Since the wax can form a relatively dense and chemically stable coating film on the substrate, it can be used as a protective coating for the substrate. Available substrates include paper, metal, plastic, wood and concrete. All waxes have some water repellency and some of them protect the substrate from acids, alkalis, salts and corrosive gases. This protection can be temporary or permanent.
The main composition of general powder coatings and the dosage range in the formula are shown in Table 2-1. The dosage of various ingredients in the formula is difficult to accurately delineate the range. It is only a rough reference data. Resin is the main film-forming substance of powder coatings. It is the most important component that determines the properties of powder coatings and film performance.
The good choice of resin variety determines the product quality of powder coatings. The nature and performance of the resin used in powder coatings determine the composition and use of powder coatings. For example, if you choose a thermoplastic resin, no curing agent is needed in the formulation. Under the conditions of baking temperature and time, the molten acid leveled into a coating film with certain physical and mechanical properties and mechanical strength. This change is reversible; the thermosetting resin must be matched with the wax curing agent, and the resin and curing The agent undergoes a chemical curing reaction under certain baking temperature and time conditions to become a coating film with certain physical and mechanical properties and mechanical strength. This change is irreversible. In addition, the epoxy resin in the thermosetting resin is selected, so this powder coating can only be used in anti-corrosion and indoor products, not outdoors; if the polyester resin is selected, this powder coating can be used both indoors and outdoors. It can be used. The type of resin determines the purpose of powder coatings. Generally, the resin used in powder coatings should meet the following conditions.
The melting temperature and decomposition degree of the resin powder coatings are generally applied to the coated object in a powder state, and then must be heated and baked, and the resin in the powder coating melts and flows into a film, or melts, flows, and solidifies to form a film. If When the melting temperature of the resin is close to the decomposition temperature, once the baking temperature is controlled too high, it is easy to decompose the resin in the coating, and it is difficult to obtain a coating film with good appearance and performance. Therefore, the temperature difference between the melting degree of the resin and the decomposition temperature must be large. Thermosetting resins such as epoxy resin, polyester resin, polyurethane resin, acrylic resin and a considerable part of thermoplastic resin can also meet this condition, but there are a small part of thermoplastic resin For example, the temperature difference between the melting temperature and the decomposition temperature of polyvinyl chloride resin is small, and the precision of controlling the baking temperature in the coating process should be high. It is precisely because of the difficulty of PVC powder coating to control the temperature in coating, the development of PVC powder coating in our country is very slow, the production volume is small, and the application range is narrow.
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