Powder spraying method for composite material

Abstract

The present application relates to the technical field of spraying methods, and provides a powder spraying method for a composite material. In the present application, conductive paint is applied onto the surface of one side of a composite material and then preheating is performed to obtain a pretreated composite material; electrostatic powder spraying is performed on the surface of the other side of the pretreated composite material that is not coated with the conductive paint, and in the electrostatic powder spraying process, an electric field is used to break down and coat the pretreated composite material, and then curing is performed. In the present application, conductive paint is sprayed on the surface of one side of a composite material, so as to improve the electrostatic and resistance characteristics of the composite material. In the electrostatic powder spraying process, the composite material is broken down by means of an electric field, such that a path is formed between the conductive paint on one side of the composite material and powder, so that the powder can be uniformly adsorbed on the surface of the composite material, thereby improving spraying efficiency and product quality, improving the yield of the product.

Description

A composite material powder coating method

[0001] This application claims priority to Chinese Patent Application No. CN202411178097.5, filed on August 27, 2024, entitled “A Method for Powder Coating of Composite Materials”, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of spraying methods, and more particularly to a composite material powder spraying method. Background Technology

[0003] In the automotive manufacturing industry, composite materials are widely used in the manufacture of body parts due to their advantages such as lightweight, high strength, and high designability. However, surface treatment of composite materials is a key technology that directly affects the appearance and performance of the product. Traditional surface treatment methods mainly include paint spraying and water-based paint spraying, but these methods have high requirements for the surface condition of the substrate. Moreover, composite materials are diverse, with complex surface conditions and poor smoothness, which leads to cumbersome pretreatment processes such as puttying before spraying.

[0004] To address these issues, researchers developed a novel powder coating technology. Using powder as a coating material, this electrostatic spraying process is applied to the surface of composite materials, successfully producing qualified products that meet the requirements of automakers. Compared to traditional paint and water-based paint spraying, electrostatic powder coating technology offers advantages such as strong adhesion, good weather resistance, and superior chemical resistance. It simplifies the construction process, facilitates fully automated coating, and reduces labor costs.

[0005] Although electrostatic powder coating technology has achieved some success in the application of composite materials, several problems remain in mass production. First, different types or batches of composite materials exhibit variations in their electrostatic and electrical properties, affecting the consistency between coating batches. Second, differences in grounding conditions, construction equipment, and construction environments between different factories or workshops can also impact the consistency of product appearance quality. These issues result in product yields that cannot meet the yield requirements of large-scale industrial production. Summary of the Invention

[0006] In view of this, the purpose of this application is to provide a method for powder coating of composite materials. This application utilizes an electric field to break down the composite material, creating a pathway between the conductive paint on one side of the composite material and the powder, thereby allowing the powder to be uniformly adsorbed on the surface of the composite material and improving the coating yield.

[0007] To achieve the above-mentioned objectives, this application provides the following technical solution:

[0008] This application provides a method for powder coating of composite materials, including the following steps:

[0009] After coating one side of the composite material with conductive paint, it is preheated to obtain a pretreated composite material.

[0010] The other side of the uncoated conductive paint of the pretreated composite material is subjected to electrostatic powder spraying. During the electrostatic powder spraying process, an electric field is used to break down and coat the pretreated composite material, and then it is cured.

[0011] Preferably, the conductive paint includes a water-based conductive paint.

[0012] Preferably, the coating is sprayed, and the spraying pressure is 0.3-0.5 MPa, the distance is 15-25 cm, and the moving speed is 600-800 mm / s.

[0013] Preferably, the process after coating and before preheating further includes drying to form a dry film, the thickness of which is 20-40 μm and the resistivity is ≤0.4 MΩ.

[0014] Preferably, the electric field is formed by charged powder sprayed out by the electrostatic powder spraying, the charged powder being negatively charged, and the pretreated composite material being grounded.

[0015] Preferably, the preheating temperature is 80–170°C and the time is 6–12 minutes.

[0016] Preferably, the voltage for the electrostatic powder spraying is 40–80 kV and the current is 20–30 μA.

[0017] Preferably, the temperature of the electrostatic powder spraying is 80–170°C.

[0018] Preferably, the curing temperature is 160–180°C and the curing time is 7–20 min.

