Detailed explanation of melt blown fabric electret process and materials
May 12, 2020
Meltblown + electret is a necessary guarantee for the filtering efficiency of masks. If the proper electret is not carried out, the static electricity carried on the meltblown is easy to dissipate. Without electret, the mask may meet the N95 standard when it is newly made, but after a few months the filtration efficiency will become very low, becoming N59.
In the past two months, with the support of strong manufacturing capabilities, the production technology and production capacity of melt-blown materials, melt-blown cloths, and masks have been rapidly improved. But for another important technical core-the technical characteristics of the electret equipment process, and its compatibility with different types of electret masterbatch, the current research is still far from enough.
Electret equipment must first consider the mode of the electret current. There are DC, AC, pulse, etc. from the broad categories, and there are different current waveforms. The voltage and current of the electret are also considered. And the line speed; the most difficult thing is its matching with different varieties of electret masterbatch, as well as the amount of charge achieved under such process conditions, the attenuation speed, and the filtration efficiency before and after attenuation.
ocess, one of the important factors for melt-blown cloth to meet the standard The process of melt-blown electrostatic electret is to add inorganic materials such as tourmaline, silica, zirconium phosphate to the PP polypropylene polymer in advance, and then roll the cloth In the past, the melt-blown material was charged by one or more sets of corona discharge through the needle electrode voltage of the electrostatic generator 35-50KV. When high voltage was applied, the air under the needle tip was ionized to produce local breakdown discharge, and the carrier passed Due to the action of the electric field and deposited on the surface of the meltblown cloth, part of the carriers will penetrate deep into the surface and be captured by the trap of the electret masterbatch, thereby making the meltblown cloth an electret filter material.
The voltage of this process is a little lower than that of the high-voltage 200Kv discharge, and not so much ozone is generated. The effects of charging distance and charging voltage are counterproductive. As the charging distance increases, the charge trapped by the material decreases.
Electret meltblown cloth needs 1. A set of meltblown equipment 2. Electret masterbatch 3. Four sets of high voltage electrostatic discharge device 4. Conveying and cutting equipment Under normal temperature and humidity conditions, PP meltblown electret materials have good Charge storage stability, but when the sample is in a high humidity environment, due to the polar groups in the water molecules, the heterogeneous particles in the atmosphere compensate the effect of the charge on the fiber, resulting in a large amount of charge loss. The charge decreases with increasing humidity, and it gets faster and faster.
Therefore, in the process of transportation and storage, the melt-blown cloth must be protected from moisture and avoid contact with high-humidity environments. Otherwise, the melt-blown cloth that meets the standard should be bought in time. One of the reasons why the inspection of the cloth made was up to standard at the time and failed after a while.