Self-warning and self-repairing coating based on microcapsules, and preparation method and application thereof

Abstract

The application belongs to the technical field of anticorrosive coating, and particularly discloses a self-warning and self-repairing coating based on microcapsules, and a preparation method and application thereof. The components are as follows: 10-13 parts of bisphenol A diglycidyl ether, 6-9 parts of a diluent, 7-9 parts of a curing agent, and 1 part of TH@PU / UF microcapsules; wherein the TH@PU / UF microcapsules comprise a core material and a shell layer coated on the surface of the core material; the core material comprises tetraphenyl ethane and hexamethylene diisocyanate, and the shell layer is a polyurethane / urea-formaldehyde shell layer. The coating can obtain a self-warning and self-repairing coating by being coated as a primer and then being coated with a topcoat. When the coating is damaged, the core material is released, thereby playing a self-repairing role and a self-warning role of the coating. In addition, the coating also has excellent corrosion resistance in a deep-sea environment, thereby solving the problem of rapid decline of the protective performance of the coating caused by deep-sea factors.

Description

Technical Field

[0001] This invention relates to the field of anti-corrosion coating technology, and in particular to a microcapsule-based self-early warning and self-healing coating, its preparation method and application. Background Technology

[0002] Compared to shallow sea environments, deep sea environments are characterized by high hydrostatic pressure, low temperature, and low dissolved oxygen, making the corrosion behavior of metallic materials more complex and significantly altering the corrosion mechanism. High hydrostatic pressure is a crucial environmental factor distinguishing deep seas from shallow seas; it significantly accelerates the diffusion of corrosive media into the coating, leading to a rapid decline in coating protective performance and exacerbating corrosion failure of metallic materials. This poses a severe challenge to the construction and maintenance of corrosion protection strategies for marine engineering equipment.

[0003] Traditional organic coatings primarily slow down corrosion by physically shielding the metal substrate from corrosive media. However, in actual service, these coatings inevitably develop defects due to mechanical scratches, external impacts, or aging. Because these defects are difficult to detect and repair in a timely manner, localized corrosion can spread rapidly, ultimately leading to coating failure.

[0004] Self-early warning and self-healing coatings have the function of early damage warning and self-repair of defects. When the coating is damaged, it can not only accurately indicate the location and extent of the damage or corrosion through color change, fluorescence signal and other means, but also repair the damage through self-healing mechanism and restore the protective performance of the coating.

[0005] Currently, most research on self-warning and self-healing coatings is applied to shallow marine environments, with limited development and application of such coatings in deep-sea environments. Furthermore, research on the corrosion protection mechanism of self-warning and self-healing coatings under high hydrostatic pressure is scarce. Therefore, in-depth exploration of this field is of significant value. Summary of the Invention

[0006] In view of this, the present invention provides a microcapsule-based self-warning and self-healing coating, its preparation method and application, to solve the problem that existing self-warning and self-healing coatings are difficult to cope with deep-sea environments.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A microcapsule-based self-warning and self-healing coating, wherein the microcapsule-based self-warning and self-healing coating comprises the following components in parts by weight: 10-13 parts bisphenol A diglycidyl ether, 6-9 parts diluent, 7-9 parts curing agent and 1 part TH@PU / UF microcapsules; The TH@PU / UF microcapsule includes a core material and a shell layer covering the surface of the core material; The core material comprises tetraphenylethylene and hexamethylene diisocyanate, and the shell is a polyurethane / urea-formaldehyde shell.

[0008] Preferably, the preparation method of the TH@PU / UF microcapsules includes the following steps: 1) A mixture of diphenylmethane diisocyanate prepolymer, tetraphenylethylene and hexamethylene diisocyanate was prepared to obtain an oil phase mixture; 2) The oil phase mixture was dispersed in an aqueous solution of gum arabic, and then mixed with an aqueous solution of polyethyleneimine to carry out an interfacial polymerization reaction to obtain polyurethane single-shell microcapsules; 3) Mix urea-formaldehyde prepolymer, resorcinol and polyethylene grafted maleic anhydride mixed solution with polyurethane single-shell microcapsules and carry out in-situ polymerization reaction to obtain TH@PU / UF microcapsules.

[0009] Preferably, the mass ratio of the diphenylmethane diisocyanate prepolymer, tetraphenylethylene and hexamethylene diisocyanate in step 1) is 1~3:0.03~0.05:7~9.

[0010] Preferably, the volume-to-mass ratio of the oil phase mixture, gum arabic aqueous solution, and polyethyleneimine aqueous solution in step 2) is 9-11 g: 50-70 mL: 1-3 g; The mass fraction of the gum arabic aqueous solution is 4~6 wt.%; The mass fraction of the polyethyleneimine aqueous solution is 40~60 wt.%.

[0011] Preferably, the temperature of the interfacial polymerization reaction in step 2) is 30~50℃ and the time is 3~5h.

