Discussion on EVA hot melt adhesive and its applic

Brief discussion on EVA hot melt adhesive and its use

according to incomplete statistics, at present, there are about 7-8 billion books published every year in China, and there are as many as 3 billion books in this book. Nearly 8000 tons of EVA hot melt adhesive are used throughout the year. Among these nearly 10billion books, more than 60% are processed by wireless binding process. With the continuous development of the publishing and printing industry and the increasing use of books, EVA hot melt adhesive has become one of the main materials for the bonding of books in China, and the wireless binding process has also become the main material for the processing of books. China is still in the stage of industrialization, informatization, urbanization, marketization and internationalization, and the process technology fully adapts to the development trend of fast publishing and short cycle in the modern publishing industry. Flour paste, bone glue and synthetic resin glue such as polyvinyl acetate (PVAc) glue, which have been used for many years, are mostly cold glue, and they all rely on ambient temperature, drying tools and drying equipment to complete the drying process after processing. This drying method is slow and not easy to set, which affects the appearance quality of books and the speed of publishing, and also affects the publishing cycle. The use of thermoplastic hot melt adhesive to bind books solves this contradiction, greatly improves the binding processing speed and shortens the publishing cycle. Here are some opinions of the author on EVA hot melt adhesive and its use, which are for reference only. Composition of EVA hot melt adhesive

simply speaking, EVA hot melt adhesive is a solid fusible polymer that does not need solvents and does not contain water. It is a solid at room temperature and becomes a flowing and viscous liquid binder when heated and melted to a certain temperature. After melting, the colloid of EVA hot melt adhesive is light brown translucent or white (adding titanium dioxide). EVA hot melt adhesive is composed of basic resin, tackifier, viscosity regulator and antioxidant. 1. Basic resin: the basic resin of EVA hot melt adhesive - EVA resin is copolymerized by ethylene and vinyl acetate under high temperature and pressure. EVA resin is the main component of hot melt adhesive. According to the required ratio, it generally accounts for 40% - 60% of hot melt adhesive. The proportion of the basic resin determines the basic properties of the hot melt adhesive, such as the bonding ability of the adhesive, the melting temperature and the selection and preparation of additives, all depend on the proportion of the basic resin. Therefore, the EVA hot melt adhesive used for binding should properly select the proportion of ethylene and vinyl acetate according to the needs of the adherend, and select the varieties with certain softness, elasticity, adhesion, small deformation, etc. 2. Tackifier tackifier is one of the main additives of EVA hot melt adhesive. If only the basic resin is used, it can only have bonding force when it melts at a certain temperature. Once the temperature drops, it will not bond firmly, or even lose the bonding ability. It is difficult to wet and penetrate the paper, and it cannot achieve the ideal bonding effect. Add some substances that can be eutectic with the basic resin in order to increase its bonding performance, which requires the addition of tackifier. Adding an appropriate amount of tackifier to EVA hot melt adhesive can also improve the fluidity of the colloid, so as to enhance the wetting and permeability of the colloid to the adherend, improve the bonding strength, and meet the needs of books for bonding strength. Rosin substances and terpene resins are generally used as tackifiers, and the proportion is generally between 15% and 20%. 3. Viscosity regulator viscosity regulator is also one of the main additives of EVA hot melt adhesive. Its function is to reduce the melt viscosity, increase the fluidity and wettability, and adjust the solidification speed, so as to achieve the purpose of fast bonding. Without the addition of viscosity regulator, the colloid will be too viscous, not easy to flow, difficult to apply, not easy to penetrate into the pages, and the pages of the book post cannot be bonded firmly. When selecting viscosity regulator, substances with low melting point should be selected, such as paraffin, whose softening point (melting point) is between 65 ~ 105 ℃, which is lower than that of basic resin (the softening point of basic resin is above 100 ℃), so wax is the most appropriate choice as viscosity regulator. When mixing, pay attention to the reasonable dosage. Too much or too little paraffin will affect the quality of EVA hot melt adhesive, and the proportion with other additives should be appropriate. Generally, the dosage should be controlled at about 10%. 4. Antioxidant colloid will oxidize and decompose due to high temperature when melting. Adding an appropriate amount of antioxidant can prevent premature aging of EVA hot melt adhesive. And under high temperature conditions, adding an appropriate amount of antioxidant, the viscosity of the adhesive will not change, which is enough to ensure the bonding effect of books. BHT (DI tert butyl p-methylphenol) is generally used as antioxidant, and its effect is relatively good. Its dosage is generally controlled at about 0.5%. 5. Anti cold and anti heat agent EVA hot melt adhesive is a thermoplastic bonding material, which has strict requirements for the working environment when used. Adding antifreeze can prevent the opening time and curing time of colloid from advancing in winter when the temperature is low, which will affect the adhesion of books; Adding anti heat agent can prevent the colloid from being difficult to solidify and cool down due to high temperature in summer and regional differences, which will affect the cutting quality and the appearance effect of books. The main function of antifreeze is to improve the plasticity of EVA hot melt adhesive. A very small amount of isobutylene can be added (generally about 2%); The main function of anti heat agent is to slightly improve the hardness of EVA hot melt adhesive, that is, to increase the basic resin composition. Due to the large temperature difference throughout the year in China, sometimes books loaded in summer are used in winter, and sometimes books loaded in winter are used in summer. Therefore, the allocation of anti cold or anti heat agents should be controlled within a small range$ Page break $characteristics of EVA hot melt adhesive

