Polyurethane dispersions are aqueous-based systems consisting of PU particles ranging from 50 to 500 nm in diameter, frequently with some additional organic solvent present. The PU particles typically comprise from 30 to 45 weight percent of the total dispersion (% solids). The Dow Chemical Company produces PUDs using a patented, continuous mechanical dispersion process DisPURsa**.1,2 This process allows the production of solvent-free PUDs with high solids levels (>50%). Solvent-free PUDs permit lower production costs as well as facilitating the ability to meet environmental regulatory pressures. In addition, these PUDs can be prepared from a variety of polyols (i.e. polyester, polyether, etc.) and with either aliphatic or aromatic isocyanates. The latitude that is provided by this process allows the production of a wide range of materials to meet a broad range of cost/performance targets.
Although PUDs have been commercially available for many years, their use has been limited due to their higher cost. The continuous dispersion process can reduce the overall cost of the PUD either through the use of lower-cost raw materials or a lower process cost. However, if the usage of PUDs is not established for a given application, it will require the development of additional formulation expertise to take full advantage of the benefits of the PU polymer. It is important to note that PUDs do not behave in a similar manner as solvent-based PU systems or even other aqueous SB latex materials. The objective of this paper is to establish an understanding of PUDs and to aid in the formulation science particularly in coatings applications.