A pH-induced confined solid-liquid transition self-healing coating material

Abstract

The present invention discloses a pH-induced confined solid-liquid transition self-repairing coating material, which belongs to the field of self-repairing coating technology, comprising the following steps: mixing an alcohol polymer, a siloxane monomer and a photoinitiator in an organic solvent, and stirring evenly under heating conditions in the dark to fully dissolve; after standing and defoaming, applying the resulting casting solution to a protected substrate, and then in-situ photocuring to form a coating by UV irradiation; placing the obtained coating sample in a boric acid aqueous solution and standing to undergo solvent exchange, and after the exchange is completed, performing reduced pressure drying in a vacuum oven to obtain a final coating. Using the coating material of the present invention, when the coating service microenvironment undergoes corrosion or other physicochemical changes that induce pH changes, the dynamic borate ester system inside the network at the coating damage site will undergo dynamic dissociation and association, manifesting as a gel-sol-like "solid-liquid" transition process, and then the coating damage is repaired by liquid-like fluidity, achieving "autonomous" self-repair of the coating body damage.

Description

Technical Field

[0001] The present invention belongs to the technical field of self-repairing coatings, and in particular relates to a pH-induced confined solid-liquid transition self-repairing coating material. Background Art

[0002] Self-healing technology, a cutting-edge technology that allows materials to repair damage with minimal or no intervention, is crucial for extending material lifespan, delaying maintenance requirements, reducing maintenance frequency, and mitigating CO2 emissions from structural upgrades and new material manufacturing. For coatings, which provide protection by isolating themselves from the external environment, self-healing technology can promptly restore the insulation properties of damaged coatings, maximizing the coating's protective properties and the expected service life of the protected structure.

[0003] The research and development of "self-repair" technology has mainly formed two major technical approaches: "external aid" and "intrinsic". Among them, the "external aid" is based on pre-embedding microcontainers (microcapsules, microvessels) loaded with corrosion inhibitors / healing agents (core materials) into the material matrix, and utilizing the accompanying rupture behavior that occurs when the material is damaged to release the repair agent core material to the damaged site to fill the crack; while the "intrinsic" is based on the design of the material body based on dynamic reversible chemical units such as DA reactions, acylhydrazone bonds, disulfide bonds, and hydrogen bonds. It relies on "molecular scale flows" such as chain migration and conformational changes between reversible reaction groups at the material damage interface to achieve intermolecular diffusion, entanglement, and even chemical association to achieve self-repair at the molecular level. The technical implementation of this process has repeatable characteristics. In contrast, due to the limitation of the microcontainer capacity, the "external aid" self-repair has greater limitations in the repeatability of the number of repairs. It can usually only achieve a single (microcapsule) or several repairs (microvessels). Therefore, the "intrinsic" self-repair that can achieve repeated repair of the material body is more popular. However, the rupture of the microcontainers of the "external-aid" self-repairing system can be triggered by non-human interference factors such as defects, pH, and H2O, which makes it have outstanding advantages in achieving "autonomous" repair. In contrast, the entanglement / diffusion / association behavior between the "intrinsic" self-repairing dynamic reversible chemical units often requires directional stimulation of external fields such as special wavelengths of light (ultraviolet, near-infrared, etc.), heat, and magnetism, making it difficult to achieve "autonomous" repair triggered by non-human conditions, resulting in operational limitations in practical applications. In this regard, combining the self-repair method triggered by characteristic factors of the material's service microenvironment in the "external-aid" strategy with the "intrinsic" self-repair system is a clever way to overcome the technical limitations of the two and organically combine the advantages of both.

