Preparation method of hydrophobic composite coating for rubber material surface and composite coating

Abstract

This invention provides a method for preparing a hydrophobic composite coating for rubber material surfaces and the composite coating itself, relating to the field of rubber material surface coating preparation technology. The steps are as follows: Argon gas is introduced into a vacuum chamber to perform plasma pretreatment on the cleaned rubber substrate; under the action of a magnetic field, Ar is ionized to generate Ar. + And high-energy electrons, Ar + Graphite targets are bombarded to obtain carbon atoms, carbon clusters, and ionized carbon. CF4 gas is introduced into a vacuum chamber, where it decomposes under electron collisions to generate fluorine-containing active substances. The mixed flux of carbon atoms, carbon clusters, ionized carbon, and fluorine-containing active substances reaches the surface of the NBR substrate and undergoes adsorption and interfacial reactions, resulting in a rubber-based fluorine-doped diamond-like carbon coating with hydrophobic and friction-reducing properties. The composite coating prepared by this invention has uniform component content and good density. By controlling the flow rate of CF4 gas, a composite coating with adjustable hybrid structure and elemental content can ultimately be achieved.

Description

Technical Field

[0001] This invention relates to the field of rubber material surface coating preparation technology, specifically to a method for preparing a hydrophobic composite coating for rubber material surface and the composite coating. Background Technology

[0002] Failure of rubber materials is mainly caused by the coupling of multiple factors, including wear, chemical swelling, extrusion, structural fatigue, pressure shock, low temperature, and material aging. The superposition and coupling of various failure modes result in the lifespan of rubber materials being far below the design requirements of deep-sea equipment. Surface coating technology can impart wear-resistant and friction-reducing properties to the surface without changing the excellent elasticity of the rubber itself. However, the mismatch in the coefficients of thermal expansion between the rubber substrate and the film leads to stress concentration at the interface during dynamic deformation, causing peeling failure. The mismatch in hardness and elasticity between the rubber substrate and the film poses a risk of coating cracking when the flexible substrate deforms.

[0003] For example, CN 111378927 A discloses a hard thin film structure and preparation method applied to an elastic substrate. This invention provides a nano-transition layer between the diamond-like carbon film and the elastic substrate to improve the film adhesion. CN116607130 A discloses a method for increasing the lubricity of a rubber surface by plasma carbonization. This invention incorporates Si into the transition layer to reduce the large hardness difference between the diamond-like carbon film and the rubber substrate, thereby enhancing the adhesion between the film and the substrate. CN112746258 A discloses a wear-resistant and corrosion-resistant rubber material and its preparation method. This invention uses SiC as a transition layer to improve the adhesion performance between the diamond-like carbon film and the rubber substrate. CN 114000147 A discloses a wear-resistant rubber material and its preparation method. This invention uses one of chromium film, titanium film, or silicon film as a transition layer to improve the adhesion performance between the functional layers of alternating stacked diamond-like carbon films and nitrogen-doped diamond-like carbon films and the substrate. Although the above method deposits diamond-like carbon (DLC) coatings onto the rubber surface by introducing a transition layer, the high sensitivity of the DLC film's tribological properties to the temperature, humidity, and gas type of the environment limits its application in high-humidity marine environments.

[0004] CN 121272343 A discloses a diamond-like composite film for wear-resistant rubber material surface, its preparation method and application. The diamond-like composite film prepared by the present invention exhibits excellent wear-resistant properties under high load and seawater medium. However, the application simplifies the marine environment it emphasizes to friction with NaCl aqueous solution, which is insufficient to match the actual service environment of marine hydraulic seals in salt spray humid environment and hydraulic oil boundary lubrication coupling.

[0005] Therefore, for marine high-humidity environments, this invention proposes a composite coating with hydrophobic properties and wear-resistant and friction-reducing properties, and its preparation method. Summary of the Invention

[0006] To address the issue of diamond-like carbon (DLC) coatings' high sensitivity to environmental conditions leading to a sharp drop in wear resistance under high humidity, and the problem of interfacial stress concentration during dynamic deformation caused by the thermal expansion coefficient and elastic mismatch between the DLC coating and the rubber substrate, resulting in coating cracking and peeling failure, this invention aims to provide a method for preparing a hydrophobic composite coating for rubber materials and the composite coating itself. By introducing fluorine (F) into the DLC coating and forming C-Fx bonds, the surface free energy of the coating is reduced, thereby significantly improving hydrophobicity and exhibiting lower adhesion tendency and better tribological properties in humid, water-lubricated, or corrosive environments. This F-DLC (fluorine-doped diamond-like carbon) coating combines excellent hydrophobic properties with good tribological properties, can be stably deposited on the surface of the rubber substrate, reduces the mismatch with the rubber substrate, and significantly extends its service life and operational reliability in marine environments and under different loads and frequencies.

[0007] Specifically, on the one hand, the present invention provides a method for preparing a hydrophobic composite coating for the surface of rubber materials, the specific implementation steps of which include: S1. Clean the rubber substrate by ultrasonic cleaning with water, deionized water and alcohol in sequence, and then dry it in a drying oven to obtain the cleaned rubber substrate.

