No class film-forming does not have such a variety of properties, such as polyurethane (PU), which provide coverage with preset properties. Currently the world market is quite wide choice of raw materials for polyurethane coatings. Variation of the polyol and isocyanate components can obtain a composition suitable for coating almost any product. In each case the choice polyurethane coatings should be guided by the type of coated material and operating conditions. Polyurethane coatings can be single - and dvuhupakovochnymi. According to international classification can be divided into several groups.
First up dvuhupakovochnye system cured at normal or elevated temperatures. The second group comprises polyurethane coatings, curing at normal temperature air moisture. The third Polyurethane coatings are a group of baking, forming a coating with high temperature (100 - 150 C). The fourth group - this is a physical drying polyurethanes, which include, in particular, aqueous dispersions. The latter group include coatings based on modified polyurethanes - uralkidy oxidative drying.
Raw materials for polyurethanes are isocyanate and polyhydric alcohols. Izotsiatnym main raw material for polyurethane film-forming is 2,4-toluene diisocyanate and its mixture with 2,6-isomer. Due to the toxicity and volatility of low molecular weight diisocyanates strong, prepare a high molecular weight product with low volatility and lower toxicity (Adduct). Solvent for the prepolymer is a toluene. Dvuhupakovochnye materials, moisture curing, consist of solutions of two components - a prepolymer and a catalyst. For high speed coating the interaction of prepolymer with atmospheric moisture as a catalyst for use triethanolamine. This was dissolved in a solvent mixture - glycol, ethyl acetate, butyl acetate, xylene and etilglikolatsetata. Glycols introduced to improve the solubility of triethanolamine, at the same time they participate in the curing of the additional formation of urethane cross-links. Catalyst solution is injected into the prepolymer prior to use. At cured polyurethane material flows dvuhupakovochnyh series of chemical reactions, but the equivalent ratio of NCO groups and OH is the predominant reaction of urethane.