[0004] The biggest challenge for the "intrinsic" self-healing process of a coating system lies in achieving "autonomous docking" of the damaged coating interface under the constraints of substrate adhesion. To this end, imparting "flow" properties to the damaged coating interface that exceed the molecular scale is a highly feasible and innovative solution. For example, invention patent ZL201910961370.4 uses paraffin wax as a phase change material, composited with a polypropylene polymer network, and doped with a carbon-based photothermal filler to obtain an anti-corrosion coating material that can achieve multiple repairs of damage by undergoing a solid-liquid transition of the paraffin wax under near-infrared laser irradiation. Invention patent ZL202211694429.6 utilizes a thermoplastic epoxy resin composited with a special engineering plastic polyethersulfone and doped with copper sulfide nanocrystals with lower visible light absorption as a photothermal filler to prepare a colorable coating material that can achieve repeated repair of damage under near-infrared light irradiation by virtue of the solid-liquid transition behavior of the thermoplastic epoxy resin. However, in these material systems, the solid-liquid transition behavior of the phase change material always relies on external light sources to trigger, and neither is "autonomous" self-healing. Summary of the Invention

[0005] The technical purpose of the present invention is to provide a method for constructing an "intrinsic" self-repairing coating material based on the characteristic factors of the material's service microenvironment, to achieve an organic combination of the "external aid" self-repair triggering method and the "intrinsic" self-repair mode, and at the same time to break through the technical limitations of the "external aid" system's limited number of repairs and the "intrinsic" system's difficulty in achieving "autonomous" repair, thereby achieving complementary advantages between the two mainstream self-repair strategies.

[0006] In order to achieve the above technical objectives, the technical solution of the present invention is:

[0007] A pH-induced confined solid-liquid transition self-repairing coating material, comprising the following steps:

[0008] (1) mixing an alcohol polymer, a siloxane monomer, and a photoinitiator in an organic solvent, and stirring them evenly under heating conditions in the dark to fully dissolve them;

[0009] (2) After standing for defoaming, the obtained casting solution is applied to a protected substrate, and then in-situ photocuring is performed by UV irradiation to form a coating;

[0010] (3) The obtained coating sample is placed in a boric acid aqueous solution and allowed to stand for solvent exchange. After the exchange is completed, it is dried under reduced pressure in a vacuum oven to obtain the final coating.

[0011] Wherein, in step (1), the alcohol polymer is a polymer with alcoholic hydroxyl groups on the side chain or at the end, or a mixture or modified product thereof; the siloxane monomer is a reactive monomer that can initiate polymerization reaction by UV, or a mixture or modified product thereof; the photoinitiator is an active substance that can generate free radicals or ions under UV light to initiate polymerization reaction of the siloxane system, or a mixture or modified product thereof.

[0012] Wherein, the alcohol polymer is polyvinyl alcohol, polypropylene alcohol or polyethylene glycol.

[0013] Wherein, the siloxane monomer is silane acrylate, silane methacrylate or silane olefin.

[0014] Wherein, the photoinitiator is dimethyl benzil ether (DMPA), Irgacure series (Irgacure 184, Irgacure 819, Irgacure 907), Darocur series (Darocur 1173, Darocur 2959), LUCIRIN series (LUCIRIN TPO, LUCIRIN TPO-L) or Esacure series (Esacure ONE, Esacure KIP 100F, EsacureKIP 150, Esacure KIP 160, Esacure KIP 75LT).

[0015] Wherein, in step (1), the solvent is any one or more of dimethyl sulfoxide (DMSO), dimethylformamide (DMF), N-methylpyrrolidone (NMP), and acetone (AC); after the alcohol polymer, siloxane monomer and photoinitiator are mixed in the organic solvent, the mass fraction of the alcohol polymer is 20wt%-25wt%; the mass fraction of the siloxane monomer is 2wt%-5wt%; the mass fraction of the photoinitiator is 0.1wt%-0.2wt%; the heating condition is between 85°C and 100°C, and the stirring time is 1.5-3h.

[0016] Wherein, in step (2), the standing defoaming time is 1 to 2 hours; the coating method is spraying, brushing, pouring, dipping or dripping; the UV irradiation wavelength is 365nm, and the irradiation power is 0.8 to 1.5W·cm -2 , the irradiation time is 1 to 2 hours.

