In the production of non-woven bags, the meltblown process is a core component, and its optimization directly impacts fiber uniformity and filtration performance. Fiber uniformity is a key indicator of meltblown fabric quality, determining the density and stability of the material structure; while filtration performance is closely related to fiber diameter, pore structure, and surface charge distribution. These two core indicators can be systematically improved through process parameter control, equipment structure improvement, and synergistic post-processing technologies.
The core of the meltblown process lies in stretching and melting the polymer using a high-temperature, high-speed airflow to form ultrafine fibers. Fiber uniformity is primarily affected by the stability of the melt extrusion. Large fluctuations in the polymer melt flow rate can lead to uneven fiber output from the spinneret, with some areas having coarser fibers and others finer fibers. Therefore, it is necessary to strictly control the melt index of the raw material and optimize the temperature gradient and speed matching of the screw extruder to ensure that the melt maintains a constant viscosity and pressure at the die. Furthermore, the die head structure design must balance the density and uniformity of the spinneret arrangement. Using a multi-row spinneret layout can increase production capacity, but bonding technology is needed to enhance the die head's high-pressure resistance and prevent fiber breakage or uneven fiber thickness due to localized leakage.
Airflow drawing is a crucial step in determining fiber diameter. The temperature, pressure, and jet angle of the hot air must be precisely coordinated: excessive temperature leads to excessive melt evaporation and fiber embrittlement; insufficient pressure weakens the drawing force, resulting in coarser fiber diameters; and a jet angle deviating from the vertical direction causes airflow turbulence, disrupting fiber distribution. In actual production, the optimal parameter combination needs to be determined experimentally. For example, an adjustable air knife can be installed below the die head to guide fibers towards the center by controlling the difference in hot air velocity on both sides, reducing fiber scattering at the edges. Simultaneously, introducing room temperature air to mix with hot air can accelerate fiber cooling and solidification, preventing fiber adhesion due to residual heat, thereby improving web uniformity.
The correlation between fiber uniformity and filtration performance is reflected in the pore structure. Uniformly distributed ultrafine fibers create more micropores, increasing the probability of particle interception. For example, when the fiber diameter decreases from 5 micrometers to 2 micrometers, the number of fibers per unit area increases exponentially, porosity decreases significantly, and filtration efficiency improves accordingly. However, simply pursuing finer fibers may increase breathing resistance; therefore, it is necessary to balance efficiency and resistance by optimizing the fiber web structure. Using a multi-layer composite process, alternating layers of coarse and fine fibers, a gradient pore structure can be constructed: the outer layer of coarse fibers intercepts large particles, while the inner layer of fine fibers captures small particles, extending the filtration path and avoiding the clogging problem of a single fine fiber layer.
Electret treatment is a key post-treatment technology for improving filtration performance. By charging the fiber surface through corona discharge, an electrostatic adsorption effect can be formed, significantly enhancing the capture capacity of submicron-sized particles. The electret effect depends on the stability of charge storage; therefore, electret masterbatches, such as tourmaline microparticles, need to be added to the raw materials. Their crystal structure can form charge traps, slowing down the rate of charge decay. Furthermore, the electret voltage and processing time need to be adjusted according to the characteristics of the fiber material: too low a voltage will result in insufficient charge density, while too high a voltage may cause fiber breakdown; too short a processing time will lead to uneven charge distribution, while too long a time will increase energy consumption and saturate the effect.
The impact of production environment control on fiber uniformity is often overlooked. Fluctuations in workshop temperature and humidity can cause changes in melt viscosity, which in turn affects fiber diameter. For example, low temperatures reduce melt fluidity, requiring increased die temperature compensation, but this may cause fiber embrittlement; high humidity environments may cause moisture adsorption on the fiber surface, reducing the electrostatic electret effect. Therefore, a constant temperature and humidity system needs to be installed around the production line, and environmental parameters should be monitored regularly to ensure process stability.
Equipment maintenance and process optimization need to form a closed loop. After long-term operation, the spinneret orifices may change in diameter due to melt residue blockage or wear, requiring periodic re-drilling with precision needles or replacement of the die. Simultaneously, by collecting real-time data on web basis weight, thickness, and air permeability through an online monitoring system, and combining this with machine learning algorithms to establish predictive models of process parameters and product performance, the root cause of problems can be quickly located and parameters adjusted, achieving dynamic optimization.
Optimization of the meltblown process requires a multi-dimensional approach, encompassing raw materials, equipment, process parameters, and post-processing. By enhancing melt extrusion stability, precisely controlling airflow stretching, constructing gradient pore structures, strengthening electrostatic electret effects, and implementing strict environmental control, fiber uniformity and filtration performance can be significantly improved, providing technical support for the high-quality production of non-woven bags.
