Spraying method for wear-resistant layer of automobile part

Abstract

The invention discloses a spraying method for a wear-resistant layer of an automobile part. The method comprises the following steps: S1, pretreating the automobile spare parts; s2, spraying primer on the automobile parts; and S3, spraying finish paint on the automobile parts. In order to solve the problem that wear resistance is affected by uneven thickness and low adhesive force of water-based paint sprayed on plastic auto parts, the system of the method performs interface plasma flame pretreatment and uniform distribution of conductive paint, and realizes accurate and controllable spraying of the auto parts in combination with electrostatic spraying. Wherein during primer spraying, secondary primer is negatively charged through high-voltage static electricity, and conductive agents in a secondary primer coating are uniformly dispersed by utilizing mutual repulsion of the conductive agents, so that a primer layer with uniform resistance is obtained; by uniformly controlling the resistance of the primer layer of the automobile part, when the finish paint is subjected to electrostatic spraying, the finish paint is uniformly and stably adsorbed on the surface of the automobile part, the thickness is uniform, sagging is avoided, a smooth coating is formed, and the adhesive force and the wear resistance of the coating are remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of automotive parts painting, and particularly to a spraying method for a wear-resistant layer of automotive parts. Background Art

[0002] With the rapid development of the new energy vehicle industry, the demand for integrated, modular, and lightweight automotive parts has increased sharply. In recent years, functional plastic technology has continuously broken through, and more and more automotive parts made of functional plastics are being used. Plastic parts are lighter than metal parts, which can significantly reduce the overall weight of the vehicle and is of great significance for extending the driving range of electric vehicles. Moreover, plastic has a low cost and can be easily injection-molded into various complex shapes, greatly improving the design freedom, meeting the innovative and personalized requirements of automotive exterior and interior decorations, quickly adapting to the integrated and modular assembly requirements of continuously innovating automotive parts, and promoting the systematic upgrade of automotive parts manufacturing technology.

[0003] New functional plastics such as acrylonitrile-butadiene-styrene copolymer (ABS), polyurethane (PU), and polyphenylene sulfide (PPS) are outstanding in terms of dimensional stability, chemical resistance, high-temperature resistance, etc., and have become the leading materials for automotive parts. For example, ABS has excellent toughness, strength, and wear resistance, and is widely used in automotive parts such as bumpers, instrument panels, consoles, grilles, lamp housings, interior trim panels, and armrests; polyphenylene sulfide (PPS) can be used for automotive parts such as automotive engine control device housings, lamp bases, and radiators after being reinforced and stiffened with glass fiber.

[0004] After injection molding, automotive parts made of plastic generally need to be subjected to surface spraying treatment. On the one hand, the products after surface spraying have a uniform and bright color, which can play a beautiful visual role; on the other hand, the surface coating can improve the corrosion resistance, wear resistance, etc. of the parts, and increase the service life of automotive parts.

[0005] Since most of the interfaces of automotive parts made of plastic are non-polar interfaces, non-polar solvent-based coatings have always had good bonding properties with plastic interfaces, but the VOCs content is relatively high. According to the requirements of automotive production environment evaluation, the national mandatory standard "GB 24409-2020 Limits of Hazardous Substances in Vehicle Coatings" strictly restricts the use of solvent-based coatings in automotive-related parts, and encourages the use of water-based coatings, solvent-free coatings, powder coatings, low-VOCs coatings, or environmentally friendly coatings with zero VOCs content.

[0006] Compared with traditional solvent-based coatings, waterborne coatings have extremely low VOCs and are more environmentally friendly. However, existing waterborne coatings have problems such as insufficient coating adhesion, more coating defects, and greater construction difficulty when coating plastic automotive parts. This is mainly because waterborne coatings are polar coatings with a relatively large surface tension and cannot well wet the non-polar plastic interface, resulting in insufficient adhesion after spraying, and the coating is prone to peeling, cracking, and bubbling. Moreover, waterborne coatings are prone to shrinkage on the plastic surface and it is difficult to form a continuous and uniform coating, thus affecting the wear resistance of the coating.

[0007] In order to form a uniformly dispersed, highly adhesive, and wear-resistant coating of waterborne coatings on the surface of plastic automotive parts, the existing technology has carried out roughening and polarization treatment on the plastic interface, but the effect is limited in improving the coating adhesion, and then the wear resistance of the coating is difficult to meet the design requirements. Moreover, when spraying waterborne coatings with polarity on plastic automotive parts, the initial adhesion of the coating is poor and it is extremely prone to sagging, resulting in uneven thickness of the paint surface, reduced flatness and gloss.

