Polypropylene Surface Film Stress Response under Folder Gluer Dynamic Tension
Dynamic tension on folder-gluers strains polypropylene film across score radii, where excessive speed triggers stress whitening and adhesive shear failure.
Crease Shoulders
Structural Geometry
Raised ridges formed on the top surface of a paperboard sheet flank the indented channel created by a creasing rule. These crease shoulders result from the displacement of material as the male rule forces the board into the female matrix. Their height and width determine how the board behaves during the folding phase.
Folding Performance
Proper formation of crease shoulders ensures that the bending stress is distributed across the ply structure. When a carton is folded, the crease shoulders act as a pivot point for the adjacent panels. If they are too low, the board might resist the fold or cause liner failure.
High shoulders provide a clear line of weakness that guides the fold with precision. This geometry is essential for high speed glueing lines where box squareness is a priority.
Ink Integrity
Surface coating layers must remain intact as the board moves through the converting equipment. Sharp or jagged crease shoulders often cause the ink or varnish to flake away at the score line. This damage occurs when the pressure of the creasing rule exceeds the internal bond strength of the board.
Adjusting the matrix width or rule depth helps to mitigate this risk. Maintaining a smooth profile preserves the visual quality of the finished packaging. Consistent shoulder height prevents the cracking of sensitive barrier coatings during the final assembly of the box.