[0012] Preferably, the method for preparing the urea-formaldehyde prepolymer in step 3) includes mixing formaldehyde, urea and water, reacting them, and obtaining the urea-formaldehyde prepolymer. The mass ratio of the total mass of formaldehyde and water to the mass of urea is 11~13:5~7; The mass fraction of formaldehyde after mixing with water is 35~40 wt.%. The reaction temperature is 60~80℃, the time is 0.5~2h, and the pH value of the system is 7~9.

[0013] The resorcinol and polyethylene-grafted maleic anhydride mixed solution is obtained by mixing resorcinol with an aqueous solution of polyethylene-grafted maleic anhydride. The mass-to-volume ratio of resorcinol to polyethylene-grafted maleic anhydride aqueous solution is 4-6 g: 50-70 mL. The mass fraction of the polyethylene-grafted maleic anhydride aqueous solution is 1~3 wt.%.

[0014] Preferably, in step 3), the mass ratio of the urea-formaldehyde prepolymer, resorcinol and polyethylene-grafted maleic anhydride mixed solution to the polyurethane single-shell microcapsules is 17~19:4~6:50~70. The in-situ polymerization reaction described in step 3) is carried out at a temperature of 30~50℃ for 0.5~2h, and the pH value of the system is 2~4.

[0015] Preferably, the diluent comprises neopentyl glycol diglycidyl ether; The curing agent includes one or more of curing agents D230 and / or D400.

[0016] Another object of the present invention is to provide a method for preparing a microcapsule-based self-warning and self-healing coating, comprising the following steps: Bisphenol A diglycidyl ether, neopentyl glycol diglycidyl ether, curing agent, and TH@PU / UF microcapsules were mixed to obtain a microcapsule-based self-warning and self-healing coating.

[0017] Another object of the present invention is to provide an application of a microcapsule-based self-warning and self-healing coating in the preparation of a self-warning and self-healing coating, wherein the preparation method of the self-warning and self-healing coating includes: The microcapsule-based self-early warning and self-healing coating is sequentially coated and dried, and then a topcoat is applied to obtain the self-early warning and self-healing coating.

[0018] As can be seen from the above technical solution, compared with the prior art, the present invention has the following beneficial effects: 1. The self-warning and self-healing coating disclosed in this invention comprises TH@PU / UF microcapsules (hereinafter referred to as microcapsules). The hexamethylene diisocyanate (HDI) in the microcapsules reacts with water to generate polyurethane, which can effectively fill scratch defects and thus slow down metal corrosion, achieving a self-healing effect of the coating. Furthermore, the internal rotors of the aggregated tetraphenylethylene (TPE) in the microcapsules are restricted in rotation due to the steric hindrance of neighboring molecules, exhibiting obvious blue fluorescence under ultraviolet light, enabling the coating to provide a self-warning effect for defective areas. The polyurethane / urea-formaldehyde shell of the microcapsules in this invention has good compatibility with the coating, resulting in good dispersion of the microcapsules in the coating.

[0019] 2. The TH@PU / UF microcapsules described in this invention have uniform particle size and weak adhesion, making them less susceptible to rupture under high hydrostatic pressure in the coating. This improves the microcapsules' tolerance to different environments. On the other hand, high hydrostatic pressure can accelerate the expansion and extension of microcracks and pores in the coating, promoting the rupture of microcapsules at defects and thus enhancing the coating's self-warning and self-healing properties.

[0020] 3. The self-early warning and self-healing coating in this invention can maintain a high impedance value and wet adhesion after deep-sea immersion experiments, and the fluorescence effect is stable.

[0021] 4. The preparation process of the present invention is simple and suitable for industrial production. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0023] Figure 1 Characterization images of polyurethane single-shell microcapsules and TH@PU / UF microcapsules prepared in Example 1 of this invention are shown below. Figure 1 (a) is the SEM image of TH@PU / UF microcapsules, (b) is the particle size distribution diagram of TH@PU / UF microcapsules (Fraction—percentage, Particle—particle size), (c) is the SDM image of polyurethane single-shell microcapsules, and (d) is the SDM image of TH@PU / UF microcapsules. Figure 2 FT-IR images (Transmittance, Wavenumber) of TPE, HDI, diphenylmethane diisocyanate prepolymer, TH@PU / UF microcapsules and shell material. Figure 3 TGA curves (Weight, Temperature) for TH@PU / UF microcapsules and shell material. Figure 4 The image shows the TPE fluorescence test results. Figure 4 (a) shows photographs of HDI solution, TPE / HDI solution, PU solid, and TPE / PU solid taken under natural light and ultraviolet light, (b) shows the fluorescence emission spectra (Emission intensity, Wavelength) of TPE / HDI solution and TPE / PU solid, and (c) shows the CIE 1931 standard chromaticity diagram of TPE / PU solid. Figure 5 The image shows the fluorescence effect of the TH@PU / UF microcapsules prepared in this invention. Figure 6 FT-IR images (Transmittance, Wavenumber) of EP scratch coating, TFP scratch coating and TH@PU / UF microcapsules. Figure 7 Schematic diagram of a deep-sea environment simulation test device; Figure 8 Bode plots (|Z|—impedance modulus, Frequency—frequency, phase angle—phase angle) of TFP and EP coatings under different hydrostatic pressures and immersion times are shown. Figure 8 (a) corresponds to TFP coating / 0.1MPa, (b) corresponds to EP coating / 0.1MPa, (c) corresponds to TFP coating / 6MPa, (d) corresponds to EP coating / 6MPa, (e) corresponds to TFP coating / 15MPa, and (f) corresponds to EP coating / 15MPa. Figure 9 The graphs show the adhesion variation of EP and TFP coatings under different hydrostatic pressures (Wet adhesion, Immersion time). Figure 9 (a) corresponds to 0.1 MPa, (b) corresponds to 6 MPa, and (c) corresponds to 15 MPa. Figure 10 Fluorescence effects of the inner surfaces of EP coating and TFP coating under natural light and ultraviolet light after immersion in different hydrostatic pressures for 1008 hours. Figure 11 Fluorescence emission spectra (Intensity, Wavelength) of EP coating and TFP coating after immersion in different hydrostatic pressures for 1008 h. Figure 12 Macroscopic morphology and fluorescence effects of EP and TFP coatings under natural and ultraviolet light after immersion in different hydrostatic pressures for 1008 hours. Detailed Implementation