[0008] S2. Place the rubber substrate obtained in step S1 on the rotating frame inside the vacuum chamber of the pulse magnetron sputtering system and rotate it.

[0009] S3. Based on step S2, argon gas is introduced into the vacuum chamber to perform plasma pretreatment on the cleaned rubber substrate to obtain a surface-active rubber substrate.

[0010] S4. After pretreatment, the DC magnetron power supply is turned on to clean the graphite target material placed above the vacuum chamber. Under the influence of the magnetic field, Ar is ionized to produce Ar. + And high-energy electrons, Ar + By bombarding a graphite target, carbon atoms, carbon clusters, and ionized carbon in the graphite target are obtained.

[0011] S5. CF4 gas is introduced into the vacuum chamber. CF4 is decomposed by electron collisions, generating CF3, CF2, CF and F, neutral active substances, and CF3. + In step S6, these fluorine-containing active substances are fully mixed with the carbon atoms, carbon clusters and ionized carbon obtained in step S4 in the deposition atmosphere, so that the deposited coating has a uniform and dense content.

[0012] S6. The mixed flux composed of carbon atoms, carbon clusters, and ionized carbon obtained in step S4 and the fluorine-containing active material obtained in step S5 reaches the surface of the NBR matrix and undergoes adsorption and interfacial reaction. In the initial stage of deposition, the surface activation groups of the NBR group combine with carbon atoms, carbon clusters, and ionized carbon to form a carbonized interface, which interacts with the fluorine-containing CF group. x A fluorinated carbon interface is formed; as deposition proceeds, carbon atoms, carbon clusters, and ionized carbon combine to form an amorphous carbon host structure; carbon atoms, carbon clusters, and ionized carbon combine with fluorinated groups to form CF, C-CF2, and C-CF3 terminal structures modified by fluorinated groups; due to the strong electronegativity of fluorine and the high bond energy of the CF bond, terminal structures are formed and a network rearrangement effect is generated, resulting in a rubber-based fluorine-doped diamond-like coating with hydrophobic and friction-reducing properties on the NBR substrate surface, with amorphous carbon as the host and surface and local structures modified by fluorinated groups.

[0013] Preferably, in step S1, the temperature of the drying oven is 80°C and the drying time is 5 minutes.

[0014] Preferably, in step S3, the argon flow rate is 50~80 sccm, the power supply for plasma pretreatment is a cathode arc power supply with a bias voltage of -300~-500V, the ion source power is 1.4kW, the frequency is 80kHz, and the gas pressure in the vacuum chamber is 1~10Pa.

[0015] Preferably, in step S3, the microscopic particle expression for plasma pretreatment of the cleaned rubber substrate is: ; .

[0016] Preferably, in step S4, Ar + The microscopic particle expression for carbon atoms, carbon clusters, and ionized carbon sputtered from a graphite target after bombardment is as follows: .

[0017] Preferably, in steps S2 and S5, the purity of the graphite target is 99.99%, the purity of the argon gas is 99.99%, and the purity of the CF4 gas is 99.99%. In step S5, the flow rate of the CF4 gas is 10~30 sccm, and the pressure in the vacuum chamber is 0.1~1 Pa.

[0018] Preferably, in step S6, the frequency of the pulsed magnetron sputtering system is 80 kHz, the bias voltage is less than or equal to -100 V, and the thickness of the rubber-based fluorine-doped diamond-like coating with hydrophobic and anti-friction properties is 0.4~0.6 μm.

[0019] Preferably, in step S6, the microscopic particle expression for the adsorption and interfacial reaction that occurs after the mixed flux of the carbon atoms, carbon clusters, and ionized carbon obtained in step S4 and the fluorine-containing active material obtained in step S5 reaches the surface of the NBR matrix in step S6 is as follows: ; ; ; .

[0020] On the other hand, the present invention provides a method for preparing a hydrophobic composite coating for a rubber material surface, comprising a rubber substrate and a rubber-based fluorine-doped diamond-like carbon (DLC) coating, wherein the rubber-based DLC coating is located on the rubber substrate, and the rubber substrate is a nitrile rubber substrate; in the rubber-based DLC coating, the size and chemical properties of fluorine atoms cause F atoms to preferentially form CF with high free energy and high chemical reactivity carbon sites, including DLC ​​surface dangling bonds, unsaturated coordinated carbon atoms, and defect edges. x The coating surface is terminated by CF, CF2 and CF3 groups, thereby achieving chemical termination of these unstable surface sites.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention uses fluorine as a dopant element, which can induce the formation of polar bonds and CF2 / CF3 groups and terminate some dangling bonds. This can significantly reduce surface energy, improve the hydrophobicity of the coating surface, give the coating excellent resistance to high humidity environments, and improve the service life of rubber materials in marine environments.

[0022] 2. This invention introduces fluorine (F) into the DLC coating to weaken the adsorption of water molecules on the surface and the surface energy of the coating, thereby reducing the adhesion tendency of the coating in humid environments and further reducing the friction coefficient of the DLC coating under various working conditions, significantly improving the tribological performance of the sealing ring in humid environments.

