1. The role of curing agent
The initiation of the curing reaction of low temperture cured protective coating depends largely on the participation of curing agent. Curing agent is a substance that can react chemically with the resin in the coating. In low temperature environment, specific curing agents are selected. For example, certain amine curing agents are critical for low temperature curing of epoxy resin systems. When the components of the coating are mixed, the active groups (such as amine groups) in the curing agent molecules will contact with active sites such as epoxy groups in the resin molecules. These active groups have high reactivity and can start reactions through intermolecular collisions and the formation of chemical bonds even under low temperature conditions. This chemical reaction based on active groups is the beginning of the curing reaction. Just like the "key-lock" mechanism in chemical reactions, the active groups of the curing agent are like keys that find and open the reaction sites on the resin molecules, thereby starting the entire curing process.
2. Promotion of catalysts
In addition to curing agents, catalysts also play an important role in the initiation of the curing reaction of low temperture cured protective coating. The catalyst itself does not directly participate in the reaction, but it can reduce the activation energy of the reaction. For low temperature curing coatings, commonly used catalysts include metal organic compounds. When a catalyst is added to the coating system, it will adsorb on the molecular surface of the reactants (resin and curing agent) and change the energy state of the reaction molecules. At low temperatures, the thermal motion of molecules is relatively weak, and the presence of catalysts makes it easier to carry out reactions that originally require higher energy. For example, the catalyst may change the electron cloud distribution of the reaction molecules or provide a place for the formation of reaction intermediates, so that the resin and curing agent molecules can cross the energy barrier required for the reaction at a lower temperature, thereby starting the curing reaction.
3. Influence of environmental factors
Environmental factors also have a certain influence on the initiation of the curing reaction of low temperture cured protective coating. Humidity is one of the key factors. In some coating systems, moisture may participate in the initial step of the curing reaction. For example, in some polyurethane low-temperature curing systems, trace moisture in the air can react with the isocyanate group in the curing agent to form carbamate. The heat generated by this reaction and the newly generated active substances can further promote the initiation of the entire curing reaction. In addition, although the temperature is low, as long as a certain critical temperature is reached, it can provide sufficient thermal motion energy for the molecules, so that the curing agent and resin molecules can approach each other and react. This critical temperature varies with different coating systems and is determined by optimizing the coating formula.
4. Design of coating formula
The design of coating formula is the basis for ensuring that the curing reaction starts at low temperature. Starting from the selection of resin, some resins with special structures are inherently easier to react with curing agents at low temperatures. For example, resins with more active functional groups and better molecular chain flexibility have relatively strong molecular chain mobility at low temperatures, which is conducive to contact and reaction with curing agent molecules. In addition, the ratio of each component in the formula is also crucial. A reasonable ratio of curing agent to resin can ensure that there are enough active groups to participate in the reaction while avoiding the inhibition of the reaction due to an excess of one component. The addition of additives will also affect the start of the curing reaction. For example, the presence of some plasticizers or diluents may change the viscosity of the system and the interaction between molecules, making it easier for the curing agent and resin molecules to diffuse and react with each other, thereby smoothly starting the curing reaction at low temperatures.
