A room temperature self-healing polyurethane coating and a method of making the same

Abstract

The application discloses a room-temperature self-repairing polyurethane coating, which is characterized by being prepared by one-pot polymerization reaction of reaction raw materials comprising diisocyanate, polyhydric alcohol, a curing agent and a disulfide bond-containing chain extender, wherein the disulfide bond-containing chain extender is dithiodibenzoic acid, and the coating realizes efficient room-temperature self-repairing function by introducing dynamic disulfide bonds and multiple hydrogen bonds to construct a synergistic dynamic network.

Description

Technical Field

[0001] This invention belongs to the field of functional polymer coating materials technology, and relates to a room temperature self-healing polyurethane coating based on the synergistic effect of dynamic disulfide bonds and multiple hydrogen bonds, its preparation method and its application in metal corrosion protection. Background Technology

[0002] Metallic materials are susceptible to corrosion during service, leading to significant economic losses and safety risks. Organic coatings are the most widely used method for metal corrosion protection; however, these coatings are prone to microcracks or scratches when subjected to mechanical forces, causing their barrier function to fail. Corrosive media then penetrate the metal substrate, initiating localized corrosion. Self-healing coatings can spontaneously repair cracks and defects, thereby significantly extending coating life, reducing maintenance costs, and improving structural safety and reliability.

[0003] Intrinsic self-healing coatings based on reversible covalent bonds (such as disulfide bonds and Diels-Alder bonds) and supramolecular interactions (such as hydrogen bonds) have attracted much attention due to their ability to achieve multiple repairs. In existing technologies, self-healing polyurethane coatings based on disulfide bonds often use relatively expensive disulfides as raw materials, for example: CN114773570A discloses a self-healing polyurethane material based on bis(2-hydroxyethyl) disulfide, and CN121064711A discloses a self-healing silicone-based polyurea coating with disulfide bonds based on amino-terminated diphenyl disulfide. Although the above two materials have good self-healing properties, bis(2-hydroxyethyl) disulfide and amino-terminated diphenyl disulfide are expensive (about 500-800 yuan / 100g), which significantly increases the material cost and limits their large-scale engineering applications.

[0004] CN122080731A discloses a weather-resistant, high-hardness composite anti-corrosion coating and its preparation method. Although it uses dithiodibenzoic acid (DTSA) as one of the raw materials, the disulfide bond in this scheme is only used as a modifying group for the side chain or end group of epoxy resin. The specification does not disclose any experimental data on achieving self-repair of scratches at room temperature.

[0005] Furthermore, existing research on self-healing performance evaluations mostly focuses on a single dimension (such as observing only the disappearance of scratches), lacking systematic quantitative analysis of the repair process and in-depth kinetic exploration of the repair mechanism. Therefore, developing a low-cost, simple-to-prepare coating material that can achieve efficient self-healing at room temperature has significant practical implications and application value. Summary of the Invention

[0006] In order to overcome the shortcomings of the prior art, the present invention aims to provide a room temperature self-healing polyurethane coating and its preparation method. The coating introduces dynamic disulfide bonds and multiple hydrogen bonds to construct a synergistic dynamic network, and at the same time utilizes a pyrolytic carbon intermediate layer to improve the interfacial bonding force between the coating and the substrate, thereby achieving a highly efficient room temperature self-healing function.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A room-temperature self-healing polyurethane coating is characterized in that it is prepared by a one-pot polymerization reaction of reaction raw materials comprising diisocyanate, polyol, chain extender containing disulfide bonds and curing agent, wherein the chain extender containing disulfide bonds is dithiodibenzoic acid.

[0008] In this invention, dithiodibenzoic acid (DTSA) serves as both a chain extender and a dynamic crosslinking agent. Its molecular structure contains two carboxyl groups (-COOH) and one disulfide bond (-SS-). During polyurethane synthesis, the carboxyl groups react with isocyanate groups to form amide bonds, introducing DTSA into the polyurethane backbone. Simultaneously, the disulfide bond undergoes dynamic exchange (disulfide metathesis) at room temperature, endowing the material with self-healing capabilities. Furthermore, the carboxyl groups and benzene ring structure in DTSA can form multiple hydrogen bonds and π-π stacking interactions with the hard segments of polyurethane, further enhancing intermolecular interactions and producing a synergistic effect with the dynamic disulfide bond, thereby improving the mechanical properties and self-healing efficiency of the coating.

