A protective coating with reverse enhanced adhesion and its preparation method and application
By forming an anchoring-crosslinking network through the grafting reaction of dopamine with phenolic amines and alicyclic amines, the problem of poor adhesion of anti-corrosion coatings in humid environments is solved, achieving reverse adhesion enhancement, reducing construction difficulty and cost, and making it suitable for low surface treatment maintenance of outdoor steel structures.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- ZHEJIANG YUXI CORROSION CONTROL CORP
- Filing Date
- 2026-05-22
- Publication Date
- 2026-07-28
AI Technical Summary
Existing anti-corrosion coatings have poor adhesion in humid environments and cannot be continuously strengthened. Furthermore, traditional surface treatments have high requirements, resulting in difficult construction, high costs, and serious pollution.
An anchoring-crosslinking synergistic reinforcement network is formed by using dopamine, phenolic amine, and alicyclic amine curing agents under the catalysis of 2,4,6-tris(dimethylaminomethyl)phenol. The coating is constructed through grafting reaction, and combined with the multifunctional effect of cashew phenol glycidyl ether, the adhesion is reverse-enhanced.
In humid environments, the coating adhesion continues to increase with the extension of curing time, reducing the requirements for surface treatment during construction, reducing dust pollution, and making it suitable for large-scale engineering projects.
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of protective coating technology, and relates to a protective coating with reverse adhesion enhancement, its preparation method and application. Background Technology
[0002] Outdoor steel structures are constantly exposed to environments with humidity, salt spray, and rain, making them highly susceptible to corrosion and requiring regular anti-corrosion maintenance. Traditional anti-corrosion coatings require rigorous surface treatment of the steel structure before application, including sandblasting to Sa2.5 grade, complete removal of old paint and rust, and achieving an ideal state of dryness, cleanliness, and freedom from contaminants. However, in actual maintenance projects, especially for steel structures with existing old paint films, completely removing the old paint and rust is not only difficult and costly, but also generates a large amount of dust, posing a threat to the health of construction workers and severely polluting the soil and groundwater.
[0003] To address the aforementioned issues, existing technologies have focused on developing low-surface-treatment coatings. For example, Chinese patent CN113444228A discloses a silicone-modified waterborne epoxy curing agent and its prepared waterborne epoxy high-performance bridge primer. This improves the impact toughness and water resistance of the coating film by introducing flexible silicone segments, but it exhibits poor adhesion to damp or rusty surfaces, failing to achieve sustained adhesion enhancement. CN117229692A discloses the use of dopamine hydrochloride solution in combination with cyclohexanediamine carbonate for epoxy coatings. Dopamine promotes polymerization in an alkaline environment to form polydopamine, thus enhancing adhesion. However, dopamine acts only as an alkaline self-polymer and does not form a synergistic network with the curing agent or other components, resulting in insufficient interfacial anchoring ability. Furthermore, existing low-surface-treatment coatings struggle to address the issue of adhesion being significantly affected by moisture, lacking the "reverse adhesion enhancement" characteristic where adhesion continuously increases with curing time in damp environments or on roughened old paint films.
[0004] Therefore, developing a low-surface-treatment coating that can fully utilize the synergistic effect of each component and has reverse adhesion enhancement characteristics is of great practical significance. Summary of the Invention
[0005] To address the shortcomings of existing technologies, the present invention aims to provide a low-surface-treatment coating with reverse adhesion enhancement, its preparation method, and its application. This solves the problems of traditional coatings having high surface treatment requirements, poor adhesion in humid environments, and inability to continuously enhance adhesion, thereby achieving low-cost, long-lasting anti-corrosion maintenance of steel structures in outdoor humid environments.
[0006] The present invention employs the following technical solutions to achieve its objective: One aspect of the present invention provides a protective coating with reverse adhesion enhancement, comprising component A and component B; By weight, the raw materials for preparing component A include: 40-60 parts of waterborne epoxy resin emulsion, 20-30 parts of cashew phenol glycidyl ether, 1-5 parts of wetting and penetrating agent, and 0.5-1.5 parts of defoamer; the raw materials for preparing component B include: 30-50 parts of phenolic amine curing agent, 10-20 parts of alicyclic amine curing agent, 5-10 parts of dopamine, 2-5 parts of 2,4,6-tris(dimethylaminomethyl)phenol, and 10-15 parts of pigments and fillers. In component B, dopamine undergoes a grafting reaction with phenolic amine curing agent and alicyclic amine curing agent under the action of 2,4,6-tris(dimethylaminomethyl)phenol to form a modified curing agent; The mixing mass ratio of component A to component B is 100:(20~40).
