Microcapsule type self-early-warning and self-repairing epoxy coating as well as preparation method and application thereof

Abstract

The invention provides a microcapsule type self-early-warning and self-repairing epoxy coating as well as a preparation method and application thereof, and belongs to the technical field of anticorrosive coatings. The method comprises the following steps: mixing urea, resorcinol, ammonium chloride and a polyethylene grafted maleic anhydride aqueous solution, and adjusting the pH value of the mixed solution to obtain a water phase; mixing the PU prepolymer, DCF, TO and ethyl phenylacetate to obtain an oil phase; the water phase and the oil phase are mixed, a formaldehyde solution is added into the mixed solution for a reaction, and microcapsules are obtained; and adding the microcapsule into the epoxy coating to obtain the microcapsule type self-early-warning and self-repairing epoxy coating. According to the microcapsule, PU / UF serves as a shell of DCF and TO, DCF serves as an early warning agent, and TO serves as a repairing agent; the DT coated PU / UF microcapsule has good dispersibility in the coating, when the coating is damaged, the microcapsule is broken to release DCF and TO, the self-early warning and self-repairing performance of the coating is achieved, and metal corrosion is delayed.

Description

Technical Field

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

[0002] Marine engineering equipment is constantly exposed to harsh marine environments, susceptible to corrosion from seawater, humidity, and temperature fluctuations. Applying organic coatings to metal surfaces physically isolates the metal from corrosive media, achieving corrosion protection. However, when the coating is damaged by mechanical forces or other external forces, corrosive media can penetrate the damaged area and enter the metal surface, causing the coating to separate from the metal, leading to damage to the metal and coating failure. Self-warning and self-healing coatings can respond to external stimuli, autonomously warn of damage, and complete repairs, effectively improving protective performance and providing more durable and effective protection for the metal substrate.

[0003] Currently, existing self-warning and self-healing coatings have limitations such as single warning signals, complex preparation processes, and insufficient stability of the microcapsule shell material. Furthermore, their self-warning and self-healing mechanisms require further investigation. Therefore, research on self-warning and self-healing coatings for seawater environments is particularly important. Summary of the Invention

[0004] The purpose of this invention is to provide a microcapsule-type self-warning and self-healing epoxy coating, its preparation method and application. This invention has the advantages of simple process, excellent anti-corrosion performance of coating and good self-warning and self-healing performance.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing a microcapsule-type self-warning and self-healing epoxy coating, comprising the following steps: 1) Mix urea, resorcinol, ammonium chloride and polyethylene-grafted maleic anhydride aqueous solution, adjust the pH of the mixture to 3-4, and obtain the aqueous phase; The PU prepolymer, 2',7'-dichlorofluorescein, tung oil and ethyl phenylacetate were mixed to obtain the oil phase; 2) Mix the aqueous phase and the oil phase, add formaldehyde solution to the mixture to react and obtain microcapsules; the microcapsules are then subjected to freeze-drying in sequence to obtain dried microcapsules; 3) Add the dried microcapsules to the epoxy coating to obtain a microcapsule-type self-warning and self-healing epoxy coating; the epoxy coating contains bisphenol A diglycidyl ether and a curing agent.

[0006] Preferably, the mass fraction of the polyethylene-grafted maleic anhydride aqueous solution is 0.4-0.6%, the mass ratio of urea, resorcinol, and ammonium chloride is 1:0.08-0.12:0.08-0.12, the mass-to-volume ratio of urea and the polyethylene-grafted maleic anhydride aqueous solution is 1g:55-65mL, and the reagent for adjusting the pH of the mixture is sodium hydroxide solution with a concentration of 0.08-0.12mol / L.

[0007] Preferably, the mass ratio of the PU prepolymer to 2',7'-dichlorofluorescein is 0.7~1.1:0.03~0.05, the volume ratio of tung oil to ethyl phenylacetate is 7~11:13~17, the mass-volume ratio of the PU prepolymer to tung oil is 0.7~1.1g:7~11mL, and the mass ratio of urea to the PU prepolymer is 7~9:7~11.

[0008] Preferably, the volume ratio of the formaldehyde solution in step 2) to the polyethylene-grafted maleic anhydride aqueous solution in step 1) is 2~2.5:42~55; and the mass fraction of the formaldehyde solution is 35~40%.

[0009] Preferably, the reaction temperature in step 2) is 50~60℃, the reaction time is 2~4h, the freezing time is 10~14h, and the freeze-drying time is 40~55h.

