Waterborne epoxy coating system solutions in the field of industrial protection (1)

Broadly speaking, water-based epoxy coating refers to the film resin in the coating with epoxy as the main film-forming water-based coating. Due to its excellent water and corrosion resistance, extremely fast drying speed and hardness development, excellent film-forming properties and low VOC properties, water-based epoxy coating systems are widely used in the field of industrial protection.
recommended for you this article for the current water-based epoxy coatings in the most widely used 3 systems, including single-group water-based epoxy coatings, two-group water-based epoxy coatings and two-group water-based epoxy/ acrylic hybrid coatings . From the coating system, paint preparation process and formulation and coating application of the three coatings are described.
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the structure of
and coatings determines the performance of the final coating. Epoxy coatings, due to their unique structure, have excellent adhesion, chemical resistance and corrosion resistance. Because epoxy coatings contain many hydroxyl and ether bonds, these polar chemical bonds can attract with metal substrates, so the paint film has excellent adhesion to metal substrates. When epoxy coatings are cured, epoxy resins and curing agents containing active hydrogen react to open the ring, generating co-price bonds. When epoxy open-loop reaction, the volume shrinkage of the resin is low, the internal stress is small, and the adhesion loss is less. On the other hand, epoxy resin only hydrocarbon-based and ether bonds, no ester bonds, so the epoxy system coating chemical resistance, especially alkaline resistance is very prominent. Because of its excellent adhesion and chemical resistance, epoxy coatings are the preferred system for corrosion-resistant coatings. Of course, epoxy coatings also have inherent defects. Because epoxy resin contains aromatic ether bonds, the paint film after ultraviolet light is easy to degrade the broken chain, so its outdoor weather resistance is poor.
years, after the environmental protection department's oppressive environmental supervision, the process of water-based industrial coatings has made rapid progress, of which the process of hydration of industrial coatings in epoxy system has been promoted particularly rapidly. Water-based epoxy coating refers to the film-forming resin in the coating with epoxy as one of the main film-forming materials of water-based coatings, such as water-based epoxy, two-part water-based epoxy and acrylic modified epoxy coating system. At present, in the container industry, the hydration of coatings has exceeded 90%. Container coatings mainly use a water-based epoxy zinc-rich primer, water-based epoxy coating and water-based acrylic paint composite coating system. On the other hand, the hydration of container coatings also greatly promotes the hydration of epoxy coatings. Since 2016, the preparation and application of water-based epoxy resins and coatings in China has made rapid progress, and many water-based epoxy applications have been successfully applied in the field of industrial protection.
In accordance with ISO12944-2-2017 "Color paint and varnish protective paint system corrosion protection of steel structure Part 2 environmental classification", the atmospheric environment according to the corrosion level, from low to high can be divided into C1 to C5M a total of 6 corrosion grades. The common systems of water-based coatings used in industrial protection include three: water-based acrylic system, hydro-alcoholic acid system and water-based epoxy system. Among them, the water-based epoxy system can be divided into: water-based epoxy system, two-group water-based epoxy system and two-group water-based epoxy-acrylic hybridization system. Water-based acrylic system anti-corrosion performance is the worst, but excellent weather resistance, water-based alcoholic acid and water-based epoxy esters are generally single-group system, construction is convenient, anti-corrosion performance is medium, suitable for low anti-corrosion requirements of C1 to C2 system For systems with higher anti-corrosion properties, it is generally recommended to use a two-component water-based epoxy system, while for coatings with requirements for corrosion protection and weather resistance, a two-component water-based epoxy-acrylic hybridization system can be selected. In practice, the appropriate coating system needs to be selected according to the actual performance requirements, as shown in Figure 1. This paper focuses on three water-based epoxy systems used in the field of industrial protection: single-group water-based epoxy system, two-group water-based epoxy coating and two-group water-based epoxy/acrylic hybrid coating system.