[0007] Through extensive experimental research, the inventors discovered that when dopamine, phenolic amine, and alicyclic amine curing agents undergo a pre-grafting reaction in the presence of 2,4,6-tris(dimethylaminomethyl)phenol, a unique "anchoring-crosslinking" synergistic reinforcing network can be formed. The specific reaction mechanism and structural characteristics are as follows: This invention uses 2,4,6-tris(dimethylaminomethyl)phenol as a catalyst promoter. The tertiary amine group and phenolic hydroxyl group in this promoter molecule can form a synergistic catalytic system, effectively promoting the grafting reaction between the catechol group of dopamine, the phenolic amine, and the amine group on the alicyclic amine. This process does not require an alkaline environment, thus avoiding excessive self-oxidation of dopamine (i.e., avoiding the self-polymerization of dopamine to form polymers). The reaction product is a modified mixed curing agent with a well-defined structure containing multiple anchoring units (catechol) and crosslinking units (primary amine, secondary amine). 2,4,6-tris(dimethylaminomethyl)phenol is the key to achieving the grafting reaction and constructing the target "anchoring-crosslinking" network in the system of this invention. Other common tertiary amine promoters (such as N,N-dimethylbenzylamine BDMA) lack the synergistic effect of phenolic hydroxyl groups or have large steric hindrance, and therefore cannot effectively catalyze this specific grafting reaction, thus failing to form the "anchoring-crosslinking" network described in this invention, and consequently failing to achieve the excellent "adhesion reverse enhancement" effect.
[0008] Simultaneously, this invention incorporates a phenolic amine curing agent and an alicyclic amine curing agent. The phenolic amine curing agent, the alicyclic amine curing agent, and dopamine undergo a grafting reaction with dopamine under the catalysis of 2,4,6-tris(dimethylaminomethyl)phenol to form a modified curing agent. The modified curing agent molecule formed in this invention system simultaneously possesses three key structural segments: ① a strong anchoring segment: derived from the catechol group of dopamine, exhibiting extremely strong chelating and coordination ability with the metal substrate, enabling the formation of strong chemical bonds at the coating or metal interface; ② a hydrophobic rigid segment: derived from... The C8-C18 long-chain alkyl groups of the phenolic amine curing agent provide the necessary hydrophobicity and flexibility for the coating, while the benzene ring structure in the phenolic amine provides sufficient rigidity and the ability to form π-π stacking with dopamine, thereby promoting the formation of a cross-linked and dense synergistic network. This can form microphase separation within the coating, construct a dense cross-linked network, and effectively block water molecule penetration. ③ Rigid cyclic segments: The cyclic structure from the alicyclic amine curing agent can further increase the cross-linking density between the components and increase the glass transition temperature of the coating. These three structural segments, under the promoting effect of 2,4,6-tris(dimethylaminomethyl)phenol, are connected by chemical bonds and interact with each other intermolecularly through π-π stacking and hydrogen bonding, forming an integral synergistic network with excellent interfacial anchoring ability and bulk cross-linking density, thus constructing an "anchoring-cross-linking" synergistic reinforcing network.
[0009] The protective coating of this invention is based on an "anchoring-crosslinking" synergistic enhancement network, which can achieve reverse adhesion enhancement. The principle is as follows: In the early stage of coating curing, the catechol groups in the modified curing agent preferentially accumulate on the surface of the metal substrate and form anchoring points, giving the coating initial adhesion. As the curing time increases, on the one hand, the unreacted catechol groups and amine groups inside the coating continue to migrate to the interface, forming more coordination bonds and hydrogen bonds with the substrate, thus continuously enhancing the interfacial anchoring effect; on the other hand, the bulk crosslinking network continuously densifies, hindering the penetration of water molecules to the interface and protecting the interfacial anchoring bonds from being destroyed. The combined effect of these two factors results in the coating's adhesion not only not decreasing with the humidity environment, but also continuously increasing with the extension of curing time. In addition, when the coating is applied to a roughened old paint film surface, the coating adhesion is actually enhanced, thus achieving the "reverse adhesion enhancement" characteristic.
[0010] Preferably, the aqueous epoxy resin emulsion is a nonionic self-emulsifying epoxy resin emulsion with an epoxy value of 0.15~0.25mol / 100g, a number-average molecular weight of 500~1200, a particle size D50 of 50~300 nm, and a solid content of 40~60wt%.
[0011] Preferably, the cashew phenol glycidyl ether is a product of the reaction of cashew phenol or hydrogenated cashew phenol with epichlorohydrin. Its molecular structure contains a rigid benzene ring backbone and a C15 long-chain alkyl group. The inventors have discovered that cashew phenol glycidyl ether has three functions in the system of this invention: 1) its C15 long-chain alkyl group can significantly reduce the surface tension of the coating, improving its wetting and penetration ability to old paint films and rust layers; 2) its rigid benzene ring structure can participate in the cross-linking network, improving the mechanical properties of the coating film; 3) when compounded with waterborne epoxy emulsions, it can effectively suppress the generation of bubbles in the system and reduce coating defects.
