Melt-blown non-woven fabrics are widely used in the field of filter materials, and can be described as the “heart” of the mask structure. The average fiber diameter of polypropylene melt-blown fabrics is 2 to 5 μm, and the droplets with a particle size of more than 5 μm in the air can be blocked. But can only block less than 70% of the particles. Even if the barrier rate is increased by mechanical barriers, blindly increasing the weight and thickness of the material will greatly increase the breathing resistance of the melt-blown cloth. Since the 1970s, electrostatic technology and the charging technology by mixing different fibers have the characteristics of static electricity. The filter has been developed and utilized, and finally forms the current melt-blown cloth electrostatic electret process. The electrostatic electret process makes the melt-blown cloth barrier rate reach 99.9%, which meets the KN95 standard. The pre-market electret methods mainly include electrostatic spinning method, corona charging method, triboelectric charging method, thermal polarization method, etc. Due to the different electret process, the properties of the electret formed are also different. The most efficient melt-blown cloth electrostatic electret on the market is the corona charging method.
The corona charging method refers to the method of one or more sets of corona discharge through an electrostatic generator before the melt-blown fiber web is wound. The melt-blown material carries a voltage of several thousand volts to several tens of thousands of volts, due to the repelling effect of static electricity the fibers are diffused into open mesh holes. When the dust passes through the melt-blown filter material, the electrostatic effect can not only effectively attract the charged dust particles, but also capture the neutral particles in polarization with the electrostatic induction effect. The higher the electrostatic potential of the material, the greater the charge density stored in the material and the stronger the electrostatic effect. The filtering performance of the meltblown cloth is greatly improved.
The current charging methods of the surface of the meltblown cloth include corona roller discharge, molybdenum wire discharge, and non-contact discharge. The corona roller discharge directly touch the surface of the meltblown cloth, which is easy to damage the characteristics of the material itself, and the high voltage and high current emitted by the corona roller will break down the meltblown cloth, this equipment is more expensive than other electret equipment. The molybdenum wire discharge is actually a corona machine. The molybdenum wire discharge can only generate an electrostatic potential on the surface of the material, and does not generate a charge on the fiber inside the material, which increases the rate of charge loss.
Shanghai LISUN’s melt-blown electrostatic generator is designed according to the “AATCC42-2013 Water Resistance Impact Penetration Test”. It uses a high-voltage pin-type power-retaining method, which can retain charge for a long time. The charging voltage is generally 5-50kV. As the charging voltage increases, the electrostatic potential will also increase, and the charge around the melt-blown fabric fibers will increase. However, it is not that the higher the charging voltage, the better. After the voltage reaches tens of kilovolts, spark discharge will occur, causing the material to be broken down, and tests have shown that the electrostatic potential inside the melt-blown cloth will decrease with increasing storage time. It stabilized around 30 days. Moreover, under different charging voltages, the trend of the electrostatic potential attenuation on the surface of the meltblown cloth is the same, and the final retention rate will not differ much.
Lisun’s special electrostatic electret generator for meltblown cloth consists of an electrostatic generator (rod) and a high-voltage power supply. The high-voltage power supply provides voltage to the rod, and the rod generates positive or negative electricity, so that the measured object is charged. The amount and effect of charge are very much related to the static generator (rod), so the quality of the static generator (rod) is particularly important.
The following video shows the static electret of Lishan non-contact meltblown cloth with uniform discharge:
The following video is a molybdenum wire discharge video. It can be clearly seen that sparks are generated during the discharge process.
Lisun Instruments Limited was found by LISUN GROUP in 2003. LISUN quality system has been strictly certified by ISO9001:2015. As a CIE Membership, LISUN products are designed based on CIE, IEC and other international or national standards. All products passed CE certificate and authenticated by the third party lab.
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