Three major processing technologies of non-woven fabrics —— Spinning fusion

Three major processing technologies of non-woven fabrics -——Spinning fusion

Spinning fusion is the most widely used one-step spinning forming process for forming non-woven fabrics. The spunbonded nonwovens are formed by continuous filament fibers, the production line speed is high, the product strength is high, and the dimensional stability is good, but the bulkiness is low, and the uniformity of web formation and surface coverage are slightly poor.

The spunbond method combines fiber spinning technology and non-woven molding technology, and uses the principle of melt spinning. After the raw materials are melted and mixed by the extruder, they are extruded from the spinneret of the spinning head to form a thin melt flow. The high-speed quenching air is used to cool the extruded melt stream, and at the same time, the fiber is stretched by the drawing airflow during the cooling process, forming a continuous filament with superior strength and stable performance. After the filaments are divided into filaments to form a uniformly distributed monofilament structure, they are laid on a net curtain with negative pressure to form a nonwoven fiber web. After the fiber web passes through the subsequent strengthening device, it is hot-rolled, needle-punched or spunlace-fixed, and then wound up by the coiling device to obtain the product. The key steps are melt spinning, air drawing of primary fibers, fiber forming and web setting.

1. Melt spinning

The raw materials need to be pre-dried to avoid degradation when heated and melted at high temperature, especially to avoid the vaporization of water at high temperature to form "bubble filaments", which will cause wool or broken ends, affecting product quality and normal production. The control of the spinning process is mainly carried out by the following aspects.

Spinning temperature control: mainly to control the temperature of spinning components such as spinnerets. The appropriate spinning temperature should keep the melt fluid enough to ensure smooth spinning, and the melt uniformity and spinnability are high, so that the subsequent air-drawing process can be performed

smoothly, and the fiber orientation degree is abnormal. The spinning temperature is controlled between the melting point and the decomposition temperature. Properly increasing the spinning temperature can improve the melt fluidity.

Spinning melt pressure controls: mainly to control the pressure of the melt in the spinning box. If the melt pressure is too low, melt flow will be unevenly distributed on the spinneret, and the diameter of the extruded melt stream will be uneven. If the melt pressure is too high, it is easy to provoke the melt fracture of the spinneret hole extrusion.

Control of spinning speed: Spinning speed affects the size and uniformity of fiber linear density, as well as the quality of nonwovens. If the spinning speed is too low, the fine flow of the extruded melt is cooled too quickly, resulting in effortless stretching and broken filaments. However, if the spinning speed is too high, the fine flow of melt cannot be cooled in time, resulting in parallel filaments and affecting the quality of nonwoven fabrics.

2. Air-stretching of the primary fiber

In order to improve the performance of nonwovens, it is also necessary to stretch and orient the primary fibers to increase the degree of orientation and crystallinity of the fibers, thereby improving the physical and mechanical properties of the fibers. In the production of spunbonded nonwovens, since the follow-up processes such as spinning, stretching, splitting, laying, and reinforcement are continuous and high-speed, the stretching of the fibers is completed in a short time, and the fibers must also be stretched. Provide ideal cooling effect, so the production of spunbonded nonwovens mostly adopts air stretching.

The principle of the air-drawing process: the filaments are extruded from the spinneret holes, and after being cooled by side blowing, they are directly sucked into the suction port of the air-drawing equipment. In the air duct of the stretching equipment, the stretching airflow is blown in from the direction of the fiber, and the fiber is rapidly accelerated under the clamping action of the high-speed and high-pressure stretching airflow, and the stretching is realized through the stretching nozzle. Air stretching equipment mainly includes tubular drafting machine, narrow slit drafting machine and wide slit drafting machine.

The control of the airflow stretching process is mainly through the structure of the drafting machine (under the condition of constant air volume, the smaller the drafting nozzle and air duct, the higher the drafting speed and the higher the fiber strength), the temperature of the drafting wind, the drafting Wind pressure and wind speed, cooling conditions.

