1. Alkaline resin
EVA resin is the copolymerization reaction of ethylene and vinyl acetate under high temperature and high pressure, and is the basic resin of EVA hot melt adhesive. EVA resin is the main component of hot melt adhesive. According to the required ratio, it generally accounts for 40%-60% of the hot melt adhesive. The ratio of the base resin determines the basic properties of the hot melt adhesive, such as the bonding ability, melting temperature, the choice and preparation of additives, etc., all depend on the ratio of the base resin.
Tackifier is one of the main additives of EVA hot melt adhesive. If only alkaline resin is used, it will only have adhesion when it is melted at a certain temperature. Once the temperature drops, it will not be able to bond firmly, or even lose its bonding ability. The moisture permeability is poor and the ideal bonding effect cannot be achieved. Adding some substances that can melt with the alkaline resin is to improve its bonding performance, which requires the addition of a tackifier. Adding an appropriate amount of tackifier to the EVA hot melt adhesive can also improve the fluidity of the colloid, thereby improving the wettability and permeability of the colloid to the glue, increasing the bonding strength, and meeting the requirements of the book for the bonding strength. Tackifiers generally use rosin and terpene resin, and the ratio is generally between 15% and 20%.
3. Viscosity regulator
When choosing a viscosity modifier, you should choose a material with a lower melting point, such as paraffin, whose softening point (melting point) is between 65 and 105°C, which is lower than the base resin (the softening point of the base resin is above 100°C). Therefore, wax is the most suitable viscosity modifier. Attention should be paid to the reasonable dosage when stirring. Too much or too little paraffin will affect the quality of EVA hot melt adhesive, so it should be properly proportioned with other additives. The general dose is controlled at about 10%.
The colloid will be oxidized and decomposed due to high temperature during the melting process. Adding appropriate antioxidants can prevent premature aging of EVA hot melt adhesive. In addition, at high temperatures, adding an appropriate amount of antioxidants will not change the adhesion of the adhesive, which is sufficient to ensure the booklet binding effect. Di-tert-butyl p-methylphenol (BHT) is a commonly used antioxidant. better result. The dosage of BHT is generally controlled at about 0.5%.
5. Cold and heat resistance
EVA hot melt adhesive is a kind of thermoplastic adhesive material, which requires a strict working environment in use. Adding a cold-resistant agent can prevent the opening time and curing time of the gel from advancing at low temperatures in winter, thereby affecting the adhesion of the book. Due to the high temperature in summer and regional differences, adding a heat-resistant agent can prevent the gel from being difficult to solidify and cool, which will affect the cutting quality and the appearance of the book.