Isocyanates have poor water solubility and generally require organic solvents to dissolve them. In recent years, with increasingly stringent environmental regulations and people's awareness of environmental protection, the emission of organic volatiles from traditional solvent-based coatings and adhesives has been increasingly restricted, and water-dispersible isocyanates have shown importance for the applications in the above-mentioned fields. They are currently mainly used as cross-linking components to prepare excellent water-based two-component coatings, or as additives in water dispersion adhesives.
Water-dispersible isocyanates can be roughly divided into two categories: ionic and non-ionic. Non-ionic isocyanates are mainly modified with polyethers. Although polyether-modified isocyanate has gained wide market acceptance in most applications, its disadvantage is that it requires a high content of polyether to give the isocyanate good water dispersibility. In addition, in order to ensure its complete dispersion in water, Need to resort to greater shear force.
In order to overcome the above shortcomings, researchers have introduced hydrophilic ionic groups to achieve hydrophilic modification of isocyanates, such as carboxyl groups, but the storage stability of these products is not very good; in addition, hydroxy sulfonic acids or salts have also been modified. Used to modify the isocyanate, but it will cause the color of the isocyanate to be obviously yellow, which prevents these products from being used as a cross-linking component in high-quality coating systems. Later, Bayer’s researchers used 3-(cyclohexylamine) propanesulfonic acid (CAPS) and 2-(cyclohexylamino)-ethanesulfonic acid to prepare modified isocyanates. The resulting isocyanates do not require high shear. The force can be uniformly dispersed in water, and the sulfonate-modified isocyanate system neutralized by tertiary amine has good storage stability [1].
Although the sulfamic acid-modified isocyanate has the advantages of excellent water dispersibility and good storage stability, the researchers at Bayer pointed out that other sulfamic acids with similar structures to CAPS and 2-(cyclohexylamino)-ethanesulfonic acid It cannot react with isocyanate under more severe conditions. The researchers of Wanhua Chemical broke the above-mentioned technical prejudice through process improvement, and realized the preparation of multiple sulfamic acid-modified isocyanates with similar structures to CAPS and 2-(cyclohexylamino)-ethanesulfonic acid [ 2].
In summary, after years of development, a variety of water-dispersible isocyanates have come out. In terms of performance, sulfamic acid modified products have certain advantages over other modified products.