Preparation method of functional polymer coating for exposed skeleton type oil seal

Abstract

A method for preparing a functional polymer coating for exposed skeleton oil seals is described. The method primarily uses zinc nitrate hexahydrate (Zn(NO3)2·6H2O), 2-methylimidazole (2-Melm), hexagonal boron nitride (h-BN), and sodium molybdate dihydrate (Na2MoO4·2H2O) as raw materials. A zeolitic imidazolate framework (MOF) (ZIF-8) is grown in situ on the h-BN surface via an in-situ growth method. Sodium molybdate is then added as a corrosion inhibitor and coated within the ZIF-8 to produce a composite anticorrosive filler, Na2MoO4@ZIF-8 / h-BN (denoted as MZB). An epoxy resin and a curing agent are evenly dispersed with the MZB in a ratio of 3:1 and sprayed onto the skeleton surface. After spraying the anticorrosive coating, the oil seal skeleton is subjected to performance testing to observe surface corrosion. This coating forms a passivation film, extending the life of the metal skeleton, enhancing the oil seal's endurance and improving engine safety.

Description

Technical Field

[0001] The invention belongs to the technical field of coating preparation, in particular to a method for preparing a functional polymer coating for an exposed skeleton type oil seal. Background Art

[0002] Oil seals are key sealing components in automotive engines and transmissions, sealing in lubricating oil and oil pressure. Oil seals are available in either internally enclosed or externally enclosed versions. Exposed seals require careful attention to the protection of the metal frame, as the metal surface, exposed to the external environment, is susceptible to reaction with media (such as water vapor and oxygen) due to prolonged contact. This can lead to oxidation, which can affect the seal's performance and even the engine's lifespan.

[0003] Currently, a common approach to metal corrosion protection involves adding chemically stable fillers to the surface, dissolving them in epoxy resin, and then spraying them onto the metal substrate. Adhesion testing of pure epoxy coatings revealed that the coating's adhesion to the metal substrate was average. Furthermore, even with only chemically stable fillers, significant gaps remain, allowing corrosive media to reach the metal through these gaps and cause corrosion. Summary of the Invention

[0004] The purpose of the present invention is to solve the problem that the oil seal skeleton is easily corroded by the medium when exposed to the external environment, and to provide a method for preparing a functional polymer coating for an exposed skeleton type oil seal.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A method for preparing a functional polymer coating for an exposed skeleton type oil seal, the method comprising:

[0007] Step 1: Preparation of ZIF-8 / h-BN

[0008] h-BN and Zn(NO3)2 were dissolved in methanol to obtain solution A; 2-Melm was dissolved in methanol to obtain solution B; solution A was magnetically stirred and solution B was added dropwise to solution A; stirring was continued for 3 hours, the mixture was centrifuged and washed with ethanol, and dried under high temperature in a vacuum to obtain ZIF-8 / h-BN;

[0009] Step 2: Preparation of Na2MoO4@ZIF-8 / h-BN

[0010] ZIF-8 / h-BN and Na2MoO4 were dissolved in ethanol, ultrasonically dispersed, and then vacuum dried. The powder was scraped off to obtain Na2MoO4@ZIF-8 / h-BN.

[0011] Step 3: Preparation of EP / Na2MoO4@ZIF-8 / h-BN

[0012] Mix Na2MoO4@ZIF-8 / h-BN with epoxy resin and curing agent in ethyl acetate and ultrasonically disperse until completely dissolved. Preheat the heating table to 80℃ and use a spray gun to spray evenly on the metal frame. Wait for the resin to solidify.

[0013] Furthermore, in step 1, the mass ratio of h-BN, Zn(NO3)2 and 2-Melm is 1-2:6-8:8-12.

[0014] Furthermore, in step 2, the mass ratio of ZIF-8 / h-BN to Na2MoO4 is 0.4:0.02-0.08.

[0015] Furthermore, in step 2, the vacuum drying temperature is 50° C. and the time is 6 h.

[0016] Furthermore, in step 3, the mass ratio of MZB, E51, and curing agent is 0.02:1.5:0.5.

