Preparation method of protective layer on surface of rubber composite material

Abstract

The invention provides a preparation method of a protective layer on the surface of a rubber composite material, which comprises the following steps: carrying out surface chemical conversion treatment on a metal substrate to form a phosphating film, and then coating a coupling agent to form a composite passivation layer; applying a resin-based coating containing a nanoscale filler as a bottom layer by adopting a directional one-way and cross coating mode; applying an elastic polymer coating as a middle layer through a spiral superposition coating method; integrally coating a modified acrylic polymer coating as a surface layer, and carrying out reinforced coating on a specific part; the bottom layer coating is subjected to medium-temperature thermal curing, the middle layer coating is subjected to low-temperature thermal curing, and the surface layer coating is subjected to high-temperature later-stage heat treatment after being subjected to room-temperature curing; a non-metal base material is subjected to surface activation and then coated with a coupling agent. According to the invention, by designing a multi-layer and functionalized protective coating system and optimizing the coating and curing process, the overall efficiency of the protective layer is effectively improved.

Description

Technical Field

[0001] This invention relates to the field of composite material surface treatment technology, and specifically to a method for preparing a protective layer on the surface of a rubber composite material. Background Technology

[0002] Rubber-to-rubber composite components are widely used in industry, especially in automotive manufacturing, aerospace, and machinery, serving as key components such as seals and shock absorbers. However, in complex working environments, these composite components are prone to interface separation due to rubber corrosion and aging. Traditional waterproofing methods, particularly those targeting the rubber-to-rubber interface, have several limitations. Traditional waterproofing methods typically employ a single-coat brush application. However, single-material coatings often fall short in terms of weather resistance, leak resistance, and adaptability to complex working conditions, particularly being prone to cracking under temperature variations or vibration. Furthermore, pretreatment methods for the substrate before applying traditional coatings are often inadequate for the characteristics of rubber composite components. For instance, rubber surfaces often have an oxide layer; improper pretreatment can significantly reduce coating adhesion, leading to peeling and detachment. Additionally, the surface inertness of the rubber substrate requires special treatment to ensure good coating adhesion. Traditional brushing methods tend to create sharp-angled coatings at joints, which not only easily cause stress concentration but also, under prolonged external influences such as UV radiation and salt spray corrosion, readily cause coating cracking. This allows moisture and corrosive media to penetrate, ultimately leading to interface separation and failure.

[0003] Because existing technologies for waterproofing rubber-rubber composite components fail to fully consider the special characteristics of composite materials and the requirements of complex working environments, the functionality and durability of the waterproofing layer are poor, especially at rubber-rubber joints, which become the weakest link in the entire waterproofing system. Therefore, this invention studies and designs a method for preparing a protective layer on the surface of rubber composite materials. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the defect of poor interface protection of composite materials in the prior art, thereby providing a method for preparing a protective layer on the surface of a rubber composite material.

[0005] To address the above problems, this invention provides a method for preparing a protective layer on the surface of a rubber composite material, comprising the following steps: S1: The surface of the metal substrate is chemically converted to form a phosphating film, and then a coupling agent is coated to form a composite passivation layer as a pretreatment. S2: A resin-based coating containing nanoscale fillers is applied as the underlayer using directional unidirectional and cross-coating methods; S3: An elastic polymer coating is applied as an intermediate layer using a spiral overlay coating method; a modified acrylic polymer coating is applied as a top layer, and a reinforcing coating is applied at the joints of the composite material. S4: Apply a reinforcing coating to the joint of the two composite materials to improve the protective performance of the joint; for non-metallic substrates, perform surface activation before coating with the coupling agent to complete the pretreatment; The bottom layer coating is cured at medium temperature, the middle layer coating is cured at low temperature, and the top layer coating is cured at room temperature and then subjected to high temperature post-heat treatment.

[0006] Preferably, the phosphating film is formed using a phosphate solution selected from one or more of zinc phosphate, manganese phosphate, and iron phosphate, and the thickness of the phosphating film is controlled within the range of 5-8 μm.

[0007] Preferably, the nanoscale filler contained in the bottom coating is selected from one or more of graphene, carbon nanotubes, nano-silica and nano-alumina, and the content of the filler is 2-3 wt%.

[0008] Preferably, the brushes used in the directional unidirectional and cross-coating methods have hardnesses of 70-80 Shore A and 40-50 Shore A, respectively, and the brush head material is polytetrafluoroethylene modified nylon; furthermore, when the underlying epoxy resin is brushed, axial unidirectional brushing is used to ensure the uniformity and directionality of the coating; for the rubber surface, radial cross-coating is used, with an angle of 90° between the first and second coats.

