Formulation of high temperature resistant powder coating
Powder coating is a kind of coating with 100% solid powder. It is different from general solvent coating and water-based coating. It does not use solvent or water as the dispersion medium, but with the help of air as the dispersion medium. It has the characteristics of no volatiles, easy cleaning, no solvent, little harm to operators, high spraying utilization rate, excellent performance and so on. With the increasing global attention to environmental protection, the application field of Powder coatings is becoming more and more extensive. The use of Powder coatings in China has exceeded 1 million tons.
High temperature resistant Powder coatings are special functional coatings. According to the different temperatures, they are generally divided into 200 ℃, 300 ℃, 350 ℃, 400 ℃, 500 ℃ and above. It is widely used in barbecue ovens, stewing ovens, heaters, heating pipes, silencing, ovens, vehicle exhaust pipes, chimneys and other equipment. Because of the advantages of high temperature resistant Powder coating in environmental protection, safety and utilization, it will gradually replace the traditional high temperature paint. 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 scenario of 500 ℃ and above, the coating directly bears the burning of open fire, and the minimum requirement of the coating shall be no pulverization and no falling off. This paper focuses on this type of product.
The formulation of high temperature resistant Powder coating is mainly as follows: resin and its curing agent, which is the basis of coating film formation; Additives to improve the appearance or performance of the coating; Pigment to give the coating covering and color; The filler mainly plays the role of physical enhancement.
When the commonly used saturated polyester resin, epoxy resin and other materials are above 350 ℃, the carbon oxygen bond will soon break and decompose, which is manifested in the powdering and falling off of the coating. Silicone resin is the first choice for the main resin of high temperature resistant Powder coating because it takes silicone oxygen bond as the main chain and gives silicone resin high oxidation stability due to its high bond energy.
Pigments and fillers are the key to affect the performance of high temperature resistant coatings. Fillers should have high stability and can react with siloxane functional groups of silicone resin. Therefore, silicate fillers are the first choice, such as mica powder, silicon micro powder, etc. In addition, silicate materials, mainly because their phosphate can react with the metal, so as to ensure the adhesion between the coating and the substrate. In terms of pigments, most conventional pigments can not withstand high temperatures above 500 ℃. Titanium dioxide can be selected for white, iron oxide black, iron manganese black, red, yellow and blue can be selected for black. It is recommended to select wrapped products, and the overall formula will ensure that heavy metals will not exceed the standard.
The production process of high temperature resistant Powder coating is not different from that of ordinary products. The production process is shown in the table below. The process parameters need to be controlled mainly in the melt extrusion stage. Due to the low softening point of silicone resin, it is necessary to control the appropriate extruder temperature to ensure the mixing uniformity 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 high-temperature resistant Powder coating will expand when heated. The better the uniformity of the coating, the lower the possibility of damage caused by expansion.