[0012] Preferably, the phenolic amine curing agent is prepared by the Mannich reaction of C8-C18 alkylamines, phenolic compounds and aldehydes.
[0013] More preferably, the phenolic amine curing agent has the structure shown in formula (I): R1NH[CH2(C6H2(OH)(R2))CH2] n NHR1(I) Wherein, R1 is a C8-C18 alkyl group, R2 is selected from H or C1-C4 alkyl groups, and n is an integer from 1 to 5.
[0014] Preferably, the alicyclic amine curing agent is one or more of isophorone diamine, 1,3-cyclohexanedimethylamine, and N-(3-aminopropyl)cyclohexylamine.
[0015] Preferably, the wetting and penetrating agent is an organosilicon wetting agent, such as polyether-modified polysiloxane. The wetting and penetrating agent can further reduce surface tension and improve the wetting and spreading properties of rust layers and old paint films.
[0016] The defoamer in component A is used to eliminate air bubbles during the application and curing process, preventing pinholes and peeling of the coating. The defoamer is not particularly limited; any defoamer applicable to epoxy resin coatings is within the scope of this invention, including polyether defoamers, silicone defoamers, polyether-modified polysiloxane defoamers, or mineral oil defoamers.
[0017] Preferably, the pigment / filler is a mixture of mica iron oxide, zinc phosphate, and talc. More preferably, the mass ratio of mica iron oxide, zinc phosphate, and talc is 2~5:1~3:1.
[0018] Preferably, the grafting reaction conditions in component B include: dopamine, phenolic amine curing agent, alicyclic amine curing agent, and 2,4,6-tris(dimethylaminomethyl)phenol reacting at 50-70°C for 1-3 h in an inert atmosphere. The grafting reaction of dopamine, phenolic amine curing agent, and alicyclic amine curing agent occurs in a solvent-free environment catalyzed by 2,4,6-tris(dimethylaminomethyl)phenol.
[0019] The inert atmosphere in this article is one or both of nitrogen and argon.
[0020] More preferably, the preparation method of component B includes the following steps: heating phenolic amine curing agent and alicyclic amine curing agent to 50~70℃, then adding dopamine and 2,4,6-tris(dimethylaminomethyl)phenol, and stirring the reaction for 1~3 h under an inert atmosphere; then adding pigments and fillers, dispersing and grinding to a fineness ≤50μm to obtain component B.
[0021] A second aspect of the present invention provides a method for preparing the aforementioned adhesion-enhancing protective coating, comprising the following steps: Preparation of component A: The aqueous epoxy resin emulsion was heated to 40~60℃, cashew phenol glycidyl ether was added, and the mixture was stirred evenly. Then, wetting and penetrating agent and defoamer were added to obtain component A. Preparation of component B: Phenolic amine curing agent and alicyclic amine curing agent were heated to 50~70℃, then dopamine and 2,4,6-tris(dimethylaminomethyl)phenol were added, and the mixture was stirred and reacted for 1~3 h under an inert atmosphere; then pigments and fillers were added, dispersed and ground to a fineness ≤50μm to obtain component B; Mix component A and component B at a mass ratio of 100:(20~40).
[0022] The third aspect of the present invention provides the application of the protective coating with reverse adhesion enhancement in the maintenance of steel structure surfaces. Before construction, component A and component B are mixed to obtain a protective coating, which is then applied to the surface of the steel structure and cured at 5~40°C to obtain a protective coating layer.
[0023] When using the protective coating of this invention for the maintenance of steel structure surfaces, the steel structure surface can be sandblasted, manually derusted, or applied directly to rusted or old paint film surfaces. The coating has low requirements for surface treatment and has excellent adhesion to various surfaces.
[0024] When using the protective coating of this invention for the maintenance of steel structure surfaces, the application can be carried out in a dry environment with a relative humidity of ≤80% or a humid environment with a relative humidity of >80%. The coating has excellent adhesion in both dry and humid environments.
[0025] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention is the first to propose using a specific curing accelerator to catalyze the grafting of dopamine onto a mixed curing agent composed of phenolic amines and alicyclic amines, forming a precisely structured "anchoring-crosslinking" synergistic reinforcing network. This is completely different from existing methods that use dopamine as a simple additive or perform self-polymerization modification under alkaline conditions. This network perfectly combines the strong interfacial anchoring ability of dopamine with the bulk crosslinking density and hydrophobicity of phenolic amines / alicyclic amines, providing a structural basis for "reverse adhesion enhancement".
