Binding Solutions, LLC

Honeycomb Film
There are many reasons why the hot melt applied to the book block on a soft cover book will develop a honeycomb appearance. The most common reason is moisture. Of course, moisture is present in all paper, whether it is the cover material or the pages of the book block. When hot melt is applied to the surface of the book block, the available moisture will boil and expand to 7-1/2 times its volume. Most paper contains about 5-6% moisture, so this expansion can cause a considerable amount of bubbles or honeycomb. The higher the temperature of application, the more bubbles will form.
In order to minimize this problem, the application temperature of the hot melt should be as low as possible while still achieving the penetration necessary to make a strong book. For instance, cross-grained paper will require more penetration than straight grained paper to mechanically lock around the fibers of the paper. However, higher temperature of application will decrease the viscosity of the hot melt and allow better penetration. It is very important that the actual temperature of the hot melt is known since it is a key factor in the formation of bubbles in the backbone of a book.
Use of 250°F hot melts such as COOL-BIND will greatly reduce the honeycomb appearance of the hot melt and give a smoother appearance to the back of the book.
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