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In March 2026, a textbook printing factory in Wuhan increased the speed of the glue line from 400 books/hour to 600 books/hour in order to meet the autumn textbook orders. As a result, the page drop rate skyrocketed from 0.3% to 4.2%, with almost 1 out of every 25 books experiencing page drop, forcing the production line to slow down.
The factory has tried increasing the amount of glue, raising the glue temperature, and adjusting the milling depth, but none of them have fundamentally improved. Where is the problem?
Sunlife’s technical team conducted on-site calculations: at a rate of 400 copies per hour, each book takes approximately 9 seconds from gluing to cover pressing; 600 books/hour shortened to 6 seconds. And the fast curing type used by the factoryhot melt adhesive pelletsThe process window with an opening time of 8 seconds to 6 seconds has exceeded the opening time of the glue, and the glue has not fully wetted the spine before it is pressed and solidified, resulting in insufficient penetration and page dropping.
Replace with Sunlife hot melt adhesive granules of medium speed solidification type (opening time 10-12 seconds), while reducing the adhesive temperature from 175 ° C to 170 ° C (cooling can extend the opening time by 1-2 seconds). After adjustment, there is sufficient wetting time within the 6-second process window, and the page drop rate is reduced to 0.1%.
Key experience: Before speeding up, it is necessary to calculate the entire process time of “coating pressing” and match it with the opening time of the hot melt adhesive particles, rather than blindly adding adhesive.
Q: Is the longer the opening time of the adhesive, the better?
A: No, it’s not. The opening time is too long and the solidification is slow, resulting in long waiting times for subsequent processes and a decrease in production capacity. Choose the model that perfectly covers the process window for optimal performance.
Q: How to quickly calculate the process window?
A: The minimum opening time requirement is to measure the entire process from the contact of the glue roller with the spine of the book to the release of the cover pressure plate with a stopwatch. The opening time of the adhesive should be 1-2 seconds greater than this value.
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