The influence of milling depth on the adhesion of hot melt adhesive particles: How to adjust 0.8mm to 2.0mm for firmness

Direct answer: It is recommended to control the milling depth of conventional wireless adhesive packaging at 1.0-1.5mm, with thin materials up to 0.8mm and thick materials or copperplate paper up to 2.0mm. If the milling is too shallow, the adhesive will only stick to the surface of the crease and will fall off when flipping the page; The milling is too deep, and the effective fibers of the paper are cut off,Hot melt adhesive granulesNo matter how good it is, it cannot be eaten. The matching of depth and adhesive is the first hurdle for adhesive fastness.

Why does the milling depth directly determine the adhesive effect

The adhesive strength of hot melt adhesive particles comes from two parts: one is the cohesion of the adhesive layer itself, and the other is the mechanical bite formed by the penetration of the adhesive into the paper fibers. The function of milling back is to cut open the folds and expose the fiber end face, allowing the molten glue to “eat” in. The milling back is not in place, and the adhesive can only rely on the area attached to the smooth crease to bear the force. When torn open, a clean interface damage appears – there is still a complete adhesive film on the spine of the book, but the paper has fallen off.

Reference for milling depth of different live parts

Operation tutorial: Five steps to adjust depth accurately

• First stepUse the same batch of paper to make three samples, with 0.8mm, 1.2mm, and 1.6mm respectively.
• The second stepAfter milling, immediately look at the cross-section. The qualified cross-section should have a uniform rough surface, with visible fiber hairs and no uncut folds.
• Step ThreeClean the paper powder. The residual paper powder will form an isolation layer between the adhesive and the paper, which is easier to ignore than adjusting the depth.
• Step FourAfter regular gluing, perform a folding test and fold the spine of the book repeatedly for 20 times without peeling off, which is considered qualified.
• Step 5After determining the depth, fix the parameters, change the paper and retest, do not use one set of parameters to dominate the world.

Common misjudgments

• If the page falls off, increase the amount of glue applied – the glue becomes thicker and more brittle, making the spine harder and unable to open.
• The more grooves there are, the better – too dense grooves will weaken the strength of the paper, and a spacing of 1-2mm is sufficient.
• Only look at the depth, not the tool – after the milling cutter wears out, it cuts an indentation rather than a cross-section, and even the most accurate depth value is useless.

Suggestions for matching Sunlife hot melt adhesive

Guangzhou Sunlife Trading will also understand the milling depth and paper weight when matching book binding customers. For example, for desktop machines with shallow milling backs, it is usually recommended to choose Sunlife hot melt adhesive models with better permeability and slightly lower viscosity; If the milling back is fully linked, a model with slightly higher viscosity and better bending resistance can be used to increase the strength. Only when the glue and process are aligned can the fastness be stable.

Frequently Asked Questions

Is milling deeper and more secure?

No. After exceeding 2mm, the effective connection area of the paper decreases, and the spine is more likely to fall off as a whole, which also increases paper powder and milling cutter wear.

Can we just pull the hair without milling the back?

Thin temporary items can be used, but for formal products, it is recommended to mill first and then roughen. Simply roughening cannot fully open the folds, and it is difficult for glue to enter the fibers.