[0019] Preferably, the material of the composite material includes automotive exterior composite materials, which include sheet molding compounds, bulk molding compounds, and resin transfer molding materials.

[0020] This application provides a method for powder coating of composite materials, comprising the following steps: coating one side of the composite material with conductive paint and then preheating it to obtain a pretreated composite material; performing electrostatic powder coating on the other side of the pretreated composite material that is not coated with conductive paint, wherein an electric field is used to break down the pretreated composite material during the electrostatic powder coating process, followed by curing. This application sprays conductive paint onto one side of the composite material to improve its electrostatic and resistive properties. During the electrostatic powder coating process, an electric field is used to break down the composite material, creating a pathway between the conductive paint and the powder on one side of the composite material, allowing the powder to be uniformly adsorbed onto the surface of the composite material, improving coating efficiency and product quality, thereby increasing product yield.

[0021] Compared with the prior art, the beneficial effects of this application are as follows:

[0022] 1. Improve spraying efficiency and product quality: By spraying conductive paint on one side of the composite material, the powder particles have a better adsorption effect on the composite material during electrostatic powder spraying, which improves the powder application rate and thus improves spraying efficiency and product quality.

[0023] 2. Ensuring consistency in mass production: The composite material powder coating method of this application effectively solves the problem of differences in electrostatic and electrical properties between different types or batches of composite materials, thereby ensuring consistency between coating batches. Simultaneously, it also solves the problem that differences in grounding conditions, construction equipment, and construction environment between different factories or workshops can affect the consistency of product appearance quality, thus ensuring consistency in mass production.

[0024] 3. Meeting the yield requirements of industrial production: By implementing the composite material powder spraying method of this application, the consistency of mass production of composite material powder spraying process has been successfully improved, meeting the yield requirements of industrial production. Attached Figure Description

[0025] Figures 1 and 2 are actual edge images of the coating obtained in Example 1 at different angles;

[0026] Figures 3 and 4 are actual images of the coating surface obtained in Example 1 at different magnifications;

[0027] Figures 5 to 7 are actual images of the coating surface obtained in Comparative Example 1 at different magnifications;

[0028] Figures 8 and 9 show the edge images of the coating obtained in Comparative Example 2 at different magnifications. Detailed Implementation

[0029] This application provides a method for powder coating of composite materials, including the following steps:

[0030] After coating one side of the composite material with conductive paint, it is preheated to obtain a pretreated composite material.

[0031] The other side of the uncoated conductive paint of the pretreated composite material is subjected to electrostatic powder spraying. During the electrostatic powder spraying process, an electric field is used to break down and coat the pretreated composite material, and then it is cured.

[0032] Unless otherwise specified, all raw materials used in this application are commercially available products in the field.

[0033] This application involves coating one side of the composite material with conductive paint and then preheating it to obtain a pretreated composite material.

[0034] In this application, the composite material is preferably an automotive composite material, which preferably includes SMC (Sheet Molding Compound), BMC (Bulk Molding Compound), and RTM (Resin Transfer Molding). In a specific embodiment of this application, the composite material is the roof or hood of an off-road vehicle.

[0035] In this application, the composite substrate is preferably surface-treated before coating. The surface treatment preferably includes cleaning and degreasing in sequence to ensure that the surface is smooth, flat, and free of grease and other contaminants.

[0036] In this application, isopropanol is preferably used for degreasing.

[0037] In this application, the conductive paint preferably includes a water-based conductive paint. This application does not specifically limit the type of water-based conductive paint; any water-based conductive paint well-known to those skilled in the art can be used. In a specific embodiment of this application, the water-based conductive paint is the water-based collinear primer disclosed in CN117683439A.

[0038] In this application, the coating is preferably sprayed, the spraying pressure is preferably 0.3-0.5 MPa, the spraying distance is preferably 15-25 cm, more preferably 18-20 cm, and the moving speed is preferably 600-800 mm / s.

[0039] In this application, the process after coating and before preheating preferably includes drying to form a dry film. The thickness of the dry film is preferably 20–40 μm, and the resistivity is preferably ≤0.4 MΩ. This application does not impose specific limitations on the drying parameters; methods well-known to those skilled in the art can be used.

