The water soluble polymer may include natural polymers or modified products thereof such as gelatin, casein, starch, gum arabic, sodium alginate, hydroxyethyl cellulose, carboxyethyl cellulose and the like; polyvinyl alcohols; complete or partially saponified products of vinylacetate and other monomers; homopolymers or copolymers with other monomers of unsaturated carboxylic acids such as (meth)ac