Aluminum veneer surface weather-resistant coating curing process and temperature control system

Abstract

This application relates to the field of aluminum single-panel manufacturing and surface treatment technology, and discloses a weather-resistant coating curing process and temperature control system for aluminum single-panel surfaces. The process includes: spraying a coating composition onto the surface of the aluminum single-panel and feeding it into a curing oven; initially using infrared heating and a vertical impingement flow directed towards the panel surface; when the coating surface temperature reaches 130–138°C, reducing the infrared heating power and adjusting the airflow direction to parallel laminar flow to maintain a gradual increase in temperature; when the temperature exceeds 145–155°C, restoring the heating power and switching back to the vertical impingement flow; heating continues until curing is complete when the temperature exceeds 170°C. The temperature control system uses a PLC control unit to perform closed-loop adjustment of the infrared output and airflow direction based on temperature feedback. This invention, through the combination of temperature gradient adjustment and airflow direction switching, provides a buffer period for the evaporation and degassing of the underlying solvent, alleviating pinholes and blistering caused by premature film formation on the coating surface, and improving the overall curing uniformity of substrates with uneven thickness.

Description

Technical Field

[0001] This invention relates to the field of aluminum panel manufacturing and surface treatment technology, specifically to a weather-resistant coating curing process and temperature control system for aluminum panels. Background Technology

[0002] Aluminum panels are widely used in building curtain walls and other fields due to their light weight and high rigidity. To obtain the physical and chemical properties required for long-term outdoor exposure, aluminum panels are usually coated with a weather-resistant coating and then cured at high temperatures. In conventional coating curing processes, continuous heating or baking within a fixed temperature range is often used, relying on convection or thermal radiation to quickly bring the coating to the cross-linking temperature.

[0003] However, in actual production, aluminum panels often have complex structures such as back reinforcement ribs, resulting in uneven thickness distribution of the substrate. This thickness difference causes variations in heat capacity in different areas. In a conventional continuously heated furnace, the thinner, flatter surfaces of the substrate heat up faster, while the thicker areas, such as those with reinforcement ribs, heat up relatively slower. This asynchronous heat transfer process, combined with traditional centralized heating methods, easily leads to a mismatch between the solvent evaporation rate and the resin crosslinking rate within the coating.

[0004] Specifically, when heating is too direct or the temperature rises too quickly, the coating surface rapidly reaches the cross-linking conditions and prematurely undergoes a film-forming reaction, leading to surface sealing. At this point, a large amount of solvent that has not yet completely evaporated remains in the coating layer and in areas adhered to thicker substrates. When these solvents subsequently absorb heat and transform into a gaseous state, the obstructed outward exhaust channels cause the gas to forcefully break through the surface of the initial film formation, leaving pinholes in the coating or forming blistering defects internally. Furthermore, due to localized temperature differences and inconsistent reaction progress, the cross-linking density of the finally cured coating is prone to uneven distribution across the entire board surface, which to some extent affects the overall adhesion and long-term weather protection effect of the coating. Summary of the Invention

[0005] The technical problem solved by this invention is that, during the high-temperature curing process of existing aluminum single-panel coatings, especially in areas with uneven substrates such as reinforcing ribs, a mismatch often occurs between the solvent evaporation rate and the resin crosslinking rate. This mismatch easily leads to premature film formation on the coating surface, hindering the vaporization and escape of the underlying solvent, which in turn causes defects such as pinholes and blistering in the coating, and affects the uniformity of the overall crosslinking density.

[0006] To address the above problems, the present invention provides the following technical solution: In a first aspect, the present invention provides a weather-resistant coating curing process for aluminum single-panel surfaces, employing the following technical solution: A weather-resistant coating curing process for aluminum single-panel surfaces includes the following steps: The raw materials are mixed evenly according to the weight percentage to prepare a coating composition. The coating composition is sprayed onto the surface of the aluminum single panel and sent into a curing oven. The infrared heating module inside the curing oven is controlled to output heating, and the circulating air module is controlled to generate a vertical impact flow that blows vertically toward the surface of the aluminum panel. When the absolute temperature of the coating surface is detected to reach 130-138℃, the output power of the infrared heating module is reduced to control the rise of the absolute temperature of the coating surface. At the same time, the airflow direction of the circulating air module is adjusted to parallel laminar flow parallel to the surface of the aluminum single panel to maintain a slow rise buffer state. After the gradual rise and buffering phase ends, the output power of the infrared heating module is restored. When the absolute temperature of the coating surface exceeds 145-155°C, the supply air temperature is increased and the vertical impingement flow is switched back. Heating continues after the absolute temperature of the coating surface exceeds 170°C. Cool and remove from the oven.

[0007] By incorporating staged heat input regulation and airflow direction switching during the coating heating process, the risk of surface sealing during the concentrated solvent evaporation stage can be reduced, and the curing consistency of different areas can be improved. The process can be understood as follows: In the initial curing stage, high-power infrared heating and vertical airflow are introduced. Infrared radiation and vertical airflow together improve the heat transfer efficiency of the coating surface, allowing the wet film to heat up quickly to the temperature range where the solvent begins to evaporate. When the surface temperature reaches 130–138°C, the medium-to-high boiling point solvents inside the coating begin to vaporize. At this point, the infrared power is reduced and the airflow direction is changed to parallel laminar flow to weaken the thermal and aerodynamic impact on the coating surface. Parallel laminar flow reduces the disturbance of the coating surface caused by vertical impact and allows the volatile gases to escape more gently, thus slowing down the rapid film formation on the surface and allowing the underlying solvent to continue to diffuse outward before the surface layer is completely cured. After the buffering phase, the residual amount of underlying solvent decreases. At this point, the infrared output is restored and the vertical airflow is switched back to continue increasing the coating temperature and promoting subsequent cross-linking and curing.

[0008] Preferably, in the step of generating the vertical impact flow, the infrared heating module is controlled to output heating at 80% to 100% of its rated power; in the step of maintaining the gradual rise buffer state, the output power of the infrared heating module is reduced to 30% to 50% of its rated power, and the absolute temperature of the coating surface is controlled to rise at a rate of 0.5 to 1.5°C / min within the range of 135°C to 148°C, and maintained for 3 to 6 minutes; when the absolute temperature of the coating surface exceeds 145 to 155°C, the air supply temperature is set to 215 to 230°C; after the absolute temperature of the coating surface exceeds 170°C, heating continues for 8 to 12 minutes.

[0009] Controlling the heating rate during the buffer stage to 0.5–1.5 °C / min can reduce the risk of surface blockage during the concentrated solvent evaporation stage; continuing to hold the temperature above 170 °C for 8–12 min can provide heat for the subsequent crosslinking reaction.

[0010] Preferably, the raw material consists of the following components by weight percentage: 40.0-48.0% alternating copolymer fluoroolefin-vinyl ether resin; 15.0-22.0% 3,5-dimethylpyrazole-blocked hexamethylene diisocyanate trimer curing agent; 6.0-12.0% phase change endothermic buffer solvent; 0.25-0.55% step bimetallic catalyst; 1.0-2.0% functional additives; 10.0-20.0% rutile titanium dioxide; and 5.45-17.75% xylene; the sum of the weight percentages of the above components is 100%. The phase change endothermic buffer solvent consists of 4.0–8.5 wt% propylene glycol methyl ether acetate and 2.0–3.5 wt% divalent ester; the step-by-step bimetallic catalyst consists of 0.05–0.15 wt% zinc acetylacetonate and 0.2–0.4 wt% bismuth neodecanoate; the functional additive consists of 0.3–0.5 wt% polyether-modified polydimethylsiloxane, 0.2–0.5 wt% polymethylalkylsiloxane solution, and 0.5–1.0 wt% bis(1,2,2,6,6-pentamethyl-4-piperidinyl) sebacate.

