Meltblown non-woven fabric is the core filter material of the mask, which is mainly determined by the filtering mechanism of the meltblown filter material, which is mainly divided into mechanical barrier and electrostatic adsorption.
Mechanical barriers include the following:
1. Droplets with a particle size greater than 5um in the air can be blocked by the filter material.
2. When the diameter of the dust particles is less than 3um, the dust particles are mechanically intercepted by the curved pore fiber layer in the filter material of the non-woven mask.
3. When the particle size and airflow velocity are large, the particles are captured due to the collision with the fiber due to inertia. When the particle size is small and the flow rate is low, the particles are captured due to Brownian motion hitting the fiber.
Usually, electret treatment is carried out in the production process of meltblown cloth, so that the meltblown nonwoven fabric has more static electricity and has electrostatic adsorption effect. 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.
There are two approaches to improving the charge storage capacity of electret materials:
1. By improving the crystallinity and mechanical deformation of the material, the structure of the melt-blown non-woven fabric is changed, and a slender hole channel is formed to prevent charge drift.
2. Generate charge traps to capture charges by introducing additives with charge storage properties.
3. Electret treatment of melt-blown non-woven fabrics
The key to improving the filtration efficiency of non woven fabric face mask is the electrostatic storage of meltblown non-woven fabrics. At the current flow rate of masks, the attenuation of static electricity is not a concern, and normal medical masks are valid for 6 months, while some masks in Japan are valid for three years.
Melt-blown non-woven electrets are very sensitive to ambient humidity, and stored for 7 days under normal temperature and high humidity (relative humidity greater than 95%), the surface potential of positive and negative corona-charged samples has decayed to 28% of the initial value respectively. and 36%.
At this time, because the melt-blown non-woven fabric has an open structure, its specific surface area is large, and it has a larger contact surface with the surrounding environment, making it more sensitive to water vapor, corrosive gases, and charged particles of the opposite sex in the environment.
At the same time, the corona charging system can only generate ionic charges with low beam energy, and most of the charges injected during the charging process are deposited on the near-surface layer of the fabric surface fibers.
When the sample is stored or worked in a high-humidity environment, a large amount of charge is lost due to the compensation effect of polar groups in water molecules and anisotropic ions in the atmosphere on the high concentration of surface charge on the fiber. Therefore, in the meltblown nonwoven In the process of cloth transportation and storage, be sure to avoid high humidity environment.