Discuss the drying methods of coatings and their corrosion-resistant properties

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Let’s discuss the drying methods of coatings and their corrosion-resistant properties. The drying methods for coatings generally fall into three categories: natural drying, baking drying, and radiation drying. The features are as follows: 1. Natural drying. Natural drying refers to a drying method in which no external heat energy is required; the material can solidify into a film at room temperature. It is also known as air drying, or simply self-drying. Solvent-evaporating coatings, oxidation-polymerizing coatings, room-temperature cross-linking curing coatings, and others can all be dried naturally. Typically, the painted workpieces are placed in a well-ventilated area to dry through natural ventilation. Drying time is affected by temperature, humidity, and ventilation conditions. During drying, the temperature should be between 20–30°C with a relative humidity of ≤70%. When working outdoors in winter, do not leave the undry coating on the surface overnight to prevent dew and moisture from damaging it. To accelerate oxidation and the natural drying of polymeric and room-temperature crosslinking coatings, an appropriate amount of drying agent or curing agent can be added, and they can be baked at a temperature below 80°C for a period of time; this improves the adhesion and corrosion resistance of the coating film. After painting many large-scale devices and equipment, as well as precision instruments and meters, they are usually left to dry naturally ； This method is also used when painting outdoors, due to the limitations of heating equipment. 2. Baking drying: The drying method that uses heat to cure the coating and form a film is called baking drying, or simply drying. Placing the painted workpiece in a drying room or oven for heating can **significantly reduce the drying time of the paint**, and it also leads to substantial improvements in the hardness, adhesion, and corrosion resistance of the paint film. Drying by baking can be divided into three types based on temperature: low temperature (below 100°C), medium temperature (100–150°C), and high temperature (above 150°C). Different types of coatings require different baking temperatures; low-temperature baking is suitable for drying the coating on wood and plastics that are prone to deformation when heated (usually not exceeding 80°C), while medium- and high-temperature baking can only be used for drying the coating on metal products. Reducing the baking and drying temperature of coatings helps save energy, lower costs, improve efficiency, and expand the range of applications for coating products; therefore, it is one of the main goals in improving existing coating types and developing new ones. 3. Radiation drying: Radiation drying is a drying method in which coatings are cured into films through radiation heating, or using ultraviolet light and electron beam energy. Radiant heating achieves drying and film formation by heating the painted workpiece through the action of infrared or far-infrared radiation; this is referred to as infrared drying and far-infrared drying, respectively. UV curing involves exposing a UV-curable coating containing a photosensitizer to ultraviolet light of a specific wavelength. The photosensitizer decomposes to produce highly reactive free radicals, which in turn initiate a polymerization reaction that allows the coating to cure into a film within an extremely short time range (from a few dozen seconds to a few minutes), thereby achieving drying at room temperature. It is suitable for drying coatings on wood, plastic, and similar materials that cannot be heated; it is only used for drying UV-curable varnishes, and enamel cannot be dried using this method. Electron beam curing involves irradiating a coated film with high-energy electron beams, which generates active groups within the molecules and triggers a polymerization reaction; the film can thus be cured in 1–2 seconds, achieving rapid drying at room temperature. Its feature is that it can be used for curing opaque paints, but it has blind spots in terms of illumination, and thus is not suitable for curing the interiors of pipes or the inner surfaces of car bodies. It is mainly used for the drying and film formation after coating on wooden sheet materials, plastics, metal sheets or coils, paper, fabrics, and leather.