[0017] The beneficial effects of the present invention compared to the prior art are:

[0018] (1) To address the issues of single filler and large gaps, the present invention upgrades the traditional single-layer filler isolation to a three-layer filler isolation. h-BN serves as the first line of defense, dispersed in epoxy resin, and its physical shielding properties extend the corrosion path. ZIF-8 serves as the second line of defense, grown in situ on h-BN. At the same time, its nanocontainer properties are used to encapsulate the third line of defense, Na2MoO4. When the corrosive medium invades, the ZIF-8 is damaged and the Na2MoO4 hidden inside is released. The Na2MoO4 reacts with the corrosive medium to form a passivation film that isolates the corrosive medium.

[0019] (2) To address the problem of poor adhesion of pure epoxy coatings, the ZIF-8 used in the present invention has a strong metal coordination ability and can form a stable complex with the metal matrix, which is not easy to peel off. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The preparation flow chart of ZIF-8 / h-BN;

[0021] Figure 2 The preparation flow chart of Na2MoO4@ZIF-8 / h-BN;

[0022] Figure 3 This is a diagram of the EP / MZB preparation process;

[0023] Figure 4 is the FT-IR image of MZB;

[0024] Figure 5 is the XRD pattern of MZB;

[0025] Figure 6 SEM images of MZB at 2 μm and 5 μm respectively;

[0026] Figure 7 is the EDS diagram of MZB;

[0027] Figure 8 This is the coating adhesion performance test result diagram;

[0028] Figure 9 This is the corrosion degree diagram of the coating after immersion in salt water;

[0029] Figure 10 is the Nyquist plot of each coating;

[0030] Figure 11 is the Bode diagram of each coating;

[0031] Figure 12 This is the anti-corrosion mechanism diagram of hexagonal boron nitride;

[0032] Figure 13 This is the anti-corrosion mechanism diagram of ZIF-8;

[0033] Figure 14 This is the anti-corrosion mechanism diagram of Na2MoO4. DETAILED DESCRIPTION

[0034] The technical solution of the present invention is further described below with reference to the accompanying drawings and embodiments, but is not limited thereto. Any modification or equivalent replacement of the technical solution of the present invention that does not depart from the spirit and scope of the technical solution of the present invention should be included in the scope of protection of the present invention.

[0035] A functional polymer coating for exposed-type skeleton oil seals is primarily based on zinc nitrate hexahydrate (Zn(NO3)2·6H2O), 2-methylimidazole (2-Melm), hexagonal boron nitride (h-BN), and sodium molybdate dihydrate (Na2MoO4·2H2O). Zeolitic imidazolate framework MOFs (ZIF-8) are grown in situ on the h-BN surface via an in-situ growth method. Sodium molybdate is then added as a corrosion inhibitor and coated onto the ZIF-8 to create a composite anticorrosive filler, Na2MoO4@ZIF-8 / h-BN (denoted as MZB). Epoxy resin and curing agent are evenly dispersed with MZB in a 3:1 ratio and sprayed onto the skeleton surface. After spraying this anticorrosive coating, performance tests were conducted on the seal skeleton to observe surface corrosion. This coating extends the life of the metal skeleton by forming a passivation film, enhancing the oil seal's endurance and improving engine safety.

[0036] Example 1:

[0037] A method for preparing a functional polymer coating for an exposed skeleton type oil seal, the method comprising:

[0038] 1. Preparation of ZIF-8 / h-BN

[0039] 0.4g h-BN and 2.8g Zn(NO3)2 were dissolved in 30mL methanol and ultrasonically dispersed for 30min to obtain liquid A. 4g 2-Melm was dissolved in 30mL methanol and ultrasonically dispersed for 5min to obtain liquid B. Liquid A was placed on a magnetic stirrer and liquid B was added dropwise to liquid A. Stirring was continued for 3h, centrifuged and washed with ethanol, and dried under high temperature and vacuum to obtain ZIF-8 / h-BN. ZIF-8 was obtained without adding h-BN in the above process. Figure 1 shown.