1 The EVA hot melt adhesive, which is fast curing and easy to keep, is a solid at room temperature. When it is heated and melted to a certain temperature, it becomes a liquid binder. The colloid is separated from the heating device, cooled below the melting point, and quickly becomes a solid (it recovers to the original solid rubber block after hardening). Due to the high melting point of the colloid (generally at 80 ℃, the melting point of the colloid is about 30kg for domestic high-end cars or foreign models), it is massive at room temperature, which is simple to package and easy to store. Its storage period is generally about one and a half years. 2. Low pollution and strong adhesion. EVA hot melt adhesive has a slight taste when melting into liquid. General equipment is equipped with odor absorption devices, so it is not harmful to human body; Because of the high melting point of this kind of glue, there will be no colloid loss and environmental pollution. The adhesive layer of EVA hot melt adhesive has certain flexibility and hardness after coating, and the bonded books are firm and durable, which is very suitable for the bonding of books, periodicals, books, etc. 3. The adhesive layer of EVA hot melt adhesive with re adhesion property applied to the adherend can be softened when heated above the melting point after curing or cooling and hardening, and become a liquid colloid with the increase of glue temperature to restore the re adhesion. In case of binding errors such as slanted cover and uneven Book stickers during processing, the applied adhesive layer can be locally heated with a back ironing machine or a heating plate to separate the book stickers or back from the cover, and then bonded into a qualified finished product after correction, which can avoid the waste of the cover and is conducive to the repair of defective products. 4. Easy to use. When using EVA hot-melt adhesive, just put the adhesive block into a container for hot melting to make it a liquid adhesive with the required viscosity, and then apply it on the object to be adhered. After neat, clamping and pressing, the bonding and curing can be completed in a few seconds, and the degree of hardening, cooling and drying can be achieved in 2 ~ 3 minutes. At the same time, it can be cut into volumes$ Page break $preparation before use of EVA hot melt adhesive

