Often as designers and print buyers, we’re so focused on the page design or the texture of the press sheet that we forget the physical properties of the custom printing paper itself. Here are some thoughts on paper folding and scoring, two elements of your print job that will be essential, but invisible to the reader, if done correctly.
What Is Paper Grain?
Like wood, paper has grain. There’s a single direction in which the majority of paper fibers that make up a sheet of paper will align. It is parallel to the direction the paper traveled through the paper-making machine.
You can determine the direction of the fibers easily by tearing a press sheet. If you’re tearing with the grain, your tear will be much straighter than if you tear the paper against the grain.
You can also moisten one side of the sheet to determine the paper grain direction. In this case, the paper will curl parallel to the grain.
Fold With the Grain or Against the Grain?
Why does the direction of the paper grain matter?
If you’re designing a brochure and you fold with the grain, the press sheet will be less likely to crack, delaminate, or wrinkle. This is because you’re not folding the fibers; you’re folding the other elements of the paper mixture: the fines and the fillers.
That said, a fold “with the grain” is not as strong as a fold made “against the grain.” This may be a concern when you’re producing a pocket folder. In this case, to strengthen the spine of the pocket folder, you might want the printer to fold the spine against the grain rather than with the grain. In this case, you’re actually folding the paper fibers.
The paper fibers comprise the hinge between the front and back cover. This gives a strength to the fold on the spine that would not be present if the fibers ran parallel to the spine. In contrast, the parallel folds of the two pockets of the pocket folder are not structural and do not move back and forth as the spine fold does. Therefore, they can afford to be less durable than the fold of the spine.
Books Have Special Folding Requirements
If you’re producing a perfect-bound or case-bound print book, you do not have as much flexibility in choosing the paper grain direction. In this case, you will want the book printer to ensure that the paper grain of the text sheets runs parallel to the spine. If the paper grain were to run perpendicular to the direction of the print book’s spine, the pages would not lie flat, and the book might not open or close correctly.
Scoring to Allow for a Crisp, Flat Fold
When you fold thicker commercial printing paper against the grain, you need to score the press sheet before you fold it. Otherwise, the fold will be uneven, cracked, or buckled.
Scoring involves placing a metal rule (or some other device: even a string) against the press sheet as it goes through a rotary press or flatbed press (usually a letterpress rather than an offset press, although scoring can be done on an offset press as well; it just will damage the offset blanket). The weight of the printing press cylinders forces the rule into the paper, creasing it, and allowing for a later, more even folding process.
The bump that the scoring rule creates should be inside the final fold rather than outside of it. This allows for more even folding and less stress on the paper fibers.
Why You Should Score Before Folding
When a commercial printing vendor scores a sheet prior to folding it, any heavy-coverage ink, or varnish, will be less likely to crack when the sheet is folded. This may be useful for you to consider if you’re producing a pocket folder with a flood coating of ink, or even a brochure with photos, screens, or solid colors that cross a fold.
A good rule of thumb is that you should score any commercial printing sheet heavier than 80# text if you’re folding against the paper grain, and you should score any cover stock thicker than 50# regardless of whether you’re folding with, or against, the grain.
This entry was posted
on Monday, October 14th, 2013 at 12:43 pm and is filed under Paper and finishing.
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