Surface scratch-resistant treatment method for polypropylene composite material for automotive exterior trim

Abstract

The application relates to a surface scratch-resistant treatment method for a polypropylene composite material for automobile exterior decoration, and belongs to the technical field of automobile polymer material modification. Nano-aluminum oxide is used as a core, is modified on the surface through a silane coupling agent KH-570, and is coated with polymethyl methacrylate to form a core-shell structure nano particle; a base material is modified through blending; the modified polypropylene base material is subjected to degreasing and dust removal treatment; the pretreated base material is placed into a plasma treatment equipment and is subjected to activation treatment; gradient coating deposition is carried out; the deposited base material is subjected to ultraviolet curing or heat curing treatment, and a scratch-resistant polypropylene composite material product for automobile exterior decoration is obtained; the coating layer is formed into a stable crosslinked structure through curing, and the scratch resistance and durability are ensured. Through the synergistic effect of the "core-shell nano particle-hyperbranched fluorosilane blending modified base material" and the "plasma activation-gradient coating deposition", double scratch-resistant protection from the material body to the surface is realized, and excellent mechanical properties and long-term use durability are considered.

Description

Technical Field

[0001] This invention relates to the field of automotive polymer material modification technology, specifically to a method for treating the surface of polypropylene composite materials for automotive exteriors to improve scratch resistance. Background Technology

[0002] Polypropylene is widely used in automotive exterior parts such as bumpers, grilles, and rearview mirror housings due to its light weight, low cost, and excellent processability. However, its one-dimensional surface has low hardness, high coefficient of friction, low surface polarity, and poor adhesion, making it easily scratched by sand, gravel, and car wash tools. At the same time, conventional modification schemes have obvious defects: single blending modification (such as adding organosilicon or nanoparticles) can improve the hardness of the substrate, but the surface protection is insufficient and it is prone to failure after long-term use; single surface coating treatment (such as simple plasma activation + coating) has a drastic decrease in scratch resistance after the coating peels off due to the weak properties of the substrate, and the poor interfacial bonding between the coating and the substrate makes it prone to aging and peeling under complex environments such as high and low temperatures and ultraviolet radiation. Summary of the Invention

[0003] The purpose of this invention is to address the deficiencies and shortcomings of existing technologies by providing a method for treating the surface of polypropylene composite materials for automotive exteriors that provides scratch resistance. Through the synergistic effect of "core-shell nanoparticle-hyperbranched fluorosilane blend modified substrate" and "plasma activation-gradient coating deposition", a dual scratch-resistant protection is achieved from the material body to the surface, taking into account both excellent mechanical properties and long-term durability.

[0004] To achieve the above objectives, the present invention adopts the following technical solution, which includes the following operational steps: Step 1: Preparation of core-shell nanoparticles: Using nano-alumina as the core (due to its high hardness, which enhances the material's resistance to deformation), and after surface modification with silane coupling agent KH-570, polymethyl methacrylate is coated to form core-shell structured nanoparticles. The alkoxy groups in the silane coupling agent KH-570 molecule can undergo hydrolytic condensation reactions with the hydroxyl groups on the surface of the nano-alumina, while the double bonds at the other end can undergo polymerization reactions with the coated polymethyl methacrylate, forming a chemically bonded interface layer. The core-shell structure design improves the compatibility between the nanoparticles and polypropylene resin, preventing agglomeration. Step 2, Substrate Blending Modification: A premix was prepared by mixing block copolymer polypropylene, the core-shell nanoparticles prepared in step 1, hyperbranched fluorosilane anti-scratch agent, nucleating agent, and antioxidant in a certain proportion. After granulation by twin-screw extrusion, the premix was formed by injection molding or extrusion to obtain a modified polypropylene substrate. Block copolymer polypropylene was selected as the substrate resin because it has both rigidity and toughness, which is suitable for the mechanical requirements of automotive exterior parts. The hydroxyl groups at the ends of the hyperbranched fluorosilane anti-scratch agent molecular chains can interact with the functional groups on the surface of polypropylene and core-shell particles to improve the interfacial bonding force. At the same time, fluorine can reduce the surface friction coefficient, and silicon can enhance the surface lubricity, thus synergistically improving the scratch resistance. Step 3, Substrate Pretreatment: The modified polypropylene substrate obtained in step 2 is degreased and dust removed to provide a clean surface for subsequent plasma activation and coating deposition. Step 4, Plasma activation: The pretreated substrate is placed in a plasma treatment device and activated by an argon-oxygen mixed gas. Argon can generate high-energy particles to bombard the substrate surface, etching to form a micro-rough structure and increasing the specific surface area. Oxygen can introduce polar functional groups such as hydroxyl and carboxyl groups on the substrate surface, enhancing the surface polarity. Plasma bombardment enhances the surface activity of the substrate and strengthens the interfacial adhesion with subsequent coatings. Step 5, Gradient coating deposition: Using a vacuum spraying process, an adhesive layer, a transition layer, and a functional layer are sequentially deposited on the surface of the activated substrate to form a gradient scratch-resistant coating. The gradient coating design solves the problem of imbalance between hardness and toughness in a single coating, achieving a protective effect of "strong adhesion - buffered transition - high surface hardness". Step 6, Curing treatment: The deposited substrate is subjected to UV curing or heat curing treatment to obtain scratch-resistant polypropylene composite material products for automotive exteriors; curing enables the coating to form a stable cross-linked structure, ensuring scratch resistance and durability.

