US Patent 7348067 Composite paperboards and method of making composite paperboards

A laminate composite sheet comprising a two-ply base layer comprised of a bottom ply and a top ply, wherein the bottom ply is comprised of unbleached cellulosic fibers and wherein the top ply is comprised of bleached or brightened cellulosic fibers and a further layer attached to the top ply with a layer of adhesive; said further layer having a top and a bottom surface, said further layer selected from the group consisting of paper or film; said layer of adhesive containing no pigment, and said top surface of said further layer having no coating.