[0009] Preferably, the rounded transition at the rubber joint is achieved using a special arc-shaped brush head with a radius of curvature of 1-2 mm, ensuring uniform pressure distribution during brushing.

[0010] Preferably, the bottom epoxy resin coating is cured at a medium temperature of 60-70°C for 30-40 minutes; the intermediate elastic polyurethane coating is cured at a low temperature of 50-60°C for 60-80 minutes; and the surface fluorocarbon modified acrylic coating is initially cured at room temperature for 24 hours, followed by a post-heat treatment at 80-85°C for 20-30 minutes.

[0011] Preferably, the intermediate layer of elastic polyurethane coating is applied by spiral overlapping brushing, with each overlap being 1 / 4 of the total brush width, and the coating forms a continuous and seamless protective layer after drying.

[0012] Preferably, the dry film thickness of the bottom epoxy resin coating is 20-25 μm, the dry film thickness of the middle elastic polyurethane coating is 30-35 μm, and the dry film thickness of the top fluorocarbon modified acrylic coating is 10-15 μm, with each layer connected by micropores.

[0013] Preferably, the pretreatment of the non-metallic substrate, in addition to coating with a coupling agent, also includes surface activation using an organic solvent or plasma.

[0014] Preferably, when performing the reinforcing coating at the composite interface, a surface cleaning treatment is required before each coating pass.

[0015] The method for preparing a protective layer on the surface of a rubber composite material provided by this invention has the following beneficial effects: This invention effectively improves the overall performance of the protective layer by designing a multi-layered, functional protective coating system and optimizing the coating and curing process. 2. The present invention also employs a phased and temperature-controlled curing strategy, where the bottom layer, intermediate layer, and surface layer each reach their optimal curing state, forming a dense and uniform coating structure. 3. This invention also effectively solves the problem of susceptibility to corrosion and fatigue damage at the joints of composite materials by performing special reinforcement treatment. For non-metallic substrates, plasma activation and coating with coupling agents are used to improve the chemical activity of the surface, thereby increasing the adhesion strength between the coating and the non-metallic substrate. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the method flow of the present invention. Detailed Implementation

[0017] like Figure 1 As shown, the present invention provides a method for preparing a protective layer on the surface of a rubber composite material, which includes the following steps: The metal substrate undergoes surface chemical conversion treatment to form a phosphating film, followed by coating with a coupling agent to form a composite passivation layer as a pretreatment. A resin-based coating containing nanoscale fillers is applied as the bottom layer using directional unidirectional and cross-coating methods. An elastic polymer coating is applied as the intermediate layer using a spiral superposition coating method. A modified acrylic polymer coating is applied as the top layer, and a reinforcing coating is applied at the joint of the composite materials. The bottom layer is cured at medium temperature, the intermediate layer is cured at low temperature, and the top layer is cured at room temperature followed by a high-temperature post-heat treatment. A reinforcing coating is applied at the joint of the two composite materials to improve the protective performance of the joint. For non-metallic substrates, surface activation is performed before coating with a coupling agent to complete the pretreatment.

[0018] This application addresses the problem of poor interfacial protection in composite materials by designing a multi-layered, functional protective coating system and optimizing the coating and curing processes to effectively improve the overall performance of the protective layer. Specifically, the metal substrate is phosphated to form a dense phosphate film, and then the surface properties are further optimized using a coupling agent to enhance the coating's adhesion. A resin base layer containing nanoscale fillers is used to improve the coating's density and enhance its corrosion resistance. The intermediate layer uses an elastic polymer to adapt to the thermal expansion and contraction of the composite material under different environmental conditions, relieving stress and preventing coating cracking. The surface layer uses a modified acrylic polymer with excellent weather resistance and chemical stability, and is reinforced in specific areas to improve the protective layer's resistance to complex environments. Through a staged, temperature-controlled curing strategy, the bottom layer, intermediate layer, and surface layer each reach their optimal curing state, forming a tight and uniform coating structure. Reinforcement treatment is applied at the joints of the composite materials to effectively solve the problem of susceptibility to corrosion and fatigue damage at the joints. For non-metallic substrates, plasma activation and the application of a coupling agent improve the surface's chemical activity, thereby increasing the adhesion strength between the coating and the non-metallic substrate. This technical solution can significantly improve the interface protection performance of composite materials in harsh environments, extend their service life, and meet the high requirements of industrial applications.

