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The gap between non-woven masks and medical masks turned out to be their

May 30, 2020

Medical masks are divided into inner, middle and outer layers, the inner layer is skin-friendly material (general hygienic gauze or non-woven fabric), the middle layer is isolation filter layer (superfine polypropylene fiber melt-blown material layer), and the outer layer is special material Bacteriostatic layer (non-woven fabric or ultra-thin polypropylene melt-blown material layer).

The non-woven fabric is used, and it has a three-layer structure. Can the masks that are dust-proof and hygroscopic have the same anti-virus effect as medical masks?

The answer is of course: different.

What is the difference between a three-layer non-woven mask and a medical mask?

The answer is: processing technology. 1. Meltblowing process 2. Electrostatic electret process. The gap of using non-woven fabrics also lies in the polypropylene non-woven fabrics using the melt-blown process. Polypropylene non-woven fabric fibers are very fine and can block bacteria and fine particles. The use of electrostatic electret technology makes it easier for the fibers to become static electricity, attracting small diameter substances, thereby blocking bacteria and viruses in the air.

meltblown fabric face mask

Meltblown process

The spinning method of rapidly extruding the polymer melt by high-speed hot air drawing and solidification molding by means of high-speed hot air flow. The advantage is that the process flow is short, and the non-woven fabric can be directly produced by spinning. The polymer masterbatch is put into the extruder and melted in the extruder at a temperature of about 240 ° C (for the main resin used in the polypropylene-meltblown method). The melt passes through the metering pump and reaches the meltblown die head.

The metering pump measures the melt flow output to the nozzle. The spinneret is a row of capillaries with a pitch of less than 1 mm and a diameter of 0.2 to 0.4 mm. On both sides of the capillary are air intake holes, adding 250 ~ 300 ℃ compressed air. When the polymer just formed is extruded from the spinneret, the end of the compressed air acts on the polymer, and the hot filament is drawn to a diameter of 1 ~ 10μum with a flow higher than the speed of sound (550m / s), according to its physical characteristics Such a net is called a microfiber net. The hot air flows down and mixes with the surrounding air, cooling the fibers and eventually consolidating into short and thin fibers. The main process flow of the melt blown method is as follows:

Melt preparation → Filtration → Metering → Melt extrusion from the spinneret → Melt fine flow drafting and cooling → Netting.

Meltblown process

Electrostatic electret process

Since the 1970s, various charged electrostatic filters and various charged electrostatic filters by mixing different fibers have been developed and utilized. The direct result is the current electrostatic electret method (process). The current electret methods mainly include electrostatic spinning method, corona discharge method, triboelectric method, thermal polarization method, and low energy electron beam bombardment method. Due to the different electrostatic electret methods (processes) of the materials, the properties of the formed electrets are also very different.

The electret air filter material requires a large storage charge density of the material, a long storage life of the charge density and a strong storage charge stability, etc. The stability of the stored charge mainly depends on the nature of the material, the charging method, the state of charge distribution, and the environmental conditions of storage. According to the above requirements, in terms of the nature of electrostatic electrets, the corona discharge method is currently the best electrostatic electret method; the thermal polarization method is also a better electrostatic electret method when the environment is relatively stable; The electrical method should be further improved in the experiment; the electrospinning method requires further development of science and technology; the low energy electron beam bombardment method needs to improve and simplify the process of electrostatic electret.

Static electret air filter material

The electrostatic force of the electric charge is used to capture the dust particles, which is made of a small strip of polypropylene film. Electrostatic electret: Electret for short, refers to those dielectric materials that can store space charge and dipole charge for a long time, that is, from the perspective of time span, their charge decay time constant is much longer than the period of electret formation. The electret charge can be a real charge (or space charge), a dipole charge, or both. The electret air filter material uses the electrostatic force of electric charge to capture dust particles.

Types of electrostatic electret materials

In recent years, the development of polymer chemical fiber production technology has enabled the use of electret fibers to produce HEPA and ULPA filters; materials used as electret air filters require excellent dielectric properties, such as high body resistance and surface resistance , High dielectric breakdown strength, low moisture absorption and air permeability. This type of material is mainly organic polymer electret materials, such as non-polar materials: polypropylene, polytetrafluoroethylene, hexafluoroethylene / polytetrafluoroethylene copolymer, etc .; polar materials or weak polarity Materials: Teflon, polypropylene (blend) and polyester.

Types of electrostatic electret materials

Electret electrostatic synthetic fiber filter material

The polypropylene fiber is electrostatically charged in the melt-blown manufacturing process to make it an electrostatic electret melt-blown nonwoven fabric (filter paper) with a fiber diameter of 2 to 5 μm. In addition to the filtering mechanism of traditional air filter materials, this filter material also uses the coulomb force of the charged fiber to achieve the capture of particles, so the efficiency increases and the resistance decreases. This filter material is currently used in 3M surgical masks (N95, N97, N99) that have anti-virus functions (including SARS virus) in the world, and this type of anti-SARS air filter launched in the United States in April 2003 material.

Due to the high efficiency, low resistance, and low price of this filter material, this material is used in general air filters for air conditioning and ventilation. When the wind speed on the windward side is 0.5m / s, the filter efficiency for 0.5μm dust It can reach more than 95%, and the air resistance is only 40Pa, which is incomparable with the traditional cabinet air conditioner unit air filter (generally nylon mesh). This air filter has been used in large shopping malls, supermarkets, and hospital air-conditioning systems for nearly 10 years, and has been applied to households, such as the Phil extract air purifier has achieved good air purification effect. The production process has been comprehensively improved. At present, the electret electrostatic filter material with a sodium flame method efficiency of 99.9999% has been produced. At the same time, it also solves the shortcomings of poor uniformity and low strength of this filter material. The air filter provides an ideal filter material. The commercialization of electret electrostatic synthetic fiber filter materials has largely solved the contradiction between air filter efficiency and resistance.