Influence of the grain direction of the hottest pa

The influence of the grain direction of paper on printing and binding

in the actual production process, the grain direction of paper has an important influence on the overprint during printing and the appearance effect after binding into a volume in early November this year. To a large extent, it not only affects the internal quality of books, but also affects the appearance of books

I. grain direction of paper

paper is a fabric of fibers. Traditionally, we call the direction of arrangement of most fibers consistent with the direction of papermaking as the straight grain direction; The direction perpendicular to it is called the horizontal grain direction of the paper

paper fiber is a hydrophilic substance, which absorbs water to expand and release water to shrink. The penetration and disappearance of water between fibers cause relative displacement between fibers, and their length and width change. This is the flexibility of paper. According to the experiment, the diameter of a dry fiber can be increased by 30% after it is completely wetted, while the length direction can only be increased by 1% - 2%. Therefore, the expansion and contraction rate of paper in the straight grain direction and the horizontal grain direction is different. Generally speaking, the horizontal grain expansion rate of paper is 2 ~ 8 times that of straight grain

II. Identification of grain direction

due to the significant differences in a series of physical properties such as the expansion rate and stiffness between the straight grain direction and the horizontal grain direction of the paper, there are many ways to distinguish the grain direction of the paper. Here are several simple and easy methods

1. Folding method: fold the paper once in two directions respectively. The crease is smooth and the straight direction is the straight grain direction

2. Hanging law enforcement: cut strips of the same length along the vertical and horizontal planes of the paper, hold one end with your fingers, and the direction with small bending degree is the straight grain direction (as shown in Figure 1)

3. Moistening: put the paper on the water for a period of time and observe its curling direction. The axis direction of paper curling is the straight grain direction (for example, the metal material tensile testing machine has a variety of curve modes: stress-strain, pneumatic displacement, pneumatic time, strength time and other curve modes, Fig. 2)

III. consideration of paper grain in offset printing process

offset printing uses the principle of ink and water balance to make graphics and texts appear on the paper, and the contact between the paper and the fountain solution will cause the paper to stretch. As mentioned earlier, the paper's flexibility is related to the direction of fiber arrangement, and the expansion rate in the straight grain direction is less than that in the horizontal grain direction. Therefore, in the offset printing process, it is customary to print with the straight grain direction of the paper parallel to the axis of the drum, so as to minimize the inaccurate overprint of pictures and texts caused by the moisture absorption and elongation of the paper. This is particularly important in multicolor color printing

another view is that from the perspective of paper feeding, the straight grain direction of the paper is relatively rigid, which is convenient for blowing and conveying; The paper stiffness in the horizontal grain direction is not enough. Jinan experimental machine factory reminds you that you should regularly check all kinds of sprockets on the electronic universal experimental machine. Both ends are easy to curl downward or upward, which affects blowing and conveying. Therefore, you should print the paper in the straight grain direction parallel to the paper feeding direction. This view is certainly reasonable, but it is a bit "discarding the basics". Because our ultimate goal is to produce high-quality prints. In this regard, it is more important to grasp the main contradiction and avoid inaccurate overprint than to facilitate paper feeding

in addition, if the same batch of purchased paper cannot be used when printing a book, or the small offset press uses the cutting residues with small format, it must be ensured that the same book printed in the same batch cannot be mixed with papers with different grain directions. Otherwise, it will not only cause inaccurate overprint due to different paper expansion conditions, but also lead to uneven cutting edges of finished products after a period of inventory

IV. consideration of the direction of the paper grain in the binding process

the direction of the paper grain is particularly important for the ring lining in the binding process. The ring lining is an indispensable part of hardcover books. The cover and the book block are firmly bonded by glue, which can not only protect the book block, but also increase the beauty. Due to the different expansion rates in different fiber directions of the paper, the horizontal grain direction of the ring lining is consistent with the setting mouth, which is easy to wrinkle (as shown in Figure 3). When the straight grain direction is consistent with the setting mouth, the appearance is flat

it is easy to wrinkle when the horizontal grain direction of the ring lining is consistent with the setting mouth. This is because: when the ring lining is pasted by the glue, the water in the glue moistens the ring lining to make it elongate, and the elongation in the transverse grain direction is larger. With the gradual loss of moisture in the drying process, the horizontal grain direction shrinks, and the glue at the stapling position has fixed the ring lining. In this way, the paper produces an internal stress, and wrinkles are formed where the internal stress is concentrated. On the contrary, when the straight grain direction and setting will make the oil cylinder consistent with the wear opening on the surface of the oil plug, the expansion and contraction of the horizontal grain direction is very limited by the glue fixation, and the sticking place is flat. Therefore, when cutting the ring lining, the direction of the straight grain must be parallel to the setting opening. If the ring lining is not blank, its arrangement direction should also be considered when making up. ※

source: Nanjing aide Printing Co., Ltd