High-adhesion high-wear-resistance polyimide coating and preparation method thereof

Abstract

The invention discloses a high-adhesion and high-wear-resistance polyimide coating and a preparation method thereof, and relates to the technical field of polyimide coatings, and the preparation method of the polyimide coating comprises the following steps: (1) stripping defective multilayer MoS2 obtained by Li < + > intercalation hydrothermal synthesis to obtain few-layer MoS2; (2) replacing the few-layer MoS2 into a solvent system of polyamide acid (PAA) from ethanol rotary evaporation, and then adding PTFE to adsorb the few-layer MoS2 in ultrasound to obtain an efficient PTFE wear-resistant agent which is dispersed in a solvent and is loaded with the few-layer MoS2; (3) in-situ synthesis of polyamide acid in the presence of the efficient PTFE wear-resistant agent loaded with few layers of MoS2; and (4) coating the PAA on a metal substrate, drying the solvent in an air dry oven, and transferring into a muffle furnace for thermal imidization to obtain the high-adhesion polyimide wear-resistant coating. The friction coefficient (COF) of the prepared polyimide coating is reduced to 0.073, the wear rate is reduced to 0.0554 * 10 <-5 > mm < 3 > / (N.m), and the adhesive force of the coating on a 304 stainless steel plate and an h62 brass plate is improved to level 0.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of polyimide coating, in particular to a high-adhesion and high-wear-resistance polyimide coating and a preparation method thereof. BACKGROUND

[0002] Bearing is a key component in modern machinery and equipment, used to reduce wear and tear during operation. The drive system of pure electric vehicles of brands such as Tesla and Weilai mainly adopts single-speed fixed gear ratio gearbox. The gear speed increases with the acceleration of vehicle speed, and the motor speed can reach 20000r / min. The bearing is severely worn and heated at high speed, and the long-term working temperature is 110-120℃, and it also needs to operate stably at-40-150℃. The wear resistance and high temperature resistance of the coating are more demanding.

[0003] Polyimide (PI) is a high-potential wear-resistant coating matrix due to its high temperature resistance, high flexibility and high strength. Existing research usually adds 20wt%-40wt% of micron MoS2 and micron PTFE to pure PI through melt blending. Although the wear resistance is significantly improved, the adhesion and flexibility of the coating are sharply decreased, which cannot meet the actual processing and application requirements. Therefore, it is the key to improve the application ability of wear-resistant coating to research a more efficient wear-resistant agent, which provides excellent wear resistance for PI coating without losing the adhesion and flexibility of PI itself or even further increasing it. It is of great significance to improve the working efficiency of electric vehicle motor and prolong the service life of single-speed gearbox components under high-speed operation. SUMMARY

[0004] Based on the technical problems existing in the background art, the present application provides a high-adhesion and high-wear-resistance polyimide coating and a preparation method thereof. The performance of the coating meets the wear resistance and high temperature resistance requirements of bearing components under high-speed transmission of electric vehicles, and the adhesion and flexibility of the coating are considered in actual production and processing.

[0005] The high-adhesion and high-wear-resistance polyimide coating provided by the present application comprises the following raw materials by weight: 2-8 parts of polytetrafluoroethylene wear-resistant agent loaded with few-layer molybdenum disulfide, 27-38 parts of diamine monomer, and 54-71 parts of dianhydride monomer.

[0006] The polyamide acid is synthesized in situ from the diamine and the dianhydride in the presence of the polytetrafluoroethylene wear-resistant agent loaded with few-layer molybdenum disulfide, and then the high-adhesion and high-wear-resistance polyimide coating is obtained by thermal imidization treatment. The adhesion grade of the coating on the metal substrate (GB / T 9286-2021) is at least 1, the friction coefficient is not more than 0.2, and the wear rate is not more than 0.5*10 -5 mm 3(N.m), the coating does not break and debond under 1m height paint film impact test (GB / T 1732-2020), 2mm thick shaft bar paint film elasticity test (GB / T 1731-2020).

[0007] Preferably, the diamine monomer is at least one of 4, 4'-bis (3-aminophenoxy) diphenyl sulfone, 4, 4'-diamino diphenyl ether.

[0008] Preferably, the dianhydride monomer is at least one of bisphenol A type diether dianhydride, 4, 4'-diphenyl ether dianhydride.

[0009] The application provides a preparation method of the high-adhesion and high-wear-resistance polyimide coating.

[0010] S1: preparation of few-layer molybdenum disulfide;

[0011] S2: preparation of polytetrafluoroethylene wear-resistant agent loaded with few-layer molybdenum disulfide;

[0012] S3: in-situ synthesis of polyamic acid from diamine and dianhydride in the presence of the polytetrafluoroethylene wear-resistant agent loaded with few-layer molybdenum disulfide;

[0013] S4: heat imidization treatment of the polyamic acid prepared in S3 to obtain the high-adhesion and high-wear-resistance polyimide coating.

