What is the appropriate thickness for the hot melt adhesive layer? Explain the reference values for book and magazine packaging and sealing in one go

Direct answer: The back adhesive layer of wireless adhesive packaging for books and periodicals is usually controlled at 0.6-1.0mm, and the side adhesive is 0.2-0.4mm; the thickness of the adhesive dots/lines for corrugated cardboard box sealing is generally 0.3-0.8mm; the thinnest layer for color box pasting is 0.15-0.3mm.The thickness is not necessarily better, sufficient, uniform, and well penetrated are the standards.

Why is there such a big difference in thickness

The function of the adhesive layer is to establish a continuous stress surface between two substrates. The spine of the book needs to withstand the peeling force of repeated folding, and the paper fibers need to be “bitten” by the glue, so the thickness should be sufficient; The sealing process involves the overlapping surface being subjected to shear force, and since the cardboard box itself has a large area, a thin layer of continuous adhesive thread is sufficient; The speed of the box pasting line is fast and the paper is flat, but if it is too thick, it may overflow and contaminate the finished product.

Reference values for different scenarios

How to determine if the current thickness is correct

• Tearing calligraphyThe finished adhesive product should be torn along the spine of the book, and the cross-section of the adhesive layer should show that the paper fibers have been pulled up, indicating that the penetration is in place; If the adhesive layer is completely peeled off and the paper surface is clean, it is usually too thick and lacks penetration.
• Weighing methodFixed sampling of 20 finished products, weighing the difference in weight before and after gluing, dividing it by the spine area, converting it to gram weight and then converting it to thickness, is much more stable than visual inspection.
• Look at the overflow glueSlight glue overflow within 1mm on both sides of the spine is normal, and if it exceeds 2mm, the amount of glue should be reduced.

Incorrect thickness adjustment is often not a problem with the adhesive

The first reaction of many factories is to change the glue, but in fact, three things need to be checked first: whether the melt temperature is too low, which leads to insufficient fluidity of the glue, whether the gap between the scraper roller is worn out and increased, and whether the paper feeding speed and glue output are matched. The actual coating thickness of the same adhesive may differ by more than 20% for every 10 ℃ temperature difference. Sunlife hot melt adhesive provides recommended adhesive temperature range and scraper roller gap reference when making samples for customers, so that thickness adjustment can be based on evidence.

Frequently Asked Questions

Q: Is a thicker adhesive layer more secure?
Answer: Yes within a reasonable range, but it gets worse beyond that range. Thick adhesive layers have slow cooling, high internal shrinkage stress, and the spine is prone to bulging. They are even more brittle in low temperature environments.

Q: Do I need to readjust the thickness of the same adhesive particle after changing the paper?
Answer: Yes. Copperplate paper and laminated paper have poor absorption and require slightly thinner and longer opening time adhesive; Offset paper and lightweight paper absorb quickly and can be slightly thicker.

Q: How to quickly find the optimal thickness for your production line?
Answer: Fixed other parameters, only divide the adhesive amount into three levels for trial production of 50 copies each, conduct page fatigue and peeling tests, and select the level that saves the most adhesive under the premise of qualification.

Guangzhou Sunlife Trading has long provided hot melt adhesive particle selection and process parameter support for book binding, packaging and sealing, and graphic and text fast printing customers. If you need a thickness solution for your own equipment, you can contact us with paper samples and equipment models for free sampling.