Steel, as an important material for national infrastructure construction and industrial production, has a wide range of applications in fields such as automobiles, ships, aerospace, construction, railways, and bridges due to its advantages of light weight, high strength, high seismic resistance, high plasticity, and low cost. At the same time, the corrosion problem of steel structures is becoming increasingly serious. At present, the direct economic losses caused by steel corrosion worldwide amount to hundreds of billions of dollars annually, and disasters and accidents caused by steel corrosion also occur frequently. Therefore, researching and developing anti-corrosion technologies for steel structures to slow down and prevent corrosion is not only a key direction for national scientific and technological development, but also an urgent task to reduce corrosion losses, minimize casualties, and promote the rational utilization of resources.
Among various anti-corrosion technologies, applying anti-corrosion coatings is the most economical and common method. However, before painting, in order to ensure the anti-corrosion effect of the coating, traditional surface treatment is required to completely remove rust. This process is not only time-consuming and costly, but also prone to serious dust and noise pollution; For special equipment and complex structural components, it is even impossible to perform surface treatment using mechanical or manual methods. In order to achieve ideal coating anti-corrosion quality, the use of low surface treatment coatings directly applied to the surface of rusted steel is an environmentally friendly and cost-effective treatment method. It can not only reduce the workload of surface treatment, but also meet the anti-corrosion needs of corroded steel surfaces.
With the increasingly prominent environmental issues, traditional solvent based coatings generate a large amount of volatile organic compounds (VOCs) during production, construction, and drying curing processes. Therefore, many countries in the world have formulated strict environmental regulations to control VOC content. Therefore, environmentally friendly powder coatings, water-based coatings, UV curable coatings, and solvent-free high solid content coatings have become research hotspots in the coatings industry.
Among them, water-based coatings are environmentally friendly coatings with extremely low or no VOC content. With their good permeability, water-based coatings are the most suitable environmentally friendly coatings for rusted metal surfaces. Low surface treatment water-based coating is a water-based environmentally friendly coating that can be coated with rust and has good anti-corrosion function. The active pigments and rust conversion agents contained in it can react chemically with rust, passivating, stabilizing or transforming the rust layer into chelates or complexes with strong adhesion to the substrate, achieving rust removal and protection on the surface of steel.
In this study, a low surface treatment water-borne acrylic acid coating was prepared by using high salt spray resistant acrylic lotion as the film-forming material, matching with active antirust pigments such as zinc phosphate and aluminum tripolyphosphate, and selecting appropriate film-forming additives, wetting agents, salt spray resistant additives, rust conversion additives and other additives, which solved the problems of poor stability, high heavy metal content and complex construction process of water-based low surface treatment antirust coatings, and reduced the maintenance cost and labor force of the coating. This coating has the function of rust and anti-corrosion coating, with a salt spray resistance of>360h under a film thickness of 30-45 μ m. Other anti-corrosion performance indicators also meet or even exceed similar products, and it has important practical application value in the anti-corrosion engineering of steel structures in the construction, bridge, and petroleum and petrochemical industries.
1. Protection mechanism of low surface treatment water-based anti-corrosion coatings
The anti-corrosion mechanisms of low surface treatment water-based anti-corrosion coatings include shielding, corrosion inhibition, and cathodic protection mechanisms. The shielding mechanism is mainly based on the shielding effect of the coating film, which achieves the purpose of protecting the substrate by shielding against corrosive factors such as water, oxygen, and ions; The corrosion inhibition mechanism mainly relies on the corrosion inhibition effect of active anti rust pigments to achieve protection of steel. Active anti rust pigments can hydrolyze to produce complex anions that combine with metal ions at the corrosion anode, generating shielding complexes to protect the substrate; The cathodic protection mechanism is based on the active metal powder contained in the coating, which sacrifices the anode to achieve the protective effect on the substrate. At the same time, the generated corrosion products can fill the gaps of the coating, enhance the density of the coating, and prevent the penetration of corrosion factors. In this study, water-based acrylic lotion is used as film-forming material, zinc phosphate and aluminum tripolyphosphate are used as active antirust pigments, together with rust conversion additives, to develop a low surface treatment water-based acrylic anti-corrosive coating that integrates wetting, penetration, conversion and stabilization of various anti-corrosion mechanisms. This coating can be applied with rust, wet and penetrate the surface of rusted steel, and transform the rusted part into a composite passivation layer to achieve the protective effect on the base material.