[0014] Preferably, the preparation method of the few-layer molybdenum disulfide is as follows:

[0015] S11: dissolving sodium molybdate dihydrate, polyethylene glycol and thiourea in deionized water, washing and drying the product after hydrothermal reaction to obtain multi-layer molybdenum disulfide;

[0016] S12: under an inert atmosphere, adding the multi-layer molybdenum disulfide into a n-butyl lithium solution in n-hexane, washing and vacuum drying the product after reaction to obtain Li x MoS2, adding deionized water, ultrasonic treatment, centrifugation, strong acid polystyrene cation exchange resin treatment and washing to obtain few-layer molybdenum disulfide, and ultrasonic dispersion in anhydrous ethanol for storage.

[0017] Preferably, the mass ratio of sodium molybdate dihydrate, polyethylene glycol and thiourea in S11 is 8-9:1:11-12; the temperature of hydrothermal reaction is 180-220℃, and the time is 18-24h;

[0018] In S12, the mass ratio of the multi-layer molybdenum disulfide and n-butyl lithium is 1.45-1.65:1; the reaction condition is standing for 5d, and ultrasonic treatment for 1h every 24h.

[0019] Preferably, the preparation method of the polytetrafluoroethylene wear-resistant agent loaded with few-layer molybdenum disulfide is as follows: first, the few-layer molybdenum disulfide dispersed in anhydrous ethanol is spin-exchanged into a first solvent, and then the polytetrafluoroethylene is also ultrasonically dispersed in the first solvent to obtain the polytetrafluoroethylene wear-resistant agent loaded with few-layer molybdenum disulfide.

[0020] Preferably, the first solvent is at least one of high-boiling N-methylpyrrolidone (202℃) and dimethyl sulfoxide (189℃); and the mass ratio of the few-layer molybdenum disulfide to the polytetrafluoroethylene is 1:1-5.

[0021] Preferably, the method for in-situ synthesizing polyamic acid is as follows: under an inert atmosphere, the polytetrafluoroethylene wear-resistant agent loaded with few-layer molybdenum disulfide is dispersed in a second solvent, a diamine monomer and a dianhydride monomer are sequentially added, and reaction is carried out at room temperature for 4-8h to obtain the polyamic acid.

[0022] Preferably, the second solvent is one or more of N,N-dimethylacetamide, N-methylpyrrolidone and dimethyl sulfoxide.

[0023] Preferably, the heat imidization treatment is carried out at a rate of 200℃ / h from 30℃ to 200-230℃, then at a rate of 100℃ / h from 200-230℃ to 330-350℃, and finally at 330-350℃ for 1h, and then the product is taken out after natural cooling to room temperature.

[0024] The beneficial technical effects of the present application are as follows:

[0025] (1) The high-efficiency PTFE wear-resistant agent loaded with few-layer MoS2 prepared by the present application contains a large amount of few-layer MoS2 with negative charge, which is loaded on PTFE through electrostatic adsorption, promotes the dispersion of PTFE in PAA, fills the gap of large particles, and adds the wear-resistant agent to the PI coating layer through in-situ polymerization, so that the surface protrusion of the coating layer is only 0.05μm (such as Figure 10 a), which is very smooth.

[0026] (2) The wear-resistant agent of the present application has high efficiency and strong effect, and the coating layer containing 3 mass parts of the high-efficiency PTFE wear-resistant agent loaded with few-layer MoS2 has a friction coefficient of 0.073, which is 50% of the coating layer containing the same mass parts of micron MoS2 and micron PTFE, and the wear rate is reduced by 90% to 0.0554×10 -5 mm 3 / (N·m).

[0027] (3) The prepared high-efficiency PTFE wear-resistant agent loaded with few-layer MoS2 has the effect of promoting the adhesion of the coating, compared with the adhesion force and flexibility of the coating decreased by adding a large amount of micron MoS2 and micron PTFE, the high-efficiency PTFE wear-resistant agent of the present application does not lose the original adhesion and flexibility of PI after being added to the coating, and even improves the adhesion to 0 level, and has good performance in paint film impact and elasticity test. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 XRD spectra of standard MoS2, defect multi-layer MoS2 and few-layer MoS2 prepared in Example 1 proposed in the present application;

[0029] Figure 2 HT-TEM morphology proposed in the present application; wherein A, B and C are defect multi-layer MoS2 prepared in Example 1; D and the local magnification (d1, d2, e) of D are few-layer MoS2 prepared in Example 1;

[0030] Figure 3 SEM images of the wear-resistant agent proposed in the present application; wherein A-B are SEM images of PTFE at different magnifications; C-D are SEM images of PTFE loaded with few-layer MoS2 at different magnifications;