[0023] 3. This invention employs controlled CF4 flow rate to regulate the structure and elemental content of the composite coating, achieving systematic control over the coating structure and composition. Through the doping of F and the formation of CFx (x=1, 2, 3) bonds, not only is internal stress reduced and the performance mismatch between the coating and the substrate alleviated, but the wear resistance and interfacial bonding performance of the film are also significantly improved.

[0024] 4. This invention uses a DC magnetron sputtering system to sputter a graphite target and uses CF4 gas to dope the element F. The preparation method is simple to operate, has good process stability, low energy consumption, no special requirements for equipment, and is easy to operate, which is conducive to large-scale mass production in industry. This wear-resistant and corrosion-resistant rubber material can be widely used in different application scenarios.

[0025] 5. This invention regulates the bombardment energy and intensity of plasma by adjusting deposition parameters such as bias voltage and ion source power during the deposition process, ensuring that the entire preparation process is completed under low temperature conditions. This avoids aging and performance degradation of rubber materials caused by high temperatures, and guarantees the elasticity and sealing performance of rubber materials. Attached Figure Description

[0026] Figure 1 This is a flowchart of the method for preparing a hydrophobic composite coating for rubber material surface according to the present invention; Figure 2 This is a surface morphology diagram of the wear-resistant and friction-reducing fluorinated diamond-like composite coating on the surface of a rubber substrate obtained in an embodiment of the preparation method of the hydrophobic composite coating on the surface of rubber materials according to the present invention. Figure 3 This is a diagram showing the elemental composition and proportions of the wear-resistant and friction-reducing fluorinated diamond-like composite coating on the surface of a rubber substrate obtained in an embodiment of the method for preparing a hydrophobic composite coating on a rubber material surface according to the present invention. Figure 4 This is a graph showing the relationship between the friction coefficient and friction test time between the wear-resistant and friction-reducing fluorinated diamond-like composite coating on the surface of the rubber substrate and the uncoated rubber substrate obtained in the embodiment of the preparation method of the hydrophobic composite coating on the surface of rubber materials according to the present invention. Figure 5 This is a graph showing the friction coefficient-friction time relationship between the wear-resistant and friction-reducing diamond-like composite coating on the rubber substrate surface and the wear-resistant and friction-reducing fluorinated diamond-like composite coating on the rubber substrate surface under normal working conditions in the preparation method of the hydrophobic composite coating on the surface of rubber materials of the present invention. Figure 6 This is a graph showing the friction coefficient-friction time relationship between the wear-resistant and friction-reducing diamond-like composite coating on the rubber substrate surface and the wear-resistant and friction-reducing fluorinated diamond-like composite coating on the rubber substrate surface under harsh working conditions in the preparation method of the hydrophobic composite coating on the surface of rubber materials of the present invention. Detailed Implementation

[0027] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0028] A method for preparing a hydrophobic composite coating for rubber materials addresses the problems of insufficient adhesion due to thermal expansion coefficient mismatch and fracture and peeling failure caused by interfacial stress concentration during dynamic deformation in existing hard coatings deposited on rubber surfaces. This method utilizes a pulsed magnetron sputtering system for efficient deposition of graphite targets and uniform doping with CF4 to improve the hydrophobic and tribological properties of the coating. Figure 1 As shown, the specific implementation steps are as follows: S1. First, clean the rubber substrate with 80℃ warm water for 15-20 minutes, then clean it with deionized water using ultrasound for 10-15 minutes, and finally clean it with alcohol using ultrasound for 30 minutes to remove surface oil and contaminants. The number of times the alcohol is used for ultrasound is 3-6 or even more. The indicator of complete cleaning is that there is no color precipitation of alcohol after ultrasound. Finally, dry it in a drying oven to remove the moisture from the surface of the rubber substrate, and obtain the cleaned rubber substrate.

[0029] Specifically, the temperature of the drying oven is 80℃, and the drying time is 5 minutes.

[0030] S2. Place the rubber substrate obtained in step S1 on the revolution rod of the rotating frame in the vacuum chamber of the pulse magnetron sputtering system, and rotate it at a certain speed to move the position of the rubber substrate.

[0031] S3. Based on step S2, turn on the power supply to provide energy for plasma bombardment of the substrate surface. A higher bias voltage will further enhance interfacial activity, but to prevent local heat accumulation and substrate damage caused by high bombardment energy, it is set within the range of -300 to -500V. Turn on the gas inlet system to introduce argon gas at a flow rate of 50 to 80 sccm, and adjust the throttle valve to set the pressure of the vacuum chamber at 1 to 10 Pa to ensure the Ar atom density in the vacuum chamber. Appropriately increasing the gas pressure and Ar atom density can increase the probability of collision between electrons and Ar atoms, making it easier for the neutral Ar gas in the vacuum chamber to be broken down and form stable Ar atoms under the bias voltage within the range of -300 to -500V. + Plasma; Plasma pretreatment is applied to the cleaned rubber substrate to remove surface contaminants and increase surface roughness. Simultaneously, energy bombardment breaks the surface molecular chains of the substrate, generating free radicals, dangling bonds, and other active sites, resulting in a surface-active rubber substrate. The microscopic particle expression is: ; ; Specifically, the power supply for plasma pretreatment is a cathode arc power supply with a bias voltage of -600V, an ion source power of 1.4kW, and a frequency of 80kHz.

