Innovative Self-Initiating UV-Curable Polyurethane Dispersions

By Laurie Morris, Terri Carson

Waterborne (WB) UV-curable polyurethane dispersions (PUDs) are the binders of choice in many industrial wood applications. These resins are formulated with photoinitiators that absorb energy and initiate consecutive free radical-curing reactions. Traditional photoinitiators include both Type I (photo cleavage) and Type II (H- abstraction) classes, which are effective for surface curing.¹

Because these products are classified as environmentally damaging (toxic to aquatic life) and can be a health hazard (suspected carcinogen), it is essential to fully react these components during curing because of potential migration of unreacted residual amounts. Such concerns are especially important considering the use of these materials for skin – or food-contact applications.

New-generation UV-curable PUDs have been developed with initiating sites based on Type II photoinitiators incorporated into the backbone of the polymer. These new self-initiating (SI) polymers have been evaluated for use in industrial wood applications and benchmarked against traditional WB UV PUDs formulated with both conventional and polymeric photoinitiators.

The performance of both clear and pigmented coatings has been investigated. A series of five SI WB UV resins has been developed. These polymers are SI versions of existing WB UV resins. These WB UV resins are all acrylic/polyester polyurethane dispersion hybrids with a minimum film formation temperature (MFFT) of approximately 0 oC. Table 1 summarizes the physical properties and characteristics of the resins evaluated.