[0017] In step (3), the solute of the boric acid aqueous solution is a compound containing a boric acid group and a derivative group, and the mass fraction of the solute is 1.5 wt% to 2 wt%; the solution exchange time is 0.5 to 1.5 h, and the reduced pressure drying method is drying at room temperature in a vacuum oven for 3 to 5 h.

[0018] Wherein, the solute of the boric acid aqueous solution is boric acid, borate, boric ester, boric acid amide or boric acid alcohol ester.

[0019] pH change is a typical physicochemical characteristic of a variety of service environments such as ocean, oil, and acid rain. It is also a macroscopic manifestation of the change in the chemical potential of the redox reaction in the local "microenvironment" when material corrosion occurs. In addition, the concept of pH is only applicable to aqueous media. The service environment in the fields of marine equipment, hydraulic equipment, and wearable electronic devices all involves water. Therefore, using pH changes as a non-artificial trigger factor for the self-repair process of protective coating materials for the above-mentioned equipment materials has universal significance and significant advantages. Using the fluidity advantage of "liquid-like" substances to assist in the repair of coating damage is of great benefit to the facing contact of the coating damage interface under the adhesion restriction of the substrate. The borate bond is a chemical unit with pH-responsive dynamic reversible characteristics. It has four forms in aqueous solution: neutral boric acid (H3BO3), monoborate anion (B(OH)4 - ), triborate anion (B3O4(OH)3 - ), tetraborate anion (B4O5(OH)4 - ) etc. Among them, neutral H3BO3 tends to dissociate, while anionic forms tend to associate. According to research reports, at pH = 7, about 60% of the borate system is dominated by neutral H3BO3, and the rest is almost all B3O4(OH)3 - , the overall state is a liquid sol after dissociation; at pH = 9, the composition of neutral H3BO3 drops sharply to about 10%, and the remaining 90% is in the form of anions (30% each), presenting an associated gel form; and at pH = 11, the neutral form will completely disappear, leaving only B(OH)4 - (>90%), but the association strength is much lower than that of pH=9, so the system still exhibits liquid-like characteristics, and the viscosity is slightly higher than the liquid sol in the pH=7 system. In short, the borate ester bond composite system has the characteristics of dynamic reversible "solid-liquid transition" triggered by pH changes. Inspired by this, this patent provides a method of introducing a polysiloxane network as a confined skeleton based on in-situ photopolymerization in an alcohol polymer network, and then through solvent exchange with a boric acid solution, based on the esterification reaction between the hydroxyl group of the alcohol polymer and the carboxyl group of the boric acid, in situ generating a pH-responsive solid-liquid transition gel microdomain containing a large number of pH-sensitive dynamic borate ester bonds inside the skeleton, so as to obtain a preparation method for a confined solid-liquid transition self-healing coating material with pH-responsive characteristics, thereby realizing stable and reversible intrinsic self-repair of coating damage triggered by pH changes.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The present invention provides a method for preparing a coating material that realizes autonomous repair of "intrinsic" damage based on confined solid-liquid transition induced by pH changes. The repair process does not require human intervention and has significant promotion potential in application fields involving water and having pH change characteristics in corrosive microenvironments, such as marine engineering, water conservancy projects, and wearable electronic devices. The raw materials required in the invention are all existing commercial products, and the coating methods are diversified, the UV curing time is short, and it is suitable for large-scale production. When the coating service microenvironment undergoes corrosion or other physicochemical changes that induce pH changes, the dynamic borate system inside the network at the coating damage site will undergo dynamic dissociation and association, which manifests as a gel-sol-like "solid-liquid" transition process. Then, the coating damage is repaired by means of liquid-like fluidity, thereby realizing "autonomous" self-repair of the coating body damage. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The drawings in the specification, which constitute a part of this application, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0023] Figure 1 Schematic diagram of the preparation steps of the coating of the present invention;

[0024] Figure 2 The solid-liquid transition process and corresponding mechanism of the gel material in the present invention triggered by pH change;

[0025] Figure 3 Microscopic images of pure polysiloxane coating, alcohol polymer / polysiloxane composite coating, and gel-polysiloxane composite coating before and after self-repair at pH = 7 and pH = 11. The repair treatment time is 30 min. DETAILED DESCRIPTION

[0026] The following will be combined with specific embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0027] The schematic diagram of the preparation steps of the coating of the present invention is as follows Figure 1 As shown, the solid-liquid transition process and corresponding mechanism of the gel material in the present invention triggered by pH change are as follows Figure 2 shown.