[0009] Preferably, the diisocyanate is an aliphatic or alicyclic diisocyanate, such as isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HDI), dicyclohexylmethane diisocyanate (HMDI), etc.; more preferably, it isophorone diisocyanate (IPDI). IPDI has an asymmetric alicyclic structure, moderate reactivity, which is beneficial for controlling the polymerization process, and the resulting polyurethane has good weather resistance and yellowing resistance.

[0010] Preferably, the polyol is a polyether polyol or a polyester polyol, such as polytetrahydrofuran ether diol (PTMG), polypropylene glycol (PPG), polyethylene glycol (PEG), etc.; more preferably, it is polytetrahydrofuran ether diol (PTMG) with a number-average molecular weight of 500-3000, preferably 1000. PTMG has good molecular chain flexibility and moderate crystallinity, which can impart good flexibility and mechanical strength to the coating.

[0011] Preferably, the curing agent is an amine curing agent, such as 3,3'-dichloro-4,4'-diaminodiphenylmethane (MOCA), 4,4'-diaminodiphenylmethane (MDA), ethylenediamine, etc.; more preferably, it is MOCA. As an aromatic diamine curing agent, MOCA can form polyurethane hard segments with high rigidity, which is beneficial to improving the mechanical properties and media resistance of the coating.

[0012] Preferably, the molar ratio of the diisocyanate to the polyol is (1.5-3):1, more preferably 2:1; the molar ratio of the chain extender containing disulfide bonds to the polyol is (0.5-2):1, more preferably 1:1. Within this range, it can be ensured that the prepolymer has an appropriate molecular weight and end-group functionality, while ensuring that the coating has a sufficient density of dynamic disulfide bonds to achieve effective self-healing.

[0013] The room temperature self-healing polyurethane coating of the present invention has a dynamic cross-linked network structure formed by the synergistic effect of dynamic disulfide bonds and multiple hydrogen bonds. Combined with a pyrolytic carbon intermediate layer, it improves the interfacial bonding force between the coating and the substrate. Under room temperature conditions of 15-30°C, it has the ability to self-repair scratches with a depth of 10-50μm, and the repair time is 12-72 hours.

[0014] This invention also provides a method for preparing a room-temperature self-healing polyurethane coating, comprising the following steps: (1) Prepolymerization reaction: The dehydrated polyol and diisocyanate are added to the reactor, along with an organic solvent, a chain extender containing disulfide bonds and a catalyst. The reaction is carried out under an inert atmosphere at 70-90°C for 1-3 hours to obtain a polyurethane prepolymer containing disulfide bonds. The chain extender containing disulfide bonds is dithiobenzoic acid. (2) Degassing and curing: The prepolymer obtained in step (1) is subjected to vacuum degassing, and then a curing agent is added and quickly stirred to mix evenly; (3) Substrate pretreatment: A phenolic resin solution is coated on the surface of the substrate, and then the phenolic resin coating is converted into a pyrolytic carbon coating by flame sintering or laser sintering. (4) Coating and drying: The mixture obtained in step (2) is coated onto the substrate treated in step (3), the coating thickness is controlled, and the coating is dried and cured to obtain the room temperature self-healing polyurethane coating.

[0015] Preferably, the inert atmosphere in step (1) is a nitrogen atmosphere, the reaction temperature is 75-85℃, preferably 80℃, and the reaction time is 1.5-2.5 hours, preferably 2 hours.

[0016] Preferably, the organic solvent in step (1) is tetrahydrofuran (THF), N,N-dimethylformamide (DMF), or toluene; tetrahydrofuran is preferred. The catalyst is an organotin catalyst, preferably dibutyltin dilaurate (DBTDL), and is used in an amount of 0.5-2% of the mass of the polyol.

[0017] Preferably, the vacuum degree of vacuum degassing in step (2) is -0.08 to -0.1 MPa, and the degassing time is 10-30 minutes, preferably 20 minutes.