[0011] The above component configuration is combined with a segmented curing process. The specific mechanism is as follows: The deblocking of the blocked curing agent occurs after a gradual rise in temperature. During this buffer phase, the degree of deblocking is relatively low, reducing premature crosslinking due to insufficient solvent evaporation. The deblocking reaction is triggered above 145°C, where free NCO groups condense with the hydroxyl groups in the fluoropolymer. Additionally, the phase change solvent, composed of propylene glycol methyl ether acetate and divalent ester, vaporizes around 140°C. This type of solvent absorbs heat during vaporization, mitigating the risk of excessively rapid localized heating within the coating. In the catalytic system, zinc acetylacetonate is used to regulate the reaction at lower temperatures, while bismuth neodecanoate promotes the crosslinking reaction at higher temperatures. Their combined action allows the crosslinking process to proceed in stages, reducing shrinkage differences caused by concentrated crosslinking.

[0012] Preferably, the preparation method of the 3,5-dimethylpyrazole-blocked hexamethylene diisocyanate trimer curing agent includes the following steps: In a reactor equipped with a reflux condenser, mechanical stirrer, and nitrogen protection device, 100 parts by weight of hexamethylene diisocyanate trimer and 30 parts by weight of anhydrous butyl acetate are added. Stirring is started and nitrogen protection is introduced to raise the temperature inside the reactor to 50-55°C. 3,5-Dimethylpyrazole is weighed according to a molar ratio of isocyanate groups to 3,5-dimethylpyrazole active hydrogen of 1:1.01-1:1.10, and the weighed 3,5-dimethylpyrazole is added to the reactor in equal batches. During the feeding process, the temperature rise caused by the exothermic reaction is controlled to not exceed 75-85°C by adjusting the flow rate of the cooling water in the reactor jacket. After the feeding is complete, the temperature inside the reactor is kept constant at 75-85°C, and the reaction is continued for 3-4 hours. When the free NCO group content decreases to 0.04-0.12 wt%, heating is stopped, and the mixture is cooled to room temperature. The curing agent solution is then discharged.

[0013] By employing the above technical solution, the exothermic process and endpoint of the sealing reaction are rationally controlled, ensuring that the residual free isocyanate in the synthesized curing agent remains at a low level. This reduces the risk of premature reaction caused by residual free isocyanate and concentrates the desealing reaction of the curing agent at a higher temperature stage.

[0014] Preferably, in the step of spraying the coating composition onto the surface of the aluminum panel, the wet film thickness is controlled to be 80–120 μm; in the steps of generating vertical impingement flow and cutting back vertical impingement flow, the wind speed is set to 5.0–8.0 m / s; and in the step of adjusting to parallel laminar flow, the relative airflow velocity in the surface area is reduced to 0.5–1.5 m / s.

[0015] By adopting the above technical solution and setting corresponding convection parameters based on the specific wet film thickness, a vertical impinging flow of 5.0–8.0 m / s is used to improve heat exchange efficiency; a parallel laminar flow of 0.5–1.5 m / s is used to mitigate the exhaust process and reduce the direct impact of airflow on the wet film surface.

[0016] Preferably, the curing oven is equipped with an exhaust module and an LEL concentration probe. The exhaust module is linked with the LEL concentration probe inside the curing oven to ensure that the concentration of volatile organic compounds (VOCs) inside the oven is below 25% of the lower explosive limit.

[0017] By adopting the above technical solution, during the buffer stage of concentrated solvent evaporation, the linkage system can prevent the concentration of flammable gas in the local space from being too high, thereby maintaining the safe operation of the curing process.

[0018] Preferably, the aluminum panel is a complex geometric aluminum panel with a back reinforcing rib structure, wherein the aluminum substrate thickness in the flat area is 2.0 mm, and the equivalent thickness of the aluminum substrate in the reinforcing rib area is 8.0 mm.

[0019] For areas with high heat capacity, the gradual heating stage can extend the time for heat to be conducted to the thick-walled area, thereby reducing the curing difference between the flat surface area and the reinforcing rib area.

[0020] Secondly, the present invention provides a temperature control system for curing a weather-resistant coating on the surface of an aluminum panel, employing the following technical solution: A temperature control system for curing a weather-resistant coating on an aluminum panel surface, used to implement the above-mentioned curing process, includes: The curing oven is equipped with a conveyor belt for transporting aluminum panels, and is divided into independent temperature zones along the transport direction. The temperature measurement module is independently installed on the curing oven and is used to monitor the absolute temperature of the coating surface; An infrared heating module is placed on the inner surface of the curing oven and is connected to the PLC control unit to dynamically adjust the output power of the infrared radiation heating tube according to the feedback command of the surface heating rate. The exhaust module is independently installed on the curing oven and is linked to the LEL concentration probe signal inside the oven. It is used to operate at a preset exhaust frequency during the normal curing cycle and to increase the exhaust frequency or trigger an alarm when the concentration of volatile organic compounds (VOCs) in the oven approaches a preset threshold. The circulating air supply module, located inside the curing oven, includes a hot air circulating variable frequency fan and an air nozzle angle deflection device. The air nozzle angle deflection device is controlled by a PLC control unit to control the airflow direction of the circulating hot air inside the oven to switch between vertical impingement flow mode and parallel laminar flow mode.

[0021] By adopting the above technical solution, the system adjusts the infrared heating power through temperature feedback and switches between vertical impingement flow and parallel laminar flow through nozzle deflection. In actual operation, the temperature measurement module collects surface temperature signals and transmits them to the control unit, which then calculates the temperature rise to adjust the output of the infrared module. This adjustment based on the actual surface thermal state helps compensate for the heat capacity differences caused by uneven aluminum plate thickness. Simultaneously, the nozzle angle deflection device receives commands from the control unit to change its mechanical posture, adapting the flow field morphology to the coating's reaction state. For example, it provides tangential exhaust channels during solvent vaporization and vertically downward convective heat during crosslinking. Furthermore, the exhaust module is linked with the probe; when the concentration of volatile organic compounds (VOCs) in the furnace rises to near a set safety threshold, it automatically increases the exhaust volume, dynamically responding based on the exhaust situation.

[0022] Preferably, the curing oven integrates a temperature measurement module, an infrared heating module, an exhaust module, and a circulating air supply module; the PLC control unit is used to adjust the output power of the infrared heating module through closed-loop feedback control, and to send a signal to the air supply nozzle angle deflection device to control the airflow direction to be adjusted between vertical impingement flow mode and parallel laminar flow mode.

[0023] By adopting the above technical solution, the hardware for temperature measurement, heating, and ventilation is uniformly integrated into the curing oven, and the control unit manages the overall operation. This arrangement allows temperature measurement, heating, and ventilation to be coordinated by the same control unit, reducing the response deviation between temperature control and airflow switching when heating power is reduced or airflow direction is switched.

[0024] This invention provides a weather-resistant coating curing process and temperature control system for aluminum single-panel surfaces. It offers the following advantages: 1. This invention provides a buffer environment for a gradual temperature rise during the concentrated evaporation period of the coating solvent by combining the phased adjustment of infrared radiation power with the switching of airflow direction. Parallel laminar flow removes surface volatile gases while slowing down the film formation rate of the surface resin, allowing the underlying solvent relatively ample time to diffuse outward. This synergistic operation of temperature control and airflow improves the problem of pinholes or blistering caused by premature sealing of the coating, and improves the density of the final coating.

[0025] 2. The closed-type isocyanate curing agent and phase change endothermic buffer solvent used in this invention enable the chemical reaction characteristics of the coating to better conform to the aforementioned heating curve. The temperature of the gradual rise buffer stage is set below the concentrated desealing temperature of the curing agent, avoiding premature crosslinking when the solvent is not completely drained; at the same time, the phase change solvent vaporizes and absorbs heat in a specific temperature range, playing a certain temperature damping role inside the coating. Combined with the step-by-step bimetallic catalyst to regulate the reaction process, it helps to reduce the internal stress during the coating film formation process, making the overall crosslinking distribution more uniform.

