High-glossiness automobile exterior trimming part surface spraying process

Abstract

The invention provides a high-glossiness automobile exterior trimming part surface spraying technology, and relates to the technical field of spraying, the high-glossiness automobile exterior trimming part surface spraying technology comprises the following steps: S1, cold plasma surface treatment: starting a low-temperature plasma generation device, and preparing a low-temperature plasma working gas which is formed by mixing argon and oxygen according to a ratio of 3: 1; the discharge power is set to be in a range of 50-100W, and the pressure of the reaction chamber is controlled to be in a range of 100-300Pa. A micro-nano structure is formed on the surface of a workpiece through cold plasma, the bonding performance of the surface of the automobile exterior trimming part to a coating material is improved, and the adhesive force of a substrate and subsequent paint is enhanced; the plasma treatment gas ratio and discharge parameters are accurately controlled, the number and distribution density of surface active groups are effectively increased, and the interface bonding strength and durability between the coating and the substrate are improved.

Description

Technical Field

[0001] The invention relates to the technical field of spraying, and in particular to a high-gloss surface spraying process for automobile exterior trims. Background Art

[0002] Spraying technology refers to a surface treatment process that uses a spray gun or spraying equipment to evenly atomize and deposit paint, varnish or other functional coating materials on the surface of an object through pressure to form a protective, decorative or special functional coating film. Spraying technology is widely used in many industrial fields such as automobile manufacturing, mechanical equipment, home appliances, furniture, building materials, etc.

[0003] In the actual application process of existing spraying technology, the bonding strength between the coating and the workpiece substrate is insufficient. During the spraying process, the surface of the workpiece is often not effectively pretreated, and the surface state lacks effective control, which makes the coating adhesion unstable, resulting in defects such as peeling, shedding or local bulging of the coating. At the same time, the environmental control accuracy of the traditional spraying method is low, and it is easy to produce uneven sizes of paint mist particles, which directly affects the flatness and gloss effect of the coating surface, causing obvious orange peel phenomenon or uneven glossiness of the coating film. Therefore, improvements are needed. Summary of the invention

[0004] The purpose of the present invention is to solve the shortcomings of the prior art and to propose a high-gloss automotive exterior surface spraying process.

[0005] In order to achieve the above object, the present invention adopts the following technical scheme: a high gloss automotive exterior surface spraying process, comprising the following steps: S1, cold plasma surface treatment, turn on the low-temperature plasma generator, prepare the low-temperature plasma working gas, which is a mixture of argon and oxygen in a ratio of 3:1; set the discharge power in the range of 50-100W, control the pressure of the reaction chamber in the range of 100-300Pa, control the distance between the nozzle and the workpiece surface in the range of 80-120mm, and control the treatment time in the range of 30-60s; the workpiece moves at a uniform speed of 0.5-1m / min on the conveyor belt to promote the generation of micro-nano structures on the surface; the humidity is maintained in the range of 30%-50%, and after the ion bombardment is completed, a preliminary activated surface is obtained; S2, surface activation, spraying a surfactant on the preliminarily activated surface; the spraying pressure is maintained in the range of 0.2-0.4 MPa, and the nozzle diameter of the spray gun is in the range of 1.0-1.5 mm; after the solution is evenly covered, the surface temperature is maintained in the range of 40-50° C. by heating with an infrared lamp, and the heating period is controlled at 60-120 s to obtain an activated surface; S3, primer spraying, spraying the activated surface with primer, the primer is mixed with polyurethane resin, anionic water-based dispersant, leveling agent and solvent, and the ratio is 4:1:0.5:6-5:1.5:1:8; the negative pressure environment of 80-120Pa is maintained in the spraying room, the atomization pressure of the spray gun is in the range of 0.3-0.5MPa, and the spraying distance is controlled at 150-200mm; the rotation speed of the turntable in the spraying room is set at 230-500rpm; the room temperature is controlled in the range of 20-25℃, the humidity is controlled at 40%-50%, the spraying interval is about 20-40s, and it is repeated five times to obtain a primer layer.

