The binder may be a natural, modified natural or synthetic water-insoluble resin, e.g. a cellulose derivative such as ethylcellulose, cellulose ester, e.g. cellulose nitrate, a polymer derived from ??,??-ethylenically unsaturated compounds such as polyvinyl chloride, after-chlorinated polyvinyl chloride, a copolymer of vinyl chloride and vinylidene chloride, a copolymer of vinyl chloride and vinyl