[0024] This invention provides a microcapsule-based self-warning and self-healing coating, which comprises the following components in parts by weight: 10-13 parts bisphenol A diglycidyl ether, 6-9 parts diluent, 7-9 parts curing agent and 1 part TH@PU / UF microcapsules.

[0025] In this invention, the TH@PU / UF microcapsule comprises a core material and a shell layer covering the surface of the core material; the core material comprises tetraphenylethylene and hexamethylene diisocyanate, and the shell layer is a polyurethane / urea-formaldehyde shell layer.

[0026] In this invention, the preparation method of the TH@PU / UF microcapsules includes the following steps: 1) A mixture of diphenylmethane diisocyanate prepolymer, tetraphenylethylene and hexamethylene diisocyanate was prepared to obtain an oil phase mixture; 2) The oil phase mixture was dispersed in an aqueous solution of gum arabic, and then mixed with an aqueous solution of polyethyleneimine to carry out an interfacial polymerization reaction to obtain polyurethane single-shell microcapsules; 3) Mix urea-formaldehyde prepolymer, resorcinol and polyethylene grafted maleic anhydride mixed solution with polyurethane single-shell microcapsules and carry out in-situ polymerization reaction to obtain TH@PU / UF microcapsules.

[0027] In this invention, the mass ratio of diphenylmethane diisocyanate prepolymer, tetraphenylethylene and hexamethylene diisocyanate in step 1) is 1~3:0.03~0.05:7~9, preferably 1.5~2.5:0.04:7.5~8.5, and more preferably 2:0.04:8.

[0028] In this invention, the organic solvent includes one or more of formaldehyde solution, urea, and resorcinol.

[0029] In this invention, the volume-to-mass ratio of the oil phase mixture, gum arabic aqueous solution, and polyethyleneimine aqueous solution in step 2) is 9~11g:50~70mL:1~3g, preferably 9.5~10.5g:55~65mL:1.5~2.5g, and more preferably 10g:60mL:2g.

[0030] In this invention, the mass fraction of the gum arabic aqueous solution is 4~6 wt.%, specifically 4.2 wt.%, 4.5 wt.%, 4.8 wt.%, 5 wt.%, 5.2 wt.%, 5.5 wt.%, and 5.8 wt.%.

[0031] In this invention, the mass fraction of the polyethyleneimine aqueous solution is 40~60 wt.%, specifically 42 wt.%, 45 wt.%, 48 wt.%, 50 wt.%, 52 wt.%, 55 wt.%, and 58 wt.%.

[0032] In this invention, the temperature of the interfacial polymerization reaction in step 2) is 30~50℃, specifically 32℃, 35℃, 38℃, 40℃, 42℃, 45℃, or 48℃; the time is 3~5h, specifically 3.2h, 3.5h, 3.8h, 4h, 4.2h, 4.5h, or 4.8h.

[0033] In this invention, the preparation method of the urea-formaldehyde prepolymer in step 3) includes mixing formaldehyde, urea, and water, reacting them, and obtaining the urea-formaldehyde prepolymer; the mass ratio of the total mass of formaldehyde and water to the mass of urea is 11~13:5~7, preferably 11.5~12.5:5.5~6.5, and more preferably 12:6; the mass fraction of formaldehyde after mixing with water is 35~40 wt.%, specifically 36 wt.%, 37 wt.%, 38 wt.%, or 39 wt.%; the reaction temperature is 60~80℃, specifically 62℃, 65℃, 70℃, 72℃, or 75℃; the reaction time is 0.5~2h, specifically 0.8h, 1h, 1.2h, 1.5h, or 1.8h; the pH value of the system is 7~9, specifically 7.2, 7.5, 7.8, 8, 8.2, 8.5, or 8.8.