[0006] Preferably, the method further comprises: S4, preheating the primer by microwave, performing microwave preheating treatment on the primer layer, setting the microwave output power in the range of 800-1200W, and controlling the heating period in the range of 40-80s; monitoring the primer surface temperature by an infrared thermometer and maintaining it in the range of 50-60°C; the microwave chamber is equipped with a rotating tray, and the rotation speed is set in the range of 3-6rpm to obtain a preheated primer layer; S5, color layer spraying, spraying the preheated primer layer with color layer paint; maintaining 70-120Pa in the spraying room, using an electrostatic spray gun, the electrostatic voltage is controlled in the range of 40-60kV, the spray gun moving speed is maintained in the range of 0.2-0.4m / s, and the spraying angle is 25-45°; the ambient temperature is maintained at 18-22°C, and the humidity is between 35%-45%. After the operation is completed, a color layer is obtained.

[0007] Preferably, the method further comprises: S6, curing the color layer by microwave, curing the color layer by microwave, wherein the microwave output power is in the range of 900-1300W, and the curing period is maintained in the range of 60-90s; the film temperature is collected in real time by an optical sensor and maintained between 60-70°C; a circulating fan is installed in the microwave chamber, and the wind speed is in the range of 0.5-1.0m / s to take away heat; the chamber pressure is maintained between 150-250Pa, and after the microwave irradiation is completed, a cured color layer is obtained; S7, varnish coating, covering the varnish material on the solidified color layer; using a two-component spray gun, the working pressure is maintained in the range of 0.25-0.45MPa, and the nozzle diameter is controlled at 1.2-1.8mm; using a laser thickness gauge to monitor the coating thickness, the thickness is between 20-30µm; the temperature of the spray chamber is maintained in the range of 20-26℃, and the humidity is 40%-50%, to obtain a varnish layer; S8, microwave curing of the varnish layer, performing microwave curing treatment on the varnish layer, the microwave source power is controlled in the range of 800-1200W, the curing period is in the range of 80-120s; the film layer temperature is maintained in the range of 50-65°C by collecting data with a contact thermocouple, and the turntable speed is 2-4rpm; the wind speed in the microwave chamber is controlled at 0.5-1.0m / s, and after the curing is completed, it enters a dust-free oven for 5-10min of static cooling to obtain a cured varnish layer.

[0008] Preferably, it also includes: S9, electron beam scanning treatment, performing low-energy electron beam scanning on the cured varnish layer, the electron beam energy is maintained in the range of 20-30keV, the beam density is controlled at 0.1-0.3mA / cm²; the scanning speed is maintained in the range of 100-300mm / s, and the workpiece is reciprocated in the XY direction in the vacuum chamber by a stepper motor; the beam spot diameter is set in the range of 2-5mm, the chamber pressure is maintained between 5×10^-3-1×10^-2Pa, the temperature is controlled in the range of 25-35℃, and the scanning period is about 5-10min, so as to obtain an electron beam treated layer; S10, gloss enhancement treatment, mirror polishing and surface finishing are performed on the electron beam treated layer, and a polishing agent is used to improve the overall reflectivity; the polishing device is equipped with a speed-adjustable polishing disc, the rotation speed is controlled in the range of 400-800rpm, and the surface is covered in a reciprocating manner, and the moving speed is in the range of 10-15mm / s; the surface gloss value is recorded by a gloss meter, and polishing is stopped after reaching the target, and the dust particles on the surface are blown off and the polishing residues are cleaned to obtain high-gloss automotive exterior parts.

[0009] Preferably, in step S2, the surfactant is a mixture of aminosilane, tertiary amine and methanol in a ratio of 1:0.5:2-1:1:3.

[0010] Preferably, in step S5, the color layer coating is mixed with acrylic resin, pigment dispersant, propylene glycol methyl ether acetate and solvent in a ratio of 3:2:1:4-4:3:1.5:5.

[0011] Preferably, in step S7, the varnish material is mixed with polyurethane resin, weathering agent, light stabilizer and solvent in a ratio of 3:1:0.5:5-4:1.2:0.8:6.

[0012] Preferably, in step S10, the polishing agent is mixed with cerium oxide particles, surface lubricating oil, citric acid and paraffin wax powder in a ratio of 1:1:0.5:1.5-2:2:1:3.