2. Experimental section
2.1 Main raw materials and experimental equipment
Water-borne acrylic lotion; Alcohol ester twelve: propylene glycol butyl ether, alcohol ester sixteen, carbon black, zinc phosphate, aluminum tripolyphosphate, precipitated barium sulfate, defoamer, dispersant, wetting agent, anti flash rust agent, pH regulator AMP-9, salt spray resistant additive, rust conversion additive, thickener. Multi purpose machine for sanding, dispersing, and mixing; Coating thickness gauge; Analytical balance, pH meter; Precision oven; Wet film preparation device; Circulating corrosion salt spray box, UV accelerated aging testing machine.
2.2 Preparation of Coatings
In order to improve the storage stability of the coating, this study first added deionized water, dispersant, defoamer, pH regulator, carbon black precipitate barium sulfate, and two types of active anti rust pigments to the dispersion kettle, stirred thoroughly, and mixed. Then, it was ground to a fineness of ≤ 25 μ m using a sand mill. Mix the grinding black slurry and lotion evenly under low shear force, use the step thickening process to first add some thickening agents to improve the shear force in the kettle, then slowly add the film forming agent, wetting agent, anti flash rust agent, salt spray resistant agent, rust conversion agent and the remaining thickening agent, and then mix them at high speed to make them disperse evenly to prepare low surface treatment water-borne acrylic anti-corrosion coating.
2.3 Performance testing of coatings
Performance testing of coatings according to national or enterprise standards: Determine the drying time of the coating film according to GB/T 1728-2020; According to GB/T9755-2014, visually inspect the appearance of the coating film; Determine the impact resistance of the coating film according to GB/T 1732-2020; Determine the flexibility of the coating film according to GB/T 6742-2007; Determine the adhesion of the coating film according to GB/T 9286-2021; According to GB/T 1733-1993 method A, determine the water resistance of the coating film; Determine the salt water resistance of the coating film according to GB/T 9274-1988 method A; Determine the salt spray resistance of the coating film according to GB/T 1771-2007; According to GB/T1865-2009, the resistance of coatings to artificial weather aging is determined; Determine the freeze-thaw stability of coatings according to HG/T 4758-2014.
3. Experimental Results and Discussion
3.1 Study on corrosion resistance of lotion to coating
In order to test the corrosion resistance of water-based acrylic lotion from different manufacturers, this study takes the type of lotion as a variable, and adds an appropriate amount of film forming additives, pigments, fillers and various additives to form a basic formula, and compares the performance of coatings prepared by different lotion.
The comprehensive test results show that, HG-300、 The salt spray resistance of 1524 and 2403 basic formula coatings is more than 72 h, and the water resistance, salt water resistance and artificial weather aging resistance are also better than other lotion. Among them, 1524 has relatively poor adhesion, so the water-based acrylic lotion HG-300 and 2403 are given priority. Because the water resistance of HG-300 is relatively poor and the cost is high, the water-based acrylic lotion 2403 is selected as the film forming resin for subsequent formula design experiments in this study.
In the process of coating production, in order to promote the swelling flow and extrusion deformation of lotion polymer, it is necessary to add appropriate film forming additives to control the film forming temperature of latex particles, so as to ensure the dryness, gloss and corrosion resistance of the film. In order to meet the needs of users to reduce construction time and improve production efficiency, it is necessary to study the ratio of film-forming additives to improve the drying speed of coatings. Compared with other types of film forming substances, water-borne acrylic lotion has a faster drying speed, but the minimum film forming temperature (MFFT) of different lotion is different, and it is usually necessary to reduce the MFFT of finished coatings to below 10 ℃. The MFFT of 2403 used in this study is 16 ℃, and a certain amount of film-forming agent needs to be added. Considering that different film-forming aids have different effects on MFFT, three film-forming aids with different boiling points (alcohol ester twelve, propylene glycol butyl ether, and alcohol ester sixteen) were selected for experiments to explore the influence of different film-forming aid ratios on coating properties.
