Self-repairing anti-corrosion water-based paint

Abstract

The invention relates to a self-repairing anti-corrosion water-based paint applied to the field of paint compositions, which is prepared by the following steps: firstly, preparing a self-repairing microcapsule encapsulated with a self-repairing agent and a corrosion inhibitor, and then uniformly dispersing the self-repairing microcapsule into water-based base resin under a low-shear condition; the prepared coating can be applied to the surface of a pretreated metal base material in a brush coating, spray coating or blade coating mode and the like, a micron-sized anti-corrosion coating is formed after curing, under the normal condition, the microcapsules are placed in the coating in a standing mode and do not work, when scratches occur, the self-repairing microcapsules are broken and play a role, and the corrosion resistance of the coating is improved. The self-repairing agent rapidly fills and heals the damaged part of the coating to form a new barrier layer, the corrosion inhibitor forms a protective film on the exposed metal surface to inhibit the corrosion reaction, and the synergistic mechanism can effectively delay the corrosion diffusion of the scratched part, so that the protection integrity of the coating on the base material is maintained, and the service life of the coating is prolonged. And the coating can be suitable for metal structure protection in severe environments such as ocean climate, high-humidity and high-salt environments, acid rain regions, chemical environments and the like.

Description

Technical Field

[0001] The present invention relates to a coating, and in particular to a self-healing anti-corrosion waterborne coating applied to the field of coating compositions. Background Art

[0002] Metal materials (such as steel) are extremely prone to corrosion in environments such as the atmosphere, water vapor, and salt spray. The direct economic losses and potential safety hazards caused by metal corrosion every year are extremely huge. Coating anti-corrosion coatings is one of the most commonly used and effective means to protect metal structures at present. Traditional anti-corrosion coatings isolate corrosive media by forming a dense barrier layer or achieve corrosion inhibition by adding cathodic protection pigments (such as zinc powder). However, when defects appear in the anti-corrosion coating due to mechanical damage (scratches, impacts, etc.), the exposed metal substrate will immediately come into contact with the environment and rust. If maintenance cannot be carried out in time at this time, the corrosion will spread rapidly from the scratched point, causing large-area rusting of the substrate under the coating, seriously affecting the life and safety of the structure.

[0003] In response to the problem of protection failure caused by local damage to the coating, the concept of self-healing anti-corrosion coatings has emerged in recent years. Self-healing coatings usually introduce functional components that can automatically repair cracks or scratches into the coating system. For example, using microcapsule technology to encapsulate corrosion inhibitors or repair agents in microcapsules with diameters ranging from a few micrometers to several hundred micrometers. When the coating is damaged by stress and cracks appear, the microcapsules are stressed and rupture, releasing the active substances encapsulated therein to fill, repair, and protect the damaged area. Researchers have successfully microencapsulated a variety of corrosion inhibitors and self-healing agents and introduced them into the anti-corrosion coating system to achieve the autonomous wound healing and corrosion inhibition of the coating. For example, vegetable oils such as linseed oil and tung oil are encapsulated in microcapsules as self-healing agents. When damaged, the oil flows out and solidifies to form a protective film to delay corrosion. Another example is to encapsulate organic corrosion inhibitors (such as benzotriazole BTA) in microcapsules. When the coating is scratched, the corrosion inhibitor is released and adsorbs on the metal surface to form a molecular film to block the corrosion reaction. These self-healing coatings have shown significant corrosion delay effects in laboratory tests.

[0004] However, at present, many studies on self-healing anti-corrosion coatings still use solvent-based or high-VOC coatings as carriers, and there are also deficiencies in the compatibility and long-term stability between microcapsules and coating binders, and there is still a gap from actual engineering applications.

