Why does hot melt adhesive stick to knives and cure slowly? Reasons and solutions for sticking and cutting loose pages on book pages

#Why does hot melt adhesive stick to knives and cure slowly? Reasons and solutions for sticking and cutting loose pages on book pages

Sometimes there is a strange phenomenon on the glue assembly line: as soon as the book is taken off the machine, the cutting knife presses it down and the pages stick together, or there is still glue hanging on the pressure plate or glue roller that hasn’t dried yet. When torn open, the spine of the book is torn apart and the pages are scattered. The old master often says, ‘The glue hasn’t dried yet.’. Most likely behind this isCuring not completedBelow, using the actual process parameters of Sunlife, we will explain “sticking knife and slow curing” in one go.

1、 First of all, the conclusion is that the essence of sticking knives is that the glue is touched before it solidifies

Hot melt adhesive is a thermoplastic material that relies onCooling and solidificationForming strength does not rely on chemical reactions. From gluing to complete shaping, it generally takes 3-5 minutesIn this window, the glue is still soft and sticky – if the book page touches the knife, pressure plate, or conveyor belt in advance, it will:

• Stick to the cutting blade/pressure plate, tear off the spine of the book when torn open;
• The pages are stuck together, and after cutting, they become loose;
• The back of the book is deformed and uneven.

So ‘sticky knife’ is not a quality issue with the glue, but ratherInsufficient curing time+temperature/machine speed mismatchResulting in process issues.

2、 Four common reasons (sorted by frequency of occurrence)

1. The actual temperature of the glue pot is too low (highest frequency)

Sunlife training repeatedly emphasizes:90% of after-sales service actually stems from equipment temperature control failure——The displayed temperature is 160 ℃, but the actual temperature of the glue pot may only be 100 ℃. The temperature is not enough, the viscosity of the adhesive is high, the infiltration is poor, and it seems that it has not reached the process window when applied, resulting in slow downstream curing. First, calibrate the glue pot with a thermometeractualTemperature is more effective than changing the glue.

2. The machine speed exceeds the opening/curing capacity of the adhesive

The opening time varies randomly (15-20 seconds at low speeds of about 2000 km/h, 5-10 seconds at medium speeds, and 2-7 seconds at high speeds of over 4000 km/h). As the machine speed increases, the pages are pushed forward for cutting/stacking while the glue is still soft, naturally sticking to the blade. Before speeding up, confirm whether the model used matches the speed of the machine, and if necessary, switch to a faster fixed model.

3. Low workshop environment temperature

In winter, the temperature is low, and although the glue cools quickly, the internal heat dissipation of the stacked pages is slow, and local curing is delayed; At the same time, if the glue pot is not preheated properly at low temperatures, it is more likely to slow down overall. Maintain a process environment temperature of 15-26 ℃ in the workshop, and preheat the glue pot thoroughly before starting up.

4. Excessive glue application or uneven glue layer

If the adhesive coating is too thick, the surface will form a crust, but the interior has not yet cured, making it the easiest to “dry on the outside and stick on the inside” and stick to the knife. Control the adhesive layer according to the thickness of the book (add thin adhesive layer for thin book cores and appropriate adhesive layer for thick books), do not add too much blindly.

3、 On site processing checklist

1. First, use a thermometer to measure the actual temperature of the glue potConfirm within the process window of 160-180 ℃;

2. Verify machine speed and model opening timeWhether it matches, replace the fast fixing adhesive on the high-speed line;

3. Check the temperature in the workshopExtend preheating at low temperatures and slow down the pace if necessary;

4. Adhesive layerThin books should be applied less, thick books should be applied evenly to avoid external dryness and internal adhesion;

5. If the knife still sticks, pause the line and let the book slide pass through an additional cooling channel before cutting.

Frequently Asked Questions

Q: Can changing to a faster drying adhesive solve the problem?

A: Can alleviate, but the root cause often lies in temperature/machine speed. First calibrate the actual temperature of the glue pot, check the matching of the machine speed, and then consider changing to a quick fix model, otherwise it will be in vain.

Q: It’s particularly easy to stick knives in winter, can’t glue work?

A: Mostly due to low ambient temperature and insufficient preheating of the glue pot. Maintaining a temperature of 15-26 ℃ in the workshop, sufficient preheating, and checking the machine speed are more targeted than changing the glue urgently.

Don’t blame the glue when encountering a sticky knife, it’s mostly because the glue was touched before it even dried. Follow the above five steps to investigate temperature, machine speed, environment, and adhesive layer one by one – if it is not picked up on time, inform Sunlife of the model and on-site situation, align the curing window according to the model and process card, and the adhesive knife and loose pages can be basically eliminated.

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