At present, the global pandemic is still not optimistic. The United States has a total of 29150068 confirmed cases of COVID-19 and a total of 529,102 deaths. US President Biden announced on the same day that he plans to purchase another 100 million doses of the single-dose covid-19 vaccine produced by Johnson & Johnson, so that the US vaccine supply is sufficient for the entire American population. Johnson & Johnson has reached an agreement with the US government to provide 100 million doses of vaccine by the end of June.

Brazil has newly confirmed 79,876 cases and a total of 11,202,305 confirmed cases; recently, there have been 2,286 new deaths, a single-day high since the outbreak of the pandemic, with a total of 270,656 deaths. In Brazil's 27 state capitals, 25 intensive care units are full or overstaffed.（Click to share to LinkedIn）

German Chancellor Merkel said that the German covid-19 pandemic is expected to have a difficult period of three to four months, and the pandemic tension is likely to continue until the summer. She also said that after this difficult period, as the effects of vaccination continue to show, the situation will improve. Many German states began to "unblock" public life and commercial activities in a small amount from March 8. The German disease control agency announced on the 10th that the number of new confirmed cases and the number of new deaths were 9,146 and 300, respectively.

In addition, Professor Willer, director of the Robert Koch Institute, a German disease control agency, warned on the 10th that if Europe does not vaccinate enough people with covid-19 in the shortest time, the third wave of covid-19 pandemic will soon be swept through. Europe.

On the 10th local time, the total number of confirmed cases in France exceeded 3.96 million, and the total number of deaths was 89,565. Due to the saturation of the medical system, the French health department began to transfer covid-19 patients to neighboring Belgium. French officials plan to evacuate hospitalized patients in the Paris region in the next few days. At present, the intensive care beds in the Paris region are very tight, and COVID-19 critically ill patients have occupied 90% of the intensive care beds.（Click to share to Facebook）

In the near future, wearing masks is still the main method of epidemic prevention, and we cannot relax. The mask is mainly composed of non-woven fabric, the inner and outer layers are spunbonded non-woven fabric, and the middle layer is melt blown fabric. Spunbond non-woven fabrics are widely used. In addition to making masks, they can also be used to make disposable protective clothing. They are widely used in the medical field and can be used in sanitation, environmental protection filtration, geotechnical construction, automobiles, artificial leather, packaging and clothing.

In recent years, due to the surge in demand for masks and protective equipment, spunbond non-woven fabrics have begun to be mass-produced. How to increase the output of spunbond non-woven fabrics? Perhaps we can start with spunbond technology.（try Suntech spunbond nonwoven machine）

Spunbond technology production system

The concept of spunbond technology was developed simultaneously in Europe and the United States in the late 1950s. Since then, many innovations have been disclosed in the spunbond production system. This technology is derived from filament spinning technology. Filament spinning technology has obtained many patents. The basic principles proposed by Hartman are explained with the help of Figure 1.

Figure 1 illustrates the filament forming system. Here, air as hot as the melting temperature emerges from near the nozzle hole, pulling the filaments tight and stretching. At the same time, the gushing air mixes with the surrounding air. It uses a longitudinal spinneret with air gaps on both sides for exhausting the draw gas "1" (primary air). Carry room air (secondary air) "2", and after putting down the filament, use suction "3" to remove the air. This method is very suitable for viscous polymers, such as linear polyurethane. The continuous filaments after the collection of the fibrous web bond to themselves (self-adhesive) at their intersections due to their inherent stickiness. Then it crystallizes and then crystallizes, eliminating the stickiness of the filaments after bonding.

figure 1

Figure 1 depicts another system. Here, the discharged air and filaments are brought to the suction channel. Blow in additional compressed air to achieve a stretching effect. It uses a higher draw ratio, thereby increasing the molecular orientation of the filament. Use a drawing catheter to draw multiple air streams or air streams into filaments. After the fiber web is formed, use suction "4" to remove air.

Figure 1 depicts yet another system. Here, the cooling air and the suction air are separated. It uses conventional cooling air duct "1" and traction jet "3" to operate. The drafting and cooling device can be operated to provide very high spinning speeds, resulting in highly oriented filaments. The temperature and moisture content of indoor air "2" can be controlled to control the development of filament performance. After the fiber web is formed, use suction "4" to remove air.

Figure 1 illustrates another system with a mechanical stretching step "2" between the spinneret and the lofting area. This route is similar to conventional spinning and is especially useful for polymers. In conventional air drawing, polymers cannot provide the best filament "4". This particular system is usually used to make webs with high strength and low elongation.