[0028] Example 1

[0029] This embodiment provides a pH-induced confined solid-liquid transition self-healing coating material, comprising the following steps:

[0030] (1) Polyvinyl alcohol, silane acrylate, and benzil dimethyl ether were mixed in dimethyl sulfoxide at a mass ratio of 20 wt%: 2 wt%: 0.1 wt%, heated to 85°C in the dark, and stirred for 3 h until fully dissolved;

[0031] (2) After standing for 1 hour to defoam, the obtained casting solution was sprayed on the protected substrate and then irradiated with a UV lamp with a wavelength of 365 nm and an irradiation power of 1.0 W·cm -2 , irradiation time is 1.5h;

[0032] (3) The obtained coating sample was placed in an aqueous solution containing 2 wt % boric acid and allowed to stand for 1 h, and then dried under reduced pressure in a vacuum oven at room temperature for 3 h to obtain the final coating.

[0033] Example 2

[0034] This embodiment provides a pH-induced confined solid-liquid transition self-healing coating material, comprising the following steps:

[0035] (1) Polyethylene glycol, silane methacrylate, and Irgacure 184 were mixed in N-methylpyrrolidone at a mass ratio of 25 wt%: 5 wt%: 0.2 wt%, heated to 100 °C in the dark, and stirred for 1.5 h until fully dissolved;

[0036] (2) After standing for 2 hours to defoam, the obtained casting solution was brush-coated on the protected substrate and then irradiated with a UV lamp with a wavelength of 365 nm and an irradiation power of 1.5 W·cm -2 , irradiation time is 1h;

[0037] (3) The obtained coating sample was placed in an aqueous solution containing 1.5 wt% boric acid amide and allowed to stand for 0.5 h, and then dried under reduced pressure in a vacuum oven at room temperature for 4 h to obtain the final coating.

[0038] Example 3

[0039] This embodiment provides a pH-induced confined solid-liquid transition self-healing coating material, comprising the following steps:

[0040] (1) Polypropylene alcohol, silane olefin, and Darocur 1173 were mixed in acetone at a mass ratio of 22 wt%: 3 wt%: 0.15 wt%, heated to 85 °C in the dark, and stirred for 2 h until fully dissolved;

[0041] (2) After standing for 1.5 hours to defoam, the obtained casting solution was drop-coated on the protected substrate and then irradiated with a UV lamp with a wavelength of 365 nm and an irradiation power of 0.8 W·cm -2 , irradiation time is 2h;

[0042] (3) The obtained coating sample was placed in an aqueous solution containing 2 wt% borate and allowed to stand for 1.5 h, and then dried under reduced pressure in a vacuum oven at room temperature for 5 h to obtain the final coating.

[0043] Comparative Example 1

[0044] Preparation method of pure polysiloxane coating:

[0045] (1) Silane acrylate and benzil dimethyl ether were mixed in dimethyl sulfoxide at a mass ratio of 2 wt%:0.1 wt% and stirred in the dark for 20 min until fully dissolved;

[0046] (2) After standing for 1 hour to defoam, the obtained casting solution was sprayed on the protected substrate and then irradiated with a UV lamp with a wavelength of 365 nm and an irradiation power of 1.0 W·cm -2 , irradiation time is 1.5h;

[0047] (3) The obtained coating sample was dried under reduced pressure in a vacuum oven at room temperature to evaporate the solvent for 3 h to obtain a polysiloxane coating.