[0032] S4. After pretreatment, the DC magnetron power supply is turned on to clean the graphite target placed above the vacuum chamber. This sputters oxides and impurities from the graphite target surface, which are then extracted from the vacuum chamber along with the gas. Argon gas is introduced to sputter carbon ions from the cleaned graphite target. Under the influence of the magnetic field, electrons are trapped in the area in front of the target, increasing the probability of collisions between electrons and gas molecules. Therefore, high ionization efficiency can be maintained even at lower pressures. Ar is ionized to produce Ar. + In this invention, high-energy electrons refer to electrons with high kinetic energy. These electrons move rapidly under the influence of an electric field and can further collide with Ar or reactant gas molecules, initiating excitation, ionization, or decomposition processes. + By bombarding a graphite target, carbon atoms, carbon clusters, and a small amount of ionized carbon are sputtered out. The microscopic particle expression is as follows: .

[0033] Specifically, before cleaning the graphite target, the angle of the baffle between the graphite target and the rubber substrate needs to be adjusted to protect the rubber substrate and prevent oxides and contaminants splashed out during the cleaning process from splashing onto the surface of the rubber substrate and contaminating the pre-treated surface of the rubber substrate.

[0034] S5. Introduce CF4 gas into the vacuum chamber at a flow rate of 10-30 sccm for 40 minutes to ensure a sufficiently high F content in the vacuum chamber and on the deposited coating. Simultaneously, adjust the throttle valve to set the vacuum chamber pressure at 0.1-1 Pa to reduce sputtering particle collisions and improve the effective energy and transport efficiency of sputtered particles and fluorine-containing active species reaching the graphite target. CF4 also decomposes under electron collisions, generating CF3, CF2, CF and F neutral active materials, as well as CF3... + The expression for ions, microscopic particles, is: ; .

[0035] S6, the carbon atoms, carbon clusters, and ionized carbon obtained in step S4, and the CF obtained in step S5 x A mixed flux composed of free radicals, F atoms, and Ar ions undergoes synergistic deposition and surface reactions on the surface of a surface-active rubber substrate. Due to the strong electronegativity of fluorine and the high bond energy of the CF bond, F-containing substances preferentially occupy some highly active carbon sites, forming terminal structures and generating network rearrangement effects, allowing fluorine to be deposited as CF and C-CF bonds. xThe bonding-in-place carbon ion-formed coating helps reduce lattice distortion of the carbon network, improves local bonding stability and fracture resistance, and, by adjusting the bias voltage to less than or equal to -100V, reduces the incident energy and bombardment effect of charged C and F particles reaching the graphite target surface, reduces stress concentration at the coating interface and damage to the polymer surface, and improves the hydrophobicity and anti-friction properties of the coating surface. This ultimately yields a fluorine-doped rubber-based diamond-like carbon coating with hydrophobic and anti-friction properties, with a thickness of 0.4–0.6 μm. Finally, a coating with amorphous carbon as the main component and fluorine-containing groups modifying the surface and local structure is obtained on the NBR substrate surface. The microscopic particle expression is as follows: ; ; ; ; In the initial stage of deposition, the surface-activating groups of the NBR group combine with carbon atoms, carbon clusters, and ionized carbon to form a carbonization interface, which then interacts with the fluorine-containing CF group. x A fluorinated carbon interface is formed; as deposition progresses, carbon atoms, carbon clusters, and ionized carbon combine to form an amorphous carbon matrix (sp). 2 / sp 3 (A mixed carbon network); carbon atoms, carbon clusters, and ionized carbon combine with fluorine-containing groups to form CF, C-CF2, and C-CF3 terminal structures modified by fluorine-containing groups. With the introduction of fluorine, a significant C-CF network is generated within the membrane. x Bonded structures are achieved by terminating dangling bonds, breaking some C-C crosslinks, and altering sp... 2 / sp 3 The entire coating structure is reshaped by balancing. Specifically, the frequency inside the vacuum chamber of the pulsed magnetron sputtering system is 80 kHz.

[0036] Specifically, during the deposition process in step S6, the carbon ions sputtered from the graphite target surface are not uniformly dispersed in the vacuum chamber under the action of the directional electric field, while the CF4 gas is relatively uniform. Therefore, it is necessary to rotate and move the rubber substrate in the vacuum chamber at an appropriate speed to reduce the carbon ion deposition caused by positional differences and the uneven fluorine doping degree, thereby improving the controllability of the coating deposition process.

[0037] Furthermore, from an atomic scale perspective, fluorine's smaller atomic radius helps reduce lattice distortion in the carbon network; its shorter CF bond length and higher bond energy improve local bonding stability and fracture resistance; and its high electronegativity, significantly higher than common doping elements like C, Si, and N, induces the formation of polar bonds and terminates some dangling bonds, thereby reducing stress concentration points, lowering surface energy, and enhancing the hydrophobicity and friction-reducing properties of the coating surface. Doping with fluorine can reduce modulus, release internal stress, enhance elastic recovery, and improve dielectric resistance without significantly sacrificing basic hardness. Simultaneously, fluorine doping introduces CF2 / CF3 groups, further reducing the coating surface energy and improving hydrophobicity.

