Integrated coating method and system, composite workpiece and automobile

Abstract

The invention relates to an integrated coating method and system, a composite workpiece and an automobile, a dual-curing coating system is adopted and matched with a light curing process, so that structural parts with different heat resistance can be collinearly sprayed and cured, part color difference caused by independent processing and heat treatment environment difference is effectively avoided, the process period can be greatly shortened, and the production efficiency is improved. The occupied area and the investment cost of a production line are saved, the energy consumption level and the greenhouse gas emission are remarkably reduced, a photocured workpiece can be subjected to a non-illumination-driven secondary cross-linking reaction after being separated from an irradiation environment, and a finally formed paint film has excellent overall hardness and scratch resistance; the paint is especially suitable for links of finished automobile manufacturing, aftermarket paint surface repairing and the like, and can effectively guarantee and prolong the appearance quality of the automobile used in a daily complex environment.

Description

Technical Field

[0001] This disclosure relates to an integrated coating method, system, composite workpiece, and automobile. Background Technology

[0002] In the automotive manufacturing industry, painting processes primarily utilize thermosetting coatings, which cure to form a paint film through heating. In conventional vehicle production, the main body is typically constructed from metal materials such as steel and aluminum, while exterior components like side mirrors and bumpers are mostly made from non-metallic materials like plastics. Due to differences in the heat resistance of the substrates, the vehicle body and exterior components must be processed independently in separate painting lines and high-temperature ovens. This not only increases the floor space required for the production line and overall investment costs, but also introduces color and gloss matching errors in components subjected to different painting processes. Furthermore, maintaining the high-temperature environment of large convection ovens requires continuous energy consumption, resulting in high carbon emissions. Summary of the Invention

[0003] To overcome the problems existing in related technologies, this disclosure provides an integrated coating method, system, composite workpiece, and automobile.

[0004] This disclosure provides an integrated coating method for composite workpieces, the method comprising a first structural component and a second structural component, wherein the first structural component and the second structural component are made of different materials and the heat distortion temperature of the first structural component is higher than that of the second structural component, the method comprising: S1. Apply a dual-curing coating to the inner and outer surfaces of the composite workpiece and flash-dry it to obtain a composite workpiece with a dual-curing coating. S2. Perform a first photocuring on the outer surface of the composite workpiece with the dual-curing coating, and perform a second photocuring on the inner surface and the shadow area of ​​the outer surface of the composite workpiece with the dual-curing coating, so that the dual-curing coating reaches a first preset hardness, and obtain the photocured composite workpiece. S3. The photocured composite workpiece is left to stand in a natural environment for a preset time so that the dual-cured coating reaches a second preset hardness, which is higher than the first preset hardness.

[0005] Optionally, in step S1, the dual-curing coating comprises, by weight percentage: 10-30% acrylic oligomer, 5-10% acrylic monomer, 10-40% diluent, 0.5-3% photoinitiator, 10-30% modified acrylic resin, and 5-20% isocyanate.

[0006] Optionally, in step S1, the flash-drying conditions include: a temperature of 40~60℃ and a time of 4~10 minutes; and / or, The method further includes: in step S1, after the flash drying is completed, cooling the inner and outer surfaces of the composite workpiece to 30~50°C.

[0007] Optionally, in step S2, performing a first photocuring on the outer surface of the composite workpiece with the dual-curing coating includes: having the composite workpiece pass through a first UV light source at a preset running speed, wherein the first UV light source includes multiple surface light sources, and the multiple surface light sources are sequentially spliced ​​to form a portal frame that surrounds the outer contour of the composite workpiece. The conditions for the first photocuring include: the emission wavelength of the first UV light source is 250~450nm, and the peak light intensity is 0.05~5W / cm². 2 The preset operating speed of the composite workpiece is 3~6 m / min, and the total irradiation energy density is 1~5 J / cm³. 2 .