[0040] In this application, the preheating temperature is preferably 80-170°C, more preferably 100-150°C, and most preferably 120-140°C, and the preheating time is preferably 6-12 min, more preferably 8-10 min.

[0041] After obtaining the pretreated composite material, this application performs electrostatic powder spraying on the other side of the uncoated conductive paint of the pretreated composite material. During the electrostatic powder spraying process, an electric field is used to break down the pretreated composite material, and then it is cured.

[0042] In this application, the electric field is preferably formed by charged powder sprayed out by the electrostatic powder spraying, the charged powder is preferably negatively charged, and the pretreated composite material is preferably grounded, which is the neutral line.

[0043] This application utilizes an electric field to break down the composite substrate, creating a pathway between the conductive paint and powder on one side of the composite substrate. This allows the powder to be uniformly adsorbed onto the surface of the composite substrate, improving spraying efficiency and product quality.

[0044] In this application, the voltage for electrostatic powder spraying is preferably 40-80kV, and the current is preferably 20-30μA.

[0045] In this application, the parameters of the electrostatic powder spraying are preferably set according to different shapes of the workpiece. When the workpiece is preferably a flat part, the voltage of the electrostatic powder spraying is preferably 80kV and the current is preferably 30μA. When the workpiece is preferably a complex part with grooves, the voltage of the electrostatic powder spraying is preferably 80kV and the current is preferably 22μA. When the electrostatic powder spraying is preferably a recoating, the spraying voltage is preferably 40kV and the current is preferably 30μA.

[0046] In this application, the preferred temperature for electrostatic powder spraying is 80–170°C, more preferably 80–130°C, and most preferably 95–110°C.

[0047] In this application, during the electrostatic powder spraying process, the distance between the spray gun and the surface of the pretreated composite material, the spraying angle, and the speed are ensured to be appropriate to guarantee the uniformity and quality of the coating.

[0048] In this application, the curing temperature is 160–180°C and the curing time is 7–20 min.

[0049] In this application, taking a powder electrostatic spraying film thickness of 60-90 μm as an example, a recovery system is preferably provided during the powder electrostatic spraying process, and the amount of powder coating is preferably 6-10 mg / m³. 2 / kg, no recycling system, the preferred dosage of powder coating is 5-6mg / kg. 2 / kg.

[0050] In this application, the powder electrostatic spraying coating is preferably a special powder coating for ultra-weather-resistant composite materials, and the special powder coating for ultra-weather-resistant composite materials preferably comprises the following components by mass percentage:

[0051] The composition comprises 0-50% modified acrylate, 20-75% polyester resin, 15-20% IPDI adduct, 0.1-0.8% texture agent, 4.3-22.7% transparent filler powder, 0.8-1.2% pigment, 0.1-0.2% toughening agent, 0.1-0.3% nano-alumina, and 0-2% conductive agent, wherein the sum of the mass percentages of all components is 100%.

[0052] The modified acrylate in the ultra-weather-resistant composite material powder coating provided in this application is preferably 40-48% by mass, and the modified acrylate has low-temperature melting and curing properties and ultra-strong durability.

[0053] In this application, the modified acrylate is preferably a polyurethane acrylate or an epoxy acrylate.

[0054] In this application, the epoxy acrylate is preferably an epoxy-type acrylic powder coating resin, which can be prepared according to the method disclosed in CN115651473A.

[0055] In this application, the method for preparing the polyurethane acrylate preferably includes the following steps:

[0056] Isocyanate, polyester polyol, hydroxyl-containing acrylic monomer and organic solvent are mixed and subjected to a prepolymerization reaction to obtain polyurethane prepolymer;

[0057] The polyurethane prepolymer, terminal double-bonded silane, acrylate monomer, initiator, chain transfer agent and organic solvent are mixed and subjected to free radical polymerization to obtain the polyurethane acrylate.

[0058] This application involves mixing isocyanate, polyester polyol, hydroxyl-containing acrylic monomer and organic solvent to carry out a prepolymerization reaction to obtain a polyurethane prepolymer.

[0059] In this application, the molar ratio of the isocyanate, polyester polyol and hydroxyl-containing acrylic monomer is preferably 1:0.5:0.5 to 1:0.3:1.2, more preferably 1:0.5:1.

