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Introduction of Blow Molding Process of Low Density Polyethylene Film

Author:yltpacking    Time:17/05/27    Click:

Most thermoplastic bags can be blown to produce blown film, blown film principle is to squeeze the plastic thin tube, and then hot with compressed air to plastic inflation, and then after cooling and stereotypes obtained from the cylindrical Thin film roll products, this thin
The performance of the film is between the oriented film and the cast film, the strength is better than the cast film, the heat sealing property is worse than the cast film. There are many varieties of film produced by blow molding, polypropylene (pp), such as low density polyethylene (ldpe), high density polyethylene (hdpe), ethylene
Acid ethylene copolymer (eva), nylon (pa), etc., here we are commonly used low-density polyethylene (ldpe) film blow molding process for a brief introduction.

In the polyethylene blown film production process, mainly to do the following several process parameters control:
1. Extruder temperature
Blowing low-density polyethylene (ldpe) film, the extrusion temperature is generally controlled between 160 ℃ ~ 170 ℃, and must ensure that the head temperature uniformity, extrusion temperature is too high, the resin is easy to break down, and the film brittle, especially So that the longitudinal tensile strength significantly
The temperature of the film is too low, the resin is poorly plasticized, can not be smoothly expanded and stretched, the tensile strength of the film is low, and the surface gloss and transparency is poor, even appear like wood-like pattern and unmelted Of the crystal point (fish eyes).
2. Blowout ratio
Blowing ratio is one of the key points in the control of the blown film production process, which is the ratio between the diameter of the bubble after inflation and the diameter of the unburned tube ring. Blowing ratio is the transverse expansion of the film, in fact, the film is stretched laterally, stretching will
The plastic molecules to produce a certain degree of orientation, the expansion ratio increases, so that the lateral strength of the film increased. However, the inflation ratio can not be too large, or likely to cause instability of the bubble, and the film prone to wrinkles. Therefore, the inflation ratio should be
With the traction ratio with the appropriate job, in general, low-density polyethylene (ldpe) film inflation ratio should be controlled in the 2.5 ~ 3.0 is better than the range.
Traction ratio
The traction ratio refers to the ratio between the traction speed of the film and the extrusion speed of the tube. The traction ratio is the longitudinal stretching ratio, so that the film has a directional effect in the direction of extraction. Traction ratio increases, the longitudinal strength will be increased, and the thickness of the film
Degree of thinning, but if the traction ratio is too large, the thickness of the film is difficult to control, and even may be broken film, resulting in film phenomenon. Low-density polyethylene (ldpe) film traction ratio is generally controlled between 4 to 6 for a better range.
4. dew point
Dew point, also known as frost line, refers to the plastic from the sticky state into the high elastic state of the dividing line. In the blown film process, low density polyethylene (ldpe) in the extrusion from the die when the molten state, good transparency. When leaving the die, go through the cooling air ring
The bubble area of ​​the bubble is cooled and the cooling air is blown at a certain angle and speed to the plastic film bubble extruded from the head. When the high temperature bubble is in contact with the cooling air, the heat of the bubble is cooled by the cold air Go, the temperature will drop significantly to low density
The viscosity of the polyethylene (ldpe) is below, so that it is cooled and solidified and becomes blurred. In the blown film bubble we can see a transparent and fuzzy between the dividing line, which is dew point (referred to as the cream line).
In the blown film process, the level of dew point on the film performance have a certain impact. If the dew point is high above the bubble above the bulging, the inflation of the film is carried out in the liquid state, the inflation only thins the film and the molecules are not subjected to tensile orientation
, When the blown film performance close to the cast film.
On the contrary, if the dew point is relatively low, the inflation is carried out in the solid state, when the plastic is in a high elastic state, the inflation as the lateral stretching, so that the role of molecular orientation, so that the performance of inflation film close to Oriented film.

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