[0031] Figure 4 Attenuated total reflection infrared (FTIR) images of the high-adhesion and high-wear-resistant polyimide coating prepared in Example 3 and Example 4 proposed in the present application;

[0032] Figure 5 Adhesion and flexibility test images proposed in the present application; wherein, A is the adhesion test image of the coating of Comparative Example 1 on 304 stainless steel and h62 brass, B is the adhesion test image of the coating of Comparative Example 2 on 304 stainless steel and h62 brass, C is the adhesion test image of the coating of Example 3 on 304 stainless steel and h62 brass, and D is the adhesion test image of the coating of Example 4 on 304 stainless steel, h62 brass, tinplate, Gcr15 bearing steel and 100Cr6 bearing steel;

[0033] Figure 6 Enlarged adhesion and flexibility test images proposed in the present application; wherein, A is the enlarged adhesion and flexibility test image of the coating of Comparative Example 2 on h62 brass plate, B is the enlarged adhesion and flexibility test image of the pure polyimide coating prepared from the monomers of molar ratio 1:1 of pyromellitic dianhydride (PMDA) and oxydianiline (ODA) on h62 brass plate, C is the enlarged adhesion and flexibility test image of the coating of Example 3 on h62 brass plate, and D is the enlarged adhesion and flexibility test image of the coating of Example 4 on h62 brass plate.

[0034] Figure 7 The morphology of the adhesion test of the coating of the present application on 304 stainless steel, h62 brass under microscope is the magnification of the grid position; wherein A is the coating of Comparative Example 1, B is the coating of Comparative Example 2, C is the coating of Example 3, and D is the coating of Example 4; Figure 5

[0035] Figure 8 The appearance of the coating for friction test prepared from Example 3-4 and Comparative Example 1-2 of the present application;

[0036] Figure 9 The friction test results of the coating prepared from Example 3-4 and Comparative Example 1-2 of the present application; wherein (A) is the friction coefficient, (B) is the wear rate, and (C) is the wear scar depth;

[0037] Figure 10 The wear scar morphology of the present application; wherein A is the 2D graph of the wear scar of the coating of Example 3, a is the 3D graph of the wear scar of the coating of Example 3; B is the 2D graph of the wear scar of the coating of Example 4, b is the 3D graph of the wear scar of the coating of Example 4; C is the 2D graph of the wear scar of the coating of Comparative Example 1, c is the 3D graph of the wear scar of the coating of Comparative Example 1; D and E are the 2D graphs of the wear scar of the coating of Comparative Example 2, d and e are the 3D graphs of the wear scar of the coating of Comparative Example 2;

[0038] Figure 11 The SEM morphology and corresponding EDS spectrum of the steel ball surface after the coating of the present application is worn; wherein A is the SEM morphology of Comparative Example 1, a1 is the C element spectrum, a2 is the F element spectrum, a3 is the Fe element spectrum, and a4 is the Mo element spectrum; B is the SEM morphology of Example 4, b1 is the C element spectrum, b2 is the F element spectrum, b3 is the Fe element spectrum, and b4 is the Mo element spectrum; C and D are the SEM morphologies of Example 4 with higher magnification. DETAILED DESCRIPTION

[0039] The present application will be further described below in combination with specific examples.

[0040] Example 1

[0041] ​Take 4 g (0.0165 mol) Na2MoO4·2H2O, 5.3 g (0.068 mol) of excess thiourea (NH2CSNH2), 0.463 g polyethylene glycol (PEG-1500) into a 100 ml PTFE-lined, pour into 60 g of deionized water after stirring to dissolve the transparent colorless solution, the lining back to stainless steel autoclave, autoclave tightly, in the air oven at 200 ℃ constant temperature for 24 h, the autoclave cooled to room temperature after pouring off the yellow waste liquid and collect the black precipitate, washed with 300 ml deionized water centrifugation (3000 r / min x 5 min), discard the waste liquid and repeat 4 times, the black precipitate collected at 80 ℃ vacuum drying 6 h, get 2.8 g of dry defect multilayer MoS2.

[0042] The hydrothermal synthesis reaction formula is as follows:

[0043]

[0044] Put 4 g of defect multilayer MoS2 into a 25 ml inclined two-necked flask, seal the flask and replace it with a nitrogen atmosphere, inject 2 ml of n-hexane to wet the multilayer MoS2, then inject 4 ml of n-butyllithium hexane solution (Sigma-Aldrich, 1.6 mol / L), stand for 5 days (every 24 h with 35 kHz ultrasonic for 1 h). The unreacted n-butyllithium is washed with 300 ml of n-hexane (3000 r / min x 5 min). The black precipitate is collected and vacuum dried at 80 ℃ for 10 min, then 150 ml of deionized water is added and transferred to a beaker, ultrasonic for 1 h to obtain a black MoS2 powder suspension. The suspension is centrifuged at 3000 r / min for 5 min, and the precipitate (unexfoliated multilayer MoS2) is discarded. The remaining suspension is added to 4 g of strongly acidic polystyrene cation exchange resin to remove Li + , stir for 1 h, filter the resin with a filter screen, and wash the remaining suspension with deionized water at high speed (13000 r / min x 5 min) for 4 times to obtain a wet few-layer MoS2 precipitate. The few-layer MoS2 precipitate is ultrasonically dispersed in 50 ml of ethanol (35 kHz, 15 min) to obtain a few-layer MoS2 ethanol dispersion solution with a concentration of 0.01 g / ml.