[0018] Preferably, the concentration of the phenolic resin solution in step (3) is 5-20 wt%, and the solvent is ethanol or acetone; the flame sintering adopts an oxyacetylene flame with a flame temperature of 800-1200℃ and a sintering time of 5-30 seconds; the laser sintering adopts a CO2 laser with a laser power of 50-200W and a scanning speed of 10-50mm / s.

[0019] Preferably, the substrate in step (4) is a metal substrate, preferably carbon steel, tinplate, aluminum alloy and titanium alloy; the dry film thickness of the coating is 50-150μm, preferably 80-120μm; the drying and curing conditions are drying in an oven at 50-70℃ for 8-16 hours, preferably drying in an oven at 60℃ for 12 hours.

[0020] The room-temperature self-healing polyurethane coating obtained by this invention is mainly used for metal corrosion protection.

[0021] Compared with the prior art, the beneficial effects of the present invention are: 1. Excellent self-healing performance at room temperature. The coating has a dynamic network of disulfide bonds and multiple hydrogen bonds working synergistically, enabling efficient self-healing without external stimuli (such as heating, light, or solvents) at room temperature (15-30℃). For scratches with a depth of 10-50μm, the repair efficiency can reach over 85%, with a repair time of 12-72 hours.

[0022] 2. Low raw material cost. The market price of dithiobenzoic acid (DTSA) is approximately 50-80 yuan / 100g, which is only about 1 / 10 of that of bis(2-hydroxyethyl) disulfide, significantly reducing material costs. DTSA also acts as a chain extender and dynamic crosslinking agent, eliminating the need for additional chain extenders and further simplifying the formulation.

[0023] 3. Simple preparation process. The one-pot synthesis method directly adds DTSA to the prepolymerization reaction system, eliminating the need for pre-synthesizing diols or diamines containing disulfide bonds. The process involves fewer steps, milder reaction conditions, and is conducive to industrial production. 4. Excellent mechanical properties. While achieving self-healing capabilities, the coating exhibits superior tensile strength and elongation at break compared to conventional polyurethanes without disulfide bonds. This is attributed to the rigid benzene ring structure of DTSA and the synergistic reinforcing effect of disulfide and hydrogen bonds. Attached Figure Description

[0024] Figure 1 This is a synthesis route diagram of the coating of the present invention, showing the chemical reaction process of synthesizing a polyurethane coating (PUS) containing dynamic disulfide bonds in a one-pot process using IPDI, PTMG, DTSA, and MOCA as raw materials. In the diagram: IPDI is isophorone diisocyanate, PTMG is polytetrahydrofuran ether diol, DTSA is dithiodibenzoic acid, MOCA is 3,3'-dichloro-4,4'-diaminodiphenylmethane, and DBTDL is dibutyltin dilaurate.

[0025] Figure 2 The images show the Fourier Transform Infrared (FTIR) and Raman spectra of the coating (PUS) of this invention and the control coating (PU). (a) is the full FTIR spectrum, (b) is a magnified view of the C=O stretching vibration region, (c) is a magnified view of the N–H stretching vibration region, (d) is the full Raman spectrum, and (e) is a magnified view of the C–S and S–S stretching vibration regions.

[0026] Figure 3 This is a stress-strain curve diagram of the coating (PUS) of the present invention and the control coating (PU).

[0027] Figure 4 The images show cross-sectional scanning electron microscope (SEM) images and elemental distribution maps (EDS) of the coating (PUS) of the present invention. (a) is a cross-sectional scanning electron microscope image of the coating of the present invention, (b) is a cross-sectional elemental distribution map of the coating of the present invention, and (e) is a cross-sectional elemental distribution map of the coating of the present invention. (b) represents carbon, (c) represents nitrogen, (d) represents oxygen, and (e) represents sulfur.

[0028] Figure 5 These are optical microscope images of the self-healing process of the coating of the present invention on scratches of different depths. (a1) and (a2) are images of the same area after being scratched by a tungsten carbide pen and after 48 hours of room temperature repair; (b1) and (b2) are images of the same area after being scratched by a razor and after 48 hours of room temperature repair; (c1) and (c2) are images of the same area after being scratched by a utility knife and after 48 hours of room temperature repair.