at present, EVA hot melt adhesive suitable for post press binding produced and used in China is generally divided into high-speed adhesive and low-speed adhesive. The curing speed of high-speed adhesive is slightly faster than that of low-speed adhesive, which can be used in high-speed linkage production line; The curing speed of low-speed adhesive is relatively slow, which can be used for low-speed single machine. According to the different texture of the stickies, it can be divided into letterpress paper, offset paper and coated paper, and can be divided into back glue (book back glue) and side glue (sticky mouth glue), so as to meet the needs of the strength of the stickies and achieve the purpose of both good bonding effect and cost reduction. Therefore, when choosing the type of glue, you must see the type, model and technical parameters clearly according to your needs, and then purchase and use it after confirmation. Before using EVA hot melt adhesive for processing, it is necessary to prepare the glue, such as glue storage, preheating, temperature regulation, etc. 1. The type and model of glue shall be correctly selected according to the needs of glue storage, and glue blocks shall be added in the preheating glue pot. The quantity of glue storage shall be determined by the number of books bonded. Do not store too much or too little glue. If you store too much glue, the colloid accumulated in the glue pot will melt repeatedly and carbonize; There is too little glue storage, so it needs to be preheated again, which wastes time and affects production. 2. Preheat EVA hot melt adhesive before use, the solid rubber block must be preheated to melt into liquid before use. It is strictly forbidden to put the rubber block directly into the working rubber pot for heating. There are two preheating methods: one is preheating with oil bath, that is, preheating with jacketed melting pot; The utility model relates to preheating with an electric heating plate, that is, using an electric heating plate device to preheat directly in a preheating pot. The preheating time generally takes 2 hours. When the colloid reaches the required heating temperature and has good fluidity, the glue solution is put into the working glue pot with appropriate temperature (160 ~ 180 ℃) through the thermostatic pipe for binding books, etc. 3. Temperature regulation refers to adjusting the temperature of the used adhesive according to the technical parameters of EVA hot melt adhesive. The use temperature of EVA hot melt adhesive is extremely strict (only ± 5 ℃ floating amount is allowed in foreign countries), which must be adjusted according to standard parameters. It is not allowed to arbitrarily increase or reduce the glue temperature and damage the viscosity of normal fluid, Professor Martin Dunn (now dean of the school of engineering and Applied Sciences at the University of Colorado Denver), another person in charge of the project, said: "Generally speaking, there are some losses. In case of special circumstances, the floating amount is up to ± 10 ℃, and normal processing can be carried out after all preparations are made. $page break $bonding suitability of EVA hot melt adhesive

in the actual production and use process, the adhesion of EVA hot melt adhesive will change with the heating temperature of hot melt adhesive, sticky material, the width and depth of milling back, the height of rubber wheel and the running speed of binding machine, and different bonding effects will be obtained. We Analyze from the following points: a when the hot melt adhesive is used to bond books and periodicals, the softening point (melting point) of EVA hot melt adhesive is generally about 80 ℃, that is, when heated to 80 ℃, the colloid begins to soften and gradually melts, but this temperature is only the melting temperature of EVA hot melt adhesive, not the temperature used. Only when the temperature is heated to 130 ~ 180 ℃, the working temperature of hot melt adhesive can be reached. The colloid reaching this temperature, whether viscosity, viscosity, fluidity, etc., is suitable for the bonding of books and periodicals. According to foreign data, when the glue temperature is 170 ℃, the tensile test value of EVA hot melt adhesive (according to the different glue models) can reach 8.83 ± 0.44n/cm when it is applied to ordinary book board paper; When the glue temperature rises to 180 ℃, the exchange and cooperation with the British Ministry of Commerce, energy and industrial strategy in the field of green manufacturing is included in the policy outcome of the 9th China UK economic and financial dialogue ℃, the tensile test value of the glue will drop to 7.33 ± 0.33n/cm; When the glue temperature drops to 155 ℃, the tensile value is only 5.22 ± 0.25n/cm. It can be seen that the use temperature of EVA hot melt adhesive must be strictly controlled, not too high or too low. When the glue temperature is too high, although the fluidity and permeability of the glue increase (dilute), the bonding strength decreases; The glue temperature is too low. Although the viscosity of the colloid increases (thickens), it affects the fluidity of the colloid and the smoothness of the coating