[0013] Compared with the prior art, the present invention forms a micro-nano structure on the surface of the workpiece through cold plasma, improves the bonding performance of the surface of the automotive exterior parts to the coating material, and strengthens the adhesion of the substrate to the subsequent coating; accurately controls the plasma treatment gas ratio and discharge parameters to effectively increase the number and distribution density of surface active groups, and improve the interface bonding strength and durability between the coating and the substrate. The combined use of surfactant spraying and infrared heating methods makes the surface active state more uniform and stable, and further guarantees the flatness and uniformity of the primer coating. Through the optimized combination of polyurethane resin, leveling agent and solvent components in a specific proportion in the primer formula, the leveling and glossiness of the spray coating are effectively improved, and the probability of coating defects is reduced. The negative pressure environment and the rotary spraying method work together to ensure that the atomized particles of the coating are finer and more evenly dispersed on the surface of the workpiece, achieving a dual improvement in the uniformity of the coating thickness and the surface gloss, and overall improving the coating quality and appearance visual effect of automotive exterior parts. The technical scheme of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0015] Figure 1 The present invention provides a preparation step diagram of a high-gloss automotive exterior surface spraying process. DETAILED DESCRIPTION

[0016] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0017] Embodiment 1, a high gloss automotive exterior surface spraying process, comprising the following steps: S1, cold plasma surface treatment, turn on the low-temperature plasma generator, prepare the low-temperature plasma working gas, which is a mixture of argon and oxygen in a ratio of 3:1; set the discharge power at 100W, the reaction chamber pressure at 300Pa, the distance between the nozzle and the workpiece surface at 120mm, and the treatment time at 60s; the workpiece moves at a constant speed of 1m / min on the conveyor belt to promote the generation of micro-nano structures on the surface; the humidity is maintained at 50%, and after the ion bombardment is completed, a preliminary activated surface is obtained; S2, surface activation, spraying surfactant on the preliminary activated surface; the spraying pressure is maintained at 0.4MPa, and the nozzle diameter of the spray gun is 1.5mm; after the solution is evenly covered, the surface temperature is maintained at 50℃ by infrared lamp heating, and the heating period is controlled at 120s to obtain the activated surface; S3, primer spraying, the activated surface is sprayed with primer, the primer is mixed with polyurethane resin, anionic water-based dispersant, leveling agent and solvent in a ratio of 5:1.5:1:8; the negative pressure environment of 120Pa is maintained in the spraying room, the atomization pressure of the spray gun is 0.5MPa, and the spraying distance is controlled at 200mm; the rotation speed of the turntable in the spraying room is set at 500rpm; the room temperature is controlled at 25℃, the humidity is controlled at 50%, the spraying interval is about 40s, and it is repeated five times to obtain a primer layer.

[0018] S4, microwave preheating primer, the primer layer is subjected to microwave preheating treatment, the microwave output power is set at 1200W, and the heating period is controlled at 80s; the primer surface temperature is monitored by an infrared thermometer and maintained at 60°C; the microwave chamber is equipped with a rotating tray, and the speed is set at 6rpm to obtain a preheated primer layer; S5, color layer spraying, spray the color layer paint on the preheated primer layer; maintain 120Pa in the spraying room, use an electrostatic spray gun, the electrostatic voltage is controlled at 60kV, the spray gun moving speed is maintained at 0.2m / s, and the spraying angle is 45°; the ambient temperature is maintained at 22℃, and the humidity is between 45%. After the operation is completed, the color layer is obtained.

[0019] S6, microwave curing of the color layer. The color layer is cured by microwave, the microwave output power is 1300W, and the curing period is maintained at 90s. The film temperature is collected in real time by an optical sensor and maintained at 70°C. A circulating fan is installed in the microwave chamber with a wind speed of 1.0m / s to take away heat. The chamber pressure is maintained at 250Pa. After the microwave irradiation is completed, a cured color layer is obtained. S7, varnish coating, covering the varnish material on the cured color layer; using a two-component spray gun, the working pressure is maintained at 0.45MPa, and the nozzle diameter is controlled at 1.8mm; using a laser thickness gauge to monitor the coating thickness, the thickness is 30µm; the spray room temperature is maintained at 20℃, the humidity is 50%, and the varnish layer is obtained; S8, microwave curing of the varnish layer. The varnish layer is subjected to microwave curing treatment. The microwave source power is controlled at 800 W and the curing period is 80 s. The film layer temperature is maintained at 50 °C by collecting data using a contact thermocouple and the turntable speed is 2 rpm. The wind speed in the microwave chamber is controlled at 0.5 m / s. After the curing is completed, the varnish layer is placed in a dust-free oven for 5 minutes of static cooling to obtain a cured varnish layer.

