Corrugated paperboard strength enhancing process

A process for increasing the strength of combined corrugated paperboard using a strength enhancing resin, comprising:

• providing a fluted medium having side edges and flutes extending transversely between the side edges, the flutes having flute tips, flute troughs and flute side walls between the flute tips and flute troughs;
• moving the fluted medium in a direction with the flutes extending transversely to the direction of travel of the medium;
• applying a preselected amount of uncured strength enhancing isocyanate resin to the moving fluted medium after it has been fluted so as to create continuous spaced apart columns of resin in the fluted medium of a first concentration extending transversely relative to the direction of travel of the fluted medium, said resin extending from one side edge to the opposite side edge of the fluted medium, said resin being applied so as to create bridging areas of resin in the fluted medium of a second concentration lower than the first concentration and extending between the continuous columns of resin;
• adhesively securing at least a first liner to the fluted medium;
• and
• curing the isocyanate resin to harden to the resin with columns and bridging areas in the fluted medium and so as to provide enhanced strength to the paperboard.