Polyurethane Dispersion Chemistry
Polyurethane dispersions were developed several decades ago to
address the increasing environmental demands
on the adhesive industry to produce adhesives containing
little or no solvent.
These types of products are aqueous, anionic dispersions of high
molecular weight aliphatic polyester polyurethanes, which are especially suitable
for the manufacture of heat activated adhesives. They are high performance adhesive
raw materials comparable to polyurethane resins used in solvent-based adhesives.
A bit of chemistry:
- In the first step, a prepolymer is made from the
reaction between an aliphatic polyester polyol and an aliphatic diisocyanate,
which is then diluted with acetone.
- The introduction of anionic groups, such as
sulfonates, enables this prepolymer to be dispersed in water.
- The acetone is finally removed from the emulsion
by distillation and then recycled for further production. Some types of products
are also manufactured through an acetone-free process.
Crystallization of polyurethane dispersions:
Through cooling of the adhesive film and crystallization of the PU, a high initial
bond strength is obtained after a short time, even with one-component processing.
Moreover, the tackiness of these systems can be switched on and off, enabling a
highly effective production process.