[0045] Li + The reaction formula for intercalation and exfoliation of multilayer MoS2 to obtain few-layer MoS2 and removal of Li + is as follows:

[0046]

[0047] As Figure 1In the XRD spectrum of the multi-layer MoS2, the (002) crystal face diffraction peak is slightly shifted to the left, and the crystal face spacing of about 0.64 nm is basically the same as that of the standard micron MoS2; in the XRD spectrum of the dried few-layer MoS2, the (002) crystal face diffraction peak is obviously shifted to the left, and the crystal face spacing is increased to 0.9440 nm, which indicates that the number of stacked layers of the few-layer MoS2 is reduced.

[0048] As Figure 2 Part A and Part B of the present application, the defects of the multi-layer MoS2 expose more reactive sites; the surface cracks provide more channels for Li + and reduce the diffusion energy barrier; the Mo vacancies and S vacancies provide more storage locations for Li + As Figure 2 Part D, d1, d2 and e of the present application, the few-layer MoS2 is a two-dimensional layered MoS2 nanosheet with a thickness of about single layer (0.4 nm) to 5 layers (4.2 nm). By comparing the crystal face spacing obtained by Fourier transform with the theoretical values of 1T-MoS2 and 2H-MoS2, the few-layer MoS2 belongs to the 2H-MoS2 crystal type.

[0049] Example 2

[0050] Take 10 ml of the few-layer MoS2 ethanol dispersion prepared in Example 1, pour into a 100 ml single-neck flask, add 30 ml of NMP (N-methyl pyrrolidone), and rotary evaporate at 60°C under reduced pressure for 4 h to remove water and ethanol. Drop the suspension on the SAP water-absorbing resin, and no swelling phenomenon is found, indicating that the water is basically removed. Then add 0.5 g of polytetrafluoroethylene (PTFE, particle size 2 μm), and ultrasonic at 35 kHz for 1 h to obtain 0.6 g of high-efficiency PTFE wear-resistant agent loaded with few-layer MoS2 dispersed in 30 ml of NMP. The morphology of the dried wear-resistant agent is as shown in Figure 3 Part C and Part D of the present application.

[0051] Put 0.2 g of high-efficiency PTFE wear-resistant agent loaded with 0.1 g of few-layer MoS2, and 0.2 g of PTFE loaded with 0.1 g of micron MoS2 (<2 μm) into two 50 ml centrifuge tubes containing 38 g (about 40 ml) of solvent, respectively. After ultrasonic at 35 kHz for 1 h, stand still, and every 2 h, take 5 ml of the suspension at the 10 ml scale line of the centrifuge tube using a pipette, weigh and calculate the density, as shown in Table 1.

[0052] Table 15 ml suspension time-mass table

[0053]

[0054] As shown in Table 1, the average of 0.14g per 5ml suspension is added after 0.1g few-layer MoS2, which shows that few-layer MoS2 may have adsorption effect on PTFE, while the common micron MoS2 is simply mixed with PTFE without adsorption effect. This is because the surface energy of few-layer MoS2 is higher than PTFE, and carries a large amount of negative charge (as shown in Table 2), and few-layer MoS2 powder is adsorbed to larger PTFE particles in ultrasonic, and Figure 3 there is also electrostatic repulsion between other powders, and the PTFE loaded with few-layer MoS2 is not easy to agglomerate.

[0055] Table 2 Zeta potential and nanoparticle size of MoS2

[0056]

[0057] Example 3

[0058] A high-attached and high-wear-resistant polyimide coating was prepared by in-situ polymerization with 4,4'-diphenyl ether dianhydride (ODPA), 4,4'-diamino diphenyl ether (ODA), and 4,4'-bis(3-aminophenoxy) diphenyl sulfone (M-BAPS) as monomers, and the mass ratio of the high-efficiency PTFE wear-resistant agent loaded with few-layer MoS2 in the coating was 3%. Among them, n(ODPA):n(ODA):n(M-BAPS) = 1:0.8:0.2, m(NMP):m(NMP) = 8:2.

