Sodium alginate for paper industry
The main use for alginate in the paper industry is in surface sizing. Alginate added to the normal starch sizing gives a smooth continuous film and a surface with less fluffing. The oil resistance of alginate films give a size with better oil resistance and enhances greaseproof properties. An improved gloss is obtained with high gloss inks. If papers or boards are to be waxed, alginate in the size will keep the wax mainly at the surface. They give better coating runability than other thickeners, especially in hot, on-machine coating applications. Alginates are also excellent film formers and improve ink holdout and printability. The quantity of alginate used is usually 5-10 percent of the weight of starch in the size.
Alginate is also used in starch adhesives for making corrugated boards because it stabilizes the viscosity of the adhesive and allows control of its rate of penetration. One percent sodium alginate, based on the weight of starch used, is usually sufficient.
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