Paper shredding roller for a paper shredder

A paper shredding roller, comprising:

• a rotatable knife shaft which has a polygonal cross-section;
• a plurality of circular knives provided on said knife shaft, each of said circular knives having a polygonal central through hole that corresponds with the cross-section of said knife shaft so as to permit said knife shaft to extend fittingly therethrough, each of said circular knives being provided with a number of equiangularly spaced unidirectional cutting elements, the number of said cutting elements being unequal to a number of sides of said knife shaft, said cutting knives being provided on said knife shaft in such a manner that said cutting elements of each said circular knife are displaced angularly by a predetermined angle from corresponding cutting elements of an adjacent said circular knife so that said cutting elements of each said circular knife are displaced angularly by a predetermined angle from corresponding cutting elements of an adjacent said circular knife so that said cutting elements of said circular knives are arranged in a number of helical rows that extend along said rotatable knife shaft;
• and
• a circular spacer provided on said knife shaft between every two adjacent said circular knives;
• wherein each of said cutting elements includes a cutting groove formed on a periphery of said circular knife and provided with a leading edge and a lagging edge, said cutting groove having a depth that increases gradually from said leading edge to said lagging edge and a groove bottom formed at said lagging edge thereof, each of said cutting elements further including a cutting edge formed at said cutting groove, said cutting edge having a sloping portion which extends from said leading edge to said groove bottom of said cutting groove and a substantially U-shaped curve portion which extends from said groove bottom of said cutting groove to the periphery of said circular knife.