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

Abstract

The invention relates to a preparation method of a functional polymer coating for an exposed framework type oil seal, which mainly comprises the following steps: taking zinc nitrate hexahydrate (Zn (NO3) 2.6 H2O), 2-methylimidazole (2-Melm), hexagonal boron nitride (h-BN) and sodium molybdate dihydrate (Na2MoO4. 2H2O) as raw materials; a zeolite imidazate framework MOFs (ZIF-8) is grown on the surface of h-BN in situ through an in-situ growth method, and sodium molybdate is added as a corrosion inhibitor to be coated in the ZIF-8 to obtain the composite anticorrosive filler Na2MoO4 ZIF-8 / h-BN (recorded as MZB). Epoxy resin and a curing agent are uniformly dispersed with MZB according to the proportion of 3: 1, and the mixture is sprayed on the surface of the framework. After the anti-corrosion coating is sprayed on the oil seal framework, a performance experiment is carried out, and the corrosion condition of the surface of the framework is observed. According to the coating, the service life of the metal framework is prolonged by forming a passive film, the cruising ability of the oil seal is enhanced, and the safety of an engine is improved.

Description

Technical Field

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

[0002] An oil seal is a main sealing component in an automobile engine or transmission, which plays a role in sealing lubricating oil and oil pressure. Oil seals are divided into an inner package skeleton type and an exposed skeleton type. For the exposed skeleton type, attention should be paid to the protection of the skeleton because the metal skeleton surface is prone to react with some media (such as water vapor, oxygen) due to long-term contact with the external environment, and the metal surface is oxidized, which will affect the use of the oil seal and even the life of the engine.

[0003] At present, a common way to prevent metal corrosion is to add chemically stable fillers to its surface and incorporate epoxy resin to spray on the metal substrate surface. Through the adhesion test of the pure epoxy coating, it is found that the adhesion performance of the coating to the metal substrate is average, and there are still large gaps when only adding simple chemically stable fillers, and the corrosive medium will contact the metal through the gaps to 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 preparation method of a functional polymer coating for an exposed skeleton type oil seal.

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

[0006] A preparation method of a functional polymer coating for an exposed skeleton type oil seal, and the method is as follows:

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

[0008] Dissolve h-BN and Zn(NO 3 ) 2 in methanol to obtain solution A; dissolve 2-Melm in methanol to obtain solution B; magnetically stir solution A, and dropwise add solution B to solution A; continuously stir for 3 h, centrifuge and wash with ethanol, and obtain ZIF-8 / h-BN after high-temperature vacuum drying;

[0009] Step 2: Preparation of Na 2 MoO 4 @ZIF-8 / h-BN

[0010] Take ZIF-8 / h-BN and Na 2 MoO 4 in ethanol, ultrasonically disperse and then perform vacuum drying, scrape off the powder to obtain Na 2 MoO 4@ZIF-8 / h-BN;

[0011] Step 3: EP / Na 2 MoO 4 Preparation of @ZIF-8 / h-BN

[0012] Put Na 2 MoO 4 Mix @ZIF-8 / h-BN with epoxy resin and curing agent into ethyl acetate, ultrasonically disperse until completely dissolved, preheat the heating table, set the temperature to 80 °C, use a spray gun to evenly spray on the metal skeleton, and wait for the resin to cure.

[0013] Further, in Step 1, the mass ratio of h-BN, Zn(NO 3 ) 2 to 2-Melm is 1-2:6-8:8-12.

[0014] Further, in Step 2, the mass ratio of the ZIF-8 / h-BN to Na 2 MoO 4 is 0.4:0.02-0.08.

[0015] Further, in Step 2, the temperature of vacuum drying is 50 °C and the time is 6 h.

[0016] Further, 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 with the prior art are as follows:

[0018] (1) Aiming at the problems 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 extends the corrosion path by virtue of its physical shielding performance. ZIF-8 serves as the second line of defense, in-situ growing on h-BN, and at the same time using its nano-container characteristics to encapsulate the third line of defense Na 2 MoO 4 inside. When the corrosive medium invades, ZIF-8 is damaged and releases the Na 2 MoO 4 hidden inside. Na 2 MoO 4 reacts with the corrosive medium to form a passivation film to isolate the corrosive medium.