[0019] Specifically, a phosphate solution, such as zinc phosphate, manganese phosphate, or iron phosphate, is used to phosphate the metal substrate to form a phosphate film with a thickness of 5-8 μm. This film not only acts as a physical barrier to prevent metal corrosion but also improves the adhesion of subsequent coatings. Based on the phosphate film, a coupling agent is further coated to construct a composite passivation layer, enhancing the bonding strength between the substrate surface and the coating and preventing coating peeling off in complex environments.

[0020] Specifically, the bottom coating uses one or more nanoscale fillers such as graphene, carbon nanotubes, nano-silica, or nano-alumina, with their content controlled at 2-3 wt%. The selection and filling ratio significantly enhance the mechanical properties and corrosion resistance of the coating. In particular, the addition of graphene, due to its excellent conductivity and impermeability, effectively prevents electrochemical corrosion and reduces the penetration of water and corrosive media, thereby extending the service life of the waterproof layer. The overall waterproof performance of the composite component is enhanced through a combination of substrate pretreatment, gradient waterproof layer design, and directional brushing process. Specifically, the bottom layer (epoxy resin containing nanoscale fillers) forms a strong physicochemical bond with the substrate, and the nanoscale fillers fill the micropores, improving the coating's impermeability. The middle layer (elastic polyurethane) alleviates the stress caused by the difference in thermal expansion coefficients between rubber and metal or between rubbers, preventing cracking of the coating under temperature differences. The top layer (fluorocarbon-modified acrylic) provides excellent outdoor protection; the low surface energy of the fluorocarbon groups results in a water contact angle greater than 110°, achieving self-cleaning while enhancing the waterproof performance of the composite material surface. Within a wide temperature range of -40℃ to 120℃, the waterproof layer treated with a segmented curing mechanism maintains its integrity, significantly improving its stability and durability under complex working conditions. Furthermore, the basic solution employs different pretreatment methods for metallic and non-metallic substrates. Metallic substrates undergo phosphating-silane composite treatment, while non-metallic substrates are first plasma-activated and then coated with a coupling agent. This differentiated pretreatment ensures good adhesion and compatibility of the coating on different materials, allowing the waterproof layer to effectively cover metal surfaces and tightly adhere to rubber materials, providing comprehensive waterproof protection for the composite material. Optimization of the underlying coating composition further enhances the overall performance of the waterproof layer, giving it not only basic waterproofing capabilities but also stronger corrosion resistance and mechanical strength, achieving a comprehensive upgrade in surface protection for the composite material.

[0021] Specifically, the hardness of the brush bristles for the coating tool is precisely selected: 70 to 80 Shore A for metal substrates to ensure a tight adhesion of the coating to rigid surfaces, and 40 to 50 Shore A for rubber substrates to accommodate their flexible nature and avoid damage during coating. Using brush heads made of PTFE-modified nylon not only enhances the tool's corrosion resistance but also ensures a smooth and consistent coating process due to its low coefficient of friction. This differentiated brush coating strategy significantly improves coating uniformity and adhesion, especially at the interface between different materials in metal-rubber composite components, effectively preventing protective gaps caused by excessively thick or thin coatings in certain areas.

[0022] The coating utilizes both directional and cross-coating methods, combining the characteristics of the base layer (epoxy resin containing nano-zinc oxide) and the intermediate layer (elastic polyurethane). Unidirectional brushing ensures coating continuity and uniformity, making it particularly suitable for textured or geometrically complex metal surfaces, preventing coating buildup and uneven distribution. Cross-coating, on the other hand, leverages the overlapping of layers to enhance coverage and mechanical properties, especially on soft and potentially deformable rubber surfaces, compensating for the lack of elasticity that may result from unidirectional coating alone. The top acrylic polymer coating is applied after the intermediate layer has fully cured, ensuring good adhesion between layers and enhancing the overall coating's density and weather resistance through high-temperature post-treatment, achieving long-term stable waterproofing.

[0023] In summary, by selecting brush head materials with specific hardness and employing directional brushing paths, the preparation process of the protective layer on the composite material surface is further optimized. This allows the coating to more precisely match the properties of different substrates, especially in critical areas of metal-rubber composite components, effectively enhancing the protective capabilities at the joints through enhanced coating treatment. The segmented curing mechanism ensures full cross-linking of the coating at different temperatures, thereby enhancing the overall strength and environmental adaptability of the entire protective system. The technical benefits are reflected in extending the service life of composite material components, reducing maintenance costs due to waterproofing layer failure, and broadening the application range of such components in harsh environments.