[0034] In this invention, the resorcinol and polyethylene-grafted maleic anhydride mixed solution is obtained by mixing resorcinol with an aqueous solution of polyethylene-grafted maleic anhydride; the mass-to-volume ratio of the resorcinol to the aqueous solution of polyethylene-grafted maleic anhydride is 4-6 g: 50-70 mL, preferably 4.5-5.5 g: 55-65 mL, more preferably 5 g: 60 mL; the mass fraction of the aqueous solution of polyethylene-grafted maleic anhydride is 1-3 wt.%, specifically 1.2 wt.%, 1.5 wt.%, 1.8 wt.%, 2 wt.%, 2.2 wt.%, 2.5 wt.%, or 2.8 wt.%.

[0035] In this invention, the mass ratio of the urea-formaldehyde prepolymer, resorcinol, and polyethylene-grafted maleic anhydride mixed solution to the polyurethane single-shell microcapsules in step 3) is 17~19:4~6:50~70, preferably 17.5~18.5:4.5~5.5:55~65, and more preferably 18:5:60; the temperature of the in-situ polymerization reaction in step 3) is 30~50℃, specifically 32℃, 35℃, 38℃, 40℃, 42℃, 45℃, or 48℃; the time is 0.5~2h, specifically 0.8h, 1h, 1.2h, 1.5h, or 1.8h; and the pH value of the system is 2~4, specifically 2.2, 2.5, 2.8, 3, 3.2, 3.5, or 3.8.

[0036] In this invention, the diluent comprises neopentyl glycol diglycidyl ether.

[0037] In this invention, the curing agent includes one or more of curing agents D230 and / or D400.

[0038] This invention also provides a method for preparing a microcapsule-based self-warning and self-healing coating, comprising the following steps: Bisphenol A diglycidyl ether, neopentyl glycol diglycidyl ether, curing agent, and TH@PU / UF microcapsules were mixed to obtain a microcapsule-based self-warning and self-healing coating.

[0039] In this invention, the mixing process preferably includes vacuum degassing, and the vacuum degassing time is preferably 20 minutes.

[0040] This invention also provides an application of microcapsule-based self-warning and self-healing coatings in the preparation of self-warning and self-healing coatings, wherein the preparation method of the self-warning and self-healing coating includes: The microcapsule-based self-early warning and self-healing coating is sequentially coated and dried to obtain a primer, and then a topcoat is applied on the primer to obtain a self-early warning and self-healing coating.

[0041] In this invention, the thickness of the primer is preferably 215~245μm, specifically 220μm, 225μm, 230μm, 235μm, or 240μm; the thickness of the topcoat is preferably 85~115μm, specifically 90μm, 95μm, 100μm, 105μm, or 110μm.

[0042] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0043] Example 1

[0044] Preparation of PU single-shell microcapsules via interfacial polymerization: A certain amount of diphenylmethane diisocyanate prepolymer (Huntsman International LLC, Suprasec 2379) and TPE / HDI were mixed to obtain an oil phase mixture. The mass ratio of diphenylmethane diisocyanate prepolymer, TPE, and HDI was 2:0.04:7.96. 10 g of the oil phase mixture was added dropwise to 60 mL of gum arabic aqueous solution (5 wt.%), with mechanical stirring for 15 min to ensure uniform dispersion of the oil droplets and form a stable emulsion system. The stirring speed was reduced, and 2 g of polyethyleneimine aqueous solution (50 wt.%) was slowly added to initiate interfacial polymerization. The temperature was increased from 25 °C to 40 °C, and the reaction was carried out for 4 h. After rinsing several times with deionized water until the supernatant was clear, the bottom precipitate was collected to obtain polyurethane single-shell microcapsules.

[0045] Urea-formaldehyde shells were deposited onto polyurethane single-shell microcapsules via in-situ polymerization. A urea-formaldehyde prepolymer was prepared by reacting 12.66 g of formaldehyde solution (37 wt.%) with 6 g of urea for 1 h at 70 °C and pH=8. A mixed solution of resorcinol and polyethylene-grafted maleic anhydride (2.5 wt.%) was obtained by dissolving 5 g of resorcinol in 60 mL of polyethylene-grafted maleic anhydride aqueous solution. This mixed solution was then mixed with the urea-formaldehyde prepolymer and polyurethane single-shell microcapsules (mass ratio of the mixed solution of urea-formaldehyde prepolymer, resorcinol, and polyethylene-grafted maleic anhydride to polyurethane single-shell microcapsules was 18.66:5:60), and the pH of the mixture was adjusted to 3. The reaction was carried out at 40 °C for 1 h. After the reaction, the microcapsules were rinsed several times with deionized water, frozen for 3 h, and freeze-dried for 24 h to obtain TH@PU / UF microcapsules.

[0046] Weigh 5.44g of bisphenol A diglycidyl ether and 3.46g of neopentyl glycol diglycidyl ether, and stir them evenly. Then add 3.68g of polyetheramine curing agent D230 to the system and sonicate for 1 hour to ensure that all components of the epoxy coating are fully mixed. Next, add 0.52g of TH@PU / UF microcapsules to the above system, shake to disperse the microcapsules evenly, and place in a vacuum drying oven for vacuum degassing for 20 minutes to obtain a self-warning and self-healing coating.

