Enhanced crush strength construction multi-grade paperboard tubes

摘要

The invention provides multi-grade spirally wound paperboard tubes of enhanced flat crush strength construction. The multi-grade spirally wound paperboard tubes (10) of the invention include a plurality of structural paperboard plies having at least two predetermined densities including a lower density and a higher density wherein the higher density is at least about 3% greater than the lower density. The cylindrical bodywall (12) is defined in radial cross section by at least one centrally located paperboard layer (26,28) disposed between at least one radially inwardly located structural paperboard layer (30,32) and at least one radially outwardly located structural paperboard layer (22,24). The centrally located paperboard layer is formed from the higher density paperboard and the inwardly and outwardly located structural paperboard layers are formed from lower density paperboard.