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How to improve the filtration efficiency of meltblown cloth?
As the core material of medical masks, meltblown non-woven fabrics have a direct impact on the protective effect of the masks. There are many factors that affect the filtration performance of meltblown cloth, such as fiber linear density, fiber web structure, thickness and density. However, as the air filter material of a mask, if the material is too tight, the pores are too small, and the breathing resistance is too large, the user cannot inhale the air smoothly, and the mask will lose its use value. This requires the filter material not only to improve its filtration efficiency, but also to reduce its respiratory resistance as much as possible, and the respiratory resistance and filtration efficiency are a pair of contradictions. The electrostatic electret treatment process is the best way to solve the contradiction between breathing resistance and filtration efficiency. The filtration mechanism of meltblown non-woven fabrics. Among the filtration mechanisms of meltblown filter materials, the generally recognized mechanisms mainly include Brownian diffusion, interception, inertial collision, gravity sedimentation and electrostatic adsorption. Since the first four principles are mechanical barrier, the filtering mechanism of meltblown cloth can be simply summarized as mechanical barrier and electrostatic adsorption. The fiber diameter of the mechanical barrier polypropylene melt blown cloth is 2-5 μm on average, and droplets with a particle size greater than 5 μm in the air can be blocked by the melt blown cloth. When the diameter of the dust is less than 3μm, the fibers in the meltblown cloth are randomly arranged and formed with the interlayers to form a fibrous filter layer with multiple curved channels. When the particles pass through various types of curved channels or paths, the dust is mechanically The filter-type van der Waals force is adsorbed on the surface of the fiber. When the particle size and the air velocity are both large, the airflow approaches the filter material due to obstruction and circumvents the flow, while the particles leave the streamline due to inertia and directly collide with the fibers and be captured. When the particle size is very small and the flow velocity is very low, the particles are captured by the fibers due to the diffusion of Brownian motion. Electrostatic adsorption Electrostatic adsorption means that when the fibers of the filter material are charged, the particles are captured by the Coulomb force of the charged fibers (electrets). When dust, bacteria, viruses and other particles pass through the filter material, the electrostatic force can not only effectively attract the charged particles, but also use the electrostatic induction effect to capture the polarized neutral particles. As the electrostatic potential increases, the electrostatic adsorption effect becomes stronger. Electrostatic electret technology. Since the filtration efficiency of ordinary meltblown non-woven fabrics is less than 70%, it is not enough to rely solely on the mechanical barrier effect of the three-dimensional aggregates of meltblown ultrafine fibers with fine fibers, small voids and high porosity. Meltblown filter materials generally add electrostatic charge effect to the meltblown cloth through the electrostatic electret process. The electrostatic method is used to improve the filtration efficiency, so that the filtration efficiency can reach 99.9% to 99.99%, which can be achieved by a very thin layer. The expected standard, the respiratory resistance is still small. The current electrostatic electret methods mainly include electrospinning, corona discharge, friction electrification, thermal polarization, low-energy electron beam bombardment, etc. The corona discharge method is currently the best electrostatic electret method. The corona discharge method is that the meltblown fiber web passes through one or more sets of corona discharges through the needle electrode of the electrostatic generator (the voltage is generally 5-10KV) before winding to make the meltblown material charge, and the needle tip is applied when high voltage is applied. The air below produces corona ionization and local breakdown discharge. Carriers are deposited on the surface of the meltblown cloth under the action of the electric field. Some of the carriers will go deep into the surface and be trapped by the electret master particle traps, thus making the meltblown cloth. Become an electret filter material. Increasing the charge on the surface of the meltblown cloth can be obtained by the corona discharge electret treatment process, but to make this electrostatic storage not attenuate, the composition and structure of the meltblown electret material are needed to facilitate charge retention. The way to improve the charge storage capacity of electret materials can be by introducing additives with charge storage properties to generate charge traps to capture charges. Therefore, compared with ordinary melt-blown production lines for the production of air filter materials, a high-voltage electrostatic discharge device needs to be added to the production line, and electret masterbatch, such as tourmaline, needs to be added to the production raw material polypropylene (PP). particle.
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