How to control the tensile strength of woven bag flat yarn

  • Categories:Trade News
  • Time of issue:1566962940000

How to control the tensile strength of woven bag flat yarn

  • Categories:Trade News
  • Time of issue:2019-08-28 11:29

In the production process of woven bags, the relative breaking force of the flat yarn is one of the main links to control the strength of the woven bag. How to control the relative breaking force of the flat wire is mainly reflected in the ratio of the raw material ratio, the cooling forming of the diaphragm and the stretching of the flat yarn. Different equipments and environments may control different methods. According to the theory of plastic weaving, combined with the experience of the actual production process, briefly talk about how to control the strength of the flat wire.

First, the ratio of raw materials

The filler masterbatch is one of the main components of the raw material ratio, and the function is to improve the physical properties of the flat yarn and reduce the cost. As the filling amount of the filler masterbatch increases, the tensile strength of the flat yarn will gradually decrease. Because the main component of the filler masterbatch is calcium carbonate, there is no tensile force. After a small amount of filler masterbatch is added, it is dispersed in the gap of the polyolefin polymer chain, which has little effect on the tensile strength of the flat yarn. improve. When the addition amount exceeds 20%~25%, the filler masterbatch occupies the position of the polymer chain to hinder the elastic deformation of the polymer, so that the polymer chain can not be fully stretched along the longitudinal external force, affecting the polymer chain. The tensile orientation effect, the strength of the flat yarn, and the stiffness are all significantly reduced. The relative breaking force of the flat yarn is less than 0.32 N/tex, which cannot meet the requirements of the national standard GB/T8946. In the actual production process, the amount of the filler masterbatch is more suitable in the range of 8% to 12%.

Second, the cooling formation of the diaphragm

The water tank is an integral part of the wire drawing machine. The temperature of the cooling water in the water tank affects the physical properties of the film after cooling and forming, and is also the main factor affecting the strength of the flat wire. This is because polypropylene is a crystalline polymer material and has various crystal forms. In the natural cooling process, relatively large α-type spherulites are formed, which is difficult to stretch and is not conducive to drawing. In the case of quenching in a water tank, a twin structure is easily formed, and the arrangement of the twin crystal molecular chains is poor, and the structure is loose, so that the orientation is easy to be stretched.

From the perspective of crystallinity, when the water temperature is too low, the twin crystal molecular chains have not been arranged in time to form a crystal array, and the mobility is lost, and the crystallinity is lowered. When slowly cooled, the crystallinity increases. The tensile strength greatly increases as the crystallinity increases. This is because the greater the degree of crystallinity, the greater the force is required to destroy the dense crystalline structure, and the intragranular slip is more difficult than the amorphous crystalline structure. However, quenching can cause the crystallization rate to be too fast and delicate. If the water temperature is too high, the cooling is slow, the crystal nucleus grows too much, and the tensile strength will decrease. In the actual production process, the following two phenomena are often encountered: the cooling water temperature is too low, the film is brittle, and cracks are easily generated. The breaking rate is high, the diaphragm is hard, and the yarn is easily broken when the wrinkles are creased; when the cooling water temperature is high, the film effluent is soft and easy to flatten. If the cooling water temperature continues to rise, the crystal grows too large, and the slub wire tends to appear after stretching. Considering comprehensively, the cooling water temperature is preferably between 40 ° C and 60 ° C. In the long-term production process of our factory, the thickness of the flat wire ranges from 0.035mm to 0.065mm, and the temperature of the cooling water is set at about 40 °C. In the process of processing an outlet woven bag having a thickness of 0.029 mm, a fineness of 70 tex and a width of 2.78 mm, the use of a new polypropylene material to produce a flat yarn is difficult to process due to a low thickness requirement. When the initial cooling water is 40 ° C, the strength of the cooled flat yarn is low, and some broken filaments appear during stretching. When the temperature of the cooling water rises to 55 ° C, the strength of the flat yarn is improved, and the problem of broken yarn is solved, and weaving is solved. The strength of the sacking fabric has been enhanced.

Third, the tension of the flat wire

In the production process, the drawing of the flat wire is to heat the flattened wire to a temperature above the glass transition temperature and below the softening point, so that the polymer molecular chains are arranged in an orderly manner along the stretching direction. The attraction between the molecular chains increases, increasing the relative pull-off force of the flat yarn. Therefore, an effective way to control the relative breaking force of the flat wire is to set a suitable stretching factor. The greater the draw ratio, the higher the relative pull-off force of the flat yarn. The magnitude of the draw ratio of the flat yarn is determined by the relative pull-off force and elongation at break of the flat yarn. When the draw ratio is 5 times, the relative pull-off force of the flat yarn is about 0.32 N/tex, and the general manufacturer sets the draw ratio to 4 to 7 times. Our factory produces flat wire of container bag. Its process index thickness is 0.1mm and line density is 150tex. As a special requirement for flat woven bag, the tensile strength of the base cloth of the container bag is 1470N/50mm. The draw ratio was set to 7 times, and after the flat yarn was tested, the relative pull-off force was 0.48 N/tex (elongation at break 21%), and the tensile strength of the base bag of the package was 1920 N/50 rpan, which was much larger than the national standard. The specified value fully guarantees the safety of container bag filling.

The draw ratio in the actual production is constant, and the relative tensile force and elongation at break are controlled by adjusting the stretching temperature of the flat yarn. In the case where the stretching ratio and the stretching rate are constant, the lower the stretching temperature, the better the degree of orientation. The tensile strength after orientation decreases as the temperature rises, but the extent of the decrease is not large. When the stretching temperature is increased, although the tensile strength is lowered, the elongation at break is increased more rapidly. When the stretching temperature is lowered, the tensile strength increases rapidly, but the elongation at break decreases more.

The above three aspects are the problems often encountered in the actual production process. The tensile strength of the control flat yarn may vary with different environments and different equipments, and specific analysis of specific problems is needed to find an effective solution to the problem. .

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