Soybean protein In Paper Coating
Soybean protein is a very important binder type, especially in North America. It has properties very similar to those of casein. Isolated soybean proteins are hydro¬lyzed, isoelectric proteins. They are used in the form of alpha and delta proteins with four different viscosities (extra low, low, medium, and high). The viscosity refers to the dissolved soybean protein, the solvent of choice being aqueous ammo¬nia (26 Bé).
Proteins dissolved in this way exhibit very low sensitivity to water after drying. Like casein, soybean protein is mostly used as a mixture with polymer dispersions. This combination permits the preparation of coating colors with high solids content and a relatively low viscosity. Solids contents of ca. 60 %, suitable for blade coaters, can be achieved.