[0048] Comparative Example 2

[0049] Preparation method of alcohol polymer / polysiloxane composite coating:

[0050] (1) Polyethylene glycol, silane methacrylate, and Irgacure 184 were mixed in N-methylpyrrolidone at a mass ratio of 25 wt%: 5 wt%: 0.2 wt%, heated to 100 °C in the dark, and stirred for 1.5 h until fully dissolved;

[0051] (2) After standing for 2 hours to defoam, the obtained casting solution was brush-coated on the protected substrate and then irradiated with a UV lamp with a wavelength of 365 nm and an irradiation power of 1.5 W·cm -2 , irradiation time is 1h;

[0052] (3) The obtained coating sample was dried under reduced pressure in a vacuum oven at room temperature to evaporate the solvent for 4 h, thereby obtaining an alcohol polymer / polysiloxane composite coating.

[0053] Test example

[0054] The pure polysiloxane coating prepared in Comparative Example 1, the alcohol polymer / polysiloxane composite coating prepared in Comparative Example 2, and the gel-polysiloxane composite coating prepared in Example 1 were taken before and after self-repair at pH = 7 and pH = 11. The repair treatment time was 30 minutes. The microscopic images are as follows: Figure 3 shown.

[0055] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A pH-induced confined solid-liquid transition self-repairing coating material, characterized in that The steps include: (1) An alcohol polymer, a siloxane monomer, and a photoinitiator are mixed in an organic solvent, and stirred evenly under heating conditions in the dark to fully dissolve to obtain a casting solution; the mass fraction of the alcohol polymer in the casting solution is 20 wt%-25 wt%, the mass fraction of the siloxane monomer is 2 wt%-5 wt%, and the mass fraction of the photoinitiator is 0.1 wt%-0.2 wt%; the heating conditions are between 85 and 100°C, and the stirring time is 1.5 to 3 h; (2) After standing for defoaming, the obtained casting solution is applied to a protected substrate, and then in-situ photocuring is performed by UV irradiation to form a coating; (3) The obtained coating sample is placed in a boric acid aqueous solution and allowed to stand for solvent exchange. After the exchange is completed, it is dried under reduced pressure in a vacuum oven to obtain the final coating; the mass fraction of the solute in the boric acid aqueous solution is 1.5wt%~2wt%; the solvent exchange time is 0.5~1.5 h; The alcohol polymer is polyvinyl alcohol, polypropylene alcohol or polyethylene glycol; The siloxane monomer is silane acrylate or silane methacrylate; The solute of the boric acid aqueous solution is boric acid, borate, boric acid ester, boric acid amide or boric acid alcohol ester.

2. The pH-induced confined solid-liquid transition self-healing coating material according to claim 1, characterized in that: In step (1), the photoinitiator is an active substance that can generate free radicals or ions to initiate the polymerization reaction of the siloxane system under UV light, or a mixture or modified product thereof.

3. The pH-induced confined solid-liquid transition self-healing coating material according to claim 2, characterized in that: The photoinitiator is benzil dimethyl ether, Irgacure series, Darocur series, LUCIRIN series or Esacure series.

4. The pH-induced confined solid-liquid transition self-healing coating material according to claim 1, characterized in that: In step (1), the solvent is any one or more of dimethyl sulfoxide, dimethylformamide, N-methylpyrrolidone, and acetone.

5. The pH-induced confined solid-liquid transition self-healing coating material according to claim 1, characterized in that: In step (2), the standing defoaming time is 1 to 2 hours; the coating method is spraying, brushing, pouring, dipping or dripping; the UV irradiation wavelength is 365 nm, and the irradiation power is 0.8 to 1.5 W·cm -2 , the irradiation time is 1~2 h.

6. The pH-induced confined solid-liquid transition self-healing coating material according to claim 1, characterized in that: In step (3), the reduced pressure drying method is drying at room temperature in a vacuum oven, and the drying time is 3 to 5 hours.

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