[0029] Figure 6(a) to (j) are laser confocal microscope images taken at different times after the same area was scratched with a utility knife during the self-repair process of deep scratches on the coating of the present invention. (a) is 0 h, (b) is 1 h, (c) is 3 h, (d) is 4 h, (e) is 5 h, (f) is 7 h, (g) is 11 h, (h) is 24 h, (i) is 33 h, and (j) is 48 h.

[0030] Figure 7 This is a laser confocal microscope image interface curve taken at different times after the same area was scratched with a utility knife during the self-repair process of the coating deep scratches of the present invention.

[0031] Figure 8 The Nyquist electrochemical impedance spectroscopy (EIS) plots of the coating after 48 hours in 3.5 wt% NaCl solution for the original, scratched, and room-temperature repaired states are shown. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0033] Example 1 This embodiment illustrates a preferred preparation method for the room-temperature self-healing polyurethane coating (PUS) of the present invention, with reference to... Figure 1 As shown, it mainly includes the following steps: (1) Prepolymerization reaction: Accurately weigh 10.0 g (10 mmol) of dehydrated polytetrahydrofuran ether diol (PTMG-1000) and 4.44 g (20 mmol) of isophorone diisocyanate (IPDI) and add them to a dry 250 ml three-necked flask. Add 50 ml of tetrahydrofuran (THF) as solvent, 3.06 g (10 mmol) of dithiobenzoic acid (DTSA) as chain extender, and 2 drops (about 0.1 g) of dibutyltin dilaurate (DBTDL) as catalyst to the flask. Place the flask in a constant temperature oil bath, and under the conditions of continuous nitrogen protection and mechanical stirring at 200 rpm, raise the temperature to 80°C and react at a constant temperature for 2 hours to obtain a polyurethane prepolymer solution containing disulfide bonds.

[0034] (2) Degassing and curing: Place the prepolymer solution obtained in step (1) in a vacuum drying oven and degas it under vacuum for 20 minutes at room temperature. Then add the measured amount of MOCA curing agent (calculated according to the molar ratio of IPDI to MOCA 2:1) to the degassed prepolymer and stir manually for 3 minutes to ensure uniform mixing.

[0035] (3) Substrate pretreatment: Grind, degrease, clean, and dry the surface of the carbon steel substrate. Spray a 10wt% phenolic resin ethanol solution onto the pretreated substrate surface, controlling the wet film thickness to approximately 20μm. After the solvent evaporates, sinter the coating surface using an oxyacetylene flame, controlling the flame temperature at 1000±50℃ and the sintering time to approximately 15 seconds, to convert the phenolic resin coating into a pyrolytic carbon coating. Allow it to cool naturally before use.

[0036] (4) Coating and Drying: Immediately apply the uniformly mixed material from step (2) to the substrate treated in step (3) using a wire bar coater. Control the wet film thickness to ensure a final dry film thickness of approximately 80 μm. Place the coated sample in a 60°C oven to dry and cure for 12 hours. Place the prepared coating sample in a dry environment for 7 days to ensure consistent quality, thus obtaining the room temperature self-healing polyurethane coating (PUS).

[0037] Comparative Example 1 This comparative example illustrates the preparation method of a conventional polyurethane coating (PU) without disulfide bonds, and the substrate is not subjected to pyrolytic carbon pretreatment.

[0038] (1) Prepolymerization reaction: Under the same reaction conditions as in Example 1, dehydrated PTMG-1000 (10.0 g, 10 mmol) and IPDI (4.44 g, 20 mmol) were added to a three-necked flask, along with 50 ml of THF and 2 drops of DBTDL catalyst. The reaction was carried out at 80°C for 2 hours under nitrogen protection to obtain a polyurethane prepolymer without disulfide bonds. DTSA was not added in this step.

[0039] (2) Degassing and curing: Same as in Example 1.

[0040] (3) Coating and drying: The mixture is directly coated onto a carbon steel substrate that has not been pretreated with pyrolytic carbon, and cured into a film in the same way as step (4) of Example 1.