[0047] Using 1cm×1cm×0.5cm 907A low-alloy steel as the substrate, the metal was polished with water-based sandpaper, then the surface oil was removed with ethanol and acetone, and finally dried with a hair dryer. A self-monitoring and self-healing coating was prepared according to GB / T 20777-2006 "Inspection and Preparation of Paint and Varnish Samples". The self-monitoring and self-healing coating prepared in this invention was uniformly coated as a primer onto the 907A low-alloy steel after water-based sandpaper polishing, with a thickness of 230μm, and dried in a forced-air drying oven at 60℃ for 24 h. After the primer cured, a layer of commercial epoxy topcoat (Shanghai Jinshidi Industrial Co., Ltd.) with a thickness of 100μm was applied to the surface. Finally, it was dried at room temperature for 24 h, and the coating sample preparation was completed. A control group without TH@PU / UF microcapsules was also set up. For ease of discussion, the coating samples with and without TH@PU / UF microcapsules were designated as TFP coating and EP coating, respectively.

[0048] Test case

[0049] The polyurethane single-shell microcapsules and TH@PU / UF microcapsules prepared in Example 1 of this invention were characterized. The SEM image of the TH@PU / UF microcapsules is shown below. Figure 1 As shown in (a) above, the particle size distribution diagram is as follows: Figure 1 As shown in (b) above, the SDM image of the polyurethane single-shell microcapsule is as follows. Figure 1 As shown in (c), the SDM diagram of TH@PU / UF microcapsules is as follows. Figure 1 As shown in (d) in the diagram. From Figure 1 As shown in (a) and (b), the TH@PU / UF microcapsules are regularly spherical, with good particle dispersion, no significant agglomeration, and a uniform particle size distribution concentrated in the 95~115μm range. Figure 1 (c) It can be seen that the surface of the PU single-shell microcapsule is smooth, and Figure 1 (d) The double-shell structure of the TH@PU / UF microcapsules consists of an inner PU shell and an outer stacked UF shell. The urea-formaldehyde particles on the outer surface are evenly distributed, facilitating the integration of the microcapsules and the epoxy coating. In addition, the polar groups in the UF can form hydrogen bonds with the epoxy coating, making the connection between the microcapsules and the epoxy coating even tighter.

[0050] FT-IR images of TPE, HDI, diphenylmethane diisocyanate prepolymer (MDI prepolymer), TH@PU / UF microcapsules, and shell materials are shown below. Figure 2 As shown, through Figure 2 It can be seen that the HDI sample is at 2260 cm⁻¹ -1 A strong absorption peak appeared nearby, corresponding to the stretching vibration of the isocyanate group (-N=C=O), a characteristic functional group signal of HDI. A similar -N=C=O stretching vibration peak, consistent with pure HDI, was also detected at the same position in the TH@PU / UF microcapsules, proving that the repair agent HDI in the core material was successfully encapsulated within the microcapsules. Furthermore, the TH@PU / UF microcapsules exhibited absorption in the 500~800 cm⁻¹ range. -1 Absorption peaks corresponding to the stretching and bending vibrations of the aromatic CH groups in TPE were detected nearby, indicating that the warning agent TPE was successfully encapsulated. The MDI prepolymer showed an absorption peak at 2260 cm⁻¹. -1 A distinct -N=C=O stretching vibration peak is also present at this location, while in the spectrum of the pure shell material, this characteristic peak completely disappears. This indicates that the MDI prepolymer has been consumed to form the microcapsule PU shell, with no unreacted MDI prepolymer residue. The pure shell material exhibits a peak at 3150~3550 cm⁻¹. -1 The broad absorption peak at 1620 cm⁻¹ corresponds to the NH and OH stretching vibrations of the urethane and urea groups in the PU and UF shells. -1 The presence of a stretching vibration peak at -C=O in the urea-formaldehyde resin particles indicates that the double-shell structure has been successfully formed. Based on the above analysis, the successful preparation of TH@PU / UF microcapsules has been confirmed.

[0051] The TGA curves of TH@PU / UF microcapsules and shell materials are as follows: Figure 3 As shown, through Figure 3It can be seen that during the thermogravimetric analysis at 180℃ for 1 hour, the core material of the microcapsules completely evaporated. The encapsulation rate of the microcapsule core material can be calculated using the following formula: C core +C shell =C microcapsules C shell / 1-C core = 5.74wt.% In the above formula, C microcapsules C core and C shell The values ​​represent the weight loss of the microcapsule, core material, and shell material during the isothermal process, respectively. The shell of the TH@PU / UF microcapsule has a moderate and dense thickness, which can effectively encapsulate and protect the core material, with an encapsulation rate of up to 63.58 wt.%.

