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characteristic property to the final film, such as
stiffness, heat-sealability, impermeability or
1
resistance to some environment, all of which
properties would be impossible to attain with any
2 single material. This technology is used on any of the
3
processes as blown film, overjacketing, tubing and
sheets extrusions.

CAST FILM EXTRUSION: The cast film process
differs from the blown film process through the fast
quench and virtual unidirectional orientation capabilities. These characteristics allow
a cast film line to operate at higher production rates while producing amazing optics.
Polymer melt is extruded through a flat die. Immediately after exiting the die, the
molten curtain is passed onto rotating water cooled chill roll or into water quench tank
to “freeze” the film. The speed of the roller controls the draw ratio and final film
thickness which then is passed downstream where the edges are trimmed, corona
treatment is applied (if a fabrication process such as printing or coating is required)
and the film is wound into rolls. Cast film is usually made in a thickness range of 20 to
200 microns, and is used in applications with good optical properties such as gloss,
transparency, surface smoothness, good tear resistance with toughness and
flexibility.
DRY SPINNING: is used to form polymeric fibers from solution. The polymer is
dissolved in a volatile solvent and the solution is pumped through a spinneret (die)
with numerous holes (one to thousands). As the fibers exit the spinneret, air is used
to evaporate the solvent so that the fibers solidify and can be collected on a take-up
wheel. Stretching of the fibers provides for orientation of the polymer chains along
the fiber axis. Cellulose acetate (acetone solvent) is an example of a polymer which
is dry spun commercially in large volumes. Due to safety and environmental
concerns associated with solvent handling this technique is used only for polymers
which cannot be Melt spun. (Fig.A)

rotating
mandrel
head

resin
bath

guides
A B C fiber tows

MELT SPINNING: is the preferred method of manufacture for polymeric fibers. The
polymer is melted and pumped through a spinneret (die) with numerous holes (one
to thousands). The molten fibers are cooled, solidified, and collected on a take-up
wheel. Stretching of the fibers in both the molten and solid states provides for
orientation of the polymer chains along the fiber axis. Polymers such as PET and
nylon 6,6 are melt spun in high volumes. (Fig.B)

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