[0008] Optionally, in step S2, the second photocuring is performed using a multi-axis actuator equipped with a second UV light source, and the maximum size of the light-emitting surface of the second UV light source is no more than 30cm. The conditions for the second photocuring process include: the emission wavelength of the second UV light source is 250~450nm, and the peak light intensity is 0.1~5W / cm². 2 The moving speed of the second UV light source is 300~500mm / s, and the total irradiation energy density is 1~5J / cm². 2 .

[0009] Optionally, in step S3, the natural environmental conditions include: humidity of 30-80% and temperature of 5-40℃; the preset time is 3-7 days; and / or, The first preset hardness is 3B or higher, and the second preset hardness is HB or higher.

[0010] This disclosure also provides an integrated coating system for implementing the aforementioned method, the system comprising: A spraying unit is used to apply a double-curing coating to the inner and outer surfaces of the composite workpiece, and then flash-dry it to obtain a composite workpiece with a double-curing coating. A photocuring unit is used to perform a first photocuring on the outer surface of the composite workpiece with a dual-curing coating, and a second photocuring on the inner surface and the shadow area of ​​the outer surface of the composite workpiece with a dual-curing coating, so that the dual-curing coating reaches a first preset hardness, and a photocured composite workpiece is obtained. The settling unit is used to allow the photocured composite workpiece to stand in a natural environment for a preset time so that the dual-cured coating reaches a second preset hardness, which is higher than the first preset hardness.

[0011] This disclosure also provides a composite workpiece prepared by the aforementioned method or system, the composite workpiece comprising a first structural component and a second structural component, wherein the first structural component and the second structural component are made of different materials and the heat distortion temperature of the first structural component is higher than that of the second structural component, and the inner and outer surfaces of the composite workpiece are formed with a double-cured coating.

[0012] Optionally, the first structural component is made of a metallic material, and the second structural component is made of a non-metallic material; and / or, The first structural component is a car body, and the second structural component is a car exterior component.

[0013] This disclosure also provides an automobile that includes the aforementioned composite workpiece.

[0014] Through the above technical solution, this disclosure adopts a dual-curing coating system combined with a photocuring process, which enables structural parts with different heat resistance to be sprayed and cured in the same line. This effectively avoids color differences in parts caused by differences in independent processing and heat treatment environments, significantly reduces the process cycle, saves production line floor space and investment costs, and significantly reduces energy consumption and greenhouse gas emissions. The workpiece after photocuring can undergo a non-photo-driven secondary cross-linking reaction after leaving the irradiation environment, so that the final paint film has excellent overall hardness and scratch resistance. It is particularly suitable for automobile manufacturing and aftermarket paint repair, and can effectively guarantee and extend the appearance quality of vehicles in daily complex environments.

[0015] Other features and advantages of this disclosure will be described in detail in the following detailed description section. Attached Figure Description

[0016] The accompanying drawings are provided to further illustrate the present disclosure and form part of the specification. They are used together with the following detailed description to explain the present disclosure, but do not constitute a limitation thereof. In the drawings: Figure 1 This is a flowchart illustrating an integrated coating method according to a specific embodiment of the present disclosure.

[0017] Figure 2 This is a schematic diagram of the structure of a first UV light source according to a specific embodiment of the present disclosure.

[0018] Explanation of reference numerals in the attached figures 1—First UV light source. Detailed Implementation

[0019] The specific embodiments of this disclosure will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit this disclosure.

[0020] To address the color differences and high costs associated with separate painting lines, some low-temperature integrated painting solutions have been proposed. These solutions attempt to reduce curing temperatures, allowing metal body panels and plastic exterior parts to be sprayed and baked on the same production line. However, lowering the baking temperature results in lower curing levels within the coating, softer film hardness, and scratch resistance and other physical and chemical properties that often fail to meet the requirements of subsequent vehicle transfer and assembly processes. Furthermore, this solution still relies on the traditional heated drying oven system, requiring a relatively long period of heat accumulation for coating formation, thus offering limited improvements in reducing process time, factory space requirements, and energy consumption.

[0021] In a first aspect, this disclosure provides an integrated coating method for a composite workpiece, the composite workpiece comprising a first structural component and a second structural component, wherein the first structural component and the second structural component are made of different materials and the heat distortion temperature of the first structural component is higher than that of the second structural component.