[0008] Electrostatic spraying technology has been maturely applied in the spraying of metal parts. It mainly uses the high-voltage electric field of the spray gun to generate a corona region, making the paint particles negatively charged, and the workpiece to be sprayed is grounded and positively charged. Under the action of the high-voltage electrostatic field, the paint microparticles are ejected and evenly adsorbed on the surface of the metal part under the influence of the electric field. The spraying process has no paint splashing and no sagging, greatly saving paint. Electrostatic spraying not only has uniform and controllable thickness, but also has strong adhesion, uniform coating, and high gloss, and is easy to realize automated pipeline spraying operations.

[0009] However, when using electrostatic spraying for plastic automotive parts, due to the plastic material of the workpiece, the high-resistance characteristic makes it difficult to achieve electrostatic spraying. The existing technology mainly pre-treats the surface of the plastic part to form a conductive layer to reduce the resistance, so that the surface resistance of the plastic part is reduced, and a high-voltage electrostatic field can be formed, thus meeting the requirements of electrostatic spraying. For example, Chinese Invention Patent Publication No. CN113798148B discloses a pre-treatment process for ABS plastic parts before painting. It uses an amine salt compound as a conductive agent and isopropanol and pure water to prepare a conductive liquid, and sprays a fine mist to reduce the surface resistance of the ABS plastic part. Chinese Invention Patent Publication No. CN104941885B discloses a process for electrostatic painting on a non-conductive substrate. This process reduces the resistance by forming a uniform, extremely thin and non-flowing conductive water film on the surface of the workpiece. Although the above technologies reduce the resistance of plastic parts to meet the needs of electrostatic spraying through relatively simple methods, due to the fact that the conductive water film is extremely prone to change due to changes in the environment, temperature, parking time, etc., in specific practices, the resistance uniformity of its interface is poor, there is local evaporation of the conductive water film, which easily leads to uneven thickness of the paint adsorbed on the workpiece and obvious sagging, affecting the film-forming effect of the workpiece coating, having a greater impact on the coating adhesion and wear resistance, and easily producing more defective products. Summary of the Invention

[0010] To improve the adhesion and uniformity of waterborne coatings sprayed on plastic automotive parts and enhance the wear resistance of the parts, the present invention discloses a spraying method for a wear-resistant layer of automotive parts. By increasing the conductivity and resistance uniformity of the surface of plastic automotive parts, the waterborne coating is evenly adsorbed at the interface of the parts, with strong adhesion, no sagging, and significantly increased wear resistance.

[0011] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0012] A spraying method for a wear-resistant layer of automotive parts, comprising the following steps:

[0013] S1. Pretreatment of automotive parts:

[0014] S11. Clean the automotive parts to remove the surface release agent and oil.

[0015] S12. Fix the automotive parts on the suspension track and suspend them in the air, dry them, and use compressed air to blow and discharge static electricity on the parts through a high-pressure nozzle.

[0016] S13. The automotive parts enter the plasma flame treatment chamber through the suspension track, and the plasma flame moves uniformly up and down and left and right to uniformly activate the surface.

[0017] S2. Spray primer on the automotive parts:

[0018] S21. The automotive parts enter the primary primer spraying chamber through the suspension track, spray the primary primer, transfer to the pre-baking chamber, pre-bake at 80 - 90 °C for 3 - 5 min; air-cool to 20 - 25 °C.

[0019] S22. The automotive parts enter the secondary primer spraying chamber through the suspension track, spray the secondary primer, bake at 50 - 60 °C for 30 - 60 min, and cool naturally; wherein the secondary primer is a conductive paint with a conductivity ≤ 10 6 Ω prepared by adding a conductive agent; the secondary primer spraying is carried out using a high-voltage electrostatic spray gun.

[0020] S3. Spray topcoat on the automotive parts:

[0021] S31. Randomly check that the surface grounding resistance of the automotive parts ≤ 10 6 Ω, transfer to the electrostatic spraying chamber, ground the automotive parts, and use a rotary cup electrostatic spraying machine to evenly spray the waterborne coating as the topcoat on the surface of the automotive parts, and send them to the drying oven, and bake at 50 - 60 °C for 60 - 120 min.

