Even though two pieces of paperboard may appear to be the same, they may respond differently to being folded. Bend one way and the paperboard will follow the crease smoothly. Rotate the sample 90 degrees and the fold may be harder, show surface stresses, or refuse to hold a shape. Grain direction is one reason why this happens, and recognizing the grain direction makes folding issues easier to diagnose.
Paperboard is formed from fibers that line up more consistently in one direction. This gives the board a grain direction. It generally will fold more easily along the grain, and will resist folding across the grain. While this distinction may not be obvious when you pick up a piece of paperboard off your desk, you will see the grain effect more around sharp creases, thick stock, and during converting.
Creasing can help guide paperboard to fold in the right place, but it doesn’t override the board’s tendencies. The score creates a weakened area for the board to fold. With a combination of grain direction, caliper, stiffness, and crease, the paperboard may fold properly with minimal surface stress. With opposing properties, however, the board may spring open, crack along the print side, swell at the fold, or require more force to fold to the desired angle.
To observe how grain direction affects paperboard, take two similar pieces of paperboard. Gently bend the first piece of paperboard from the edges without actually creasing it. Then, take the second piece of paperboard and bend it in the opposite direction. You may find that one direction feels much easier to bend. Next, take apart a carton and examine the folds, looking at longer panel creases as well as smaller flaps. Although this isn’t a substitute for measuring the paperboard in production, it helps build your skill at matching what you feel with what you see.
When a carton folds incorrectly, it can be tempting to blame the dieline. Although the dieline plays an important role by establishing the panels, flap sizes, cuts, and creases, a correct dieline can still have different outcomes depending on the substrate. When there are cracks or significant spring-open in the fold, you’ll want to look at both the material and the geometry. Rather than examining a single carton, look at multiple pieces of the same product and determine if one fold direction seems to behave differently than another.
Printing and finishing can make it easier to recognize grain direction. It can be easier to see surface cracking near a crease if the piece is coated and printed, while it can be more difficult to spot surface defects if the piece isn’t printed. As you’re inspecting the carton, don’t just look at the corner of the fold; instead, look along the fold and note if the crease is straight, if the panel is sitting as it should, and if the surface opens or cracks during conversion. Keeping notes on these details along with the material type and fold direction will make your inspection record more helpful than simply stating the carton “folds poorly.”
Grain direction is only one aspect of the formation process, so it shouldn’t be used as a blanket explanation for every damaged crease. Other factors such as score depth, material thickness, stiffness, coating, storage conditions, and alignment can also have an impact. One sign of improvement in your inspection skills is slowing down before making assumptions, and taking more time to compare: take a closer look at the fold and its orientation, examine multiple pieces, and correlate the visual evidence with the materials and converting factors that contributed to the problem.
