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Success in the bindery starts
with choosing the right paper for your job. If post press processes
include folding, consider important factors such as paper thickness,
coatings, fillers, grain direction and grain length.
Generally, the thicker your stock, the more variables you will face on
folding machines. A good rule of thumb is to pre-score any stock that
calipers at 0.005 (5-points) or thicker. In case you didn't know,
today's high-speed rotary scoring technology yields just as good quality
as die scoring.
In some cases, jobs without
critical color breaks printed on paper thicker than 0.005 can be
successfully folded without pre-scoring. However, as usual, always ask for
an opinion before skipping this step. When folding stock thicker than
10-points on buckle folders, carefully watch your job for signs of ripple
cracking. Knife folders will still ripple crack your stock, but generally
problems begin a couple of thousands thicker than they do on buckle
folders.
Know your grain direction before printing. Folding with the grain reduces cracking and the need for
pre-scoring or inline wet scoring - both of which decrease productivity
and increase costs. If you must fold against the grain, consider choosing
a stock with short paper fibers and "off machine" coating for better
moisture control. Making matters worse, inks tend to be brittle and may
crack when bent, exposing raw paper fibers underneath.
Paper
Irregularities
Paper irregularities affect folding performance. Variable thickness,
frequent waves and ripples and excessively brittle stock all serve to
decrease bindery performance. Paper bulk can be incredibly variable. For
example, 80# uncoated cover stock can caliper anywhere from 8- to
13-points. This is significant because pre-scored 10-point stock folds
well, but stocks thicker than 12-points require different folding
techniques and machines (i.e., plow folders).
If a job has thickness variation, folding will be sloppy. Be careful of
running odd lots. Since changing paper in the middle of a job will affect
folding accuracy, be sure to mark the change spot and advise your bindery.
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