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Nov 12, 2020
With the development of heat-resistant powder coatings, there are many applications of silicone resins in heat-resistant powder coatings. So what are the applications of silicone resins in heat-resistant powder coatings? Next, let's introduce relevant knowledge for everyone, let's take a look.
With the development of the coating industry, powder coatings have been widely used in the coating of metal substrates. In recent years, the development and application of functional products such as antibacterial, high wear resistance, and heat resistance have become the most important part of powder coatings. Direction of development.
Heat-resistant powder coatings refer to powder coatings that can withstand temperatures above 200°C for a long time, have a good coating film, and enable the protected object to function normally in a high-temperature environment. In terms of polymer thermal stability mechanism, the heat resistance of a polymer mainly depends on its molecular structure. The thermal stability of the polymer can be improved by introducing larger or more polar side groups on the main chain and increasing the intermolecular interaction force. Another way to improve the heat resistance of powder coatings is to add heat-resistant pigments and fillers to the polymer. Commonly used pigments and fillers are aluminum powder, mica powder, stainless steel powder, cadmium powder, silica and so on.
Resin as the main film-forming substance of the coating is the basic factor determining the heat resistance of the coating. The heat resistance index of the usual resin products is shown in Table 1. The powder coating is generally cured into a film under the conditions of 180~200℃ and 20min. It is a thermosetting coating. The coating forms a network cross-linked structure, so the heat resistance of the thermoplastic coating is improved to a certain extent. Through the heat resistance test of epoxy type, epoxy-polyester hybrid type, polyester/TGIC type and other powder coatings (Table 2), it is shown that these coatings can basically be used for a long time under the condition of less than 150 ℃, but the In an environment above 250°C, the coating exhibits damage such as loss of gloss, decreased adhesion, embrittlement of the coating, reduced flexibility, and chalking, which makes the coating lose its protective effect on the substrate.
Currently, the widely used heat-resistant resins are mainly silicone resins and fluororesins. Silicone resins have silicon-oxygen bonds (—Si—O—) as the main chain. Due to their high bond energy, they have high oxidation stability, and silicone resins can generate stable chains—Si—O—Si on the coating surface. —The protective layer reduces the impact on the inside of the polymer; silicone resin has a wide range of applications in heat-resistant coatings, but the use of silicone resin alone has small intermolecular forces, poor adhesion, and high prices. According to preliminary test results, the epoxy resin is modified by adding an appropriate amount of silicone resin to achieve the goal of not only ensuring a certain heat resistance, but also meeting market demand.
Through the application of silicone resin in different systems, it can be seen that the addition of silicone resin significantly improves the heat resistance of the coating. The continuous baking failure test proved that the heat resistance time of the coating has been extended from the original 10h to more than 100h. On the other hand, the flexibility of the coating has also been significantly improved, and it can maintain considerable flexibility during continuous 9h use. Sex.
The performance of the two different silicone resins is different with different dosages. When the silicone resin accounts for 0.1 of the total amount, the flexibility of the coating can be significantly improved, but its heat resistance time is still relatively low, about 50 hours. But when the ratio is increased to 0.3, the service life of the coating can exceed 100h. This shows that the increase in the content of silicone increases its graft ratio with epoxy resin, so that the coating can maintain good performance in high temperature environments.