When I learned that the back of the book was born due to the presence and loss of moisture in the adhesive, the text, the cover, and the adhesive first swelled and the post-shrinkage was prevented. Pay attention to the following two aspects:
1. When using water-soluble adhesives, their consistency should be increased as much as possible. Water-soluble adhesives should be prepared to minimize moisture, in order to reduce the impact of moisture absorption and swelling, drying shrinkage on the inner paper, cover paper, reduce the shrinkage of the adhesive after drying, and the influence of internal stress caused by shrinkage and angle change .
2. Use a solvent-free hot melt adhesive, hot melt adhesive, as much as possible. Hot melt adhesive is 100% solid raw material. It can be melted into liquid state by heating. It can be brushed onto the inner document core and attached to the cover. It can be cured at room temperature within a few seconds from the heat source to form a firm fit. The film has re-stickiness. When the back of a book has a sudden death or the cover is skewed, it can be reconstructed after warming, which will not cause loss and waste.
The reason for the warpage of the cover can be seen from Fig. 2. When the initial fit, the angle between the back of the book and the back of the cover is both 90°. When the shrinkage of the adhesive behind the scald deforms the volume, the angle between the back of the book and the back of the cover is expanded to 105°, and the folding stress is from cos90°=1-cos105°=-0.342. This change in the folding stress causes the cover to be folded back to a 90° angle, causing the cover and the book block to overlap in a flat, overlapping manner and change into a "open mouth" shape or "trumpet shape" overturn. This “open mouth†or “trumpet†state is more prone to moisture swelling due to the overexposed face of the cover sheet. The rate of change after moisture absorption on the reverse side of the paper is greater than on the front side, and the curl on the front side of the cover sheet must be added.
To solve the cover warpage, it is necessary to prevent the shrinkage of the adhesive after shrinkage. On the one hand, a higher consistency adhesive is used, preferably a hot melt adhesive. More importantly, while brushing the adhesive on the back of the book, on the front and back sides of the booklet album, it is also necessary to brush the adhesive evenly on both sides of the original bookback, creating a 3 to 7mm wide side ( (b) The glue line, in this position, the cover and the back cover are fixed so that the included angle with the back of the book is kept within 90°, forming the front cover and the back cover parallel to the internal text, keeping it tightly and without overturning and curling. (Figure 3)
Automatic bonders already have such devices and features. In manual operation, after brushing the adhesive on the back of the book, the book can be staggered by a small step of 3.5 to 5.0 mm backwards, and then evenly brushed once so that a small amount of adhesive is left on the staggered small steps. A 3.5 to 5.0 mm wide side adhesive tape is evenly left in the booked mouth line position. Then it is corrected, and the adhesive tape is evenly moved to the same position on the other side of each book, so that both the front and back sides of the book are guaranteed to have the side (edge) glue for positioning the front cover of the cover.
Source: Printing Technology