Manufacture of strong, lightweight carrier granules

Abstract

Method for manufacturing carrier granules. The method forms a mixture comprising fibers, mineral filler, and binder. The mixture contains 32-45 weight-% cellulose fibers having a bulk density of less than 20 pounds per cubic foot, at least 35 weight-% of which fibers are retained on a 50-Mesh U.S. Sieve Series screen. The fibers have a moisture content of less than 15 weight-%. The mixture also contains 53-65 weight-% mineral filler having a moisture content of less than 12 weight-% and a bulk density of less than 65 pounds per cubic foot. In addition, the mixture contains 3-7 weight-% binder. The mixture is agglomerated by conditioning and agglomerating it in a pin mixer to form small particles followed by agglomerating it in a disc or pan pelletizer to form substantially spherical granules. The method then dries the granules to a moisture content of less than about 5 weight-%, and screens the granules to select granules that pass through a 10-Mesh U.S. Sieve Series screen but are retained on a 40-Mesh U.S. Sieve Series screen. The carrier granules have a bulk density of less than 40 pounds per cubic foot and a Resistance to Attrition of at least 95%.

1 . A carrier granule comprising 
 32-45 weight-% of cellulose fibers having a bulk density of less than 20 pounds per cubic foot, wherein at least 35 weight-% of said fibers are retained on a 50-Mesh U.S. Sieve Series screen,    53-65 weight-% mineral filler having a bulk density of less than 65 pounds per cubic foot, and    3-7 weight-% binder,    wherein said granule passes through a 10-Mesh U.S. Sieve Series screen and is retained on a 40-Mesh U.S. Sieve Series screen, said granule has a moisture content of less than 5 weight-%, said granule has a Resistance to Attrition of at least 95%, and said granule has a bulk density of less than 40 pounds per cubic foot.    
   
   
       2 . The carrier granule of  claim 1 , wherein said granule has a bulk density of 25-30 pounds per cubic foot.  
   
   
       3 . The carrier granule of  claim 1 , wherein the mineral filler is selected from the group consisting of kaolin, titanium dioxide, sodium bicarbonate, calcium carbonate, lime, fly ash, dolomite, gypsum, and mixtures thereof and wherein the mineral filler has a particle size range within the range 10 to 500 microns.  
   
   
       4 . The carrier granule of  claim 1 , wherein the binder is selected from the group consisting of granules of superabsorbent polymer, water-soluble starch, acrylic polymer, polyvinyl acetate, guar gum, and mixtures thereof, and wherein at least 70% of the binder granules pass through a 200-Mesh U.S. Sieve Series screen.  
   
   
       5 . The carrier granule of  claim 1 , comprising 35-40 weight-% of cellulose fibers at least 35 weight-% of which are retained on a 50-Mesh U.S. Sieve Series screen, 54-60 weight-% calcium carbonate having a bulk density of about 60 pounds per cubic foot, and 5-6 weight-% unmodified starch binder, said granule having a bulk density of 25-30 pounds per cubic foot.  
   
   
       6 . A method for making a carrier granule of  claim 1 , which method comprises the steps of: 
 forming a mixture comprising 32-45 weight-% cellulose fibers having a bulk density of less than 20 pounds per cubic foot and at least 35 weight-% of which are retained on a 35-Mesh U.S. Sieve Series screen, said fibers having a moisture content of less than 15 weight-%, 53-65 weight-% mineral filler having a moisture content of less than 12 weight-% and a bulk density of less than 65 pounds per cubic foot, and 3-7 weight-% binder;    agglomerating said mixture by conditioning and agglomerating the mixture in a pin mixer to form small particles followed by agglomerating the mixture in a disc or pan pelletizer to form substantially spherical granules;    drying said granules to a moisture content of less than about 5 weight-%; and    screening said granules to select granules that pass through a 10-Mesh U.S. Sieve Series screen and are retained on a 40-Mesh U.S. Sieve Series screen.