[0038] By adjusting the ion source power, the plasma density, ion flux, and the degree of CF4 fragmentation can be altered, thereby regulating the ratio of F and CFx active materials reaching the substrate surface, the surface activation level, and the ion bombardment intensity. This influences the relative distribution of fluorinated bonds (CF, C-CFx, CF2, and CF3) in the F-DLC coating. Moderate ion source power is beneficial for the generation of fluorinated active materials and promotes the introduction of low surface energy groups; however, excessively high power leads to enhanced deep fragmentation, etching, and resputtering, which may inhibit the retention of highly fluorinated CF2 / CF3 end groups, hindering further improvement in hydrophobicity.

[0039] In a preferred embodiment of the present invention, the purity of the graphite target is 99.99%, the purity of the argon gas is 99.99%, and the purity of the CF4 gas is 99.99%. In the preparation method of the present invention, the Ar gas and the CF4 gas are respectively connected to two independent control valves, which can independently control the presence and flow rate of each gas, thereby regulating the doping and content of fluorine in the coating.

[0040] The composite coating obtained by the method for preparing a hydrophobic composite coating on the surface of rubber materials consists of a fluorine-doped diamond-like carbon (DLC) coating. The fluorine-doped DLC coating is located on a rubber substrate, which is an nitrile rubber substrate with dimensions of 20 mm × 20 mm × 2 mm. This coating is deposited onto the surface of the rubber substrate using a pulsed magnetron sputtering system, significantly improving the hydrophobic and friction-reducing properties of the rubber material. The diamond-like carbon framework of the coating is provided by a sputtering graphite target. Fluorine is provided by introducing CF4 gas into the deposition atmosphere, achieving fluorine doping of the DLC coating and enhancing the hydrophobic, tribological, and environmental adaptability of the composite coating material.

[0041] The doped fluorine (F) atoms possess the following fundamental characteristics: small size (F's covalent radius is approximately 0.64 Å, significantly smaller than C's 0.77 Å), meaning F can more easily enter surface and near-surface local sites without severely disrupting deposition continuity like large-sized metal doping; high electronegativity (F has the highest electronegativity at approximately 3.98, while C's is only 2.55), meaning it significantly pulls on the electron clouds of neighboring carbon atoms, adjusting the local hybridization state of carbon atoms; and high bond energy (CF bond energy is approximately 485 kJ / mol, higher than CC single bond energy of 332 kJ / mol and CH bond energy of 414 kJ / mol), meaning the resulting fluorine-terminated or fluorocarbon structures are often relatively stable under normal conditions.

[0042] The size and chemical properties of fluorine atoms cause F atoms to preferentially form CF with high-free-energy, highly chemically reactive carbon sites such as dangling bonds, unsaturated coordinated carbon atoms, and defect edges on the DLC surface. x The coating surface is terminated by CF, CF2, and CF3 groups, which chemically terminate these unstable surface sites. The high electronegativity of these sites depletes their electrons and reduces their activity, while the high CF bond energy stabilizes this low-energy termination state. Thus, the coating surface transforms from "exposed high-energy carbon sites" into "stable fluorinated terminals." After the coating surface is terminated by CF, CF2, and CF3 groups, the previously exposed high-energy carbon sites, dangling bonds, and unsaturated sites are sealed. External molecules face a layer of fluorinated terminals instead of an active carbon skeleton. Fluorinated terminals, especially CF2 / CF3 groups, are more difficult to establish strong intermolecular attraction with the outside world, thus suppressing the adhesion contribution to the surface free energy. The outermost layer of the surface has a weaker attraction to external molecules, and the surface's adhesion to water and oil decreases. Therefore, droplets are less willing to spread on the surface, the contact angle increases, and it exhibits hydrophobicity.

[0043] Undoped DLC surfaces still retain some active carbon sites; after fluorine doping, these active sites are terminated by C-F3 groups, resulting in decreased surface energy, weakened interfacial adhesion, and thus a decrease in the adhesive term during friction. With increasing fluorine content, the surface layer shifts from a more cross-linked three-dimensional carbon network to a more easily rearranged low-shear structure, reducing the coefficient of friction. Low surface energy and low adhesion reduce adhesive tearing and localized cracking, thus decreasing wear.

[0044] The pulsed magnetron sputtering equipment used to prepare composite coatings mainly includes a vacuum chamber, a DC magnetron sputtering power supply, a rotating unit, a pulsed bias power supply, an ion source, and a mechanical pump. The DC magnetron sputtering power supply is connected to the required target material, and the vacuum chamber is equipped with a rotating frame that can achieve self-rotation and revolution.

