Multi-grade paperboard winding cores for yarns and films having enhanced resistance to inside diameter reduction

DETAILED DESCRIPTION The invention provides multi-grade paperboard winding cores of enhanced resistance to inside diameter reduction during winding processes.
The multi-grade paperboard tube constructions of the invention can provide substantially improved efficiencies in film and yarn winding processes by minimizing or eliminating yarn and film loss from ID comedown failures during winding.
The multi-grade winding cores of the invention can provide winding cores of enhanced ID comedown resistance without requiring increases in tube wall thickness and/or while minimizing the necessity for using substantial quantities of resource-intensive high density paperboards.
In accordance with the invention, it has been found that tube constructions which optimize flat crush strength, or which optimize radial crush strength, do not normally result in optimization of resistance to ID reduction during winding processes.
Although not wishing to be bound by theory, it is believed that tube ID reduction, i.
e.
, comedown, is not accurately predicted based on tube strength; rather, ID reduction is more accurately predicted based on tube stiffness (modulus), at the inside periphery of the tube wall.
Tube strength tests, such as flat crush and radial crush, measure the forces causing complete failure of a tube.
However, the radial compression forces applied to a paperboard tube during a yarn or film winding process are normally much less than the radial crush strength of the tube at failure.
Nevertheless, ID comedown occurs under these conditions.
The winding cores of the invention are based on the recognition that ID comedown "failure" of paperboard tubes results from excessive radial deformation at the interior of the tube structure, and not necessarily from the complete failure, or destruction, of the tubular structure.
Because prior art winding core designs for minimizing ID comedown have been based on tube strength at failure, as determined by flat or radial crush strength tests, such prior art winding cores can still exhibit poor inside diameter stiffness, and thus poor resistance to ID comedown, during winding processes