[0010] Preferably, the curing agent in step 3) is polyetheramine D230; the mass ratio of bisphenol A diglycidyl ether to curing agent is 5~6:3~3.7; and the mass of the dried microcapsules is 8~10% of the mass of the epoxy coating.

[0011] The present invention also provides a microcapsule-type self-early warning and self-healing epoxy coating prepared by the preparation method described above.

[0012] The present invention also provides the application of the aforementioned microencapsulated self-early warning and self-healing epoxy coating in seawater environment coating protection. The microencapsulated self-early warning and self-healing epoxy coating is coated on the surface of a metal substrate and then cured and dried to obtain a microencapsulated self-early warning and self-healing epoxy coating.

[0013] Preferably, the curing and drying time is 6 to 8 days.

[0014] The beneficial effects of this invention are: 1) This invention provides a method for preparing DT@PU / UF microcapsules. PU / UF is used as the shell for 2',7'-dichlorofluorescein (DCF) and tung oil (TO), with DCF acting as an early warning agent and TO as a repair agent. The DT@PU / UF microcapsules of this invention exhibit good compatibility with epoxy coatings, resulting in good dispersion within the coating. When the coating is damaged, the microcapsules in the DP coating respond to the damage by rupturing and releasing DCF and TO. DCF reacts with residual amine groups in the coating to produce DCF ion precipitates, which exhibit a distinct red color under natural light and a striking yellow fluorescence under ultraviolet light. TO undergoes a cross-linking polymerization reaction with oxygen, forming a new protective film in the damaged area, thereby repairing microcracks in the coating and delaying metal corrosion. This achieves self-warning and self-repairing properties of the coating, thus delaying metal corrosion.

[0015] 2) The DT@PU / UF / EP coating prepared by this invention uses microcapsules to protect the epoxy coating, which can effectively repair microcracks in the coating and delay metal corrosion; the preparation process of this invention is simple and suitable for industrial production. Attached Figure Description

[0016] Figure 1 SEM images (a) and particle size distribution diagram (b) of the DT@PU / UF microcapsules of Example 1 are shown. Figure 2 EDS image of DT@PU / UF microcapsules from Example 1; Figure 3 The image shows the FT-IR chromatograms of DT@PU / UF microcapsules, TO, and DCF from Example 1. Figure 4 The following are TG images of the DT@PU / UF microcapsules, TO, DCF, EPA of Example 1 and the PU / UF shell of Comparative Example 1; Figure 5 The color rendering effect of DT@PU / UF microcapsules in Example 1 under different lights is shown, where a1~a3 are natural light and b1~b3 are ultraviolet light; Figure 6 The images show the color development of different coating scratches under natural light and ultraviolet light. Among them, a1, b1, and c1 are scratches of the EP coating in Comparative Example 2, and a2, b2, and c2 are scratches of the DP coating in Example 1. Figure 7 This is a schematic diagram of the self-early warning mechanism of the DP coating in Example 1; Figure 8 FT-IR images of DT@PU / UF microcapsules, TO and DCF, DP damaged coating of Example 1 and EP coating of Comparative Example 2; Figure 9The Nyquist curves (a1, a2) and Bode curves (b1, b2) of the DP coating of Example 1 and the EP coating of Comparative Example 2 are shown, where a1 and b1 are the EP coating and a2 and b2 are the DP coating. Figure 10 Equivalent circuit fitting models for coating / low alloy steel systems under different immersion times; Figure 11 This is a schematic diagram of the self-healing mechanism of the DP coating in Example 1. Detailed Implementation

[0017] This invention provides a method for preparing a microcapsule-type self-warning and self-healing epoxy coating, comprising the following steps: 1) Mix urea, resorcinol, ammonium chloride and polyethylene-grafted maleic anhydride (EMA) aqueous solution, adjust the pH of the mixture to 3-4, and obtain the aqueous phase; The PU prepolymer, 2',7'-dichlorofluorescein (DCF), tung oil (TO), and ethyl phenylacetate (EPA) were mixed to obtain the oil phase; 2) Mix the aqueous phase and the oil phase, add formaldehyde solution to the mixture to react and obtain microcapsules. The microcapsules are then freeze-dried sequentially to obtain dried microcapsules (DT@PU / UF microcapsules). 3) Add the dried microcapsules to the epoxy coating to obtain a microcapsule-type self-warning and self-healing epoxy coating; the epoxy coating contains bisphenol A diglycidyl ether and a curing agent.

