Put a folding carton, a shipping box made of corrugated board, and a flexible film package side by side. Each one is a piece of packaging, but they have very different properties before they become a completed product. Paperboard is a thin, relatively rigid sheet. Corrugated board consists of two or more flat sheets with a wavy inner layer sandwiched between them. Flexible film is a pliable material that can be bent or folded, but does not maintain its shape on its own. Because these materials have such different physical characteristics, they react quite differently to each stage of the manufacturing process, including printing, cutting, folding, gluing, and quality inspection.
Paperboard is often made into a carton from a flat printed sheet. The process begins with printing and finishing operations. Once the paper is printed and coated, it can be die cut and creased to form the various parts of the carton. A crease allows the paperboard to bend in a specific location. Creasing is a critical step in paperboard conversion. The thickness, stiffness, surface condition, and orientation of the paperboard all determine how it will crease. If the crease is not properly aligned with the die cut, the paperboard can crack, spring back, or result in a crooked edge, even if the die cut is correctly positioned.
Corrugated board introduces a new consideration: the flutes between the paperboard layers. The flutes provide both cushioning and stiffness to the material, but they also impact how the board reacts to pressure. Compressing the flutes can damage the board, and if the score is not accurately placed, the cardboard may be difficult to fold or the fold may not occur at the right place. Printing on corrugated board requires a different technique than printing on a flat piece of paper. When looking at a sample of corrugated board, focus on the board’s condition, the accuracy of the score marks, whether the flutes are undamaged, and whether the finished product closes easily.
In contrast, flexible film relies primarily on sealing rather than folding and creasing to create a package. Flexible packaging can be manufactured from laminates in which the different materials contribute to the printability, strength, or barrier properties of the film. For someone new to packaging, the key takeaway is that a sealed seam can substitute for a variety of joints that are necessary for carton construction. The width and alignment of the seal, any wrinkles in the film, foreign material on the seal, or incomplete bonding can become points of concern.
It’s possible to compare these materials without specialized equipment. Gather several samples and examine them closely. Fold the paperboard in multiple directions to determine how the stiffness or grain affects the bend. Gently squeeze the side of a piece of corrugated board to see the difference between undamaged and crushed flutes. Bend a pouch and inspect how the printed area deforms as it passes over the fold and seal. Note what each material does, instead of simply stating that one is more robust, delicate, thick, or thin than the other. These simple descriptors do not capture the nuances of material behavior during manufacturing.
It’s not always true that the easiest material to work with is the most desirable. Overly stiff board can be challenging to form, lightweight corrugated board can lose some of its protective qualities if crushed, and a flexible laminate can be highly dependent on the consistency of the seal. Consequently, the choice of material impacts all aspects of the manufacturing process, from printing to inspection. When reviewing packaging samples, consider one important question: what must the substrate do to function effectively as a package once it is complete?