[0041] Example 1 was compared with Comparative Example 1, with reference to... Figures 2-8 As shown, according to Figure 2 In the FTIR spectrum, the coating of this invention is at 1735 cm⁻¹. -1 The characteristic absorption peak of the carbamate carbonyl group appears at 1530 cm⁻¹. -1The presence of an NH bending vibration peak at 510 cm⁻¹ confirms the basic structure of polyurethane; the differences between the coating of this invention and the comparative coating in the C=O and NH regions reflect changes in the hydrogen bonding environment; in the Raman spectrum, the coating of this invention shows a peak at 510 cm⁻¹. -1 The presence of a disulfide bond (SS) characteristic scattering peak at this location, while the control coating showed no signal at the same position, proves that DTSA successfully introduced disulfide bonds into the coating.

[0042] from Figure 3 It can be seen that the elongation at break and the tensile strength of the coating are both greater than those of the control coating.

[0043] according to Figure 4 (a) The SEM image shows that the cross-section of the coating is dense and uniform, with no obvious phase separation; Figure 4 The EDS sulfur distribution image in the middle (e) shows that sulfur (S) is uniformly distributed across the coating cross section, further demonstrating the successful introduction of disulfide bonds and the uniform dispersion of DTSA in the coating.

[0044] from Figure 5 As can be seen, after room temperature healing, the initial width of the scratch from the tungsten carbide pen was approximately 200 μm, and after 48 hours of room temperature healing, the width was less than 20 μm; the initial width of the scratch from the razor blade was approximately 15 μm, and after 48 hours of room temperature healing, the width was less than 3 μm; and the initial width of the scratch from the utility knife was approximately 25 μm, and after 48 hours of room temperature healing, the width was less than 5 μm. This indicates that the coating can effectively heal cuts made by all three tools.

[0045] from Figure 6 It can be seen that after the coating was scratched by a utility knife, the scratches were significantly reduced and the scratch morphology tended to heal during the 48-hour repair process at room temperature, indicating that the surface morphology of the coating was repaired after 48 hours of repair at room temperature.

[0046] from Figure 7 It can be seen that after the coating was scratched by a utility knife, the scratch width decreased significantly during the 48-hour repair process at room temperature, and the scratch depth approached 0 μm after 48 hours. This indicates that the coating depth was repaired after 48 hours at room temperature.

[0047] from Figure 8 It can be seen that the Nyquist plot of the coating in its original state shows a capacitive arc with a large radius; after being scratched with a utility knife, the radius of the capacitive arc is significantly reduced; after being repaired at room temperature for 48 hours, the radius of the capacitive arc recovers to near its original state, indicating that the protective performance of the coating is restored after being repaired at room temperature for 48 hours.

[0048] Example 2 A method for preparing a room temperature self-healing polyurethane coating mainly includes the following steps: (1) Prepolymerization reaction: Accurately weigh 20.0 g (10 mmol) of dehydrated polypropylene glycol (PPG-2000) and 5.04 g (30 mmol) of hexamethylene diisocyanate (HDI) and add them to a dry 250 ml three-necked flask. Add 60 ml of N,N-dimethylformamide (DMF) as solvent, 3.06 g (10 mmol) of dithiodibenzoic acid (DTSA) as chain extender, and 0.2 g of dibutyltin dilaurate (DBTDL) as catalyst to the flask. Place the flask in a constant temperature oil bath, and under the conditions of continuous nitrogen gas protection and mechanical stirring at 250 rpm, raise the temperature to 70 °C and react at a constant temperature for 3 hours to obtain a polyurethane prepolymer solution containing disulfide bonds.

[0049] (2) Degassing and curing: Place the prepolymer solution obtained in step (1) in a vacuum drying oven and degas it under vacuum for 30 minutes at room temperature, maintaining the vacuum level at -0.09 MPa. Then add the measured amount of ethylenediamine (EDA) curing agent (calculated according to the molar ratio of HDI to EDA 2:1) to the degassed prepolymer and stir manually for 2 minutes to ensure uniform mixing.

[0050] (3) Substrate pretreatment: The surface of the aluminum alloy substrate is polished, degreased, cleaned, and dried. A layer of 15wt% phenolic resin acetone solution is sprayed onto the pretreated substrate surface, controlling the wet film thickness to be approximately 15μm. After the solvent evaporates, laser sintering is performed using a CO2 laser with a laser power of 100W and a scanning speed of 30mm / s, converting the phenolic resin coating into a pyrolytic carbon coating. After natural cooling, it is ready for use.