[0052] The TPE fluorescence test results are as follows: Figure 4 As shown, where Figure 4 (a) shows photographs of HDI solution, TPE / HDI solution, PU solid, and TPE / PU solid taken under natural light and ultraviolet light irradiation; (b) shows the fluorescence emission spectra of TPE / HDI solution and TPE / PU solid; (c) shows the CIE 1931 standard chromaticity diagram of TPE / PU solid. HDI and TPE / HDI solution (0.5 wt.%) were subjected to a water-curing experiment. The -N=C=O in HDI can undergo a polymerization reaction with water to form polyurethane (PU) solid. Figure 4 As shown in (a), both the pure HDI solution and the PU solid exhibit virtually no fluorescence under 365 nm UV light irradiation. In the TPE / HDI solution, TPE exists in a dispersed state within HDI and produces almost no fluorescence. However, while HDI undergoes the aforementioned polymerization reaction with water, TPE, although not participating in the chemical reaction, is uniformly encapsulated within the PU as it forms, simultaneously solidifying to form a TPE / PU solid. At this point, the TPE molecules are in an aggregated state, and their intramolecular rotation and vibration are spatially restricted, exhibiting a distinct blue fluorescence under UV light irradiation. The results indicate that HDI and PU have almost no interference with the fluorescence phenomenon of TPE. Figure 4 As shown in (b), the emission peak of the TPE / PU solid is located around 470 nm, a photoluminescence phenomenon consistent with that of pure TPE powder. Using CIE 1931 standard colorimetric software, the CIE chromaticity coordinates of TPE / PU under 365 nm ultraviolet light excitation were determined to be (0.17107, 0.22625), indicating blue light emission. Figure 4 (c) in the middle.

[0053] The TH@PU / UF microcapsules prepared in Example 1 were placed in a petri dish for artificial disruption, and deionized water was added. The results are as follows: Figure 5 As shown, when the microcapsules rupture, the core material TPE / HDI solution flows out from the microcapsules. While HDI solidifies upon contact with water, TPE aggregates to form a TPE / PU solid. Under ultraviolet light, it exhibits a distinct blue fluorescence, a phenomenon consistent with the results of the aforementioned core material water-curing experiment, providing experimental evidence for subsequent research on the coating's self-warning and self-healing properties.

[0054] The cured coating sample was artificially scratched, and the scratched area was placed on an infrared spectroscopy ATR component for testing. Microcapsules and potassium bromide powder were mixed and ground at a mass ratio of 1:200, compressed into tablets, and then subjected to infrared spectroscopy testing.

[0055] FT-IR images of EP scratched coating, TFP scratched coating, and TH@PU / UF microcapsules are shown below. Figure 6 As shown in the figure. It can be seen from the figure that HDI and TH@PU / UF microcapsules at 2260 cm⁻¹... -1 A strong absorption peak appears nearby, corresponding to the stretching vibration of -N=C=O. Pure shell material exhibits absorption in the range of 3150~3550 cm⁻¹. -1 The presence of broad peaks corresponds to the stretching vibrations of the NH and OH groups of the urethane and urea groups in the PU and UF shells. The TFP scratch coating exhibits the characteristic peaks of the HDI, TH@PU / UF microcapsules, and pure shell material at the corresponding positions, but the EP scratch coating does not show these characteristic peaks. This indicates that after artificial scratching, the microcapsules in the scratched area rupture, and the core material is effectively released, filling the scratched area.

[0056] A schematic diagram of the deep-sea environment simulation test device is shown below. Figure 7 As shown, the core components of the device include an autoclave, a metering pump pressurization system, and an industrial chiller. During the experiment, a 3.5 wt.% NaCl solution was delivered into the autoclave via the metering pump to regulate the hydrostatic pressure inside the autoclave to the target value. Simultaneously, the industrial chiller drove the condensate to circulate along the outer wall of the autoclave. The industrial chiller maintained the experimental temperature at 5°C, and the pH of the NaCl solution was adjusted to 8.0 using dilute NaOH solution. The dissolved oxygen content of the solution was controlled by continuously introducing high-purity N2, maintaining it at 3.0 mg / L. Three hydrostatic pressure conditions were set for the experiment: 0.1 MPa (atmospheric pressure), 6 MPa, and 15 MPa.

[0057] Bode plots of TFP and EP coatings under three hydrostatic pressures and different immersion times simulated in the aforementioned deep-sea environment simulation device are shown below. Figure 8 As shown, where, Figure 8 (a) corresponds to TFP coating / 0.1MPa, (c) corresponds to TFP coating / 6MPa, (e) corresponds to TFP coating / 15MPa, (b) corresponds to EP coating / 0.1MPa, (d) corresponds to EP coating / 6MPa, and (f) corresponds to EP coating / 15MPa. Electrochemical impedance spectroscopy (EIS) tests were performed on samples with different immersion times to compare and analyze the changes in the impedance model under different hydrostatic pressures. The test procedure is as follows: Electrochemical impedance spectroscopy measurements were performed under constant potential control at an open-circuit potential, with a sinusoidal signal amplitude of 20mV and a test frequency range of 10... 5 ~10 -2 Hz. The electrolytic cell employs a classic three-electrode system, with the electrochemical test sample as the working electrode, high-purity graphite as the auxiliary electrode, and an Ag / AgCl electrode as the reference electrode. Figure 8 It can be seen that the TFP coating exhibits good protective effects under all three hydrostatic pressures. Under high hydrostatic pressure, the penetration rate of corrosive media into the coating interior and the coating / metal interface accelerates. As the hydrostatic pressure increases, the decline in the protective performance of the EP coating is significantly aggravated, and the gap in protective performance between the EP coating and the TFP coating further widens. When the hydrostatic pressure increases from 0.1 MPa to 15 MPa and the immersion time is 1008 h, the advantage of the low-frequency impedance modulus of the TFP coating over the EP coating increases from one order of magnitude to more than two orders of magnitude. This indicates that hydrostatic pressure promotes the self-healing effect of the TFP coating to a certain extent.

