Non-woven fabrics' knowledge

Melt-blowing (melt-blowing) is to blow the melt extruded by the screw with a high-speed and high-temperature airflow, so that the thin stream of the melt is stretched at a higher magnification to form ultra-fine short fibers, and then piled on the condensation screen or into the on the net drum, a continuous short fiber net is formed, and then a non-woven fabric is made by self-adhesive or other reinforcement processes.

Melt blown in nonwoven fabric

The processing of meltblown non-woven fabrics also uses the melt spinning method, that is, extruding the melt streamlined fibers from the spinneret holes. But the difference from the spunbond method is that the spinneret head used in the melt blown method has specially designed air ducts (air slits) on both sides of the spinneret hole. The thin stream is stretched at a high speed to be blown into ultra-fine short fibers. After the ultra-fine short fibers are cooled by the cold air blowing under the spinneret, they are sprayed at a high rate to a fiber collection device with negative pressure, mainly a net curtain or a net-forming drum, to form a fiber web. Finally, the molded non-woven fabric is obtained by adding a fixed type through methods such as self-adhesive or thermal bonding. 

This method can be made into thin sheets or thicker felt-like materials. Meltblown non-woven fabrics are formed from ultra-short fine fibers, with low production line speed and short process flow, but they are more complicated. Meltblown non-woven products have large specific surface, high bulkiness, low transition resistance, high filtration efficiency, good surface coverage and shielding performance, but low strength, poor dimensional stability, poor wear resistance, and large air consumption during processing , High energy consumption.

Although the production process of meltblown non-woven fabrics is shorter than that of spunbond, the process is more complicated and has many influencing factors:

1. Melt spinning

In the process of meltblown spinning, the spinning fiber is thin, the processing volume is large, and the drafting speed is fast, so it has higher requirements for the melt of the extrusion spinning. In order to meet the higher requirements of product quality, it is required that the extrusion melt pressure is stable, the melt stream is uniform, and the raw materials are completely plasticized. 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 filtering device before entering the meltblowing die.

2. Blowing and stretching

During the production process, the heated high-pressure air is blown out at a high speed from the stretching air duct, and the thin stream of melt extruded from the spinneret is stretched at a high speed to be ejected into ultra-fine short fibers. Therefore, the stretching The speed and temperature of the airflow have a greater impact on the forming and drawing of meltblown staple fibers. The higher the drawing airflow velocity, 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, and it should be able to keep the melt in a viscous flow state.

3. Fabric forming

The ultra-fine short fibers obtained by hot air blowing and stretching are blown and cooled, and then blown onto a collecting device such as a net curtain or a roller with mesh. The lower part of the net curtain or the inside of the porous roller is sucked by vacuum The device forms a negative pressure, and the fibers are collected on a condensed mesh curtain or a porous roller, relying on self-bonding or heating to form a type. The vertical distance from the outlet of the spinneret of the machine head to the surface of the condensation curtain or porous roller is called the receiving distance of the fiber web. Affect the draw ratio of short fibers and the laying range of fibers. The receiving distance of the fiber web increases, the time for the sprayed 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 network structure is more fluffy, so the pore size and porosity of the nonwoven fabric become larger, and it is breathable. The performance becomes better, the filtering effect is improved, and the hand feels fluffy, but the tensile strength and bursting strength of the non-woven fabric are reduced. The receiving distance is reduced, the cooling effect of the fibers is poor, the fibers are easy to bond, and become a crimped agglomeration state, thus reducing the bulkiness of the fiber web. Externally, according to the influence of the receiving distance on the structure of the fiber web, if the process of continuously changing the receiving distance is adopted during the forming of the web, a non-woven fabric with a density gradient can be produced, which can be used as a filter element material for graded filtration.