Process of adding a polyethylene iminecalcium carbonate filler to cellulosic fibers and paper thereof

Calcium carbonate and other water-insoluble metal carbonates are treated with an aqueous polyalkylene imine solution to yield improved fillers. The treatment may be carried out by adding the imino compound to either, an aqueous solution of the metal salt and then precipitating by the addition of an alkali metal or ammonium carbonate solution, or to an aqueous suspension of the stirred carbonate. An alternative treatment comprises adding the monomeric imine to a suspension of the carbonate and polymerizing the imine on the surface of the carbonate in known manner. The imino compound may be polyethylene imine having a degree of polymerization between 200 and 1500, the amount used being between 0.05% and 1% by weight based on the carbonate. All examples refer to calcium carbonate modified with polyethylene imine. Magnesium and barium carbonate are also specified.ALSO:An improved filler for paper comprises calcium carbonate or other water insoluble metal carbonates which have been surface treated with a polyalkylene imine e.g. polyethylene imine (see Division C1). An example describes the addition of a paper pulp of 50% Hardwood Soda Pulp and 50% Softwood Bleached Sulphite Pulp which had been beaten to a freeness of 30 DEG S.R. being added to a suspension of the above treated carbonate. Paper sheets made from resulting pulp contained 13.41% of calcium carbonate which corresponds to a retention of 51.8%.