[0059] Take 28ml of few-layer MoS2 ethanol dispersion prepared in Example 1, pour into a 100ml single-necked flask, add 12.768g of N-methyl pyrrolidone (NMP) and 3.192g of N,N-dimethylacetamide (DMAC), and rotary evaporation at 60°C under reduced pressure for 4h to remove water and ethanol, add 0.56g (particle size 2μm) PTFE, and ultrasonic at 35khz for 1h to obtain 0.84g of high-efficiency PTFE wear-resistant agent loaded with few-layer MoS2 dispersed in 15.96g of solvent.

[0060] Into a 250ml three-necked flask, 16.8g of high-efficiency PTFE wear-resistant agent loaded with few-layer MoS2 was added in 44.832g of NMP and 11.208g of DMAC under an Ar atmosphere, and a magnetic stirrer was used to heat to 40°C at a speed of 350r / min. 7.8126g of ODA was added, and stirring was continued for 20min until the monomer was completely dissolved. 15.1289g of ODPA was added in two portions, followed by the addition of 4.2185g of M-BAPS. After the temperature was allowed to return to room temperature, the reaction was continued for 6h at a speed of 350r / min in situ polymerization. The reaction yielded 100g of polyamic acid (PAA) containing high-efficiency PTFE wear-resistant agent loaded with few-layer MoS2 with a solid content of 28%, which was poured into a glass bottle, sealed, and stored in a refrigerator for 24h to remove bubbles.

[0061] After 24h, the PAA was removed, thawed to room temperature, and 5ml was drawn up with a needle tube. A strip of PAA was extruded uniformly on the left side of a metal plate. If bubbles were observed, they were removed with a dropper. A wet film applicator with a scale of 200μm was used to apply the PAA uniformly from left to right. The coated metal plate was placed in an aluminum box with a lid with vents on both sides, and the solvent was dried in a forced air drying oven. The drying oven was raised from room temperature to 150°C, held at this temperature for 15min, and then raised to 180°C and held at this temperature for another 15min. The aluminum box was removed after cooling and placed in a muffle furnace for thermal imidization. The temperature was raised according to the following schedule: 1h at room temperature, 1h at 230°C, 1h at 330°C, and 1h at 330°C. The sample was removed after natural cooling to room temperature and was ready for use.

[0062] As Figures 5-7 The adhesion of the coating prepared in Example 3 containing high-efficiency PTFE wear-resistant agent loaded with few-layer MoS2 was improved from level 1 to level 0 compared to Comparative Example 1, and the COF Figure 9 of Part A of the specification), and the wear rate Figure 9 of Part B of the specification) decreased sharply to 0.073, 0.0554x10 -5 mm 3 / (N.m) compared to Comparative Example 1, indicating that the high-efficiency PTFE wear-resistant agent loaded with few-layer MoS2 can improve the adhesion of the PI coating while maintaining the wear resistance of the PI coating, and the original high flexibility of the pure PI coating.

[0063] Example 4

[0064] A polyimide coating was prepared using bisphenol A diether dianhydride (BPADA), ODA, and M-BAPS as monomers. The mass ratio of the high-efficiency PTFE wear-resistant agent loaded with few-layer MoS2 in the coating was 6%. n(BPADA):n(ODA):n(M-BAPS)=1:0.7:0.3, and m(NMP):m(NMP)=8:2.

[0065] Take 17.5 ml of the ethanol dispersion of few-layer MoS2, pour it into a 100 ml single-necked flask, add 15.96 g of NMP and 3.99 g of DMAC, and evaporate it at 30 r / min at 60 ° C for 4 h to remove water and ethanol. Add 0.875 g (particle size 2 μm) of PTFE and ultrasonicate it at 35 khz for 1 h to obtain 1.05 g of a high-efficiency PTFE wear-resistant agent loaded with few-layer MoS2 dispersed in 19.95 g of solvent.

[0066] Under an Ar atmosphere, a 250ml three-necked flask was first charged with a high-efficiency PTFE wear-resistant agent loaded with few-layer MoS2, dispersed in 19.95g of solvent. 26.04g of NMP and 6.51g of DMAC were then added. A magnetic stirrer was heated to 40°C at 350r / min, and 2.9172g of ODA was added. Stir for 20 minutes until the monomers were completely dissolved. 10.8325g of BPADA was weighed and added in two portions, followed by 2.7003g of M-BAPS. After heating to room temperature, in-situ polymerization was continued at 350r / min for 6 hours to yield 70g of PAA containing a high-efficiency PTFE wear-resistant agent loaded with few-layer MoS2, with a solids content of 25%. The PAA was then poured into a sealed glass bottle and refrigerated for 24 hours to remove air bubbles.

