No.8: Characteristics and Uses of Polyisocyanate

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Key Points

Polyisocyanate is used as a curing agent in paints with polyol resins as the main component, often in the form of high molecular weight modified versions or blocked isocyanates. 

1. What is Polyisocyanate? 

Polyisocyanate is a highly reactive functional group containing isocyanate groups. “Poly” in its name does not refer to polymers but rather signifies its multifunctionality. This functional group consists of nitrogen, carbon, and oxygen atoms, making it highly suitable for chemical reactions. 

2. Features

Common monomers with isocyanate groups are known for their high toxicity and require careful handling. They primarily react with hydroxyl groups to create urethane bonds, resulting in coatings with high strength, wear resistance, excellent adhesion to substrates, and resistance to chemicals and solvents. 

3. Usage

Isocyanates are primarily used as curing agents in two-component air-drying paints with polyester or acrylic polyols as the main component. Usually, high molecular weight modified isocyanates are chosen for this purpose. They are not suitable for water-based paints as is, so they are reacted with alcohols or phenols, called blocking agents, to produce blocked isocyanates. This makes them suitable for one-component heat-curing paints and water-based paints. The dissociation temperature of blocking agents varies by type, with alcohols being around 170-210°C, and phenols and caprolactam around 140-145°C. 


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