[0018] In this invention, the mass fraction of the polyethylene-grafted maleic anhydride aqueous solution is preferably 0.4-0.6%, more preferably 0.45-0.55%, and even more preferably 0.5%; the mass ratio of urea, resorcinol, and ammonium chloride is preferably 1:0.08-0.12:0.08-0.12, more preferably 1:0.09-0.11:0.09-0.11, and even more preferably 1:0.1:0.1; the mass-volume ratio of urea and the polyethylene-grafted maleic anhydride aqueous solution is preferably 1g:55-65mL, more preferably 1g:57-62mL, and even more preferably 1g:60mL; the reagent for adjusting the pH value of the mixture is preferably sodium hydroxide solution, the concentration of which is preferably 0.08-0.12mol / L, more preferably 0.09-0.11mol / L, and even more preferably 0.1mol / L; the pH value of the mixture is preferably adjusted to 3.3-3.7, and even more preferably to 3.5.

[0019] In this invention, the preferred mass ratio of the PU prepolymer to 2',7'-dichlorofluorescein is 0.7~1.1:0.03~0.05, more preferably 0.8~1.0:0.035~0.045, and even more preferably 0.9:0.04; the preferred volume ratio of tung oil to ethyl phenylacetate is 7~11:13~17, more preferably 8~10:14~16, and even more preferably 9:15; the preferred mass-volume ratio of the PU prepolymer to tung oil is 0.7~1.1g:7~11mL, more preferably 0.8~1.0g:8~10mL, and even more preferably 0.9g:9mL; the preferred mass ratio of urea to the PU prepolymer is 7~9:7~11, and even more preferably 8:9.

[0020] In this invention, the volume ratio of the formaldehyde solution in step 2) to the polyethylene-grafted maleic anhydride aqueous solution in step 1) is preferably 2~2.5:42~55, more preferably 2.1~2.4:45~52, and even more preferably 2.2~2.3:48~50; the mass fraction of the formaldehyde solution is preferably 35~40%, more preferably 37~39%, and even more preferably 38%.

[0021] In this invention, the reaction temperature in step 2) is preferably 50~60℃, more preferably 52~58℃, and even more preferably 55~56℃; the reaction time is preferably 2~4h, more preferably 2.5~3.5h, and even more preferably 3h; the freezing time is preferably 10~14h, more preferably 11~13h, and even more preferably 12h; the freezing temperature is preferably -22~-15℃, more preferably -20~-18℃; the freeze-drying time is preferably 40~55h, more preferably 45~52h, and even more preferably 48~50h; the freeze-drying temperature is preferably -45~-35℃, and even more preferably -42~-40℃.

[0022] In this invention, the mixing rate in step 2) is preferably 5500~6500 rpm, more preferably 5700~6300 rpm, and even more preferably 6000 rpm; during the addition of formaldehyde solution, the mixture is stirred, and the stirring is carried out during the reaction. The stirring rate is preferably 350~450 rpm, more preferably 370~420 rpm, and even more preferably 400 rpm.

[0023] In this invention, the microcapsules are preferably washed and then frozen and freeze-dried, and then sieved after freeze-drying; the washing reagent is preferably water; the mesh size of the sieve used for sieving is preferably 80-120 mesh, and more preferably 100 mesh.

[0024] In the DT@PU / UF microcapsules of the present invention, PU / UF is the outer shell and DT (DCF / TO) is the core material; in the DT@PU / UF microcapsules, the loading rate of DCF is preferably 1.2~1.4%, more preferably 1.3%; the loading rate of TO is preferably 34~37%, more preferably 35~36%, and more preferably 35.82%.

[0025] In this invention, the curing agent in step 3) is preferably polyetheramine D230; the mass ratio of bisphenol A diglycidyl ether to curing agent is preferably 5~6:3~3.7, more preferably 5.2~5.8:3.2~3.5, and even more preferably 5.4~5.5:3.3~3.4; the mass of the dried microcapsules is preferably 8~10% of the mass of the epoxy coating, more preferably 8.5~9.5%, and even more preferably 9%.

[0026] The present invention also provides a microcapsule-type self-early warning and self-healing epoxy coating prepared by the preparation method described above.

[0027] The present invention also provides the application of the aforementioned microencapsulated self-early warning and self-healing epoxy coating in seawater environment coating protection. The microencapsulated self-early warning and self-healing epoxy coating is coated on the surface of a metal substrate and then cured and dried to obtain a microencapsulated self-early warning and self-healing epoxy coating.

[0028] In this invention, the curing and drying time is preferably 6 to 8 days, more preferably 7 days; the metal substrate is preferably steel.

