No.9: Characteristics and Uses of Polyurethane Resin

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Key Points

Urethane resin is used in 1-component air-drying paints and, like 2-component or blocked urethane paints, it produces a strong, flexible, and resilient film with excellent wear resistance, adhesion, chemical resistance, and solvent resistance.

1. What is Polyurethane Resin? 

Polyurethane resin is a type of resin where polyol and polyisocyanate are bonded together through urethane links, and the structure of the cured film is called polyurethane. Polyurethane resin is obtained through reactions between long-chain diols and polyisocyanates. There are various types of polyurethane resins, including moisture-curing, lacquer-type, and water-based emulsion-type resins. Moisture-curing resins retain isocyanate groups and cure by reacting with moisture in the air. Oil-modified polyurethane resins are also available. 

2. Features 

Polyurethane resin forms a resilient and durable film with excellent wear resistance, adhesion, chemical resistance, and solvent resistance. This is due to the strong urethane bonds in the film, some of which are linked by hydrogen bonds to form hard segments that connect with flexible soft segments. The hard segments create a pseudo-crosslinking structure, maintaining the film’s overall structure even with stretching of the soft segments, making it resistant to plastic deformation. Additionally, strong adhesion is achieved through hydrogen bonds between the urethane bonds and the substrate’s surface. However, when using polyisocyanates containing benzene rings like TDI or MDI, one must be cautious of yellowing and whitening of the film. 

3. Usage 

Moisture-curing polyurethane resins are sensitive to humidity and require the use of molecular sieves for moisture removal. They are mainly used as clear coats. Water-based emulsion types are suitable for floor coatings and automotive chip-resistant primers. Oil-modified types utilize unsaturated bonds and are used as air-drying paints with oxidation polymerization, similar to medium to long oil alkyd resins.