Fiber Construction
Heavy paper sheets in this category are manufactured primarily from virgin softwood pulp to provide high tensile strength and burst resistance for corrugated boxes. The kraft linerboard provides the flat outer facing of a corrugated board structure. It provides a durable surface for printing and protects the package contents from mechanical damage during distribution.
Pulping Method
Production utilizes the sulfate chemical process to digest wood chips under high temperature and pressure, which dissolves the lignin and preserves the long cellulose fibers. This process yields a pulp with high tear strength and puncture resistance. The resulting paperboard is typically brown, but it can be bleached or coated to provide a white surface for high quality graphics.
Adding a small amount of recycled fiber is common, but virgin fibers are maintained to ensure maximum stiffness and moisture resistance.
Performance Standard
Achieving the required strength necessitates controlling the moisture content and basis weight of the linerboard during the papermaking process. This sheet must resist cracking when folded along scores and must withstand high compression forces in a stacked warehouse. The material does not apply to lightweight folding cartons where high density and flexibility are required.
Standard specifications dictate the ring crush and short span compression strength for each board grade.