[0005] Furthermore, in step 1, the nano-alumina particle size is 20-50 nm, the amount of silane coupling agent KH-570 added is 3-8% of the mass of nano-alumina, and the amount of polymethyl methacrylate coating is 15-30% of the mass of the core; the preparation of core-shell nanoparticles also includes an ultrasonic dispersion step, with an ultrasonic power of 150-250 W and an ultrasonic time of 20-40 min.

[0006] Further, in step 2, the mass fractions of each component are as follows: 80-95 parts of block copolymer polypropylene, 2-8 parts of core-shell nanoparticles (too little addition will result in insufficient hardness improvement, while too much will easily lead to material embrittlement), 1-5 parts of hyperbranched fluorosilane anti-scratch agent, 0.2-1 parts of nucleating agent, and 0.1-0.5 parts of antioxidant; wherein, the melt flow rate (230℃×2.16kg) of the block copolymer polypropylene is 10-30g / 10min, and the ethylene content is 5-10mol.

[0007] Furthermore, in step 2, the hyperbranched fluorosilane antiscratch agent has a molecular weight of 8000-15000, a fluorine content of 18-25%, and hydroxyl functional groups at the end of the molecular chain; the nucleating agent is an organophosphate salt, and the antioxidant is a compound system of hindered phenols and phosphites, with a mass ratio of 1:1-2:1.

[0008] Furthermore, in step 2, the stirring speed of the premix preparation is 300-500 r / min, the stirring time is 15-30 min, and the stirring temperature is 60-80℃ (this temperature allows the hyperbranched fluorosilane to initially melt and uniformly coat the resin and nanoparticle surface); the twin-screw extruder processing temperature is 180-220℃, the screw speed is 200-350 r / min, and the feeding speed is 20-50 kg / h.

[0009] Furthermore, in step 3, the degreasing treatment uses anhydrous ethanol ultrasonic cleaning with an ultrasonic power of 100-200W and a cleaning time of 5-15 minutes (ethanol, as a polar solvent, can effectively dissolve oil stains on the substrate surface, and ultrasonic vibration can enhance the cleaning effect). Then, it is dried at 60-80℃ for 10-20 minutes (to remove residual ethanol on the surface and avoid residual solvent from affecting the coating adhesion). The dust removal treatment uses high-pressure air blowing with a blowing pressure of 0.4-0.6MPa (to quickly remove surface dust while avoiding secondary scratches caused by wiping, ensuring that the surface cleanliness of the substrate meets the requirements of subsequent processes).

[0010] Furthermore, in step 4, the volume ratio of the argon-oxygen mixture is 3:1-5:1 (excessive argon will lead to over-etching, while excessive oxygen will easily cause excessive surface oxidation), the plasma treatment power is 80-150W, the treatment time is 30-120s, the treatment distance is 5-15mm, and the chamber pressure is 10-50Pa; after activation, the contact angle of the substrate surface is ≤65° to ensure the wetting and spreading effect of the coating and the substrate and improve the interfacial adhesion.