[0005] Therefore, there is an urgent need to develop a waterborne environmentally friendly self-healing anti-corrosion coating, which can achieve automatic healing and corrosion self-inhibition functions after the coating is scratched while providing excellent anti-corrosion performance, reduce the maintenance frequency of coating damage, and ensure the long-term use safety of metal structures in harsh environments. It is of great significance for marine engineering (such as offshore wind power equipment, ships, and seaport facilities) and structures such as large bridges and petrochemical facilities that are difficult to maintain frequently. Summary of the Invention

[0006] In view of the above-mentioned prior art, the technical problem to be solved by the present invention is that it is difficult for existing anti-corrosion coatings to achieve automatic healing after coating scratches and inhibit corrosion functions.

[0007] To solve the above problems, the present invention provides a self-healing anti-corrosion waterborne coating, which includes a waterborne base resin, self-healing microcapsules, anti-corrosion fillers, additives, and solvents. The waterborne base resin is one of two-component waterborne epoxy resin, waterborne polyurethane dispersion, or acrylic-modified copolymer emulsion. The self-healing microcapsules include a capsule shell, and the inside of the capsule shell is filled with a self-healing agent and a corrosion inhibitor. The capsule shell is one of urea-formaldehyde resin, phenolic resin, polyurea, polyurethane, polystyrene, or polyethersulfone. The thickness of the capsule shell is 1-5 microns, and the particle size of the self-healing microcapsules is 1-100 microns.

[0008] As a further supplement to this application, the self-healing agent includes one of drying vegetable oil, low-viscosity resin monomer, or a curing agent with a curing function, and the corrosion inhibitor includes organic corrosion inhibitors and inorganic corrosion inhibitors.

[0009] As a further supplement to this application, the anti-corrosion filler includes one of zinc phosphate, modified graphene, flaky iron oxide, or aluminum powder.

[0010] As a further supplement to this application, the additives include a dispersant, an antifoaming agent, a preservative, and a thickener, and the solvent uses deionized water.

[0011] As a further supplement to this application, the self-healing agent uses drying vegetable oil, and the capsule shell uses urea-formaldehyde resin. The method for making self-healing microcapsules from drying vegetable oil, corrosion inhibitor, and urea-formaldehyde resin includes the following steps: S1. Dissolve the self-healing agent in the corrosion inhibitor to form a core phase solution; S2. Dissolve urea and the formaldehyde polymerization promoter NH4Cl in water according to the mass ratio, heat to 45-55 °C, and under vigorous stirring conditions, add the core phase solution to form a water-in-oil emulsion. Then slowly dropwise add a formaldehyde solution to polymerize urea-formaldehyde at the interface. After reacting for 1.5-2.5 hours, cool to obtain a microcapsule dispersion of urea-formaldehyde resin wall material; S3. Collect the microcapsules in the microcapsule dispersion, wash and dry them to obtain dry powder self-healing microcapsules.

[0012] A method for preparing a self-healing anti-corrosion waterborne coating includes the following steps: Add the waterborne base resin to the solvent, mix evenly, add the anti-corrosion filler to provide cathodic protection performance, then add the prepared self-healing microcapsule powder and additives, and stir evenly at low speed to obtain the self-healing anti-corrosion waterborne coating of the present invention.

