of 30-40℃ for 20 minutes, and then naturally cooled to room temperature. The finished product is obtained by removing the hanger.

2. The outdoor box powder coating process according to claim 1, characterized in that, The phosphating cleaning solution described in step S2 comprises the following components by weight percentage: 8-10% zinc dihydrogen phosphate, 3-5% surfactant, 2-3% complexing agent, and the balance being water.

3. The outdoor box powder coating process according to claim 2, characterized in that, The surfactant is a fatty alcohol polyoxyethylene ether; the complexing agent is trisodium citrate.

4. The outdoor box powder coating process according to claim 1, characterized in that, The hanging points of the anti-dust special hanger mentioned in step S4 are designed with arc shape, and the contact area with the workpiece is ≤0.5cm². The surface of the hanger is anodized.

5. The outdoor box powder coating process according to claim 1, characterized in that, The powder used for powder coating in step S4 comprises the following raw materials in parts by weight: 58-63 parts resin base material, 3-5 parts nano silica, 4-6 parts compound anti-aging agent, 8-10 parts titanium dioxide, 5-8 parts barium sulfate, 1.5-2.5 parts leveling agent, 1-2 parts coupling agent, 2-3 parts triglycidyl isocyanate, 3-5 parts multi-component synergistic enhancement system, and 1-2 parts amino fluorosilicone oil.

6. The outdoor box powder coating process according to claim 5, characterized in that, The resin substrate is a compound of end-carboxyl hyperbranched polyester HyPer C104 and epoxy modified polyester resin SGR-3340 in a mass ratio of 1:(3-5); the amino fluorosilicone oil is amino fluorosilicone oil AFS®-O-1300.

7. The outdoor box powder coating process according to claim 5, characterized in that, The average particle size of the nano-silica is 20-80 nm; the particle size of the titanium dioxide is 1200-1600 mesh; the particle size of the barium sulfate is 1500-2000 mesh; the compound anti-aging agent is composed of UV-327, HALS-944, and antioxidant 168 in a mass ratio of 3:2:1; the leveling agent is leveling agent BYK-3550; and the coupling agent is at least one of silane coupling agent KH550, silane coupling agent KH560, and silane coupling agent KH570.

8. The outdoor box powder coating process according to claim 5, characterized in that, The multi-component synergistic system is composed of graphene nanosheets, nano zinc oxide, and organic nano montmorillonite in a mass ratio of 0.3:(0.5-0.8):(3-5); the graphene nanosheets are XGnP® graphene nanosheets C-300; the average particle size of the nano zinc oxide is 10-60 nm; and the organic nano montmorillonite is Fenghong DK2 nano organic bentonite.

9. The outdoor box powder coating process according to claim 5, characterized in that, The method for preparing the plastic powder includes the following steps: after mixing the raw materials evenly, extruding and granulating them through a twin-screw extruder, crushing them, and passing them through a 180-200 mesh sieve to obtain the plastic powder; the barrel temperature of the twin-screw extruder is 110-130℃, and the screw speed is 30-40 r / min.

10. The outdoor box powder coating process according to claim 1, characterized in that, In step S5, the hot air velocity in the segmented drying tunnel is 0.8-1.2 m / s, and hot air circulation is used to ensure temperature uniformity with a temperature difference of ≤ ±2℃.