Why Do Bubbles Form on the Spine of a Glued Book?

Bubbles on the spine of a glued book are frustrating, but they’re rarely random. They usually stem from problems with equipment, glue, operation, or the book’s spine itself. Let’s break down the reasons and solutions:

1. Misadjusted Binding Equipment

• Glue roller height: The glue roller smooths the glue layer after application. If it’s too low or too high, it can create uneven glue distribution—leaving gaps that look like bubbles.

• Book support table height: This table clamps the spine after gluing. If it’s too low, the spine isn’t held tightly enough during cover wrapping, allowing air pockets (bubbles) to form.

Fix: Adjust the glue roller to ensure even pressure on the spine, and set the book support table high enough to clamp the spine firmly without crushing it.

2. Issues with the Binding Glue

• Overheating: If the glue is heated too much, it releases gas. This gas gets trapped in the glue layer, forming real bubbles.

• Poor-quality glue: Cheap hot melt adhesives use low-grade materials. Their molecules evaporate easily at high temperatures, causing the glue to shrink, crack, and form bubbles.

Fix: Stick to the glue manufacturer’s recommended heating temperature. Use high-quality hot melt adhesives designed for book binding to avoid shrinkage and gas.

3. Unstandardized Operation

• Dirty milling grooves: Paper dust or fibers left in the grooves (where the spine is glued) can block the glue from sticking to the book’s back. These unglued spots look like bubbles.

• Mismatched glue wheels: If the glue-coating wheel and scraping wheel aren’t aligned, they may leave gaps in the glue layer. These gaps harden into bubbles.

Fix: Clean the milling grooves thoroughly before gluing. Check that the glue wheels are positioned to spread glue evenly, with no gaps.

4. An Uneven Book Spine

If the spine itself is warped or uneven, even perfectly applied glue will dry with bubbles. The uneven surface creates spaces where air gets trapped.

Fix: Ensure the book’s pages are stacked evenly, and the spine is pressed flat before gluing.

Bubbles on a book spine are fixable with careful equipment setup, quality glue, clean operations, and a flat spine. By checking these factors, you can achieve a smooth, professional bind every time!