How does the blown film process of the bubble film machine (air cushion film machine) operate?
The bubble film machine (air cushion film machine) has a very important process, that is, blown film. This article Wenzhou Hongxin Machinery Co., Ltd. explains how the blown film process of the bubble film machine (air cushion film machine) is operated. In the film blowing process, low density polyethylene (LDPE) is in a molten state when extruded from a die, and the transparency is good. After leaving the die, the inflated zone of the bubble is cooled by the cooling air ring. When the cooling air is blown at a certain angle and speed to the plastic bubble just extruded from the handpiece, the high temperature bubble and cooling air Upon contact, the heat of the bubble is carried away by the cold air, and its temperature drops significantly below the viscous temperature of the low-density polyethylene (LDPE), causing it to cool and solidify and become blurred. On the blown bubble we can see a dividing line between transparency and blur, which is the dew point (or frost line). During the blown film blowing process, the height of the dew point has a certain influence on the film properties. If the dew point is high and is located above the inflated bubble, the inflation of the film is carried out in a liquid state, and the inflation only thins the film, and the molecules are not subjected to the stretching orientation, and the performance of the inflation film is close to Cast film. Conversely, if the dew point is relatively low, the inflation is carried out in the solid state. At this time, the plastic is in a high elastic state, and the inflation is like the transverse stretching, causing the molecules to be oriented, so that the performance of the inflation film is close to Oriented film. Extruder temperature: When blowing low density polyethylene (LDPE) film, the extrusion temperature is generally controlled between 160 ° C ~ 170 ° C, and the temperature of the head must be uniform, the extrusion temperature is too high, the resin is easy to decompose, and The film is brittle, especially the longitudinal tensile strength is significantly decreased; if the temperature is too low, the resin is poorly plasticized, and the expansion and stretching cannot be performed smoothly, the tensile strength of the film is low, and the gloss and transparency of the surface are poor, and even appear Patterns like wood rings and unmelted crystal nuclei (fish eyes). Blowing ratio: The inflation ratio is one of the control points of the blown film production process, and refers to the ratio between the diameter of the bubble after inflation and the diameter of the uninflated tube. The inflation ratio is the transverse expansion factor of the film. In fact, the film is stretched transversely. The stretching exerts a certain degree of orientation on the plastic molecules, and the inflation ratio is increased, so that the transverse strength of the film is improved. However, the inflation ratio should not be too large, otherwise the bubble is unstable and the film is prone to wrinkles. Therefore, the inflation ratio should be properly matched with the traction ratio. Generally, the inflation ratio of the low density polyethylene (LDPE) film should be controlled to 2.5 to 3.0. Traction ratio: The traction ratio refers to the ratio between the pulling speed of the film and the extrusion speed of the tube. The draw ratio is a longitudinal draw ratio that imparts an orientation in the direction of the draw. When the traction ratio is increased, the longitudinal strength is also increased, and the thickness of the film is thinned. However, if the pulling ratio is too large, the thickness of the film is difficult to control, and even the film may be broken, causing a film breakage. The traction ratio of low density polyethylene (LDPE) film is generally controlled between 4 and 6. Dew point: Dew point, also known as frost line, refers to the boundary line between plastic and viscous fluid into a high elastic state.
The above is the knowledge point that Hongxin as a professional manufacturer of bubble film machine (air cushion film machine) to introduce to you, for customers' reference.