The use of EVA hot melt adhesive in binding

In book and periodical binding, for EVA hot melt adhesives, they are generally classified into high-speed adhesives and low-speed adhesives based on different curing times. The curing speed of high-speed glue is slightly faster, while that of low-speed glue is slightly slower. Books are classified into offset paper adhesive and coated paper adhesive based on their different materials. According to different uses, there are back adhesive and side adhesive atmospheres. To achieve a good bonding effect, different hot melt adhesives should be selected to meet the strength and requirements of the bonded objects. When using hot melt adhesive, it is essential to master the preparatory procedures before use, such as preheating and temperature control.

1. Preheating of EVA hot melt adhesive

Before using hot melt adhesive, the solid adhesive must be preheated to melt. There are two preheating methods: one is oil bath preheating. That is, preheating the jacket furnace; Another method is to preheat with an electric heating plate, that is, to preheat directly in the preheating furnace with an electric heating plate device. The preheating time is generally 2 hours. When the gel reaches the required heating temperature and has good fluidity, the glue is released into the working glue pot with a temperature of 140 to 170℃ through a constant-temperature pipeline for binding books and the like.

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In the actual production process, the adhesive force of hot melt adhesive will vary depending on the heating temperature of the hot melt adhesive, the type of material to be bonded, the width and depth of the milling back, the height of the adhesive, and the operating speed of the binding machine, resulting in different bonding effects.

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The softening point of hot melt adhesive is generally above 80℃. That is to say, when heated to 80°C, the colloid will start to soften and melt. This temperature is only the melting point of the hot melt adhesive. To melt it to the extent that it can bond books, the heating temperature must be raised to 140-170°C. At this temperature, the viscosity of the colloid, fluid and viscosity can all be suitable for book binding.

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The quality of the paper used for making books varies, and so should the temperature for gluing. This is not only because the fibers of the paper are different, but more importantly, due to the different types and textures of the paper, the thermal conductivity of the paper varies, thereby changing the cooling rate. Taking the thermal conductivity of coated paper (also known as coated paper) and letterpress paper (non-coated paper) as examples, the cooling speed of the glue in the former is faster than that in the latter. Because the inorganic matter contained in coated paper is about ten times higher than that in non-coated paper such as letterpress, newsprint and offset paper, and inorganic matter has good thermal conductivity, it can make the hot melt adhesive cool down faster.

For instance, when the gluing temperature is all 170℃, the tensile test value of the hot melt adhesive for non-coated paper can meet the expected requirements, while that for coated paper cannot. Therefore, when applying adhesive to coated paper, it is necessary to increase the temperature of the adhesive solution to enhance its strength.

(3) The relationship between the open time of EVA hot melt adhesive and the operating speed of production equipment.

In the production of glue-free binding processing, when using hot melt adhesive, three time stages must be strictly controlled, namely the open time, curing time and the drying time for cooling and hardening. The opening time refers to the time when glue is applied to the back of the book. The curing time is the time it takes for the cover and back of a book to bond together. The cooling, hardening and drying time refers to the time it takes for a book with a cover to cool and set after curing. Only after going through these three time stages can this book be finalized and reach the expected shape.

These several time periods when hot melt adhesive is used are closely related to the operating speed of the equipment. For instance, the open time of hot melt adhesive is generally 7 to 15 seconds. And this is precisely the time for the perfect adhesive to be milled and transferred. The gluing process for the cover and back of the book (excluding the card back) must be completed within 15 seconds so that the hot melt adhesive can achieve a good bonding effect. If the equipment operates very slowly and the bonding work cannot be completed within 15 seconds, then the bonding effect is definitely not ideal. And problems such as poor adhesion, non-stickiness, the book falling apart after binding, and page dropping may occur. Therefore, the open time of hot melt adhesive should take into account the normal working speed of the adhesive without glue. The curing time of hot melt adhesive is generally the same as the open time. Of course, users hope that the curing time can be shorter to facilitate the binding and setting of books.

In addition to the opening and curing times, the cooling, hardening and drying times are also required to be basically accurate, especially for the adhesives used in the wireless glue binding production line. That’s because this kind of production line is a linked assembly line from the collating machine to the collating and cutting of books, with all parts interconnected. After the book is glued to the foreskin, the time for the book to be transferred to the cutting part must follow a certain rule, so that the book cutting can meet the ideal requirements. Cooling, hardening and drying can ensure the finished product.