What is the most difficult problem with film extruder?

Many blown film machine operation technicians concluded that in the blown film process, the most puzzling and difficult problem to solve is the crystal spot.Crystal spots will bring certain difficulties to compounding and printing.

What is a Crystal spots? When transparent dots or irregularly shaped convex particles appear in the blown film product, this situation is called crystal spots.

How are crystal spots produced? The crystal spots is actually an excessive polymer. Generally speaking, it means that the local molecular weight is high, so the crystal point has a higher melting point. The melt has a high viscosity, does not uniformly disperse and mix when the film is blown, and solidifies before the surrounding polymer.

What are the reasons for the appearance of crystal spots?

1.Blown film machine equipment failure.

Such as heater damage or temperature controller failure and other problems, resulting in the barrel temperature is too low or too high. If the barrel temperature is low, the raw material can not be completely plasticised, on the contrary, if the barrel temperature is too high. The melting pressure is small, the shear force is small, which is not good for plasticising the plastic.

2.The problem of raw materials.

When the blown film machine uses new raw materials, which may contain impurities or do not meet the standard requirements.
When the blown film machine uses recycled materials, it may be the recycled material itself. In the recycling process, looking at the ordinary single raw material, there may be composite material. The melting point of different raw materials is not the same, there may be crystal points.
When the raw materials used in the blown film machine with filler masterbatch appear crystal dots, it may be caused by the mismatch between the melting value of the filler masterbatch and the raw materials. The mismatch of melting values will lead to poor plasticisation of the filler masterbatch and the raw material in the screw, thus affecting the fluidity.

3.The problem with the filter screen.

The filter mesh is too small, which cannot filter impurities effectively.
The number of layers of the filter screen is small, and the filtration effect is poor.
The deformation of screen plate will lead to decreased filtration effect.
Displacement of the screen plate will lead to unstable filtration effect.

4.Improper manipulation.Such as adding too much or too little raw material.

Find out the specific problem areas and then solve them accordingly.

1.Clean the film blowing machine equipment and check whether the heater and temperature controller are working normally. Adjust the parameters of film blowing machine.Such as temperature, pressure, etc., to adapt to different product needs.

2.Strictly control the quality of raw materials, make sure the raw materials are pure and free of impurities, and choose high quality raw materials.

3.Check the filter mesh.

Increasing the mesh number as well as the number of layers of the filter mesh can improve the filtering effect on impurities.
Regularly check the condition of the mesh plate. Replace defective mesh panels in time. Check the position of the mesh plate.

If there is any displacement problem, adjust and fix the mesh plate in time. Adjust and fix the mesh plate in time..

4.Operate the film blowing machine correctly, and control the amount of raw materials added, temperature and other parameters.

5.After cutting out the film with crystal spots, cut the crystal spots with a double-sided knife. After cutting it open, see what color his core is.

If it is white, it proves that the ingredients are not completely melted. The solution at this time is to see if there are holes in the filter.
If it’s a clear colour, that proves that the material is a crystalline mass formed by recrystallisation. Then you have to check if the film is particularly thin and the extrusion volume is particularly small. The material stays in the mould for too long. The solution for this kind of problem is usually to add PPA, or increase the extrusion volume.
The centre of the material has a yellowing or blackening phenomenon, which indicates that it is a paste. It is easy to appear this situation in frequent starting and stopping. The solution is also can add PPA, can also increase the extrusion amount, or clean up the equipment to solve.

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