[0011] Further, in step 5, the adhesive layer is a polyurethane acrylate resin coating with a thickness of 5-10 μm (to ensure tight bonding with the substrate); the transition layer is a composite coating of epoxy acrylate and polysiloxane (mass ratio 3:1-5:1) with a thickness of 10-20 μm (to alleviate stress differences between the substrate and the functional layer and prevent coating cracking); the functional layer is a nano-silica modified acrylate coating with a thickness of 20-30 μm; the diluent for each coating is a mixed solution of ethyl acetate and propylene glycol methyl ether acetate (volume ratio 2:1-3:1), with a solid content of 40-60% after dilution; the adhesive layer uses polyurethane acrylate resin, which has excellent flexibility and adhesion, and can form hydrogen bonds or chemical bonds with the polar functional groups on the surface of the activated substrate; the transition layer adopts a composite system of epoxy acrylate and polysiloxane, where epoxy acrylate provides rigidity and polysiloxane provides flexibility.

[0012] Furthermore, in step 5, the nano-silica particles in the functional layer have a particle size of 5-20 nm, and the amount added is 5-15% of the mass of the acrylate resin, and is modified by silane coupling agent KH-560; the vacuum degree of vacuum spraying is 0.01-0.1 MPa, the spraying pressure is 0.3-0.6 MPa, the spraying distance is 20-40 cm, and the spray gun moving speed is 50-100 mm / s; the functional layer uses nano-silica modified acrylate resin, and nano-silica can significantly improve the coating hardness.

[0013] Furthermore, in step 6, the UV curing wavelength is 365nm, the curing energy is 800-1500mJ / cm², and the curing time is 30-120s; the heat curing temperature is 80-120℃, and the curing time is 30-60min. The curing process is gentle, which can avoid internal stress caused by rapid curing. After curing, the coating forms a three-dimensional cross-linked network, forming a strong bond with the substrate and between each coating, ultimately achieving a dual scratch resistance effect of "body reinforcement + surface protection". The surface pencil hardness of the prepared product is ≥6H, the critical scratch load tested according to ASTM D7027 standard is ≥12N, the adhesion grade of the cross-cut adhesion test is 0, the Taber abrasion amount (CS-17 grinding wheel, 1000 rpm) is ≤3mg, and the scratch color difference ΔE after xenon lamp aging for 1000h is ≤1.0.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention provides a method for treating the surface of polypropylene composite material for automotive exteriors with scratch resistance. Through the synergistic effect of "core-shell nanoparticle-hyperbranched fluorosilane blend modified substrate" and "plasma activation-gradient coating deposition", dual scratch resistance protection from the material body to the surface is achieved, taking into account both excellent mechanical properties and long-term durability. Attached Figure Description

[0015] Figure 1This is a performance comparison test data table of the products prepared in Examples 1-3 of this invention with blank control, single blend modified sample, and single surface coating sample. Detailed Implementation

[0016] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. The preferred embodiments described are only examples. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] Example 1: Step 1, Preparation of core-shell nanoparticles: Take 5g of 20nm alumina nanoparticles, add 50mL of ethanol solution, and disperse by ultrasonication at 200W for 30min; add 0.2g of KH-570, stir and react at 75℃ for 2.5h; add 1.0g of methyl methacrylate and 0.03g of initiator AIBN, react at 85℃ for 3.5h, and centrifuge and dry to obtain core-shell nanoparticles; Step 2, Substrate Co-mixing Modification: Take 85 parts by weight of block copolymer polypropylene, 4 parts by weight of core-shell nanoparticles, 3 parts by weight of hyperbranched fluorosilane anti-scratch agent (molecular weight 10000, fluorine content 20%), 0.5 parts by weight of organophosphate salt nucleating agent, and 0.3 parts by weight of antioxidant 1010 and 168 compound system (1:1). Stir at 70℃ and 400r / min for 25min to obtain a premix. Add the premix to a twin-screw extruder, with a processing temperature of 190-215℃, screw speed of 300r / min, and feeding speed of 35kg / h. After extrusion granulation, injection molding is performed to obtain modified polypropylene bumper substrate. Step 3, Substrate pretreatment: Immerse the substrate in anhydrous ethanol, ultrasonically clean it at 150W for 10 minutes, dry it at 70℃ for 15 minutes, and then blow it with 0.5MPa high-pressure air to remove dust. Step 4, Plasma activation: Introduce an argon-oxygen mixture (volume ratio 4:1), chamber pressure 30Pa, processing power 120W, processing distance 10mm, processing time 80s; Step 5, Gradient Coating Deposition: Prepare the adhesive layer (polyurethane acrylate, solid content 45%, diluent ethyl acetate: propylene glycol methyl ether acetate = 2.5:1), vacuum sprayed (0.05MPa, 0.45MPa, 30cm, 80mm / s), thickness 8μm; transition layer (epoxy acrylate: polysiloxane = 4:1, solid content 55%), sprayed thickness 15μm; functional layer (acrylate + 10% modified nano silica, solid content 60%), sprayed thickness 25μm. Step 6, Curing treatment: UV curing, 365nm wavelength, 1200mJ / cm² energy, 80s curing time, to obtain the final product.