[0026] 3. The temperature control system provided by this invention utilizes temperature measurement feedback and a control unit to perform closed-loop adjustment of the infrared heating output, and is linked to the angle deflection action of the air nozzle. This dynamic response based on the actual surface thermal state of the coating provides sufficient heat conduction time for complex aluminum panels with uneven thickness areas such as reinforcing ribs, compensating for the asynchronous heat transfer caused by differences in the heat capacity of substrates of different thicknesses, thereby reducing the curing differences between various areas of complex structural components. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the temperature control system architecture for the weather-resistant coating on the surface of an aluminum single-panel, according to an embodiment of the present invention.

[0028] Figure 2 This is a graph showing the consumption of isocyanate groups by in-situ FTIR testing in Test Example 1 of this invention; Figure 3 This is a graph showing the solvent evaporation behavior in thermogravimetric analysis based on programmed temperature rise and gas flow intervention in Test Example 2 of the present invention. Subplot (a) shows the residual mass (TG) change curve of each test sample, and subplot (b) shows the weight loss rate (DTG) change curve of each test sample. Detailed Implementation

[0029] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] See attached document Figure 1 This invention provides a temperature control system for curing a weather-resistant coating on an aluminum single-panel surface, which may include: The curing oven is equipped with a conveyor belt for transporting aluminum panels, and is divided into independent temperature zones along the transport direction. The temperature measurement module is independently installed on the curing oven and is configured to monitor the absolute temperature of the coating surface. An infrared heating module is placed on the inner surface of the curing oven and is connected to the PLC control unit to dynamically adjust the output power of the infrared radiation heating tube according to the feedback command of the surface heating rate. The exhaust module is independently installed on the curing oven and is linked to the LEL concentration probe signal inside the oven. It is configured to operate at a preset exhaust frequency during the normal curing cycle and increase the exhaust frequency or trigger an alarm when the VOCs concentration inside the oven approaches a preset threshold. The circulating air supply module, located inside the curing oven, includes a hot air circulating variable frequency fan and an air nozzle angle deflection device. The air nozzle angle deflection device is controlled by a PLC control unit to control the airflow direction of the circulating hot air inside the oven to switch between vertical impingement flow mode and parallel laminar flow mode.

[0031] Preparation Examples 1-3: Preparation Example 1: This preparation example provides a method for preparing a 3,5-dimethylpyrazole-blocked hexamethylene diisocyanate trimer curing agent, comprising the following steps: (1) In a reactor equipped with a reflux condenser, a mechanical stirrer and a nitrogen protection device, add 100 parts by weight of hexamethylene diisocyanate trimer and 30 parts by weight of anhydrous butyl acetate, turn on the stirrer and introduce nitrogen protection to raise the temperature inside the reactor to 55°C.

[0032] (2) Weigh 52.4 parts by weight of 3,5-dimethylpyrazole according to a molar ratio of isocyanate group to active hydrogen of 3,5-dimethylpyrazole of 1:1.05. Slowly add the weighed 3,5-dimethylpyrazole into the reactor in four equal portions, with an interval of 15 minutes between each addition. During the addition process, control the stirring speed at 200 rpm, and control the temperature rise caused by the exothermic reaction of the system to not exceed 80°C by adjusting the flow rate of cooling water in the reactor jacket.

[0033] (3) After the addition of materials, the temperature inside the reactor was kept constant at 80℃, and the reaction was continued for 3.5 hours. The content of free NCO groups in the reaction system was monitored by di-n-butylamine back titration. When the content of free NCO groups decreased to 0.08wt%, heating was stopped, the temperature was lowered to room temperature, and the target curing agent solution was discharged. It was determined that the effective NCO group mass fraction of the curing agent solution was 11.9wt%, and the unsealing temperature was 155℃.

[0034] Preparation Example 2: This preparation example provides a method for preparing a 3,5-dimethylpyrazole-blocked hexamethylene diisocyanate trimer curing agent, comprising the following steps: (1) In a reactor equipped with a reflux condenser, a mechanical stirrer and a nitrogen protection device, add 100 parts by weight of hexamethylene diisocyanate trimer and 30 parts by weight of anhydrous butyl acetate, turn on the stirrer and introduce nitrogen protection to raise the temperature inside the reactor to 50°C.

[0035] (2) Weigh 50.4 parts by weight of 3,5-dimethylpyrazole according to a molar ratio of isocyanate group to active hydrogen of 3,5-dimethylpyrazole of 1:1.01. Add the weighed 3,5-dimethylpyrazole into the reactor in three equal portions, with an interval of 15 minutes between each addition. During the addition process, control the stirring speed at 200 rpm and control the temperature rise caused by the exothermic reaction of the system to not exceed 75°C by adjusting the cooling water flow rate of the reactor jacket.

[0036] (3) After the addition of materials, the temperature inside the reactor was kept constant at 75°C, and the reaction was continued for 3 hours. The content of free NCO groups in the reaction system was monitored by di-n-butylamine back titration. When the content of free NCO groups decreased to 0.12 wt%, heating was stopped, the temperature was lowered to room temperature, and the target curing agent solution was discharged. It was determined that the effective NCO group mass fraction of the curing agent solution was 12.1 wt%, and the unsealing temperature was 150°C.

[0037] Preparation Example 3: This preparation example provides a method for preparing a 3,5-dimethylpyrazole-blocked hexamethylene diisocyanate trimer curing agent, comprising the following steps: (1) In a reactor equipped with a reflux condenser, a mechanical stirrer and a nitrogen protection device, add 100 parts by weight of hexamethylene diisocyanate trimer and 30 parts by weight of anhydrous butyl acetate, turn on the stirrer and introduce nitrogen protection to raise the temperature inside the reactor to 55°C.

[0038] (2) Weigh 54.9 parts by weight of 3,5-dimethylpyrazole according to a molar ratio of isocyanate group to active hydrogen of 3,5-dimethylpyrazole of 1:1.10. Add the weighed 3,5-dimethylpyrazole to the reactor in four equal portions, with an interval of 15 minutes between each addition. During the addition process, control the stirring speed at 200 rpm and adjust the cooling water flow rate of the reactor jacket to ensure that the temperature rise caused by the exothermic reaction does not exceed 85°C.

[0039] (3) After the addition of materials, the temperature inside the reactor was kept constant at 85℃, and the reaction was continued for 4 hours. The content of free NCO groups in the reaction system was monitored by di-n-butylamine back titration. When the content of free NCO groups decreased to 0.04wt%, heating was stopped, the temperature was lowered to room temperature, and the target curing agent solution was discharged. It was determined that the effective NCO group mass fraction of the curing agent solution was 11.8wt%, and the unsealing temperature was 160℃.

[0040] Examples 1-4: Example 1:

[0041] This embodiment provides a weather-resistant coating curing process for aluminum single-panel surfaces, including the following steps: (1) Preparation of coating composition: 45.0 wt% alternating copolymer fluoroolefin-vinyl ether resin, 20.0 wt% curing agent obtained in Preparation Example 1, 9.0 wt% phase change endothermic buffer solvent (composed of 6.0 wt% propylene glycol methyl ether acetate and 3.0 wt% divalent ester mixture), wherein the phase change endothermic buffer solvent vaporizes and absorbs heat in the temperature range of 140°C to 160°C and forms a solvent vapor boundary layer on the coating surface; 0.4 wt% step bimetallic catalyst (composed of 0.1 wt% zinc acetylacetonate and 0.3 wt% bismuth neodecanoate), 1.5 wt% functional additive (composed of 0.4 wt% polyether modified polydimethylsiloxane, 0.3 wt% polymethylalkylsiloxane solution and 0.8 wt% bis(1,2,2,6,6-pentamethyl-4-piperidinyl) sebacate), 15.0 wt% rutile titanium dioxide and 9.1 wt% xylene are mixed uniformly.

[0042] (2) The above coating composition is sprayed onto the surface of the aluminum single panel, and the wet film thickness is controlled to be 100 μm. Then it is sent into a curing oven that integrates a temperature measurement module, an infrared heating module, an exhaust module and a circulating air supply module. The exhaust module of the curing oven operates at a preset frequency throughout the process and is linked with the LEL concentration probe to ensure that the VOCs concentration in the oven is less than 25% of the lower explosive limit.