[0013] In summary, the beneficial effects of this application are as follows: (1)When the coating suffers from slight mechanical damage (such as scratches), without manual intervention, the coating can automatically repair itself. The self-healing agent released from the self-healing microcapsules quickly fills the cracks and solidifies, effectively healing the coating. At the same time, the inhibitor component forms a protective film on the metal surface, greatly delaying the speed of corrosion initiation and development. This self-healing function effectively prevents the scratched area from becoming a corrosion "hole", effectively improves the coating integrity, and extends the protection life; (2)The coating of the present invention is applicable to steel structures in marine climates, high-humidity and high-salt environments, as well as metal protection in acid rain areas and chemical industrial atmospheric environments. For infrastructure with high durability requirements (such as bridges, storage tanks, pipelines, etc.), as well as shipbuilding and offshore engineering equipment, using this coating can improve their anti-corrosion performance and self-healing ability, reduce corrosion accidents caused by accidental damage. In severe corrosive media, the corrosion rate of this coating after damage is much lower than that of ordinary anti-corrosion coatings. The corrosion current density of the coating added with self-healing microcapsules in the corrosive medium is significantly reduced, and the coating impedance is significantly increased, showing excellent corrosion resistance. After a period of self-healing treatment after the coating is scratched, its corrosion potential and impedance almost return to the level before scratching, proving that the self-healing and corrosion inhibition mechanisms effectively prevent the further expansion of rust; (3)This coating uses a water-based formula with extremely low volatile organic compound (VOC) content, having environmental protection characteristics. Compared with traditional solvent-based anti-corrosion coatings, it is more friendly to construction workers and the environment, and is especially suitable for marine engineering and indoor steel structure protection with strict environmental protection requirements; (4)Due to the self-healing ability of the coating, the frequency of paint repair and maintenance required due to small-area damage can be greatly reduced during use. For facilities such as offshore wind power equipment and cross-sea bridges that are difficult to repair in a timely manner, this coating can handle daily small damages by itself, prevent corrosion from getting out of control, and reduce maintenance and downtime costs. This will improve the reliability and service life of key structures, with significant economic benefits. Description of the Drawings

[0014] Figure 1 It is a schematic diagram of the components of this application; Figure 2 It is a schematic diagram of the action mechanism of this application. Detailed Embodiments

[0015] The following will describe in detail two embodiments of this application with reference to the drawings.

[0016] The first embodiment: The present invention provides a self-healing anti-corrosion water-based coating. Please refer to Figure 1, including an aqueous base resin, self-healing microcapsules, anti-corrosion fillers, additives and solvents. The aqueous base resin is one of two-component aqueous epoxy resin, aqueous polyurethane dispersion or acrylic modified copolymer emulsion. The above materials have good adhesion and resistance to medium penetration, making the formed coating dense and water-resistant. The self-healing microcapsules include a capsule shell, and the inside of the capsule shell is filled with a self-healing agent and a corrosion inhibitor. The capsule shell is one of urea-formaldehyde resin, phenolic resin, polyurea, polyurethane, polystyrene or polyethersulfone. The thickness of the capsule shell is 1-5 microns, and the particle size of the self-healing microcapsules is 1-100 microns. Through the capsule shell, the self-healing microcapsules can stably exist in the coating and are prone to rupture when the coating is damaged, realizing the characteristics of releasing the internal self-healing agent and corrosion inhibitor.

[0017] The self-healing agent includes one of drying vegetable oils (such as linseed oil, tung oil, etc.), low-viscosity resin monomers (such as epoxy resin prepolymers, acrylate monomers, etc.) or curing agents with curing functions. When the microcapsules rupture, these self-healing agents flow into the scratch cracks and undergo a curing reaction after contacting air or the curing components in the coating, forming solid substances to fill the cracks, thereby healing the coating. For example, linseed oil will spontaneously polymerize and cure when exposed to oxygen in the air, filling the wound to form a hydrophobic protective film. The corrosion inhibitor includes organic corrosion inhibitors (such as BTA benzotriazole, 2-MBI, imidazoline, etc.) and inorganic corrosion inhibitors (such as nitrites, molybdates, phosphates, etc.). When the coating is damaged, the corrosion inhibitor is released and preferentially adsorbed on the exposed metal substrate, forming a molecular film or a deposition product to hinder the attack of corrosive media (such as water, oxygen, chloride ions) on the metal, significantly reducing the corrosion rate. For example, BTA can form an insoluble coordination film on the surface of copper or steel, inhibiting the cathodic / anodic reaction; molybdate can promote the formation of a dense oxide film on the surface of steel.