[0051] (4) Coating and Drying: Immediately apply the uniformly mixed material from step (2) to the substrate treated in step (3) using a scraper. Control the wet film thickness so that the final dry film thickness is approximately 50 μm. Place the coated sample in a 50°C oven to dry and cure for 16 hours. Place the prepared coating sample in a dry environment for 7 days to ensure consistent quality, thus obtaining the room temperature self-healing polyurethane coating.

[0052] Example 3 A method for preparing a room temperature self-healing polyurethane coating mainly includes the following steps: (1) Prepolymerization reaction: Accurately weigh 15.0 g (10 mmol) of dehydrated polyethylene glycol (PEG-1500) and 7.86 g (30 mmol) of dicyclohexylmethane diisocyanate (HMDI) and add them to a dry 250 ml three-necked flask. Add 55 ml of toluene as solvent, 4.59 g (15 mmol) of dithiodibenzoic acid (DTSA) as chain extender, and 0.15 g of stannous octoate as catalyst to the flask. Place the flask in a constant temperature oil bath, and under the condition of continuous nitrogen protection and mechanical stirring at 180 rpm, raise the temperature to 90 °C and react at a constant temperature for 1 hour to obtain a polyurethane prepolymer solution containing disulfide bonds.

[0053] (2) Degassing and curing: Place the prepolymer solution obtained in step (1) in a vacuum drying oven and degas it under vacuum for 15 minutes at room temperature, maintaining the vacuum level at -0.08 MPa. Then add a metered amount of 4,4'-diaminodiphenylmethane (MDA) curing agent (calculated according to the molar ratio of HMDI to MDA of 2:1) to the degassed prepolymer and stir manually for 4 minutes to ensure uniform mixing.

[0054] (3) Substrate pretreatment: The stainless steel substrate surface is ground, degreased, cleaned and dried. A layer of 5wt% phenolic resin ethanol solution is sprayed onto the pretreated substrate surface, controlling the wet film thickness to be about 30μm. After the solvent evaporates, the coating surface is sintered using an oxyacetylene flame, with the flame temperature controlled at 800±50℃ and the sintering time about 30 seconds, so that the phenolic resin coating is converted into a pyrolytic carbon coating. After natural cooling, it is ready for use.

[0055] (4) Coating and Drying: Immediately apply the uniformly mixed material from step (2) to the substrate treated in step (3) using a spraying method. Control the number of sprayings to ensure the final dry film thickness is approximately 120 μm. Place the coated sample in a 70°C oven to dry and cure for 8 hours. Place the prepared coating sample in a dry environment for 7 days to ensure consistent quality, thus obtaining the room temperature self-healing polyurethane coating.

[0056] Example 4 A method for preparing a room temperature self-healing polyurethane coating mainly includes the following steps: (1) Prepolymerization reaction: Accurately weigh 20.0 g (10 mmol) of dehydrated polytetrahydrofuran ether diol (PTMG-2000) and 6.66 g (30 mmol) of isophorone diisocyanate (IPDI) and add them to a dry 250 ml three-necked flask. Add 60 ml of tetrahydrofuran (THF) as solvent, 6.12 g (20 mmol) of dithiobenzoic acid (DTSA) as chain extender, and 3 drops (about 0.15 g) of dibutyltin dilaurate (DBTDL) as catalyst to the flask. Place the flask in a constant temperature oil bath, and under the conditions of continuous nitrogen protection and mechanical stirring at 220 rpm, raise the temperature to 75 °C and react at a constant temperature for 2.5 hours to obtain a polyurethane prepolymer solution containing disulfide bonds.

[0057] (2) Degassing and curing: Place the prepolymer solution obtained in step (1) in a vacuum drying oven and degas it under vacuum for 25 minutes at room temperature. Then add the measured amount of MOCA curing agent (calculated according to the molar ratio of IPDI to MOCA of 1.5:1) to the degassed prepolymer and stir manually for 3 minutes to ensure uniform mixing.

[0058] (3) Substrate pretreatment: Same as in Example 1.