[0043] (3) Stage 1: Set the power output of the infrared radiation heating tube to 90% of the rated power, control the hot air circulation system to blow the air nozzle vertically downwards onto the aluminum plate surface, and set the wind speed to 6.5 m / s. The temperature measurement module monitors the absolute temperature T of the coating surface at a frequency of 1 Hz.

[0044] (4) Stage Two: When the surface temperature of the coating reaches 135℃, the system reduces the power of the infrared heating tube to 40% of the rated power and controls the surface temperature of the coating to continue to rise to about 140℃. Then, through closed-loop feedback control, the surface temperature of the coating is slowly increased at a rate of about 1.0℃ / min in the range of 140℃ to 148℃. At the same time, the air nozzle angle is deflected and the airflow direction is adjusted to parallel laminar flow parallel to the surface of the aluminum plate. The relative airflow velocity in the surface area is reduced to 1.0m / s. This slow rise buffer state is maintained for 4.5min.

[0045] (5) Stage 3: After the gradual rise and buffering state of Stage 2 ends, the power of the infrared heating tube is restored to 90%, allowing the surface temperature of the coating to continue to rise; when the surface temperature exceeds 150℃, the supply air temperature of the hot air system is set to 220℃. The air nozzle is instantly reset and switched back to the vertical impact flow, and the wind speed is restored to 6.5m / s. After the surface temperature of the coating exceeds 170℃, heating continues for 10 minutes.

[0046] (6) Stage 4: The aluminum single panel enters the cooling section and is subjected to forced convection heat exchange using ambient temperature cold air. After the surface temperature drops to below 60°C, it is taken out of the furnace.

[0047] Example 2:

[0048] This embodiment provides a weather-resistant coating curing process for aluminum single-panel surfaces, including the following steps: (1) Preparation of coating composition: 40.0 wt% alternating copolymer fluoroolefin-vinyl ether resin, 15.0 wt% curing agent obtained in Preparation Example 2, 6.0 wt% phase change endothermic buffer solvent (composed of 4.0 wt% propylene glycol methyl ether acetate and 2.0 wt% divalent ester mixture), 0.25 wt% step bimetallic catalyst (composed of 0.05 wt% zinc acetylacetonate and 0.2 wt% bismuth neodecanoate), 1.0 wt% functional additive (composed of 0.3 wt% polyether modified polydimethylsiloxane, 0.2 wt% polymethylalkylsiloxane solution and 0.5 wt% bis(1,2,2,6,6-pentamethyl-4-piperidinyl) sebacate), 20.0 wt% rutile titanium dioxide and 17.75 wt% xylene are mixed evenly.

[0049] (2) The above coating composition is sprayed onto the surface of the aluminum single panel, and the wet film thickness is controlled to be 80 μm. Then it is sent into a curing oven that integrates a temperature measurement module, an infrared heating module, an exhaust module and a circulating air supply module. The exhaust module of the curing oven operates at a preset frequency throughout the process and is linked with the LEL concentration probe to ensure that the VOCs concentration in the oven is less than 25% of the lower explosive limit.

[0050] (3) Stage 1: Set the power output of the infrared radiation heating tube to 80% of the rated power, control the hot air circulation system to blow the air nozzle vertically downwards onto the aluminum plate surface, and set the wind speed to 5.0 m / s. The temperature measurement module monitors the absolute temperature T of the coating surface at a frequency of 1 Hz.

[0051] (4) Stage Two: When the surface temperature of the coating reaches 130°C, the system reduces the power of the infrared heating tube to 30% of the rated power and controls the surface temperature of the coating to continue to rise to about 135°C. Then, through closed-loop feedback control, the surface temperature of the coating is slowly increased at a rate of about 1.5°C / min in the range of 135°C to 140°C. At the same time, the air nozzle angle is deflected and the airflow direction is adjusted to parallel laminar flow parallel to the surface of the aluminum plate. The relative airflow velocity in the surface area is reduced to 0.5m / s. This slow-rise buffer state is maintained for 3 minutes.

[0052] (5) Stage 3: After the gradual rise and buffering state of Stage 2 ends, the power of the infrared heating tube is restored to 80%, allowing the surface temperature of the coating to continue to rise; when the surface temperature exceeds 145℃, the supply air temperature of the hot air system is set to 215℃. The air nozzle is instantly reset and switched back to the vertical impingement flow, and the wind speed is restored to 5.0m / s. After the surface temperature of the coating exceeds 170℃, heating continues for 8 minutes.

[0053] (6) Stage 4: The aluminum single panel enters the cooling section and is subjected to forced convection heat exchange using ambient temperature cold air. After the surface temperature drops to below 60°C, it is taken out of the furnace.

[0054] Example 3:

[0055] This embodiment provides a weather-resistant coating curing process for aluminum single-panel surfaces, including the following steps: (1) Preparation of coating composition: 48.0 wt% alternating copolymer fluoroolefin-vinyl ether resin, 22.0 wt% curing agent obtained in Preparation Example 3, 12.0 wt% phase change endothermic buffer solvent (composed of 8.5 wt% propylene glycol methyl ether acetate and 3.5 wt% divalent ester), 0.55 wt% step bimetallic catalyst (composed of 0.15 wt% zinc acetylacetonate and 0.4 wt% bismuth neodecanoate), 2.0 wt% functional additive (composed of 0.5 wt% polyether modified polydimethylsiloxane, 0.5 wt% polymethylalkylsiloxane solution and 1.0 wt% bis(1,2,2,6,6-pentamethyl-4-piperidinyl) sebacate), 10.0 wt% rutile titanium dioxide and 5.45 wt% xylene are mixed evenly.

[0056] (2) The above coating composition is sprayed onto the surface of the aluminum single panel, and the wet film thickness is controlled to be 120 μm. Then it is sent into a curing oven that integrates a temperature measurement module, an infrared heating module, an exhaust module and a circulating air supply module. The exhaust module of the curing oven operates at a preset frequency throughout the process and is linked with the LEL concentration probe to ensure that the VOCs concentration in the oven is less than 25% of the lower explosive limit.

[0057] (3) Stage 1: Set the power output of the infrared radiation heating tube to 100% of the rated power, control the hot air circulation system to blow the air nozzle vertically downwards onto the aluminum plate surface, and set the wind speed to 8.0 m / s. The temperature measurement module monitors the absolute temperature T of the coating surface at a frequency of 1 Hz.

[0058] (4) Stage Two: When the surface temperature of the coating reaches 138°C, the system reduces the power of the infrared heating tube to 50% of the rated power and controls the surface temperature of the coating to continue to rise to about 145°C. Then, through closed-loop feedback control, the surface temperature of the coating is slowly increased at a rate of about 0.5°C / min in the range of 145°C to 148°C. At the same time, the air nozzle angle is deflected, and the airflow direction is adjusted to parallel laminar flow parallel to the surface of the aluminum plate. The relative airflow velocity in the surface area is reduced to 1.5m / s, and this state is maintained for 6min.

[0059] (5) Stage 3: After the gradual rise and buffering state of Stage 2 ends, the power of the infrared heating tube is restored to 100%, allowing the surface temperature of the coating to continue to rise; when the surface temperature exceeds 155℃, the supply air temperature of the hot air system is set to 230℃. The air nozzle is instantly reset and switched back to the vertical impact flow, and the wind speed is restored to 8.0m / s. After the surface temperature of the coating exceeds 170℃, heating continues for 12 minutes.

[0060] (6) Stage 4: The aluminum single panel enters the cooling section and is subjected to forced convection heat exchange using ambient temperature cold air. After the surface temperature drops to below 60°C, it is taken out of the furnace.