[0020] S9, electron beam scanning treatment, low-energy electron beam scanning is carried out on the cured varnish layer, the electron beam energy is maintained at 30keV, the beam density is controlled at 0.3mA / cm²; the scanning speed is maintained at 300mm / s, and the workpiece is reciprocated in the XY direction in the vacuum chamber by a stepper motor; the beam spot diameter is set at 5mm, the chamber pressure is maintained at 5×10^-3, the temperature is controlled at 35℃, and the scanning period is about 5min to obtain the electron beam treated layer; S10, gloss enhancement treatment, mirror polishing and surface finishing of the electron beam treated layer, use polishing agent to improve the overall reflectivity; the polishing device is equipped with a speed-adjustable polishing disc, the speed is controlled at 800rpm, and the surface is covered by reciprocating motion at a moving speed of 10mm / s; the surface gloss value is recorded by a gloss meter, and polishing is stopped when the target is reached, the surface dust particles are blown off and the polishing residue is cleaned to obtain high-gloss automotive exterior parts.

[0021] Cold plasma surface treatment is used to generate micro-nano structures on the workpiece surface, enhance the adhesion between the coating and the substrate, and improve the wettability and bonding performance of the material surface. In the surface activation treatment process, spray activator and infrared heating are used to effectively increase the reaction activity of the substrate surface, further improving the uniformity and density of the subsequent spray layer. In primer spraying, high-quality and uniformly thick base coatings are obtained through polyurethane resin ratio control, negative pressure environment and precise turntable speed control, laying the foundation for subsequent coating. Microwave preheating and curing provide conditions for uniform heating of the coating, effectively eliminate residual solvents and bubbles in the coating, significantly shorten the curing time and improve the coating structure. The stability of the structure; the electrostatic spraying and varnish coating process is carried out under strict environmental conditions and process parameter control, so that the paint particles are evenly distributed on the surface of the workpiece, the coating effect of the color layer and the varnish layer is enhanced, and the gloss and visual quality of the overall coating are significantly improved; the electron beam scanning processing process uses a low-energy beam to finely modify the surface, further improve the wear resistance, weather resistance and surface density of the coating, and effectively extend the service life of the coating; the final mirror polishing treatment optimizes the surface smoothness, significantly improves the overall visual texture, and comprehensively improves the decorative effect and durability of the coating, meeting the stringent requirements of automotive exterior parts for high gloss, high weather resistance and high wear resistance in actual applications.

[0022] In this embodiment, in step S2, the surfactant is a mixture of aminosilane, tertiary amine and methanol in a ratio of 1:0.5:2.

[0023] In this embodiment, in step S5, the color layer coating is mixed with acrylic resin, pigment dispersant, propylene glycol methyl ether acetate and solvent in a ratio of 4:3:1.5:5. The pigment dispersant is BASF Dispex Ultra PX 4585.

[0024] In this embodiment, in step S7, the varnish material is mixed with polyurethane resin, weathering agent, light stabilizer and solvent in a ratio of 4:1.2:0.8:6. The weathering agent is Ranbar KSN high weathering agent, and the light stabilizer is Basf BASF ultraviolet absorber Tinuvin 477-DW.

[0025] In this embodiment, in step S10, the polishing agent is mixed with cerium oxide particles, surface lubricating oil, citric acid and paraffin-based wax powder in a ratio of 1:1:0.5:1.5.

