Laminated paperboard or pasted chipboard, which has two or more flat plies glued together, is normally used for coverboards in books, loose-leaf binders and as panels in gameboards and the like, which require the characteristics of rigidity, strength, stability, smooth outer surfaces, and resistance to bending and folding. In order to provide these characteristics, the laminated paperboard or pasted chipboard is made of flat layers glued together to form a solid mass which is relatively heavy and is costly to produce because of the amount of paperboard required.
To overcome these problems, corrugated paperboard has been utilized, since it includes an internal corrugated layer of paperboard to replace one or more of the flat layers and provides internal spaces. However, such corrugated paperboard does not have the rigidity and strength to replace solid laminated paperboard which is typically used for coverboards in loose-leaf binders, books, panels for gameboards, and the like. In particular, such corrugated paperboard, although light in weight, is easily folded and bent. It is also unsatisfactory in providing a smooth outer surface, as the ridges of the fluted or corrugated ply are transferred through the thin outer liners or plies commonly used in corrugated paperboard. Thus, corrugated paperboard is not satisfactory in replacing solid laminated paperboard to reduce its weight and cost for such purposes.
In addition, it has also been known to use a form of corrugated paperboard, referred to in the industry as E flute corrugated, which has approximately 295 corrugations per lineal meter of paperboard. This relatively high number of flutes, compared to other commonly-used corrugations, is not sufficiently resistant to bending and folding and does not have sufficiently smooth outer surfaces and, therefore, cannot be used to satisfactorily replace solid laminated paperboard typically used in loose-leaf binders, books, gameboards, and the like.
It has also been known to use heavier weight outer plies with an E Flute corrugated center ply to add smoothness and rigidity. Such paperboard is still not sufficiently resistant to bending and folding, and the ridges of the corrugated center ply still transfer through the outer ply to create an uneven outer surface.