[0018] The anti-corrosion filler can be a micro flake or a conductive anti-corrosion pigment, such as zinc phosphate, modified graphene, flaky iron oxide or aluminum powder. Specifically, zinc-rich powder (flaky zinc powder) is preferably used. Traditional zinc-rich coatings are mostly solvent-based, but in this embodiment, an aqueous epoxy zinc-rich formulation is used, and its zinc powder exists in a high-solid content and is dispersed and suspended in the aqueous epoxy, fully meeting the requirements of the aqueous system. The additives include a dispersant, an antifoaming agent, a preservative and a thickening agent. The solvent is deionized water, making the prepared coating have a suitable construction viscosity.

[0019] The following is one of the preparation methods of this application: 1. First, prepare self-healing microcapsules encapsulating corrosion inhibitors and self-healing agents: S1. Select linseed oil as the self-healing agent (which can be slowly oxidized and cured in the air), and dissolve 5% of benzotriazole BTA (as the corrosion inhibitor) in it to form a core phase solution. Linseed oil has a low viscosity, is easy to flow and has a certain corrosion inhibition property itself; S2. Dissolve 2.5 g of urea and 0.25 g of the formaldehyde polymerization promoter NH4Cl in 250 mL of water, heat to 50 °C, add the core phase oil phase under vigorous stirring to form a water-in-oil emulsion (the oil phase accounts for 10%), then slowly dropwise add the formaldehyde solution to carry out interfacial polymerization of urea-formaldehyde. After reacting for 2 hours, cool to obtain a microcapsule dispersion of the urea-formaldehyde resin wall material; S3. Collect the microcapsules in the microcapsule dispersion, wash with water and dry to obtain dry self-healing microcapsules. The average particle size of the microcapsules is about 50 microns, the shell wall thickness is about 2 microns. Microscopic observation shows that the microcapsules are round, with complete coating and no rupture or adhesion phenomenon.

[0020] II. Preparation of the self-healing anti-corrosion waterborne coating: waterborne epoxy zinc-rich anti-corrosion coating: The waterborne base resin uses a two-component waterborne epoxy resin coating (the main agent is a waterborne epoxy emulsion, and the curing agent is a waterborne polyamine). Add flaky zinc powder (particle size 10 μm, volume fraction 20%, and the used zinc powder is flaky zinc powder with a high specific surface area. Through additives and dispersion processes, stable dispersion in the waterborne resin is achieved, and a zinc-based cathodic protection effect is formed after the coating film is cured) to provide cathodic protection performance in the main agent component. Then add the prepared self-healing microcapsule powder (accounting for 10% of the solid content of the main agent), additives and an appropriate amount of deionized water. After stirring evenly at a low speed, the additives include: dispersant 0.5–1 wt%, defoamer 0.05–0.2 wt% and thickener 0.1–0.5 wt%. The total amount of additives is controlled within the range of 2–3 wt% of the coating solid content. Add the curing agent according to the weight ratio of the main agent:curing agent = 4:1 and mix to prepare the waterborne epoxy zinc-rich anti-corrosion coating with the required viscosity, that is, the self-healing anti-corrosion waterborne coating of the present application.

[0021] Test method: Spray the coating on the pretreated steel plate specimen, with a wet film thickness of about 150 μm, and cure at room temperature for 7 days to obtain a gray coating with a thickness of about 100 μm. This is the experimental group; the control group is a waterborne coating with the same other components but without the self-healing microcapsule powder, and it is coated and cured on the steel plate. The coating method, thickness and treatment method are the same as those of the above experimental group.

[0022] Self-healing anti-corrosion performance test (i.e., salt spray test): Use a blade to make the same cross scratches penetrating the coating on the two groups of coating specimens to expose the steel substrate. The scratch width is about 0.5 mm, and then place the specimens in a salt spray corrosion test chamber (5% NaCl, 35 °C) for salt spray testing for 240 hours. The test method complies with the GB / T 2423.17 or ASTM B117 standard.