[0026] Embodiment 2, the steps are the same as those of Embodiment 1, except that: a high-gloss automotive exterior surface spraying process comprises the following steps: S1, cold plasma surface treatment, turn on the low-temperature plasma generator, prepare the low-temperature plasma working gas, which is a mixture of argon and oxygen in a ratio of 3:1; set the discharge power at 100W, the reaction chamber pressure at 150Pa, the distance between the nozzle and the workpiece surface at 80mm, and the treatment time at 40s; the workpiece moves at a constant speed of 1m / min on the conveyor belt to promote the generation of micro-nano structures on the surface; the humidity is maintained at 40%, and after the ion bombardment is completed, a preliminary activated surface is obtained; S2, surface activation, spraying surfactant on the preliminary activated surface; the spraying pressure is maintained at 0.4MPa, and the nozzle diameter of the spray gun is 1.0mm; after the solution is evenly covered, the surface temperature is maintained at 50°C by infrared lamp heating, and the heating period is controlled at 60s to obtain the activated surface; S3, primer spraying, the activated surface is sprayed with primer, the primer is mixed with polyurethane resin, anionic water-based dispersant, leveling agent and solvent in a ratio of 4:1:0.5:6; the negative pressure environment of 100Pa is maintained in the spraying room, the atomization pressure of the spray gun is 0.5MPa, and the spraying distance is controlled at 200mm; the rotation speed of the turntable in the spraying room is set at 500rpm; the room temperature is controlled at 25℃, the humidity is controlled at 50%, the spraying interval is about 40s, and it is repeated five times to obtain a primer layer.

[0027] S4, microwave preheating primer, the primer layer is subjected to microwave preheating treatment, the microwave output power is set at 1200W, and the heating period is controlled at 50s; the primer surface temperature is monitored by an infrared thermometer and maintained at 60°C; the microwave chamber is equipped with a rotating tray, and the rotation speed is set at 6rpm to obtain a preheated primer layer.

[0028] Experimental methods: 60° gloss measurement method: This test is carried out in accordance with GB / T 9754-2007 Determination of paint film gloss at 20°, 60° and 85° specular gloss and ASTM D523. First, place the sprayed and cured sample under constant temperature and humidity conditions (temperature 23±2℃, relative humidity 50±5%) for at least 24 hours to ensure the stability of the film properties. Then use a calibrated 60° angle gloss meter for testing. The specific steps are as follows: Place the sample flat on the test platform of the gloss meter, ensure that the contact surface between the paint film surface and the gloss meter probe is flat and free of contamination, and make the angle between the gloss meter's measuring beam and the sample surface 60°. After turning on the instrument, calibrate it on black glass and white standard plates first to make the instrument reading within the standard value range. After calibration, gently place the gloss meter probe on the surface of different areas of the sample, test at least 3 to 5 different points on each sample, and record the readings. During the test, factors that may affect the results, such as strong light interference from the surroundings, unstable operator holding, or scratches on the sample surface, should be avoided. In order to obtain more accurate data, the average value of the glossiness values ​​measured in different areas of the same sample surface can be taken as the final result. If it is necessary to evaluate the uniformity of sprayed workpieces in mass production, multiple workpieces should be randomly selected for the same operation, and the glossiness results should be collected and counted to determine the stability of the process. Finally, the measured glossiness is compared with the other sample data of the comparative example and the embodiment to evaluate the effect of each process parameter on the glossiness improvement of the film layer.

[0029] Adhesion (cross-cut method) test method: Adhesion test is mainly carried out according to GB / T 9286-1998 Cross-cut test for paint and varnish film, and can also refer to international standards such as ISO 2409 or ASTM D3359. The specific experimental steps are as follows: First, prepare the sample that has been sprayed and fully cured. If necessary, wipe the surface with a clean dust-free cloth to ensure dust and oil-free. Then select a suitable cross-cut knife according to the film thickness, and in accordance with the standard requirements, cross-cut the surface of the sample into a vertical and horizontal grid. Generally, a 1mm or 2mm spacing is used when the film thickness does not exceed 250μm. The depth of the cross-cut must ensure that it penetrates the paint film and reaches the substrate, but it should not cut into the substrate excessively to cause damage. After completing the cross-cutting, use a special tape (such as 3M tape) to stick to the surface of the cross-cut area, apply uniform pressure and hold for a few seconds, and then quickly peel it off at an angle of about 45° or 60°. Then observe the peeling of the paint film at the edge or inside of the grid, and judge according to the grading method in the standard (such as 0 to 5): 0 means no peeling of the paint film, the best adhesion; 5 means large-area peeling, the worst adhesion. During the operation, it is necessary to control the accuracy of the parallelism and spacing of the grid, and repeat the test in multiple areas to reduce accidental errors. After the test is completed, the average grade obtained by statistics is the adhesion grade of the sample. If necessary, the peeling edge can also be observed with the help of a microscope or a high-power magnifying glass to more carefully evaluate the bonding quality between the paint film and the substrate. This method can intuitively and quickly reflect the adhesion strength of the paint film to the substrate, which is of great significance for evaluating whether the automotive exterior parts can be stably attached in the actual service environment.