[0061] Example 4:

[0062] This embodiment provides a weather-resistant coating curing process for aluminum single-panel surfaces, including the following steps: (1) Preparation of coating composition: 45.0 wt% alternating copolymer fluoroolefin-vinyl ether resin, 20.0 wt% curing agent obtained in Preparation Example 1, 9.0 wt% phase change endothermic buffer solvent (composed of 6.0 wt% propylene glycol methyl ether acetate and 3.0 wt% divalent ester mixture); 0.4 wt% step bimetallic catalyst (composed of 0.1 wt% zinc acetylacetonate and 0.3 wt% bismuth neodecanoate), 1.5 wt% functional additive (composed of 0.4 wt% polyether modified polydimethylsiloxane, 0.3 wt% polymethylalkylsiloxane solution and 0.8 wt% bis(1,2,2,6,6-pentamethyl-4-piperidinyl) sebacate), 15.0 wt% rutile titanium dioxide and 9.1 wt% xylene are mixed evenly.

[0063] (2) The above coating composition is sprayed onto the surface of a complex geometric aluminum panel with a back-side reinforcing rib structure (where the aluminum substrate thickness in the flat area is 2.0 mm and the equivalent thickness of the aluminum substrate in the reinforcing rib area is 8.0 mm), and the wet film thickness is controlled to be 100 μm. Then, it is sent into a curing oven that integrates a temperature measurement module, an infrared heating module, an exhaust module, and a circulating air supply module. The exhaust module of the curing oven operates at a preset frequency throughout the process and is linked with the LEL concentration probe to ensure that the VOCs concentration in the oven is below 25% of the lower explosive limit.

[0064] (3) Stage 1: Set the power output of the infrared radiation heating tube to 90% of the rated power, control the hot air circulation system to blow the air nozzle vertically downwards onto the aluminum plate surface, and set the wind speed to 6.5 m / s. The temperature measurement module monitors the absolute temperature T of the coating surface at a frequency of 1 Hz.

[0065] (4) Stage Two: When the surface temperature of the coating reaches 135℃, the system reduces the power of the infrared heating tube to 40% of the rated power and controls the surface temperature of the coating to continue to rise to about 140℃. Then, through closed-loop feedback control, the surface temperature of the coating is slowly increased at a rate of about 1.0℃ / min in the range of 140℃ to 148℃. At the same time, the air nozzle angle is deflected and the airflow direction is adjusted to parallel laminar flow parallel to the surface of the aluminum plate. The relative airflow velocity in the surface area is reduced to 1.0m / s, and this state is maintained for 4.5min.

[0066] (5) Stage 3: After the gradual rise and buffering state of Stage 2 ends, the power of the infrared heating tube is restored to 90%, allowing the surface temperature of the coating to continue to rise; when the surface temperature exceeds 150℃, the supply air temperature of the hot air system is set to 220℃. The air nozzle is instantly reset and switched back to the vertical impact flow, and the wind speed is restored to 6.5m / s. After the surface temperature of the coating exceeds 170℃, heating continues for 10 minutes.

[0067] (6) Stage 4: The aluminum single panel enters the cooling section and is subjected to forced convection heat exchange using ambient temperature cold air. After the surface temperature drops to below 60°C, it is taken out of the furnace.

[0068] Comparative Examples 1-4: Comparative Example 1: Compared with Example 4, the difference is that in the second stage of the curing process, the air nozzle angle was not deflected to adjust the air direction, and the vertical impact flow blowing vertically downward toward the surface of the aluminum plate was always maintained, and the wind speed was maintained at 6.5m / s without decreasing. All other aspects are the same.

[0069] Comparative Example 2: Compared with Example 1, the difference is that when preparing the coating composition, the phase change endothermic buffer solvent composed of a mixture of propylene glycol methyl ether acetate and divalent ester was not added, but was replaced by an equal mass of the conventional solvent xylene, and all other aspects were the same.

[0070] Comparative Example 3: Compared with Example 4, the difference is that the ladder bimetallic catalyst composed of zinc acetylacetonate and bismuth neodecanoate was not used when preparing the coating composition. Instead, it was replaced by a single second-stage catalyst, bismuth neodecanoate (added at 0.4 wt%), with all other aspects remaining the same.

[0071] Comparative Example 4: Compared with Example 4, the difference is that the slow rise buffer platform control and heating rate intervention in stage two are cancelled in the curing process. That is, after the coating surface temperature reaches 135°C, the power of the infrared heating tube is not reduced, and the low-speed parallel laminar flow intervention is not performed. The infrared heating tube continues to maintain 90% of the rated power output, the air nozzle continues to maintain vertical impingement flow, and the wind speed is maintained at 6.5 m / s until the coating surface temperature exceeds 170°C and then heating continues for 10 minutes. Everything else is the same.

[0072] Test Examples 1-5: Test Example 1: Reaction Kinetic Monitoring Test Based on In-situ Fourier Transform Infrared Spectroscopy (In-situ FTIR) Test steps: (1) The coating composition prepared in Example 1 and the coating composition prepared in Comparative Example 3 were selected as experimental samples. Each coating composition was uniformly coated on the surface of the KBr infrared salt window, and the wet film thickness of the coating was controlled to be 15 μm using a wire bar coater.

[0073] (2) Fix the coated salt window into the sample chamber of the Fourier transform infrared spectrometer, which is equipped with a programmable heating attachment and a gas purging attachment. Set the scanning wavenumber range of the spectrometer to 4000 cm⁻¹. -1 Up to 400cm -1 The resolution is 4cm.-1 The cumulative number of scans for a single spectral acquisition is 16.

[0074] (3) Set the temperature control program for the heating accessory for different samples. For the samples of Example 1 and Comparative Example 3, input the temperature change parameters over time for stages one to three as described in Example 1; select another coating composition sample of Example 1 and input the continuous heating parameters for canceling the constant temperature platform as described in Comparative Example 4 into the heating accessory.

[0075] (4) Start the temperature control program and trigger the spectrometer to perform continuous scanning at the preset time points. Extract wavenumber 2270cm. -1 The retention rate relative to the initial time was calculated by integrating the peak area of ​​the characteristic absorption peak of the nearby isocyanate group (-NCO).

[0076] Test data: Table 1. Data on the retention rate of isocyanate groups during the reaction of different test samples Test conclusion: From Table 1 and Figure 2 It can be seen that the -NCO retention rate decreased at different rates in Example 1, Comparative Example 3, and continuously heated samples, indicating that the catalyst composition and heating program affect the consumption process of isocyanate groups.

[0077] Figure 2 The horizontal axis represents reaction time, and the vertical axis represents the isocyanate group retention rate. The curve for Example 1 shows a decreasing trend in the 5-10 min range. Combined with the data in Table 1, when the reaction reached 10 min (the end of stage two), the isocyanate group retention rate decreased to 73.4%. At 10 min, the -NCO retention rate of Example 1 decreased to 73.4%, lower than the 94.8% of Comparative Example 3, indicating that the zinc acetylacetonate system had undergone a certain degree of -NCO consumption in the 140℃-148℃ stage, reflecting the presence of an early chain extension reaction in this stage. After 13 min, the downward slope of the curve for Example 1 increased, entering stage three above 170℃, where the retention rate decreased to 1.1%, indicating that the blocking agent further deblocked at this point, and bismuth neodecanoate exerted a catalytic effect, promoting the three-dimensional cross-linking process of the system.

[0078] For the test sample of Comparative Example 3, its curve showed little change in the first 10 minutes of reaction time. Since no first-stage catalyst was added to the formulation, the isocyanate group retention rate of this sample was 94.8% at the end of stage two, indicating a low degree of chain extension reaction in the early stage. After entering the later high-temperature stage at 170℃, the curve showed an increased rate of decline. Comparative Example 3 showed less -NCO consumption in the first 10 minutes, but the increased rate of decline in the subsequent high-temperature stage indicates that its crosslinking reaction was more concentrated in the later stages; for workpieces with significant thickness differences, this concentrated reaction may increase the curing differences between regions.

