Is the spine of the bound book too hard to open? 4 common reasons for a strong spine and improvement methods

After binding the wireless adhesive book, sometimes the pages do not fall off and the back of the book is also flat, but when you hold it in your handThe spine of the book is stiff, difficult to open when closed, and the flipping of pages is “clunking” and laborious——Customers often say ‘the book is too hard’ and ‘cannot be opened’. This kind of “hard spine, stiff flipping”, “peeling and peeling”, “uneven back”, “round back and square back shape” are not the same thing: it affectsFlipping through the texture and grade of the finished productIn severe cases, readers are unwilling to flip through, and are particularly sensitive to hardcover/picture books/notebooks. Let’s explain why it’s hard, how to judge it, and how to improve it.

1、 First and foremost, the hardness of the spine of a book is determined by the combination of glue, craftsmanship, and paper, resulting in a unique tactile sensation

The softness of the spine of a book is mainly determined by three things:What kind of glue is used (flexibility), how thick the glue is applied, and how hard the book is pressedConventional book and magazine adhesive pursues firmness and good shaping, which is inherently hard; And formulas like Sunlife S-391 for flat spread glue are softer, able to achieve 180 ° flat spread without hardening the spine. So ‘hard’ may not necessarily be a problem, butToo hard to openWe need to investigate the following four reasons.

2、 4 common triggers (by frequency of occurrence)

1. Too thick adhesive coating (most common)

The thicker the glue is applied, the more and harder the spine accumulates. The reference for adhesive layer provided in the training is: the adhesive layer for 10-12mm thin book cores is about 0.4mm, and for ≥ 20mm thick book cores it is about 0.8-1.0mm. Thin book cores are actually the strongest. Beyond this amount, the spine of the book becomes a ‘thick rubber block’, naturally hard and unable to be flipped. Excessive gap between the glue rollers and high glue level can cause the glue layer to become thicker.

2. The pressure of pressing the book is too great/pressing it too hard

After gluing, the book press machine should compact and shape the book core. Excessive pressure or prolonged holding can cause the adhesive layer and the book to become tightly compressed and compacted, resulting in loss of elasticity and hardening of the spine. Thick books and picture books are prone to heavy lifting in order to avoid being empty, resulting in being too hard to open.

3. Excessive glue temperature, localized carbonization and brittleness

Hot melt adhesive usage temperature 160–180℃ The viscosity and wettability are optimal; Exceeding it will cause thermal depolymerization, carbonization, and the adhesive layer will become brittle, hard, and crack easily (similar to “yellowing and discoloration”). The failure of the glue pot temperature control and the actual temperature being much higher than the set value are typical manifestations of “90% after-sales comes from equipment temperature control” in the training, which can also make the spine of the book hard and brittle.

4. The flexibility of the adhesive itself has been chosen to be high (stiff type vs flat type)

The conventional adhesive is a rigid formula for shaping; If a notebook/business book that should have been “flat and soft to the touch” uses the wrong adhesive, it will be hard and unable to open. Sunlife S-391, a type of flat rubber flooring that is soft and designed specifically for 180 ° leveling, exists to solve the problem of “hard, non foldable, and non leveling”. When selecting, the flexibility should be determined based on whether it should be evenly distributed or not.

3、 Key distinction: Don’t confuse these questions with each other

Many customers confuse “hard spine” with “dropped pages and bulging book backs”, but in fact, the direction of investigation is completely different. Simple note:The spine of the book is so hard that it cannot be flipped open to read this article; Read off the scattered pages; The back of the book is bulging and uneven; Classify by round back and square back.

4、 How to improve and prevent

1. Control adhesive layerCheck the gap between the upper rubber roller and the adhesive level, and control the adhesive layer within the reference range according to the thickness of the book core (thin book ≈ 0.4mm, thick book ≈ 0.8-1.0mm). Do not blindly increase the thickness to ensure stability.
2. Pressure regulating bookThe pressure and holding time of the book should be moderate, and thick books and brochures can be held in sections to avoid crushing the adhesive layer and forming a board.
3. School glue temperatureCheck the actual temperature of the glue pot with a thermometer (training emphasizes that displaying 160 ℃ may only be 100 ℃, otherwise it may be higher), maintain the optimal range of 160-180 ℃, and prevent carbonization and brittleness.
4. Select adhesive based on flexibilityFor laptops/business books that need to be laid flat and have a soft feel, priority should be given to flat and flexible adhesives such as S-391; The corresponding adhesive for regular crisp books is sufficient, do not mix them up.
5. Offline hard booksSlight rewritable ability; Evaluate the hardness and obvious carbonization, replace the adhesive and redo.

5、 Relationship with Sunlife’s real business

Sunlife’s hot melt adhesive for books and magazines covers copperplate paper/adhesive paper/double adhesive paper/thin paper and other scenes. The back adhesive (292/296/295/298, 396/397/398), flat adhesive (391), test paper adhesive (39D), graphic and text store adhesive (393/395) and other models have flexibility positioning. When customers give feedback that the book is too hard and cannot be opened, priority should be given to the four end judgment of “adhesive layer book pressing adhesive temperature adhesive flexibility selection”. Most of them can be improved through parameter and selection adjustments, and it is not necessary to replace the adhesive; Sunlife provides “Instructions for Use/Process Card” along with the goods, and regards “Temperature Control Calibration+Process Training” as a support item to reduce such rework.

Explanation: The temperature and adhesive layer thickness described in this article are general process points, and the specific machine parameters are subject to Sunlife’s accompanying “Instructions/Process Card”; The flexibility and opening time of different models vary, please refer to the actual model technical data for selection.