[0029] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0030] In this embodiment, the PU prepolymer is Bayer L75, and the ultrasonic frequency is 40kHz.

[0031] Example 1

[0032] Dissolve 0.5 g of polyethylene-grafted maleic anhydride in 99.5 mL of deionized water and place the solution in an oil bath at 85 °C for 40 min until the solution is clear, yielding a 0.5% (w / w) aqueous solution of polyethylene-grafted maleic anhydride. Dissolve 0.8 g of urea, 0.08 g of resorcinol, and 0.08 g of ammonium chloride in 48 mL of the polyethylene-grafted maleic anhydride aqueous solution and stir to dissolve, obtaining a mixed solution. Adjust the pH of the mixed solution to 3.5 with 0.1 mol / L NaOH solution to obtain the aqueous phase.

[0033] Dissolve 0.9 g of PU prepolymer and 0.04 g of 2',7'-dichlorofluorescein in 9 mL of tung oil and 15 mL of ethyl phenylacetate, and sonicate for 40 min until the mixture becomes transparent to obtain the oil phase.

[0034] Under homogenous stirring at 6000 rpm, the oil phase was added dropwise to the aqueous phase over 2 minutes, and the mixture was stirred for 5 minutes after the addition was complete. The mixture was then transferred to a water bath at 25°C and stirred at 400 rpm for 10 minutes to obtain a mixture. 2.2 mL of a 37 wt% formaldehyde aqueous solution was added dropwise to the mixture, and the temperature was gradually increased to 55°C at a rate of 4°C / min. The mixture was stirred at 55°C at 400 rpm for 3 hours to obtain microcapsules. The microcapsules were washed and precipitated with deionized water, frozen at -18°C for 12 hours, placed in a vacuum freeze dryer, and freeze-dried at -40°C for 48 hours. The dried microcapsules (DT@PU / UF microcapsules) were then sieved through a 100-mesh sieve.

[0035] 907A low-alloy steel samples of 1cm×1cm×0.5cm and 8cm×5cm×0.2cm were used as substrates. After polishing with wet sandpaper, the 907A low-alloy steel was cleaned with deionized water and anhydrous ethanol to remove surface oil, and then dried with a hairdryer on a cool setting. A low-alloy steel containing a DT@PU / UF / EP self-warning and self-healing coating was prepared according to GB / T 20777-2006 "Inspection and Preparation of Paint and Varnish Samples". The specific process was as follows: 5.44g of bisphenol A diglycidyl ether and 3.31g of polyetheramine D230 curing agent were placed in a 250mL beaker and ultrasonically treated for 1 hour to ensure uniform mixing, resulting in an epoxy coating. Then, DT@PU / UF microcapsules (9% of the epoxy coating mass) were added to the epoxy coating, and after shaking until homogeneous, a microcapsule-type self-warning and self-healing epoxy coating (DP coating) was obtained. The DP coating was uniformly applied to the dried 907A low alloy steel and cured for 7 days to obtain the DP coating with a thickness of 300 μm.

[0036] Example 2

[0037] 0.45 g of polyethylene-grafted maleic anhydride was dissolved in 99.55 mL of deionized water and placed in an oil bath at 85 °C for 40 min until the solution became clear, yielding a 0.45% (w / w) aqueous solution of polyethylene-grafted maleic anhydride. 0.8 g of urea, 0.075 g of resorcinol, and 0.075 g of ammonium chloride were dissolved in 48 mL of the polyethylene-grafted maleic anhydride aqueous solution and stirred to obtain a mixture. The pH of the mixture was adjusted to 3.3 with 0.09 mol / L NaOH solution to obtain the aqueous phase.

[0038] Dissolve 0.8g of PU prepolymer and 0.035g of 2',7'-dichlorofluorescein in 8mL of tung oil and 14mL of ethyl phenylacetate, and sonicate for 40min until the mixture is transparent to obtain the oil phase.

[0039] Under homogenous stirring at 5700 rpm, the oil phase was added dropwise to the aqueous phase over 2 minutes, and the mixture was stirred for 5 minutes after the addition was complete. The mixture was then transferred to a water bath at 25°C and stirred at 360 rpm for 10 minutes to obtain a solution. 2.1 mL of a 38 wt% formaldehyde aqueous solution was added dropwise to the solution, and the temperature was gradually increased to 58°C at a rate of 4°C / min. The mixture was stirred at 58°C for 2.5 hours at 360 rpm to obtain microcapsules. The microcapsules were washed and precipitated with deionized water, frozen at -20°C for 11 hours, placed in a vacuum freeze dryer, and freeze-dried at -42°C for 45 hours. The dried microcapsules (DT@PU / UF microcapsules) were then sieved through a 100-mesh sieve.