[0079] For Comparative Example 4, which uses a continuous heating process, the curve slope is relatively large in the 0 to 10 min range, and the isocyanate group retention rate drops to 31.5%. The -NCO retention rate of the continuously heated sample has dropped to 31.5% at 10 min, indicating that the early reaction is faster and more likely to cause early film formation on the surface, thus affecting the continued diffusion and reaction of the underlying components. Figure 2 Subsequent data showed that the curve gradually flattened out in the later stages of the reaction, with the surface crust restricting the diffusion of underlying molecules. At the end of the 25-minute test, 6.7% of the isocyanate groups remained unreacted. These results indicate that the -NCO consumption in Example 1 exhibits a segmented characteristic of slow initial consumption followed by accelerated consumption in the later stages. Compared to Comparative Example 3 and the continuously heated sample, its reaction process better meets the curing requirements of first removing the solvent and then achieving full cross-linking.

[0080] Test Example 2: Solvent Evaporation Behavior Test Based on Temperature-Programmed Gas Flow Intervention Thermogravimetric Analysis (Variable Gas Flow TG / DTG) Test steps: (1) The coating composition prepared in Example 1, the coating composition prepared in Comparative Example 1 (with the same formulation as in Example 1), and the coating composition prepared in Comparative Example 2 (without the addition of a phase change endothermic buffer solvent) were selected as the experimental samples for this thermogravimetric test. Approximately 15.0 mg of each coating composition sample was weighed and laid flat on the bottom of the miniature crucible of the thermogravimetric analyzer to ensure that the initial state of each sample was basically the same.

[0081] (2) Set the programmable heating and airflow control module of the thermogravimetric analyzer and set the program according to the process stage described in Example 1. The temperature control program is set as follows: starting from room temperature of 25°C, the temperature is increased to 135°C at a set rate, and then the temperature is controlled between 140°C and 148°C to form a buffer plateau period of 5 minutes. After that, the temperature is increased to above 170°C and maintained.

[0082] (3) Apply corresponding airflow purging conditions to different samples. For the sample of Example 1 and Comparative Example 2, when the temperature enters the buffer plateau period, switch the instrument's purging airflow mode to low flow rate horizontal purging; when the isothermal plateau period ends and the temperature continues to rise, switch the airflow to high flow rate vertical downward purging. For the sample of Comparative Example 1, control the instrument to maintain a high flow rate vertical downward purging state throughout the entire heating and slow-rise buffer plateau period.

[0083] (4) Start the analysis program. The instrument continuously collects the remaining mass data of each sample under heating and airflow switching conditions. After the test, export the weight loss rate (DTG, in % / min) data at each time point for comparative analysis.

[0084] Test data: Table 2. Data on the rate of weight loss (DTG) of different test samples under varying temperature and airflow conditions. Test conclusion: Based on the data in Table 2, combined with Figure 3 The volatile behavior curves of each sample are shown below. Figure 3 As shown in (a), the horizontal axis represents the test time, and the vertical axis represents the remaining mass. The curve representing Example 1 shows a relatively small downward slope within the 6-8 minute range (corresponding to the buffer plateau period of 140°C to 148°C). (Synchronously...) Figure 3 (b) On the weight loss rate curve, the DTG curve of Example 1 was in the lower range of 1.13% / min to 0.92% / min during this time period. The DTG value of Example 1 in the 6-8 min stage was only 1.13% / min to 0.92% / min, lower than that of Comparative Example 1 and Comparative Example 2, indicating that the early weight loss rate of the sample was suppressed under the combined effect of horizontal low-speed purging and phase change buffer solvent. As the test progressed to the stage three airflow switching point at 10 min, the vertical high-speed airflow operation was resumed. At this time, Figure 3 (b) The curve of Example 1 shows a weight loss peak, and the weight loss rate increases to 8.74% / min, corresponding to Figure 3 The remaining mass in (a) decreased significantly. This change indicates that the switching of the external airflow disrupted the previous gas boundary layer, promoting the removal of high-boiling-point solvents from the coating.

[0085] For the test sample in Comparative Example 1, vertical airflow was maintained throughout the test. Figure 3 In (a), the TG curve of Comparative Example 1 shows a continuous downward trend in the 6-minute to 8-minute interval; Figure 3In (b), the DTG curve remained at a level of 3.15% / min to 2.86% / min within the same time period, indicating that the solvent in the surface layer and some of the interior evaporated relatively early. This early evaporation easily causes surface shrinkage of the coating, increasing the resistance to the outward diffusion of internal volatiles. Therefore, when the test reaches the 10-minute mark, Figure 3 (b) The rate of weight loss in Comparative Example 1 showed a decreasing trend, dropping to 2.41% / min, indicating that the residual volatiles inside failed to be released in a concentrated manner.

[0086] For the test sample of Comparative Example 2, an effective gas boundary layer could not be formed because its formulation did not contain a phase change buffer solvent. Figure 3 (b) The curve shows a weight loss peak of 4.12% / min at min 6, indicating that the bottom solvent was largely consumed in the early stages of the process. By the gas flow switching point at min 10, the weight loss rate had decreased to 1.88% / min. Figure 3 (a) The corresponding residual mass curve also tends to flatten. (See Table 2 and...) Figure 3 It can be seen that in Example 1, the weight loss is relatively slow during the buffering stage, and a concentrated weight loss peak appears after the airflow switch, indicating that the phase change buffer solvent and the airflow direction switch can change the solvent release process from slow release in the early stage to concentrated discharge in the later stage.

[0087] Test Example 3: Evaluation Test of Defect-Free Coating Surface and Density Test steps: (1) Cured aluminum panels prepared in Examples 1 to 4 and Comparative Examples 1 to 4 and cooled to room temperature were extracted as evaluation samples for this test. The surface of the test samples was cleaned of dust.

[0088] (2) A micro gloss meter was used, and the measurement angle was set to 60 degrees. Five test points were randomly selected in different areas of each sample surface for measurement. The instrument readings were recorded, and the arithmetic mean was calculated as the surface gloss of the sample.

[0089] (3) Use a surface roughness meter to determine the micro-flatness of the samples. Set the sampling length of the instrument to 0.8 mm and the evaluation length to 4.0 mm. Perform three scanning measurements on the surface of each sample along the transverse and longitudinal directions respectively, extract the value of the profile arithmetic mean deviation (Ra), and take the arithmetic mean as the final surface roughness.

[0090] (4) Referring to the relevant national standards for coating aging rating, the microstructure of the sample surface was observed under a standard D65 light source and with a magnifying glass. The number, size, and distribution density of blistering and pinhole defects in the test area were statistically evaluated, and a rating of 0 to 5 was given, where level 0 indicates no visible defects, and the higher the level, the more obvious the surface defects. All the above tests were repeated at least 3 times, and the test results were expressed as average values.

[0091] Test data: Table 3. Test data on surface defect-free properties and density of coatings for each test sample. Test conclusion: As shown in Table 3, the gloss, roughness and defect rating of Examples 1 to 4 are all better than those of the comparative examples.

[0092] Table 3 shows that the gloss levels of Examples 1 to 4 ranged from 80.1 GU to 84.6 GU, with corresponding surface roughness Ra remaining stable at a low level of 0.11 μm to 0.15 μm, and all surface defect ratings were 0. No visible pinholes or bubbles were observed in Examples 1 to 4, and Ra remained between 0.11 μm and 0.15 μm, indicating that this curing process can reduce the risk of solvent retention and surface defect formation.

[0093] Comparative Example 1, using a continuous vertical high-pressure airflow purging process, showed a decrease in gloss to 61.2 GU, an increase in roughness to 0.68 μm, and a pinhole rating of 3. The decrease in gloss to 61.2 GU and the increase in Ra to 0.68 μm, along with the pinhole rating of 3, indicate that continuous vertical high-pressure airflow easily leads to decreased surface smoothness and increased defects. Comparative Example 2, without the addition of a phase change buffer solvent, showed a gloss of 65.7 GU, a roughness of 0.54 μm, and a defect rating of 2, indicating that the lack of a gas boundary layer also increases film formation defects.