[0022] This disclosed method is particularly applicable to the automotive painting field. In one specific embodiment, the material of the first structural component may include metallic materials (such as aluminum alloys), and the material of the second structural component may include non-metallic materials (such as polymer plastics, composite materials, etc.). The difference in heat distortion temperature between the first and second structural components can be adjusted within a wide range; for example, the difference in their heat distortion temperatures can be above 40°C. Specifically, the first structural component can be a car body; the second structural component can be an automotive exterior part, such as front and rear bumpers, exterior rearview mirror housings, or fenders. The first and second structural components are assembled or are in a parallel configuration, allowing them to be processed in the same painting and curing environment, avoiding color differences and improving the color matching consistency of the composite workpiece. In other embodiments, this disclosed method can also be used for other composite workpieces composed of different materials and with more complex structures.

[0023] In one specific implementation, see Figure 1 The method includes the following steps S1 to S3: S1. Apply a dual-curing coating to the inner and outer surfaces of the composite workpiece and flash-dry it to obtain a composite workpiece with a dual-curing coating. S2. Perform a first photocuring on the outer surface of the composite workpiece with the dual-curing coating, and perform a second photocuring on the inner surface and the shadow area of ​​the outer surface of the composite workpiece with the dual-curing coating, so that the dual-curing coating reaches a first preset hardness, and obtain the photocured composite workpiece. S3. The photocured composite workpiece is left to stand in a natural environment for a preset time so that the dual-cured coating reaches a second preset hardness, which is higher than the first preset hardness.

[0024] Step S1 is used to prepare a dual-curing coating on the exposed surface of the composite workpiece. The inner surface of the composite workpiece refers to a spatial wall surface that is away from the main viewing angle, is geometrically concave, or is obscured by movable parts; the outer surface refers to a convex or smooth wall surface facing the external environment and located at the main viewing angle. For example, the inner surface of the composite workpiece may include internal spatial surfaces such as door inner panels, front and rear hood inner panels, or side door openings, while the outer surface may include external visible interfaces such as door outer panels, fenders, or front and rear bumpers.

[0025] The dual-curing coating is a coating composition comprising two different but synergistic curing reaction systems. It can undergo polymer crosslinking reactions through different mechanisms under two curing conditions to form a cured coating with a three-dimensional network structure. Specifically, the dual-curing coating may include a UV-thermal dual-curing coating and / or a UV-moisture dual-curing coating. These dual-curing coatings can rapidly polymerize under UV light stimulation and then continue to undergo secondary crosslinking reactions under natural conditions. Preferably, the dual-curing coating can be a UV-thermal dual-curing coating, such as a single-component or two-component UV-polyurethane dual-curing coating, which is beneficial for obtaining ideal coating performance.

[0026] In one specific embodiment, by weight percentage, the dual-curing coating may include: 10-30% acrylic oligomer, 5-10% acrylic monomer, 10-40% diluent, 0.5-3% photoinitiator, 10-30% modified acrylic resin, and 5-20% isocyanate. The above dual-curing coating can form a cured coating with excellent appearance and scratch resistance, which is beneficial to improving the protective effect of composite workpieces in long-term complex environments. The acrylic oligomer may include, for example, at least one of polyurethane acrylate (PUA), epoxy acrylate (EA), and polyester acrylate (PEA); the acrylic monomer may include a monofunctional or polyfunctional reactive diluent monomer, for example, at least one of isobornyl acrylate (IBOA), 1,6-hexanediol diacrylate (HDDA), and tripropylene glycol diacrylate (TPGDA); the diluent may include, for example, at least one of ethyl acetate, butyl acetate, and xylene; and the photoinitiator may be active under UV light irradiation at 250-450 nm, preferably 360-420 nm. The modified acrylic resin can include at least one of 2,4,6-trimethylbenzoyl diphenylphosphine oxide (TPO) and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (BAPO) to initiate the free radical polymerization reaction of acrylic oligomers and monomers. The modified acrylic resin can include acrylic polymers with active functional groups on the main chain or side chains, such as at least one of hydroxyl acrylic resins and fluorinated modified acrylic resins. The isocyanate can include aliphatic or alicyclic diisocyanates and their derivatives, such as at least one of hexamethylene diisocyanate (HDI) and isophorone diisocyanate (IPDI). The dual-curing coating can consist of a first component and a second component packaged independently and mixed in proportion before being applied to the surface of the composite workpiece. The first component contains acrylic oligomers participating in free radical polymerization, acrylic monomers, photoinitiators, diluents, and modified acrylic resins participating in the thermosetting crosslinking reaction. The second component contains isocyanates participating in the thermosetting crosslinking reaction.

