Melt filtration processing in non-woven fabric production

One way to ensure that the materials in the non-woven production are clean is to use a filter system. This article introduces two German-made filters, they do not produce fluctuations in the process when replacing the filter, and can directly use recycled materials for production to reduce costs.

　　In the process of spunbond production of non-woven fabrics, the process of fiber spinning and non-woven fabric formation are combined. The polymer raw materials enter the spinneret in a molten state through the extruder, and then directly enter the conveyor belt after spinning to form a non-woven fabric.
Spunbond production line

　　 Spunbond process for non-woven fabric production

　　After mixing and feeding, the slices enter the extruder, then pass through the filter, and enter the melt pump in the melt state. Usually, the filter is equipped with a filter screen and other components to block the impurities in the melt and avoid entering the downstream equipment.

　　For the filter, the most important requirement is that during the process of replacing the filter screen, it does not cause adverse effects on production and does not cause material interruption or reduction. The melt pump can enhance the melt pressure and ensure the stable delivery of melt materials.
According to this process, fiber spinnerets have different designs. Usually, the spinneret system is equipped with many melt pumps, which need to ensure that the spinning can proceed smoothly.

　　The spinneret system design and precise control can ensure that the melt passing through the spinneret is stable and without fluctuations. In addition, there is a filter in the spinneret to ensure that the melt is uniform and clean. The filter of the spinneret is composed of multiple layers of woven mesh, and the residual impurities in the melt are blocked by it, so the filter mesh needs to be replaced regularly.

　　 When replacing the spinneret filter, it is necessary to stop the work of this station, and sometimes the entire production line needs to be stopped. The thinner the filter, the longer the life of the spinneret. Therefore, the filter before the spinneret should remove as much impurities in the melt as possible to increase the service life of the filter.
Spunbond process

In the 　　 melt spinning process, the melt is directly injected into a hot high-speed air stream, and the melt changes from liquid to fibrous. The diameter of the fiber is 0.5~30um, usually 2~7um. The fibers enter the stacking net together with the hot air, and are cooled and solidified after being in contact with the cold air.

　　 Airflow fluctuations cause the fibers to align randomly, and the randomization of fiber orientation is exactly the requirement of the non-woven melt spinning process, so it can meet the homogeneity requirements of non-woven production. These opaque non-woven fabrics have low tear strength, large surface area, insulation and filtration properties.

The remarkable feature of the melt spinning process is that the melt is heated to a higher temperature. Therefore, the design of the melt channel, the internal structure of the spinneret and the optimization of the melt flow are very important.

　　The melt flow rate is too low or the existence of dead corners will cause the melt to be thermally degraded. If the degraded material enters the spinneret, holes or black blocks will be formed in the final product, which will have to stop the entire production line to clean the conveyor belt.
In the process, the filaments enter the cold air zone after being extruded. At this time, due to changes in air flow and static electricity, the fibers do not stick together.

　　The non-woven fabric accumulation process takes place in a porous accumulation belt, which is conveyed until the non-woven fabric is rolled and packaged. The diameter of a single filament is 15~35um. Similar to the melt spinning process, the fiber structure is disordered, but it is light, warm and highly absorbent. Compared with other fabrics, non-woven fabrics have excellent tensile strength per density/weight, and are mainly used in waterproof sealing materials, sanitary products or geotextiles, such as preventing soil erosion.

In the 　　 "Reicofil" process, air is spread throughout the fabric, and in the subsequent process, the fibers are separated and mixed by a cyclone.
The production line supplied to Turkey by Neumag, a subsidiary of Saurer, uses ASON Spunbound technology. Due to the variable positions of the spinneret, syringe and accumulation belt, production flexibility is greatly enhanced. Therefore, a single production line can produce many kinds of products, and the switching time is very short. At the same time, different raw materials can also be used, such as composite fibers and polyester materials that are currently growing extremely rapidly in the non-woven market.

　　The accumulation of non-woven fibers

　　 Filtration system in non-woven fabric production

　　In the non-woven fabric production process, the role of the melt filtration system is to remove impurities in the melt and protect the spinneret. Because even small impurities may force the replacement of the spinneret, causing the entire production line to stop. At the same time, the breakage of each fiber can cause defects and irregularities in the non-woven fabric. In addition, during the fiber spinning process, the spinneret replacement frequency is also required to be low.
The requirements for filter fineness depend on the structure and application of the non-woven fabric. For geotextile products, visible impurities are allowed, while for medical products, any tiny impurities must be removed. The filtration fineness of the spinneret filter is determined by the diameter of the final product and fiber, usually 20~75um.

　　 In most cases, the replacement of the filter of the spinneret can only be done at the stop stage of the production line, and the pressure is relieved through the upstream melt filter. Generally, the filtration fineness of the upstream melt filter is equivalent to or finer than that of the spinneret filter to extend the life of the spinneret.
When selecting the filter type, it must be considered that the filter will not have any effect on the melt characteristics. Blind corners, long residence time, air entering the filter or oxidized melt may cause polymer degradation, change the characteristics of the raw materials and cause product quality defects, so it must be shut down for cleaning.

　　 On the other hand, rising raw material prices and operating costs require that the economic factors of the filter system must be considered. Extending the spinneret filter screen change time and improving product quality can save costs. At the same time, investment and operating costs must also be considered.

In addition, it is important to consider whether recycled materials can be used. Since raw materials account for a large proportion of the entire production cost, the use of cheaper recycled materials can quickly recover the investment. Generally, the payback period of the investment filter should be less than 12 months .