One of the things I like about the finishing business is that there's more to it than meets the eye. Each postpress operation has special guidelines, considerations and limitations. Take an apparently straightforward operation, like folding. Simple, right? Wrong! For folded projects to be successful, you have to know the score.
Paper, ink and coatings, like people, can crack under stress. Folding places tremendous pressure on a printed piece, often causing cracking at the fold and a major flaw in an otherwise perfect job. It's especially unattractive and noticeable if there's ink on the fold. One surefire way to prevent cracking and create a smooth, strong fold is to score the paper prior to folding.
How to Score. Scoring is essentially the embossing of a narrow ridge into the paper. It's done both to reduce or eliminate cracking and determine a fold's location. There are several ways to score, but all methods are based on the same concept-the paper fibers are weakened by an indentation (hinge) in the paper. This produces a precise fold line (register) that reduces stress to the paper and permits a crisp fold. Scoring does not have to entail a separate finishing step, a score can be applied during off-line machine folding (rotary scoring on a folding machine, for example).
Litho scoring is performed on-press. A scoring rule is mounted onto one of the impression cylinders so that scoring can be performed during a printing pass. This method is generally not used on top-quality jobs, the score rules tend to move and bow, and the score has a shoulder that some people find objectionable. Litho scoring does not prevent cracking, but does help lessen the odds of it happening.
A second method is letterpress scoring. Performed using either a platen letterpress or a flatbed-cylinder letterpress, this method creates a ridge in the paper with either a male die and matrix set or a scoring/creasing rule and channel-creasing matrix. The result is an accurate, high-quality score that's great for the prevention of cracking.
Rotary scoring, the third method, involves the use of a scoring wheel, which is less effective than a metal rule for making a proper score. Like litho scoring, this method is best for locating a fold; only in some cases does it prevent cracking.
For years, rotary scoring has been done with a single shaft of scoring wheels. Recently, two companies, Dick Moll & Sons and Rollem Corp. of America, began selling double-shafted scoring/perforation machines. The first score shaft makes a light score, while the second shaft is set to the final desired depth. Both companies claim that double-shaft scoring is as good as the letterpress method. In fact, Dick Moll has stated that his system does a better job on UV-coated products (which are the toughest to score and fold) than letterpress equipment does.
On some jobs, the paper might undergo wet scoring to make it more pliable. Applied by hydraliners on a paper-folding machine, wet scoring is used mainly on uncoated stocks. A hypodermic needle feeds a mixture of 35 percent isopropyl alcohol and 65 percent water along the area of the paper that will be folded, softening the fibers sufficiently to make folding less torturous to the stock. This method is not recommended for use on coated stocks, since the water tends to bead up on the coating rather than penetrate to the fibers. Bleach can be added to the mixture to help it bite through the coating, but this weakens the coating and causes inks to change color.
Regardless of the method, the score should be wider and deeper than the thickness of the paper, and should be made so that the hinge will be on the inside of the fold. When stock is letterpress scored, a small bump will be visible at the base of the fold (see illustration).
When to Score. Scoring requires upfront planning with your finishing house. To highlight the factors that must be considered, let's look at a hypothetical project that practically cries out for scoring: a product brochure with full bleeds printed on coated cover stock, with folds going with and cross-grain. This could be a nightmare or a four-star success, the secret's in the score.
Since coated papers are difficult to fold and have a high tendency to crack, scoring is essential. To prevent fractures to the coating, a broad score should be made with a rounded rule. Cast-coated sheets, like Kromekote and Lustrokote, present a special challenge, scoring may not prevent unsightly cracking. For the same high-class look with crack-free folding, opt for premium coated sheets, such as Phoenix or Ikonolux. Some of our customers have requested us to score 70 to 80# coated text paper. While scoring may have decreased the likelihood of cracking, the problem was not entirely eliminated because the stock wasn't heavy enough to hold the hinge.
Heavy uncoated papers, book stocks over 80# and all cover stocks, are also likely to crack and will benefit from scoring. And anytime you have full ink coverage over the fold area, scoring is a must to avoid damage to the ink film.
Generally, the smoothest folds run parallel to the grain. Cross-grain folds are more likely to produce buckling and cracking, but they're also stronger and more flexible. If you need extra durability, plan a cross-grain fold, and remember to specify a score.
Other factors that must be taken into account are moisture content and number of folds. The relative humidity of the paper should be high. If the stock has been dried in an oven, it may take weeks to regain enough moisture; scoring won't stop the ink or stock from cracking.
Finally, if your printed piece involves more than four folds, it's vitally important that client, printer and finisher meet at the outset.