[0024] Specifically, a rounded transition is used at the rubber-to-rubber joints, employing a specialized curved brush head (1-2mm radius of curvature) to ensure a smooth transition of the coating at the joint. This effectively prevents wrinkles and bubbles at sharp angles, significantly enhancing the integrity and tightness of the waterproof layer at the joint. Utilizing the uniform pressure distribution characteristic of the rounded transition surface in contact with the joint surface, even in complex geometries, coating uniformity is guaranteed, thus blocking potential water penetration paths at the joint at a microscopic level and improving the overall waterproof performance of the composite component. By applying coatings with different properties in layers, combined with directional brushing path control and segmented curing, the problems of traditional single-coat waterproofing methods are solved. Phosphating and silane composite pretreatment form a stable passivation layer, enhancing the adhesion between the coating and the rubber substrate; an epoxy resin underlayer containing nano-zinc oxide improves impermeability; an elastic polyurethane intermediate layer alleviates stress caused by differences in the thermal expansion coefficients of materials, preventing coating cracking; and a fluorocarbon-modified acrylic surface layer provides excellent weather resistance and self-cleaning properties. The directional brushing path adapts to the elastic deformation of the rubber, ensuring the uniformity and durability of the coating, while the segmented curing mechanism avoids damage to the rubber from high temperatures and ensures full cross-linking of the coating, improving overall density. The technical effects are reflected in the waterproof layer remaining stable within a temperature range of -40℃ to 120℃, salt spray resistance exceeding 1000 hours, and water permeability as low as 0.1 mL / (m²). 2•d) The following methods effectively extend the service life of rubber and rubber composite components and reduce maintenance costs.

[0025] Specifically, the bottom epoxy resin coating undergoes medium-temperature thermosetting at 60-70 degrees Celsius for 30-40 minutes to ensure chemical bonding between the coating and the phosphate film, enhancing the coating's adhesion to the rubber substrate. Simultaneously, the addition of nano-zinc oxide significantly improves the coating's impermeability, effectively preventing moisture erosion. The intermediate elastic polyurethane coating undergoes low-temperature thermosetting at 50-60 degrees Celsius for 60-80 minutes. This not only prevents accelerated aging of the rubber due to high-temperature treatment but also maintains the elastic characteristics of polyurethane, mitigating stress caused by different coefficients of thermal expansion between rubbers under temperature changes or mechanical vibrations, preventing coating cracking. The surface fluorocarbon-modified acrylic coating is first cured at room temperature, followed by a high-temperature post-treatment at 80-85 degrees Celsius. This not only accelerates the cross-linking process of the coating, forming a denser protective layer, but also, due to the low surface energy of the fluorocarbon groups, gives the coating excellent self-cleaning ability and chemical corrosion resistance, greatly extending the service life of the composite component in harsh environments.

[0026] By employing a segmented thermosetting process, combined with directional brushing and specialized reinforcement measures, long-term waterproof protection for the rubber-to-rubber composite components proposed in the basic solution is achieved. This not only meets the surface pretreatment requirements of different substrate materials but also, through the synergistic effect of the coatings, solves problems that traditional single-coating systems struggle with, such as waterproof performance degradation, coating cracking, and easy water seepage at joints. It ensures the stability of the composite components within a temperature range of -40 to 120 degrees Celsius, achieves salt spray resistance exceeding 1000 hours, and reduces water permeability to below 0.1 ml / (m²·day), demonstrating excellent weather resistance and adaptability to complex working conditions. For non-metallic rubber substrates, plasma activation and silane coupling agent pretreatment steps effectively enhance the coating's adhesion strength, further optimizing the reliability of the entire protective system.

[0027] Specifically, the surface fluorocarbon-modified acrylic coating is first pre-cured at room temperature to ensure basic film formation. Then, a post-treatment heat treatment at 80-85℃ is performed. This process significantly enhances the coating's weather resistance and chemical resistance because the high-temperature heat treatment promotes further cross-linking of polymer molecules, forming a denser coating structure that effectively resists erosion from harsh environments such as ultraviolet radiation and salt spray, extending the service life of the waterproof layer. Simultaneously, this process ensures the uniformity and stability of the coating on the surfaces of composite components made of different materials, especially at rubber-to-rubber joints. The enhanced coating treatment improves the protective performance of the joint areas, preventing premature failure due to thin coatings.