[0060] In this application, the hydroxyl-containing acrylic monomer preferably includes one or more of hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxyethyl acrylate, and hydroxypropyl acrylate.

[0061] In this application, the isocyanate preferably includes one or more of hexamethylene diisocyanate, isophorone diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, and dicyclohexylmethane diisocyanate.

[0062] In this application, the polyester polyol preferably includes polycarbonate polyol and / or polycaprolactone polyol.

[0063] In this application, the organic solvent preferably includes one or more of DMF, xylene and PMA. This application does not have a special limitation on the amount of the organic solvent used, as long as it can ensure that the raw materials are completely dissolved.

[0064] In this application, the temperature of the prepolymerization reaction is preferably 85-95°C, more preferably 90°C, and the time is preferably 3-4 hours.

[0065] After obtaining the polyurethane prepolymer, this application mixes the polyurethane prepolymer, terminal double-bonded silane, acrylate monomer, initiator, chain transfer agent and organic solvent to carry out a free radical polymerization reaction to obtain the polyurethane acrylate.

[0066] In this application, the molar ratio of the polyurethane prepolymer, the terminal double-bonded silane, and the acrylate monomer is preferably 1:0.3:4 to 1:2:12, more preferably 3:1:16, 3:3:14, or 1:2:12.

[0067] In this application, the terminal double-bonded silane preferably includes one or more of the following: terminal vinyl silane, terminal acrylic silane, terminal acryloyloxy silane, and terminal methpropylene silane, wherein the terminal vinyl silane is preferably... 3572, wherein the silane with acrylic acid at the end is preferably Shin-Etsu KBM-503, the silane with acryloyloxy at the end is preferably Shin-Etsu KBM5103, and the silane with methacrylic acid at the end is preferably Shin-Etsu KBM5803.

[0068] In this application, the acrylate monomer preferably includes one or more of methyl methacrylate, butyl acrylate, butyl methacrylate, glycidyl methacrylate, isobornyl methacrylate, cyclohexyl methacrylate, (meth)acrylate-modified polycaprolactone, ethyl acrylate, and ethylene glycol dimethacrylate.

[0069] In this application, the initiator is preferably a peroxide, more preferably benzoyl peroxide (BPO), di-tert-butyl peroxide, or di-tert-pentyl peroxide.

[0070] In this application, the molar ratio of the polyurethane prepolymer to the initiator is preferably 1:0.05 to 1:1, more preferably 3:0.43, 1:0.33 or 3:0.23.

[0071] In this application, the chain transfer agent is preferably n-dodecyl mercaptan.

[0072] In this application, the molar ratio of the polyurethane prepolymer to the chain transfer agent is preferably 1:0.02 to 1:1, more preferably 1:0.05, 1:0.1 or 3:0.1.

[0073] In this application, the organic solvent preferably includes one or more of xylene, PMA, toluene, ethylene glycol n-butyl ether, and solvent oil. This application does not have a special limitation on the amount of the organic solvent used, as long as it can ensure that the raw materials are completely dissolved.

[0074] In this application, the temperature of the free radical polymerization reaction is preferably 100-140°C, more preferably 130-135°C, and the time is preferably 4-7 hours.

[0075] Preferably, the organic solvent is first preheated to the reaction temperature, the acrylate monomer and chain transfer agent are mixed evenly to obtain a mixture, and then the mixture and the initiator are added dropwise to the preheated organic solvent at a uniform rate. When 1 / 3 of the mass of the mixture remains, the polyurethane prepolymer and the terminal double-bonded silane are added dropwise to carry out the free radical polymerization reaction. Preferably, the initiator is added during the free radical polymerization reaction.

[0076] After the free radical polymerization reaction is completed, this application preferably removes the solvent by vacuuming and discharges the material while it is still hot to obtain the polyurethane acrylate.

[0077] In this application, when the mass fraction of modified acrylate in the special powder coating for ultra-weather-resistant composite materials is not 0, the mass fraction of polyester resin is preferably 20-24%. When the mass fraction of modified acrylate in the special powder coating for ultra-weather-resistant composite materials is 0, the mass fraction of polyester resin is preferably 68-76%. Polyester resin has a low glass transition temperature, and when combined with polyurethane acrylate, it balances the melt flow properties in various temperature ranges and provides certain durability.

