Polyurethane Dispersion Sunscreen Water Resistance

The patent changes the chemical composition parameters by using specific polyurethane prepolymers with controlled molecular weight (1000-10000 g/mol) and specific functional groups (isocyanate groups), along with amino-functional compounds containing sulfonate groups, to achieve water resistance without the unpleasant feel of conventional formulations. This parameter optimization allows the formulation to maintain water resistance while improving spreadability and skin comfort.

The patent creates a composite system by combining polyurethane prepolymers with amino-functional compounds containing sulfonate groups. This composite approach produces a synergistic effect where the polyurethane provides film-forming and water resistance properties while the amino-functional compounds with sulfonate groups enhance water solubility and prevent the waxy/sticky feel, achieving both water resistance and ease of application.

The patent converts the typically harmful hydrophobic property into a benefit by using polyurethane prepolymers that form water-resistant films while incorporating amino-functional compounds with sulfonate groups that provide hydrophilic character. This conversion allows the formulation to achieve water resistance without the balling effect and sticky feeling associated with conventional hydrophobic film formers.

The patent applies local quality by having different components perform different functions within the same formulation: the polyurethane prepolymer provides localized water-resistant film formation, while the amino-functional compounds with sulfonate groups provide localized hydrophilicity and prevent aggregation. This spatial differentiation of properties eliminates the balling effect while maintaining water resistance.