[0058] The adhesion curves of EP coating and TFP coating under different hydrostatic pressures are shown below. Figure 9 As shown, where, Figure 9 In the diagram, (a) corresponds to 0.1 MPa, (b) corresponds to 6 MPa, and (c) corresponds to 15 MPa. (From...) Figure 9It can be seen that before immersion, the adhesion of the two coatings was not significantly different. With prolonged immersion time, the adhesion of both coatings gradually decreased. Under high hydrostatic pressure, the wet adhesion of the TFP coating deteriorated significantly less than that of the EP coating, mainly due to the self-healing effect of the TFP coating. After immersion at 0.1 MPa hydrostatic pressure for 1008 hours, the wet adhesion of the EP coating was 4.58 MPa, with an adhesion loss of 57.36%, while the wet adhesion of the TFP coating was 6.11 MPa, with an adhesion loss of 44.81%. The adhesion of the EP coating remained consistently lower than that of the TFP coating, but its adhesion loss was higher. This is mainly because the repair agent released from the microcapsules in the TFP coating can react with water to generate polyurethane, repairing the damaged areas of the coating. As the hydrostatic pressure increased from 0.1 MPa to 15 MPa, the decreasing trend of the wet adhesion of the EP coating became more pronounced. When the immersion time was extended to 1008 h, the wet adhesion of the EP coating at 6 MPa and 15 MPa decreased to 3.54 MPa and 2.63 MPa, respectively, while the adhesion loss gradually increased to 67.25% and 75.78%, respectively. This is because the high hydrostatic pressure accelerates the penetration of corrosive media into the coating interior and the coating / metal interface, promoting the occurrence and development of electrochemical reactions at the interface, leading to a decrease in the interfacial bonding strength between the coating and the metal. In contrast, the wet adhesion of the TFP coating decreased more slowly. After immersion for 1008 h, the wet adhesion of the TFP coating at 6 MPa and 15 MPa was 5.96 MPa and 5.77 MPa, respectively, with adhesion losses of 45.72% and 47.60%, respectively. This result indicates that although high hydrostatic pressure accelerates coating degradation, the corrosive media diffuses along the damaged area to the microcapsules, causing them to rupture and release HDI. The HDI reacts with water to generate polyurethane, which promptly repairs the damaged area of ​​the coating. In addition, the microcapsules are uniformly dispersed in the coating, which can fill the micropores formed during curing and prolong the diffusion channels of corrosive media.

[0059] Figure 10 The images show the fluorescence effects of the inner surfaces of the EP and TFP coatings under natural and ultraviolet light after immersion in three hydrostatic pressures for 1008 hours. Under natural light, after immersion at 0.1 MPa for 1008 hours, a small amount of corrosion products were observed on the inner surface of the EP coating, while almost no corrosion products were found on the inner surface of the TFP coating. With increasing hydrostatic pressure, the amount of corrosion products on the inner surface of the EP coating increased, while only sporadic corrosion products appeared on the inner surface of the TFP coating. This indicates that the EP coating deteriorates more severely with increasing hydrostatic pressure, while the TFP coating still exhibits good corrosion resistance. Under ultraviolet light, the EP coating showed almost no fluorescence at 0.1 MPa, 6 MPa, and 15 MPa, while the TFP coating showed obvious and uniformly distributed blue fluorescence. Figure 11Further analysis of the fluorescence emission spectra under different hydrostatic pressures revealed that the maximum emission peak of the TFP coating was located at approximately 470 nm under all three hydrostatic pressures, with the peak positions remaining largely consistent. This indicates that the increase in hydrostatic pressure did not significantly affect the fluorescence emission mechanism, and the fluorescence signal of the TFP coating did not show significant attenuation. These results demonstrate that the TFP coating maintains good fluorescence response stability under long-term immersion under different hydrostatic pressures, and can provide reliable self-warning performance.

[0060] Figure 12 The images show the macroscopic morphology and fluorescence of the EP and TFP coatings under natural and ultraviolet light after immersion in hydrostatic pressure for 1008 h under three different pressure conditions. Under natural light, it can be observed that the corrosion degree of the scratched areas of both coatings gradually intensifies with increasing hydrostatic pressure; however, under all three hydrostatic pressure conditions, the corrosion degree of the TFP coating in the scratched area is significantly lower than that of the EP coating, indicating that the TFP coating plays a certain self-healing role during immersion, thus improving its protective performance. After immersion in 15 MPa hydrostatic pressure for 1008 h, the metal corrosion at the scratched area of ​​the EP coating is significantly aggravated, exhibiting localized protrusions and blistering morphology. Under ultraviolet light, the EP coating did not show fluorescence under hydrostatic pressures of 0.1 MPa, 6 MPa, and 15 MPa. Meanwhile, the TFP coating showed obvious blue fluorescence under all three hydrostatic pressures, indicating that it can maintain a stable fluorescence signal without significant attenuation under hydrostatic pressure.

