Due to their technological advances, water based polyurethane dispersion is one of the most increasing choice for the surface coating industry. Also known as PUDs (polyurethane dispersions), they contain lower amount of volatile organic compounds and hazardous air pollutants. This makes water based PUDs a great alternative for solvent based analogs. They are formulated as baked or air dried industrial coatings applicable for both rigid and flexible substrates, including paper, fabric, plastics, ceramics and leather.
The main drawback of using a dispersion is the cost of formulating it which is relatively higher. So, to compensate for this, acrylic emulsion is used as blending material. To further understand the process of making PUDs, here are the detailed steps involved.
- Polymerization process - the dispersion of polyurethane particles is done with the blend of prepolymer and dispersing it in aqueous medium. Usually, this process of polymerization is made possible by polymerizing the different ingredients of polyurethane prepolymer. These can include the hydrogen-containing compounds and water-dispersibility compounds.
- Dispersion process - this second industrial coatings step is done after the prepolymer blend has been successfully formed. The dispersion of this blend in aqueous medium can be done in various techniques, even in the same way as how polyurethane dispersion is done. One great approach is doing the dispersion without adding emulsifiers or any surfactants. This is to make the final industrial coating product have better film formation, reduced bacterial growth and less water sensitivity.
- Neutralization process - this step is necessary is water-dispersibility enhancing compounds are used during the dispersion process above. The produces carboxyl groups can be neutralised by using different agents such as ammonium hydroxide, tertiary amines, or phosphines.
- Chain extension process - while PUDs can be simply produced as such using regular prepolymer identified, they can be converted to become more complex polyurethanes. There are various organic amines that can be used as chain extenders for industrial coatings, depending on the product’s intended application.