EVA hot melt adhesive is a solvent-free, water-free, 100% solid fusible polymer. It is solid at room temperature and becomes a liquid adhesive that can flow and has a certain viscosity when heated and melted to a certain degree. It is light brown translucent or white after melting.
EVA hot melt adhesive is mainly made of the following four components: base resin, namely EVA resin, tackifying resin, wax, antioxidant, and a small amount of filler can be added in some occasions to increase the gap filling and reduce costs.
EVA hot melt adhesive has the following characteristics:
(1). It has fast curing, low pollution, strong adhesion, and the adhesive layer has certain flexibility, hardness, and toughness;
(2). After the adhesive liquid is applied to the adherend and cooled and solidified, the adhesive layer can be heated and melted again to become an adhesive body and then bonded to the adherend, with a certain degree of re-adhesion;
(3). When using, just heat and melt the hot melt adhesive into the required liquid state and apply it to the adherend. After pressing, the bonding and curing can be completed within a few seconds, and the hardening, cooling and drying can be achieved within a few minutes.
The type of EVA determines the cohesive strength, flexibility, adhesion to the substrate and processability of the hot melt adhesive. For hot melt adhesive, the following properties of EVA should be paid attention to: molecular weight and its distribution, vinyl acetate (VA) content, crystallinity, softening point, melting point, melt index (MI) and melt viscosity, etc., because these properties directly affect the various properties of hot melt adhesive.
As the melt index of EVA increases, its strength, hardness, softening point and viscosity all decrease regularly; and the more VA content in EVA, the greater the elongation at break and the lower the hardness. In addition, when the VA content exceeds 30%, although the adhesion to polar and various non-porous non-polar substrates is improved, this EVA polymer is incompatible with wax, which is a point to be noted when designing hot melt adhesive formulas. In a formula, it is often necessary to use EVA with different MI or EVA with different VA content to obtain satisfactory comprehensive performance.
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