[0067] After 24 hours, PAA was taken out, thawed to room temperature, 5 ml was drawn with a syringe, and a line of PAA was evenly squeezed out on the left side of the metal plate. If bubbles were observed, they were sucked out with a dropper. A wet film applicator with a scale of 200 μm was used to apply it uniformly from left to right. The coated metal plate was placed in an aluminum box with a lid and vents on both sides, and placed in a blast drying oven to dry the solvent. The drying oven was raised from room temperature to 150°C, kept at a constant temperature for 15 minutes, then raised to 180°C and kept at a constant temperature for 15 minutes. The aluminum box was taken out and cooled, then placed in a muffle furnace for thermal imidization. The heating program was: room temperature for 1 hour to 230°C, then raised to 330°C for 1 hour, kept at 330°C for 1 hour, and then naturally cooled to room temperature before being taken out for use.

[0068] exist Figure 10 In part B, it can be observed that Example 4 has very obvious adhesive wear marks. The high wear resistance of Example 4 is also related to its smooth surface. Figure 11 The surface fluctuation does not exceed 1.53μm. Compared with micron MoS2 and PTFE, Figure 11 No Mo was detected in the transfer film in part a4, and the transfer of MoS2 to the counter-friction surface was more obvious in the PTFE loaded with a few layers ( Figure 11 Part B of Figure 11 b4 was measured to have 0.18% Mo, and nano-sized few-layer MoS2 ( Figure 11The transfer film of Example 4 is more uniform, smooth, and complete, with a lower COF and improved wear resistance. The introduction of a few layers of MoS2 does not affect the adhesion of the coating, but also improves the dispersibility of PTFE and provides a nanoscale lubrication effect.

[0069] Example 4: Coating of high-efficiency PTFE wear-resistant agent containing few layers of MoS2 prepared by in-situ polymerization ( Figure 7 D, Figure 8 ), its adhesion is better than that of the comparative example 2 ( Figure 7 B, Figure 8 ) was improved from level 1 to level 0, and the friction coefficient (COF) and wear rate dropped sharply to 0.116 and 0.3713×10 -5 mm 3 / (N·m), which shows that the high-efficiency PTFE wear-resistant agent loaded with a few layers of MoS2 can improve the adhesion of the PI coating while ensuring the wear resistance and maintain the high flexibility of the original pure PI coating.

[0070] Comparative Example 1

[0071] A polyimide coating was prepared using ODPA, ODA, and M-BAPS as monomers, with the weight ratio of the wear-resistant agent in the coating accounting for 3%, wherein n(ODPA):n(ODA):n(M-BAPS)=1:0.8:0.2, and m(NMP):m(NMP)=8:2.

[0072] Take 0.28g of micron MoS2, 0.56g (particle size 2μm) PTFE, 12.768g NMP and 3.192g DMAC and add them to a 50ml centrifuge tube. Ultrasonicate at 35kHz for 1h to obtain 0.84g of micron MoS2 and micron PTFE dispersed in 15.96g of solvent.

[0073] Under an Ar atmosphere, 16.8 g of a solvent containing a dispersion of micronized MoS2 and micronized PTFE was added to a 250 ml three-necked flask. 44.832 g of NMP and 11.208 g of DMAC were then added. A magnetic stirrer was heated to 40°C at 350 rpm. 7.8126 g of ODA was added and stirred for 20 minutes until the monomers were completely dissolved. 15.1289 g of ODPA was then added in two portions, followed by 4.2185 g of M-BAPS. After heating to room temperature, the reaction was continued at 350 rpm for 6 hours to in situ polymerize polyamic acid. The reaction yielded 100 g of PAA containing a high-efficiency PTFE wear-resistant agent loaded with few-layer MoS2 and a solids content of 28%. The mixture was then sealed in a glass bottle and refrigerated for 24 hours to remove air bubbles.

[0074] After 24h, the PAA was removed, thawed to room temperature, and 5ml was drawn up with a syringe. A uniform strip of PAA was squeezed out on the left side of the metal plate. If bubbles were observed, they were drawn up with a dropper. A wet film applicator with a 200pm scale was used to apply the coating from left to right at a uniform speed. The coated metal plate was placed in an aluminum box with a lid on both sides with vents and placed in a forced air drying oven to dry the solvent. The drying oven was raised from room temperature to 150°C, held for 15min, then raised to 180°C and held for another 15min. The aluminum box was removed and allowed to cool before being placed in a muffle furnace for thermal imidization. The temperature program was as follows: 1h at room temperature, raised to 230°C, another 1h, raised to 330°C, held for 1h, and then allowed to cool to room temperature before removal.

[0075] The appearance of the coating after the friction test was as follows: Figure 8 The coating of Comparative Example 1 had a sudden decrease in light transmittance due to the addition of micron MoS2 (particle size < 2pm). The micron MoS2 increased the surface roughness of the coating (Table 4), and the abrasive wear was severe, resulting in a loss of wear resistance. The coating of Example 3 containing 3 parts by mass of the high-efficiency PTFE wear-resistant agent loaded with few-layer MoS2 was extremely smooth, with a COF and wear rate only half that of the coating of Comparative Example 1 containing micron MoS2, and even better wear resistance than many PI coatings containing a large amount of micron MoS2 and micron PTFE.