[0030] Pencil hardness test method: Pencil hardness determination can refer to GB / T 6739-2006 Determination of film hardness by pencil method for paint and varnish or ASTM D3363. Specifically, place the sample in a constant temperature and humidity environment for at least 24 hours to ensure that the film layer is in a stable state before hardness testing. The test uses a set of pencils with different hardness (usually from 6B to 6H), which are required to be sharpened into a consistent shape in advance according to the standard method: remove the wood part, expose the lead core to a length of about 3-5mm, and rub it vertically on sandpaper to keep the top of the lead core flat and without a gap. At the beginning of the test, fix the sample horizontally on the table, clamp the pencil on the hardness test stand, make the lead core at a fixed angle with the paint film surface (usually 45° or other specified angles), and push the pencil forward evenly with a pressure of about 750±10g or 1000±10g (depending on the standard requirements and the thickness of the paint film). If the pencil fails to scratch the paint film during the forward movement, use a harder pencil until obvious scratches or penetration appear; if the paint film is easily scratched, use a softer pencil and test step by step to find the highest hardness pencil grade that will not scratch the paint film under a certain load, which is the pencil hardness of the paint film. When testing, it should be noted that the evaluation of "scratch" should be based on revealing the base material or producing obvious depressions. Slight light marks on the surface are not considered real scratches. At the same time, the test needs to be repeated in at least three different areas, and the hardness values ​​are recorded and the consistent grade is taken as the final hardness evaluation result of the sample. The pencil hardness test has a certain reference significance for the scratch resistance and wear resistance of the paint film of automotive exterior parts, and can quickly and preliminarily determine the scratch resistance of the product in daily use.

[0031] Impact resistance test method: Impact resistance is usually tested using GB / T 1732-93 Determination of impact resistance of paint film or ASTM D2794. The test instrument is generally a drop ball or impact hammer impact tester. The principle is to release a heavy object at a certain height and let it hit the surface of the sample vertically to observe whether the paint film and the substrate are cracked, peeled or deformed. During the test, the sprayed and cured sample is first clamped flat on the impact tester with the paint film facing up. According to the thickness of the paint film and the actual use environment of the automotive exterior parts, select an appropriate impact height or weight (such as the standard requires the use of a 1kg or 2kg drop weight, released from a certain height). After releasing the drop weight, the drop weight impacts the sample instantly, and then the sample is removed and the paint film around the impact point is observed with the naked eye or a magnifying glass to see if there are cracks, peeling or bulging. The maximum impact value that the sample can withstand is usually expressed in terms of drop weight height or impact energy (kg cm or J). In order to ensure the reliability of the test, it is necessary to impact multiple times at different points to find the critical height or energy between the paint film being damaged and not damaged, or to directly give a height to determine whether the paint film can withstand the energy impact. This method can simulate the actual situation when the automotive exterior parts are hit by sand, stones, bumps, etc. during use, so as to evaluate the ability of the coating to withstand instantaneous impact in a short period of time. The results are usually quantified as "the highest impact value without damage" or "maximum impact energy". If the paint film is still intact after the test, it can be regarded as having excellent impact resistance.

