A usable binder includes a water-soluble polymer and latex, and specific examples include the followings: polyvinyl alcohol or a denatured compound thereof, starch or a denatured compound thereof, gelatin or a denatured compound thereof, and gum Arabic; a cellulose derivative such as carboxymethyl cellulose, hydroxyethyl cellulose and hydroxypropyl methyl cellulose; vinyl copolymer latex such as S