Techniques for bonding of densified liners, Technical Information Paper TIP 0304-40 (2008)
In the quest to provide the end user with high-performance corrugated containers which achieve better stacking strength, the mills have developed a range of liners that have superior ring crush levels. If properly combined, they will yield high-performance top-to-bottom compression characteristics. This property is particularly important as the end use demands of stronger boxes, at reduced fiber levels, that will survive taller than ever before stacking levels in modern high-density warehouses.
Mills utilize a number of techniques to achieve higher compression strength, including improved fiber orientation and cross-linking, and high density formation of paper fibers through high loading rates of their presses. This densification process compresses the fibers together tighter, thus increasing the sheet’s density and strength.
Densified sheets as defined above are often much less porous than the typical kraft liners utilized in the past. Decreased porosity levels can translate into reduced levels of adhesion penetration, potential bonding problems, and box performance failures. Typical adhesives formulated to bond conventional kraft liners may appear to bond well initially, but can delaminate after curing.
Densified liners are thought to bind up their moisture differently than standard or more open liners. These liners require reduced heat transfer levels and preheater wrap techniques to prevent premature adhesive gelatinization and brittle bond formation. This Technical Information Paper describes techniques to successfully combine a range of densified liners now available to the corrugated industry.