[0018] Example 2: Step 1, Preparation of core-shell nanoparticles: Take 5g of 30nm alumina nanoparticles, add 50mL of ethanol solution, and disperse by ultrasonication at 250W for 40min; add 0.3g of KH-570, and stir at 80℃ for 3h; add 1.2g of methyl methacrylate and 0.04g of initiator AIBN, and react at 90℃ for 4h; centrifuge and dry to obtain core-shell nanoparticles; Step 2, Substrate Blending Modification: Take 90 parts by weight of block copolymer polypropylene, 2 parts by weight of core-shell nanoparticles, 2 parts by weight of hyperbranched fluorosilane anti-scratch agent (molecular weight 8000, fluorine content 18%), 0.3 parts by weight of organophosphate salt nucleating agent, and 0.2 parts by weight of antioxidant 1010 and 168 compound system (2:1). Stir at 300 r / min for 20 min at 60℃ to obtain a premix; process the material in a twin-screw extruder at a temperature of 180-210℃, a screw speed of 250 r / min, and a feeding speed of 40 kg / h. After extrusion granulation, extrusion molding is performed to obtain modified polypropylene grid substrate. Step 3, Substrate pretreatment: Ultrasonic cleaning with anhydrous ethanol at 100W for 5 min, drying at 60℃ for 10 min, and dust removal by blowing with 0.4MPa high-pressure air; Step 4, Plasma activation: Argon-oxygen mixed gas (3:1), chamber pressure 10Pa, power 80W, distance 5mm, time 30s; Step 5, Gradient Coating Deposition: Adhesive layer (40% solids content, 2:1 diluent), 5μm thickness; Transition layer (3:1, 50% solids content), 10μm thickness; Functional layer (5% modified nano-silica, 60% solids content), 20μm thickness; Vacuum spraying parameters: 0.01MPa, 0.3MPa, 20cm, 50mm / s; Step 6, Curing treatment: UV curing, 365nm wavelength, 800mJ / cm² energy, 30s curing time, to obtain the final product.

[0019] Example 3: Step 1, Preparation of core-shell nanoparticles: Take 5g of 50nm alumina nanoparticles, add 50mL of ethanol solution, and disperse by ultrasonication at 150W for 20min; add 0.4g of KH-570, and stir at 70℃ for 2h; add 1.5g of methyl methacrylate and 0.02g of initiator AIBN, and react at 80℃ for 3h; centrifuge and dry to obtain core-shell nanoparticles; Step 2, Substrate Blending Modification: Take 80 parts by weight of block copolymer polypropylene, 8 parts by weight of core-shell nanoparticles, 5 parts by weight of hyperbranched fluorosilane anti-scratch agent (molecular weight 15000, fluorine content 25%), 1 part by weight of organophosphate salt nucleating agent, and 0.5 parts by weight of antioxidant 1010 and 168 compound system (1.5:1). Stir at 80℃ and 500r / min for 30min to obtain a premix; process the material in a twin-screw extruder at a temperature of 200-220℃, a screw speed of 350r / min, and a feeding speed of 20kg / h. After extrusion granulation, injection molding is performed to obtain the modified polypropylene rearview mirror shell substrate. Step 3, Substrate pretreatment: Ultrasonic cleaning with anhydrous ethanol at 200W for 15 min, drying at 80℃ for 20 min, and dust removal by blowing with 0.6MPa high-pressure air; Step 4, Plasma activation: Argon-oxygen mixed gas (5:1), chamber pressure 50Pa, power 150W, distance 15mm, time 120s; Step 5, Gradient Coating Deposition: Adhesive layer (50% solids content, 3:1 diluent), 10μm thickness; Transition layer (5:1, 60% solids content), 20μm thickness; Functional layer (15% modified nano-silica, 60% solids content), 30μm thickness; Vacuum spraying parameters: 0.1MPa, 0.6MPa, 40cm, 100mm / s; Step 6, Curing treatment: heat curing at 120℃ for 60 minutes to obtain the final product.

