Bonding Success
Deep structural rupture within the paper or board layer during a peel or tear test confirms that the adhesive bond is stronger than the internal strength of the substrate itself. A substrate fiber tear occurs when an attempt to separate the laminate forces a fracture that runs deep into the paper fibers, pulling them completely away from the paper web. This outcome is the target failure mode for folder-gluer operations, carton sealing, and corrugated box manufacturing.
It indicates that the adhesive has successfully penetrated and anchored itself into the paper.
Paper Characteristics
Extent of this tear depends heavily on the internal bond strength of the paperboard, as measured by standard tests like the Scott Bond method. Low-density boards or recycled papers are easier to tear because their fibers are less tightly bound together than those in high-density, virgin kraft boards. When adhesive penetration is shallow, the tear might only affect the top surface, resulting in a superficial fiber pull rather than a deep tear.
Ensuring proper adhesive viscosity and open time is critical to achieving a full tear.
Line Verification
Converters monitor the percentage of fiber tear during quality control checks to confirm that the package will not fail at the glue line. A tear rate of over eighty percent is usually required to pass inspection.