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Water-based epoxy coating system
1.1 single-component water-based epoxy coating system
1.1.1 coating system
water-based epoxy coating at the same time has the excellent characteristics of epoxy system and dry oil: of which epoxy components have high corrosion resistance; Therefore, water-based epoxy coating has a higher hardness and better hydrolysis resistance, paint film in the film process also faster dry speed, and has excellent corrosion resistance, especially suitable for industrial corrosion protection. At present, the mainstream water-based epoxy products are self-emulsified prepared products, mainly using vinyl modified method to obtain self-emulsified water-based epoxy esters. The prepared water-based epoxy esters use acrylic joint epoxy esters, the prepared products combined with epoxy resin adhesion, water resistance and corrosion resistance and acrylic resin film-forming good, high gloss advantages. Especially after coating filming, under the action of drying agent and oxygen, the double bond in water-based epoxy esters has an oxidation cross-linking reaction, forming a cross-networked structure, which can greatly improve the water resistance and corrosion resistance of the coating.
table 1 gives the parameters of water-based epoxy resin. The resin can be diluted with water into a pan-blue phase micro-white emulsion, in the process of use need to be added to the drying agent for oxidation crosslinking. This resin is self-emulsification system, has excellent shear stability, can participate in grinding. In order to meet the requirements of HJ 2537-2014", issued by the Ministry of Environmental Protection in 2014, "Water-based coatings for environmental marking products", water-based epoxy products with low benzene content have been developed, and benzene products (benzene, toluene, xylene) Ethyl benzene) content is less than 100 ppm, and the performance is comparable to conventional products
1.1.2 preparation process and formulation
single-part water-based epoxy coating preparation process is shown in Figure 4, reference formula is shown in Table 2. The specific process is as follows:
(1) preparation of water-based epoxy ester dispersion: water-based epoxy resin CTW-6070, drying agent, pH regulator, in turn added to the reactor, 300 to 500rpm low-speed mixing uniform, speed increased to 800 to 1000rpm, add resin quality 60 to 90% of the deionized water, get the water-based epoxy dispersion CTW-6042;
(2) grinding pigment slurry: water-based epoxy ester resin, wetting dispersant, de-foaming agent, leveling agent in turn into the reactor, low-speed stirring uniform, and then add pigments, fillers for grinding, grinding to a fineness of less than 30 m, out of the pigment slurry;
(3) coating preparation: the remaining water-based epoxy dispersion into the reactor, while stirring to add steps (1) to obtain the pigment slurry, stirring 20min after slowly adding thickener and solvent-assisted mixture solution, adjust the viscosity to the specified viscosity, get a single-part water-based epoxy ester coating.
1.1.3 Automotive chassis coating application case
Taking into account the construction of coatings, currently in the field of automotive spare parts (e.g. transmission shafts, axles, water tanks, heat dissipators, compressors, etc.) in the field of low-temperature baking water-based coatings (generally less than 100 degrees C), can be used water-based epoxy system. Using low temperature baking type single-part water-based epoxy ester coating as the bottom surface of the one-in-one coating, sprayed car suspension bust. The spraying process of the automobile suspension bus includes the following steps: (1) surface treatment of the work piece, (2) spraying and (3) curing. Specific construction steps include the following parts: degreasing →washing→ table tone→phosphate →washing→ pre-baking→ spraying 1→ leveling→ spraying 2→ baking curing→ spray repair paint→ work parts offline.
used prepared water-based epoxy coating to spray automotive suspension work parts, testing performance such as Table 3. As can be known from the data in Table 3, the coating is smooth, non-foaming and looks good. The coating gloss is 45, the coating has good adhesion to the substrate, and the hardness reaches H. In particular, sprayed models and work pieces have better water and salt spray resistance. According to the experimental data, the coating products of this project can be dry at room temperature, with good paint film adhesion, excellent corrosion resistance, good storage stability, can replace the traditional solvent-based coatings, can be widely used in the field of automotive parts coatings.
(Text selected from the 2019 Water Technology Annual Meeting Paper Collection, (reference slightly) Xu Fei, Zhuang Zhenyu, Zhang Hanqing, etc., CNOOC Changzhou Environmental Protection Coatings Co., Ltd., Hydroelectrelectrelectroric Coatings Branch, CNOOC Changzhou Coatings Chemical Research Institute Co., Ltd., National Paint Engineering and Technology Research Center)
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