Preparation And Application Of Maleic Anhydride Grafted Modified EVA Hot Melt Adhesive For Shoes

Solvent-based adhesives have been widely used in shoe materials because of their high bonding strength and flexibility.Due to its high content of harmful solvent,which is damage to the environment and human body,solvent-based adhesives has been restricted applied by the state.Hot melt adhesives are 100% solids without solvents.They have little effect on the environment and become one of the types of adhesives that the country encourages.The EVA hot melt adhesives commonly used in the market are difficult to achieve all the performance in terms of adhesive strength,heat resistance,and flexibility.Therefore,to balance the performance of EVA physical mixed hot melt adhesives,it is important to develop hot melt adhesives with excellent overall performance.Based on the EVA resin with VA content of 30% and melt flow index of 30,this product was grafted with EVA to improve its bonding performance and heat resistance.The adhesion strength and initial adhesion were improved by adding tackifier resin.The EVA resin and filler with a high content of VA were further added to obtain EVA hot melt adhesive for footwear with excellent properties such as adhesive strength,heat resistance and flexibility.The grafting modification was carried out by a single screw extruder mixed with the high VA content EVA and maleic anhydride.The EVA of different grades,manufacturers,or processing technologies etc.affect to the performance,was studied.Better graft modification conditions were obtained: extrusion temperature of 175°C,MAH 1.5%,DCP 0.15%,and antioxidant 0.2%.The maleic anhydride grafting ratio was 0.8% to 1.0%.In order to prepare modified EVA hot melt adhesive that can be adapted to long-term melt processing,an ungrafted EVA with VA content of 70% and melt index of 6 was added to the universal EVA to improve the heat stability.At the same time,the tackifier resin was also added to the hot melt adhesive for increasing the adhesive strength.When the content of tackifier was less than 50%,the adhesive strength of the hot melt adhesive was increased with the higher content of the tackifier.Considering that actual EVA hot melt adhesives for shoes require soft,heat-resistant and high-strength adhesive properties,and individual users also require that the film-like hot melt adhesives be dry,it is determined that 5% to 20% of hydrogenated petroleum resins should be added.Adding a certain amount of filler can not only reduce the cost,but also improve the dryness of the adhesive surface.Its comprehensive properties of adhesive strength,flexibility,and film forming effect were also investigated.Research showed that adding 3% to 10% of talc powder can meet the application requirements.The modified EVA hot melt adhesives for shoes formulation is: general graft modification EVA 40% to 60%,EVA-3335 15% to 40%,EVA-7010 10% to 15%,petroleum resin 5% to 20%,and modified talc powder 5% to 10%.