An article to understand the research status, application and future directions of moisture-curing PUR hot melt adhesives

Introduction
reaction polyurethane (PUR) hot melt is divided into closed hot melt and wet-cured hot melt. Due to the high desolytic temperature of the former closed agent (generally higher than 100 degrees C), it causes the adhesive layer to foam, so it is only used for maintenance treatment, while the wet-cured PUR hot melt has the characteristics of both hot melt adhesive and reactive adhesive - hotter than traditional The application temperature of molten adhesive is low, the bonding strength is high after curing, heat resistance, chemical resistance, can be such as wood, ceramics, fabrics and other raw materials containing lively hydrogen and metal, glass, plastic, rubber and other finished substrates show excellent bonding properties. At present, PUR hot melt is widely used in various industries, has become one of the fast-growing adhesive varieties

. According to the China Adhesive and Adhesive Belt Industry Association, China's consumption of PUR hot melt in 2018 is about 42,000 tons, an increase of nearly 40% over 2017, accounting for about 20% of the global total consumption.
In recent
years, researchers have done a lot of work in reducing the melting temperature and viscosity of wet-cured PUR hot melts, improving initial viscosity, shortening positioning time, and enhancing product flexibility, heat resistance and flame retardant resistance.
PUR hot melt with polyols and isocyanate as the base material, with non-reactive thermoplastic resins, adhesive resins, antioxidants, catalysts, fillers and so on. In recent years, in order to further improve pur's performance, broaden its application field and meet the needs of various application scenarios, the researchers have made in-depth exploration of the physical and chemical properties of its raw material compositions and their ratio, and made great progress in research.
/PUR hot melts/
because most polyphools prepared for PUR pre-polyurethane polyols are polyester or polyether polyols. Polyester polyol main chain ester polarity is large, internal polyurethane energy is large, but easy to hydrolyze, so polyester-type PUR has better heat resistance, oil resistance, but water-resistant performance is not ideal; Therefore, many researchers try to mix the two to make up for each other.
Researchers often add thermoplastic resins (e.g. EVA, non-reactive acrylics, reactive waxes, and crystalline branched polyester polyols containing hydroxyl) to improve the positioning time of PUR hot melts, improve initial viscosity and film-forming. At present, researchers mostly by screening different raw materials and ratios to prepare different performance of PUR hot melt, to solve its slow curing speed, poor weather resistance and low initial adhesion to meet the needs of different applications.
Looking ahead to
in the future, China's wet-cured PUR hot melt research still needs to work in the following areas: reducing melting temperature, improving initial viscosity, and improving adhesive properties in a variety of applications such as flexibility, heat resistance, flame retardant resistance, hydrolysate resistance and so on. In addition, we need to further improve the preparation process and glue equipment, do a good job of supporting services, the development of more practical, convenient, intelligent production, transportation, storage and glue application equipment. While improving the performance of PUR hot melt, further reduce its production costs, so that PUR hot melt to achieve the lowest overall cost. It is believed that with the excellent comprehensive performance of wet-cured PUR hot melt, it will usher in a broader development space in the future.
.