Meltblown polypropylene non-woven fabric is the core filter material of mask, which is mainly determined by the filtering mechanism of meltblown filter material, and is mainly divided into mechanical barrier and electrostatic adsorption.
1. Mechanical barrier
Mechanical barrier has the following situations:
The droplets with particle size larger than 5um in the air can be blocked by the filter material.
When the diameter of the fine dust is less than 3um, the fine dust is mechanically intercepted by the fiber layer of the curved channel in the filter material of the mask.
When the particle size and airflow velocity are both large, the particles are captured due to the collision between inertia and fibers. When the particle flow velocity is low, the particles are captured due to Brownian motion impacting on the fibers.
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2. Electrostatic adsorption
Electrostatic adsorption refers to the capture of dust, bacteria and viruses by the coulomb force of the charged fibers when the fibers of the filter material are charged.
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The key to improving the filtering efficiency of masks lies in the electrostatic storage of meltblown non-woven fabrics. Under the current circulation speed of masks, electrostatic attenuation is not considered enough (e.g. half a month to the user after leaving the factory), while normal medical masks are valid for 6 months, while some masks in Japan are valid for 3 years.
There are two ways to improve the charge storage capacity of electret materials:
1. By improving the crystallinity and mechanical deformation of the material, the structure of the material is changed to form slender hole channels to prevent charge drift.
2. Generate charge traps to capture charge by introducing additives with charge storage properties.
The core component of the mask for filtering particles in the outside air is meltblown non-woven fabric, which serves as the "heart" of the mask, while the research and development of resident masterbatch is the core technology of meltblown non-woven fabric.
