How many times should books and magazines be coated with glue? How to choose between single pass and double pass adhesive backing

The vast majority of wireless adhesive packaging for books and magazines is a combination of a single layer of back glue and one layer of side glue (edge glue): the spine back is coated once to provide the main bonding, and the joint between the covers on both sides of the spine is coated again to fix the cover.The so-called “how many times to apply” usually refers to whether or not to apply the backing glue twice. The answer is not fixed – a single pass is sufficient for regular books, only for thick books, dense paper, loose paper, and high demand books should double pass or touch up be considered. Explain the decision-making logic clearly below.

1、 Why is it a single pass adhesive for regular use

The standard process for wireless adhesive installation is: milling back and pulling hair → single pass back adhesive application → side adhesive application → packaging cover → book pressing and cutting. A single layer of adhesive can fill the spine of the book and penetrate the brushed fibers, providing enough adhesive force to prevent the pages from falling apart. High single pass efficiency and easy control of opening time windows are mainstream practices.

Whether a single pass is sufficient depends on three conditions:Paper ordinary (adhesive paper/double adhesive paper), book not thick, machine speed matchingAll three are met, and there is basically no problem with single pass adhesive.

2、 Under what circumstances should double coating/touch up be considered

When encountering the following types of situations where single penetration or strength may not be sufficient, only then will consideration be given to applying two coats or partial touch up on the backing adhesive:

1. Thick books and dense paper have poor penetration.The book core is thick and the paper is dense (such as high weight adhesive paper and some copperplate paper). A single layer of adhesive does not penetrate deeply, and two layers of backing adhesive can separate layers and improve penetration and strength;
2. Paper powdering and weak surface.Paper with a high amount of paper powder and low surface strength has limited adhesive strength in a single pass, but applying a second coat can improve it;
3. High requirement for spine strength.For reference books, textbooks, and other materials that require frequent and durable flipping, apply two layers of adhesive backing to enhance fatigue resistance;
4. The spine shape of the book is irregular.The end face of the book block is uneven or unevenly brushed, and cannot be filled in a single pass. Apply and level it.

3、 The cost of double pass (don’t blindly increase the number of passes)

Applying adhesive twice on the back is not like ‘the more times, the stronger’, and the cost is obvious:

• Opening hours have been compressedIf the first pass has already been partially cured between two passes, the second pass will have poor bonding at the interface and instead will result in delamination; To do it twice, you need to adjust the machine speed, temperature, and interval well;
• Decreased efficiency and increased costsApplying glue once more slows down the pace and increases glue consumption;
• Risk of excessive adhesive layer, overflow/exposed adhesive rootsApplying too thick will overflow into the incision, resulting in the appearance defect of another article in this series, ‘Exposed Glue Root’.

So the essence of ‘whether or not to repeat’ isIs the penetration and strength sufficientThe judgment is not that thicker is better.

4、 Sunlife selection and testing suggestions

To decide whether to use single pass or double pass, first make a sample according to your paper, book thickness, and machine speed to compare the cut penetration and drawing strength, and then determine the process. Sunlife will provide recommended adhesive layer thickness and number of adhesive passes based on your paper and machine speed when using hot melt adhesive for books and magazines. It also supports sending samples, making samples on the machine, and determining the process according to the actual effect. The specific adhesive amount, temperature, and opening time are as followsConclusion of accompanying process card and sampleBased on experience, do not rely on hard estimation; If it meets the standard in a single attempt, there is no need to blindly repeat it twice for the sake of being “more secure”.

Explanation: This article only provides a process decision explanation for the number of adhesive passes on the wireless adhesive packaging of books and periodicals. The specific adhesive layer thickness, machine speed, and opening time 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 ‘.