In recent years, with the restrictions of laws and regulations on environmental protection and people’s attach importance to health, water-dispersible polyisocyanates have received more and more attention. They are mainly used as cross-linking components for the preparation of water-dilutable two-component polyurethanes, or used as an additive in aqueous dispersion adhesives and crosslink aqueous dispersions in textile finishing or formaldehyde-free textile printing inks.

The researchers not only explored the basic formulation, but also tried to prepare the water-dispersible polyisocyanate by adding an ionic group for hydrophilic modification.

1. Improvement of the basic formula

A water-dispersible polyisocyanate was prepared by using 2-3 wt% of 3-cyclohexylaminopropanesulfonic acid (CAPS) under the reaction conditions of 90°C in an amount of 110% of N,N-dimethylcyclohexylamine. In order to further obtain water-dispersible polyisocyanate which is excellent in water dispersibility, storage property and coating film performance, hydrophilic modification is continued by using a nonionic hydrophilic modifier: 5-7 wt% of PEGME 400 is continuously used at 60°C (CAPS/PEGME 400=40wt%), the hydrophilic modification can effectively improve the water dispersibility of polyisocyanate.

Compared with commercially available high quality curing agents of the same type, the water dispersible polyisocyanate has good storage stability, storage at room temperature for 6 months and 50°C for 4 weeks, and the coating period is more than 3 hours, with good transparency and heat stability. In the process of lacquering, the dry speed of the coating film is related to the amount of water-dispersible polyisocyanate, and the hardness and gloss index are positively correlated with the amount of water-dispersible polyisocyanate.

2. Add ionic groups for hydrophilic modification

The ion-modified group includes carboxyl group, sulfuric acid group, hydroxyl group, hydroxysulfonic acid, etc. Patent CN1429240A reported that CAPS modified polyisocyanate can achieve fine dispersion in water and product storage stability. Specific example is as follows: 950g of polyisocyanate were stirred with 50g of CAPS, 29g of dimethylcyclohexylamine and 257g of 1-methoxypropan-2-yl acetate under dry nitrogen at 80°C for 5 hours. After cooling to room temperature, a colorless transparent polyisocyanate solution was obtained. The polyisocyanate modified with CAPS (CAS 1135-40-6) exhibits certain advantages over other ionic or nonionic modified products.

With the increasingly strict environmental protection requirements and the increasing awareness of environmental protection, water-based environmentally friendly coatings are an inevitable trend in the future coatings market. Two-component water-based polyurethanes have broad prospects, and water-dispersible polyisocyanate curing agents as a component still have potential for excavation, which not only meets the needs of sustainable development, but also further protects the safety of workers and consumers. We believe that in the future, the market acceptance of water-based coatings will be further enhanced, gradually surpassing solvent-based coatings.