In the production of non-woven bags, the meltblown process is the core element determining fiber uniformity and strength. Its optimization requires coordinated adjustments across multiple dimensions, including raw material selection, temperature control, airflow stretching, spinneret design, and post-processing. The meltblown process uses high-temperature, high-speed airflow to stretch polymer melt into ultrafine fibers, with fiber diameters reaching the micrometer level. This structure endows non-woven bags with high filtration efficiency and mechanical properties. However, even slight fluctuations in process parameters can lead to uneven fiber thickness or insufficient strength, thus affecting the load-bearing capacity and durability of the non-woven bags.
Raw material selection is fundamental to meltblown process optimization. Polypropylene (PP) is a commonly used raw material for meltblown non-woven bags, and its melt flow index (MFI) directly affects the fiber forming effect. High MFI raw materials have strong fluidity and are easily stretched into fine fibers by airflow. However, if the MFI is too high, the fibers are prone to breakage, resulting in "flying" or holes on the fabric surface. Low MFI raw materials may lead to insufficient stretching, resulting in coarse fibers and reduced uniformity. Therefore, it is necessary to select raw materials with appropriate MFI (Medium-to-Fiber Index) based on the performance of the target product, and improve the fiber's crystalline structure and toughness by adding nucleating agents or toughening agents, thereby enhancing strength.
Temperature control is a key parameter in the meltblown process. The extruder temperature must be precisely matched to the raw material characteristics to ensure that the polymer melts fully and does not degrade. Excessive temperature will cause the melt viscosity to decrease, resulting in over-stretching and thinning of the fibers, but insufficient cooling may lead to fiber adhesion and reduced uniformity. Conversely, insufficient temperature will increase melt viscosity, increase stretching resistance, and cause fibers to break easily or become uneven in thickness. Furthermore, the die temperature and hot air temperature must be adjusted in tandem. Excessive die temperature will cause the melt to expand at the spinneret, leading to fiber diameter fluctuations; insufficient hot air temperature will fail to effectively cool the fibers, affecting forming stability.
The airflow stretching system directly affects the fineness and uniformity of the fibers. The meltblown process stretches the melt stream into ultrafine fibers using a high-speed hot airflow; airflow velocity, angle, and uniformity are the core control points. Too low an airflow velocity leads to insufficient drafting and fiber coarsening; too high a velocity may cause fiber breakage or turbulence, resulting in "streaks" or holes on the fabric surface. The airflow angle needs to be close to 90° to create highly dispersed turbulence, allowing fibers to distribute randomly on the condenser screen and avoiding anisotropic differences caused by parallel fiber bundles. Furthermore, airflow uniformity must be achieved through optimized air duct structure and air knife design to ensure consistent airflow pressure across the width of the fiber web, reducing weight deviation.
The design and maintenance of the spinneret are crucial to fiber uniformity. The spinneret's orifice diameter, orifice shape, and processing precision directly affect the initial state of the melt stream. Too small an orifice diameter increases melt extrusion resistance, making fibers prone to breakage; too large an orifice diameter coarsens the fibers, reducing uniformity. The spinneret needs regular cleaning to prevent orifice deformation or blockage caused by melt residue, which can lead to localized fiber loss or uneven fiber thickness. In addition, the assembly precision of the spinneret and die head must be strictly controlled to prevent melt leakage or impurity contamination, affecting fiber quality.
Post-processing is the final step in enhancing fiber strength. Meltblown non-woven bags require thermal rolling or chemical bonding to reinforce the fiber web structure. The thermal rolling temperature, pressure, and linear speed must be matched to the fiber characteristics. Excessive temperature leads to over-melting of the fibers, reducing strength; insufficient temperature results in inadequate bonding and easy delamination of the web. Chemical bonding requires the selection of environmentally friendly adhesives, and the application amount and curing time must be controlled to prevent adhesive penetration that could cause fiber hardening or embrittlement. Furthermore, electret treatment enhances the filtration efficiency of non-woven bags by imparting an electrostatic charge to the fibers. Simultaneously, corona discharge parameters must be optimized to ensure a stable and lasting charge, preventing performance degradation due to electrostatic decay.
Production environment control is a hidden factor in process optimization. Fluctuations in ambient temperature and humidity affect melt viscosity and fiber cooling rate, requiring stability through temperature and humidity control workshops or local environmental control systems. For example, high temperatures may cause a decrease in melt viscosity and fiber thinning; high humidity may cause fibers to absorb moisture, reducing strength. In addition, equipment vibration or mechanical deviations can also cause fiber uniformity issues, requiring regular calibration and maintenance to ensure equipment stability.
Optimization of the meltblown process requires consideration of the entire process, including raw material selection, temperature control, airflow stretching, spinneret design, post-processing, and environmental control. By systematically adjusting process parameters and equipment status, the fiber uniformity and strength of non-woven bags can be significantly improved, thereby meeting market demand for high-load-bearing and durable non-woven bags.
