Water-Dispersible Polyisocyanates

Water-dispersible polyisocyanates are polyisocyanates that can be dispersed (emulsified) in water. These polyisocyanate products themselves do not contain water, and most do not contain solvents. They are generally hydrophilic modified derivatives of aliphatic diisocyanates, although there are also a few hydrophilic modified PAPI (MDI) products. They are used as crosslinking agents for water-based resins such as water-based polyurethanes, forming two-component water-based resins.

These liquid hydrophilic aliphatic polyisocyanates can be emulsified in aqueous polymer dispersions. They can be used as crosslinking components for water-based polyurethanes, and also as crosslinking agents for polyvinyl acetate emulsions, polyacrylate dispersions, and synthetic rubber dispersions to improve heat resistance, water resistance, plasticizer resistance, and solvent resistance. For 100 parts by weight of a polymer dispersion with a solid content of 40% to 60%, the amount of crosslinking agent can be between 3% and 10%. The recommended dosage for Bayer’s Desmodur XO 672 is 1% to 5%. Mechanical mixing can achieve more uniform dispersion of the polyisocyanate. Tables 1-78 to 1-81 show the quality indicators or typical physical properties of water-dispersible isocyanates from several well-known manufacturers. Some emulsifiable blocked aliphatic polyisocyanates used in one-component baking paints are discussed in the “Blocked Polyisocyanates” section.

Perstorp’s Easaqua series products are self-emulsifying in water and are very easy to mix with water-based coatings. Excellent mixing can be achieved with simple hand stirring, without the need for specialized high-shear or high-speed dispersion equipment. They have excellent compatibility, fast drying, high gloss, low odor, and low viscosity. The cured resin has better hardness, which in turn improves the anti-sticking properties of the coating film. Coatings formulated with Easaqua X D 401 and X D 803 can reduce the tack-free time by 25% to 60%, thus improving production efficiency and reducing coating film defects. In addition, Trixene BI7985 from Baxenden, UK, is a water-dispersible polyisocyanate with a viscosity (at 25℃) of 250 mPa.s, a solid content of 70%, and N-methylpyrrolidone as the solvent. Its deblocking temperature is 120℃.

Huntsman Polyurethanes offers several hydrophilically modified, emulsifiable MDI (PAPI) products. These can be dispersed and diluted with water and are suitable for water-based coatings and adhesives, reducing the emission of organic solvents. The pot life after water dispersion is generally 1–2 hours.