What are the reasons for the uneven back and raised spine of the laminated book? How to adjust hot melt adhesive and process

After the wireless adhesive book is finished, the back of the book is not flat, but has edges, waves, local bulges, or a spine that is high on one side and low on the other – this is called “uneven back/spine with ridges”. It is similar to “falling pages and opening glue”Two different types of defectsPage drop isCan’t stickThe back of the book is unevenIrregular shapeNext, explain the reasons and troubleshooting by clicking on the three ends of “paper glue equipment”.

1、 First of all, a direct answer: uneven book backs often occur during the “gluing and pressing” process

The core of uneven book backs isUneven thickness of adhesive layer, insufficient pressing, or substandard milling of book core backResulting in uneven shape of the cured adhesive. The quality of the adhesive itself is only one end, and the process and equipment are often the main factors.

2、 Paper end: milling back and pulling hair not in place

Wireless adhesive packaging relies on the infiltration of adhesive into the book core fibers for bonding. IfInsufficient or uneven depth of milling back (pulling hair)The root of the book page is not opened, the fibers are not exposed, and the glue can only stick to the surface. When pressed, the back of the book will be uneven and angular.

• Inspection: Draw a spine incision from a book and check if the paper is evenly layered and brushed.
• Processing: Adjust the milling depth of the back according to the thickness of the paper (thin paper core is the strongest, thick book core needs to be sufficiently brushed), and regularly replace the milling cutter.

3、 Adhesive end: The thickness of the adhesive layer does not match the opening time

• The adhesive layer is too thickStacking glue leads to insufficient compaction and edge warping;The adhesive layer is too thinFill in the grooves on the back of the book, leaving some areas empty and uneven.
• The opening time does not match the line speedThe low-speed line uses high-speed adhesive (with an opening time of 2-7s), which has already formed a film before clamping and cannot be pressed firmly; On the contrary, using low-speed glue on high-speed lines will cause glue overflow and accumulation. The opening time of book and magazine adhesive is divided according to the line speed (low speed ≈ 15-20 seconds/medium speed 5-10 seconds/high speed 2-7 seconds, subject to the process card).
• Processing: Select the corresponding opening time model according to the line speed, and match the adhesive layer thickness within the range according to the book core thickness (based on the accompanying process card).

4、 Equipment end: book pressing, book clamping, and temperature control

1. Inappropriate pressure on booksUnder excessive pressure, the book core is flattened and the book back is deformed; The pressure is too low, and the adhesive layer is not solid or bulging. Adjust the pressure curve according to the thickness of the book.
2. Book holder/tray not centeredThe book core is not properly aligned, and the back of the book is raised on one side and lowered on the other, resulting in a naturally crooked shape.
3. The temperature of the glue pot is not accurateThis is the most easily overlooked.On site training data shows that about 90% of after-sales problems are caused by equipment temperature control failure——The display shows that at 160 ℃, the actual temperature is only 100 ℃, and the viscosity and wettability of the glue have completely changed. This may cause the pages to fall off or uneven flow, resulting in uneven stacking or lack of glue on the back of the book. Calibrating the glue pot with a thermometer is a low-cost and high return step.

5、 Troubleshooting sequence (easy first, difficult later)

1. Check the milling back: whether the book core is evenly brushed → adjust the milling back depth/change the tool.
2. Calibration of glue temperature: Temperature gun measured glue pot vs display → Calibrate temperature control.
3. Nuclear selection: Whether the opening time matches the current line speed → Change to the corresponding model.
4. Adjust pressure: Press book pressure/clamp book in the center → set according to book thickness.
5. Glue control layer: The amount of adhesive used is matched with the thickness of the book block within the specified range.

6、 Relationship with Sunlife’s real business

Sunlife (Sunlife) hot melt adhesive covers copperplate paper/adhesive paper/double adhesive paper/thin paper and other scenes. The back adhesive, edge adhesive, and flat adhesive (such as S-391) have their own opening time and soft and hard positioning. When customers provide feedback that the book back is uneven, prioritize following the five steps aboveMilling back – temperature control – selection – pressure – adhesive layerThrough investigation, most of them can be located at the process end, and there is no need to directly replace the glue; When it is necessary to change the adhesive, match the model with the paper according to the line speed.

Explanation: The temperature, opening time, and adhesive layer thickness in this article are general process points. The specific machine parameters are subject to Sunlife’s accompanying “Instructions/Process Card”; The temperature control calibration of the equipment should be carried out by qualified mechanics according to the manufacturer’s specifications.