[0020] Comparative Experiment: The products prepared in Examples 1-3 were compared with the blank control, single blend modified samples, and single surface coating samples. The test standards are as follows: pencil hardness (ASTM D3363), critical scratch load (ASTM D7027), adhesion (ISO 2409 cross-cut adhesion test), Taber abrasion (ASTM D1044, CS-17 grinding wheel, 1000 rpm), and scratch color difference (PV 3952) after xenon lamp aging (ISO 11341, 1000 h). Specific data can be found in […]. Figure 1 .

[0021] Compared with the prior art, the beneficial effects of the present invention are: 1. Significantly improved scratch resistance: The surface pencil hardness of the product is ≥6H, which is much higher than that of unmodified polypropylene (2H) and single blend modified and single surface coating samples (all 5H); the critical scratch load is ≥12N, which is significantly better than that of single blend modified (6.5N) and single surface coating (8.2N), achieving a synergistic scratch resistance effect of "body reinforcement + surface protection"; 2. Extremely strong coating adhesion: The adhesion level in the cross-cut adhesion test reaches level 0, which is better than level 1 of the single surface coating sample. Through the adaptation design of plasma activation and blended modified substrate, the problem of poor interface bonding between coating and substrate is solved, avoiding coating aging and peeling under complex environments. 3. Excellent wear resistance: Taber wear (CS-17 grinding wheel, 1000 rpm) ≤3mg, which is much lower than that of unmodified polypropylene (18.6mg) and better than single blend modification (3.5mg) and single surface coating (4.2mg) samples. It can resist daily wear such as sand, gravel and car wash tools. 4. Stable weather resistance: After 1000 hours of xenon lamp aging, the scratch color difference ΔE is ≤1.0, which is significantly better than unmodified polypropylene (5.2), single blend modification (2.8) and single surface coating (1.5) samples. It can withstand complex environments such as high and low temperatures and ultraviolet rays, ensuring long-term durability. 5. Balancing mechanical properties: Through the synergistic modification of core-shell nanoparticles and hyperbranched fluorosilanes, scratch resistance is improved while the rigidity and toughness of the polypropylene substrate are preserved, making it suitable for the mechanical requirements of automotive exterior parts (bumpers, grilles, rearview mirror housings, etc.) and avoiding material embrittlement. 6. Strong process adaptability: The integrated process is coherent, and the adaptability of each link (core-shell particle preparation, substrate blending, plasma activation, gradient coating deposition, curing) is good. It solves the problem of poor synergistic effect caused by simply superimposing two technologies in the existing technology. Moreover, the processing is stable and there are no defects such as poor raw material compatibility and complicated process.

[0022] For those skilled in the art, modifications can be made to the technical solutions described in the foregoing embodiments, and equivalent substitutions can be made to some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this invention should be included within the protection scope of this invention.

Claims

1. A method for treating the surface of polypropylene composite material for automotive exterior trim to improve scratch resistance, characterized in that: It includes the following steps: Step (1), Preparation of core-shell nanoparticles: Using nano-alumina as the core, after surface modification with silane coupling agent KH-570, polymethyl methacrylate is coated to form core-shell structured nanoparticles. Step (2), substrate blending modification: Block copolymer polypropylene, core-shell nanoparticles prepared in step (1), hyperbranched fluorosilane anti-scratch agent, nucleating agent and antioxidant are mixed in proportion to prepare a premix, which is then granulated by twin-screw extrusion and molded by injection molding or extrusion process to obtain modified polypropylene substrate. Step (3), Substrate pretreatment: The modified polypropylene substrate obtained in step (2) is subjected to degreasing and dust removal treatment; Step (4), Plasma activation: The pretreated substrate is placed in a plasma treatment device and activated by an argon-oxygen mixed gas. Step (5), gradient coating deposition: A gradient scratch-resistant coating is formed by sequentially depositing an adhesive layer, a transition layer, and a functional layer on the surface of an activated substrate using a vacuum spraying process. Step (6), Curing treatment: The deposited substrate is subjected to ultraviolet curing or heat curing treatment to obtain scratch-resistant polypropylene composite material products for automotive exteriors.

