single film. The first step is to melt the polymer in an extruder. Polymer resin,
often in the form of beads, is loaded into a hopper, then fed into a heated barrel
which employs a screw to transport the polymer down its length. The beads are
gradually heated to melt the polymer. The heat profile is an important aspect of
extrusion, because the polymer may thermally degrade if overheated. When the
molten material reaches the end of the barrel it is extruded through a die. It is at
this point that blown film extrusion differs from other extrusion processes.
Several different types of dies are used in blown film extrusion, with the most
common being annular (a simple circle die). The molten polymer enters the die
head and air is injected via a hole in the die center to radially inflate the polymer
into a thin tube many times its original, extruded diameter. It is this step that can
be adjusted to achieve the desired film thickness and width.
The hot tube film is then cooled, typically with high speed air, and pulled up by
an apparatus known as nip rollers. On most medium to large size film lines, this
vertical tube might easily extend several stories into the air. As the film cools it
crystallizes at what is called the frost line. As the tube reaches the top of the line,
the film is cool enough to flatten, and is now referred to as lay-flat or collapsed
tubing. The film is then transported downstream by rollers for further processing
(e.g. slit, printed, vented, converted into bags) and is eventually wound into rolls.
There are several advantages to manufacturing film by the blown film extrusion
process, including the ability to manipulate the mechanical properties of the final
plastic based on the process conditions and base polymer(s) used. For example, it
inflates the polymer radially while at the same time drawing the polymer upward
using rollers. As these forces stretch the polymer in both the transverse and draw
directions, they give strength to the film. The extent of inflating and drawing can
be adjusted to attain the desired strength in the transverse and draw directions of
the final product. Blown film extrusion is also versatile and able to manufacture a
variety of single or multi-layer films with a range of film thicknesses and widths.
For a 34 minute video of the Lab Tech Blown Film complete process, go to:
https://youtu.be/FHfaVNk2Gyg
You will appreciate that it took a bit of genius just to design the factory to support
the process.
3.1.7 Film Technology and Tests
The introduction of StratoFilm in 1965 overcame a number of materials problems
that had plagued the balloon community prior to that time. As payloads and float
altitudes increased over the years, the balloons became much larger. It was found
that as a balloon penetrated high into the tropopause and the temperature dropped
as low as –57°C (–70°F) the balloon film became brittle and lost its strength. The
confidence of the scientific community was eroded by catastrophic failures in the
late 1970’s and early 1980’s.
36 Balloon Elements
often in the form of beads, is loaded into a hopper, then fed into a heated barrel
which employs a screw to transport the polymer down its length. The beads are
gradually heated to melt the polymer. The heat profile is an important aspect of
extrusion, because the polymer may thermally degrade if overheated. When the
molten material reaches the end of the barrel it is extruded through a die. It is at
this point that blown film extrusion differs from other extrusion processes.
Several different types of dies are used in blown film extrusion, with the most
common being annular (a simple circle die). The molten polymer enters the die
head and air is injected via a hole in the die center to radially inflate the polymer
into a thin tube many times its original, extruded diameter. It is this step that can
be adjusted to achieve the desired film thickness and width.
The hot tube film is then cooled, typically with high speed air, and pulled up by
an apparatus known as nip rollers. On most medium to large size film lines, this
vertical tube might easily extend several stories into the air. As the film cools it
crystallizes at what is called the frost line. As the tube reaches the top of the line,
the film is cool enough to flatten, and is now referred to as lay-flat or collapsed
tubing. The film is then transported downstream by rollers for further processing
(e.g. slit, printed, vented, converted into bags) and is eventually wound into rolls.
There are several advantages to manufacturing film by the blown film extrusion
process, including the ability to manipulate the mechanical properties of the final
plastic based on the process conditions and base polymer(s) used. For example, it
inflates the polymer radially while at the same time drawing the polymer upward
using rollers. As these forces stretch the polymer in both the transverse and draw
directions, they give strength to the film. The extent of inflating and drawing can
be adjusted to attain the desired strength in the transverse and draw directions of
the final product. Blown film extrusion is also versatile and able to manufacture a
variety of single or multi-layer films with a range of film thicknesses and widths.
For a 34 minute video of the Lab Tech Blown Film complete process, go to:
https://youtu.be/FHfaVNk2Gyg
You will appreciate that it took a bit of genius just to design the factory to support
the process.
3.1.7 Film Technology and Tests
The introduction of StratoFilm in 1965 overcame a number of materials problems
that had plagued the balloon community prior to that time. As payloads and float
altitudes increased over the years, the balloons became much larger. It was found
that as a balloon penetrated high into the tropopause and the temperature dropped
as low as –57°C (–70°F) the balloon film became brittle and lost its strength. The
confidence of the scientific community was eroded by catastrophic failures in the
late 1970’s and early 1980’s.
36 Balloon Elements