[0027] The application of dual-curing coatings to the inner and outer surfaces of the composite workpiece can be done in a manner conventional to the art, such as using air spray guns or electrostatic rotary cups, or employing a spraying robot. For example, for the outer surface, an electrostatic rotary cup mounted on the end effector of a multi-axis industrial robot can be used for large-area, high-efficiency atomized spraying; for the inner surface, an air spray gun mounted on the end effector of a small six-axis robot can be used for deep spraying. Furthermore, to facilitate the spraying of the inner surface, a dedicated door-opening robot can be configured to automatically grasp and open the doors, hoods, or trunk lids of the composite workpiece before or during spraying to expose the inner surfaces to be sprayed. The application sequence can be flexibly adjusted according to the production line layout or production cycle requirements; for example, the inner surface can be sprayed first, followed by the outer surface. The coating thickness can be adjusted within a certain range; for example, the film thickness on the inner surface can be 15-40 μm, and the film thickness on the outer surface can be 30-60 μm.

[0028] The flash-drying process parameters can be adjusted within a certain range. Specifically, the flash-drying conditions may include a temperature of 40~60℃ and a time of 4~10 minutes. Further, the method may also include: in step S1, after the flash-drying is completed, cooling the inner and outer surfaces of the composite workpiece to 30~50℃. Specifically, a forced cooling device can be installed at the outlet of the flash-drying equipment, and the cooling can be performed by blowing cold air.

[0029] In some embodiments, prior to step S1, the method may further include at least one of the following steps: surface pretreatment of the composite workpiece (such as degreasing), deposition of a metal conversion film, electrophoretic primer coating, weld sealant application, spraying of a water-based intermediate coat and a color paint layer, and pre-drying. The specific operations of the above steps are well known to those skilled in the art and will not be described in detail here.

[0030] Step S2 is used to photocur the dual-curing coating, employing a two-stage photocuring process to achieve a certain initial hardness for the coatings on the inner and outer surfaces of the composite workpiece. This disclosure uses photocuring technology to replace the traditional high-temperature baking process. The production line does not require a high-temperature drying oven or the use of non-renewable energy sources such as natural gas. This significantly reduces the floor space required for the coating workshop, lowers equipment investment and overall energy consumption, significantly shortens the process cycle, and reduces the carbon footprint.

[0031] In one specific implementation, see Figure 2The step of performing a first photocuring on the outer surface of the composite workpiece with the dual-curing coating may include: allowing the composite workpiece to pass through a first UV light source 1 at a preset running speed. The first UV light source 1 includes multiple surface light sources, and the multiple surface light sources are sequentially spliced ​​to form a portal frame that encloses the outer contour of the composite workpiece. The outer contour of the composite workpiece is the cross-sectional outer contour perpendicular to the running direction of the composite workpiece. Thus, the multiple surface light sources can span the conveying trajectory of the composite workpiece, irradiating the outer surface of the composite workpiece with ultraviolet light, which has the advantages of a large irradiation range and high curing efficiency. The type of light source for the surface light source can be common in the art, such as a high-pressure mercury lamp, a UV-LED light source, etc., preferably a UV-LED light source.

