When you need to fold a printed project that is on heavier paper we recommend scoring. Scoring puts a groove in the paper so that the fold is crisp, clean and accurate, with no damage done to the ink or paper. Many jobs need to be folded after printing, and customers won’t tolerate a finished, folded piece that’s marred by any ‘cracking’ or splitting of the sheet. Some printed papers will fold just fine (usually text weight stocks and lightweight covers folding with the grain.) It is on jobs where fiber cracking or splitting occurs that creasing becomes important.
Paper is fiber-based, and the mechanical folding process causes a lot of stress to the sheet, so the fibers and the coating on the sheet can crack and expose an ugly, rough texture at the fold. This is most noticeable on a fold against the grain of a heavier sheet. So we score, because scoring is the process of creasing the sheet of paper to compress the paper fibers and decrease stiffness, which enables a high quality fold.
First, let’s look at 3 factors that affect the paper. Second, we’ll see how creasing works and why it is an important solution.
- The paper structure varies with coating thickness, fiber content, length of fibers, bond between base and coating and how pulp is treated. Heavy coatings and low fiber content means less stability and a greater tendency to crack. No sheet is immune to cracking, but since the coated sheet is more complex than the uncoated it’s more prone to fiber cracking. There’s simply more that can go wrong. But coated papers tend to reproduce originals better than uncoated sheets; which is why you see more full color jobs printed on coated sheets.
- The printing process makes the paper less flexible with the addition of countless combinations of inks, varnishes and coatings. Heat applied to rapidly dry the printed sheet as it exits the press affects the humidity content of the sheet, further reducing flexibility.
- The environment, especially with regard to the paper’s moisture content, makes a difference in whether paper will crack. A pressroom or bindery at 50% relative humidity will be less likely to have cracking problems than an environment at 25% relative humidity.
Scoring is any method of reducing paper stiffness along a line in order to aid in folding. Press scores (litho score) and old style folding machine scores (e.g. steel scoring blade between steel or rubber collars) are two examples. They simply weaken the sheet to aid in folding.
Creasing refers to the internal de-lamination of a sheet by compression along the line where folding needs to occur (shown at right using the Technifold Tri-Creaser.). Creasing Paper with Tri-CreaserCreasing refers to the internal de-lamination of a sheet by compression along the line where folding needs to occur (shown at right using the Technifold Tri-Creaser.).
When the sheet is bent (folded) at the crease, all the outward force that normally would split or crack the sheet is directed inwards towards the weak, delaminated line. As the fold Crease Paper Delaminationcontinues, (left) the sheet further de-laminates internally and a rounded bead is formed on the inside of the fold, absorbing all the force, while the outside of the folded piece remains smooth and unbroken. Creasing can be done by either a platen method (both sheet and die board are flat) or rotary method (paper passes between cylinders or wraps around a cylinder.) Both methods use a male die to force the sheet into a female channel, the dimensions of which vary according to the density of paper.
Sometimes simple scoring will eliminate splitting and fiber cracking, but as the sheets get heavier, this is less likely and the stronger compression forces of creasing are needed to prevent cracking. In high-quality commercial printing, creasing is thus the second critical strategy used to combat the fiber cracking problem. Not only does it aid in folding, but when done successfully, it achieves the commercial printers and designer’s goal of faithful print reproduction.
What are the different types of scoring methods?
There are several ways to score, and there are also different reasons why you might choose one scoring technique over another—some related to budget, printing method, direction and placement of the score, paper finish, equipment, and nature of the product being produced. I’ll do my best to help make the decision easy for you.
- Litho Score: A Litho Score, or Press Score, allows the application of a score in line while the job is on press. A thin metal rule, kind of like the thickness of a cookie cutter, is adhered to the impression cylinder on the press. Metal rules can cut, crease, or perforate. In this case, the scoring rule creases the sheet as it passes underneath.
- Heat Score: Heat Scoring is a Litho scoring technique that requires the use of special offset presses that can hold heat. This process can apply up to 350 degrees of heat to a copper die that can score, stamp, or emboss in line during the printing process. Heat scoring is especially effective on heavier coated stocks.
- Rotary Score: A Rotary Score utilizes a special wheel attachment for the folding machine, and the wheel, with pressure applied, rolls as the sheet passes underneath before it’s folded, and creates the crease inline during the finishing process.
- Letterpress Score: Letterpress is the highest quality—and the most expensive scoring process. It’s an offline process in which a steel rule is formed into the desired shape and is set within a piece of wood that is locked into a metal frame. The frame is clamped to a letterpress printing machine that forces the paper between the steel rule and the impression of the press. The process is slower, but the result is outstanding.
- Impact Score: Impact scoring is a technique that is used primarily for short-run digital printing. A knife-and-channel configuration strikes the sheet to create a crease. This technique creates a quality crease, but is slower than the other techniques due to the reciprocating action of the knife.
- Wet Score: Although not scoring in the literal sense (where paper fibers are compressed), a wet score is a process that is used specifically for an uncoated sheet. A special water attachment on the folding machine applies a thin, straight stream of solution where they want the paper to fold. With a fine line of dampness, the paper can’t help but to create a perfectly clean fold.