[0026] 2. The dopamine-grafted phenolic amine and alicyclic amine anchoring-crosslinking synergistic enhancement network constructed in this invention relies on the strong chelating anchoring effect of dopamine catechol groups and the dense crosslinking effect of mixed curing agents. During the curing process, the number of interface anchoring points in the coating continuously increases and the bulk crosslinking network becomes denser. In humid environments and on roughened old paint film substrates, the adhesion not only does not decrease, but also continues to increase with the extension of curing time, achieving "reverse adhesion enhancement" and significantly improving the interfacial bonding stability of the coating.
[0027] 3. The coating of this invention has low requirements for surface treatment. It does not require the steel structure surface to be sandblasted to Sa2.5 grade. It only requires simple removal of loose rust and oil stains, or roughening of the old paint film before direct application. It does not require complete removal of the old paint film and rust layer, and the adhesion performance is similar to that of sandblasted surfaces. It greatly reduces the construction difficulty, labor costs and equipment investment, and is especially suitable for large-scale engineering scenarios such as cross-sea bridges and port steel structures that are difficult to enclose for construction.
[0028] 4. This invention breaks through the traditional application of cashew phenol glycidyl ether as a common diluent, enabling it to play a synergistic role in the system by reducing surface tension, enhancing wetting and penetration, inhibiting bubble generation, and participating in cross-linking film formation, which significantly improves the application performance and film quality of coatings on low surface treatment substrates.
[0029] 5. The coating of this invention can be cured normally at temperatures of 5-40℃ and relative humidity of 80% or higher. The surface drying time is ≤4 hours and the actual drying time is ≤24 hours. The curing rate is fast and not restricted by the humid environment. The coating has a neutral salt spray resistance of ≥1500 hours and a water resistance of ≥1000 hours without any abnormalities. Moreover, the VOCs content is ≤120g / L, which is much lower than that of solvent-based coatings, reducing dust and waste generated during surface treatment and meeting environmental protection requirements. Its overall performance is superior to existing similar products. Detailed Implementation
[0030] In the description of this invention, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, and includes both a and b. "Multiple" includes two or more types, and can be two, three, four, five, or more.
[0031] The technical solution of the present invention will be further described and illustrated below through specific embodiments. It should be understood that the specific embodiments described herein are only for the purpose of helping to understand the present invention and are not intended to limit the present invention. Unless otherwise specified, the raw materials used in the embodiments of the present invention are all commonly used raw materials in the art, and the methods used in the embodiments are all conventional methods in the art.
[0032] In the following examples and comparative examples, the sources of raw materials are as follows: Waterborne bisphenol A type epoxy emulsion: epoxy value 0.20mol / 100g, particle size D50 280nm, number average molecular weight: 1000, solid content 45wt%.
[0033] Cashew phenol glycidyl ether: Hubei Nordina Biotechnology Co., Ltd., ND-CGE.
[0034] Polyether-modified polysiloxane: Evonik, TEGO® Wet 270.
[0035] Defoamer: Zhongke Hongtai, ZKHT-301.
[0036] Phenolic amine curing agent (synthesized from C12 alkylamine, phenol, and formaldehyde): Cardolite, NX-2070.
[0037] Phenolic amine curing agent (synthesized from diethylenetriamine, phenol, and formaldehyde): Cardolite, HDH-2.
[0038] Isophorone diamine, N-(3-aminopropyl)cyclohexylamine, diethylenetriamine, dopamine, tris(dimethylaminopropyl)amine, and 1,6-hexanediamine were all purchased from Aladdin Reagents.
[0039] 1,3-Cyclohexanedimethylamine and N,N-dimethylbenzylamine were purchased from Wuhan Kemic Biomedical Technology Co., Ltd.
[0040] Polyetheramine D400: Huntsman, D-400.
[0041] Polyamide 650: Zhenjiang Danbao Resin Co., Ltd.
[0042] 2,4,6-Tris(dimethylaminomethyl)phenol: Hubei Hanqing Biomedical Technology Co., Ltd., DMP-30.
[0043] Example 1
[0044] The protective coating of Example 1 was prepared by the following method: Preparation of component A: 40 parts of waterborne bisphenol A type epoxy emulsion, 20 parts of cashew phenol glycidyl ether, 1.5 parts of polyether modified polysiloxane wetting agent, and 0.5 parts of defoamer were stirred and mixed evenly at 45°C to obtain component A; Preparation of component B: 30 parts of phenolic amine curing agent (synthesized from C12 alkylamine, phenol, and formaldehyde) and 10 parts of isophorone diamine were heated to 55°C, and 8 parts of dopamine and 2.5 parts of 2,4,6-tris(dimethylaminomethyl)phenol were added. The mixture was stirred and reacted for 1.5 hours under nitrogen protection. Then, 10 parts of pigments and fillers (mica iron oxide: zinc phosphate: talc = 3:2:1) were added, and the mixture was dispersed and ground to a fineness ≤50μm to obtain component B. Mix component A and component B at a weight ratio of 100:25 to obtain a protective coating.