[0022] Preferably, the material of the automotive parts is one of ABS, PU, PPS, PP, PE, and PBT.

[0023] Preferably, for the cleaning, a plastic degreaser PARCO PLASTIC CLEANER 2595 from Henkel of Germany is used as the cleaning agent, which can effectively remove the surface release agent and oil stains carried during the injection molding process of plastic automotive parts.

[0024] Preferably, the plasma flame selects oxygen plasma. Through the treatment of oxygen plasma, chemical reactions will occur at the interface of automotive parts, generating a large number of polar functional groups such as hydroxyl groups, increasing the surface polarity and hydrophilicity, improving the wettability and bonding performance. The highly active particles generated increase the surface roughness of automotive parts, thereby increasing the plastic surface energy, significantly improving the hydrophilicity of the plastic surface, and enhancing the adhesion between the waterborne coating and the plastic interface.

[0025] Particularly preferably, the treatment time of the plasma flame is determined by the surface energy of the automotive parts reaching the set requirements. Through random inspection, the surface energy of the automotive parts reaching above 55 mN / m is sufficient. The surface energy of plastic automotive parts is generally less than 30 mN / m, while the surface energy of waterborne coatings is relatively high. By roughening and polarizing the interface of automotive parts, its surface energy is increased, making it easier to be wetted by waterborne coatings.

[0026] Preferably, the first primer is a commercially available waterborne modified acrylic paint specifically for plastic parts spraying, and particularly preferably a waterborne epoxy modified acrylic paint.

[0027] Preferably, the second primer is prepared by adding a conductive agent to the waterborne modified acrylic paint, and the resistance is adjusted by adding at least one of conductive agents such as aluminum powder, copper powder, carbon nanotubes, and conductive carbon black.

[0028] Further preferably, the resistance of the second primer is (0.1 - 0.7)×10 6 Ω.

[0029] Preferably, the spraying control thickness range of the first primer is 30 - 40 μm; the spraying control thickness range of the second primer is 15 - 20 μm.

[0030] Preferably, the first primer is sprayed by air spraying, the jet pressure is controlled at 0.35 - 0.50 MPa, and the distance between the spray gun and the surface of the automotive parts is controlled at 25 - 40 cm.

[0031] Preferably, the electrostatic high voltage of the high - voltage electrostatic spray gun is set at 40 - 50 kV, and the spraying pressure is controlled at 0.35 - 0.4 MPa.

[0032] The second - level primer is sprayed using a high - voltage electrostatic spray gun. The negative high voltage generated by a high - voltage electrostatic generator is led to the spray gun, causing the second - level primer to carry a negative charge. When the negatively charged second - level primer is sprayed, the coating particles carry negative charges and the conductive agents repel each other and disperse evenly, so that the second - level primer forms a uniform coating, ensuring that the obtained uniform coating has a uniform resistance.

[0033] Preferably, the water - borne coating is selected from one of commercially available water - borne epoxy coatings, water - borne epoxy - modified acrylic coatings, water - borne acrylic coatings, water - borne alkyd coatings, and water - borne polyurethane coatings. The resistance value of the water - borne coating is 20 - 50 MΩ so that it can be effectively charged during corona discharge.

[0034] Preferably, the spray cup of the rotary cup electrostatic spraying machine is connected to a negative electrostatic high voltage of 60 - 90 kV. The rotary cup electrostatic spraying machine uses a high - speed rotating airflow to atomize the water - borne coating into fine particles, which evenly adhere to the surface of automotive parts under the action of an electrostatic field, forming a smooth coating. The rotary cup electrostatic spraying machine is controlled by a robot, greatly increasing the work efficiency and achieving energy - saving and emission - reduction effects.

[0035] Preferably, the spraying control thickness range of the topcoat is 40 - 50 μm.

[0036] When spraying water - borne coatings on plastic - material automotive parts, there are problems such as poor adhesion, uneven coating thickness, and easy sagging, which in turn affect the wear resistance and appearance quality of the coating. The spraying method of the present invention uses the negative high voltage generated by a high - voltage electrostatic generator for spraying the second - level primer, causing the second - level primer to carry a negative charge. When the negatively charged second - level primer is sprayed, the conductive agents dispersed therein repel each other and thus disperse evenly, overcoming the technical problem of difficult dispersion of conductive agents, so that the second - level primer forms a uniform coating. This uniform coating ensures the uniformity of the surface resistance of automotive parts. By uniformly controlling the resistance of the surface of automotive parts, when electrostatically spraying the topcoat, the topcoat will be evenly and stably adsorbed on the surface of automotive parts, with uniform thickness, avoiding sagging, significantly improving the adhesion and wear resistance of the coating, and enhancing the consistency of batch spraying.