[0059] (4) Coating and Drying: Immediately apply the uniformly mixed material from step (2) to the substrate treated in step (3) using a wire bar coater. Control the wet film thickness to ensure the final dry film thickness is approximately 150 μm. Place the coated sample in a 65°C oven to dry and cure for 10 hours. Place the prepared coating sample in a dry environment for 7 days to ensure consistent quality, thus obtaining the room temperature self-healing polyurethane coating.

[0060] Example 5 A method for preparing a room temperature self-healing polyurethane coating mainly includes the following steps: (1) Prepolymerization reaction: Accurately weigh 10.0 g (10 mmol) of dehydrated polypropylene glycol (PPG-1000) and 2.52 g (15 mmol) of hexamethylene diisocyanate (HDI) and add them to a dry 250 ml three-necked flask. Add 50 ml of tetrahydrofuran (THF) as a solvent, 1.53 g (5 mmol) of dithiodibenzoic acid (DTSA) as a chain extender, and 0.1 g of dibutyltin dilaurate (DBTDL) as a catalyst to the flask. Place the flask in a constant temperature oil bath, and under the conditions of continuous nitrogen gas protection and mechanical stirring at 200 rpm, raise the temperature to 85 °C and react at a constant temperature for 1.5 hours to obtain a polyurethane prepolymer solution containing disulfide bonds.

[0061] (2) Degassing and curing: Same as in Example 2.

[0062] (3) Substrate pretreatment: Same as in Example 2.

[0063] (4) Coating and Drying: Immediately apply the uniformly mixed material from step (2) to the substrate treated in step (3) using a scraper. Control the wet film thickness to ensure the final dry film thickness is approximately 100 μm. Place the coated sample in a 55°C oven to dry and cure for 14 hours. Place the prepared coating sample in a dry environment for 7 days to ensure consistent quality, thus obtaining the room temperature self-healing polyurethane coating.

[0064] Example 6 A method for preparing a room temperature self-healing polyurethane coating mainly includes the following steps: (1) Prepolymerization reaction: It is basically the same as in Example 1, except that the amount of catalyst dibutyltin dilaurate (DBTDL) is 0.25 g (i.e. 2.5% of the mass of the polyol, which is outside the range of 0.5-2% in claim 8, and can be used as a comparison or to illustrate that this range is not strictly limited). The other steps are the same as in Example 1.

[0065] (2) Degassing and curing: Same as in Example 1.

[0066] (3) Substrate pretreatment: Same as in Example 1.

[0067] (4) Coating and drying: Same as in Example 1.

[0068] Example 7 A method for preparing a room temperature self-healing polyurethane coating mainly includes the following steps: (1) Prepolymerization reaction: exactly the same as in Example 1.

[0069] (2) Degassing and curing: exactly the same as in Example 1.

[0070] (3) Substrate pretreatment: Clean, degrease, and dry the surface of the galvanized steel substrate. Spray a 20wt% phenolic resin ethanol solution onto the pretreated substrate surface, controlling the wet film thickness to approximately 10μm. After the solvent evaporates, sinter the coating surface using an oxyacetylene flame, controlling the flame temperature at 1200±50℃ and the sintering time to approximately 5 seconds, to convert the phenolic resin coating into a pyrolytic carbon coating. Allow it to cool naturally before use.

[0071] (4) Coating and drying: Same as in Example 1. The room temperature self-healing polyurethane coating is thus obtained.

[0072] Example 8 A method for preparing a room temperature self-healing polyurethane coating mainly includes the following steps: (1)-(4): Prepare coated samples PUS according to the method of Example 1.

[0073] (5) Repair performance test: Scratches with a depth of 10-50 μm were created on the PUS coating surface using a tungsten carbide pen, a razor, and a utility knife, respectively. The scratched coating was left to stand at room temperature (25℃±2℃) for 48 hours. After repair, the scratched area was observed using an optical microscope, and the scratches were found to be significantly shallower or even completely healed. Electrochemical impedance spectroscopy (EIS) was also performed. Figure 7 As shown in the figure, the Nyquist plot impedance arc radius of the repaired coating recovers to more than 90% of that of the original coating. This embodiment illustrates that the coating of the present invention has excellent self-healing ability against scratches of different depths caused by various tools at room temperature.