[0028] Specifically, when applying reinforcing coatings at composite interfaces, surface cleaning is required before each coat to ensure coating adhesion. This process removes potential stains, grease, and dust, allowing the coating to adhere better to the substrate and reducing coating failure due to interface contamination. The resulting improvement is enhanced overall durability and waterproofing, particularly in stress-concentrated areas like composite joints where impurities easily accumulate; the coating's durability and sealing performance are significantly improved.

[0029] The preparation process of the protective layer on the material surface is further optimized by incorporating a surface activation treatment for non-metallic substrates and a step of reinforcing coating at the composite interface into the basic scheme. These additional steps not only improve the adhesion quality of the coating on the non-metallic substrates but also form a stronger and denser protective layer at the composite joint. Through enhanced surface cleaning before coating and activation treatment of the non-metallic surface, uniform distribution and high-strength bonding of the coating are ensured throughout the composite structure, thereby providing more stable waterproof and corrosion-resistant protection over a wide temperature range and under harsh environmental conditions.

[0030] Specifically, the dry film thickness of the bottom epoxy resin coating is set at 20 to 25 micrometers, the intermediate elastic polyurethane coating at 30 to 35 micrometers, and the top fluorocarbon modified acrylic coating at 10 to 15 micrometers. The layers are connected by pre-reserved micropores, which not only enhances the overall breathability of the coating but also significantly improves its corrosion resistance, ensuring the durable performance of the protective layer in harsh environments. By meticulously controlling the thickness and application method of each layer, the overall protective effect of the coating is effectively improved. The refined process of directional unidirectional and cross-coating of the bottom layer, as well as spiral superposition of the intermediate layer coatings, allows the coating to better adapt to the surface characteristics of the two composite materials. At the junction of the metal and non-metal composite materials, enhanced coating and rounded transition treatment significantly strengthen the protective strength of the joint, preventing the intrusion of moisture and corrosive media. For the pretreatment of the non-metallic substrate, a strategy of surface activation followed by coupling agent coating is adopted to improve the adhesion between the non-metallic substrate and the coating, further ensuring the overall adhesion and durability of the coating.

[0031] Specifically, the epoxy resin coating for the rubber substrate is applied using an axial unidirectional brush to ensure uniform distribution and good directionality of the coating on the rubber surface. This effectively enhances the adhesion between the coating and the rubber substrate, reduces internal stress within the coating, and prevents peeling and flaking. The base coat for the rubber substrate is applied using a radial cross-brush method, with a 90° angle between the first and second coats. This effectively accommodates the elastic deformation that may occur during use, ensuring the integrity and stability of the coating under the elastic deformation of the rubber, and significantly improving the coating's adhesion strength and waterproofing effect.

[0032] Specifically, the intermediate layer of elastic polyurethane coating is applied using a spiral overlay brush, with each layer overlapping 1 / 4 of the total brush width. After drying, this forms a continuous, seamless protective layer, improving the coating's toughness and adhesion to the substrate. This coating method ensures a tight bond between the layers, enhancing the overall toughness and adhesion to the substrate. By precisely controlling the coating thickness and distribution, this method not only strengthens the coating's resistance to external stresses but also effectively prevents the penetration of moisture or other corrosive media, significantly improving the durability and reliability of the composite material surface protective layer.

[0033] By pre-forming a composite passivation layer on the surface of a metallic substrate and applying surface activation and coupling agent coating to the surface of a non-metallic substrate, the chemical bonding between the coating and the substrate is enhanced, ensuring strong adhesion of the coating. A directional, unidirectional, and cross-coated base resin-based coating, combined with a spirally layered intermediate layer and a monolithically coated top acrylic polymer coating, constructs a gradient protective system from the inside out. The multi-layer gradient coating design, combined with a segmented curing heating strategy, adapts to the thermal expansion characteristics of the composite material, ensuring coating stability over a wide temperature range. Reinforced coating treatment at the joints of the composite materials, especially at the junctions of two composite materials, effectively improves the protective performance of the joints, reduces the risk of localized stress concentration, and extends the service life of the composite material in harsh environments. This results in a protective layer with excellent corrosion resistance, water resistance, and weather resistance, meeting the needs of complex industrial applications.

