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Offset of crease lines on hardcover book covers is a common quality control issue, manifested as the bending of the cover not being in the design position, and in severe cases, causing the cover to warp and the spine to be uneven. Many people initially blame inaccurate die-cutting, but actual testing has found that the impact of adhesive position deviation is equally significant.
| factor | Proportion of offset contribution | Typical deviation amount | Repair difficulty |
|---|---|---|---|
| Die cutting/indentation accuracy | 35-45% | 0.5-1.5mm | Die cutting machine |
| Offset of glue application position | 30-40% | 0.3-2.0mm | Glue adjustment machine electric eye |
| Paper thread direction | 10-15% | 0.2-0.8mm | Change paper or adjust the material |
| Uneven thickness of adhesive layer | 5-10% | 0.1-0.5mm | Adjust the coating roller |
On the standard glue line, a deviation of 0.5mm in the glue application position will result in a 0.3mm level difference in the indentation line on both sides of the spine. If there is a deviation in both die-cutting and gluing, the superposition effect is more pronounced. It is recommended to prioritize calibrating the positioning accuracy of the adhesive machine’s electric eye, then adjusting the die-cutting, and finally checking the paper threads.
Q: Sunlifehot melt adhesive pelletsWill it affect the position of the indentation line?
A: The type of adhesive particles does not affect positioning, but there is a difference in the shrinkage rate of the adhesive layer – the high shrinkage adhesive layer causes displacement by pulling the cover after curing. Sunlife hot melt adhesive particle shrinkage rate<1.5%，远优于行业平均3%。
Q: How much deviation of the indentation line is considered unqualified?
A: The standard for hardcover books requires a deviation of ≤ 1mm, exceeding which is considered unqualified. High end picture books require ≤ 0.5mm.
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