Hot melt adhesive (EVA). Hot melt adhesive is a kind of solid soluble polymer without water and solvent. EVA is processed into a solid at room temperature, heated to a certain temperature, and then melted to become a liquid that can move and bond. There are many kinds of hot-melt adhesive. The hot-melt adhesive used for book binding is polyvinyl acetate.

The main component of hot-melt adhesive is the resin which is copolymerized by ethylene and vinyl acetate under high pressure. It determines the basic function of hot-melt adhesive. In addition, the tackifier (rosin), viscosity and setting speed regulator (Bela) and a few antioxidants (such as tert 4-methyl-benzenol) are added to improve the bonding strength to slow down the aging speed of hot-melt adhesive. The hot-melt adhesive is mainly used for the wireless binding linkage line of books and periodicals. After the hot-melt adhesive is preheated in the glue pot of the binding line, it is brushed on the back of the book after milling and roughening.

The primary characteristics of hot melt adhesives are:

① There is no water and solvent in EVA processing. It is a solid at room temperature and a liquid with outstanding activity at high temperature. It is nonflammable. Harmless to human body;

② Fast setting speed. After leaving the glue pot, it coagulates within 7-30s without drying or adding other curing agent, which fully adapts to the requirements of high-speed automation, so it has become the adhesive data of the linkage line of paperback wireless glue factory;

③ The hot-melt adhesive can bond a variety of substances, especially the porous homogeneous material, which has stronger adhesive force, and the cured adhesive film has good flexibility;

④ The hot melt adhesive can be reused by heating from the beginning, and has strong chemical resistance. EVA processing is not heat-resistant and its softening point is low. When using hot melt adhesive, heat treatment should be selected to melt the solid EVA resin. In order to ensure the quality of wireless binding, we should strictly control the temperature of hot-melt adhesive processing. The normal working temperature is 150-180 ℃, which is the binding temperature of books. The preheating temperature of the preheating glue pot is generally 15-20 ℃ lower than the working temperature. According to the thickness of the book core and the quality of the paper, the glue temperature is also different. If the book core is thick and the paper is good, the working temperature of the glue can be improved to 175-185 ℃. The higher the glue temperature is, the faster the activity is. When the temperature is over 200 ℃, the glue will start to change color and age, and the setting time will be longer, resulting in poor bonding quality of wireless binding.