[0045] The method of this invention prepares a hydrophobic composite coating for rubber materials by doping with fluorine, which improves the coating's elasticity, effectively alleviates the performance mismatch between the coating and the substrate, and enhances the coating's friction-reducing and wear-resistant properties. By adjusting the CF4 gas flow rate in the deposition atmosphere, the fluorine doping ratio of the coating can be flexibly controlled, enabling the regulation and optimization of the composite coating's microstructure, elemental composition, and tribological properties. The wear-resistant and friction-reducing composite coating possesses advantages such as a low coefficient of friction, high wear resistance, and excellent bonding performance, and can be used for surface strengthening and service life extension of rubber seals in various environments. Exhibiting excellent hydrophobic and friction-reducing wear-resistant properties, it can be used for surface strengthening and service life extension of hydraulic cylinder rubber sealing materials in high-humidity marine environments, making it suitable for large-scale industrial production.

[0046] The following describes in further detail a method for preparing a hydrophobic composite coating for rubber material surfaces according to the present invention, with reference to specific embodiments: Example 1:

[0047] S1. Clean the rubber substrate with 80℃ warm water for 15 minutes to remove oil and contaminants from the surface. After cleaning, place the rubber substrate in deionized water for ultrasonic cleaning for 10 minutes. Then, use alcohol for ultrasonic cleaning 5 times for 30 minutes each time until the rubber substrate does not precipitate any color after ultrasonication, i.e., the alcohol does not change color after ultrasonication. Finally, place the cleaned rubber in a drying oven and set it to 80℃ for 5 minutes to dry in order to remove moisture from the surface of the rubber substrate.

[0048] S2. The cleaned rubber substrate is bonded to the rotating frame within the vacuum chamber of the pulsed magnetron sputtering system using double-sided adhesive tape. The rotating frame speed is set to 3 rpm. The vacuum chamber pressure is then evacuated to 5.0 × 10⁻⁶ using the vacuum system. -3 Pa.

[0049] S3. After the vacuum level meets the requirements, use a vacuum gauge to introduce high-purity argon gas at a flow rate of 70 sccm (99.99% purity) to bring the pressure in the vacuum chamber to and stabilize at around 5 Pa. Turn on the cathode arc power supply and adjust the bias voltage to -600V, adjust the ion source power to 1.4kW, and adjust the frequency to 80kHz for a continuous 15-minute Ar plasma etching pretreatment.

[0050] S4. After the Ar plasma etching pretreatment is completed, the graphite target is blocked by adjusting the angle of the baffle. The pulse magnetron power supply connected to the graphite target is turned on and the power is adjusted to 4kW to remove oxides and contaminants on the surface of the graphite target. The baffle is then removed and argon gas with a flow rate of 70sccm is introduced to sputter carbon ions from the cleaned graphite target.

[0051] S5. Introduce CF4 gas into the vacuum chamber at a flow rate of 20 sccm, and simultaneously adjust the throttle valve to set the pressure of the vacuum chamber at 0.5 Pa, so that it collides and decomposes with argon gas to produce fluorine-containing active substances such as F, CF, CF2 and CF3.

[0052] S6. The carbon ions obtained in step S4 and the fluorine-containing active material obtained in step S5 undergo synergistic deposition and surface reaction on the surface of the pretreated rubber substrate. The substrate negative bias voltage is adjusted to -50V, the ion source power is 4kW, and the frequency is adjusted to 80kHz for coating deposition. The deposition time is 40min. After deposition, the temperature in the vacuum chamber is allowed to cool naturally to room temperature, and finally a rubber-based fluorine-doped diamond-like coating with hydrophobic and friction-reducing properties with a thickness of 0.5μm is obtained.

[0053] Example 2:

[0054] The main difference between Example 2 and Example 1 is that in step S5, the flow rate of CF4 gas is changed to 40 sccm, and the pressure of the vacuum chamber is set at 1 Pa.

[0055] In this embodiment, to further improve the hydrophobic properties of the coating and increase the fluorine content in the coating, measures were taken to increase the flow rate of the introduced CF4 gas and the deposition pressure. When the flow rate of the introduced CF4 gas was 40 sccm and the vacuum chamber pressure was set at 1 Pa, the coating surface appeared loose and rough. This was because the excessively high flow rate and pressure of the CF4 gas caused a severe etching effect on the coating.

[0056] Example 3:

[0057] The main difference between Example 3 and Example 1 is that in step S3, the argon flow rate is changed to 100 sccm and the vacuum chamber pressure is set to 7.5 Pa.

[0058] In this embodiment, to further improve coating performance and enhance substrate surface activation, measures were taken to increase the flow rate of high-purity argon gas and the etching pressure. When the flow rate of high-purity argon gas was 100 sccm and the vacuum chamber pressure was stabilized at around 7.5 Pa, the coating could not be completely deposited on the rubber substrate surface. This was because the excessively high flow rate and pressure of high-purity argon gas caused severe damage to the substrate, preventing the coating from being deposited effectively on the substrate surface.

[0059] Comparative Example 1: This comparative example does not introduce CF4 gas; it directly proceeds to part of step S6 based on step S4, without needing step S5, to obtain a diamond-like composite coating on the surface of the rubber substrate. The specific operation method is as follows: S1. Clean the rubber substrate with 80℃ warm water for 15 minutes to remove oil and contaminants from the surface. After cleaning, place the rubber substrate in deionized water for ultrasonic cleaning for 10 minutes. Then, use alcohol for ultrasonic cleaning 5 times for 30 minutes each time until the rubber substrate does not precipitate any color after ultrasonication, i.e., the alcohol does not change color after ultrasonication. Finally, place the cleaned rubber in a drying oven and set it to 80℃ for 5 minutes to dry in order to remove moisture from the surface of the rubber substrate.

