Cooling Inflation film

Blown Film A plastic film produced by extrusion blowing, wherein an extruded plastic tube is continuously inflated by internal air pressure, cooled, collapsed by rolls, and wound up. The thickness of the film is controlled by air pressure and rate of extrusion. 

Bubble cooling is generally accomplished by blowing a large volume of air on the film as it exits the die (Fig. 3.10). This may take place on only the outside of the bubble or on both the inside and the outside. Additionally, the bubble is kept inflated to remove more heat from the film as it travels up through ambient air in the cooling tower. 

In extrusion blow film process, molten PLA is extruded to form a tube with an annular die. By blowing air through the die head, the tube is inflated into a thin tubular bubble and cooled. The tube is then flattened in the nip rolls and taken up by the winder (Fig. 5.19). The ratio of bubble diameter to the die diameter is called the blow-up-ratio (BUR). BUR ratios of 2 1 -4 1 with the die temperature of 190 - 200 C have been used for extrusion blowing of PLA films. By varying the BUR, screw speed, air pressure, and winder speed, films of different thicknesses (10- 150 pm) and degree of orientation can be achieved [93,94]. Compared to... 

Blown film extrusion is the most common method to fabricate polyethylene film. The process involves extruding molten polyethylene through a circular die and then inflating the interior of the molten polyethylene as it exits the die to form a bubble. The die thickness is about 20-100 times thicker than the final film thickness, so that the molten polyethylene is stretched during the time that the molten polyethylene exits the die and before the time the molten polyethylene cools to a solid. Important aspects of this process are a uniform film thickness, the time it takes to cool the molten, amorphous polyethylene to a semicrystalline solid and the molecular structure of the polyethylene used to fabricate the film. During this cooling process the volume of the polyethylene shrinks as the solid material has a higher density than the molten polyethylene. 

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