Abstract: EVA hot melt adhesive is a new type of adhesive that is widely used in the wireless glue binding process. This article describes the properties and methods of using EVA hot melt adhesives in detail from the point of view of the binding process.
In recent years, due to the continuous development of the technology of binding after printing, the book connection method has gradually changed from a wire set in paperback to a wireless glue binding process. In order to meet the needs of shortening the cycle and speeding up the speed of publishing in the modern publishing industry, EVA hot melt adhesives are used as adhesives in this process in China. For a long time, the binding materials for books—adhesives, such as flour pastes, animal glues, PVAC, PVA, VAE, and other adhesive materials, are generally cold glues, which are dried by natural temperature or drying tools and equipment. This drying method takes a long time, the book is not easy to shape, and it affects the speed of the book. The use of EVA hot melt adhesive as a binder solves this problem, greatly improving the speed of bookbinding and meeting the requirements for rapid publication. The process of bonding booklets with hot melt adhesives is a general trend; because of the slow speed and poor quality of appearance, iron wire binding books are bound to be gradually eliminated.
First, what is EVA hot melt adhesive
EVA hot melt adhesive is a kind of polymer that does not need solvent, moisture and 100% solid fusible. It is a solid at room temperature. It melts to a certain degree and becomes a viscous liquid. The agent, which is light brown translucent or white after melting.
The main component of the hot melt adhesive, ie, the base resin is copolymerized with ethylene and vinyl acetate under high pressure, and is made up of a hot melt adhesive by adding a tackifier, a viscosity modifier, and an antioxidant. EVA hot melt adhesive has the following features:
1. It is usually solid at room temperature and melts when heated to a certain degree. Once cooled to below the melting point, it rapidly solidifies (ie, solidifies);
2. It has fast curing, low pollution, and strong adhesion. The adhesive layer has certain flexibility, hardness, and certain toughness;
3. The adhesive is applied on the adherend and cooled and solidified. The adhesive layer can be reheated and melted, re-adhesively bonded to the adherend, and has a certain degree of re-adhesion.
4. When used, as long as the hot melt is heated and melted into the desired liquid state, and applied to the adhered object, the adhesive curing can be completed in a few seconds after being pressed, and hardening, cooling, and drying can be achieved within several minutes. degree.
Second, the use of EVA hot melt adhesive
In EVA hot-melt adhesives currently produced and used in China, the binding is generally divided into two types: high-speed adhesive and low-speed adhesive. The high-speed adhesive has a slightly faster curing speed and the low-speed adhesive cures slightly slower; it is divided into offset papers according to different adhesive substances. , Coated paper with plastic, etc.; and back glue and side glue points, in order to adapt to the strength and needs of the adherend, so as to achieve a good bonding effect. The use of hot melt adhesive to master the pre-preparation process, such as pre-adhesive, temperature and so on.
1. Preheating of EVA hot melt adhesive
Before using the EVA hot melt adhesive, the solid glue must be preheated and melted. There are two methods for preheating: one is preheating with an oil bath, that is, preheating with a jacket, and the other is preheating with a hotplate, which is directly heated in a preheated fryer. The preheating time is generally 2 hours. When the colloid reaches the required heating temperature and has good fluidity, that is, after passing the preheating, the thermosetting pipe is used to release the glue liquid to the working glue pan whose temperature is 160-200°C. , for the use of glue bound book books.
2. Adhesion and adaptability of EVA hot melt adhesive
In the actual production process, the adhesive strength of the hot melt adhesive will vary depending on the temperature of the hot melt adhesive, the difference and superiority of the adherent material, the width and depth of the milled back, the height of the glue, and the operation of the binder. Different speeds, etc., get different bonding effects.
(1) Heating temperature of hot melt adhesive
The softening point of hot-melt adhesives should generally be above 80°C. That is, when heated to 80°C, the colloids should begin to soften and melt. This temperature is just the melting temperature of the hot melt. To melt it to the extent that it can bind books, the heating temperature also rises to 130-180°C. At this temperature, the viscosity, fluid, and viscosity of the colloid are all suitable for the binding of books.
(2) The relationship between the different papers and the glue temperature
The texture of the paper used to produce books is different, so the temperature of the glue should also be different. This is not only because the fibers of the paper are different, but more importantly, due to different types of paper and different textures, different thermal conductivities are produced for the colloids, resulting in changes in the cooling rate. Taking the thermal conductivity of coated paper (also known as coated paper) and letterpress paper (non-coated paper) as an example, the former can be cooled faster than the latter. Because the inorganic content contained in the coated paper in coated paper is about 10 times higher than that of non-coated paper, such as letterpress, news, and offset paper, and the inorganic material has good thermal conductivity, it can make the cooling rate of hot melt adhesive. accelerate.
If the sizing temperature is also 170°C, the tensile test value of the non-coated paper hot-melt adhesive can meet the expected requirements, while the tensile value of the coated paper can not reach. Therefore, when coating on paper, be sure to increase its strength and increase the temperature of the glue.
(3) The relationship between the opening time of EVA hot melt adhesives and the operating speed of production equipment.
In the process of production, the use of hot-melt adhesives must be strictly controlled and controlled for three times, namely when opening, curing, and cooling-hardening drying time. The opening time refers to the time when the glue is applied to the back of the book. The curing time is the time when the cover and the back of the book are glued together. The time of cooling and hardening and drying is the time to cool the book after the cover is cooled and set after curing. Only after these three times can the books be stereotyped and ideally processed.
The use of hot melt adhesives is closely linked with the operating speed of the equipment. For example, the open time of hot melt adhesives is generally 7 to 15 seconds. This time is the time for the binderless mill to carry out the milling and back transfer. After applying the glue, the process of sticking the cover to the back of the book (without sticking the backing paper) must be completed in less than 15 seconds, so that the use of hot melt adhesive can achieve a good bonding effect if the equipment is operated. The speed is very slow. In 15 seconds, no adhesive work can be done. The effect of bonding is certainly not satisfactory. Bonding will not be firm or sticky. After the book becomes a book, it will spread out and page faults will occur. Therefore, when choosing the hot melt adhesive opening time, it is necessary to consider the normal operation speed of the glue binding machine. The curing time of the hot melt adhesive is generally the same as the open time. Of course, the user wants the curing time to be shorter to facilitate the binding and setting of the book.
In addition to the opening and curing time, it is also required that the cooling hardening and drying time is basically accurate, especially for the adhesive bonding in the wireless adhesive bonding production line. Because this kind of production line is an interlocking line from the start of the collation of the collation machine to the cutting of the book, its parts are all connected to each other. The time that the book is sent to the book-cutting site after the book is printed on the front cover of the bag must conform to certain rules, so that the book can be cut to achieve the desired requirements. That is to say, the book delivery time must ensure that the book has reached the location of the book-cutting machine. Cooling, hardening and drying ensure that the cut finished product can be guaranteed. This process should be completed in 3 minutes, otherwise it will result in back deformation, unstable product dimensions, and sticking knife phenomenon, affecting the quality of the finished product and causing undue loss. . Therefore, the length of the delivery conveyor (conveyor belt) of the linkage production line must be selected according to the different operating speeds. Generally, the common conveyor belt length is between 40 and 55 meters, but it can be longer or shorter, but it must be guaranteed. Cover the books to cool the conveyor belt for more than 3 minutes.
The quality of book binding is determined by many factors such as paper, hot-melt adhesives, binding materials and processes.