[0045] Example 2
[0046] The protective coating of Example 2 was prepared by the following method: Preparation of component A: 50 parts of waterborne bisphenol A type epoxy emulsion, 25 parts of cashew phenol glycidyl ether, 2 parts of polyether modified polysiloxane wetting agent, and 0.8 parts of defoamer were stirred and mixed evenly at 45°C to obtain component A; Preparation of component B: 40 parts of phenolic amine curing agent (synthesized from C12 alkylamine, phenol, and formaldehyde) and 15 parts of isophorone diamine were heated to 55°C, and 7 parts of dopamine and 3 parts of 2,4,6-tris(dimethylaminomethyl)phenol were added. The mixture was stirred and reacted for 1.5 hours under nitrogen protection. Then, 12 parts of pigments and fillers (mica iron oxide: zinc phosphate: talc = 3:2:1) were added, and the mixture was dispersed and ground to a fineness ≤50μm to obtain component B. Mix component A and component B at a weight ratio of 100:30 until homogeneous to obtain a protective coating.
[0047] Example 3
[0048] The protective coating of Example 3 was prepared by the following method: Preparation of component A: 60 parts of waterborne bisphenol A type epoxy emulsion, 30 parts of cashew phenol glycidyl ether, 3 parts of polyether modified polysiloxane wetting agent, and 1.0 part of defoamer were stirred and mixed evenly at 45°C to obtain component A; Preparation of component B: 50 parts of phenolic amine curing agent (synthesized from C12 alkylamine, phenol, and formaldehyde) and 20 parts of N-(3-aminopropyl)cyclohexylamine were heated to 55°C, and 10 parts of dopamine and 4 parts of 2,4,6-tris(dimethylaminomethyl)phenol were added. The mixture was stirred and reacted for 1.5 hours under nitrogen protection. Then, 15 parts of pigments and fillers (mica iron oxide: zinc phosphate: talc = 3:2:1) were added, and the mixture was dispersed and ground to a fineness ≤50μm to obtain component B. Mix component A and component B at a weight ratio of 100:35 to obtain a protective coating.
[0049] Example 4
[0050] The protective coating of Example 4 was prepared by the following method: Preparation of component A: 55 parts of waterborne bisphenol A type epoxy emulsion, 28 parts of cashew phenol glycidyl ether, 2.5 parts of polyether modified polysiloxane wetting agent, and 0.8 parts of defoamer were stirred and mixed evenly at 40°C to obtain component A; Preparation of component B: 45 parts of phenolic amine curing agent (synthesized from C12 alkylamine, phenol, and formaldehyde) and 18 parts of 1,3-cyclohexanedimethylamine were heated to 60°C, and 6 parts of dopamine and 3.5 parts of 2,4,6-tris(dimethylaminomethyl)phenol were added. The mixture was stirred and reacted for 2 hours under nitrogen protection. Then, 13 parts of pigments and fillers (mica iron oxide: zinc phosphate: talc = 3:2:1) were added, and the mixture was dispersed and ground to a fineness ≤50μm to obtain component B. Mix component A and component B at a weight ratio of 100:32 to obtain a protective coating.
[0051] Example 5
[0052] The protective coating of Example 5 was prepared by the following method: Preparation of component A: 45 parts of waterborne bisphenol A type epoxy emulsion, 22 parts of cashew phenol glycidyl ether, 2 parts of polyether modified polysiloxane wetting agent, and 0.6 parts of defoamer were stirred and mixed evenly at 55°C to obtain component A; Preparation of component B: 35 parts of phenolic amine curing agent (synthesized from C12 alkylamine, phenol, and formaldehyde) and 12 parts of isophorone diamine were heated to 65°C, and 9 parts of dopamine and 3 parts of 2,4,6-tris(dimethylaminomethyl)phenol were added. The mixture was stirred and reacted for 1 hour under nitrogen protection. Then, 11 parts of pigments and fillers (mica iron oxide: zinc phosphate: talc = 3:2:1) were added, and the mixture was dispersed and ground to a fineness ≤50μm to obtain component B. Mix component A and component B at a weight ratio of 100:28 to obtain a protective coating.
[0053] Example 6
[0054] The only difference between Example 6 and Example 2 is that the phenolic amine curing agent in Example 6 is Cardolite HDH-2, and the amount of the phenolic amine curing agent is adjusted so that the total amine value is the same as in Example 1. Everything else is the same as in Example 2.
[0055] Comparative Example 1 The only difference between Comparative Example 1 and Example 2 is that dopamine was not added to component B of Comparative Example 1; otherwise, they are the same as in Example 2.
