Powder coating is a 100% solid powder coating. It is different from general solvent-based coatings and water-based coatings. Instead of using solvent or water as the dispersion medium, it uses air as the dispersion medium. It has the characteristics of no volatile matter generation, easy cleaning, no solvent, little harm to the operator, high spraying utilization rate, and excellent performance. With the increasing global attention to environmental protection, the application of powder coatings has become more and more extensive, and the use of powder coatings in my country has exceeded 1 million tons.
High temperature resistant powder coatings belong to special functional coatings. According to different temperatures, they are generally divided into 200°C, 300°C, 350°C, 400°C, 500°C and above. It is widely used in barbecues, braising stoves, heaters, heating pipes, silencers, ovens, car exhaust pipes, chimneys and other equipment. Because of the advantages of high temperature resistant powder coatings in terms of environmental protection, safety, and utilization, it will gradually replace traditional high temperature paints. In recent years, due to the trend of "paint to powder", the market demand for temperature resistance of 500 ℃ and above is increasing. In the application scenarios of 500°C and above, the coating directly bears the burning of an open flame, and the minimum requirement for the coating to be non-chalking and non-shedding. This article focuses on this type of product.
The composition of high temperature resistant powder coatings is mainly as follows: resin and its curing agent, which are the basis of coating film formation; additives, used to improve the appearance or various properties of the coating; pigments, which give the coating hiding and color; fillers , Mainly plays a role of physical enhancement.
When the commonly used saturated polyester resins, epoxy resins and other materials are above 350℃, the carbon-oxygen bonds will soon be broken and decomposed, which is manifested in the powdering and shedding of the coating. Due to its silicone-oxygen bond as the main chain, silicone resins give silicone resins higher oxidation stability due to their higher bond energy, and are the first choice for the main resin of high-temperature powder coatings.
Pigments and fillers are the key to the performance of high temperature resistant coatings. Fillers should be selected with high stability and can react with the siloxane functional groups of silicone resins. Therefore, silicate-based fillers are the first choice, such as mica powder and silica powder. The other is silicate materials, they are mainly because their phosphate can react with the metal to ensure the adhesion between the coating and the substrate. In terms of pigments, most conventional pigments cannot withstand high temperatures above 500°C. Titanium dioxide can be used for white, and iron oxide black, iron manganese black, red, yellow and blue can be used for black. It is recommended to use packaged products. The overall formula ensures that heavy metals are not Will exceed the standard.
The production process of high temperature resistant powder coatings is not much different from ordinary products. The production process is as shown in the table below. The process parameters that need to be controlled are mainly in the melt extrusion stage. Because the softening point of silicone resin is low, it must be controlled properly. The exit temperature can ensure the uniformity of mixing in the melt extrusion stage. In the crushing stage, it is necessary to ensure that the particle size division is as narrow as possible, because the coating of the high temperature resistant powder coating will expand to a certain extent when heated. The better the uniformity of the coating, the lower the possibility of damage due to expansion.