[0032] The specific number and arrangement of the multiple surface light sources can be flexibly adjusted. For example, the multiple surface light sources may include a top surface light source, side surface light sources, and transition surface light sources interspersed between them. The top surface light source is horizontally positioned directly above the composite workpiece conveyor track to irradiate horizontal surfaces such as the roof, hood, and trunk lid. The side surface light sources are vertically positioned on both sides of the composite workpiece conveyor track to irradiate vertical surfaces such as the lower part of the doors and fenders. The transition surface light source is inclined relative to the horizontal plane to connect the top and side surface light sources and irradiate inclined surfaces such as the window frames (e.g., A-pillar and C-pillar areas) and the upper part of the doors. The specific shape and size of each surface light source can be adaptively set according to the geometric characteristics of the outer contour of the composite workpiece. For example, the shape of the surface light source can be rectangular, and its width can be 0.3~1m. Furthermore, the surface light source can be equipped with a heat dissipation device, such as an air-cooled device and / or a liquid-cooled device, to avoid damage caused by overheating of the light source itself and to maintain a high electro-optical conversion efficiency. Preferably, the heat dissipation device is a liquid-cooled device.

[0033] The process parameters for the first photocuring can be adjusted within a certain range. Specifically, the conditions for the first photocuring may include: the emission wavelength of the first UV light source is 250~450nm, preferably 360~420nm, and the peak light intensity is 0.05~5W / cm². 2 The preset operating speed of the composite workpiece is 3~6 m / min, and the total irradiation energy density is 1~5 J / cm³. 2 .

[0034] The outer surface shadow area refers to the outer surface area that is blocked by the three-dimensional structure of the composite workpiece itself, where light cannot directly reach it in the first photocuring stage or the irradiance is lower than the photo-induced polymerization threshold.

[0035] In one specific embodiment, the second photocuring is performed using a multi-axis actuator equipped with a second UV light source. The maximum size (e.g., diameter or diagonal length) of the emitting surface of the second UV light source is no more than 30 cm, preferably no more than 15 cm. This utilizes the flexibility and mobility of the multi-axis actuator to perform localized irradiation, ensuring that the coatings on the inner and outer surfaces of the composite workpiece achieve a uniform curing state. The type of light source for the second UV light source can be common in the art, such as a high-pressure mercury lamp or a UV-LED light source, preferably a UV-LED light source.

[0036] The multi-axis actuator can be a robotic arm with a preset motion trajectory or a six-axis industrial robot with vision guidance, enabling it to perform contour irradiation along a pre-planned trajectory. During localized irradiation, the vertical distance between the emitting surface of the second UV light source and the irradiated surface of the composite workpiece can be controlled to be maintained at 100-200mm. In this case, the effective irradiation area width projected onto the irradiated surface can reach over 200mm, achieving high single-pass coverage efficiency. For composite workpieces with openable / closable doors (e.g., car doors, engine hoods, or trunk lids), during the second photocuring process, the multi-axis actuator can also be configured to grasp and open the door before or during directional irradiation to expose the inner cavity surface to be cured.

[0037] The process parameters for the second photocuring can be adjusted within a certain range. Specifically, the conditions for the second photocuring may include: the emission wavelength of the second UV light source is 250~450nm, preferably 360~420nm, and the peak light intensity is 0.1~5W / cm². 2 The moving speed of the second UV light source is 300~500 mm / s, and the total irradiation energy density is 0.5~5 J / cm². 2 .

[0038] The dual-cured coating, after the first and second photocuring processes, can quickly reach a first preset hardness. This first preset hardness can meet the requirements of continuous production line operation without damage or peeling. Specifically, the coating pencil hardness test grade corresponding to the first preset hardness can be 3B or higher.

[0039] In some embodiments, after step S2, the method may further include at least one of the following steps: grinding, polishing, and filling with functional materials (such as anti-rust wax, foaming materials, etc.) on the photocured composite workpiece. The specific operations of the above steps are well known to those skilled in the art and will not be described in detail here.

[0040] Step S3 is used to achieve deep curing of the coating. Through the continuous non-light-driven secondary cross-linking reaction of the active reactants (such as modified acrylic resin and isocyanate) in the dual-curing coating system, a complete paint film with higher hardness and more stable performance is finally formed.