3. Fiber forming

Fiber netting is the process of dividing the continuous filaments formed after melt spinning and air drawing, so that the monofilaments are evenly dispersed, and then laid on the netting curtain to form a uniform web. For the forming process of spunbonded nonwovens, due to the use of continuous filaments to form a web, the time for separating and laying the web is short, and the disturbance of the high-speed drawing airflow is severe, so it is difficult to control the movement of the fiber filaments and affect the fiber web formation. Uniformity, so the spunbond process cannot form thin nonwovens.

The fiber web forming process first needs to separate the fiber filaments that have been stretched by air. The purpose is to separate the tow into single filaments to prevent fiber adhesion during web laying and affect the uniformity of the web. . The methods of splitting mainly include electrostatic splitting, mechanical splitting, and air splitting. The fiber filaments after the separation treatment are evenly laid on the web curtain by different processes to form a non-woven web. The web laying process needs to control the movement of the fiber filaments according to the set trajectory, so as to ensure that the formed web is firm and uniform. The control of fiber movement can be mechanical and airflow, so the methods of laying mainly include pen laying, scattered laying, jet laying and runner laying. During the web laying process, in order to quickly fix the structure of the fiber web and avoid the influence of external factors, the method of negative pressure web laying is adopted, that is, the space under the web forming curtain is vacuum suctioned to make the web forming A negative pressure is created on the upper surface of the curtain, which facilitates the collection and fixation of the fiber filaments. On the one hand, the negative pressure laying method has a certain stretching effect on the fibers, on the other hand, it can dissipate the high-speed airflow from the tubular drafting machine, and prevent the fibers from flying due to severe airflow disturbance. Therefore, in the process of web laying, the requirements for fiber web curtains are higher, and web curtains often require good air permeability, high tensile strength, sufficient web width and good antistatic properties, and It is also equipped with a mesh curtain seal to meet the requirements of the carrier, conveying the web and separating the airflow.

4. Fiber net shaping

The non-woven fibers formed by the filament separation and web laying process are only simple physical entanglement between the fiber filaments, and the structure is not firm yet, so reinforcement and shaping treatment are required to finally produce high-strength, low-elongation non-woven fabrics cloth. The fixed methods include hot rolling reinforcement method, acupuncture reinforcement method and spunlace reinforcement method.

Hot rolling reinforcement method: it is mainly suitable for fiber webs of thermoplastic polymer materials such as PP. The principle is to heat and melt polymer fibers in a hot rolling mill, and under pressure, they are fused together at the hot rolling point/surface, thereby significantly Improve the strength of the fiber and realize the fixed type of non-woven fabric. The hot rolling mill consists of heated steel rolls and elastic rolls, which can be bonded by point bonding and surface bonding. Engraved rolls with different nip shapes are used for point bonding, and polished steel rolls are used for surface bonding.

Acupuncture reinforcement method: use rows of needles with triangular cross-sections (or other cross-sections) and barbs on the edges to repeatedly puncture the fiber web. During the needle puncture process, the fibers on the surface layer of the web are forced into the interior of the web and form an entangled structure that does not recover. Under the action of friction and entanglement between fibers, the fluffy fiber web is compressed, and many entanglement points are formed after repeated punctures, and finally the fiber web is fixed. Acupuncture reinforcement processes mainly include pre-punching, main needling, pattern needling, ring needling and tubular needling. The movement direction of needle punching is usually perpendicular to the fiber web, but there are also upward or downward oblique punching directions. Oblique punching can increase the depth of needle punching, greatly improve the strength of the product, and improve the dimensional stability of the product. The fibers of needle-punched nonwovens are flexibly entangled, so they have good dimensional stability and elasticity, good permeability and filterability, and a full hand feel.

Spunlace reinforcement method: Use a number of very fine high-pressure water jets to spray at high speed onto the laid fiber net. The water flow pierces the fiber net and hits the bottom conveyor net. Under the action of repeated penetration and complex turbulent water flow, the fibers in the fiber web produce different forms of entanglement structures and a large number of entanglement points, thus making the fiber web more fixed. The spunlace reinforcement method can increase the single-line production speed of spunbonded non-woven fabrics. This method has many entanglement points and does not damage the fibers. The non-woven fabrics produced have high strength, soft hand feeling, and no adhesives.