Three major processing technologies of non-woven fabrics ——melt-blowing

Three major processing technologies of non-woven fabrics ——melt-blowing

The melt-blowing method is to blow the melt extruded by the screw with high-speed and high-temperature airflow, so that the melt stream is stretched at a higher ratio to form ultra-fine short fibers, and then piled up on the condensed net curtain or into a On the net roller, a continuous short fiber web is formed, and then a non-woven fabric is made by self-bonding or other reinforcement processes.

The processing of melt-blown non-woven fabrics also adopts the method of melt spinning, that is, extruding a thin flow of melt from a spinneret hole to form fibers. However, the difference from the spunbond method is that the spinneret used in the melt blown method has specially designed air ducts (air slots) on both sides of the spinneret holes, and the heated high-pressure air is blown out from the air ducts to affect the melt. The fine stream is stretched at high speed to be blown into ultra-fine short fibers. After being cooled by the cold air below the spinneret head, the ultra-fine short fibers are sprayed at a high speed to a fiber collection device with negative pressure, mainly a condensing screen or a web forming drum, to form a web. Finally, the shaped non-woven fabric is obtained after being fixed by self-bonding or thermal bonding.

This method can be made into thin sheets or thicker felt-like materials. The melt-blown non-woven fabric is formed by ultra-short fibers, the production line speed is low, the process is short, but it is more complicated. Melt-blown non-woven products have large

specific surface area, high bulkiness, small transition resistance, high filtration efficiency,

good surface coverage and shielding performance, but low strength, poor dimensional stability, poor wear resistance, and large gas consumption during processing , high energy consumption.

Although the production process of meltblown nonwovens is shorter than that of spunbond, its process is more complicated and there are many influencing factors:

1. Melt spinning

In the melt-blown spinning process, the spinning fibers are fine, the processing volume is large, and the drafting speed is fast, so there are high requirements for the melt that is extruded and spun. In order to respond to the higher requirements of product quality, it is required to have stable extrusion melt pressure, uniform melt flow and complete plasticization of raw materials. In order to avoid excessive impurities in the melt from clogging the spinneret and affecting the continuity of the spinneret, the melt must pass through a filter device before entering the melt blown die.

2. Injection stretching

During the production process, the heated high-pressure air is blown out at a high speed from the drawing air duct, and the melt stream extruded from the spinneret hole is stretched at a high speed to be ejected into ultra-fine short fibers. Therefore, the speed and temperature of the airflow have a great influence on the forming and stretching of the melt-blown staple fiber. The higher the velocity of the drawing airflow, the finer the diameter of the short fibers blown out, but too high a velocity will affect the collection of fibers. The temperature of the stretching hot air should not be too low to keep the melt in a viscous state.

3. Web forming

The ultra-fine short fibers obtained by blowing and stretching with hot air are blown to the collecting device such as the condensing screen or the roller with mesh after being blown and cooled, and the lower part of the condensing screen or the inside of the porous roller is sucked by vacuum. The device forms a negative pressure, and the fibers are collected on a condensation screen or a perforated roller, and are formed by self-bonding or heating. The vertical distance from the nozzle outlet of the machine head to the surface of the condensing screen or the porous roller is called the receiving distance of the fiber web. The receiving distance of the fiber web has a great influence on the air permeability and strength of the nonwoven product, and it affects the draw ratio of short fibers and the laying range of fibers. The receiving distance of the fiber web is increased, the time for the blown short fibers to reach the surface of the collection device is prolonged, the number of fibers collected at the same position is reduced, and the fiber web structure is more fluffy, so the pore size and porosity of the nonwoven fabric become larger and breathable. The performance becomes better, the filtering effect is improved, and the hand feels fluffy, but the tensile strength and bursting strength of the nonwoven fabric are both decreased. The receiving distance is reduced, the fiber cooling effect is poor, the fibers are easy to bond, and become a crimped and agglomerated state, thus reducing the bulkiness of the fiber web. From the outside, according to the influence of the receiving distance on the fiber web structure, if the process of continuously changing the receiving distance is adopted in the fiber web forming process, non-woven fabrics with density gradients can be produced, which can be used for filter materials for graded filtration, etc.