Z-Direction Density

Structural Design

Fiber plies are organized on multi-ply forming machines to place high-quality fibers on the surfaces and cheaper fibers in the center. A balanced z-direction density maintains a low-density core that keeps the board thick and stiff, while the dense outer layers provide a smooth, flat surface. This structural arrangement prevents the board from warping or twisting when exposed to moisture.

It maximizes the bending resistance of the carton without adding excessive fiber weight.

Printing Performance

Surface strength is controlled by the dense surface plies to prevent fiber lifting and delamination during printing runs. If the z-direction density is too low at the surface, high-tack offset inks can tear the fibers or pull the coating layer off the sheet. This surface failure ruins the print quality and disrupts the production run on the printing press.

Measuring this density profile ensures that each batch of paperboard holds up to the mechanical forces of high-speed printing.