Quality of non-woven material "Spunlace" - influence of production factors

With development of the nonwovens industry in the world and the growing scale of their consumption, technologies and processes of their production are becoming more mature, their fields of application are expanding, and manufacturers of nonwovens, in addition to market and price competition, face many issues related to offering consumers a high-quality and balanced product.

Physical properties of the fibers used as the basic raw material for the production of non-woven fabric "spunlace" have a huge impact on the quality of the final product. Therefore, all manufacturers of such materials have special requirements both for their raw materials and for the technological characteristics of the equipment they use.

1 - Fiber strength

The strength of nonwovens «spunlace» under the conditions of a certain production process is mainly determined by the tensile strength of the fibers used. Various methods of subsequent processing of non-woven fabrics "spunlace" have a certain physico-chemical effect on them, so many consumers take into account the high strength and wear resistance of materials when buying them, and this is possible only if the manufacturer of raw materials strives to ensure a constant high strength of the offered fibers.

2 - Moisture absorption

The moisture absorption parameter of staple fiber is a parameter indicating the water content in the fiber. If the moisture recovery of the fiber goes beyond the norm and the moisture content of the fiber does not meet the requirements for a particular field of application, this affects not only the quality of the final product, but also has a negative impact on the production equipment. If too wet fiber is constantly used, it can lead to damage and corrosion of the equipment. If too dry fibers are used – fiber bundles begin to fly in the air of the production room and excessive static electricity is generated on the production line. Therefore, along with strength, it is recommended to pay increased attention to the hygroscopic properties (indicators) of the fibers used, including not only the input control of raw materials received from the manufacturer, but also special storage conditions.

3 - Content of oiling agent

The fiber contains a certain amount of oiling agent, which reduces the friction between the fibers, prevents the formation of static electricity and promotes the carding process. If the content of the oiling agent on the fiber exceeds the standard value, this leads to insufficient adhesion between the fibers, difficulties during carding, easy tearing of the non-woven fabric, damage to equipment, etc. If the oil content is too low, this leads to increased friction between the fibers, generation of static electricity and instability of the quality of the finished product.

4 - Denier and fiber length

Under the same technological conditions for the production of non-woven fabric "spunlace", a product with completely different physical properties can be obtained at the output. The thinner the fiber used, the greater the number of single fibers, and, accordingly, more points (areas) of contact between the fibers after carding and hydro-weaving, which increases the strength of the finished product. And the longer the fiber, the more points and edges of contact of the fibers with each other, the stronger the adhesion between them and the higher the strength of the finished product.

5 - Fiber orientation

Mechanical properties, including tensile strength and elongation, depend on the orientation of the fibers in the fabric structure. The orientation of the fibers is determined at the stage of formation of the primary web. As a standard, the fiber is oriented in the transverse direction during the operation of the line. Therefore, the tensile strength in the transverse direction will be higher than the corresponding strength in the longitudinal direction, since the preferred orientation of the fibers is in the transverse direction. Depending on the field of application of the finished product (industrial segments: for example, a substrate for artificial leather), a transverse stacker can be installed in the line, which provides almost the same strength and elongation of the material in the longitudinal and transverse directions (MD/CD≈1).

6 - Line speed and water pressure

As a rule, if the production rate of the material remains unchanged, then the strength of the product increases with an increase in the pressure of the water needles, which allows to increase the entanglement of the fibers and reduce the thickness of the web. Although not everything is so clear here. A higher jet pressure, a smaller number of hydro-entanglement nodes (injectors) and a greater distance between them lead to non-woven structures with areas of uneven density, whereas a low jet pressure, a larger number of injectors with a smaller distance between them ensures a uniform distribution of fibers in the web. As an independent factor affecting the strength, elongation, and pore size of the web, specific energy is usually taken, i.e. the energy of the water jet per unit weight of the fiber.  «Spunlace» with double-sided hydro-entanglement, they show higher mechanical properties compared to canvases produced by single-sided hydro-entanglement.

7 - Forming belt

The forming conveyor  belt provides sufficient support to the web, and also helps to remove water from the hydro-entanglement zone. Stagnation of water on the surface of the web is a serious problem with hydro-entanglement. The mesh size of the forming belt  affects the mechanisms responsible for the actual entanglement of the fibers. Tensile strength of «spunlace» nonwovens decreases with a decrease in the size of the belt meshes. At the same time, tapes with a too open structure of the structure at high pressure in the injector tend to squeeze the fibers out of the web. Also, an unreasonable increase in the speed of the forming belt during the production process reduces the tensile strength of the final product.

8 - Water quality

In the requirements for water quality in the production of non-woven fabric "spunlace", it is necessary to properly configure the filtration system, pay attention to the purification of recycled water, regularly replace the filter cloth, bag filters and filter inserts. It is necessary to precisely regulate the chemical and mechanical parameters of the process water and regularly add fungicides to prevent the growth of bacteria and other microorganisms. A process-based schedule for draining recycled water and adding fresh water must be approved to maintain a certain purity of process water.

Conclusion

The parameters of the hydro-entanglement process play an important role in determining the properties of non-woven materials "spunlace". Currently, there are many scientific studies on the influence of velocity, pressure, diameter, angle of impact of water jets on the structure and properties of nonwovens. The review of factors carried out in this article helps to understand how the structure and properties of the web change when the qualitative characteristics of raw materials, parameters of hydro-entanglement and the use of various technical equipment of equipment change. The information will be useful in planning and optimizing the production process to achieve the desired properties of nonwovens produced using the "spunlace" technology.