PUR glue is solid at room temperature. When used, it is heated to around 120 degrees Celsius, at which point the PUR glue transforms from a solid to a liquid for dispensing or spraying applications.
PUR glue is liquid at around 120 degrees Celsius. When it is applied or sprayed onto the surface of an object, it returns to room temperature. The process of PUR glue crystallizing is called the physical curing of PUR hot melt adhesive. The adhesive force generated after the physical curing of PUR can fix and position the adhered objects.
The chemical reaction mechanism of PUR hot melt adhesive:
The main component of PUR hot melt adhesive is the isocyanate-terminated polyurethane prepolymer. Isocyanate is abbreviated as NCO in English. NCO reacts with moisture in the air to form allophanate, thereby generating adhesive strength. The specific molecular reaction is as follows:
OCN--OCN+2HOHOOC HN R NH-COOH (1)
Among them, the carbamate link (-NHCOO-) and urea link (-NHCONH-) have high polarity and constitute the rigid link of the polyurethane molecular structure in PUR hot melt adhesives.
