Starch bound paper

A non-asbestos flexible sheet material of thickness 0.1-0.5 mm comprising a matrix of unfired ball clay which is reinforced by (1) vitreous fibers derived from wool-form material, (2) rayon fibers as additional reinforcement, and by (3) cellulose web-forming fibers, the whole being bound together by hydrolyzed starch;

• said flexible sheet material being made by dewatering on a water-permeable conveyor a layer of aqueous slurry of unfired ball clay, wool-form vitreous fibers, cellulose web-forming fibers and hydrolyzed starch, and compressing and drying the dewatered layer;
• said aqueous slurry containing, by weight of solids content,
• ______________________________________ ball clay 45-70% vitreous fibers 20-40% cellulose [organic] web-forming fibers of freeness 60-90.degree. (Schopper-Riegler) 3-15% rayon fibers 1-10% hydrolyzed starch 2-6% ______________________________________
• and said flexible sheet material having a degree of flexibility such that a specimen thereof measuring 50 mm.times.230 mm, with the 230 mm side parallel to the grain of the material, shows no evidence of breaking when bent through 180.degree. around a mandrel of 50 mm diameter, with the use of just enough force to keep the specimen in contact with the mandrel.