Method of manufacture of paperboard

Claim 1

A method of making a stiff three-ply paperboard which is substantially stiffer than three-ply paperboard of the same basis weight in which the middle ply has the same degree of fiber convolution as the outer ply, comprising the steps of: (a) preparing a conventional cellulosic papermaking fiber furnish in an aqueous carrier fluid in which the fibers are not highly convoluted; (b) preparing a treated papermaking fiber furnish in an aqueous carrier fluid in which the fibers differ from those in said conventional cellulosic papermaking fiber furnish by being characterized by twists, kinks and curls without substantial fibrillation or breakage of the fibers; (c) dispensing conventional fiber furnish onto a web-forming foraminous support where aqueous carrier fluid is drained from the dispensed conventional fiber furnish forming therefrom a first outer ply in which the fibers are not highly convoluted; (d) dispensing treated fiber furnish onto said first outer ply on said forming support forming therefrom a middle ply in which the fibers are highly convoluted and which is intimately bonded to said first outer ply to resist delamination therefrom; (e) dispensing conventional fiber furnish onto said middle ply on said forming support forming a second outer ply in which the fibers are not highly convoluted and which is intimately bonded to said middle ply to resist delamination thereof; and (f) dewatering the resulting three-ply paperboard said paperboard to thereby provide a stiff three-ply paperboard which is substantially stiffer than three-ply paperboard of the same basis weight in which the middle ply has the same degree of fiber convolution as the outer ply.

Claim 2

A method of making a stiff three-ply paperboard which is substantially stiffer than three-ply paperboard of the same basis weight in which the middle ply has the same degree of fiber convolution as the outer ply, comprising the steps of: (a) preparing a conventional cellulosic papermaking fiber furnish in an aqueous carrier fluid in which the fibers are not highly convoluted; (b) preparing a treated papermaking fiber furnish in an aqueous carrier fluid in which the fibers differ from those in said conventional cellulosic papermaking fiber furnish by being characterized by twists, kinks and curls without substantial fibrillation or breakage of the fibers; (c) dispensing conventional fiber furnish onto a web-forming foraminous support where aqueous carrier fluid is drained from the dispensed conventional fiber furnish forming therefrom a first outer ply in which the fibers are not highly convoluted; (d) dispensing treated fiber furnish onto said first outer ply on said forming support forming therefrom a middle ply in which the fibers are highly convoluted and which is intimately bonded to said first outer ply to resist delamination therefrom; (e) dispensing conventional fiber furnish onto said middle ply on said forming support forming a second outer ply in which the fibers are not highly convoluted and which is intimately bonded to said middle ply to resist delamination thereof; and (f) dewatering the resulting three-ply paperboard said paperboard to thereby provide a stiff three-ply paperboard which is substantially stiffer than three-ply paperboard of the same basis weight in which the middle ply has the same degree of fiber convolution as the outer ply.