[0056] Comparative Example 2 The only difference between Comparative Example 2 and Example 2 is that no grafting reaction was performed during the preparation of component B in Comparative Example 2; otherwise, they are the same as in Example 2. The preparation process of component B in Comparative Example 2 is as follows: 40 parts of phenolic amine curing agent (synthesized from C12 alkylamine, phenol, and formaldehyde) and 15 parts of isophorone diamine are heated to 55°C, 7 parts of dopamine and 3 parts of 2,4,6-tris(dimethylaminomethyl)phenol are added, and then 12 parts of pigments and fillers (mica iron oxide: zinc phosphate: talc = 3:2:1) are added, dispersed and ground to a fineness ≤50μm to obtain component B.
[0057] Comparative Example 3 The only difference between Comparative Example 3 and Example 2 is that no phenolic amine curing agent was added during the preparation of component B in Comparative Example 3, and the amount of isophorone diamine was adjusted to make the total amine value the same as in Example 1. Everything else was the same as in Example 2.
[0058] Comparative Example 4 The only difference between Comparative Example 4 and Example 2 is that isophorone diamine was not added during the preparation of component B in Comparative Example 4, and the amount of phenolic amine curing agent was adjusted to make the total amine value the same as in Example 2. Everything else was the same as in Example 2.
[0059] Comparative Example 5 The only difference between Comparative Example 5 and Example 2 is that BDMA was used instead of 2,4,6-tris(dimethylaminomethyl)phenol in the preparation of component B in Comparative Example 5. Otherwise, they are the same as in Example 2.
[0060] Comparative Example 6 The only difference between Comparative Example 6 and Example 2 is that in the preparation of component B in Comparative Example 6, tris(dimethylaminopropyl)amine was used instead of 2,4,6-tris(dimethylaminomethyl)phenol. Otherwise, they were the same as in Example 2.
[0061] Comparative Example 7 The only difference between Comparative Example 7 and Example 2 is that in the preparation of component B in Comparative Example 7, polyetheramine D400 curing agent was used instead of phenolic amine curing agent, and the amount of polyetheramine D400 curing agent was adjusted so that the total amine value was the same as in Example 2; otherwise, it was the same as in Example 2.
[0062] Comparative Example 8 The only difference between Comparative Example 8 and Example 2 is that in the preparation of component B in Comparative Example 8, polyamide 650 curing agent was used instead of phenolic amine curing agent, and the amount of polyamide 650 curing agent was adjusted so that the total amine value was the same as in Example 2; otherwise, it was the same as in Example 2.
[0063] Comparative Example 9 The only difference between Comparative Example 9 and Example 2 is that 1,6-hexanediamine was used instead of isophoronediamine in the preparation of component B in Comparative Example 9, and the amount of 1,6-hexanediamine was adjusted so that the total amine value was the same as in Example 2; everything else was the same as in Example 2.
[0064] Comparative Example 10 The only difference between Comparative Example 10 and Example 2 is that in the preparation of component B in Comparative Example 10, diethylenetriamine was used instead of isophorone diamine, and the amount of diethylenetriamine was adjusted so that the total amine value was the same as in Example 2; otherwise, they were the same as in Example 2.
[0065] Comparative Example 11 The only difference between Comparative Example 11 and Example 2 is that 1,4-butanediol glycidyl ether was used instead of cashew phenol glycidyl ether in the preparation of component B in Comparative Example 11. Otherwise, they are the same as in Example 2.
[0066] The protective coatings prepared in the examples and comparative examples were applied to steel plates that had only been derusted and cleaned of surface rust and oil. Areas with old paint films did not require thorough sanding; only the surface of the old paint film was roughened. Dry coating conditions were 25°C and RH 40-50%, and wet coating conditions were 25°C and RH 85-95%. Application was by spraying or brushing. After coating, the coatings were cured for 7 days under the same conditions before performance testing. The test methods are as follows: adhesion according to GB / T5210-2006 (pull-off method); neutral salt spray resistance according to GB / T1771-2007; VOCs according to GB / T23985-2009. The experimental results are shown in Table 1.
[0067] Table 1. Performance test results of protective coatings
[0068] *Adhesion enhancement rate of old paint film surface = (Adhesion of old paint film after roughening coating - Initial adhesion of old paint film after roughening) / Initial adhesion of old paint film after roughening * 100%.
[0069] As can be seen from the data in Table 1: The coatings of Examples 1-5 of this invention have excellent dry and wet adhesion. As time goes on, their adhesion to the roughened old paint film surface not only does not decrease, but increases significantly, achieving a significant "adhesion inverse enhancement" characteristic. The phenolic amine curing agent prepared by Example 6 using short-chain amines has a lower adhesion than that of Example 2, indicating that long-chain carbon alkane in the reinforcing network plays a very important role.