2. The method for treating the surface of polypropylene composite material for automotive exterior trim to resist scratches according to claim 1, characterized in that: In step (1), the nano-alumina particle size is 20-50nm, the amount of silane coupling agent KH-570 added is 3-8% of the mass of nano-alumina, and the amount of polymethyl methacrylate coating is 15-30% of the mass of the core; the preparation of core-shell nanoparticles also includes an ultrasonic dispersion step, with an ultrasonic power of 150-250W and an ultrasonic time of 20-40min.

3. The method for treating the surface of polypropylene composite material for automotive exterior trim to resist scratches according to claim 1, characterized in that: In step (2), the mass fractions of each component are as follows: 80-95 parts of block copolymer polypropylene, 2-8 parts of core-shell nanoparticles, 1-5 parts of hyperbranched fluorosilane anti-scratching agent, 0.2-1 parts of nucleating agent, and 0.1-0.5 parts of antioxidant; wherein, the melt flow rate of the block copolymer polypropylene is 10-30 g / 10 min, and the ethylene content is 5-10 mol.

4. The method for treating the surface of polypropylene composite material for automotive exterior trim to resist scratches according to claim 1, characterized in that: In step (2), the hyperbranched fluorosilane antiscratching agent has a molecular weight of 8000-15000, a fluorine content of 18-25%, and hydroxyl functional groups at the end of the molecular chain; the nucleating agent is an organophosphate salt, and the antioxidant is a compound system of hindered phenols and phosphites, with a mass ratio of 1:1-2:

1.

5. The method for treating the surface of polypropylene composite material for automotive exterior trim to resist scratches according to claim 1, characterized in that: In step (2), the stirring speed of the premix preparation is 300-500 r / min, the stirring time is 15-30 min, and the stirring temperature is 60-80℃; the processing temperature of the twin-screw extruder is 180-220℃, the screw speed is 200-350 r / min, and the feeding speed is 20-50 kg / h.

6. The method for treating the surface of polypropylene composite material for automotive exterior trim according to claim 1, characterized in that: In step (3), the degreasing treatment is performed by ultrasonic cleaning with anhydrous ethanol, with an ultrasonic power of 100-200W and a cleaning time of 5-15min, followed by drying at 60-80℃ for 10-20min; the dust removal treatment is performed by high-pressure air blowing, with a blowing pressure of 0.4-0.6MPa.

7. The method for treating the surface of polypropylene composite material for automotive exterior trim according to claim 1, characterized in that: In step (4), the volume ratio of argon-oxygen mixed gas is 3:1-5:1, the plasma treatment power is 80-150W, the treatment time is 30-120s, the treatment distance is 5-15mm, and the cavity pressure is 10-50Pa; the contact angle of the substrate surface after activation is ≤65°.

8. The method for treating the surface of polypropylene composite material for automotive exterior trim to resist scratches according to claim 1, characterized in that: In step (5), the adhesive layer is a polyurethane acrylate resin coating with a thickness of 5-10 μm; the transition layer is a composite coating of epoxy acrylate and polysiloxane with a thickness of 10-20 μm; the functional layer is a nano-silica modified acrylate coating with a thickness of 20-30 μm; and the diluent for each coating is a mixed solution of ethyl acetate and propylene glycol methyl ether acetate with a solid content of 40-60% after dilution.

9. The method for treating the surface of polypropylene composite material for automotive exterior trim to resist scratches according to claim 1, characterized in that: In step (5), the nano-silica particles in the functional layer have a diameter of 5-20 nm, the amount added is 5-15% of the mass of the acrylate resin, and it is modified by silane coupling agent KH-560. Vacuum spraying requires a vacuum level of 0.01-0.1 MPa, a spraying pressure of 0.3-0.6 MPa, a spraying distance of 20-40 cm, and a spray gun moving speed of 50-100 mm / s.

10. The method for treating the surface of a polypropylene composite material for automotive exterior trim according to claim 1, characterized in that: In step (6), the UV curing wavelength is 365nm, the curing energy is 800-1500mJ / cm², and the curing time is 30-120s; the heat curing temperature is 80-120℃, and the curing time is 30-60min; the surface pencil hardness of the prepared product is ≥6H, the critical load for scratch testing according to ASTM D7027 standard is ≥12N, the adhesion grade of the cross-cut adhesion test is 0, the Taber abrasion loss is ≤3mg, and the scratch color difference ΔE after xenon lamp aging for 1000h is ≤1.0.

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