[0037] The spraying method of a wear - resistant layer of automotive parts in the present invention has beneficial effects as follows:

[0038] (1) The method of the present invention makes the second - level primer carry a negative charge through high - voltage static electricity, and uses the mutual repulsion of conductive agents to evenly disperse the conductive agents in the second - level primer coating, thereby obtaining a primer layer with uniform resistance; by uniformly controlling the resistance of the primer layer of automotive parts, when electrostatically spraying the topcoat, the topcoat will be evenly and stably adsorbed on the surface of automotive parts, with uniform thickness, avoiding sagging, and realizing precisely controllable spraying of automotive parts.

[0039] (2) The method of the present invention performs interface plasma flame pretreatment on the plastic automotive parts system and uniform distribution of conductive paint, combined with electrostatic spraying, to form a smooth coating on the surface of the sprayed automotive parts, significantly improving the adhesion and wear resistance of the coating.

[0040] (3) The method of the present invention can be used for the transformation of existing conventional waterborne paint spraying production, improving the application technology level of waterborne paint spraying on automotive parts, providing technical support for the intelligent automotive parts spraying line, and improving the yield requirements of industrial spraying. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a process flow diagram of the spraying method for the wear-resistant layer of the automotive parts of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0042] To enable those skilled in the art to further understand the technical means, technical objectives, and technical effects achieved by the present invention, the present invention will be described in detail below in conjunction with embodiments. Figure 1 It is a process flow diagram of the spraying method for the wear-resistant layer of the automotive parts of the present invention. Through the process flow diagram, it is convenient for those skilled in the art to intuitively understand the spraying method. Based on the described disclosed embodiments, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of the present invention's disclosure and protection.

[0043] Embodiment 1

[0044] S1. Pretreatment of automotive parts made of ABS material:

[0045] S11. Prepare a cleaning solution by mixing the degreaser PARCO PLASTIC CLEANER 2595 and water in a volume ratio of 1:5. Immerse the automotive parts in the cleaning solution for 10 minutes, and then rinse with clean water to remove the surface release agent and oil.

[0046] S12. Fix the cleaned automotive parts on the suspension track and suspend them in the air, dry them, and use compressed air to blow through the high-pressure nozzle for corona discharge to eliminate static electricity.

[0047] S13. Let the automotive parts enter the plasma flame treatment chamber through the suspension track, and uniformly activate the surface by moving the oxygen plasma flame up and down and left and right at a constant speed until the surface energy of the automotive parts can reach more than 55 mN / m.

[0048] S2. Spray primer on the automotive parts:

[0049] S21. The auto parts enter the primary primer spraying chamber through the suspension track. The primary primer uses a commercially available waterborne epoxy-modified acrylic paint with a viscosity (No. 4 cup) of 40S. Air spraying is adopted, the jet pressure is controlled at 0.35 MPa, the distance between the spray gun and the surface of the auto parts is controlled at 30 cm, and the designed spraying thickness is 35 μm. After spraying, it is transferred to the pre-baking chamber and pre-baked at 80 °C for 3 min, and then air-cooled to 25 °C.

[0050] S22. The auto parts enter the secondary primer spraying chamber through the suspension track. A conductive agent, aluminum powder, is added to the waterborne modified acrylic paint to prepare the secondary primer with a resistance of (0.1 - 0.7)×10 6 Ω. High-voltage electrostatic spraying is adopted, the electrostatic high voltage is set at 50 kV, the spraying pressure is controlled at 0.4 MPa, and the designed spraying thickness is 20 μm. The negative high voltage generated by the high-voltage electrostatic generator is led to the spray gun to make the secondary primer carry negative charges. When the negatively charged secondary primer is sprayed, the paint particles repel each other due to the negative charges and are evenly dispersed by the conductive agent, so that the secondary primer forms a uniform coating, which is baked at 50 °C for 60 min and then naturally cooled.