[0078] In this application, the polyester resin is preferably a saturated carboxyl polyester resin.

[0079] The preferred mass percentage of the IPDI adduct in the ultra-weather-resistant composite material powder coating provided in this application is 15-18%, and the IPDI adduct is a crosslinking agent for hydroxyl-containing saturated polyester used in polyurethane powder coatings.

[0080] In this application, the adduct of IPDI is preferably... B 1530.

[0081] The texture agent in the ultra-weather-resistant composite material powder coating provided in this application is preferably 0.3% to 0.5% by mass, and the function of the texture agent is to adjust the texture state.

[0082] In this application, the texture agent is preferably SW301 (Nanhai Chemical SW301) purchased from Foshan Nanhai Yisan Chemical Co., Ltd.

[0083] The preferred mass percentage of transparent filler powder in the ultra-weather-resistant composite material powder coating provided in this application is 7.1-8.2%, more preferably 7.6-7.9%, and the function of the transparent filler powder is to improve the hardness of the coating.

[0084] In this application, the median particle size of the transparent filler powder is preferably 3.5 nm.

[0085] In this application, the composite nano-silicon is preferably MINEX-7.

[0086] The preferred percentage of pigment in the powder coating for ultra-weather-resistant composite materials provided in this application is 1 to 1.2%, and the function of the pigment is to color the material.

[0087] In this application, the pigment is preferably ORION COLOUR BLACK FW200.

[0088] The preferred mass percentage of toughening agent in the ultra-weather-resistant composite material powder coating provided in this application is 0.15-0.2%, and the function of the toughening agent is to improve the toughness of the coating.

[0089] In this application, the toughening agent is preferably MOWITAL B60H.

[0090] The preferred mass percentage of nano-alumina in the ultra-weather-resistant composite material powder coating provided in this application is 0.1-0.15%, and the role of the nano-alumina is to promote flow properties.

[0091] In this application, the nano-alumina is preferably AEROXIDE ALU-C.

[0092] The preferred mass percentage of conductive agent in the ultra-weather-resistant composite material powder coating provided in this application is 0.3-0.6%. The function of the conductive agent is to make the powder conductive, improve the powder application, and ensure that the sprayed paint film has a completely consistent appearance. This can meet the application fields with extremely high requirements for product appearance consistency, such as the exterior surface of consumer goods and Class A automotive surfaces.

[0093] In this application, the conductive agent is preferably BC-L15 inorganic equalizing agent purchased from Shanghai Junjiang New Materials Sales Co., Ltd.

[0094] In this application, the special powder coating for ultra-weather-resistant composite materials preferably comprises the following components by mass percentage:

[0095] Modified acrylate 40-48%, polyester resin 20-24%, IPDI adduct 15-18%, texture agent 0.3-0.5%, transparent filler powder 7.1-8.2%, pigment 1-1.2%, toughening agent 0.15-0.2%, nano-alumina 0.1-0.15%, and conductive agent 0.3-0.6%, or components comprising the following mass percentages:

[0096] Polyester resin 68-76%, IPDI adduct 15-18%, texture agent 0.3-0.5%, transparent filler powder 7.1-8.2%, pigment 1-1.2%, toughening agent 0.15-0.2%, nano alumina 0.1-0.15%, and conductive agent 0.3-0.6%.

[0097] In this application, the special powder coating for ultra-weather-resistant composite materials preferably further includes double-coated aluminum powder, wherein the mass percentage of double-coated aluminum powder in the special powder coating for ultra-weather-resistant composite materials is preferably 0.5-5%, more preferably 0.5-3%, and the double-coated aluminum powder can provide a metallic shimmering effect.

[0098] In this application, the particle size of the double-coated aluminum powder is preferably 0.5-3 nm, and the double-coated aluminum powder is preferably a layered double capsule, preferably a non-floating aluminum powder that has been double-coated with silica and acrylic resin.

[0099] In this application, the double-layer coated aluminum powder is preferably ECKART PCU 1500.

[0100] This application also provides a method for preparing the special powder coating for ultra-weather-resistant composite materials described in the above technical solution, including the following steps:

[0101] Modified acrylate, polyester resin, IPDI adduct, texturer, transparent filler powder, pigment, toughening agent, nano-alumina and conductive agent are mixed to obtain the special powder coating for the ultra-weather-resistant composite material.

