Detailed explanation of meltblown cloth production technology to help you understand the 5 core influencing factors!
May 14, 2020
As the core component of masks, melt-blown cloth has become the most demanding material in the current mask production chain.
Medical surgical masks (structure shown in Figure 1) are usually composed of three layers of non-woven fabrics, the middle layer plays the most important role in filtering and blocking, and the material used is melt-blown non-woven fabrics.
1 Selection of raw materials
Polypropylene (PP) is easy to form filaments, and in the case of high melt index (MFI≥1500g / 10min), it can become quite fine fibers (diameter 2 ~ 3 μm). As shown in Fig. 3, although the gap of the melt-blown cloth produced is much larger than the size of the new coronavirus (about 0.1 μm), its ability to filter viruses in the environment is still very strong.
3. Factors affecting the quality of meltblown cloth
1. MFI of polymer raw materials
Meltblown cloth is the best barrier for masks. It is a very fine material. The interior is made up of many superfine fibers crisscrossed in random directions. Taking PP as an example, the higher the MFI, the finer the wire drawn during melt-blown processing, and the better the filtration performance.
2. Hot air velocity
Under the same temperature, screw speed and receiving distance (DCD) and other conditions, the faster the hot air speed, the smaller the fiber diameter, the nonwoven fabric feels gradually softer, and the more fibers are entangled, resulting in a denser and smoother web. Strength increased.
3. Hot air jet angle
The hot air jet angle (see Figure 5a) mainly affects the drawing effect and fiber morphology. The smaller angle will cause the fine flow to form parallel fiber bundles, resulting in poor uniformity of the nonwoven fabric. If the angle tends to 90 °, a highly dispersed and turbulent air flow will be generated, which is conducive to the random distribution of fibers on the screen, and the resulting melt-blown cloth has good anisotropy.
4. Receive distance (DCD)
Too long acceptance distance will lead to a reduction in longitudinal and transverse strength and bending strength, and a non-woven fabric with a fluffy feel. In the melt-blowing process, filtration efficiency and filtration resistance will decrease.
5. Screw extrusion speed
Under the condition of constant temperature, the screw extrusion rate should be kept within a certain range. Before a certain critical point, the faster the extrusion speed, the higher the quantitative amount of melt-blown cloth, and the greater the strength; when the critical value is exceeded, the strength of the melt-blown cloth decreases, especially when MFI> 1000. Because the extrusion rate is too high, the wire drawing is insufficient and the wire is serious, so that the bonding fiber on the surface of the cloth is reduced, and the strength of the melt-blown cloth is reduced.
Source : http://www.up-resin.com/