[0060] S2. The cleaned rubber substrate is bonded to the rotating frame within the vacuum chamber of the pulsed magnetron sputtering system using double-sided adhesive tape. The rotating frame speed is set to 3 rpm. The vacuum chamber pressure is then evacuated to 5.0 × 10⁻⁶ using the vacuum system. -3 Pa.

[0061] S3. After the vacuum level meets the requirements, use a vacuum gauge to introduce argon gas with a flow rate of 70 sccm, i.e. argon gas with a purity of 99.99%, to make the gas pressure in the vacuum chamber reach and stabilize at 5 Pa. Turn on the cathode arc power supply and adjust the bias voltage to -600V, adjust the ion source power to 1.4kW, adjust the frequency to 80kHz, and perform Ar plasma etching pretreatment for 15 minutes.

[0062] S4. After the Ar plasma etching pretreatment is completed, the graphite target is blocked by adjusting the angle of the baffle. The pulse magnetron power supply connected to the graphite target is turned on and the power is adjusted to 4kW to remove oxides and contaminants on the surface of the graphite target. The baffle is then removed and argon gas with a flow rate of 70sccm is introduced to sputter carbon ions from the cleaned graphite target.

[0063] S6. Adjust the substrate negative bias voltage to -50V, the ion source power to 4kW, and the frequency to 80kHz to perform coating deposition. The deposition time is 40min. After deposition, allow the temperature in the vacuum chamber to cool naturally to room temperature to obtain a rubber-based diamond-like coating with a thickness of 0.5μm.

[0064] Figure 2 The image shows the surface morphology of the wear-resistant and friction-reducing fluorinated diamond-like composite coating on the rubber substrate obtained in this embodiment using a scanning electron microscope. The coating surface morphology is a typical cauliflower structure with good density.

[0065] Figure 3The elemental composition and proportion of the wear-resistant and friction-reducing fluorinated diamond-like carbon composite coating on the rubber substrate surface obtained in this embodiment are shown. The F content of this coating is approximately 23%, indicating that the process successfully achieved fluorine doping of the DLC coating structure. At this point, the coating has the highest content of C-CF3 structure, the strongest hydrophobicity, the highest degree of graphitization, and the lowest coefficient of friction under all working conditions. This indicates that the F-DLC coating deposited by this process has good hydrophobic properties and a low coefficient of friction, significantly improving the tribological properties of the rubber.

[0066] Figure 4 The graphs show the friction coefficient versus friction test time relationship between the wear-resistant and friction-reducing fluorinated diamond-like carbon composite coating on the rubber substrate obtained in Example 1 and Comparative Example 1, the diamond-like carbon composite coating on the rubber substrate surface, and the uncoated rubber substrate. The graphs show that as the friction stage progresses, the friction coefficient of the NBR (Nitrile Butadiene Rubber) substrate suddenly surges from 0.4-0.45 in the initial stage to over 0.8, and continues to increase, with intensified fluctuations in the friction coefficient. The DLC coating significantly reduces the friction coefficient, but the friction coefficient increases slowly as the friction stage progresses. The F-DLC further reduces the friction coefficient of the rubber surface, with an average friction coefficient of around 0.2, and does not increase significantly throughout the entire friction stage.

[0067] Figure 5 The figures show the friction coefficient curves of the DLC coating and F-DLC coating on the rubber substrate surface obtained in Example 1 and Comparative Example 1 under different working conditions. Figure 5 For normal operating conditions under low load and low frequency, Figure 6 This is for harsh operating conditions under high load and high frequency.

[0068] exist Figure 5 In the early stages of the friction process under normal operating conditions, there was no significant difference in the friction coefficient. However, in the later stages of the friction process, the friction coefficient curve of the DLC coating fluctuated and began to rise slowly, while the friction coefficient of the F-DLC coating remained low and stable throughout the entire friction process. This indicates that the coating prepared by the F-doping preparation process provided by this invention exhibits excellent performance in reducing the friction coefficient of the NBR substrate, and this friction-reducing effect is stable and persistent, remaining for a relatively long time.

[0069] exist Figure 6Under harsh working conditions, the DLC coating exhibits a surge in friction coefficient from the initial stage, continuously increasing to around 0.5 before ceasing its significant increase but showing strong fluctuations. In contrast, the F-DLC coating maintains a friction coefficient consistently around 0.3, with only a slight increase and fluctuations occurring in the later stages of friction. This demonstrates that the coating prepared by the F-doping process provided in this invention maintains excellent friction reduction and stability under harsh conditions, demonstrating superior resistance to more extreme environments and exhibiting superior friction reduction compared to ordinary DLC coatings.

