Medical masks are generally multi-layer structures, generally referred to as SMS structure (2-layer s and 1-layer m). At present, the highest number of layers in China is 5, namely SMS (2-layer s and 3-layer m).
What is SMS?
Photo source: public information
This s represents spunbond, whose fibre diameter is about 20 microns (μ m). The main function of the two-layers-spun-bond layer is to support the whole structure of the non-woven fabric, which has little effect on the barrier. The most important part of the mask is the barrier layer or melt-blown layer m (meltblown). The fibre diameter of the meltblown layer is relatively small, about 2 microns (μ m), so it is only one-tenth of the diameter of the spunbond layer, which plays a crucial role in preventing bacteria and blood penetration.
Photo source: public information
General medical masks usually use 20g of melt blown cloth, while N95 cup masks use 40g or even heavier meltblown cloth.
According to the statistics of China Industrial Textiles Association, by the end of 2018, 1477 domestic spunbond production lines had increased by 65 over the previous year, up 4.6% year on year. Among them, PP spunbond nonwovens production line increased by 3.38%, SMS composite production line increased by nearly 13%, PET spun-bonded nonwovens production line increased by 9.32%; enterprises with an annual output of more than 50000 tons also increased compared with 2017. Spunbond enterprises are speeding up their development towards large-scale, intensive and high-end, and accelerating to meet the market demand for product upgrading and technology upgrading.
Since 2018, many domestic enterprises have developed their products in the direction of lighter, thinner and higher performance and achieved good results. The high-speed operation of SMS spunbond / melt blown composite process over 600m / min is good. About 10 g / m2 super soft, light and stable products are emerging.
Where does SMS non-woven fabric come from
SMS non-woven fabric takes polypropylene PP (with natural bacteriostasis and hydrophobicity) as the main raw material, and the fibre diameter can reach 0.5-10 μ m. These ultra-fine fibres with unique capillary structure increase the number and surface area of fibres per unit area so that the meltblown fabric has good air filtration, which is a relatively good mask material.
At present, there are three main processes for manufacturing SMS products (SMS non-woven fabric), "one-step process", "two-step process" and "one step and half process".
The one-step process is characterized by using raw material slice, using two processes of spun-bond and meltblown, directly spinning the raw material into a net after melting. As long as the spinning system engineering of the different process is arranged reasonably, the product can have a different structure. After laminating each layer of fibre mesh, it is usually consolidated into cloth by the hot rolling mill. The one-step process is characterized by the direct spinning of the melt into a web, and the state of each spinning system can be adjusted independently. The production process has strong controllability, good sanitary conditions, high operation speed, the ability to adjust the proportion of each layer of fibre mesh at will, and the ability to produce various specifications of SMS products, which is the mainstream technology today.
two-step process: when SMS products are produced by two-step method, spin bonded fabric products and meltblown fabric products are detailed and laminated in a certain order and then consolidated by hot rolling machine to form SMS products. The two-step method is characterized by simple equipment and low cost. In fact, the "two-step" technology is also widely used laminated composite technology. It can also composite other materials, and use different other materials, and use different methods, such as ultrasonic, hot-melt adhesive, etc., to consolidate three layers of materials together.
one step and half process: in the two-step method, the meltblown layer fibre net produced on-site can also be replaced by the melt-blown cloth product, thus the so-called "one step and a half method" composite process is derived. The spunbond fabric is used as the bottom layer and the surface layer by two unwinding devices. The melt-blown fibre mesh of the middle layer is directly spun into a mesh by the melt-blown system and laid on the surface of the bottom spun-bond fabric. Then cover the upper layer of spun-bond, preferably with a hot rolling mill to form SMS products.