Method of manufacturing paper or cardboard products

Claim 1

A method of manufacturing a paper or cardboard product of improved strength characteristics which method comprises in sequence the steps of mixing an aqueous solution or dispersion of a cationic starch which contains primary, secondary or tertiary amino groups or quaternary ammonium groups and has a nitrogen content ranging from about 0.1 to about 0.25% by weight, with an aqueous suspension of a kaolinitic clay filler which contains not more than 50% by weight of particles smaller than 2 microns and not more than 35% by weight of particles smaller than 1 micron, to form a mixture containing flocs consisting essentially of starch and clay filler; thereafter adding the mixture thus obtained to an aqueous stock of cellulosic fibres to form a furnish containing the flocs of starch and clay filler, and the cellulosic fibres; and then forming the furnish into a paper or cardboard product; wherein the product of the rate at which shear is applied to, and the period for which the shear is applied to, said flocs during the formation of said mixture and said furnish is such that the flocs are reduced in size sufficiently to enable substantially all of the mixture to pass through a No. 200 mesh British Standard sieve but not so much that more than 90% of the mixture can pass through a No. 300 mesh British Standard sieve.

Claim 2

A method of manufacturing a paper or cardboard product of improved strength characteristics which method comprises in sequence the steps of mixing an aqueous solution or dispersion of a cationic starch which contains primary, secondary or tertiary amino groups or quaternary ammonium groups and has a nitrogen content ranging from about 0.1 to about 0.25% by weight, with an aqueous suspension of a kaolinitic clay filler which contains not more than 50% by weight of particles smaller than 2 microns and not more than 35% by weight of particles smaller than 1 micron, to form a mixture containing flocs consisting essentially of starch and clay filler; thereafter adding the mixture thus obtained to an aqueous stock of cellulosic fibres to form a furnish containing the flocs of starch and clay filler, and the cellulosic fibres; and then forming the furnish into a paper or cardboard product; wherein the product of the rate at which shear is applied to, and the period for which the shear is applied to, said flocs during the formation of said mixture and said furnish is such that the flocs are reduced in size sufficiently to enable substantially all of the mixture to pass through a No. 200 mesh British Standard sieve but not so much that more than 90% of the mixture can pass through a No. 300 mesh British Standard sieve.