[0040] 2. Preparation of Na2MoO4@ZIF-8 / h-BN

[0041] Take 0.4g ZIF-8 / h-BN and add 0.02g, 0.04g and 0.08g Na2MoO4 respectively in 10mL ethanol, ultrasonically disperse for 30min, then vacuum dry at 50℃×6h, and scrape off the powder to obtain Na2MoO4@ZIF-8 / h-BN (hereinafter referred to as MZB). Figure 2 shown.

[0042] 3. Preparation of EP / Na2MoO4@ZIF-8 / h-BN

[0043] Mix 0.02g MZB, 1.5g epoxy resin E51, and 0.5g curing agent D230 in 20mL ethyl acetate and disperse by ultrasonic until completely dissolved and the solution becomes transparent. Preheat the heating table to 80℃ (ethyl acetate will evaporate at 78℃), use a spray gun to spray evenly on the metal frame, and wait for 1-2 days for the resin to solidify. Figure 3 shown.

[0044] The present invention prepares MZB-1, MZB-2, and MZB-3 by loading different amounts of corrosion inhibitors, performs Fourier transform infrared spectroscopy (FT-IR) on the fillers to characterize the chemical structure of the fillers, performs X-ray diffraction (XRD) on the fillers to characterize the crystal form of the fillers, performs scanning electron microscopy (SEM) on the fillers to characterize the microstructure, and simultaneously performs energy dispersive spectroscopy (EDS) on the fillers to determine the element content, performs Tafel test on the coating to calculate the corrosion inhibition efficiency of each filler, performs adhesion test and salt water immersion test on the coating to determine its corrosion resistance, performs electrochemical impedance spectroscopy (EIS) test to evaluate the corrosion inhibition performance of the coating by Nyquist plot, and evaluates the corrosion resistance of the coating by Bode plot. In order to simulate the skeleton working in a corrosive medium, the present invention prepares 3.5wt.% salt water as the service environment. The corrosion situation of the skeleton surface in the salt water can effectively judge its corrosion resistance, and more effectively evaluate the corrosion resistance of the coating.

[0045] The functional group vibration peaks of ZIF-8, h-BN, and Na2MoO4 were obtained by consulting the literature. Figure 4 As shown in the figure, the vibration peaks of the three can be found in MZB, proving that MZB was successfully prepared.

[0046] The 2θ angles of ZIF-8, h-BN and Na2MoO4 and their corresponding crystal planes were found using the "MDIjade6.5" software. Figure 5 As shown in the figure, MZB can correspond to the crystal planes of the three fillers at the corresponding 2θ angles. This proves that the MZB was successfully prepared.

[0047] Scanning electron microscopy of the MZB revealed numerous regular dodecahedrons distributed across the two-dimensional lamellar structure, indicating in situ growth of ZIF-8 on the h-BN surface. Furthermore, energy spectrum scanning confirmed the presence of Mo in the sample, derived from sodium molybdate. This led to the conclusion that the MZB had been successfully prepared.

[0048] The characterization of FT-IR, XRD, SEM and EDS showed that MZB was successfully synthesized by the in situ growth method.

[0049] Scratch a 5×5 grid on the coating surface, tear it off repeatedly with tape, and take photos of the adhesive peeling off of each coating. Figure 8 The results show that the addition of fillers does not affect the adhesion performance of the coating.

[0050] The coatings were simultaneously immersed in 3.5 wt.% NaCl (aq). After 5 days, the pure epoxy coating had cracked and blistered, while the coatings with h-BN, MZB-1, and MZB-3 exhibited pitting corrosion. After 10 days, all coatings except MZB-2 showed accumulation of corrosion products, demonstrating that the EP / MZB-2 coating had the best corrosion protection.

[0051] The most commonly used methods for EIS to evaluate corrosion resistance are the capacitance arc radius and the low-frequency impedance modulus. A larger capacitance arc radius indicates better corrosion resistance, and a higher low-frequency impedance modulus indicates better corrosion resistance. A Nyquist plot is drawn with -Z" versus Z', as shown in the following example: Figure 10 As can be seen in the figure, the corrosion resistance of the coating gradually weakened as the number of days increased. Pure EP was the first to develop a double-capacitive arc, indicating that its performance was affected first. Similarly, EP / MZB-2 developed a double-capacitive arc last, indicating the best corrosion resistance.

