How to Solve the Issue of Pages Falling Out in Wireless Glue Binding of Books and Journals?

In bookbinding, wireless glue binding accounts for approximately 60% of the annual production of 8 billion copies of books and journals. Its advantages are evident: short production cycles, simple processes, interconnectivity, and standalone capabilities. The introduction and application of wireless glue binding production lines, especially, have further promoted the development of this technology. However, due to various reasons, there are many quality issues in wireless glue-bound books and journals, such as pages falling out. This problem not only troubles manufacturers but also causes inconvenience for readers. The frequent occurrence of page falling issues in textbooks, especially in primary and secondary schools, has attracted the attention of relevant authorities. Consequently, publishers and printing enterprises are facing an unprecedented crisis in terms of quality and reputation.

There are numerous factors contributing to the issue of pages falling out in wireless glue-bound books and journals. If key steps in the production process are not handled properly or are not standardized, it can lead to page falling problems. However, by identifying the causes of page falling and implementing effective solutions, the quality of wireless glue-bound books and journals can be ensured. Based on years of work experience and practical knowledge, the following key steps in the binding process can be controlled to effectively prevent page falling issues.

Milling Back and Grooving

Milling back and grooving is a crucial step in the wireless glue binding production process. It involves using a high-speed rotating flat milling cutter to mill the entire book into individual pages and creating grooves or notches on the book spine using a standing milling cutter. The key to ensuring strong adhesion on the book spine is the depth of the groove, and adjusting the height of the standing milling cutter is the most challenging factor. If the standing milling cutter is set too low, the groove depth may be insufficient, while setting it too high can lead to collisions with the book clamp, causing damage. Especially with disc-type binding machines, stability issues may arise after a few years of use, making the milling cutter more prone to damage. Therefore, the following points should be considered during the milling back and grooving process:

. Adjust the distance between the standing milling cutter and the book clamp. This involves fixing the height of the flat milling cutter and then using a thickness gauge to determine the distance between each standing milling cutter and the book clamp, keeping it at 0.3mm. After determining the height of each standing milling cutter, measure its distance from all book clamps. If the groove depth is insufficient, lower the height of the flat milling cutter to raise the position of the standing milling cutter, ensuring an appropriate groove depth.

. Regularly inspect the milling cutter and replace it with the appropriate tool based on the specifications and requirements of the bound books and journals.

. Determine whether to replace a single milling cutter, part of it, or the entire set based on the wear and tear of the milling cutter.

. When replacing the milling cutter, use a gauge to install it, ensuring that all flat milling cutters remain at the same radius to avoid blade damage. The height deviation should be controlled within 0.1mm.

Glue Application

Wireless glue binding primarily uses hot melt adhesive for bonding. Hot melt adhesive, with its high melting point, quick solidification, and strong adhesion, is convenient to use. Improper application methods during the glue coating process can lead to uneven glue distribution, a major cause of pages falling out.

1. Control the Thickness of the Glue Layer

Balancing the thickness of the glue layer is crucial. If the layer is too thin, it can affect the binding strength of the books and increase production costs if too thick. Therefore, it is essential to control the thickness of the glue layer based on the thickness and type of paper used in the books.

After the book core passes through the milling back and grooving process, the first glue roller encountered in the glue coating process is located 1.5mm below the book spine. This roller, with a large diameter (120mm) and high position, generally has a 1.5-2mm thick glue layer controlled by a damper on its surface. Its function is to apply a small amount of glue to the book spine and allow some glue to penetrate into the grooves on the book spine. The second glue roller evens out the glue on the book core, with a smaller diameter (117mm) and positioned 2mm below the book spine.

In the glue coating process, the primary control of the thickness of the glue layer on the book spine comes from the glue roller that reverses outside the glue pot. If the layer is too thin, reduce the height of the glue roller for compensation; if it is too thick, raise the height of the glue roller to reduce the thickness. Adjusting the roller to the appropriate position ensures the desired thickness of the glue layer. This reversing glue roller is generally positioned 1-1.5mm below the book spine, ensuring a dried glue layer of around 1mm. Additionally, it has another function, using reverse rotation to cut off excess glue, maintaining machine cleanliness.

2. Control the Glue Pot Temperature

Hot melt adhesive used in wireless glue binding is a high-speed hot melt adhesive, typically controlled at around 160°C. Achieving the optimal adhesion strength of the glue requires precise control of the glue pot temperature.

The temperature of the glue pot should not be too high or too low. High temperatures can cause the glue to age, become thin, darken in color, and not adhere well to the book spine, leading to pages falling out. Low temperatures can result in thickening and hardening of the glue, making the book spine prone to breakage and page falling.

To control the temperature of the hot melt adhesive, consider the following:

. Do not start the machine if the glue temperature has not reached the target temperature.

. If the glue temperature is significantly above the target, lower the glue pot temperature promptly or add a small amount of glue blocks for stirring until it reaches the target temperature before starting the machine.

. If the color of the glue turns from light yellow to dark brown, indicating aging, the glue must be completely removed from the pot, and new adhesive material should be used.

. Preheat the hot melt adhesive before use, and the preheating temperature should match the working temperature of the glue pot.

Regularly Clean the Glue Pot

Regularly cleaning the glue pot is an essential step in the wireless glue binding process. During the use of any type of adhesive, sediment may accumulate at the bottom of the pot, affecting the heating speed of the glue pot. If not cleaned promptly, some sediment may solidify and block the flow of glue between the glue roller and the damper, causing poor flow. In severe cases, the glue roller may experience intermittent adhesion, directly affecting the thickness and uniformity of the glue applied to the book spine, resulting in inconsistent glue presence on the book spine. If not identified promptly, this issue will lead to page falling problems, requiring extensive rework of finished books. Therefore, regular cleaning of the glue pot is crucial.

Generally, the cleaning cycle of the glue pot can be determined based on the production volume or intermittent production. This ensures the cleanliness of the glue pot while maintaining the quality of bookbinding and production cycles.

Promptly Repair Books with Falling Pages

Books produced using hot melt adhesive in wireless glue binding possess repairability. Any bonding quality issues identified during quality inspections can be repaired using the re-adhesive properties of hot melt adhesive.

Especially during the trimming process, due to certain pressures applied, quality issues in books are easily exposed. Therefore, when trimming books with three-side knives, careful observation is required to promptly discover and accurately identify the causes of problems and remediate books, eliminating the production of faulty books. For example:

. If the book spine shows signs of looseness, it may be due to double sheets on the cover or inadequate bonding between the cover and book spine.

. If the book spine feels soft, it may be due to insufficient glue layer thickness or the occurrence of adhesive breaks.

. If there are many wrinkles on the book spine, it may be due to inadequate glue layer thickness or insufficient clamping force during pressing.

. Issues such as page skipping or uneven binding can be identified from the top and bottom edges of the book.

It’s important to note that repaired books will not be as aesthetically pleasing as books formed in one go on the machine. Therefore, reliance on repairs should not overshadow quality control during the production process. In conclusion, while there are many factors influencing pages falling out in wireless glue-bound books and journals, strict quality control at various stages of production and standardized operations can effectively solve this issue. With the rapid development of printing technology in China and the continuous improvement of post-press binding process requirements, ongoing learning of new techniques and knowledge is essential when researching and solving practical problems that arise during production.