[0023] Observe the corrosion condition at the scratch after the test: Obvious rust diffusion appeared at the edge of the scratch on the coating of the control group, and the rust spread outward along the scratch to an area about 3-5 mm wide; while there was only extremely little rust at the scratch of the coating in the experimental group, and no large-area outward expansion of rust was seen. After disassembling the specimen, it was found that a layer of light yellow solidified filler was formed at the scratch of the coating in the experimental group, covering the substrate again, which proved that the linseed oil released from the self-healing microcapsules had polymerized into a film and successfully healed the scratch; at the same time, the BTA corrosion inhibitor played a role on the metal surface, effectively inhibiting the corrosion of the scratched part.

[0024] Conduct further electrochemical impedance spectroscopy (EIS) tests on the scratched specimens: The results showed that after self-healing, the impedance modulus of the coating in the experimental group recovered to the order of 10^7 Ω·cm² in the low-frequency region, approaching the level of the non-scratched coating; while at the scratch of the coating in the control group, it was only about 10^5 Ω·cm². This indicates that the self-healing coating restored the anti-corrosion impedance by more than two orders of magnitude after being scratched, and has significant scratch self-healing and anti-corrosion capabilities. In addition, the coating of the present invention still showed a stable repair function in the repeated scratch-healing cycle test, and the expansion of the corrosion area after multiple scratches was still effectively controlled, proving that the reserve of self-healing microcapsules in the coating was sufficient to provide multiple self-healing effects.

[0025] Figure 2 It is a schematic diagram of the mechanism of the self-healing and anti-corrosion function of the present self-healing anti-corrosion coating on the surface of a metal substrate (i.e., the pipe substrate in the figure). Self-healing microcapsules containing self-healing agents and corrosion inhibitors are dispersed in the coating. When the coating is scratched and cracked by external force, the shell walls of the microcapsules near the corresponding position rupture, releasing the self-healing agents encapsulated inside. The self-healing agents flow and fill the scratch to form a "self-healing area", covering and protecting the exposed metal surface again; at the same time, the corrosion inhibitors released by the microcapsules form an adsorption protective film on the metal surface, jointly inhibiting the erosion of the corrosion medium on the substrate. After the self-healing effect, the integrity of the coating at the scratched part is restored, effectively preventing further rust expansion, and the protective performance of the coating on steel substrates such as pipes can be maintained for a long time.

[0026] The second implementation method: This embodiment provides a self-healing heavy-duty anti-corrosion coating applicable to marine environments: the water-based binder resin uses a water-based acrylic-epoxy hybrid emulsion, which contains active groups that can crosslink with amine curing agents and has good weather resistance; the capsule shell of the self-healing microcapsules adopts a double-shell structure, with the inner shell encapsulating epoxy resin E-51 monomer, and a curing agent (such as polyamide amine) encapsulated between the inner shell and the outer shell; when the double-shell self-healing microcapsules are scratched, the double layers rupture, and the epoxy resin E-51 monomer and the curing agent are mixed and react to form a cured product to repair the coating notch. The corrosion inhibitor is a mixture formed by sodium nitrate and cyclohexylamine, which is pre-loaded on porous silica particles and is also encapsulated in the inner shell. Among them, the main components and typical dosages are the same as those in the first embodiment (that is: the volume fraction of zinc powder is 20%, the microcapsules account for 10% of the solid content of the main agent, the main agent:curing agent = 4:1, the dispersant is 0.5-1 wt%, the defoaming agent is 0.05-0.2 wt%, the thickening agent is 0.1-0.5 wt%, and the total amount of additives is controlled within the range of 2-3 wt% of the coating solid content).

[0027] The above self-healing heavy-duty anti-corrosion coating is applied to a sandblasted steel specimen, and after curing into a film through hydrothermal curing, it is found through testing that after the coating is scratched, a transparent cured product can be automatically generated in a humid sea salt environment to fill the scratch, and the visible scratch gradually becomes shallower until it is covered. At the same time, in an outdoor coastal exposure test lasting up to 6 months, only extremely slight pitting rust appears at the scratched part of the above coating and does not spread, while obvious rusting occurs at the scratched part of the compared traditional epoxy zinc-rich paint and spreads several millimeters along the bottom of the coating. Thus, it is verified that the self-healing anti-corrosion water-based coating in this embodiment greatly improves the anti-damage corrosion ability in the actual marine atmosphere environment and has excellent engineering application value.

