Causes of extrusion failure of propylene packing belt and Countermeasures
Causes of extrusion failure of propylene packing belt and CountermeasuresPacking belt deflection
(1) Creep of polymer materials is the main cause of deflection. There are many reasons for the deviation of packing belt, but
In principle, it is a creep phenomenon of polymer materials. When the packing belt is reeled in, due to a transverse reeling stress
At a certain temperature, the molecular chain of polypropylene will gradually undergo conformational displacement and molecular chain reorientation due to the constant action
The friction between the molecular chains prevents the deformation from being completed instantaneously. Therefore, the deformation of the molecule or material increases gradually with time
To form a stable structure, so that the packing belt deformation, deflection. Therefore, we should try to change the coalescence of polymers
The orientation degree of the molecular chain and the creep resistance of the packing belt are improved.
(2) Improper amount of filler. Adding a proper amount of filler will not only reduce the production cost, but also improve the rigidity of packing belt
Improve creep resistance. In general, when the amount of packing is increased, the skewness of packing belt will decrease, but excessive packing will
It affects normal production and destroys the physical and mechanical properties of packing belt. In actual production, it should be based on the properties of polypropylene materials
Yes, it is better to add 8% - 12% (mass percentage) filler. If random polypropylene is used as filler, the lower limit should be taken.
(3) Improper control of tensile ratio. The drawing ratio is the most critical process parameter in the production process of packing belt. Increasing the drawing ratio can make
The degree of skewness is greatly reduced, because when the tensile ratio increases, the tensile force on the polymer chain increases, and the molecular chain will be neat and tight
They are arranged together so as to improve the orientation of the polymer chain and the creep resistance of the polymer material, reduce the high elastic deformation and
Plastic shape variable. However, it is impossible to increase the tensile ratio infinitely. Due to the influence of raw material properties, the tensile ratio will be too large
It brings difficulties to forming. Generally, the tensile ratio is 1:9.
The temperature control of packing belt deflection (4) is improper. The stretching of polypropylene packing belt is carried out in a hot oven or hot water tank, generally
The tensile temperature should be controlled above the glass transition temperature and below the viscous flow or melting point temperature. When the tensile temperature increases, the skewness also increases
Increase, otherwise, decrease. Therefore, when other process conditions are determined, the lower the drawing temperature is, the greater the effect of drawing orientation is, and the molecular
The orientation degree of the chain increases, which improves the creep resistance of the packing belt and reduces the skewness. However, the drawing temperature in actual production
The degree cannot be too low. Otherwise, it will make it difficult to stretch, affect the increase of stretching ratio and stretching speed, and make the orientation degree of molecular chain ght: 150% "> unable to effectively reduce the skewness. Generally, the tensile temperature is about 175 ℃. If the filler content in the raw material is high, it can be slightly increased
High tensile temperature.
(5) Improper post-treatment (heat treatment) process control. The post-treatment process is an important means to reduce the deformation of polymer materials, which is advantageous
In order to maintain the dimensional stability and straightness of the packing belt and reduce the skewness. Generally, the aftertreatment temperature is 120 ℃, and the traction of aftertreatment is
The speed is 10% less than the drawing speed.
(6) Other factors lead to deviation of packing belt. To ensure that the die size and blank size are uniform can avoid uneven thickness. Under pressure
In the flower process, the gap between the embossing rollers shall be even. In the winding process, the tightness shall be moderate. If the reels are too loose, the reels are scattered; if
If the winding is too tight and the stress is too large, the belt will creep and increase the inclination
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