Is it feasible to heat the hot melt adhesive particles for rework after solidification? A genuine record of a batch of returns and rework

The return has arrived, can it be reworked

A certain graphic and text fast printing factory received a batch of customer returns: 3000 adhesive manuals with covers and book cores offset by 2mm were rejected by the customer. The factory director’s first reaction was’ can we open it and reattach it? ‘, buthot melt adhesive pelletsThe feasibility of reheating and reworking after solidification is uncertain.

This problem is very common in the book binding and packaging industry. Hot melt adhesive particles belong to thermoplastic materials and can theoretically be repeatedly heated and melted – but “being able to rework” and “meeting quality standards after rework” are two different things. The key is to observe the degree of performance degradation of the adhesive after secondary heating.

Rework actual testing

The factory conducted a control experiment using standard EVA type Sunlife hot melt adhesive particles:

• First bondingPeel strength is 4.2N/cm, and the adhesive layer is uniform without bubbles.
• Secondary heating reworkHeat the old adhesive layer to 170 ℃ and melt it again, reducing the peel strength to 3.5N/cm (a decrease of 17%), and causing slight yellowing of the adhesive layer.
• Triple heatingThe peel strength decreased to 2.8N/cm (a 33% decrease), and the adhesive layer became significantly brittle with an increase in carbides.

Conclusion: Rework with secondary heating is feasible, but there is a decline in quality, and it is not recommended to do it more than three times. The factory ultimately chose to perform a one-time rework on the return manual – heating and softening the spine adhesive layer, then disassembling and re gluing and pressing it. The reworked product passed the customer’s page turning tensile test.

Key points of rework operation

The secondary heating temperature is 5-10 ℃ higher than the initial heating temperature to compensate for the decrease in fluidity; After rework, new glue needs to be applied (old glue cannot be used purely); Rework products should be marked to track quality. Guangzhou Sunlife suggests controlling the rework ratio within 5% of the total production.

Frequently Asked Questions (FAQ)

Q: Can PUR hot melt adhesive particles be reworked?

A: I can’t. PUR is cured by moisture cross-linking and belongs to thermosetting, and will not melt after secondary heating. Rework can only be done by changing the adhesive.

Q: How long can the reworked book last?

A: Secondary reworked products can be used normally for 1-2 years at room temperature, but their lifespan will be shortened by about 30% in high temperature and high humidity environments.