The process that Dallas Plastics Corporation utilizes to extrude its films is called blown film. This extremely efficient and versatile form of extrusion is achieved by melting and pumping plastic resin through an annular die (Figure 1).

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The circular extrudate is then inflated to the desired size, formed and cooled by a ring of air that blows onto the molten polyethylene, hence the name 'blown' film. The inflated tube is then transported vertically by two nip rolls that pull the film upward through a collapsing A frame, squeezing the air out and resulting in a flat tube.

Once the flat tube passes through the upper nip rollers, a secondary set of nip rollers pulls the film downward through the tower (Figure 2) while it continues to cool.

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Finally, the flat tube is cut to the desired size and roll configuration and wound onto a paper core (Figure 3).

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Some of the advantages of blown film processing over
other forms of extrusion are (1) excellent size versatility,
(2) enhanced strength, shrink and barrier properties,
(3) inherently less waste, (4) ease of changeover, and
(5) natural tube shape readily forms into a bag, sleeve
or like configurations.