[0034] Specifically, for the pretreatment of non-metallic substrates, surface activation using organic solvents or plasma significantly enhances the chemical activity of the substrate surface, providing more favorable conditions for the adhesion of subsequent coatings. This pretreatment step ensures the coupling agent fully integrates with the non-metallic substrate, forming a robust interface layer, thereby improving the adhesion and durability of the entire coating system. Differentiated pretreatment strategies are employed for different substrate materials. Metallic substrates undergo phosphating and silane treatment to form a composite passivation layer, while non-metallic substrates are first surface activated before coating with the coupling agent. This differentiated pretreatment, combined with a multi-layer coating system consisting of directional and cross-coated underlayers, an elastic polymer intermediate layer, and modified acrylic as the top layer, provides enhanced protection at composite material joints, particularly in rubber-rubber seams, where reinforced coating effectively improves the waterproofing and corrosion resistance of the joint. By controlling the coating method, thickness, and curing conditions of each layer, the entire coating system maintains stable performance over a wide temperature range, meeting the protection requirements under complex working conditions.

[0035] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention. The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the protection scope of the present invention.

Claims

1. A method for preparing a protective layer on the surface of a rubber composite material, characterized in that, Includes the following steps: S1: The surface of the metal substrate is chemically converted to form a phosphating film, and then a coupling agent is coated to form a composite passivation layer as a pretreatment. S2: A resin-based coating containing nanoscale fillers is applied as the underlayer using directional unidirectional and cross-coating methods; S3: An elastic polymer coating is applied as an intermediate layer using a spiral overlay coating method; The entire surface is coated with a modified acrylic polymer coating, and a reinforcing coating is applied at the joints of the composite material. S4: Apply a reinforcing coating to the joint of the two composite materials to improve the protective performance of the joint; for non-metallic substrates, perform surface activation before coating with the coupling agent to complete the pretreatment; The bottom layer coating is cured at medium temperature, the intermediate layer coating is cured at low temperature, and the top layer coating is cured at room temperature and then subjected to high-temperature post-heat treatment.

2. The method for preparing a protective layer on the surface of a rubber composite material according to claim 1, characterized in that: The phosphate film is formed using a phosphate solution selected from one or more of zinc phosphate, manganese phosphate, and iron phosphate, and the thickness of the phosphate film is controlled within the range of 5-8 μm.

3. The method for preparing a protective layer on the surface of a rubber composite material according to claim 1 or 2, characterized in that: The bottom coating contains nanoscale fillers selected from one or more of graphene, carbon nanotubes, nano-silica, and nano-alumina, and the content of the fillers is 2-3 wt%.

4. The method for preparing a protective layer on the surface of a rubber composite material according to claim 3, characterized in that: The brushes used in the directional unidirectional and cross-coating methods have hardnesses of 70-80 Shore A and 40-50 Shore A, respectively, and the brush head material is polytetrafluoroethylene modified nylon. Furthermore, when the underlying epoxy resin is brushed, axial unidirectional brushing is used to ensure the uniformity and directionality of the coating. For the rubber surface, radial cross-coating is used, with an angle of 90° between the first and second coats.

5. The method for preparing a protective layer on the surface of a rubber composite material according to claim 4, characterized in that: The rounded transition at the rubber joint is applied using a special arc-shaped brush head with a radius of curvature of 1-2 mm. During brushing, the pressure in contact with the joint surface is evenly distributed.

6. The method for preparing a protective layer on the surface of a rubber composite material according to claim 5, characterized in that: The bottom epoxy resin coating is cured at medium temperature at 60-70℃ for 30-40 minutes; the intermediate elastic polyurethane coating is cured at low temperature at 50-60℃ for 60-80 minutes; the surface fluorocarbon modified acrylic coating is initially cured at room temperature for 24 hours, followed by a post-heat treatment at 80-85℃ for 20-30 minutes.

7. The method for preparing a protective layer on the surface of a rubber composite material according to claim 1, characterized in that: The intermediate layer of elastic polyurethane coating is applied by spiral overlapping brushing, with each overlap being 1 / 4 of the total brush width. After drying, the coating forms a continuous and seamless protective layer.

8. The method for preparing a protective layer on the surface of a rubber composite material according to claim 1, characterized in that: The dry film thickness of the bottom epoxy resin coating is 20-25 μm, the dry film thickness of the middle elastic polyurethane coating is 30-35 μm, and the dry film thickness of the top fluorocarbon modified acrylic coating is 10-15 μm. The layers are connected by micropores.

9. The method for preparing a protective layer on the surface of a rubber composite material according to claim 1, characterized in that: The pretreatment of the non-metallic substrate, in addition to coating with a coupling agent, also includes surface activation using organic solvents or plasma.

10. The method for preparing a protective layer on the surface of a rubber composite material according to claim 1, characterized in that: When performing the reinforcement coating at the composite interface, surface cleaning is required before each coating pass.

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