[0051] S3. Spraying topcoat on the auto parts:

[0052] S31. Randomly check that the surface grounding resistance of the auto parts ≤ 10 6 Ω, then transfer it to the electrostatic spraying chamber. Ground the auto parts, use a rotary cup electrostatic spraying machine, connect the negative electrostatic high voltage of 80 kV, use the ABS special waterborne acrylic paint (provided by Anhui Sigel Coating Technology Co., Ltd., the paint resistance value is 30 MΩ) as the topcoat, use the high-speed rotating air flow to atomize the waterborne paint into fine particles, and evenly adhere to the surface of the auto parts under the action of the electrostatic field. The paint flow is controlled at 115 mL / min, the spraying distance is 15 cm, forming a smooth coating, and the designed spraying thickness is 42 μm. Then send it into the drying oven and bake at 60 °C for 60 min.

[0053] Example 2

[0054] S1. Pretreatment of auto parts with 35% glass fiber reinforced polyphenylene sulfide (PPS):

[0055] S11. Prepare a cleaning solution by mixing the degreaser PARCO PLASTIC CLEANER 2595 and water in a volume ratio of 1:5. Immerse the auto parts in the cleaning solution for 10 min, and then rinse with clean water to remove the surface release agent and oil.

[0056] S12. Fix the cleaned auto parts on the suspension track and suspend them, dry them, and use compressed air to blow through the high-pressure nozzle for corona discharge to purge the parts and eliminate static electricity.

[0057] S13. The automotive parts enter the plasma flame treatment chamber through the suspension track, and the surface is evenly activated by the oxygen plasma flame moving uniformly up and down and left and right until the surface energy of the automotive parts reaches more than 55 mN / m;

[0058] S2. Primer spraying on automotive parts:

[0059] S21. The automotive parts enter the primary primer spraying chamber through the suspension track. The primary primer uses a commercially available waterborne polyurethane coating with a viscosity (No. 4 cup) of 55 S. Air spraying is used, the jet pressure is controlled at 0.35 MPa, the distance between the spray gun and the surface of the automotive parts is controlled at 30 cm, and the designed spraying thickness is 35 μm; after spraying, it is transferred to the pre-baking chamber and pre-baked at 80 °C for 5 min; air-cooled to 25 °C;

[0060] S22. The automotive parts enter the secondary primer spraying chamber through the suspension track. Conductive agent conductive carbon black is added to the waterborne modified acrylic coating to prepare the resistance of the secondary primer to be (0.1 - 0.7)×10 6 Ω; High-voltage electrostatic spraying gun is used for spraying, the electrostatic high voltage is set at 45 kV, the spraying pressure is controlled at 0.4 MPa, and the designed spraying thickness is 20 μm; The negative high voltage generated by the high-voltage electrostatic generator is led to the spray gun to make the secondary primer carry negative charges. When the negatively charged secondary primer is sprayed, the coating particles repel each other due to the negative charges and are evenly dispersed, so that the secondary primer forms a uniform coating, baked at 50 °C for 60 min, and cooled naturally;

[0061] S3. Topcoat spraying on automotive parts:

[0062] S31. Randomly check that the surface grounding resistance of the automotive parts ≤ 10 6 Ω, transfer to the electrostatic spraying chamber, ground the automotive parts, use a rotary cup electrostatic spraying machine, connect the negative electrostatic high voltage to 80 kV, use the waterborne polyurethane coating as the topcoat, the coating resistance value is 40 MΩ, use the high-speed rotating air flow to atomize the waterborne coating into fine particles, and evenly adhere to the surface of the automotive parts under the action of the electrostatic field to form a smooth coating. The coating flow rate is controlled at 115 mL / min, the spraying distance is 15 cm, and the designed spraying thickness is 50 μm; sent to the drying oven and baked at 50 °C for 120 min.

[0063] Comparative Example 1

[0064] S1. Pretreatment of automotive parts made of ABS material:

[0065] S11. Prepare a cleaning solution by mixing the degreaser PARCO PLASTIC CLEANER 2595 and water in a volume ratio of 1:5. Immerse the automotive parts in the cleaning solution for 10 min, then rinse with clean water to remove the surface release agent and oil;

[0066] S12. Fix the cleaned auto parts on the suspension track and suspend them in the air for drying. Then, use compressed air to blow and purge the parts through a high-pressure nozzle with corona discharge to eliminate static electricity.

