Definition

Sizing is a characteristic pertaining to the sheet’s ability to resist water penetration and absorption.

Influence

Most of the combining, joint-making, and sealing adhesives employed in the manufacture and use of corrugated products are water-based. Thus, the rate at which linerboard will absorb water can affect the quality of corrugator bonding, manufacturer’s joints, and the glueability of boxes on packaging lines. Sizing may also affect the printability of linerboards with water-based flexographic inks. While adhesive and ink formulations can be modified to suit high, moderate, or low levels of substrate sizing, problems generally arise when the range of linerboards used varies widely in sizing characteristics.

Potential Problems

Linerboards that are slack-sized (very bibulous, or prone to absorb water) on the wire side(bottom) may dewater corrugating adhesives before the gel temperature is reached, leaving insufficient water to swell the starch granules, resulting in a weak, "chalky" bond.

Linerboards that are hard-sized (not bibulous) on the wire side may inhibit penetration of the adhesive into the fiber structure, resulting in a poor bond with little fiber pull.

Weak glue-lap or case-seal bonds that pop open readily can occur when linerboard felt-side surfaces absorb adhesive rapidly, leaving little glue available to form a bond with the surface brought in contact with the one to which the glue has been applied. Linerboards with hard-sized top surfaces can influence the speed with which glued manufacturer’s joints and glued or gummed tape case seals can be made.

Printing of the same water-based flexographic ink on surfaces of widely differing absorbencies can result in color variation. Considerably greater amount of ink will be required on the more absorbent surface to achieve the same color density. Less absorbent surfaces may require machine speed reductions to avoid smearing or tracking of the ink.

Source
McGrattan, W. "Key characteristics of linerboard, corrugating medium, and roll stock mechanical condition and their influence on the manufacture of corrugated products, part 1." Tappi Journal (1990): 99-108.

Back to Specifications