[0102] This application does not impose any special limitation on the specific method of mixing, and any method well known to those skilled in the art can be used.

[0103] In this application, when the super weather-resistant composite material powder coating preferably also includes double-layer coated aluminum powder, the preparation method preferably further includes: binding after mixing.

[0104] In this application, the binding parameters preferably include: a temperature of 60-70°C; the binding is used to solve the adhesion problem between the base powder and the metallic pigment, so that the metallic pigment and the base powder are bonded together.

[0105] In this application, the mixture preferably further includes sequentially performing melt extrusion, tableting and cooling, initial crushing, grinding and sieving to obtain the special powder coating for the ultra-weather-resistant composite material.

[0106] The technical solutions of this application will be clearly and completely described below with reference to the embodiments therein. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0107] The composite substrate used in the examples and comparative examples is the hood of an off-road vehicle;

[0108] The preparation methods of the polyurethane acrylates used in the examples and comparative examples are as follows:

[0109] 1 mol of hexamethylene diisocyanate, 1.0 mol of hydroxyethyl methacrylate, 0.5 mol of polycarbonate polyol and xylene were mixed and subjected to a prepolymerization reaction at 85°C for 4 h to obtain a polyurethane prepolymer.

[0110] Xylene was preheated to 100°C. 0.5 mol of methyl methacrylate, 0.1 mol of butyl acrylate, 0.3 mol of glycidyl methacrylate, 0.1 mol of styrene, 0.1 mol of isobornyl methacrylate, and 0.01 mol of dodecyl mercaptan were mixed thoroughly to obtain a mixture. The mixture and 0.03 mol of initiator BPO were then added dropwise to the preheated xylene at a uniform rate. The dropwise addition time for the mixture was 3 hours, and for the initiator, it was 3.5 hours. Then, when 1 / 3 of the mixture remained, 0.1 mol of polyurethane prepolymer was added… 35720.2 mol of initiator was added dropwise to the reaction system over 1.5 h. Then, a free radical polymerization reaction was carried out at 100 °C for 1 h. 0.003 mol of initiator was added, and the reaction was continued for another 1 h. After the reaction was complete, a vacuum was applied until all solvent was removed. The product was then discharged hot to obtain polyurethane acrylate.

[0111] Preparation of epoxy acrylate: Refer to Example 1 in CN115651473A.

[0112] The raw material composition (by weight percentage) of the coatings used in the examples and comparative powder electrostatic spraying was: 48% polyurethane acrylate, 48% saturated carboxyl polyester resin (… P 6504) 24%, IPDI adduct ( The preparation method is as follows: 18% B 1530, 0.3% texture agent (Nanhai Chemical SW301), 7.9% transparent filler powder (Minex 7), 1% pigment (ORION COLOUR BLACK FW200), 0.2% toughening agent (MOWITAL B60H), 0.1% nano alumina (AEROXIDE ALU-C), and 0.5% double-layer coated aluminum powder (ECKART PCU 1500).

[0113] After mixing the raw materials, they are sequentially bound (70℃), melt extruded, pressed and cooled, initially crushed, ground and sieved to obtain the special powder coating for ultra-weather-resistant composite materials.

[0114] Example 1

[0115] Pretreatment: Surface treatment of the substrate to be coated includes cleaning and degreasing (wiping with isopropyl alcohol);

[0116] A water-based conductive paint (using Example 1 in CN117683439A) was sprayed onto the back of the composite substrate. The nozzle diameter was 1.2 mm, the moving speed was 700 mm / s, the spray gun pressure was 0.4 MPa, the oil supply pressure was 0.5 MPa, the fan-shaped pressure was 0.6 MPa, the atomization pressure was 0.5 MPa, and the fan-shaped amount was 3. Baking: After the water-based conductive paint was sprayed, the composite material hood of the vehicle entered the leveling stage for leveling, and then entered the baking chamber for baking at 80°C for 60 minutes.