[0076] Comparative Example 2

[0077] The high-efficiency PTFE wear-resistant agent loaded with few-layer MoS2 described in Example 4 was directly mixed with the prepared PAA to illustrate the importance of maintaining the high dispersibility of the high-efficiency PTFE wear-resistant agent loaded with few-layer MoS2 through in-situ polymerization, while simple blending often results in uneven dispersion of the powder and severe agglomeration. The specific steps are as follows:

[0078] A polyimide coating was prepared using BPADA, ODA, and M-BAPS as monomers, with the mass ratio of the high-efficiency PTFE wear-resistant agent loaded with few-layer MoS2 in the coating being 6%. The molar ratio of n(BPADA):n(ODA):n(M-BAPS) was 1:0.7:0.3, and the mass ratio of m(NMP):m(NMP) was 8:2. 17.5ml of the few-layer MoS2 ethanol dispersion was poured into a 100ml single-neck flask, 0.875g of PTFE (particle size 2pm) was added, and ultrasonic treatment was performed at 35khz for 1h. The few-layer MoS2 / PTFE wear-resistant agent was dried at 80°C under vacuum to obtain 1.05g of dried few-layer MoS2 / PTFE wear-resistant agent.

[0079] Into a 250ml three-necked flask, 42g NMP and 10.5g DMAC were added under Ar atmosphere, and the magnetic stirrer was heated to 40℃ at a speed of 350r / min. 2.9172g ODA was added and stirred for 20min until the monomer was completely dissolved. 10.8325g BPADA was weighed and added in two portions, followed by the addition of 2.7003g M-BAPS. After the temperature was raised to room temperature, the stirring was continued at a speed of 350r / min for 6h. Then 1.05g of dry few-layer MoS2 / PTFE wear-resistant agent was added, and the stirring was continued for 4h to obtain 70g of PAA containing few-layer MoS2 / PTFE wear-resistant agent with a solid content of 25%. The PAA was poured into a glass bottle, sealed, and stored in a refrigerator for 24h to remove bubbles.

[0080] After 24h, the PAA was removed, thawed to room temperature, and 5ml was drawn into a syringe. A uniform PAA was extruded on the left side of the metal plate. If bubbles were observed, they were removed with a dropper. A wet film applicator with a scale of 200μm was used to evenly apply the coating from left to right. The coated metal plate was placed in an aluminum box with vents on both sides and placed in a forced air drying oven to dry the solvent. The drying oven was raised from room temperature to 150℃, held for 15min, then raised to 180℃ and held for another 15min. The aluminum box was removed after cooling and placed in a muffle furnace for thermal imidization. The temperature program was as follows: 1h at room temperature, then raised to 230℃, and held for another 1h. The temperature was then raised to 330℃ and held for 1h. The sample was removed after natural cooling to room temperature and stored for future use.

[0081] The coating of Comparative Example 2 had poor adhesion due to uneven dispersion and agglomeration of the powder, Figure 10 (D, E) It can be clearly observed that the agglomerated large particles are severely worn and abraded by the rotating steel balls, resulting in even worse wear resistance than pure PI.

[0082] Table 3 Coating adhesion test results

[0083]

[0084] Note: "√" indicates that the coating has no tearing, debonding, etc. after testing; the adhesion range is 0-5, with 0 being the best. Paint film grid (GB / T 9286-2021), impact (GB / T 1732-2020), and elasticity (GB / T 1731-2020).

[0085] As shown in Table 3, the examples containing few-layer MoS2-loaded PTFE wear-resistant agent all showed 0-level adhesion, excellent impact resistance and flexibility, and Figure 7 The "#" shape in Part C and Part D of the comparative example Figure 7 Part A and Part B of the comparative example are more obvious and straight, clear, without jagged tearing, and the edges of the scratches are not debonded.

[0086] Table 4 Surface roughness test results

[0087]

[0088] As shown in Table 4, the examples or comparative examples of high efficiency PTFE wear resistant agent containing supported few-layer MoS2 all have very smooth surface, the average height of surface protrusions is 0.05 μm, while the surface of comparative example 1 containing micron MoS2 is relatively rough.

[0089] Although the embodiments of the present application have been shown and described, it is to be understood that various changes, modifications, substitutions and alterations can be made to the embodiments without departing from the principles and spirit of the present application, the scope of which is defined by the appended claims and their equivalents, all of which are intended to be within the scope of the present application.

