Reactive Diluents For High Performance Polyurethane Coatings
Most of the formulators often come across a question: How to develop a high-solids
polyurethane system with low viscosity for comfortable application, as well as unbelievable performance after curing process since voc component in paints and coatings became the major target of regulations.
One answer to this question is the employment of low molecular weights polyols to deliver a lower viscosity formulation that requires less solvent. Unluckily, these reductions in molecular weight sometimes lead to systems that cure too quickly and unable to perform well in the field. These polyols pose a danger of high intrinsic viscosities without reductions in molecular weight which in turn makes it very much difficult to eliminate solvent from the formulation.
On the other hand, reactive diluents are low viscosity co reactants that are developed specifically to diminish VOCs with the help of a reaction with the polymer matrix. They are similar to solvents as they reduce polymer viscosity, but they do so without augmenting VOCs. Reactive diluents generally take the form of blocked or delayed sources of active hydrogen. For example Aldimines and ketimines are block amino compounds. Oxazolidines are also a part of blocked amino alcohols.
Reactive diluents result in higher solids and lower viscosity. This quality often goes well for error-free applications of higher-solids coatings. A possible new light for reactive diluents is the use of different functional moieties to effect cure of coatings. Today, high solids coatings mainly rely on the chemistry of hydroxyl functional groups.
There is a huge need for the development of new technologies in the coatings industry to cure thermo set coatings due to VOC reduction requirements explained by regulatory agencies. This can be attained by lowering resin molecular weight. It is well known that reducing molecular weight helps in attaining the desired goal of high-solids coatings, but on the other hand it makes formulating and curing of these coatings more difficult.