Some commercial spunbond production systems are Docan system, Lutravil system, Ason/Neumag system, Reicofil system and Rieter system.

We will discuss one system, and interested readers can learn about other systems. Figure 2 shows a schematic diagram of the Reicofil spunbond system, where polymer pellets or pellets are vacuum fed into the feeding station on top of the extruder. Inside the extruder, the polymer pellets are melted and homogenized. Then the molten polymer is passed through the filter system and the spinning machine, the melt is distributed through the coat hanger die, and the spinning plate forming the silk curtain is sent to the spinning plate. The filaments are cooled by air flow in the blowing area, sucked away by aerodynamic force, and then transported to the downstream discharge channel. Here, the main blowing pipe located below the spinneret block continuously cools the filaments with conditioned air. The auxiliary blowpipe located below the main blowpipe continuously supplies auxiliary air at room temperature.

figure 2

The ventilators running across the entire width of the machine generate negative pressure and draw filaments and mixed air out of the spinneret and cooling chamber. The filaments rotate around and are then deposited on the wire mesh belt in the form of a random non-woven material. It is transferred to a thermal bonding calender, which uses heat and pressure to set the physical properties to the tensile and elongation of the final product. After calendering, the material is cooled by a pair of water-cooled rollers and then rolled up. The continuous filaments are drawn into the distribution chamber through the venturi (high-speed and low-pressure zone), where they are elongated and tangled. Finally, the entangled filaments are deposited on the moving suction mesh belt to form a web. The orientation of filaments in the web is affected by turbulence in the airflow, which is often used to increase randomness.

（Suntech ST-ASS spunbond nonwoven machine）

Key process factors

The key process factors of spunbond nonwoven technology are polymer throughput, polymer melting temperature, quench air temperature, quench air speed and web-laying speed. These process factors play an important role in determining the shape and diameter of the filament, which is the basis of any spunbonded nonwoven fabric. Bonding parameters are also very important, and their role has been discussed earlier.

The polymer throughput rate determines the morphology and diameter of the filament. The morphology of filaments spun at lower productivity is better than that of filaments spun at higher productivity. Because rheological conditions are more conducive to the crystallinity and orientation of filaments spun at a lower throughput rate. Therefore, filaments spun at a lower throughput rate are more stable than filaments spun at a higher throughput rate. The diameter of the filament increases as the productivity increases.

The melting temperature of the polymer affects the drawing of the filament through the spinneret, which in turn determines the diameter of the filament. The lower melting temperature of the polymer leads to an increase in the melt viscosity of the polymer, which leads to difficulty in drawing. On the other hand, a higher melting temperature results in a decrease in the melt viscosity of the polymer, which makes stretching easier. Too high a polymer melting temperature can cause degradation of the polymer, which can cause filament breakage.

The influence of quenching temperature on filament diameter and morphology is controversial. A group of researchers believes that lower quenching air temperature will increase viscosity, which will slow down the drawing speed and ultimately increase the diameter of the filament. As the stretching progressed slowly, an increase in crystallinity and orientation was observed. Another group believes that lower quenching air temperature helps to generate higher spinning stress, which leads to a reduction in filament diameter. When stretching is performed under higher stress, an increase in crystallinity and orientation is observed.

The quenching gas pressure has the function of determining the diameter of the filament. Higher quench air pressure will increase the draw ratio of the spinning thread, thereby reducing the filament diameter. It is known that the pressure drop is directly proportional to the air velocity.

The fiber web is formed by pneumatically depositing filament bundles onto a moving belt. In order to obtain maximum uniformity and coverage, individual filaments must be separated before they are stretched to the conveyor belt. This can be achieved by inducing electrostatic charges on the beam under tension and before deposition. This can be achieved by high-voltage corona discharge. The tape is usually made of a grounded conductive thread that discharges the filaments during deposition. Sometimes, mechanical or aerodynamic forces also separate the filaments. If the lowered conveyor belt is moving and the filaments move quickly in the direction of movement, the filaments will be deposited on the surface of the moving belt in a zigzag shape.

With 50 years of technical precipitation and design experience, Suntech has developed and produced intelligent non-woven fabric machines, including spunbond non-woven fabric machines, spunmelt non-woven fabric machines, melt blown machines, spunlace non-woven fabric machines, wet wipe machines, etc., which will be advanced Spunbond technology is integrated into the equipment production process, using brand-level precision production components, and adding intelligent elements to ensure the high efficiency, high quality, and high quality of spunbond production. It helps the production of medical&health products and the cause of human health with "precision and intelligent manufacturing".