[0040] The process conditions for preparing the DP coating are the same as in Example 1.

[0041] Example 3

[0042] 0.55 g of polyethylene-grafted maleic anhydride was dissolved in 99.45 mL of deionized water and placed in an oil bath at 85 °C for 40 min until the solution became clear, yielding a 0.5% (w / w) aqueous solution of polyethylene-grafted maleic anhydride. 0.8 g of urea, 0.088 g of resorcinol, and 0.088 g of ammonium chloride were dissolved in 48 mL of the polyethylene-grafted maleic anhydride aqueous solution and stirred to obtain a mixed solution. The pH of the mixed solution was adjusted to 3.7 using 0.11 mol / L NaOH solution to obtain the aqueous phase.

[0043] Dissolve 1.0 g of PU prepolymer and 0.045 g of 2',7'-dichlorofluorescein in 10 mL of tung oil and 16 mL of ethyl phenylacetate, and sonicate for 40 min until the mixture becomes transparent to obtain the oil phase.

[0044] Under homogenous stirring at 6200 rpm, the oil phase was added dropwise to the aqueous phase over 2 minutes, and the mixture was stirred for 5 minutes after the addition was complete. The mixture was then transferred to a water bath at 25°C and stirred at 430 rpm for 10 minutes to obtain a mixture. 2.4 mL of a 36 wt% formaldehyde aqueous solution was added dropwise to the mixture, and the temperature was gradually increased to 53°C at a rate of 4°C / min. The mixture was stirred at 53°C at 430 rpm for 3.5 hours to obtain microcapsules. The microcapsules were washed and precipitated with deionized water, frozen at -18°C for 13 hours, placed in a vacuum freeze dryer, and freeze-dried at -40°C for 52 hours. The dried microcapsules (DT@PU / UF microcapsules) were then sieved through a 100-mesh sieve.

[0045] The process conditions for preparing the DP coating are the same as in Example 1.

[0046] Comparative Example 1

[0047] Omit 0.04g of 2',7'-dichlorofluorescein and 9mL of tung oil from Example 1, and use the same process conditions as in Example 1 for preparing microcapsules. This comparative example yields a PU / UF shell.

[0048] Comparative Example 2

[0049] 907A low-alloy steel samples of 1cm×1cm×0.5cm and 8cm×5cm×0.2cm were used as substrates. After polishing with wet sandpaper, the 907A low-alloy steel was cleaned with deionized water and anhydrous ethanol to remove surface oil, and then dried with a hairdryer on a cool setting. Following GB / T 20777-2006 "Inspection and Preparation of Paint and Varnish Samples", an epoxy coating (EP coating) was prepared on the low-alloy steel. The specific process was as follows: 5.44g of bisphenol A diglycidyl ether and 3.31g of polyetheramine D230 curing agent were placed in a 250mL beaker and ultrasonically mixed for 1 hour to obtain a uniform epoxy coating (EP coating). The EP coating was then uniformly applied to the dried 907A low-alloy steel and cured for 7 days to obtain the EP coating.

[0050] SEM images (a) and particle size distribution diagram (b) of the DT@PU / UF microcapsules in Example 1 are shown below. Figure 1 As shown; the EDS diagram of the DT@PU / UF microcapsules in Example 1 is shown below. Figure 2 As shown. By Figure 1 It can be seen that the microcapsules are spherical and have good dispersion; the microcapsule particle size distribution diagram shows that the particle size is distributed in the range of 15~75μm, and most microcapsules are distributed between 35~55μm. Figure 2 It can be seen that there are many particles on the surface of the microcapsules. This is because urea and formaldehyde react to form urea-formaldehyde particles, and urea-formaldehyde particles of different sizes are attached to the surface of the microcapsules. Due to the PU shell of the microcapsules and the urea-formaldehyde particles on the surface, C, N, and O elements are uniformly distributed in circles in the EDS image. The core material of the microcapsules contains DCF, and Cl element has no obvious signal on the surface of the microcapsules, indicating that DCF is completely encapsulated by the microcapsules.

