Is the milling depth insufficient for hot melt adhesive particles to penetrate? These 3 misconceptions keep you adjusting the glue but can’t do it well

Is the problem of falling pages always blamed on glue? Perhaps milling the back is the root cause

The most troublesome quality issue for printing factories is the loss of pages in book and magazine glue packaging, and many manufacturers’ first reaction is to replace themhot melt adhesive pelletsModel, glue temperature adjustment, and glue amount – after a lot of tinkering, there was no improvement because the real root cause was insufficient milling depth. Please self examine the following three misconceptions.

• Misconception 1: “Milling out the burrs is enough”Milling the back is not only about cutting the edges, but also about creating grooves on the paper for the adhesive to penetrate. Shallow milling with a depth of less than 1.5mm, even the best hot melt adhesive particles can only hang on the surface. The standard requirement is 1.5-2.5mm, and thick books and periodicals are recommended to be over 2.0mm.
• Misconception 2: “Slot spacing doesn’t matter”The slot spacing is too wide, and the adhesive cannot effectively penetrate between each page. The standard spacing is 1-2cm, too wide is equivalent to no slot.
• Misconception 3: “Blunt milling back knife does not affect”The roughness of the cut made by blunt blade milling is insufficient, and the grooves are shallow and uneven, which directly affects the penetration effect. It is recommended to replace or grind the milling cutter every 3-6 months.

Frequently Asked Questions (FAQ)

Q: Is there any other reason why the milling depth is sufficient but the page still drops?

A: Check the adhesive temperature and opening time. Low temperature, high viscosity of the adhesive solution, slow penetration, short opening time, and curing before the adhesive penetrates can all lead to peeling. Sunlife hot melt adhesive granules have a standard opening time of 8-12 seconds, covering the vast majority of adhesive installation speeds.

Q: What is the reason why the pages of a book that has been glued on take a few days to fall off?

A: Typical adhesive layer aging and cracking are usually caused by high adhesive temperature (>190 ° C) leading to thermal degradation of the adhesive solution. The initial adhesive strength is normal but rapidly decreases after a few days. Reducing the adhesive temperature to 170-180 ° C is key.