[0067] S13. Let the auto parts enter the plasma flame treatment chamber through the suspension track. Uniformly activate the surface by moving the oxygen plasma flame up and down and left and right at a constant speed until the surface energy of the auto parts reaches more than 55 mN / m.

[0068] S2. Spray primer on the auto parts:

[0069] S21. Let the auto parts enter the first-stage primer spraying chamber through the suspension track. The first-stage primer uses a commercially available waterborne epoxy-modified acrylic paint with a viscosity (No. 4 cup) of 40 S. Use air spraying, control the jet pressure at 0.35 MPa, control the distance between the spray gun and the surface of the auto parts at 30 cm, and the designed spraying thickness is 55 μm. After spraying, transfer to the pre-baking chamber and pre-bake at 80 °C for 3 min. Air-cool to 25 °C.

[0070] S22. Let the auto parts enter the second-stage primer spraying chamber through the suspension track and spray a water film on the surface of the parts.

[0071] S3. Spray topcoat on the auto parts:

[0072] Transfer to the electrostatic spraying chamber, ground the auto parts, use a rotary cup electrostatic spraying machine, connect the negative electrostatic high voltage to 80 kV, use the special ABS waterborne acrylic paint (provided by Anhui Siegel Coating Technology Co., Ltd., the paint resistance value is 30 MΩ) as the topcoat, use the high-speed rotating airflow to atomize the waterborne paint into fine particles, and uniformly adhere to the surface of the auto parts under the action of the electrostatic field. Control the paint flow at 115 mL / min and the spraying distance at 15 cm to form a smooth coating, and the designed spraying thickness is 42 μm. Send it to the drying oven and bake at 60 °C for 60 min.

[0073] This comparative example is carried out according to the spraying of Example 1, with the difference that the currently disclosed water film is used as the conductive film.

[0074] Comparative Example 2

[0075] Carry out the spraying according to Example 1, with the difference that during the topcoat spraying, conventional air spraying is used.

[0076] Comparative Example 3

[0077] Carry out the spraying according to Example 1, with the difference that during the spraying of the second-stage primer, conventional air spraying is used.

[0078] Comparative Example 4

[0079] Carry out the spraying according to Example 1, with the difference that the auto parts are not treated with plasma.

[0080] Performance Testing of Automobile Parts Coatings

[0081] Test the appearance, coating thickness, and adhesion of the sprayed parts coatings in Examples 1-2 and Comparative Examples 1-4. All test pieces are placed at 50 °C for 48 h to eliminate the influence of coating curing inconsistency on the test.

[0082] (1) Refer to GB / T 8807 "Test Method for Specular Gloss of Plastics" to measure the gloss of GLOSS20°. If the leveling effect of the sprayed film is good and the surface is smooth and flat, its gloss is relatively high. The leveling effect of the sprayed coating is judged by the gloss, and the surface gloss of each sprayed sample is shown in Table 1.

[0083] (2) Use an ultrasonic thickness gauge to nondestructively detect the coating thickness at 5 different points of the automobile parts. The thickness difference (△t) between the thickest and thinnest points is used as the maximum deviation to analyze the thickness uniformity of the coating. The test data are recorded in Table 1.

[0084] (3) Refer to GB / T9286-2021 "Cross-Cut Test for Paints and Varnishes" to test the adhesion grade of the coating. The test results of the coating adhesion grade are shown in Table 1. A 2b drive multi-edge cutting tool is used for cross-cutting, and the adhesion is divided into five grades after cross-cutting, where:

[0085] Grade 0: The edges of the coating scratches are completely smooth, without any signs of peeling or flaking.

[0086] Grade 1: There is slight peeling at the intersections of the coating scratches, but the affected cross-cut area does not exceed 5%.

[0087] Grade 2: There is slight peeling or flaking at the intersections and cutting edges of the coating scratches, and the affected cross-cut area is greater than 5% but does not exceed 15%.

[0088] Grade 3: There is obvious peeling or flaking at the cutting edges of the coating scratches, and the affected cross-cut area is greater than 15% but does not exceed 35%.