[0041] The natural environment is a room-temperature environment free from ultraviolet radiation and without additional heat sources, such as an indoor buffer zone or assembly workshop. Specifically, the conditions of the natural environment may include: humidity of 30-80% and temperature of 5-40℃. The preset time can be adjusted within a certain range, specifically 3-7 days. The hardness test grade of the coated pencil corresponding to the second preset hardness can be HB or higher.

[0042] A second aspect of this disclosure provides an integrated coating system for implementing the method described in the first aspect of this disclosure, the system comprising: A spraying unit is used to apply a double-curing coating to the inner and outer surfaces of the composite workpiece, and then flash-dry it to obtain a composite workpiece with a double-curing coating. A photocuring unit is used to perform a first photocuring on the outer surface of the composite workpiece with a dual-curing coating, and a second photocuring on the inner surface and the shadow area of ​​the outer surface of the composite workpiece with a dual-curing coating, so that the dual-curing coating reaches a first preset hardness, and a photocured composite workpiece is obtained. The settling unit is used to allow the photocured composite workpiece to stand in a natural environment for a preset time so that the dual-cured coating reaches a second preset hardness, which is higher than the first preset hardness.

[0043] The spraying unit, photocuring unit, and settling unit can be arranged sequentially along the conveying direction of the composite workpiece. The specific configuration of each unit is consistent with the description in the previous method implementation, and will not be repeated here.

[0044] A third aspect of this disclosure provides a composite workpiece prepared by the method described in the first aspect of this disclosure or the system described in the second aspect of this disclosure. The composite workpiece includes a first structural component and a second structural component, wherein the first structural component and the second structural component are made of different materials and the heat distortion temperature of the first structural component is higher than that of the second structural component. The inner and outer surfaces of the composite workpiece are formed with a double-cured coating.

[0045] In one specific embodiment, the material of the first structural component may include a metallic material, and the material of the second structural component may include a non-metallic material. Further, the first structural component may be a car body, and the second structural component may be a car exterior component.

[0046] The dual-curing coating has a dual-curing crosslinked network structure formed by the dual-curing coating material. Specifically, the dual-curing crosslinked network structure includes a first crosslinked network structure formed by ultraviolet light and a second crosslinked network structure driven by natural environmental conditions. For example, the first crosslinked network structure may include acrylic free radical polymer segments, and the second crosslinked network structure may include polyurethane crosslinked segments.

[0047] In a fourth aspect, this disclosure provides an automobile that includes the composite workpiece described in the third aspect of this disclosure.

[0048] There are no restrictions on the specific type and structure of the vehicle; for example, it can be a passenger car, a commercial vehicle, or a special vehicle with a special shell structure, and it can maintain excellent appearance and durable protection throughout its entire life cycle.

[0049] This disclosure enables the co-line spraying and curing of structural components made of different materials, effectively avoiding color differences in parts caused by differences in independent processing and heat treatment environments. Compared with low-temperature baking coating solutions, the method of this disclosure can prepare a uniform paint film with high cross-linking density on the surface of composite workpieces, effectively improving the overall hardness and mechanical scratch resistance. This allows for maintaining good appearance protection over a longer product life cycle, making it particularly suitable for automotive manufacturing and aftermarket paint repair, effectively ensuring and extending the appearance quality of vehicles in daily complex environments.

[0050] The preferred embodiments of this disclosure have been described in detail above with reference to the accompanying drawings. However, this disclosure is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this disclosure, various simple modifications can be made to the technical solutions of this disclosure, and these simple modifications all fall within the protection scope of this disclosure.

[0051] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, this disclosure will not describe the various possible combinations separately.

[0052] Furthermore, various different embodiments of this disclosure can be combined in any way, as long as they do not violate the spirit of this disclosure, they should also be regarded as the content disclosed in this disclosure.

