Reactive polyurethane hotmelts are produced by converting a mixture of different (polyester-)polyols with a surplus of a polyisocyanate component. This results in isocyanate-terminated prepolymers with an NCO-content of typically 2 to 5%.
Reactive polyurethane hotmelts combine the properties of regular or conventional hotmelts with the advantages of chemically crosslinking adhesives. Apart from an improved temperature and creep resistance they offer the following advantages:
Solvent-free applications
Moderate viscosity at application temperature
Improved solvent and hydrolysis resistance
Good adhesion to numerous substrates
High initial bond strength
Bayer MaterialScience offers a large range of raw materials for the production of these reactive polyurethane hotmelts.
Desmodur® polyisocyanates and Desmodur E® prepolymers
Due to the relatively low vapor pressure - also at high application temperatures of reactive polyurethane hotmelts (100 – 170 °C), usually a monomeric MDI or a modified MDI serves as polyisocyanate component.
Liquid at room temperature, contains C3-ether- and urethane groups
For specific applications, particularly when lightfast adhesives are required, Bayer MaterialScience offers a wide variety of raw materials based on aliphatic polyisocyanates:
For the formulation of very low-emission reactive polyurethane hotmelts Bayer MaterialScience hat developed specific prepolymers. With these products adhesives with a residual content of monomers (content of non-polymer-bound isocyanates) of less than 0,1%. These prepolymers make possible to produce reactive polyurethane hotmelts that comply with the upcoming european regulation R40 for the labeling of MDI-containing products with a free MDI-content of more than 1%