[0019] (2) Aiming at the problem of poor adhesion performance of pure epoxy coatings, the ZIF-8 used in the present invention has strong metal coordination ability and can form stable complexes with the metal matrix, which are not easily peeled off. Description of the Drawings

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

[0021] Figure 2 is Na 2 MoO 4 @ZIF-8 / h-BN preparation flow chart;

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

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

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

[0025] Figure 6 is the SEM diagram of MZB at 2μm and 5μm respectively;

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

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

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

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

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

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

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

[0033] Figure 14 is Na 2 MoO 4 anti-corrosion mechanism diagram. Specific implementation mode

[0034] The technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and embodiments, but are not limited thereto. Any modification or equivalent replacement of the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention shall be covered by the protection scope of the present invention.

[0035] The functional polymer coating for exposed type skeleton oil seal mainly uses zinc nitrate hexahydrate (Zn(NO 3 ) 2 ·6H2 O), 2-methylimidazole (2-Melm), hexagonal boron nitride (h-BN), and sodium molybdate dihydrate (Na 2 MoO 4 ·2H 2 O) as raw materials, in-situ growth method is used to in-situ grow zeolitic imidazolate framework MOFs (ZIF-8) on the surface of h-BN, and sodium molybdate is added as a corrosion inhibitor and coated in ZIF-8 to obtain the composite anti-corrosion filler Na 2 MoO 4 @ZIF-8 / h-BN (denoted as MZB). Epoxy resin and curing agent are dispersed evenly with MZB in a ratio of 3:1 and sprayed on the surface of the framework. The performance experiment is carried out on the oil-sealed framework after spraying this anti-corrosion coating, and the corrosion situation on the surface of the framework is observed. This coating extends the life of the metal framework by forming a passivation film, enhances the endurance of the oil seal, and improves the safety of the engine.

[0036] Example 1:

[0037] A preparation method of a functional polymer coating for an exposed framework type oil seal, the method is as follows:

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

[0039] 0.4 g of h-BN and 2.8 g of Zn(NO 3 ) 2 are dissolved in 30 mL of methanol and ultrasonically dispersed for 30 min to obtain solution A. 4 g of 2-Melm is dissolved in 30 mL of methanol and ultrasonically dispersed for 5 min to obtain solution B. Solution A is placed on a magnetic stirrer, and solution B is added dropwise to solution A. Stir continuously for 3 h, centrifuged and washed with ethanol, and dried under high temperature and reduced pressure to obtain ZIF-8 / h-BN. ZIF-8 is prepared without adding h-BN in the above process. As Figure 1 shown.

[0040] 2. Preparation of Na 2 MoO 4 @ZIF-8 / h-BN

[0041] Take 0.4 g of ZIF-8 / h-BN and add 0.02 g, 0.04 g, and 0.08 g of Na 2 MoO 4 in 10 mL of ethanol, ultrasonically disperse for 30 min, then carry out vacuum drying at 50 °C for 6 h, scrape off the powder to obtain Na 2 MoO 4 @ZIF-8 / h-BN (hereinafter referred to as MZB). The schematic diagram is as Figure 2 shown.

[0042] 3. EP / Na 2MoO 4 Preparation of ZIF-8 / h-BN

[0043] Mix 0.02 g of MZB with 1.5 g of epoxy resin E51 type and 0.5 g of curing agent D230 into 20 mL of ethyl acetate, and ultrasonically disperse until completely dissolved. The solution becomes transparent. Preheat the heating table, set the temperature to 80 °C (ethyl acetate will evaporate at 78 °C), use a spray gun to evenly spray on the metal skeleton, and wait for 1-2 days for the resin to cure. As Figure 3 shown

[0044] In this invention, MZB-1, MZB-2, and MZB-3 are respectively prepared by loading different contents of corrosion inhibitors. Fourier transform infrared spectroscopy (FT-IR) is used to characterize the chemical structure of the filler, X-ray diffraction (XRD) is used to characterize the crystal form of the filler, scanning electron microscopy (SEM) is used to characterize the microstructure of the filler, and energy-dispersive spectroscopy (EDS) is used to determine the element content. Tafel experiment (Tafel) is carried out to calculate the corrosion inhibition efficiency of each filler. Adhesion test and salt water immersion experiment are carried out on the coating to determine its anti-corrosion performance. Electrochemical impedance spectroscopy (EIS) is carried out to evaluate the corrosion inhibition performance of the coating through the Nyquist diagram, and the anti-corrosion performance of the coating is evaluated through the Bode diagram. To simulate the working of the skeleton in the corrosive medium, this invention prepares 3.5 wt.% salt water as the service environment. Through the corrosion situation on the surface of the skeleton in the salt water, the anti-corrosion effect can be effectively judged, and the anti-corrosion performance of the coating can be evaluated more effectively.

[0045] Consult the literature to obtain the functional group vibration peaks of ZIF-8, h-BN, and Na 2 MoO 4 . As Figure 4 shown, it is found that the vibration peaks of the three can be found in MZB. It is proved that MZB is successfully prepared.