[0117] Preheating: Temperature 130℃, Time 10min;

[0118] Electrostatic powder coating: The spray gun is set according to the different shapes of the workpiece. For flat parts, the voltage is 80kV and the current is 30μA; the spraying temperature is 95℃; the powder coating is evenly sprayed onto the surface of the substrate through the spraying equipment. There is a recycling system during spraying. The amount of powder coating for ultra-weather-resistant composite materials is 10ml. 2 / kg, multiple coats of paint are sprayed continuously in one go. During the spraying process, the paint is broken down by an electric field and then cured.

[0119] Curing: Temperature 180℃, time 20min.

[0120] Figures 1 and 2 are actual images of the edges of the coating obtained in Example 1 at different angles. It can be seen that no blistering occurs at the edges.

[0121] Figures 3 and 4 are magnified images of the surface of the coating obtained in Example 1 at different magnifications, showing that it has good powder adhesion.

[0122] Comparative Example 1 (The back of the composite substrate is masked with PE masking film)

[0123] Similar to Example 1, except that instead of spraying water-based conductive paint on the back of the composite substrate, a high-temperature resistant tape is used to fix the PE masking film on the back of the composite substrate.

[0124] Figures 5 to 7 are actual images of the coating surface obtained in Comparative Example 1 at different magnifications. It can be seen that the composite substrate has problems with poor powder application and uneven powder application.

[0125] Comparative Example 2 (The back of the composite substrate is shielded with an aluminum plate)

[0126] Similar to Example 1, the only difference is that instead of spraying water-based conductive paint on the back of the composite substrate, an aluminum plate is used for masking. The aluminum plate is 3mm thick and is shaped according to the workpiece shape before being fixed to the back of the composite substrate with clips.

[0127] Figures 8 and 9 show the edge images of the coating obtained in Comparative Example 2 at different magnifications. It can be seen that the composite substrate and the aluminum plate are not tightly bonded, and there are gaps between the aluminum plate and the composite substrate at the edges. Hot air accumulates heat in the gaps, causing blistering at the edge of the workpiece.

[0128] It is known that Comparative Example 1 can only serve a conventional masking function, resulting in low yield in mass production and issues with some batches of composite materials not being coated with powder. Comparative Example 2 uses aluminum plates for masking, which can provide conductivity and heat insulation, improve the uniformity of powder coating, and increase preheating and curing efficiency. However, poor adhesion of the aluminum plates can cause hot air to accumulate in the gaps during the heating and curing process, leading to localized overheating and blistering of the coating. This application sprays water-based conductive paint onto one side of the composite substrate, which provides conductivity and improves the consistency of powder coating, making the powder coating unaffected by the type of composite material, batch, equipment resistance, or spraying environment.

[0129] Example 2

[0130] Similar to Example 1, the parameters for water-based conductive paint and spraying water-based conductive paint are the same. The difference lies in the specific workpiece shape and the parameters for electrostatic powder spraying, as shown in Table 1. It can be seen that the composite material powder spraying method of this application is applicable to workpieces of different sizes and has good versatility.

[0131] Table 1. Effects of Example 2 on workpieces of different shapes.

[0132] The above description is merely a preferred embodiment of this application and does not constitute any limitation on this application. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this application, and these improvements and modifications should also be considered within the scope of protection of this application.

Claims

1. A method for powder coating of composite materials, characterized in that, Includes the following steps: After coating one side of the composite material with conductive paint, it is preheated to obtain a pretreated composite material. The other side of the uncoated conductive paint of the pretreated composite material is subjected to electrostatic powder spraying. During the electrostatic powder spraying process, an electric field is used to break down and coat the pretreated composite material, and then it is cured.

2. The composite material powder spraying method according to claim 1, characterized in that, The conductive paint includes water-based conductive paint.

3. The composite material powder spraying method according to claim 1 or 2, characterized in that, The conductive paint is applied by spraying, with a spraying pressure of 0.3–0.5 MPa, a distance of 15–25 cm, and a moving speed of 600–800 mm / s.

4. The composite material powder spraying method according to claim 1 or 2, characterized in that, The process after coating the conductive paint and before preheating includes drying to form a dry film with a thickness of 20–40 μm and a resistivity of ≤0.4 MΩ.

5. The composite material powder spraying method according to claim 1, characterized in that, The electric field is formed by the charged powder sprayed out by the electrostatic powder spraying, the charged powder being negatively charged, and the pretreated composite material being grounded.