[0070] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing a hydrophobic composite coating for rubber material surfaces, characterized in that: Specifically, it includes: S1. Clean the rubber substrate by ultrasonic cleaning with water, deionized water and alcohol in sequence, and then dry it in a drying oven to obtain the cleaned rubber substrate. S2. Place the rubber substrate obtained in step S1 on the rotating frame inside the vacuum chamber of the pulse magnetron sputtering system and rotate it. S3. Based on step S2, argon gas is introduced into the vacuum chamber to perform plasma pretreatment on the cleaned rubber substrate to obtain a surface-active rubber substrate. S4. After pretreatment, the DC magnetron power supply is turned on to clean the graphite target placed above the vacuum chamber. Under the influence of the magnetic field, Ar is ionized to produce Ar. + And high-energy electrons, Ar + By bombarding a graphite target, carbon atoms, carbon clusters, and ionized carbon in the graphite target are obtained. S5. CF4 gas is introduced into the vacuum chamber. CF4 is decomposed by electron collisions, generating CF3, CF2, CF and F, neutral active substances, and CF3. + In step S6, these fluorine-containing active substances are fully mixed with the carbon atoms, carbon clusters and ionized carbon obtained in step S4 in the deposition atmosphere, so that the deposited coating has a uniform and dense content. S6. The mixed flux composed of carbon atoms, carbon clusters, and ionized carbon obtained in step S4 and the fluorine-containing active material obtained in step S5 reaches the surface of the NBR matrix and undergoes adsorption and interfacial reaction. In the initial stage of deposition, the surface activation groups of the NBR group combine with carbon atoms, carbon clusters, and ionized carbon to form a carbonized interface, which interacts with the fluorine-containing CF group. x A fluorinated carbon interface is formed; as deposition proceeds, carbon atoms, carbon clusters, and ionized carbon combine to form an amorphous carbon host structure; carbon atoms, carbon clusters, and ionized carbon combine with fluorinated groups to form CF, C-CF2, and C-CF3 terminal structures modified by fluorinated groups; due to the strong electronegativity of fluorine and the high bond energy of the CF bond, terminal structures are formed and a network rearrangement effect is generated, resulting in a rubber-based fluorine-doped diamond-like coating with hydrophobic and friction-reducing properties on the NBR substrate surface, with amorphous carbon as the host and surface and local structures modified by fluorinated groups.

2. The method for preparing a hydrophobic composite coating on a rubber material surface according to claim 1, characterized in that: In step S1, the temperature of the drying oven is 80°C and the drying time is 5 minutes.

3. The method for preparing a hydrophobic composite coating on a rubber material surface according to claim 1, characterized in that: In step S3, the argon flow rate is 50~80 sccm, the power supply for plasma pretreatment is a cathode arc power supply with a bias voltage of -300~-500V, the ion source power is 1.4kW, the frequency is 80kHz, and the gas pressure in the vacuum chamber is 1~10Pa.

4. The method for preparing a hydrophobic composite coating on a rubber material surface according to claim 1, characterized in that: In step S3, the microscopic particle expression for plasma pretreatment of the cleaned rubber substrate is: ； 。 5. The method for preparing a hydrophobic composite coating for rubber material surface according to claim 1, characterized in that: In step S4, Ar + The microscopic particle expression for carbon atoms, carbon clusters, and ionized carbon sputtered from a graphite target after bombardment is as follows: 。 6. The method for preparing a hydrophobic composite coating for rubber material surface according to claim 1, characterized in that: In steps S2 and S5, the purity of the graphite target is 99.99%, the purity of the argon gas is 99.99%, and the purity of the CF4 gas is 99.99%. In step S5, the flow rate of the CF4 gas is 10~30 sccm, and the pressure in the vacuum chamber is 0.1~1 Pa.

7. The method for preparing a hydrophobic composite coating on a rubber material surface according to claim 1, characterized in that: In step S6, the frequency of the pulsed magnetron sputtering system is 80 kHz, the bias voltage is less than or equal to -100 V, and the thickness of the rubber-based fluorine-doped diamond-like coating with hydrophobic and anti-friction properties is 0.4~0.6 μm.

8. The method for preparing a hydrophobic composite coating for rubber material surface according to claim 1, characterized in that: In step S6, the microscopic particle expression for the adsorption and interfacial reaction that occurs after the mixed flux composed of carbon atoms, carbon clusters, and ionized carbon obtained in step S4 and the fluorine-containing active material obtained in step S5 reaches the NBR substrate surface is: ； ； ； 。 9. A composite coating prepared by the method for preparing a hydrophobic composite coating on a rubber material surface according to any one of claims 1 to 8, characterized in that: It comprises a rubber substrate and a rubber-based fluorine-doped diamond-like carbon (DLC) coating. The rubber-based fluorine-doped DLC coating is located on the rubber substrate, which is a nitrile rubber substrate. In the rubber-based fluorine-doped DLC coating, the size and chemical properties of fluorine atoms cause F atoms to preferentially form CF with high-free-energy, highly chemically reactive carbon sites, including dangling bonds on the DLC surface, unsaturated coordinated carbon atoms, and defect edges. x The coating surface is terminated by CF, CF2 and CF3 groups, thereby achieving chemical termination of these unstable surface sites.

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