Лако-красочные материалы — производство

Polyurethane reactive hot melts are 100% solid, hot-melt thermoplastic prepolymers that moisture cure slowly after application. Conventional hot melts are known for their quick setting, excellent green strength, ease of application, and low toxicity. Their primary limitation is low heat resistance (at elevated temperatures, the adhesive will soften and flow) and poor adhesion to some substrates, due to insufficient wetting. The use of a polyurethane prepolymer with low levels of free isocyanates as a hot melt offers distinct advantages: initial green strength is still achieved, and in addition, the isocyanate will moisture cure slowly, converting the thermoplastic adhesive to a thermoset. There are a number of recent patents on reactive hot melts [84-87]. The tensile strength of the adhesive increases, heat resistance is improved, and the final cured adhesive will not flow at elevated temperatures [88]. A limitation of this technology is the need for porous substrates or bond designs that will allow the diffusion of moisture into the adhesive so that moisture curing will occur. The adhesive itself must be protected from moisture prior to use. This technol­ogy should be applicable to assembly line operations which require an adhesive that gets high initial green strength.