[0061] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0062] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A self-early warning and self-healing coating based on microcapsules, characterized in that, The microcapsule-based self-warning and self-healing coating comprises the following components in parts by weight: 10-13 parts bisphenol A diglycidyl ether, 6-9 parts diluent, 7-9 parts curing agent and 1 part TH@PU / UF microcapsules; The TH@PU / UF microcapsule includes a core material and a shell layer covering the surface of the core material; The core material comprises tetraphenylethylene and hexamethylene diisocyanate, and the shell is a polyurethane / urea-formaldehyde shell.

2. The self-early warning and self-healing coating based on microcapsules according to claim 1, characterized in that, The preparation method of the TH@PU / UF microcapsules includes the following steps: 1) Mix diphenylmethane diisocyanate prepolymer, tetraphenylethylene and hexamethylene diisocyanate to obtain an oil phase mixture; 2) The oil phase mixture was dispersed in an aqueous solution of gum arabic, and then mixed with an aqueous solution of polyethyleneimine to carry out an interfacial polymerization reaction to obtain polyurethane single-shell microcapsules; 3) Mix urea-formaldehyde prepolymer, resorcinol and polyethylene grafted maleic anhydride mixed solution with polyurethane single-shell microcapsules and carry out in-situ polymerization reaction to obtain TH@PU / UF microcapsules.

3. The self-early warning and self-healing coating based on microcapsules according to claim 2, characterized in that, The mass ratio of the diphenylmethane diisocyanate prepolymer, tetraphenylethylene and hexamethylene diisocyanate mentioned in step 1) is 1~3:0.03~0.05:7~9.

4. The self-early warning and self-healing coating based on microcapsules according to claim 3, characterized in that, The volume-to-mass ratio of the oil phase mixture, gum arabic aqueous solution, and polyethyleneimine aqueous solution in step 2) is 9-11 g: 50-70 mL: 1-3 g; The mass fraction of the gum arabic aqueous solution is 4~6 wt.%; The mass fraction of the polyethyleneimine aqueous solution is 40~60 wt.%.

5. A microcapsule-based self-early warning and self-healing coating according to any one of claims 2 to 4, characterized in that, The interfacial polymerization reaction described in step 2) is carried out at a temperature of 30~50℃ for 3~5h.

6. The self-early warning and self-healing coating based on microcapsules according to claim 5, characterized in that, The preparation method of the urea-formaldehyde prepolymer in step 3) includes mixing formaldehyde, urea and water, reacting them, and obtaining the urea-formaldehyde prepolymer. The mass ratio of the total mass of formaldehyde and water to the mass of urea is 11~13:5~7; The mass fraction of formaldehyde after mixing with water is 35~40 wt.%. The reaction temperature is 60~80℃, the time is 0.5~2h, and the pH value of the system is 7~9; The resorcinol and polyethylene-grafted maleic anhydride mixed solution is obtained by mixing resorcinol with an aqueous solution of polyethylene-grafted maleic anhydride. The mass-to-volume ratio of resorcinol to polyethylene-grafted maleic anhydride aqueous solution is 4-6 g: 50-70 mL. The mass fraction of the polyethylene-grafted maleic anhydride aqueous solution is 1~3 wt.%.

7. A self-early warning and self-healing coating based on microcapsules according to claim 6, characterized in that, In step 3), the mass ratio of the urea-formaldehyde prepolymer, resorcinol, and polyethylene-grafted maleic anhydride mixed solution to the polyurethane single-shell microcapsules is 17~19:4~6:50~70. The in-situ polymerization reaction described in step 3) is carried out at a temperature of 30~50℃ for 0.5~2h, and the pH value of the system is 2~4.

8. A self-early warning and self-healing coating based on microcapsules according to claim 7, characterized in that, The diluent includes neopentyl glycol diglycidyl ether; The curing agent includes one or more of curing agents D230 and / or D400.

9. A method for preparing a microcapsule-based self-warning and self-healing coating according to any one of claims 1 to 8, characterized in that, Includes the following steps: Bisphenol A diglycidyl ether, neopentyl glycol diglycidyl ether, curing agent, and TH@PU / UF microcapsules were mixed to obtain a microcapsule-based self-warning and self-healing coating.

10. The application of the microcapsule-based self-warning and self-healing coating according to any one of claims 1 to 8 in the preparation of a self-warning and self-healing coating, characterized in that, The preparation method of the self-early warning and self-healing coating includes: The microcapsule-based self-early warning and self-healing coating is sequentially coated and dried, and then a topcoat is applied to obtain the self-early warning and self-healing coating.

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