[0089] Table 1: Performance of Automobile Parts Coatings

[0090]

[0091] Through the coating performance test of the sprayed automotive parts, the coating sprayed by the method of the present invention shows a smooth surface, high gloss, uniform and plump coating, no flow marks, strong adhesion, and good wear resistance. In Comparative Example 1, the currently disclosed electrostatic spraying using a water film as a conductive film is adopted. Due to the instability of the water film, there are still problems of uneven interface resistance, large quality differences among batches, uneven coating thickness, and flow marks in dot distribution. In Comparative Example 2, conventional air spraying is adopted, and the paint has no adsorption on the surface of the parts, with poor adhesion and uniformity, easy to appear flow marks, uneven thickness, and poor adhesion, and it is difficult to obtain automotive parts with a high wear-resistant coating. In Comparative Example 3, when spraying the second primer, conventional air spraying is directly adopted, the uniformity of the distribution of the conductive agent in the conductive coating is limited, the resistance of each point is uneven, and the adsorption uniformity is affected when electrostatically spraying the topcoat, thereby affecting the thickness uniformity and adhesion uniformity of the coating.

Claims

1. A method for spraying a wear-resistant layer of an automobile part, characterized in that: The following steps are involved: S1. Pretreatment of automotive parts: S11. Clean the auto parts and remove the surface release agent and oil stains; S12. The auto parts are fixed on the suspension track and hung in the air for drying. The parts are blown by corona discharge of compressed air through a high-pressure nozzle to eliminate static electricity. S13. Auto parts enter the plasma flame treatment chamber via a suspension track, and the plasma flame moves up and down and left and right at a uniform speed to evenly activate the surface; S2. Auto parts spray primer: S21. The auto parts enter the primary primer spraying room through the suspension track, and are sprayed with the primary primer. Then they are transferred to the pre-baking room and pre-baked at 80-90℃ for 3-5min. Then they are air-cooled to 20-25℃. S22. Auto parts enter the secondary primer spraying room through the suspension track, spray the secondary primer, bake at 50-60 ℃ for 30-60min, and cool naturally; The secondary primer is prepared by adding a conductive agent and has a resistance of ≤10 6 Ω conductive paint; the secondary primer is sprayed with a high-voltage electrostatic spray gun; S3. Auto parts spray paint: S31. Randomly inspect the surface grounding resistance of automobile parts ≤10 6 Ω, transfer to the electrostatic spraying room, ground the auto parts, use the rotary cup electrostatic sprayer to evenly spray the water-based paint as the topcoat on the surface of the auto parts, send it to the drying room, and bake it at 50-60℃ for 60-120min.

2. A method for spraying a wear-resistant layer of an automobile part according to claim 1, characterized in that: The material of the automobile accessories is one of ABS, PU, ​​PPS, PP, PE, and PBT.

3. The method for spraying a wear-resistant layer of an automobile part according to claim 1, characterized in that: The plasma flame is selected from oxygen plasma.

4. The method for spraying a wear-resistant layer of an automobile part according to claim 1, characterized in that: The plasma flame treatment enables the surface energy of the automobile parts to reach above 55 mN / m.

5. The method for spraying a wear-resistant layer of an automobile part according to claim 1, characterized in that: The first-level primer is a commercially available water-based modified acrylic paint for spraying plastic parts; the second-level primer is prepared by adding a conductive agent to the water-based modified acrylic paint, and the resistance of the second-level primer is (0.1-0.7)×10 6 Ω.

6. The method for spraying a wear-resistant layer of an automobile part according to claim 1, characterized in that: The controlled thickness range of the first-level primer spraying is 30-40 μm; the controlled thickness range of the second-level primer spraying is 15-20 μm.

7. The method for spraying a wear-resistant layer of an automobile part according to claim 1, characterized in that: The electrostatic high voltage of the high-voltage electrostatic spray gun is set to 40-50 kV, and the spraying pressure is controlled at 0.35-0.4 MPa.

8. The method for spraying a wear-resistant layer of an automobile part according to claim 1, characterized in that: The water-based paint is selected from one of commercially available water-based epoxy paint, water-based epoxy-modified acrylic paint, water-based acrylic paint, water-based alkyd paint, and water-based polyurethane paint; the water-based paint has a resistance value of 20-50 MΩ.

9. The method for spraying a wear-resistant layer of an automobile part according to claim 1, characterized in that: The spray cup of the rotary cup type electrostatic sprayer is connected to a negative electrostatic high voltage of 60-90 kV.

10. The method for spraying a wear-resistant layer of an automobile part according to claim 1, characterized in that: The spraying thickness of the topcoat is controlled to be in the range of 40-50 μm.

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