Dispersion Barrier Performance under Crease Compression in Folding Boxboard
Wide matrix channels and shallow penetration depth prevent polymer micro-fractures in dispersion-coated folding boxboard during creasing.
Machine Direction Fiber Orientation
Fiber Alignment
Predominant arrangement of cellulose strands parallel to the movement of the paper machine belt creates a distinct grain in the finished product. The machine direction fiber orientation occurs because the dilute pulp slurry accelerates as it exits the headbox onto the moving wire. This physical phenomenon dictates the strength and stiffness profile of the entire web.
Physics of Formation
As water is pulled through the mesh, the long fibers tend to point in the direction of the flow. While modern machinery uses shaking or jet to wire speed adjustments to randomize this, some degree of orientation is always present. This alignment makes the paper nearly twice as strong in the flow direction as it is in the transverse direction.
This orientation is a byproduct of the hydraulic forces acting on the suspension as it is discharged from the pressurized headbox.
Hygroexpansional Effect
Paper expands and contracts more across the width of the fibers than along their length. Because of this, a sheet will curl or change size more extensively in the cross direction when humidity levels fluctuate. Understanding this orientation is necessary for maintaining register on a printing press or ensuring a book block stays flat.