Claims

1. A high-adhesion and high-wear-resistant polyimide coating, characterized in that: The invention comprises the following raw materials in parts by weight: 2-8 parts of polytetrafluoroethylene wear-resistant agent loaded with a few layers of molybdenum disulfide, 27-38 parts of diamine monomer, and 54-71 parts of dianhydride monomer; In the presence of a polytetrafluoroethylene wear-resistant agent loaded with a few layers of molybdenum disulfide, polyamic acid is in situ synthesized from diamine and dianhydride, and then subjected to thermal imidization treatment to obtain a high-adhesion and high-wear-resistant polyimide coating; The coating has an adhesion grade of at least 1 on the metal substrate; the coefficient of friction does not exceed 0.2; The wear rate does not exceed 0.5×10 -5 mm 3 / (N·m); The coating does not break or debond in the 1m height paint film impact test and 2mm thick shaft rod paint film elasticity test.

2. The high-adhesion and high-wear-resistant polyimide coating according to claim 1, characterized in that: The diamine monomer is at least one of 4,4'-bis(3-aminophenoxy)diphenyl sulfone and 4,4'-diaminodiphenyl ether.

3. The high-adhesion and high-wear-resistant polyimide coating according to claim 1, characterized in that: The dianhydride monomer is at least one of bisphenol A diether dianhydride and 4,4'-biphenyl ether dianhydride.

4. A method for preparing a high-adhesion and high-wear-resistant polyimide coating, wherein the high-adhesion and high-wear-resistant polyimide coating is as described in any one of claims 1 to 3, characterized in that: The steps are as follows: S1: Preparation of few-layer MoS2; S2: Preparation of polytetrafluoroethylene wear-resistant agent loaded with few layers of molybdenum disulfide; S3: in situ synthesis of polyamic acid from diamine and dianhydride in the presence of a polytetrafluoroethylene wear-resistant agent loaded with a few layers of molybdenum disulfide; S4: The polyamic acid prepared in S3 is subjected to thermal imidization treatment to obtain a high-adhesion and high-wear-resistant polyimide coating.

5. The method for preparing a high-adhesion and high-wear-resistant polyimide coating according to claim 4, characterized in that: The preparation method of few-layer molybdenum disulfide is as follows: S11: dissolving sodium molybdate dihydrate, polyethylene glycol, and thiourea in deionized water, washing and drying the product after hydrothermal reaction to obtain multilayer molybdenum disulfide; S12: Under an inert atmosphere, multilayer molybdenum disulfide is added to a n-hexane solution of n-butyl lithium. The reaction product is washed and vacuum dried to obtain Li x MoS2 was added to deionized water and subjected to ultrasonication, centrifugation, strong acid polystyrene cation exchange resin treatment and washing to obtain a few-layer molybdenum disulfide, which was ultrasonically dispersed in anhydrous ethanol for storage.

6. The method for preparing a high-adhesion and high-wear-resistant polyimide coating according to claim 5, characterized in that: The mass ratio of sodium molybdate dihydrate, polyethylene glycol, and thiourea in S11 is 8-9:1:11-12; the hydrothermal reaction temperature is 180-220°C, and the time is 18-24 hours; The mass ratio of the n-hexane solution of multilayer molybdenum disulfide and n-butyl lithium in S12 is 1.45-1.65:1; the reaction conditions are standing for 5 days and ultrasonicating for 1 hour every 24 hours.

7. The method for preparing a high-adhesion and high-wear-resistant polyimide coating according to claim 4, characterized in that: The preparation method of the polytetrafluoroethylene wear resistant agent loaded with a few-layer molybdenum disulfide is as follows: first, the few-layer molybdenum disulfide dispersed in anhydrous ethanol is rotary evaporated and replaced into a first solvent, and then the polytetrafluoroethylene is ultrasonically dispersed in the first solvent to obtain the polytetrafluoroethylene wear resistant agent loaded with a few-layer molybdenum disulfide.

8. The method for preparing a high-adhesion and high-wear-resistant polyimide coating according to claim 7, characterized in that: The first solvent is at least one of N-methylpyrrolidone and dimethyl sulfoxide; the mass ratio of the few-layer molybdenum disulfide to polytetrafluoroethylene is 1:1-5.

9. The method for preparing a high-adhesion and high-wear-resistant polyimide coating according to claim 4, characterized in that: The method for in-situ synthesis of polyamic acid is as follows: under an inert atmosphere, a polytetrafluoroethylene wear-resistant agent loaded with a few layers of molybdenum disulfide is dispersed in a second solvent, and then a diamine monomer and a dianhydride monomer are added in sequence, and the reaction is carried out at room temperature for 4-8 hours to obtain polyamic acid; The second solvent is one or more of N,N-dimethylacetamide, N-methylpyrrolidone and dimethyl sulfoxide.

10. The method for preparing a high-adhesion and high-wear-resistant polyimide coating according to claim 4, characterized in that: The conditions for thermal imidization treatment are: increasing the temperature from 30°C to 200-230°C at a rate of 200°C / h, then increasing the temperature from 200-230°C to 330-350°C at a rate of 100°C / h, and finally keeping the temperature at 330-350°C for 1 hour, cooling naturally to room temperature and then taking out.

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