[0052] With |Z| 0.01Hz Make a Bode plot for f, such as Figure 11 As shown. After 15 days, the |Z| 0.01Hz The highest, almost one order of magnitude higher than pure EP, proving that the coating has the best anti-corrosion performance.

[0053] Through the above experiments, it can be concluded that EP / MZB-2 has the best anti-corrosion performance.

[0054] The present invention is an exposed skeleton type functional polymer coating. When sprayed onto the skeleton surface, h-BN acts as the first line of defense, exerting a physical shielding effect to extend the corrosion path and delay medium corrosion. The mechanism is as follows Figure 12 shown.

[0055] In addition to acting as a nano-container coated corrosion inhibitor, ZIF-8 also has a certain corrosion inhibition effect according to the literature. At the same time, ZIF-8 has a strong metal coordination ability. The coordination group formed by Zn and 2-Melm can form a stable complex with the metal elements in the skeleton to enhance the adhesion performance. When the corrosive medium penetrates, the Fe in ZIF-8 undergoes oxidation and reduction, which reduces the pH in the anode area and increases the pH in the cathode area, causing the Zn-N bond in MZB to be protonated and release Zn. 2+ and 2-Melm, in the anode region, Fe 3+ Coordination reaction with 2-Melm generates [Fe n (Cl) p (2-Melm)] m In the cathode region, Zn 2+ With OH in the medium - Generate Zn(OH)2 deposition film. This deposition film serves as the second line of defense for the coating. Figure 13 shown.

[0056] Na2MoO4 as a corrosion inhibitor is mainly composed of MoO4 2- With Fe in the framework 2+ The reaction generates a stable FeMoO4 passivation film, which forms the third line of defense to isolate the skeleton from the medium environment and realize the corrosion protection of the skeleton. Figure 14 shown.

[0057] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims, not the foregoing description, and all variations within the meaning and range of equivalents of the claims are intended to be embraced therein. Any reference sign in a claim should not be construed as limiting the claim to which it relates.

[0058] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A method for preparing a functional polymer coating for an exposed skeleton type oil seal, characterized in that: The method is: Step 1: Preparation of ZIF-8 / h-BN Dissolve h-BN and Zn(NO3)2 in methanol to obtain solution A; dissolve 2-Melm in methanol to obtain solution B; Solution A was magnetically stirred, and solution B was added dropwise to solution A; stirring was continued for 3 h, followed by centrifugation and washing with ethanol, and drying under high temperature and vacuum to obtain ZIF-8 / h-BN; Step 2: Preparation of Na2MoO4@ZIF-8 / h-BN ZIF-8 / h-BN and Na2MoO4 were dissolved in ethanol, ultrasonically dispersed, and then vacuum dried. The powder was scraped off to obtain Na2MoO4@ZIF-8 / h-BN. Step 3: Preparation of EP / Na2MoO4@ZIF-8 / h-BN Mix Na2MoO4@ZIF-8 / h-BN with epoxy resin and curing agent in ethyl acetate and ultrasonically disperse until completely dissolved. Preheat the heating table to 80℃ and use a spray gun to spray evenly on the metal frame. Wait for the resin to solidify.

2. The method for preparing a functional polymer coating for an exposed skeleton oil seal according to claim 1, characterized in that: In step 1, the mass ratio of h-BN, Zn(NO3)2 and 2-Melm is 1-2:6-8:8-12.

3. The method for preparing a functional polymer coating for an exposed skeleton type oil seal according to claim 1, characterized in that: In step 2, the mass ratio of ZIF-8 / h-BN to Na2MoO4 is 0.4:0.02-0.

08.

4. The method for preparing a functional polymer coating for an exposed skeleton oil seal according to claim 1, characterized in that: In step 2, the vacuum drying temperature is 50° C. and the time is 6 h.

5. The method for preparing a functional polymer coating for an exposed skeleton type oil seal according to claim 1, characterized in that: In step 3, the mass ratio of MZB, E51, and curing agent is 0.02:1.5:0.5.

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