6. The composite material powder spraying method according to claim 1, characterized in that, The preheating temperature is 80–170°C, and the time is 6–12 minutes.

7. The composite material powder spraying method according to claim 1, characterized in that, The voltage for the electrostatic powder spraying is 40–80 kV, and the current is 20–30 μA.

8. The composite material powder spraying method according to claim 1 or 7, characterized in that, The temperature for electrostatic powder spraying is 80–170°C.

9. The composite material powder spraying method according to claim 1 or 7, characterized in that, The parameters for the electrostatic powder coating are set according to the different shapes of the workpiece: when the workpiece is a flat part, the voltage of the electrostatic powder coating is 80kV and the current is 30μA; when the workpiece is a part with grooves, the voltage of the electrostatic powder coating is 80kV and the current is 22μA.

10. The composite material powder spraying method according to claim 1 or 7, characterized in that, When the electrostatic powder spraying is a recoating process, the spraying voltage is 40kV and the current is 30μA.

11. The composite material powder spraying method according to claim 1 or 7, characterized in that, The powder electrostatic spraying coating is a powder coating for ultra-weather-resistant composite materials, and the ultra-weather-resistant composite material powder coating comprises the following components by mass percentage: The composition comprises 0-50% modified acrylate, 20-75% polyester resin, 15-20% IPDI adduct, 0.1-0.8% texture agent, 4.3-22.7% transparent filler powder, 0.8-1.2% pigment, 0.1-0.2% toughening agent, 0.1-0.3% nano-alumina, and 0-2% conductive agent, with the sum of the mass percentages of all components being 100%.

12. The composite material powder spraying method according to claim 11, characterized in that, The modified acrylate is a polyurethane acrylate or an epoxy acrylate.

13. The composite material powder spraying method according to claim 12, characterized in that, The polyurethane acrylate is prepared by a method comprising the following steps: Isocyanate, polyester polyol, hydroxyl-containing acrylic monomer and organic solvent are mixed and subjected to a prepolymerization reaction to obtain polyurethane prepolymer; The polyurethane prepolymer, terminal double-bonded silane, acrylate monomer, initiator, chain transfer agent and organic solvent are mixed and subjected to free radical polymerization to obtain the polyurethane acrylate.

14. The composite material powder spraying method according to claim 13, characterized in that, The molar ratio of the isocyanate, polyester polyol and hydroxyl-containing acrylic monomer is 1:0.5:0.5 to 1:0.3:1.

2.

15. The composite material powder spraying method according to claim 13 or 14, characterized in that, The hydroxyl-containing acrylic monomers include one or more of hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxyethyl acrylate, and hydroxypropyl acrylate.

16. The composite material powder spraying method according to claim 13, characterized in that, The molar ratio of the polyurethane prepolymer, the terminal double-bonded silane, and the acrylate monomer is 1:0.3:4 to 1:2:

12.

17. The composite material powder spraying method according to claim 13 or 16, characterized in that, The terminal double-bonded silane includes one or more of the following: terminal vinyl silane, terminal acrylic silane, terminal acryloyloxy silane, and terminal methpropylene silane.

18. The composite material powder spraying method according to claim 13 or 16, characterized in that, The acrylate monomers include one or more of the following: methyl methacrylate, butyl acrylate, butyl methacrylate, glycidyl methacrylate, isobornyl methacrylate, cyclohexyl methacrylate, (meth)acrylate-modified polycaprolactone, ethyl acrylate, and ethylene glycol dimethacrylate.

19. The composite material powder spraying method according to claim 11, characterized in that, The polyester resin is a saturated carboxyl polyester resin.

20. The composite material powder spraying method according to claim 11, characterized in that, The powder coating for ultra-weather-resistant composite materials also includes double-coated aluminum powder, wherein the mass percentage of double-coated aluminum powder in the powder coating for ultra-weather-resistant composite materials is 0.5% to 5%.

21. The composite material powder spraying method according to claim 1, characterized in that, The curing temperature is 160–180°C, and the time is 7–20 minutes.

22. The composite material powder spraying method according to claim 1, characterized in that, The composite material includes automotive exterior composite materials, which include sheet molding compounds, bulk molding compounds, and resin transfer molding materials.

Images