This study first tested the compatibility and stability of water-borne acrylic lotion and three film forming additives. Although propylene glycol butyl ether has good compatibility in lotion, if it is added too quickly, emulsion breaking will occur; Alcohol ester 12 and 16 have good compatibility with lotion. There is no special requirement for the addition speed, so flocculation is not easy to occur, and the applicability is good. From the experimental results in Table 4, it can be seen that with the increase of propylene glycol butyl ether dosage, the surface drying speed of the coating film accelerates and the rebound viscosity improves, but the adhesion and flexibility decrease; With the increase of alcohol ester twelve or alcohol ester sixteen dosage, although the adhesion, flexibility, and resistance of the coating are ensured, the surface drying time slows down and the viscosity decreases; When m (alcohol ester twelve): m (propylene glycol ether): m (alcohol ester sixteen)=3:1:2, although it slightly reduces the surface drying speed, it enhances the various properties of the coating, making it the optimal film-forming agent ratio.
3.3 Study on the Corrosion Resistance of Coatings by Active Anti rust Pigments
Corrosion of steel structures can be classified into electrochemical corrosion, chemical corrosion, and physical corrosion based on their mechanisms. Among them, electrochemical corrosion is the most common. The main components of rust generated by electrochemical corrosion of steel structures are Fe3O4, γ – FeOOH, and α – FeOOH. In order to achieve protection of steel structures and improve the corrosion resistance of coatings, it is necessary to add an appropriate amount of anti rust pigments in the formula to enhance the passivation and anti rust ability of the substrate. There are many types of active anti rust pigments, including chromium based pigments, zinc phosphate, zinc oxide, and aluminum tripolyphosphate. Chromium based pigments, as the first generation of anti rust pigments, have excellent anti rust properties. CrO42- dissociated from water can form a passive layer on the metal surface and can also combine with metal ions to form stable complexes.
In recent years, due to environmental pollution issues, freshwater coatings have gradually taken the stage; Zinc phosphate is currently the most widely used anti rust pigment. It relies on PO43- generated by the hydrolysis of phosphate to react with Fe3+, forming insoluble iron phosphate salts on the metal surface to achieve anti rust effect. Modifying zinc phosphate can increase the reactive active sites, making it highly oxidizing and achieving passivation of the substrate; Zinc oxide is an alkaline anti rust pigment that can react with γ – FeOOH and transform it into an inert substance. The alkalinity of zinc oxide has a certain inhibitory effect on the cathodic reaction of electrochemistry, thereby improving the corrosion resistance of the coating; Aluminum tripolyphosphate is an important polyphosphate anti rust pigment, and its decomposed P3O105- can chelate with iron ions to form a protective layer. The degradation products of P3O105- also have good coordination with metal ions. By modifying aluminum tripolyphosphate, the stability of water-based coating systems can be improved. This study investigates the effect of different anti rust pigments on the corrosion resistance of coatings through comparative experiments.
Analysis shows that aluminum tripolyphosphate exhibits the best performance, with a salt spray resistance of 240 hours. It has a good passivation and protective effect on the substrate, significantly improving the corrosion resistance of the coating; Zinc phosphate and zinc oxide are second only to aluminum tripolyphosphate, with a salt spray resistance of up to 216 hours. Zinc strontium phosphate, zinc molybdate, and calcium ion exchange anti rust pigments have poor performance and do not significantly improve the corrosion resistance of the coating. Considering economic, anti-corrosion, and environmental requirements, this study selected a combination of active anti rust pigments of zinc phosphate and aluminum tripolyphosphate to further investigate the effect of their ratio on the corrosion resistance of the coating.
From the experimental results, it can be seen that the salt spray resistance is 336 hours when using only aluminum tripolyphosphate, and 288 hours when using only zinc phosphate, indicating that using a single active anti rust pigment cannot achieve the best anti rust effect; When the ratio of zinc phosphate to aluminum tripolyphosphate is 1:3, it has the best anti-corrosion effect, with a salt spray resistance of 360 hours. This is because these two active anti rust pigments can hydrolyze in water-based coating systems to produce substances such as phosphate and polyphosphate, thereby passivating the metal substrate. At the same time, the synergistic effect between zinc phosphate and aluminum tripolyphosphate also enhances the protective effect on the metal substrate.
