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Common types of water-based coatings: Water-based coatings use water as the dispersion medium and solvent. Compared to solvent-based and non-water-dispersed coatings, their most notable advantage is that the water used as the dispersion medium is non-toxic and harmless, and does not pollute the environment. They also offer other advantages such as low cost, reduced tendency to crumble, fast drying time, and ease of application. Common water-based coatings are mainly classified into four types based on the type of organic film-forming agent: water-based polyurethane type, epoxy resin type, acrylic resin type, and inorganic water-based coating type. The following outlines the research progress on several common water-based coatings. 1. Water-based epoxy coatings: Epoxy resins possess excellent physical and chemical properties, such as good adhesion, superior chemical and solvent resistance, high hardness, as well as good corrosion and thermal stability; for these reasons, they have always attracted considerable attention. Water-based epoxy resin coatings consist of two components: one component is a hydrophobic epoxy resin dispersion (emulsion) ； The other component is a hydrophilic amine curing agent, and the key lies in the emulsification of the hydrophobic epoxy resin. The research on this emulsification process went through several stages regarding the emulsification of epoxy resins. The process was as follows: from 1975 to 1977, polyvinyl alcohol was primarily used as an emulsifier, and research began on additives such as polyacylamides and epoxides, as well as polyethyleneglycol ethers, as emulsifiers. From 1982 to 1984, emulsifiers containing epoxy groups were used, and self-emulsifying epoxy resins appeared. The self-emulsification method involves reacting epoxy resin with compounds containing surfactant groups to produce epoxy resin with surfactant properties. Among them, selecting the amine used for neutralization is the most important technical formulation issue. Amines are relatively expensive compared to other materials used in water-based coatings, and they also increase VOC emissions. To improve the compatibility between epoxy resins and curing agents as well as their curing properties at room temperature, water-based epoxy resin coatings can be widely used as high-performance coatings, primers for equipment, floor coatings for industrial facilities, primers for vehicles, primers for automotive repairs, and topcoats for industrial repairs. 2. Water-based polyurethane coatings: Water-based polyurethane coatings include water-soluble types, water-emulsified types, and water-dispersed types. Based on molecular structure, they can be divided into linear and cross-linked types. There are both single-component and two-component systems. In addition to the excellent properties of solvent-based polyurethane coatings, water-based polyurethane coatings also offer advantages such as high hardness, strong adhesion, corrosion resistance, solvent resistance, low levels of volatile organic compounds, flame retardancy, being non-toxic and pollution-free, as well as being easy to store, transport, and use. However, compared to solvent-based polyurethane coatings, water-based polyurethane coatings still have many shortcomings. For example: longer drying times, the coating being prone to CO2 bubbles, higher costs for some raw materials, and insufficiently high performance and appearance of the coating due to a lack of new additives. Research on modifications to address the defects of water-based polyurethane coatings. At present, the development of water-based polyurethane coatings is still primarily constrained by raw materials, curing agents, sealants, crosslinking agents, etc. Therefore, developing the corresponding raw materials and additives is also key to the development of water-based polyurethane coatings. 3. Water-based acrylate coatings: Water-based acrylate resin coatings have advantages such as easy synthesis, durability, low-temperature resistance, environmental friendliness, and no fire hazard during manufacturing, storage, and transportation ； At the same time, there are also issues such as high hardness and poor solvent resistance. They can be roughly divided into three types: single-component type, high-performance type, and high-curing type. It is quite difficult to convert solvent-intolerant acrylic resin raw materials into solvent-resistant water-based acrylic resin coatings; as a result, there is little research being done on the production of traditional single-component acrylic resin coatings nowadays. The current focus of research is on the modification of acrylic resin raw materials, a technique known as \"living polymerization\". This technology can effectively control the molecular weight of acrylic resins, as well as their chemical structure (such as the arrangement order of monomers) and distribution. Water-based acrylic resin coatings have a wide range of applications: cross-linked acrylic resin coatings are used in the construction industry ； Cross-linked functional compounds such as 4-hydroxybutyl acrylate and cyclohexanediol monoacrylate can be used to prepare automotive coatings and powder coatings ； Ultraviolet-cured acrylic resin coatings possess excellent properties ； Of particular note are acrylic resin anti-corrosion coatings, which represent a major category within anti-corrosion coating systems. 4. Water-based alkyd resin coatings: Alkyd resin is an important resin used in coatings. It has a wide range of available monomers, low cost, many varieties, flexible formulation options, ease of chemical modification, and excellent performance. The development of water-based alkyd resins has gone through two stages: external emulsification and internal emulsification. Currently, the internal emulsification method is primarily used to synthesize water-based alkyd resin dispersions. The so-called internal emulsification method involves neutralizing the carboxyl or amino groups in the polymer with appropriate bases or acids, thereby enabling the polymer to disperse in water. Although water-based alkyd resin coatings have advantages such as good applicability and lubricity, they also have drawbacks including slow film drying, low hardness, poor water and corrosion resistance, as well as inadequate weather resistance in outdoor conditions; modifications are necessary to meet these performance requirements. Currently, the modification of water-based alkyd resins mainly includes physical and chemical modifications, among which those using acrylic resins, silicone resins, and styrene yield the most significant effects. In recent years, as research on polyurethanes has become more advanced, there has been an increasing amount of research on polyurethane-modified alkyd resins as well. Wang Ruihong and others used self-drying water-based alkyd resin modified with acrylic acid. In addition to adding water-based acrylics, neutralizers, drying agents, and solubilizers are also added to the alkyd emulsion. The modified water-based alkyd resin coating exhibits excellent color retention, gloss retention, weather resistance, durability, corrosion resistance, fast drying time, and high hardness. It overcomes the shortcomings of conventional water-based alkyd coatings, such as poor storage stability, slow drying rate, and low early hardness, water resistance, and solvent resistance, thereby expanding the application areas of water-based alkyd coatings. Zhou Liqiong and others developed sulfonate-modified water-based alkyd resins. Compared with conventional water-based alkyd resins, the modified resins exhibit a significantly improved water solubility, which reduces the amount of solubilizing agents required. The main chain of water-based alkyd resins contains ester bonds formed by the polymerization of polyols and polyacids; these ester bonds are prone to breaking under the action of acids and bases (neutralizing agents). Therefore, when synthesizing modified water-based alkyd resins, the use of water-soluble sulfonate prepolymers can significantly enhance the water solubility of the resins. A small amount of amine neutralizing agent is sufficient to achieve good water solubility, thereby reducing the impact of the neutralizing agent on the ester bonds. The modified water-based alkyd resin not only exhibits a significant increase in water solubility, but also possesses excellent flexibility, adhesion, and impact resistance. Polyurethane coatings are a type of coating with excellent comprehensive properties. Therefore, there is a desire to introduce the excellent properties of polyurethane into alkyd resins, in order to improve their physical and mechanical properties, as well as their weather resistance and chemical resistance. In fact, a type of coating has now been developed that features high production volumes and performance characteristics lying between solvent-based alkyds and two-component polyurethanes; this is the so-called urethane oil or single-component polyurethane coating. The water-based modification of urethane oil is currently a focus of research. The hybrid polymerization modification of urethane oil-acrylate microemulsions represents a new approach to the water-based formulation of such materials. The main challenge in the hybrid modification process is the difficulty of dispersing urethane oil in the dispersion medium; therefore, an ultrasonic pre-dispersion step must be added before hybrid polymerization to obtain a stable and high-performance hybrid microemulsion system. This is an important approach that combines the advantages of water-based alkyd resins with those of polyurethane coatings.