Melt blown method is a method of preparing fibers by rapidly stretching polymer melt through high-temperature and high-speed airflow blowing. Polymer slices are heated and pressurized into a molten state by a screw extruder, and then pass through the melt distribution channel to reach the nozzle hole at the front end of the nozzle. After extrusion, they are further refined by stretching two converging high-speed and high-temperature airflows. The refined fibers are cooled and solidified on the mesh curtain device to form a melt blown non-woven fabric.
The continuous melt blown non-woven fabric production technology has undergone more than 20 years of development in China. Its application fields have expanded from battery separators, filter materials, oil absorbing materials, and insulation materials to medical, hygiene, healthcare, protection, and other fields. Its production technology has also developed from single melt blown production to composite direction. Among them, melt blown composite materials that have undergone electrostatic polarization treatment can be widely used for air purification in electronic manufacturing, food, beverage, chemical, airport, hotel and other places, as well as medical high-performance masks, industrial and civilian dust collector filter bags, due to their low initial resistance, large dust holding capacity, and high filtration efficiency.
The melt blown non-woven fabric made of polypropylene material (a type of ultra-fine electrostatic fiber cloth that can capture dust) is affected by factors such as fiber pore size and thickness, which affect the filtration effect. Particles of different diameters are filtered through different principles, such as particle volume, impact, diffusion principles leading to fiber blockage, and some particles being filtered by electrostatic fibers through electrostatic attraction principles. The filtration efficiency test is conducted under the particle size specified by the standard, and different standards will use particles of different sizes for testing. BFE often uses bacterial aerosol particles with an average particle diameter of 3 μ m, while PFE generally uses particles with a sodium chloride diameter of 0.075 μ m. Simply from the perspective of filtration efficiency, PFE has a higher effect than BFE.
In the standard testing of KN95 level masks, particles with an aerodynamic diameter of 0.3 μ m are used as the test object, because particles larger or smaller than this diameter are more easily intercepted by filter fibers, while particles with an intermediate size of 0.3 μ m are more difficult to filter. Although viruses are small in size, they cannot spread alone in the air. They require droplets and droplet nuclei as carriers to disperse in the air, making them easy to filter out.
The core of meltblown fabric technology is to achieve efficient filtration while minimizing respiratory resistance, especially for N95 and above meltblown fabrics, VFE grade meltblown fabrics, in terms of the formulation of polar masterbatch, the performance of meltblown materials, the spinning effect of meltblown lines, and especially the addition of polar masterbatch, which will affect the thickness and uniformity of spun fibers. Achieving low resistance and high efficiency is the most core technology.
Factors affecting the quality of meltblown fabrics
MFI of polymer raw materials
Meltblown fabric, as the best barrier layer for masks, is an extremely fine material composed of many intersecting ultrafine fibers stacked in random directions inside. Taking PP as an example, the higher the MFI, the finer the wire pulled out during melt blown processing, and the better the filtration performance.
Angle of hot air jet
The angle of hot air injection mainly affects the stretching effect and fiber morphology. A smaller angle will promote the formation of parallel fiber bundles in fine streams, resulting in poor uniformity of non-woven fabrics. If the angle tends towards 90 °, a highly dispersed and turbulent airflow will be generated, which is conducive to the random distribution of fibers on the mesh curtain, and the resulting melt blown fabric will have good anisotropy performance.
Screw extrusion speed
Under constant temperature, the extrusion rate of the screw should be maintained within a certain range: before a critical point, the faster the extrusion speed, the higher the quantitative and strength of the meltblown fabric; When the critical value is exceeded, the strength of the meltblown fabric actually decreases, especially when MFI>1000, which may be due to insufficient stretching of the filament caused by high extrusion rate, resulting in severe spinning and reduced bonding fibers on the fabric surface, leading to a decrease in the strength of the meltblown fabric.
Hot air velocity and temperature
Under the same conditions of temperature, screw speed, and receiving distance (DCD), the faster the hot air velocity, the smaller the fiber diameter, and the softer the hand feel of the non-woven fabric, resulting in more fiber entanglement, which leads to a denser, smoother, and stronger fiber web.
Receiving distance (DCD)
An excessively long acceptance distance can lead to a decrease in longitudinal and transverse strength, as well as bending strength. The non-woven fabric has a fluffy texture, which can result in a decrease in filtration efficiency and resistance during the melt blown process.
Melt blown mold head (hard index)
Mold material and process temperature setting. Using some low-end mold steel instead may result in subtle cracks that cannot be seen by the eyes during use, rough aperture processing, poor accuracy, and direct machine operation without polishing treatment. Causing uneven spraying, poor toughness, uneven spraying thickness, and easy crystallization.
Net bottom suction
Process parameters such as air volume and pressure for net bottom suction
Net speed
The speed of the mesh curtain is slow, the weight of the meltblown fabric is high, and the filtration efficiency is higher. On the contrary, it also holds true.
Polarizing device
The parameters such as polarization voltage, polarization time, polarization molybdenum wire distance, and polarization environment humidity can all affect the filtration quality.
Dongguan Liansheng Non woven Technology Co., Ltd. was established in May 2020. It is a large-scale non-woven fabric production enterprise integrating research and development, production, and sales. It can produce various colors of PP spunbond non-woven fabrics with a width of less than 3.2 meters from 9 grams to 300 grams.
Post time: Nov-28-2024