[0070] Comparative Example 1, without the addition of dopamine, failed to form a pre-reaction network despite pre-reaction, resulting in very poor overall performance; the adhesion of the old paint film after roughening was even lower than the initial value. Comparative Example 2, although dopamine was added, the components were simply mixed without pre-reaction, thus failing to form a pre-reaction network, and its overall performance was also poor. This demonstrates the necessity of pre-reacting dopamine with a specific mixed amine (phenolic amine + alicyclic amine) to form a chemically bonded network under the action of an accelerator in this invention.
[0071] In Comparative Examples 5 and 6, after replacing the curing accelerator with BDMA and tris(dimethylaminopropyl)amine, respectively, their adhesion properties, especially the adhesion to damp and old paint film surfaces, were significantly lower than those in Example 2, and no obvious "adhesion enhancement" characteristic was observed. This verifies the irreplaceable nature of 2,4,6-tris(dimethylaminomethyl)phenol in the system of this invention; its unique molecular structure (possessing both tertiary amine and phenolic hydroxyl groups) is key to the synergistic catalysis of efficient grafting of dopamine and mixed amines to construct the target network.
[0072] Comparative Example 3 used only the grafting reaction of alicyclic amines and dopamine, and Comparative Example 4 used only the grafting reaction of phenolic amines and dopamine. Both resulted in low coating adhesion, with very limited improvement in adhesion after roughening the coating. Comparative Examples 7 and 8 used polyetheramine D400 and polyamide 650 respectively to replace the phenolic amine curing agent of this invention. Comparative Examples 9 and 10 used 1,6-hexanediamine and diethylenetriamine respectively to replace the alicyclic amine of this invention. The coatings of Comparative Examples 7-10 showed low adhesion, with limited improvement in adhesion after roughening the old paint film, lower than Example 2. This demonstrates the importance of the modified curing agent formed by the reaction of dopamine with phenolic amines and alicyclic amines under the action of an accelerator. This modified curing agent can effectively form an effective "anchoring-crosslinking" synergistic network with other components of the system (such as cashew phenol glycidyl ether and aqueous epoxy emulsion).
[0073] Comparative Example 11 used 1,4-butanediol glycidyl ether instead of cashew phenol glycidyl ether, and the coating adhesion decreased, indicating that cashew phenol glycidyl ether, unlike other diluents, plays a very important role in the system of this invention.
[0074] To verify the mechanism of the "anchoring-crosslinking" synergistic reinforcement network of the present invention, the adhesion of the coating of Example 1 at different curing times (1d, 3d, 7d, 14d) was tracked and tested. At the same time, the glass transition temperature (Tg) of the coating and the content of catechol at the interface were tested in dry and wet states. The results are shown in Table 2.
[0075] Table 2. Performance changes of the coating formed by the paint in Example 1 at different curing times.
[0076] *Note: The catechol content at the interface is characterized by the relative intensity (atomic percentage) of the characteristic peak of catechol in the coating / substrate interface region using XPS testing.
[0077] The results showed that the catechol content in the interface region continued to increase with the extension of curing time, indicating that dopamine molecules continuously accumulated at the substrate interface, forming a stronger anchoring effect, which increased both dry and wet adhesion. At the same time, the difference between wet and dry Tg gradually narrowed, indicating that the coating's resistance to plasticization was enhanced, which is the intrinsic mechanism of the "adhesion inverse enhancement" characteristic. The wet adhesion value was close to the dry adhesion value on the 14th day.
[0078] To verify that the protective coating of the present invention has low requirements for surface treatment, the coating described in Example 2 was applied to the surface of steel with different surface treatments and cured for 7 days at 25°C and 85% relative humidity. The adhesion was tested, and the results are shown in Table 3.
[0079] Table 3 Adhesion data of coatings on steel with different surface treatments in Example 2
[0080] As can be seen from Table 3, the coating of the present invention has low requirements for surface treatment and has excellent adhesion to various surfaces.
[0081] Application Example 1 The coating of Example 2 of this invention was applied to the maintenance project of a cross-sea bridge steel structure. The surface of the steel structure was only cleaned with high-pressure water to remove loose rust and dirt (no sandblasting was performed), and areas with intact old paint film were only roughened. The ambient temperature during construction was 18~25℃, and the relative humidity was 80~90%. One coat was applied (dry film thickness approximately 120μm), and an adhesion test was conducted after 7 days. The results are as follows: Corroded areas: Adhesion strength by pull-off method: 14.5 MPa; Old paint film roughened area: adhesion by pull-out test 13.8 MPa; On damp surfaces (with condensation): pull-off adhesion 12.6 MPa.
[0082] Follow-up observations at 6 and 12 months after coating showed that the coating was intact, without blistering, rust, or peeling, proving that the coating of this invention has excellent adaptability to low surface treatment and protection performance in humid environments in actual engineering.