[0094] Comparative Example 4, lacking a phased buffer plateau, suffered from a lack of overall reaction rate control, resulting in a maximum roughness of 0.82 μm, a gloss level dropping to 55.4 GU, and a defect rating deteriorating to level 4. This demonstrates that continuous rapid heating more easily leads to surface defects and a decrease in coating smoothness. Comparative Example 3, lacking the first-stage catalyst-involved chain extension process, experienced concentrated crosslinking in the later high-temperature stage, which easily caused localized shrinkage differences, resulting in a surface roughness of 0.25 μm and a gloss level of 76.3 GU. These results indicate that the examples employing phased temperature control, parallel laminar flow buffering, and phase change buffer solvents can achieve higher gloss, lower roughness, and lower defect ratings, resulting in coating surface quality superior to the comparative examples.

[0095] Test Example 4: Evaluation Test of Curing Uniformity in Complex Geometric Structures Test steps: (1) The aluminum panels with back reinforcement structure that were cured and placed for 7 days in Examples 4, 1, 3 and 4 were selected as test samples. The flat thin-walled area (substrate thickness about 2.0 mm) and the thick-walled area with reinforcement (equivalent thickness about 8.0 mm) were marked on each panel as independent test parts.

[0096] (2) The swelling ratio of the coating in different areas was determined to assess the crosslinking density. A free film of the coating was scraped from the calibration area, and after weighing the initial mass, it was immersed in a sealed container containing acetone solvent. After standing and immersing at room temperature for 72 hours, it was taken out, the excess liquid on the surface was blotted off, and the mass after swelling was weighed. The percentage increase in mass before and after swelling was calculated to obtain the swelling ratio. A relatively low swelling ratio usually indicates that the crosslinking network inside the coating is relatively dense.

[0097] (3) Test the adhesion level of the coating in different areas. Use a cross-cutting tool to cut through the coating to the aluminum substrate surface in the calibrated area to form 100 1mm×1mm grids. Apply and press standard test tape firmly into the grid area, and peel off the tape at a uniform speed. Evaluate the adhesion level from 0 to 5 according to the peeling of the coating at the intersection of the cuts and within the grid area, in accordance with GB / T9286-2021 standard.

[0098] (4) Determine the solvent resistance of the coating in different areas. Using degreased cotton balls soaked in methyl ethyl ketone (MEK), double reciprocating wiping was performed on the surface of the calibration area at a frequency of approximately 100 times / minute under a constant load of 1 kg. The number of double reciprocating wipings before the coating surface was scratched and the underlying aluminum material was exposed was recorded to evaluate the chemical resistance of the coating film.

[0099] Each of the above tests was repeated at least 3 times, and the average value of the test results was taken.

[0100] Test data: Table 4. Test data of physical and chemical properties of coatings in different regions of complex geometries Test conclusion: As shown in Table 4, the swelling rate, adhesion and MEK wiping times of the thin-walled and thick-walled regions of each sample are different to varying degrees, which can be used to evaluate the curing consistency of regions with different thicknesses.

[0101] Table 4 shows that the performance data of the thin-walled and thick-walled regions in Example 4 are similar. The swelling rate of the thin-walled region is 14.7%, and that of the thick-walled region is 15.6%, with a difference of only 0.9%. In the MEK wiping test, the two regions were tested 132 times and 128 times, respectively, and the adhesion was grade 0 in both cases. The difference in swelling rate between the thin-walled and thick-walled regions in Example 4 is only 0.9%, and the difference in the number of MEK wiping times is 4, indicating that the gradual increase buffer platform can reduce the curing difference between the thick and thin regions. Combining the similar swelling rates and MEK wiping times of the two regions in Example 4, it can be considered that the stepped catalytic system combined with segmented heating is beneficial for maintaining a similar degree of crosslinking in regions of different thicknesses.

[0102] In contrast, the performance of the comparative examples varied significantly across different thickness regions. Comparative Example 3, lacking a catalyst component with early chain-extending catalytic activity, exhibited a swelling ratio in its thick-walled region of 29.5%, a marked difference from the thin-walled region (16.9%); simultaneously, the MEK wiping count in the thick-walled region decreased to 61 times. The increased swelling ratio of the thick-walled region in Comparative Example 3 to 29.5% and the reduced MEK wiping count to 61 times indicate that the lack of an early catalytic component resulted in a significantly lower degree of solidification in the thick-walled region compared to the thin-walled region.

[0103] Comparative Example 4 did not employ a buffer platform process and used a continuous heating method for curing. The swelling rate of the thick-walled region in this sample reached 38.4%, showing the largest difference compared to the thin-walled region. Simultaneously, the MEK wiping count in the thick-walled region decreased to 27 times, and the adhesion rating deteriorated to level 4. The continuous rapid heating may have amplified the impact of the substrate's heat capacity differences. The thin-walled region reached the curing temperature faster, while the thick-walled region absorbed heat and heated up more slowly, resulting in localized under-cured states. Table 4 data shows that Example 4 exhibited the smallest performance difference between the thin-walled and thick-walled regions, indicating that the buffer platform and stepped catalytic system can reduce the regional curing differences caused by the reinforcing rib structure.

[0104] Test Example 5: Overall Physical, Mechanical and Weather Resistance Tests of Coating Test steps: (1) The cured aluminum panels prepared in Examples 1 to 4 and Comparative Examples 1 to 4 and cured at room temperature were selected as the evaluation objects of this test. All samples were placed in a standard environment with a temperature of 23±2℃ and a relative humidity of 50±5% for 48 hours to stabilize their physical state.

[0105] (2) The surface hardness of the coating was measured on the conditioned sample. A Koenig pendulum hardness tester was used. The veneer to be tested was fixed horizontally on the test platform, and the pendulum was adjusted to make it swing initially on the coating surface. The oscillation time (in seconds) during which the pendulum amplitude decreased from 6 degrees to 3 degrees was recorded to evaluate the hardness of the coating film.

[0106] (3) Evaluate the interlayer bond strength between the coating and the substrate. A hydraulic adhesion pull-out tester was used for positive pull-out testing. A 20 mm diameter aluminum alloy test ingot was vertically bonded to the coating surface using a two-component epoxy adhesive. After curing for 24 hours, the coating around the ingot was removed using a trowel until the substrate was reached. A vertical pull force was applied at a uniform speed through the pull-out tester until the coating was peeled off, and the maximum pull-out force at failure was recorded (in MPa).

[0107] (4) Evaluate the long-term weather resistance of the coating system. Cut each group of samples into standard-sized templates and place them in a QUV accelerated aging test chamber. Set the test light source to a UVB-313 lamp, and set the cycle conditions to alternate between 8 hours of irradiation at 60°C and 4 hours of condensation at 50°C, with a total test cycle of 3000 hours. After the test, measure the 60-degree gloss and surface color difference, and calculate the percentage of gloss retention relative to the initial state.

[0108] Each of the above tests was repeated at least 3 times, and the test results were taken as the arithmetic mean.

[0109] Test data: Table 5. Test data on the overall physical, mechanical, and weathering properties of the coatings for each test sample. Test conclusion: As shown in Table 5, the example group is superior to the comparative group in terms of adhesion, pendulum hardness, gloss retention after aging, and color difference.

[0110] Table 5 shows that the performance indicators of Examples 1 to 4 are relatively stable and at a high level. Their positive pull-out adhesion is concentrated between 8.1 MPa and 8.7 MPa, and the pendulum hardness is between 179 s and 188 s. After 3000 hours of aging, the gloss retention rate is distributed between 90.5% and 92.1%, and the color difference is less than 1.3. The fact that Examples 1 to 4 maintained a gloss retention rate of 90.5% to 92.1% and a color difference of less than 1.3 after 3000 hours of aging indicates that their cured film structure is relatively stable. Combined with their high adhesion and high gloss retention rate, it can be considered that the coatings formed in the example group are more effective in resisting performance degradation caused by moisture, oxygen, and ultraviolet radiation during the aging process.