[0051] FT-IR images of DT@PU / UF microcapsules, TO, and DCF in Example 1 are shown below. Figure 3 As shown. In the FT-IR plot of TO, 1159cm -1 The characteristic absorption peak at 2925 cm⁻¹ is related to the stretching vibration of the CO bond in TO. -1 and 2859cm -1 The characteristic absorption peak at 696 cm⁻¹ is related to the symmetric and antisymmetric stretching vibrations of the CH bond in TO. In the FT-IR spectrum of DCF, the peak at 696 cm⁻¹ is... -1 The characteristic absorption peak at 1250 cm⁻¹ is related to the out-of-plane bending vibration of the benzene ring. -1The characteristic absorption peaks are related to the stretching and bending vibrations of the CO bonds in DCF. Therefore, the FT-IR spectrum of the DT@PU / UF microcapsules contains characteristic absorption peaks of TO and DCF, proving that TO and DCF were successfully encapsulated.

[0052] The TG values ​​of DT@PU / UF microcapsules, TO, DCF, EPA in Example 1 and PU / UF shells in Comparative Example 1 are shown below. Figure 4 As shown. By Figure 4 It is known that all materials experience varying degrees of weight loss with increasing temperature. The weight loss of DT@PU / UF microcapsules can be divided into four stages: Stage I (0~186℃), Stage II (186~281℃), Stage III (281~488℃), and Stage IV (488~800℃). In Stage I, EPA completely decomposes, while DCF and the PU / UF shell partially decompose, with decomposition rates of 1.45% and 7.54% respectively, resulting in a weight loss of approximately 4.9% for the microcapsules. In Stage II, most of the PU / UF shell has decomposed, with approximately 87.96% decomposition, and approximately 3.13% of the DCF has decomposed, resulting in a weight loss of approximately 54.33% for the microcapsules. In Stage III, TO begins to decompose at around 280℃, and the TG curve drops from 100% to 0%, indicating that TO completely decomposes at this stage. The PU / UF shell is also completely decomposed at this stage, resulting in a weight loss of approximately 39.1% for the microcapsules. In Stage IV, approximately 18.45% of the DCF has decomposed, and a small number of microcapsules are still decomposing, resulting in a weight loss of approximately 0.24%. The TG curves of DT@PU / UF microcapsules indicate that the peak at 184 °C is attributed to the decomposition of EPA, DCF, and the PU / UF shell; the peak at 279 °C is attributed to the decomposition of the PU / UF shell and DCF; the peak at 488 °C is attributed to the decomposition of DCF and TO; and the peak at 800 °C is attributed to the decomposition of DCF.

[0053] The weight loss of DT@PU / UF microcapsules in stages I, II, III, and IV was calculated using formulas 1-4, respectively: W EPA +1.45%W DCF +7.54%W PU / UF壳 =4.9% Formula 1 87.96%W PU / UF壳 +3.13%W DCF =54.33% Formula 2 29.18%W DCF +W TO +4.5% W PU / UF壳 =39.1% Formula 3 18.45%W DCF =0.24% Formula 4 Based on the above formula, the DCF and TO loading rates in the DT@PU / UF microcapsules of Example 1 are calculated to be 1.3% and 35.82%, respectively.

[0054] The color rendering effect of DT@PU / UF microcapsules under different lights in Example 1 is as follows: Figure 5 As shown, a1~a3 represent natural light, and b1~b3 represent ultraviolet light. (From...) Figure 5 It was observed that both intact and ruptured DT@PU / UF microcapsules appeared pale yellow under natural light and remained pale yellow under ultraviolet light. When 2-3 drops of polyetheramine D230 curing agent were added to the ruptured microcapsules, the microcapsules exhibited a striking red color under natural light and a bright yellow fluorescence under ultraviolet light. This is because after the microcapsules ruptured, DCF flowed out, and the amine groups in the curing agent D230 rapidly abstracted hydrogen from the hydroxyl groups of the DCF, causing the DCF to ionize and undergo an isomerization reaction, generating a DCF ion precipitate. This precipitate showed obvious red and yellow fluorescence under natural light and ultraviolet light, respectively. Therefore, DT@PU / UF microcapsules possess excellent color development ability and self-warning performance.

[0055] The coating's self-warning performance arises because when the coating breaks, DCF is released from the ruptured DT@PU / UF microcapsules. This DCF interacts with residual amine groups in the coating, resulting in a striking red fluorescence under natural light and a bright yellow fluorescence under ultraviolet light. The color development effects of different coating scratches under natural and ultraviolet light are shown in the following figures. Figure 6 As shown, a1, b1, and c1 are scratches on the EP coating of Comparative Example 2, and a2, b2, and c2 are scratches on the DP coating of Example 1. It can be observed that the scratches on the EP coating do not show color under natural light or ultraviolet light, while the scratches on the DP coating appear red under natural light and exhibit yellow fluorescence under ultraviolet light, showing a significant fluorescence effect.

