What is the reason for the exposed glue root on the spine of a bound book? Reasons and solutions for exposed adhesive roots

The ‘exposed adhesive root’ refers to the part of the book spine (top or bottom) that is not covered by paper and directly shows the exposed adhesive layer after cutting three sides of the adhesive book.It is not the same as “insufficient glue layer (empty glue)”, “uneven book back edges”, and “surface glue overflow” – the latter are problems with the thickness, shape, or surface of the entire spine, while the exposed glue root is a local appearance defect at the edge of the incision where the glue is more than the paper and has been cut. Readers can see yellow or transparent adhesive strips on both ends of the spine of the book at a glance, which affects the appearance and grade.

Let’s explain how it is generated, how to investigate, and how to avoid it.

1、 The exposed glue root and “overflow glue” should be viewed separately

Many people mistake exposed glue roots for overflowing glue, but there are actually two things:

• glue overflowGlue is applied to the surface of the spine and the inside of the cover, which is “excess glue on the surface” and can usually be treated by pressing or scraping the glue;
• Exposed adhesive rootThe glue seeped into the cut end of the book block, and when cutting, the glue and paper were cut together, exposing the “glue in the cut”. Scratching the surface is useless, and it needs to be treated based on the amount of glue and cutting.

Simple judgment: Open the book and look at the top/bottom cut. If there is a clear glue mark and the glue feels protruding or concave compared to the paper surface, it is basically an exposed glue root.

2、 Why do adhesive roots appear (arranged in order of occurrence)

1. The adhesive layer is too thick and overflows into the incision.The amount of adhesive used on the back of the book is relatively large. The adhesive not only fills the spine of the book, but also squeezes towards the top/bottom ends of the book core, and the adhesive naturally comes out after cutting. The thickness control of the adhesive layer can refer to this series’ How much adhesive is suitable for hot melt adhesive ‘.
2. Milling too deep and excessive pulling.If the back of the book is milled too deep or the spine end is brushed too much, the glue will seep into the cut end and accumulate at the end, exposing the glue after cutting.
3. The book core is not aligned properly and the end face is not aligned.The book block is not aligned properly, and there are steps on the end face after clamping. When applying glue, the glue is poured towards the low-lying end, and the cutting height is not consistent. After cutting, the glue is exposed.
4. Cutting with incorrect blade quantity/rules.When cutting on three sides, if the adhesive layer or spine direction deviates from the cutting blade, cut the adhesive layer onto the cutting surface.

3、 How to deal with books that have already exposed their adhesive roots

It is difficult to “repair” the partially exposed glue roots of the already cut book perfectly. The common method is:

• Slight glue exposureUsing fine sand or hot air to gently shrink the adhesive marks on the incision can improve but not completely eliminate them;
• Batch adhesive exposureStop the production line first, follow the four steps of glue quantity, milling back, collision alignment, and cutting in the fourth section below, and then re sample to confirm that the incision is clean before measuring;
• Complaints have been deliveredRecycling by batch, replacing covers, reinstalling or downgrading to avoid repeatedly returning to customers.

the key isDon’t scratch hard on the finished productScratching the paper fibers is more obvious.

4、 How to prevent (list of four step machines)

1. Control the amount of adhesiveThe thickness of the backing adhesive is set according to the thickness of the paper and book, preferably thin rather than thick. First, adjust it to fill the spine of the book perfectly without overflowing at both ends;
2. Moderate back milling and hair pullingBased on visible fibers and a rough and uniform surface, do not excessively roughen to the ends;
3. Clash the book cores together and clamp them tightlyBefore starting the machine, align and clamp the book block, ensure that the end face is flat, and prevent any steps or looseness;
4. Cutting rule calibrationTrim on three sides to leave enough space for the blade, align the spine direction with the cutting blade, and avoid cutting through the adhesive layer.

5、 What can Sunlife do to help

More than 90% of the exposed adhesive root is due to equipment and process parameter issues, not the adhesive itself. Sunlife will provide recommended values for adhesive layer thickness and milling back hair according to your paper, machine speed, and book thickness when using hot melt glue for books and periodicals. It also supports sending samples, making samples on the machine, and determining the process based on the actual cutting effect. The specific amount of glue and temperature are as followsConclusion of accompanying process card and sampleBased on experience, do not rely on hard estimation.

Explanation: This article only provides an investigation and explanation of common appearance defects in wireless adhesive packaging for books and periodicals. The specific adhesive layer thickness, milling depth, and cutting parameters are subject to the conclusions of the accompanying process card and sample; Not to extend unverified statements such as’ all products have passed a certain test ‘.