[0111] The adhesion, hardness, and gloss retention after aging of Comparative Examples 1 to 4 were all lower than those of the Example Group, with Comparative Example 4 showing the most significant decrease. Comparative Example 1, due to the use of continuous strong airflow leading to early surface crusting and internal defects, experienced a drop in adhesion to 5.2 MPa. The formation of pores increased the possibility of moisture penetration, resulting in a decrease in gloss retention to 65.4% and an increase in color difference to 4.82. Comparative Example 2, lacking a phase change buffer solvent, also faced the problem of decreased structural density, with its gloss retention remaining at 70.1%.

[0112] Comparative Example 3, lacking the chain-extending effect of the first-stage catalyst, may have resulted in uneven establishment of the overall crosslinking network density, leading to a decrease in its pendulum hardness to 125s and a drop in pull-out adhesion to 6.1MPa. The pendulum hardness of Comparative Example 3 (125s) and pull-out adhesion of 6.1MPa are lower than those of the Example group, indicating insufficient crosslinking network strength and a correspondingly lower performance retention rate after aging. Comparative Example 4 exhibits the worst adhesion, gloss retention, and color difference among all groups, indicating a decline in coating curing quality after removing the buffer platform, and showing more significant gloss decay and color difference changes after aging tests. These test results demonstrate that the fluid regulation and chemical catalytic response mechanism proposed in this invention can improve the physical and mechanical strength of the coating from the microstructure level and help extend the system's weather resistance service life.

Claims

1. An aluminum veneer surface weatherable coating cure process characterized by, Includes the following steps: The raw materials are mixed evenly according to the weight percentage to prepare a coating composition. The coating composition is sprayed onto the surface of the aluminum single panel and sent into a curing oven. The infrared heating module inside the curing oven is controlled to output heating, and the circulating air module is controlled to generate a vertical impact flow that blows vertically toward the surface of the aluminum panel. When the absolute temperature of the coating surface is detected to reach 130-138°C, the output power of the infrared heating module is reduced to control the increase of the absolute temperature of the coating surface. At the same time, the airflow direction of the circulating air supply module is adjusted to a parallel laminar flow parallel to the surface of the aluminum single panel to maintain a slow rise buffer state. After the gradual rise and buffer state ends, the output power of the infrared heating module is restored. When the absolute temperature of the coating surface exceeds 145-155°C, the air supply temperature is increased and the vertical impact flow is switched back. Heating continues after the absolute temperature of the coating surface exceeds 170°C. Cool and remove from the oven.

2. The curing process of claim 1, wherein, In the step of generating the vertical impact flow, the infrared heating module is controlled to output heating at 80% to 100% of its rated power; In the step of maintaining the gradual rise buffer state, the output power of the infrared heating module is reduced to 30% to 50% of the rated power, and the absolute temperature of the coating surface is controlled to rise at a rate of 0.5 to 1.5℃ / min within the range of 135℃ to 148℃, and maintained for 3 to 6 minutes. When the absolute temperature of the coating surface exceeds 145-155°C, the air supply temperature is set to 215-230°C. The coating surface is heated for 8 to 12 minutes after the absolute temperature exceeds 170°C.

3. The curing process of claim 1, wherein, The raw material consists of the following components by weight percentage: Alternating copolymer fluoroolefin-vinyl ether resin: 40.0–48.0%; 3,5-Dimethylpyrazole-blocked hexamethylene diisocyanate trimer curing agent: 15.0–22.0%; Phase change endothermic buffer solvent: 6.0–12.0%; Stepped bimetallic catalyst: 0.25–0.55%; Functional additives: 1.0–2.0%; Rutile titanium dioxide: 10.0–20.0%; Xylene: 5.45–17.75%; The sum of the weight percentages of the above components is 100%.

4. The curing process of claim 3, wherein, The phase change endothermic buffer solvent is composed of 4.0–8.5 wt% propylene glycol methyl ether acetate and 2.0–3.5 wt% divalent ester; The stepped bimetallic catalyst is composed of 0.05–0.15 wt% zinc acetylacetonate and 0.2–0.4 wt% bismuth neodecanoate; The functional additive is composed of 0.3-0.5 wt% of polyether-modified polydimethylsiloxane, 0.2-0.5 wt% of polymethylalkylsiloxane solution, and 0.5-1.0 wt% of bis(1,2,2,6,6-pentamethyl-4-piperidinyl) sebacate.

5. The curing process of claim 4, wherein, The preparation method of the 3,5-dimethylpyrazole-blocked hexamethylene diisocyanate trimer curing agent includes the following steps: In a reactor equipped with a reflux condenser, a mechanical stirrer and a nitrogen protection device, 100 parts by weight of hexamethylene diisocyanate trimer and 30 parts by weight of anhydrous butyl acetate are added. Stirring is started and nitrogen protection is introduced to raise the temperature inside the reactor to 50-55°C. Weigh out 3,5-dimethylpyrazole according to a molar ratio of isocyanate group to active hydrogen of 3,5-dimethylpyrazole of 1:1.01 to 1:1.10, and add the weighed 3,5-dimethylpyrazole in equal batches to the reaction vessel. During the feeding process, the temperature rise caused by the exothermic reaction of the system is controlled to not exceed 75-85℃ by adjusting the flow rate of the cooling water in the jacket of the reactor. After the feeding is completed, the temperature inside the reactor is kept constant at 75-85℃, and the reaction is continued for 3-4 hours. When the content of free NCO groups decreases to 0.04-0.12wt%, heating is stopped, the temperature is lowered to room temperature, and the curing agent solution is discharged.

6. The curing process of claim 1, wherein, In the step of spraying the coating composition onto the surface of the aluminum single panel, the wet film thickness is controlled to be 80-120 μm; In the steps of generating the vertical impulsive flow and cutting back the vertical impulsive flow, the wind speed is set to 5.0–8.0 m / s; In the step of adjusting to the parallel laminar flow, the relative airflow velocity in the surface area is reduced to 0.5–1.5 m / s.

7. The curing process of claim 1, wherein, The curing oven is equipped with an exhaust module and an LEL concentration probe. The exhaust module is linked with the LEL concentration probe inside the curing oven to ensure that the VOCs concentration inside the oven is below 25% of the lower explosive limit.

8. The curing process of claim 1, wherein, The aluminum panel is a complex geometric aluminum panel with a back reinforcing rib structure, wherein the aluminum substrate thickness in the flat area is 2.0mm, and the equivalent thickness of the aluminum substrate in the reinforcing rib area is 8.0mm.

9. A temperature control system for curing a weatherable coating on the surface of an aluminum veneer, for carrying out the curing process according to any one of claims 1-8, characterized by, include: A curing oven, wherein the curing oven is equipped with a conveyor belt for transporting aluminum panels and is divided into independent temperature zones along the transport direction; A temperature measurement module, independently installed on the curing oven, is used to monitor the absolute temperature of the coating surface; An infrared heating module is arranged on the inner surface of the curing oven and is connected to the PLC control unit for dynamically adjusting the output power of the infrared radiation heating tube according to the feedback command of the surface heating rate. The exhaust module is independently installed on the curing oven and is linked to the LEL concentration probe signal inside the oven. It is used to operate at a preset exhaust frequency during the normal curing cycle and to increase the exhaust frequency or trigger an alarm when the VOCs concentration inside the oven approaches a preset threshold. The circulating air supply module, located inside the curing oven, includes a hot air circulating variable frequency fan and an air nozzle angle deflection device. The air nozzle angle deflection device is controlled by the PLC control unit to control the airflow direction of the circulating hot air inside the oven to switch between the vertical impingement flow mode and the parallel laminar flow mode.

10. The temperature control system of claim 9, wherein, The curing oven integrates the temperature measurement module, the infrared heating module, the exhaust module, and the circulating air supply module; the PLC control unit is used to adjust the output power of the infrared heating module through closed-loop feedback control, and to send a signal to the air supply nozzle angle deflection device to control the air direction to adjust between the vertical impingement flow mode and the parallel laminar flow mode.

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