Viscoelastic Resin Yield Dynamics in Score Line Coating Crease Mechanics
Selecting ductile resin binders with glass transition temperatures below minus five degrees Celsius prevents coating micro-cracking during paperboard crease folding.
Score Line Creasing
Folding Preparation
Controlled weakening of a paperboard sheet along a specific axis facilitates clean, accurate folding without surface cracking. During the conversion process, score line creasing establishes a hinge by compressing the internal structure of the board. This action displaces the fibres into a groove to form a bead on the reverse side.
It ensures that the subsequent fold occurs exactly where the design specifies.
Mechanical Action
Steel rules descend into a channel known as a matrix or makeready to deform the material. The depth of the tool and the width of the groove must match the caliper of the board to prevent the liners from bursting. If the score line creasing is too shallow, the board will resist the folding force and the corners will lose their squareness.
This step essentially delaminates the internal layers. It creates a flexible zone that absorbs the stress of a ninety degree bend.
Quality Control
Visual inspection identifies failures like rolling scores or liner splitting. When the board is folded, the score line creasing must show a clean, unbroken surface on the outside of the box. Precise alignment between the creasing rule and the grain direction of the paper prevents jagged edges.