[0032] Salt spray resistance time test method: The salt spray resistance test is mainly carried out according to GB / T 1771-2007 Determination of neutral salt spray resistance of paints and varnishes or ASTM B117, which is used to evaluate the corrosion resistance or environmental aging resistance of the paint film in a salt spray environment. First, the prepared sample needs to be placed in accordance with the standard requirements, usually in an environment with a temperature of (23±2)℃ and a relative humidity of (50±5)% for 24 hours to allow the coating to reach a relatively stable state. Then place the sample in the salt spray chamber at a certain angle (usually 15°~30°) to ensure that the paint film faces up and does not touch each other. The salt spray solution generally uses a 5% sodium chloride solution with a pH value controlled between 6.5 and 7.2. The experimental temperature is maintained at (35±2)℃, so that the salt spray solution is evenly sprayed onto the surface of the sample through the nozzle, forming a corrosive environment with high humidity and high salt content. The spray volume is controlled according to the standard requirements. The sample needs to be taken out at regular intervals (such as 24 hours) to observe whether there are defects such as blistering, cracking, shedding or rust on the surface of the paint film, and the performance is recorded. When the paint film is obviously corroded or peeled off from the substrate, it can be regarded as reaching the failure time. If a fixed test cycle is specified (such as 96 hours, 240 hours, 480 hours, etc.), it is necessary to compare whether damage occurs within the cycle and grade the damage. Ultimately, the salt spray resistance time obtained can reflect the length of time the coating remains intact in a salt spray environment, and is also an important basis for measuring the reliability of automotive exterior parts in harsh environments such as the seaside and salt-sprinkled roads in winter. This test can be combined with other aging tests (such as damp heat aging, ultraviolet aging, etc.) to comprehensively evaluate the environmental tolerance of the coating.

[0033] The finished materials prepared in Examples 1-2 were tested, wherein Comparative Example 1 is the process effect disclosed in Patent Publication No. CN114146881A, and the experimental results are as follows: Table 1 Performance test data As can be seen from Table 1, Example 1 and Example 2 show more excellent comprehensive performance in terms of gloss, adhesion and impact resistance compared with Comparative Example 1. This improvement is not only reflected in the fuller and more stable surface gloss after spraying, but also in the significant improvement in the coating hardness and resistance to external force damage. At the same time, the coating maintains a better protective effect in environmental tests such as salt spray resistance, indicating that the coordinated use of low-temperature plasma surface pretreatment, microwave curing and electron beam scanning technology proposed in the present invention has a significant effect on improving the quality of paint films on automotive exterior parts. In summary, the high-gloss exterior parts spraying process of the present invention can take into account mechanical and environmental stability while ensuring the decorative appearance, and better solves the problems of insufficient adhesion and poor gloss in traditional spraying processes, and fully meets the automotive industry's demand for high-quality and high-reliability surface treatment technology.

Claims

1. A high gloss automotive exterior surface spraying process, characterized in that: The following steps are involved: S1, cold plasma surface treatment, turn on the low-temperature plasma generator, prepare the low-temperature plasma working gas, which is a mixture of argon and oxygen in a ratio of 3:1; set the discharge power in the range of 50-100W, control the pressure of the reaction chamber in the range of 100-300Pa, control the distance between the nozzle and the workpiece surface in the range of 80-120mm, and control the treatment time in the range of 30-60s; the workpiece moves at a uniform speed of 0.5-1m / min on the conveyor belt to promote the generation of micro-nano structures on the surface; the humidity is maintained in the range of 30%-50%, and after the ion bombardment is completed, a preliminary activated surface is obtained; S2, surface activation, spraying a surfactant on the preliminarily activated surface; the spraying pressure is maintained in the range of 0.2-0.4 MPa, and the nozzle diameter of the spray gun is in the range of 1.0-1.5 mm; after the solution is evenly covered, the surface temperature is maintained in the range of 40-50° C. by heating with an infrared lamp, and the heating period is controlled at 60-120 s to obtain an activated surface; S3, primer spraying, spraying the activated surface with primer, the primer is mixed with polyurethane resin, anionic water-based dispersant, leveling agent and solvent, and the ratio is 4:1:0.5:6-5:1.5:1:8; the negative pressure environment of 80-120Pa is maintained in the spraying room, the atomization pressure of the spray gun is in the range of 0.3-0.5MPa, and the spraying distance is controlled at 150-200mm; the rotation speed of the turntable in the spraying room is set at 230-500rpm; the room temperature is controlled in the range of 20-25℃, the humidity is controlled at 40%-50%, the spraying interval is about 20-40s, and it is repeated five times to obtain a primer layer.

