EVA wax (hot melt adhesive) has a wide range of applicability, such as PA (polypropylene), PA (polyethylene) and other non-polar materials, it can also achieve better bonding effect. The adhesive layer has good low temperature resistance, water resistance and moisture resistance.
Due to the poor rigidity of EVA wax (hot melt adhesive), its softening point is lower than that of polyester and polyamide hot melt adhesives, and its ring and ball softening point is around 100*C, which limits its application range.
The basic composition of EVA wax hot melt adhesive is EVA resin, tackifying resin, wax and stabilizer.
EVA resin is a short branched chain composed of polar acetate genes introduced into the ethylene branch chain, which disrupts the original crystalline state, causing EVA to tend to “plasticizing effect” and reducing the crystallinity of ethylene on the branch chain. The distance between the polymer chains is increased, making the EVA resin more flexible and elastic.
The VA content in EVA resin can be from low to very high percentage. Therefore, the percentage content of VA and MI (melt index, reflecting the molecular weight) in the resin are the most important factors that directly determine and affect the properties of EVA.
Generally, the higher the EVA content, the higher the adhesion, the better the wettability to the bonded material, the slower the curing time, and the lower the heat resistance. A high melt index indicates that the molecular weight is low, the colloidal viscosity decreases, the wettability is good, the heat resistance decreases, and the adhesive force remains unchanged.
In ethylene-based copolymers, EVA has higher tensile strength at break compared with EEA (ethylene-ethyl acrylate), EAA (ethylene-propylene ester), and EMA (ethyl methacrylate). It varies with the content of VA. Tensile strength at break varies more if the MI of the EVA is different.
The tensile strength at the yield point of EVA wax decreases with the increase of VA content, and becomes very small if the VA content is above 25%.
The flexural rigidity of EVA is equal to that of soft PVC, which decreases with the increase of VA, while the flexural rigidity decreases with the increase of MI.
EVA resin has good compatibility, it can be mixed and blended with various other resins to improve physical properties. For example, EVA resin is blended with nitrocellulose, so that nitrocellulose has excellent flexural resistance, friction resistance and heat sealing.
Rigid PVC is mixed with 5%~10% EVA to improve fluidity and impact resistance. EVA is blended into polyamide resins to develop good flex resistance and coloring properties at low temperatures.
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