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In the production of spunbonded nonwovens, various factors may affect the physical properties of the product. Analysis of the relationship between these factors and the properties of spunbond nonwovens helps to properly control the process conditions and obtain spunbond nonwoven products with good quality and wide applicability. Here, the main influencing factors of the physical properties of the spunbonded nonwoven fabric are simply analyzed and shared with everyone.
1. Melt index and molecular weight distribution of polypropylene chips
The main quality indicators of polypropylene chips are molecular weight, molecular weight distribution, isotacticity, melt index and ash content. The PP chips used for spinning have a molecular weight of between 100,000 and 250,000. However, it has been proved that the melt has a good rheological property when the molecular weight of the polypropylene is about 120,000, and the allowable large spinning speed is also high.
The melt index is a parameter that reflects the rheological properties of the melt. The melt index of the spunbonded polypropylene chips is usually between 10 and 50. In the process of spinning into a net, the yarn is only drawn once, and the draw ratio of the yarn is limited by the rheological properties of the melt. The larger the molecular weight, the smaller the melt index, the worse the rheology. The smaller the draw ratio obtained by the strip, the larger the fineness of the obtained strand under the same conditions of the melt discharge amount of the spinneret, and thus the spunbonded nonwoven fabric exhibits a hard hand.
If the melt index is large, the viscosity of the melt decreases, the rheology is good, and the drag resistance is reduced. Under the same drafting conditions, the draw ratio is increased. The degree of orientation of the macromolecule is increased, the breaking strength of the spunbonded nonwoven fabric is increased, and the fineness of the yarn is lowered, and the fabric is soft to the touch. In the case of the same process, the higher the melt index of polypropylene, the smaller the fineness and the greater the breaking strength.
The molecular weight distribution is usually measured by the ratio of the weight average molecular weight (Mw) of the polymer to the number average molecular weight (Mn) (Mw/Mn), and the molecular weight distribution value is called. The smaller the molecular weight distribution value, the more stable the rheological properties of the melt, the more stable the spinning process, the higher the spinning speed, the lower the melt elasticity and the extensional viscosity, and the lower the spinning stress. The PP is more easily stretched and thinned, and finer denier fibers can be obtained, and the uniformity of the web formation is better, and the hand feel and uniformity are good.
2, spinning temperature
The setting of the spinning temperature depends on the melt index of the raw material and the physical properties of the product. The higher the melt index of the raw material, the higher the spinning temperature, and vice versa. The spinning temperature is directly related to the melt viscosity and the temperature is low. The viscosity of the melt is high, the spinning is difficult to carry out, and it is easy to produce broken wire, stiff wire or thick wire group, which affects the quality of the product. Therefore, in order to lower the melt viscosity and increase the rheology of the melt, a method of increasing the temperature is generally employed.
The spinning temperature has a large influence on the structure and properties of the fiber. The lower the spinning temperature, the higher the elongational viscosity of the melt, the greater the tensile resistance, and the more difficult it is to stretch the strands. To obtain fibers of the same denier, the drafting gas flow rate is relatively high at low temperatures. Therefore, in the case where the other process conditions are the same, the fiber is difficult to draw when the spinning temperature is low.
The fiber has a large fineness and a low degree of molecular orientation. The spunbonded nonwoven fabric has a low breaking strength, a large elongation at break, and a hard hand feeling. When the spinning temperature is high, the fiber is preferably stretched. The fineness is small, the degree of molecular orientation is high, and the spunbonded nonwoven fabric exhibits high breaking strength, small elongation at break, and soft handfeel.
However, it is worth noting that under certain cooling conditions, if the spinning temperature is too high, the resulting filaments will not be cooled enough in a short period of time, and some fibers will break during the drawing process, which may cause defects. In actual production, the spinning temperature is preferably selected at 220-230 °C.
3, cooling molding conditions
In the molding process of the spunbonded nonwoven fabric, the cooling rate of the yarn has a great influence on the physical properties of the spunbonded nonwoven fabric. If the molten polypropylene is cooled rapidly and uniformly after exiting the spinneret, the crystallization rate is slow and the crystallinity is low, and the structure of the obtained fiber is an unstable disc-like liquid crystal structure, and the draw ratio which may be reached during drawing is Larger, the orientation of the molecular chain is better, the crystallinity can be further improved, the strength of the fiber is increased, and the elongation is lowered. The spunbonded nonwoven fabric has a large breaking strength and a low elongation; if it is slowly cooled The obtained fiber is a stable monoclinic crystal structure, which is disadvantageous to the drawing of the fiber, and exhibits a small breaking strength and a large elongation on the spunbonded nonwoven fabric.
Therefore, in the molding process, the breaking strength and the elongation of the spunbonded nonwoven fabric are generally increased by increasing the cooling air volume and lowering the temperature of the silk chamber. In addition, the cooling distance of the yarn is also closely related to its performance. In the production of spunbonded nonwoven fabric, the cooling distance is generally selected to be between 50 and 60 cm.
Dongyang Laichi Environmental Protection Technology Co., Ltd. is based on the concept of “Seiko Quality, Fine Service”. The main production and operation: spunbond non-woven fabric, elastic non-woven fabric, medical non-woven fabric, SSS non-woven fabric, SMS non-woven fabric, etc. , is a professional non-woven fabric manufacturer.
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