Film Formation Mechanism of Polyurethane Coating

18th December 2023

Polyurethane coating is a type of protective coating or finish that is formulated with resin, polyisocyanate hardener, additive and solvents. It is now widely used in various industries, including automotive, wood furniture, marine, transportation. During the coating application process, polyurethane coatings form a robust film layer, providing both protection and aesthetic enhancement for the substrate.

The film formation mechanism of polyurethane coatings involves several key aspects: dispersion, curing, and crosslinking.

Dispersion: Dispersion refers to the uniform distribution of solid particles in a solvent. In the preparation of polyurethane coatings, ingredients such as polyurethane resin, solvent and additives need to be mixed and dispersed evenly through stirring or dispersion equipment. The goal of dispersion is to ensure the uniform mixing of coating components, which helps to improve stability and uniformity during coating application.

Curing: Curing is the process in which solid particles in the coating form a film layer in the solvent. During the coating application, the solvent gradually evaporates, allowing solid particles to come into contact and accumulate on the substrate's surface, forming a strong film layer. Throughout this process, there is mutual adsorption and repulsion between solid particles, contributing to the tightness and strength of the film layer.

Crosslinking: Crosslinking involves the formation of chemical bonds between molecules in the film layer. Polyurethane resin molecules in the coating contain multiple active functional groups, such as isocyanate groups (NCO) and hydroxyl groups (OH). During coating application, reactions occur between NCO and OH groups, forming urethane and urea bonds, leading to the formation of a crosslinked structure between molecules in the film layer. This crosslinked structure enhances the hardness, wear resistance, and weather resistance of the film layer, improving the quality and performance of the coating.

In summary, the film formation mechanism of polyurethane coatings includes dispersion, curing, and crosslinking. Through these processes, polyurethane coatings can create a durable film layer, providing both protection and aesthetic benefits. In practical applications, polyurethane coatings are known for their excellent weather resistance, chemical resistance and physical properties, making them widely used in construction, automotive, marine, furniture, electronics, and other industries. As scientific and technological advancements continue, the performance and application scope of polyurethane coatings are expected to expand, bringing more convenience and development opportunities to various industries.