How is the blowing process of bubble wrap machine operated?

How is the blowing process of bubble wrap machine operated?

 

How is the blowing process of bubble wrap machine operated?

 

The bubble film machine has a very important process, which is blown film. This article explains how the blown film process of the bubble film machine is operated.

 

During the blown film process, low-density polyethylene (LDPE) is in a molten state and has good transparency when extruded from the mold. After leaving the mold, the expansion zone of the film bubble needs to be cooled by a cooling air ring. When the cooling air is blown at a certain angle and speed towards the plastic film bubble just extruded from the machine head, the high-temperature film bubble comes into contact with the cooling air, and the heat of the film bubble will be carried away by the cooling air. Its temperature will significantly drop below the viscous flow temperature of low-density polyethylene (LDPE), causing it to cool, solidify and become blurry. On the blown film bubble, we can see a boundary between transparency and blurring, which is the dew point (or frost line).

 

The dew point has a certain impact on the film performance during the film blowing process of the film blowing machine. If the dew point is high and located above the inflated film bubble, the film is inflated in liquid state, and inflation only thins the film without stretching the molecules. At this point, the performance of the inflated film is close to that of a cast film. On the contrary, 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 transverse stretching, causing molecules to undergo orientation, thereby making the performance of the inflated film close to that of the oriented film.

 

Extruder temperature: When blowing low-density polyethylene (LDPE) film, the extrusion temperature is generally controlled between 160 ℃ and 170 ℃, and it is necessary to ensure uniform head temperature. If the extrusion temperature is too high, the resin is prone to decomposition, and the film becomes brittle, especially causing a significant decrease in longitudinal tensile strength; If the temperature is too low, the resin plasticization will be poor, and it will not be able to expand and stretch smoothly. The tensile strength of the film will be low, and the surface gloss and transparency will be poor, even resulting in patterns like wood rings and unmelted crystal nuclei (fish eyes).

 

Inflation ratio: Inflation ratio is one of the key control points in the production process of blown film, which refers to the ratio between the diameter of the film bubble after inflation and the diameter of the tube ring without inflation. The inflation ratio is the transverse expansion multiple of the film, which is actually a transverse stretching of the film. Stretching will have a certain degree of orientation effect on plastic molecules, increasing the inflation ratio and thus improving the transverse strength of the film. However, the inflation ratio should not be too high, otherwise it may cause instability of the film bubbles and the film is prone to wrinkling. Therefore, the inflation ratio should be appropriately matched with the traction ratio. Generally speaking, the inflation ratio of low-density polyethylene (LDPE) film should be controlled between 2.5 and 3.0.

 

Traction ratio: Traction ratio refers to the ratio between the traction speed of the film and the extrusion speed of the pipe ring. Traction ratio is the longitudinal stretching ratio that gives the film a directional effect in the pulling direction. As the traction ratio increases, the longitudinal strength will also increase, and the thickness of the film will become thinner. However, if the traction ratio is too large, the thickness of the film is difficult to control and may even break the film, causing the phenomenon of film breakage. The traction ratio of low-density polyethylene (LDPE) film is generally controlled between 4-6.