What is the grain of paper? Why is grain direction Important to know?How to determine grain direction of paper material

What is the grain of paper?
The grain of paper is the direction in which most of the fibers lie. Grain is determined during the papermaking process, when fibers tend to align in one direction or the other. Paper is identified as either grain short (grain is parallel to paper’s short side) or grain long (grain is parallel to the paper’s long side), depending on how the paper is cut.

Why is grain direction Important to know?

It is very important to know the grain direction because paper and cardboard stretches and bends differently along and against the grain. In wet conditions (including glue application) paper products tend to wave (with curls going along the grain).

When pages are to be bound, as in books and catalogs, the grain should be parallel to the binding edge(the spine). Pages bound with the grain perpendicular to the binding edge do not lie flat or turn easily.

Recognising the difference in board grain direction is a fundamental part of carton manufacturer.
As a rule, the direction of the grain runs opposite to the major creases on the carton for ease of erection on automatic forming/filling machines at our customer’s sites.

Grain is also very important part in the manufacturing of rigid set-up boxes since most machinery runs with grain in a certain direction, when not followed a machine may not be able to run correctly.

How to determine grain direction of paper material
1.TEARING TEST
Tearing along (with) the grain will give a much straighter even tear that follows the direction of the grain. Try to tear the paper in a straight line first along the length of the paper then in the opposite direction. The tear will be noticeably straighter and even in one direction; this is the direction in which the papers long fibers are running.

2.BENDING TEST
The grain direction of board (thicker paper) can be determined by checking the resistance of the board by bending slightly from end to end. One direction offers considerably more resistance than the other. Parallel to the grain direction the resistance is far less than against the grain.

3.FOLDING TEST
Take a board, and fold it vertically and then horizontally. The fold with the grain is straighter and smoother, while the fold against the grain is more rugged and bumpy.

4.MOISTURE TEST
Perhaps the easiest and most foolproof way to determine grain direction is to take a square of the paper say 6 x 6 inches and quickly wet one side of it with a sprayer or sponge. The paper should immediately curl up. The grain always runs parallel with the direction of the curl.

5.LOOK TEST
It can sometimes be seen by eye, by looking at the reverse of the sheet and observing which way the fibers run.

GUPRINT have experience staff, they know more ways to determine grain direction, above just simple ways to share. 

See more about how grain direction affect packaging production.