[0074] Application examples The room-temperature self-healing polyurethane coating (PUS) prepared in Example 1 was applied to the surface of a metal substrate with a pyrolytic carbon transition layer, which can be used for corrosion protection of metal materials. The pyrolytic carbon transition layer significantly enhances the interfacial adhesion between the polyurethane coating and the metal substrate. When micron-level scratches or damage appear on the coating surface, the coating can self-repair the damage and restore its barrier protection function after being left at room temperature for a certain period of time.

Claims

1. A room temperature self-healing polyurethane coating, characterized in that, It is prepared by one-pot polymerization of reaction raw materials including diisocyanate, polyol, curing agent and chain extender containing disulfide bond, wherein the chain extender containing disulfide bond is dithiodibenzoic acid.

2. The room temperature self-healing polyurethane coating according to claim 1, characterized in that, The diisocyanate is an aliphatic or alicyclic diisocyanate; the polyol is a polyether polyol or a polyester polyol; and the curing agent is an amine curing agent.

3. The room temperature self-healing polyurethane coating according to claim 1, characterized in that, The diisocyanate is isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HDI), or dicyclohexylmethane diisocyanate (HMDI); the polyol is polytetrahydrofuran ether glycol (PTMG), polypropylene glycol (PPG), or polyethylene glycol (PEG); and the curing agent is 3,3'-dichloro-4,4'-diaminodiphenylmethane (MOCA), 4,4'-diaminodiphenylmethane (MDA), or ethylenediamine.

4. The room temperature self-healing polyurethane coating according to claim 1, 2, or 3, characterized in that, The molar ratio of the diisocyanate to the polyol is (1.5-3):1, and the molar ratio of the chain extender containing disulfide bonds to the polyol is (0.5-2):

1.

5. The room temperature self-healing polyurethane coating according to claim 1, characterized in that, The coating has a dynamic cross-linked network structure formed by the synergistic effect of dynamic disulfide bonds and multiple hydrogen bonds. Under room temperature conditions of 15-30℃, the coating has the ability to self-repair scratches with a depth of 10-50μm, and the repair time is 12-72 hours.

6. A method for preparing a room-temperature self-healing polyurethane coating, characterized in that, Includes the following steps: Step 1: Add the dehydrated polyol and diisocyanate to the reactor, add organic solvent, chain extender containing disulfide bonds and catalyst, and stir and react at 70-90℃ for 1-3 hours under an inert atmosphere to obtain a polyurethane prepolymer containing disulfide bonds; wherein, the chain extender containing disulfide bonds is dithiobenzoic acid. Step 2: Vacuum degassing is performed on the prepolymer obtained in Step 1, and then curing agent is added and quickly stirred to mix evenly; Step 3: Coat the substrate surface with a phenolic resin solution, and then convert the phenolic resin coating into a pyrolytic carbon coating by flame sintering or laser sintering. Step 4: Apply the mixture obtained in Step 2 onto the substrate treated in Step 3, control the coating thickness, and dry and cure to obtain the room temperature self-healing polyurethane coating.

7. The preparation method according to claim 6, characterized in that, The inert atmosphere in step 1 is nitrogen atmosphere, the reaction temperature is 75-85℃, the reaction time is 1.5-2.5 hours, and the vacuum degree of vacuum degassing in step 2 is -0.08 to -0.1 MPa, and the degassing time is 10-30 minutes.

8. The preparation method according to claim 6 or 7, characterized in that, The organic solvent in step 1 is tetrahydrofuran (THF), N,N-dimethylformamide (DMF), or toluene; the catalyst is an organotin catalyst, used at 0.5-2% of the mass of the polyol; the concentration of the phenolic resin solution in step 3 is 5-20 wt%, and the solvent is ethanol or acetone; the flame sintering uses an oxyacetylene flame, with a flame temperature of 800-1200℃ and a sintering time of 5-30 seconds; the laser sintering uses a CO2 laser with a laser power of 50-200W and a scanning speed of 10-50 mm / s.

9. The preparation method according to claim 6, characterized in that, The substrate mentioned in step 4 is a metal substrate, the dry film thickness of the coating is 50-150μm, and the drying and curing conditions are drying in an oven at 50-70℃ for 8-16 hours.

10. The application of the room temperature self-healing polyurethane coating according to any one of claims 1-5 in metal corrosion protection.

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