Medical-surgical masks have good filterability, shielding, thermal insulation, and oil absorption properties, and are a good choice for the daily prevention of new viruses. The raw materials of surgical masks are polypropylene and non-woven fabrics. Many people are curious about how to manufacture surgical masks. Here is a brief introduction.
1. The production of the polypropylene fiber
Just as the textile industry needs plant fibers, the production of non-woven fabrics needs fabric materials. Polypropylene particles are used in the process of melting and shaping, while high-melting polypropylene fibers, or non-woven fabrics, are the core raw material of mask production.
2. The production of melt-blowing non-woven fabrics
Melt blowing belongs to the polymer extrusion non-woven technique. Its principle is that high-speed hot air is used to draft the fine flow of the polymer melt extruding from the spinneret hole at the die head. From this, the ultra-fine fibers are formed and condensed in the setting screen curtain or roller, and then become the non-woven fabrics by self-bonding.
Melt-blowing material is formed by the hot melting of its own fibers with a bigger thickness. As for the non-woven fabric produced by melt blowing, there are random crossed and interlayer arrangements of fibers, which form a multi-curved channel structure of melt blowing material. In this way, particulate matter (COVID-19 aerosol) will collide with the fiber and be trapped.
The filtering mechanisms of most of the hospital face mask are Brownian diffusion, interception, inertial collision, gravitational settlement, and electrostatic adsorption. The first four are all physical elements, which are natural characteristics of non-woven fabrics produced by melt blowing. The filterability is about 35%, which is not up to the requirements of the surgical mask. We need to process the material by the electret, making the fiber carry electric charge, and using electrostatic to capture the aerosol where the novel Coronavirus lives.
3. The electret treatment
Novel Coronavirus spray (aerosol) is captured through the coulomb force of the charged fiber, which is called electrostatic absorption. The principle is that we make the surface of the filtering material more open, enabling a better ability for the capture of the particles. And with the charge density increases, the adsorption ability of particles and the polarization effect will be stronger. Therefore, the melt blowing non-woven filter material of the filter layer has to be processed by the electret so that under the premise of keeping the respiratory resistance unchanged, 95% filterability will be achieved to make sure masks can fend off the virus.
Great masks should ensure comfort and good ventilation while achieving a barrier effect. The inspiratory resistance of the surgical mask generally does not exceed 343.2 Pascals (Pa), while that of the mask for civil use is less than 135 Pascals (Pa).
The electret treatment can greatly improve the filtration efficiency without changing the respiratory resistance, and the higher the electret voltage, the higher the filtration efficiency. Generally, the electret voltage should be from 30KV to 60KV, and the electret time should be more than 20 seconds.
4. The production line of masks
If the problem of raw materials has been solved, the production of masks is just matter of recruiting workers and stockpiling and maintaining the production capacity of the production line. It's fast to deal with these matters because production lines are all automated.
5. The disinfection of the ethylene oxide
The normal mask does not need to be disinfected, but medical surgical masks need to be disinfected in the ethylene oxide (EO) disinfection cabinet by the manufacturers. When the mask is placed in an ethylene oxide environment of 400mg/L, and the hydroxyl will be alkylated to inactivate the large molecules of microorganisms, so as to achieve the purpose of sterilization. After disinfection, it needs to be put aside for 7 days for analysis. After the amount of EO residual is lower than the required value, the masks can be packaged and shipped out of the factory for medical staff to use.
These are the surgical face mask manufacturing process. After these steps, the surgical mask will be qualified and safe to be used to prevent the transmission of the novel Coronavirus.
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