3.4 Study on the Corrosion Resistance of Coatings by Additives
3.4.1 Study on the Performance of Wetting Agents on Coating Films
Water based coatings use water as a dispersing medium, and water has a high surface tension, which makes it difficult to wet the substrate. The degree of substrate wetting by the coating directly affects the adhesion performance of the coating film. The wet film motion of paint follows three models: the contact angle model for spreading flow on the substrate, the Bernhard vortex for flowing in the vertical direction, and the sine wave model for flowing from an uneven surface to a flat surface. Wetting agents are precisely additives added to change the complex balance mentioned above. They can reduce the surface tension of the system, thereby improving the wetting and leveling properties of the coating on the substrate. In low surface treatment coatings, different types of wetting agents have different wetting abilities on rusted steel structures, resulting in differences in their penetration, wrapping, and transformation of the rust layer, which in turn leads to different anti-corrosion properties of the coating film. This study compared the effects of four different types of wetting agents on the corrosion resistance of low surface treatment coatings, and the experimental results were obtained.
Analysis shows that the comprehensive performance of low surface treatment water-based coatings made by adding modified organosilicon wetting agents is better. The anti-corrosion effect of coatings made by using alkynediol wetting agents is slightly better than that of alkyl aryl ether wetting agents. Among them, the application effect of special polyether modified organosilicon is the best, because organosilicon wetting agents can simultaneously reduce static and dynamic surface tension, quickly spread on the surface of steel, and enable the wet film to better wet the substrate and promote leveling.
3.4.2 Study on the Effect of Corrosion Conversion Additives on Coating Properties
In low surface treatment coatings, rust conversion agents play a very important role. They can quickly react with the rust layer to form stable and dense iron chelates, which protect the substrate through shielding. The performance of rust conversion agents has a significant impact on the corrosion resistance of the coating. Common rust transformation agents include phosphoric acid, chromic acid, phytic acid, oxalic acid, tannic acid, catechol, gallic acid, 2-hydroxypyridine, etc. Among them, the rust transformation mechanism of tannic acid and catechol is to use the adjacent hydroxyl groups in their own structure to chelate with divalent and trivalent iron ions in the rust layer to form a water-insoluble five membered ring.
This study screened four different types of rust conversion agents to investigate their effects on the corrosion resistance of low surface treatment coating systems. Firstly, the compatibility of different rust conversion additives with lotion was studied. From the analysis of the experimental results, it can be seen that the rust conversion additives with oxalic acid or phosphoric acid as the main component are too acidic, which can easily damage the stability of lotion and break its emulsion; In contrast, rust conversion additives with tannic acid or catechol as the main component are less acidic and have better compatibility with lotion. The influence of the compound on the film performance was studied by using the above two rust conversion additives in combination with an appropriate amount of film forming additives and lotion. As shown in Table 8, tannin acid rust conversion additives will lead to poor water resistance of the film and reduce corrosion resistance; And the catechol based rust conversion agent not only ensures the initial water resistance of the coating, but also improves the water resistance and salt spray resistance of the coating. Therefore, this study chose a rust conversion agent mainly composed of catechol as the rust conversion agent for low surface treatment coating systems.
The amount of rust conversion agent added determines the rust conversion performance and anti-corrosion performance of the low surface treatment coating system. This study compared the effects of different amounts of rust conversion agent added on the coating film. As shown in Table 9, with the continuous increase of the addition amount, the rust conversion effect becomes better and the resistance of the coating film gradually increases. When the addition amount is 5%, the salt spray resistance is the best, reaching 144 hours; when the addition amount is 5%, the coating performance slightly decreases. For cost-effectiveness considerations, this study chose the addition amount of rust conversion agent as 3-5%.
4. Conclusion
This research has prepared a water-borne acrylic coating with low surface treatment. The coating protection system uses high salt spray resistant acrylic lotion as the film-forming substance, and other additives such as active antirust pigments and rust conversion additives are added. It not only has a unique anti-corrosion mechanism such as wetting, penetration, rust transformation and stability, but also has the characteristics of fast drying speed and good adhesion. It is suitable for steel plates with rust layer thickness less than 15 μ m. Under the film thickness of 30-45 μ m, it can withstand water for 216 hours, salt water for 268 hours, and salt spray for 360 hours. It can significantly reduce the workload of surface treatment of rusted steel and the cost of renovation of anti-corrosion, reduce the downtime of rusted steel structure equipment, and reduce the maintenance time in the petroleum and petrochemical industry It has significant application value in steel structure protection.
Post time: Aug-25-2026