[0028] It can be seen from the above embodiments that the self-healing anti-corrosion water-based coating provided by the present invention can automatically heal when the coating is damaged and inhibit corrosion, significantly extending the protection life of metal structures in harsh environments. Its water-based environmental protection characteristics conform to the development direction of current green industries. The specific formulation and implementation methods of the coating of the present invention are not limited to the above embodiments. Without departing from the principle of the present invention, technical researchers can make various equivalent substitutions and optimizations for the types of self-healing microcapsules, the selection of corrosion inhibitors, the selection of water-based binder resins, etc., which are all covered within the protection scope of the present invention.

[0029] Combined with the current actual needs, the above implementation method adopted in this application, the protection scope is not limited to this. Within the scope of knowledge possessed by those skilled in the art, various changes made without departing from the concept of this application still fall within the protection scope of the present invention.

Claims

1. A self-healing anti-corrosion waterborne coating, characterized in that: It includes an aqueous base resin, self-healing microcapsules, anti-corrosion fillers, additives and solvents. The aqueous base resin is one of two-component aqueous epoxy resin, aqueous polyurethane dispersion or acrylic modified copolymer emulsion. The self-healing microcapsules include a capsule shell, and the inside of the capsule shell is filled with a self-healing agent and a corrosion inhibitor. The capsule shell is one of urea-formaldehyde resin, phenolic resin, polyurea, polyurethane, polystyrene or polyethersulfone. The thickness of the capsule shell is 1-5 microns, and the particle size of the self-healing microcapsules is 1-100 microns.

2. The self-healing anti-corrosion waterborne coating according to claim 1, characterized in that: The self-healing agent includes one of drying vegetable oil, low-viscosity resin monomer or curing agent with curing function. The corrosion inhibitor includes organic corrosion inhibitor and inorganic corrosion inhibitor.

3. The self-healing anti-corrosion waterborne coating according to claim 1, characterized in that: The anti-corrosion filler includes one of zinc phosphate, modified graphene, flaky iron oxide or aluminum powder.

4. The self-healing anti-corrosion waterborne coating according to claim 1, characterized in that: The additives include a dispersant, an antifoaming agent, a preservative and a thickener, and the solvent is deionized water.

5. The self-healing anti-corrosion waterborne coating according to claim 1, characterized in that: The self-healing agent is drying vegetable oil, and the capsule shell is urea-formaldehyde resin. The method for making self-healing microcapsules from drying vegetable oil, corrosion inhibitor and urea-formaldehyde resin includes the following steps: S1. Dissolve the self-healing agent in the corrosion inhibitor to form a core phase solution. S2. Dissolve urea and the formaldehyde polymerization promoter NH4Cl in water according to the mass ratio, heat to 45-55 °C, add the core phase solution under vigorous stirring to form a water-in-oil emulsion, and then slowly dropwise add a formaldehyde solution to polymerize urea-formaldehyde at the interface. After reacting for 1.5-2.5 hours, cool to obtain a microcapsule dispersion of urea-formaldehyde resin wall material. S3. Collect the microcapsules in the microcapsule dispersion, wash and dry them to obtain dry powder self-healing microcapsules.

6. The self-healing and anti-corrosion waterborne coating according to claim 1, wherein: Its preparation method includes the following steps: Add the aqueous base resin to the solvent, mix evenly, add the anti-corrosion filler to provide cathodic protection performance, then add the prepared self-healing microcapsule powder and additives, and stir evenly at low speed to obtain the self-healing anti-corrosion aqueous coating.

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