Development Of High-Efficiency,Low-Resistance And Long-Lasting Melt-Blown Nonwoven For COVID-19 Prevention Mask

The melt-blown cloth for COVID-19 prevention masks with high efficiency,low resistance and long-acting was finally developed using isotactic polypropylene(PP)as the melt-blown material,polytetrafluoroethylene(PTFE),tourmaline and hindered amine light stabilizer CB944 as the main electret materials,by the matching adjustment of formula design,equipment improvement and process optimization.The melt-blown cloth has been exported to South Korea for the production of children’s masks,and its requirements are that the melt-blown cloth weight is less than or equal to 22 g/m~2,the filtration efficiency of Na Cl aerosol with a flow rate of 32 L/min is higher than 95%,and the filtration resistance is less than 25 Pa.For the production of special face masks exported to Germany,the melt-blown cloth is required to meet the European standard FFP2,and at the same time,the filtration efficiency attenuation must be less than 1%after three months.The filtration efficiency attenuation of the product in this paper is still less than 1%after one year.Through the screening and surface treatment of organic and inorganic electret materials and screening of hindered amine electron trapping agent,the best formula was determined.Tourmaline was surface-treated with different silane coupling agents(KH570 or KH550),and then prepared with PTFE,CB944,other additives and melt-blown PP as the electret masterbatch.It was found that when the content of electret masterbatch was 4.8%～6.0%,the plate changing time was more than 48h(industrial production requirements),and it had continuous production value.Filtration efficiency test shows that the filter performance of the melt-blown cloth produced by electret masterbatch-570 is better than that of electret masterbatch-550;and the filter performance of melt-blown cloth is the best when the content of electret masterbatch-570 is 5.8%.The production process and equipment meeting the requirements of high efficiency,low resistance and long effect melt-blown cloth for special masks has been developed through the optimization of the production process of melt-blown cloth and the technical improvement of melt-blown equipment.The best production process of melt-blown cloth was determined by analyzing the influence of melt-blown nozzle temperature,ambient temperature,induced draft wind speed and electret process(electret voltage,electret distance,electret time)on the structure and filtration performance of melt-blown cloth.For the shortage of single screw mixing in melt-blown equipment,pins and BM grooves were added in the middle and end sections of the melt-blown single screw extruder,respectively,thus increasing the residence time and mixing effect of the melt.In order to overcome the phenomenon that the filtration performance of the melt-blown cloth in different sections varies greatly due to the slow heat dissipation in the middle and fast heat dissipation at both ends of melt-blown die head,the heating unit is reformed.After the technical modification,the phenomenon of high temperature in the middle of die head in the production process is eliminated,so that the uniformity of the filtration performance of melt-blown cloth in each section is obviously improved.