[0046] Use the "MDIjade6.5" software to find the 2θ angles and their corresponding crystal planes of ZIF-8, h-BN, and Na 2 MoO 4 . As Figure 5 shown, MZB can correspond to the crystal planes of the three fillers at the corresponding 2θ angles. It is proved that MZB is successfully prepared.

[0047] Perform scanning electron microscopy on MZB, and it can be observed that countless regular dodecahedrons are distributed on the two-dimensional sheet structure, indicating that ZIF-8 has grown in-situ on the surface of h-BN. Then, energy spectrum scanning is used to determine that the sample contains Mo element, which comes from sodium molybdate. It is comprehensively concluded that MZB is successfully prepared.

[0048] Through the characterization of FT-IR, XRD, SEM, and EDS, it can be concluded that MZB is successfully synthesized by the in-situ growth method.

[0049] Scratch a 5×5 grid on the surface of the coating and repeatedly tear it with tape. Take pictures and observe the peeling situation of each coating. The results are as Figure 8 shown. It can be seen from the results that the addition of the filler does not affect the adhesion performance of the coating.

[0050] The coatings were simultaneously immersed in 3.5 wt.% NaCl(aq). At 5 days, the pure epoxy coating had already peeled at the edges and bubbled, and pitting corrosion occurred on the coatings added with h-BN, MZB-1, and MZB-3. At 10 days, corrosion product accumulation occurred on all coatings except MZB-2. It is proved that the EP / MZB-2 coating has the best anti-corrosion performance.

[0051] The most commonly used methods for evaluating the anti-corrosion performance by EIS are the radius of the capacitive reactance arc and the low-frequency impedance modulus. The larger the radius of the capacitive reactance arc, the better the corrosion resistance of the coating, and the higher the low-frequency impedance modulus, the better the anti-corrosion performance of the coating. Make a Nyquist plot with -Z” against Z’, as Figure 10 . It can be seen from the figure that as the number of days increases, the corrosion resistance of the coating gradually weakens. The pure EP first shows a double capacitive reactance arc, indicating that its performance is first affected. Similarly, EP / MZB-2 shows a double capacitive reactance arc the latest, so it has the best corrosion resistance.

[0052] Make a Bode plot with |Z| 0.01Hz against f, as Figure 11 shown. After 15 days, the |Z| 0.01Hz of EP / MZB-2 is the highest, almost one order of magnitude higher than that of pure EP. It is proved that this coating has the best anti-corrosion performance.

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

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

[0055] In addition to acting as a nano-container to encapsulate the corrosion inhibitor, ZIF-8 is found from the literature to also have a certain corrosion inhibition effect. 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, enhancing the adhesion performance. When the corrosive medium penetrates, the Fe in ZIF-8 undergoes oxidation-reduction, causing the pH in the anodic region to decrease and the pH in the cathodic region to increase, resulting in the protonation of the Zn-N bond in MZB and the release of Zn 2+ and 2-Melm. In the anodic region, Fe 3+ reacts with 2-Melm to form [Fe n (Cl)p (2-Melm)] m . In the cathode region, Zn 2+ reacts with OH in the medium - to form Zn(OH) 2 deposition film. This deposition film serves as the second line of defense of the coating. The anti-corrosion mechanism of ZIF-8 is as Figure 13 shown.

[0056] Na 2 MoO 4 acts as a corrosion inhibitor mainly due to its MoO 4 2- reacting with Fe in the framework 2+ to form a stable FeMoO 4 passivation film, which constitutes the third line of defense to isolate the framework from the medium environment and achieve the anti-corrosion of the framework. The mechanism diagram is as Figure 14 shown.

[0057] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other forms without departing from the spirit or basic characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent conditions of the claims are intended to be included in the present invention. Any reference signs in the claims should not be regarded as limiting the claimed rights.

[0058] In addition, it should be understood that although this specification is described according to embodiments, not every embodiment only contains an independent technical solution. This narrative way of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments 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 liquid A; dissolve 2-Melm in methanol to obtain liquid B; Liquid A was magnetically stirred, and liquid B was added dropwise into liquid A; stirring was continued for 3 h, centrifuged and washed with ethanol, and dried at high temperature and in 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, dispersed by ultrasonic and then dried in vacuum, and 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, disperse them ultrasonically until they are completely dissolved, preheat the heating table, set the temperature to 80℃, use a spray gun to spray evenly on the metal skeleton, and wait for the resin to solidify.

2. The method for preparing a functional polymer coating for an exposed skeleton type 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 type 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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