The adhesive used in the adhesive bonding process of the adhesive to form a book is mainly a hot-melt adhesive agent, EVA hot melt adhesive material. The correctness of the use of hot melt adhesive is one of the key to ensure the quality of glue binding. To use hot melt adhesives correctly, first of all, the adaptability of hot melt adhesives should be studied and mastered.
Hot melt adhesive characteristics
Hot-melt adhesives, referred to as hot melt glue, are solvent-free, fast-curing adhesives. Their main features are:
(1) It is a solid at room temperature, and when it is heated to a certain temperature, it melts into a liquid. Once it cools below the melting point, it quickly becomes a solid.
(2) Fast curing, low pollution, strong adhesion, and the glue layer not only has a certain hardness, but also has a certain toughness.
(3) Has a certain re-adhesion. After being coated on the adherend to be cooled and solidified, it may be reheated and melted, and adhered to the adherend again.
(4) easy to use. In use, as long as the hot melt adhesive is melted and melted into a liquid, it is applied on the surface of the adherend, and after being pressed and cooled, bonding is completed in a matter of seconds, and it can be completely cured in a few minutes.
These characteristics of hot-melt adhesives, especially the characteristics of curing in a short time, are difficult for any water-soluble adhesives. Bookbinding is the use of hot-melt adhesives for fast curing, strong adhesion, easy to use, etc. In the production of glueless books.
Hot melt adhesive properties and composition
There are many kinds of hot-melt adhesives, such as polyamide, polyester, and EVA. Bookbinding hot melt adhesives are EVA type. EVA hot melt adhesive is made by copolymerizing ethylene and vinyl acetate under high pressure. With different proportions of ethylene and vinyl acetate, different hot melts with different molecular weights and properties can be produced to suit different needs.
The main raw material of hot melt adhesive is EVA resin. This kind of resin has high flexibility, does not need to be vulcanized, does not need to add plasticizers, and is rich in rubber-like elasticity, and at the low temperature, the elasticity is reduced, the mechanical properties are basically unchanged, and the temperature resistance is stable and is not easy. Aging, strong bonding force, good curing and so on. However, in use, in order to adjust the fluidity, permeability, softening point, and oxidation resistance of the EVA hot melt adhesive, and to reduce the cost, some additive materials may be added in addition to the polyvinyl acetate vinyl resin. Therefore, commonly used hot-melt adhesives are made of resins, tackifiers, viscosity modifiers, plasticizers, antioxidants, fillers, and other raw materials, and are composed of appropriate proportions.
1.EVA resin
EVA resin is the main body of hot melt adhesive, which determines the basic characteristics of the glue, giving the glue a certain degree of adhesion and cohesion. The higher the content of vinyl acetate in the EVA resin, the greater the viscosity of the hot melt adhesive, but the lower the heat resistance and tensile strength. Conversely, the viscosity decreases, and the heat resistance and tensile strength increase. In general, the resin component accounts for about 50% of the hot melt component.
2. Tackifier
One of the components of the hot melt adhesive is a tackifier. Its main function is to reduce the melt viscosity of the hot melt adhesive, improve the processability, make it easy to wet the adherend surface after the glue is applied, and improve the adhesive strength. In addition, you can also use this to adjust the heat-resistant temperature and open time. Therefore, the tackifier and the resin must have good compatibility. Tackifiers are often made from rosin-modified resins, such as glycerol rosin esters, pentaerythritol rosin esters, and terpene resins. Among them, hydrogenated rosin, terpene, glycerol rosin ester, and rosin hydrocarbon can improve the flowability of the adhesive and have good stability to light, heat, ozone, and low temperature. The softening point of the tackifier is selected between 80 and 100°C, and the amount thereof is about 20% to 40% of the total composition.
3. Viscosity modifier
In hot-melt adhesives, viscosity modifiers can reduce melt viscosity, improve fluidity, shorten the opening time of the glue, reduce the phenomenon of spinning and prevent the glue from sticking. At the same time, it can also reduce costs. Viscosity modifiers generally use waxes, such as paraffin wax, microcrystalline wax, and synthetic wax, in amounts less than 25% of the total composition. If the proportion is too large, the fluidity and permeability of the rubber compound will increase, but the bond strength will decrease and the shrinkage rate of the glue will increase. In severe cases, the back of the book will appear obvious “oil seepage”.
4. Antioxidants
Since hot melt adhesives are often heated to a temperature of 140-170° C. or even higher, they are susceptible to thermal oxidation or aging and decomposition. In order to prevent the rubber from oxidative deterioration by heat for a long time, antioxidants or heat stabilizers, such as di-tert-butyl-p-cresol (BHT), di-tert-butyl-phenyl phenylpropionic acid pentaerythritol, dimethyl sulfide, should be added to the ingredients. Phenol (QD) and other materials. Its amount is generally controlled at 0.1% to 1%.
The use of EVA hot melt adhesive
1.EVA hot melt adhesive preheating
EVA hot melt adhesive milky white, block, strip and granular. When used, the solid hot melt adhesive must first be preheated. The preheat can be preheated by the oil bath jacket, and can also be preheated directly in the premelting pan by the hot plate device (wireless adhesive bonding motive is adopted). When preheating, the solid hot melt adhesive is poured into a preheated pan and heated at a temperature of 160-200°C. Preheat time is controlled in 1 to 2 hours. The hot melt adhesive is preheated to the set temperature and has good fluidity before it can be used. The hot melt glue that reaches the preheating temperature is released into the rubber bucket of 160-200 DEG C through the thermostatic tube, and can be used for the glue-binding production line.
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