[0056] A schematic diagram of the self-early warning mechanism of the DP coating in Example 1 is shown below. Figure 7 As shown, when the DP coating is damaged, the ruptured microcapsules release DCF. The hydrogen on the hydroxyl group in the DCF is rapidly removed by the amine group remaining in the coating, and the DCF changes from an acidic form to a basic form, undergoing an isomerization reaction to generate DCF ion precipitates. These precipitates appear distinctly red under natural light and exhibit a striking yellow fluorescence under ultraviolet light, thus serving as a corrosion early warning for the damaged areas of the coating.

[0057] FT-IR images of DT@PU / UF microcapsules, TO and DCF, DP damaged coating of Example 1 and EP coating of Comparative Example 2 are shown below. Figure 8 As shown. In the FT-IR plot of TO, 1159cm -1 The characteristic absorption peak at 2925 cm⁻¹ corresponds to the stretching vibration peak of CO in TO. -12859cm -1 The peaks at 696 cm⁻¹ represent the symmetric and antisymmetric stretching vibrations of the CH bond in TO. In the FT-IR plot of the DCF, this peak is at 696 cm⁻¹. -1 The characteristic absorption peak at 1250 cm⁻¹ is related to the out-of-plane bending vibration of the benzene ring. -1 The characteristic absorption peaks are related to the stretching and bending vibrations of CO in DCF. Furthermore, characteristic absorption peaks of DT@PU / UF microcapsules were observed in the FT-IR spectrum of the damaged DP coating, indicating that DCF and TO flowed out of the ruptured microcapsules after coating damage. The FT-IR spectra of the EP coating and DT@PU / UF microcapsules show that no characteristic absorption peaks of epoxy groups appeared in the FT-IR spectrum of the microcapsules, indicating that the epoxy resin and DT@PU / UF microcapsules are stably present.

[0058] The Nyquist curves (a1, a2) and Bode curves (b1, b2) of the DP coating of Example 1 and the EP coating of Comparative Example 2 are as follows: Figure 9 As shown, a1 and b1 are EP coatings, and a2 and b2 are DP coatings. The equivalent circuit fitting models for the coating / low-alloy steel system under different immersion times are as follows: Figure 10 As shown, where R s R c and R ct These represent the solution resistance, coating resistance, and charge transfer resistance, respectively, Q. c and Q dl These represent the coating capacitance and the double-layer capacitance, respectively. The electrochemical parameter fitting results for the DP coating of Example 1 and the EP coating of Comparative Example 2 are shown in Table 1.

[0059] Depend on Figure 9 From a1 and b1, it can be seen that after immersion for 0.5 hours, the impedance value of the EP coating / low alloy steel system is 1.51 × 10⁻⁶. 5 Ω·cm 2 As the immersion time increased to 240 h, the impedance value of the EP coating / low alloy steel system showed a linear decreasing trend, dropping to 2.16 × 10⁻⁶. 4 Ω·cm 2 This indicates that the scratches on the EP coating were not repaired. From a2 and b2, it can be seen that after immersion for 0.5 hours, the impedance value of the DP coating / low alloy steel system is 1.96 × 10⁻⁶. 5 Ω·cm 2 The impedance value reached its maximum after immersion for 96 hours, at 3.3 × 10⁻⁶. 5 Ω·cm 2 With increasing immersion time, the impedance value of the DP coating / low alloy steel system decreased slightly and then stabilized after 240 hours of immersion, with an impedance value of 2.88 × 10⁻⁶. 5 Ω·cm 2The impedance value is higher than that after soaking for 0.5 hours, indicating that a large amount of repair agent has been released in the DP coating, and the coating has basically achieved self-healing performance.

[0060] Table 1. Fitting results of electrochemical parameters for DP and EP coatings.

[0061] Depend on Figure 9 As shown in Table 1, when the amount of microcapsules added to the epoxy coating is 9 wt%, the microcapsules can release enough TO. The TO reacts with oxygen to form a new protective film, thus enabling the coating to self-repair.

