Mask composition
Common surgical masks, non-woven fabric composed mainly of three layers. Ordinary non-woven inner layer; outer layer is a nonwoven fabric made water-repellent treatment, mainly for patients discharged isolated liquid; the intermediate layer is filtered through the electret polypropylene melt-blown nonwoven fabric treated; an inner layer for absorbing the moisture generated when the user is breathing. Finally After production of ethylene oxide after sterilization to stand for 7 days, and toxic volatile, it is sealed Packaging away.
The core material surgical masks are polypropylene meltblown nonwoven electret treated after . This is the key to filter the new crown virus aerosols.
Polypropylene fibers
First, the processing of crude oil into the polypropylene granules, and then processed into a high melt index polypropylene fiber, which is the core material of the mask production.
Meltblown nonwoven
Meltblown process (Melt Blowing) process is a non-woven polymer extrusion process, the filter material is radioactive particles to collect 1954 the US Navy nuclear tests produced ultra-fine filtering effect developed, and then after 1965, Exxon, 3M like the first generation manufactured meltblown nonwoven equipment.
Principle is drafting process of the die nozzle hole trickle polymer melt extruded using a high speed hot air, thereby forming ultrafine fibers on the coagulation and agglomeration drum or mesh screens, relying on its own to become bonded nonwoven fabric principle spinning as shown below:
Meltblown material by itself is formed by melt fibers, thicker. Producing meltblown nonwoven fabric, a random fiber arrangement and the interlayer crossover, to form a multi-channel structure meltblown material is bent, so that particulate matter (new crown virus aerosols) will collide with the fibers being retained.
Medical masks filtering mechanism is Brownian diffusion, interception, inertial impaction, gravitational settling, and electrostatic attraction. The first four are physical factors, is the production of meltblown nonwoven fabric has natural properties, filtration of about 35%; it is not up to the requirements of medical masks, we need to deal with electret material, so that the fibers take charge trapping aerosols crown new virus resides with static electricity.
Electret treatment
Electrostatic attraction is to achieve capture the crown on the new virus droplets (aerosols) by the Coulomb force charged fibers. Principle is to allow more open surface of the filter material, particulate capturing ability can be strong, and the charge density increases, the adsorption of the particles and the more polarization effects, so that a meltblown nonwoven filter layer of the filter material, must pass in under extreme processing, without changing the breathing resistance to the premise, to achieve 95% of the filter, in order to effectively prevent the virus.
Masks to ensure comfort while the air permeability of the barrier effect reaches, surgical masks inspiratory resistance is generally not more than 343.2 Pascal (Pa), civil mask inspiratory resistance of less than 135 Pascals (Pa).
Electret treatment can be greatly improved filtration efficiency without changing the breathing resistance, but in the higher voltage, higher efficiency filter material. In general need in voltage 30Kv-60kv, the electret should last more than 20 seconds.
Works of medical masks filter
1, depositing a diffusion: diffusion Brownian motion of particles to displacement of filter fibers, by gravity molecules are adsorbed. Most likely to capture particles having a small-sized particles, fine fibers and slow moving.
2, interception deposition: moving gas stream with the larger particles are retained mechanically acting filter sieve material. The particle diameter ratio of the diameter of the fiber affect the membrane intercepting efficiency.
3, deposition of inertia: When particles pass through a mesh filter material is bent passage, due to the inertia of particles from the airflow collision filter fibers and is trapped by molecular attraction effect. Large particles, high density, high speed when good retention effect.
4, the electrostatic attraction deposition: deposition of particles generated in the electrostatic filter fibers.
The more particles, the stronger 1,4 deposition effect, when larger particles, the better the effect of 2, 3, so not smaller particles are harder filtered. Comprehensive species synergy filtering mechanism, the most common mechanical filter penetrating particle size in the range of 0.1m ~ 0.3m.
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