The spinning process includes the amount of melt extrusion, drafting hot air velocity and melt temperature.
1. Melt extrusion
The amount of polymer melt extruded affects the linear density and output of the fiber.
The higher the grams per minute of the polymer melt extruded from the fuse hole, the thicker the fiber. Therefore, under the premise of ensuring the fiber fineness of the meltblown non-woven fabric, the number of spinnerets must be increased to increase the meltblown output.
2. Drafting heat flow speed
The secondary heat flow rate is the main process parameter in the melt spraying process, which directly affects the fineness of the fiber. For a quantitative polymer melt extrusion and a predetermined melt viscosity, the higher the drafting air velocity, the greater the drafting effect on the polymer melt microflow on the spinning line, and the thinner the fiber.
In industrial production, high-speed ventilated hot air is usually used to compensate for the fiber diameter change caused by the increase in polymer extrusion, that is, the flow rate of the secondary hot air must match the polymer extrusion.
3. Melting temperature
Melt blowing temperature refers to the working temperature, and the nozzle can be used to adjust the viscosity of the polymer melt. The melting temperature is usually higher than the melting point of the PP resin, making it in a viscous flow state. When other process conditions remain unchanged, the lower the viscosity of the polymer melt, the finer the melt trickle. Therefore, microfibers can be easily obtained by using high MF polymer chip materials in the melt spray process. However, if the melt viscosity is too small, the melt flow will be overextended, and the ultra-short fibers will fly into the air and cannot be collected. It is also called the "flying" phenomenon during the melt spraying process. Therefore, in order to prevent the melt from breaking under the action of shearing force, the melt viscosity of polypropylene materials usually used for meltblown is in the range of 50-300pas.