[0062] A schematic diagram of the self-healing mechanism of the DP coating in Example 1 is shown below. Figure 11 As shown, when the coating is damaged, the microcapsules rupture and release DCF (Dissolved Carbon Fluoride) warning agent and TO (Toluene Torque) repair agent. The hydrogen on the hydroxyl group of the DCF is rapidly removed by the residual amine group in the coating, changing it from an acidic to a basic form. After an isomerization reaction, the DCF forms an ion precipitate, which appears distinctly red under natural light and exhibits a striking yellow fluorescence under ultraviolet light, thus providing a corrosion warning for the damaged area. Simultaneously, the released TO repair agent fills the cracks and undergoes a cross-linking polymerization reaction under the influence of oxygen, forming a new protective film in the damaged area. This prevents contact between the metal and the corrosive medium, ultimately achieving the self-healing function of the coating.

[0063] This invention utilizes a one-step method to prepare DT@PU / UF microcapsules using 2',7'-dichlorofluorescein (DCF) as an early warning agent, tung oil (TO) as a repair agent, and polyurethane / urea-formaldehyde (PU / UF) as a double-shell material. The microcapsules exhibit both colorimetric and fluorescent signal responses and possess self-healing capabilities. The resulting coating has a smooth, uniform surface and a glossy finish, exhibiting excellent corrosion resistance in seawater environments. When the coating is damaged, the microcapsules in the DP coating react with residual amine groups in the damaged coating, resulting in a color change from colorless to red, thus achieving the coating's self-early warning performance. TO, as a repair agent, undergoes a cross-linking polymerization reaction under oxygen, forming a new protective film in the damaged area, thereby achieving the coating's self-healing properties. This effectively repairs microcracks in the coating, thereby enhancing its protective performance.

[0064] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a microcapsule type self-warning self-repairing epoxy coating, characterized in that, It includes the following steps: 1) Mix urea, resorcinol, ammonium chloride and polyethylene-grafted maleic anhydride aqueous solution, adjust the pH of the mixture to 3-4, and obtain the aqueous phase; The PU prepolymer, 2',7'-dichlorofluorescein, tung oil and ethyl phenylacetate were mixed to obtain the oil phase; 2) Mix the aqueous phase and the oil phase, add formaldehyde solution to the mixture to react and obtain microcapsules; the microcapsules are then subjected to freeze-drying in sequence to obtain dried microcapsules; 3) Add the dried microcapsules to the epoxy coating to obtain a microcapsule-type self-warning and self-healing epoxy coating; the epoxy coating contains bisphenol A diglycidyl ether and a curing agent.

2. The production method according to claim 1, characterized by, The mass fraction of the polyethylene-grafted maleic anhydride aqueous solution is 0.4-0.6%, and the mass ratio of urea, resorcinol, and ammonium chloride is 1:0.08-0.12:0.08-0.12; the mass-volume ratio of urea and polyethylene-grafted maleic anhydride aqueous solution is 1g:55-65mL; ​​the reagent for adjusting the pH of the mixture is sodium hydroxide solution with a concentration of 0.08-0.12mol / L.

3. The preparation method according to claim 1 or 2, characterized in that, The mass ratio of the PU prepolymer to 2',7'-dichlorofluorescein is 0.7~1.1:0.03~0.05, the volume ratio of tung oil to ethyl phenylacetate is 7~11:13~17, the mass-volume ratio of the PU prepolymer to tung oil is 0.7~1.1g:7~11mL, and the mass ratio of urea to the PU prepolymer is 7~9:7~11.

4. The preparation method according to claim 3, characterized in that, The volume ratio of the formaldehyde solution in step 2) to the polyethylene-grafted maleic anhydride aqueous solution in step 1) is 2~2.5:42~55; the mass fraction of the formaldehyde solution is 35~40%.

5. The preparation method according to claim 4, characterized in that, Step 2) The reaction temperature is 50~60℃, the reaction time is 2~4h; the freezing time is 10~14h, and the freeze-drying time is 40~55h.

6. The preparation method according to claim 4 or 5, characterized in that, Step 3) The curing agent is polyetheramine D230; the mass ratio of bisphenol A diglycidyl ether to curing agent is 5~6:3~3.7; the mass of the dried microcapsules is 8~10% of the mass of the epoxy coating.

7. The microcapsule-type self-early warning and self-healing epoxy coating prepared by the preparation method according to any one of claims 1 to 6.

8. The application of the microencapsulated self-early warning and self-healing epoxy coating of claim 7 in seawater environment coating protection, characterized in that, Microcapsule-type self-early warning and self-healing epoxy coating is applied to the surface of a metal substrate and then cured and dried to obtain a microcapsule-type self-early warning and self-healing epoxy coating.

9. The application according to claim 8, characterized in that, The curing and drying time is 6 to 8 days.

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