Claims

1. An integrated coating method, characterized in that, The method is used for composite workpieces, the composite workpieces including a first structural component and a second structural component, wherein the first structural component and the second structural component are made of different materials and the heat deformation temperature of the first structural component is higher than that of the second structural component, the method comprising: S1. Apply a dual-curing coating to the inner and outer surfaces of the composite workpiece and flash-dry it to obtain a composite workpiece with a dual-curing coating. S2. Perform a first photocuring on the outer surface of the composite workpiece with the dual-curing coating, and perform a second photocuring on the inner surface and the shadow area of ​​the outer surface of the composite workpiece with the dual-curing coating, so that the dual-curing coating reaches a first preset hardness, and obtain the photocured composite workpiece. S3. The photocured composite workpiece is left to stand in a natural environment for a preset time so that the dual-cured coating reaches a second preset hardness, which is higher than the first preset hardness.

2. The method according to claim 1, characterized in that, In step S1, the dual-curing coating comprises, by weight percentage: 10-30% acrylic oligomer, 5-10% acrylic monomer, 10-40% diluent, 0.5-3% photoinitiator, 10-30% modified acrylic resin, and 5-20% isocyanate.

3. The method according to claim 1, characterized in that, In step S1, the flash-drying conditions include: a temperature of 40~60℃ and a time of 4~10 minutes; and / or, The method further includes: in step S1, after the flash drying is completed, cooling the inner and outer surfaces of the composite workpiece to 30~50°C.

4. The method according to claim 1, characterized in that, In step S2, the first photocuring of the outer surface of the composite workpiece with the dual curing coating includes: letting the composite workpiece pass through a first UV light source at a preset running speed. The first UV light source includes multiple surface light sources, and the multiple surface light sources are sequentially spliced ​​to form a gate-like structure that surrounds the outer contour of the composite workpiece. The conditions for the first photocuring include: the emission wavelength of the first UV light source is 250~450nm, and the peak light intensity is 0.05~5W / cm². 2 The preset operating speed of the composite workpiece is 3~6 m / min, and the total irradiation energy density is 1~5 J / cm³. 2 .

5. The method according to claim 1, characterized in that, In step S2, the second photocuring is performed using a multi-axis actuator equipped with a second UV light source, and the maximum size of the light-emitting surface of the second UV light source is no more than 30cm. The conditions for the second photocuring include: the emission wavelength of the second UV light source is 250~450nm, and the peak light intensity is 0.1~5W / cm². 2 The moving speed of the second UV light source is 300~500mm / s, and the total irradiation energy density is 1~5J / cm³. 2 .

6. The method according to claim 1, characterized in that, In step S3, the natural environmental conditions include: humidity of 30-80% and temperature of 5-40℃; the preset time is 3-7 days; and / or, The first preset hardness is 3B or higher, and the second preset hardness is HB or higher.

7. An integrated coating system for implementing the method according to any one of claims 1 to 6, characterized in that, The system includes: A spraying unit is used to apply a double-curing coating to the inner and outer surfaces of the composite workpiece, and then flash-dry it to obtain a composite workpiece with a double-curing coating. A photocuring unit is used to perform a first photocuring on the outer surface of the composite workpiece with a dual-curing coating, and a second photocuring on the inner surface and the shadow area of ​​the outer surface of the composite workpiece with a dual-curing coating, so that the dual-curing coating reaches a first preset hardness, and a photocured composite workpiece is obtained. The settling unit is used to allow the photocured composite workpiece to stand in a natural environment for a preset time so that the dual-cured coating reaches a second preset hardness, which is higher than the first preset hardness.

8. A composite workpiece prepared by the method of any one of claims 1 to 6, or by the system of claim 7, wherein the composite workpiece includes a first structural component and a second structural component, the first structural component and the second structural component are made of different materials and the heat distortion temperature of the first structural component is higher than that of the second structural component, and a double-cured coating is formed on the inner and outer surfaces of the composite workpiece.

9. The composite workpiece according to claim 8, characterized in that, The first structural component is made of metallic materials, and the second structural component is made of non-metallic materials; and / or, The first structural component is a car body, and the second structural component is a car exterior component.

10. A car, characterized in that, Includes the composite workpiece as described in claim 8 or 9.

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