[0083] In summary, this invention has successfully developed a moisture-curing, low-surface-treatment coating with reverse adhesion enhancement properties by constructing a unique "dopamine-mixed amine" synergistic enhancement network and a cashew phenol glycidyl ether multifunctional system. It is particularly suitable for rapid maintenance of steel structures in outdoor humid environments and where thorough surface treatment is difficult, demonstrating significant technological advancements and broad application prospects.
[0084] All aspects, embodiments, and features of this invention should be considered illustrative in all respects and not limiting of the invention; the scope of the invention is defined only by the claims. Other embodiments, modifications, and uses will become apparent to those skilled in the art without departing from the spirit and scope of the invention as claimed.
[0085] In the preparation method of this invention, the order of the steps is not limited to the listed order. For those skilled in the art, variations in the order of the steps without creative effort are also within the scope of protection of this invention. Furthermore, two or more steps or actions can be performed simultaneously.
[0086] Finally, it should be noted that the specific embodiments described herein are merely illustrative examples of the invention and are not intended to limit the implementation of the invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them; it is neither necessary nor possible to exemplify all embodiments here. However, these obvious variations or modifications derived from the essential spirit of the invention still fall within the scope of protection of the invention, and interpreting them as any additional limitation would contradict the spirit of the invention.
Claims
1. A protective coating with reverse adhesion enhancement, characterized in that, Includes component A and component B; By weight, the raw materials for preparing component A include: 40-60 parts of waterborne epoxy resin emulsion, 20-30 parts of cashew phenol glycidyl ether, 1-5 parts of wetting and penetrating agent, and 0.5-1.5 parts of defoamer; the raw materials for preparing component B include: 30-50 parts of phenolic amine curing agent, 10-20 parts of alicyclic amine curing agent, 5-10 parts of dopamine, 2-5 parts of 2,4,6-tris(dimethylaminomethyl)phenol, and 10-15 parts of pigments and fillers. In component B, dopamine undergoes a grafting reaction with phenolic amine curing agent and alicyclic amine curing agent under the action of 2,4,6-tris(dimethylaminomethyl)phenol to form a modified curing agent; The phenolic amine curing agent is prepared by the Mannich reaction of C8-C18 alkylamines, phenolic compounds and aldehydes; The mixing mass ratio of component A to component B is 100:(20~40).
2. The protective coating according to claim 1, characterized in that, The aqueous epoxy resin emulsion is a nonionic self-emulsifying epoxy resin emulsion with an epoxy value of 0.15~0.25mol / 100g, a number-average molecular weight of 500~1200, a particle size D50 of 50~300 nm, and a solid content of 40~60wt%.
3. The protective coating according to claim 1, characterized in that, The cashew phenol glycidyl ether is a product of the reaction of cashew phenol or hydrogenated cashew phenol with epichlorohydrin.
4. The protective coating according to claim 1, characterized in that, The phenolic amine curing agent has the structure shown in formula (I): R1NH[CH2(C6H2(OH)(R2))CH2] n NHR1(I) Wherein, R1 is a C8-C18 alkyl group, R2 is selected from H or C1-C4 alkyl groups, and n is an integer from 1 to 5.
5. The protective coating according to claim 1, characterized in that, The cycloaliphatic amine curing agent is one or more of isophorone diamine, 1,3-cyclohexanedimethylamine, and N-(3-aminopropyl)cyclohexylamine.
6. The protective coating according to claim 1, characterized in that, The wetting and penetrating agent is an organosilicon wetting agent.
7. The protective coating according to claim 1, characterized in that, The pigments and fillers are a mixture of mica iron oxide, zinc phosphate and talc.
8. The protective coating according to claim 1, characterized in that, The grafting reaction conditions in component B include: dopamine, phenolic amine curing agent, alicyclic amine curing agent, and 2,4,6-tris(dimethylaminomethyl)phenol reacting at 50-70°C for 1-3 h in an inert atmosphere.
9. A method for preparing a protective coating with reverse adhesion enhancement as described in claim 1, characterized in that, Includes the following steps: Preparation of component A: The aqueous epoxy resin emulsion was heated to 40~60℃, cashew phenol glycidyl ether was added, and the mixture was stirred evenly. Then, wetting and penetrating agent and defoamer were added to obtain component A. Preparation of component B: Phenolic amine curing agent and alicyclic amine curing agent were heated to 50~70℃, then dopamine and 2,4,6-tris(dimethylaminomethyl)phenol were added, the temperature was maintained, and the reaction was stirred for 1~3 h under an inert atmosphere; then pigments and fillers were added, dispersed and ground to a fineness ≤50μm to obtain component B; Mix component A and component B at a mass ratio of 100:(20-40).
10. The application of the protective coating with reverse adhesion enhancement as described in claim 1 in the surface maintenance of steel structures, characterized in that, Before construction, components A and B are mixed to obtain a protective coating. The protective coating is then applied to the surface of the steel structure and cured at 5~40℃ to obtain a protective coating layer.