2. The high gloss automotive exterior parts surface spraying process according to claim 1, characterized in that: Also includes: S4, preheating the primer with microwaves, performing microwave preheating treatment on the primer layer, setting the microwave output power in the range of 800-1200W, and controlling the heating period in the range of 40-80s; monitoring the primer surface temperature by an infrared thermometer and maintaining it in the range of 50-60°C; the microwave chamber is equipped with a rotating tray, and the rotation speed is set in the range of 3-6rpm to obtain a preheated primer layer; S5, color layer spraying, spraying the preheated primer layer with color layer paint; maintaining 70-120Pa in the spraying room, using an electrostatic spray gun, the electrostatic voltage is controlled in the range of 40-60kV, the spray gun moving speed is maintained in the range of 0.2-0.4m / s, and the spraying angle is 25-45°; the ambient temperature is maintained at 18-22°C, and the humidity is between 35%-45%. After the operation is completed, a color layer is obtained.

3. The high gloss automotive exterior parts surface spraying process according to claim 2, characterized in that: Also includes: S6, microwave curing of the color layer, the color layer is cured by microwave, the microwave output power is in the range of 900-1300W, and the curing period is maintained in the range of 60-90s; the film temperature is collected in real time by an optical sensor and maintained between 60-70°C; a circulating fan is installed in the microwave chamber, and the wind speed is in the range of 0.5-1.0m / s to take away heat; the chamber pressure is maintained between 150-250Pa, and after the microwave irradiation is completed, a cured color layer is obtained; S7, varnish coating, covering the varnish material on the solidified color layer; using a two-component spray gun, the working pressure is maintained in the range of 0.25-0.45MPa, and the nozzle diameter is controlled at 1.2-1.8mm; using a laser thickness gauge to monitor the coating thickness, the thickness is between 20-30µm; the temperature of the spray chamber is maintained in the range of 20-26℃, and the humidity is 40%-50%, to obtain a varnish layer; S8, microwave curing of the varnish layer, performing microwave curing treatment on the varnish layer, the microwave source power is controlled in the range of 800-1200W, the curing period is in the range of 80-120s; the film layer temperature is maintained in the range of 50-65°C by collecting data with a contact thermocouple, and the turntable speed is 2-4rpm; the wind speed in the microwave chamber is controlled at 0.5-1.0m / s, and after the curing is completed, it enters a dust-free oven for 5-10min of static cooling to obtain a cured varnish layer.

4. The high gloss automotive exterior parts surface spraying process according to claim 3, characterized in that: Also includes: S9, electron beam scanning treatment, low-energy electron beam scanning is carried out on the cured varnish layer, the electron beam energy is maintained in the range of 20-30keV, the beam current density is controlled at 0.1-0.3mA / cm²; the scanning speed is maintained in the range of 100-300mm / s, and the workpiece is reciprocated in the XY direction in the vacuum chamber by a stepper motor; the beam spot diameter is set in the range of 2-5mm, the chamber pressure is maintained between 5×10^-3-1×10^-2Pa, the temperature is controlled in the range of 25-35℃, and the scanning period is about 5-10min to obtain an electron beam treated layer; S10, gloss enhancement treatment, mirror polishing and surface finishing are performed on the electron beam treated layer, and a polishing agent is used to improve the overall reflectivity; the polishing device is equipped with a speed-adjustable polishing disc, the rotation speed is controlled in the range of 400-800rpm, and the surface is covered in a reciprocating manner, and the moving speed is in the range of 10-15mm / s; the surface gloss value is recorded by a gloss meter, and polishing is stopped after reaching the target, and the dust particles on the surface are blown off and the polishing residues are cleaned to obtain high-gloss automotive exterior parts.

5. The high gloss automotive exterior surface spraying process according to claim 1, characterized in that: In step S2, the surfactant is prepared by mixing aminosilane, tertiary amine and methanol in a ratio of 1:0.5:2-1:1:

3.

6. The high gloss automotive exterior surface spraying process according to claim 2, characterized in that: In step S5, the color layer coating is mixed with acrylic resin, pigment dispersant, propylene glycol methyl ether acetate and solvent in a ratio of 3:2:1:4-4:3:1.5:

5.

7. The high gloss automotive exterior parts surface spraying process according to claim 3, characterized in that: In step S7, the varnish material is mixed with polyurethane resin, weathering agent, light stabilizer and solvent in a ratio of 3:1:0.5:5-4:1.2:0.8:

6.

8. The high gloss automotive exterior parts surface spraying process according to claim 4, characterized in that: In step S10, the polishing agent is mixed with cerium oxide particles, surface lubricating oil, citric acid and paraffin wax powder in a ratio of 1:1:0.5:1.5-2:2:1:3.

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