Note: Descriptions are shown in the official language in which they were submitted.
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MODULAR DISK COEXTRUSION DIE
FIELD OF INVENTION
The present invention relates to an annular die for extruding thermoplastic
materials. More particularly, the present invention relates to a modular
assembly including
a plurality of thin disks.
BACKGROUND OF THE INVENTION
Annular dies are used to form laminated products from thermoplastic melts
(hereinafter "melt"). Conventional annular dies consist of a monolithic
structure containing
a core mandrel that may contain a spiral groove and axially stacked annular
cylinders that
concentrically surround the mandrel. Gaps between the mandrel and the
innermost cylinder
as well as gaps between the innermost cylinder and the next cylinder radially
adjacent to it
form passages for melt flow. Thus, an increase in the number of melt passages
in a
conventional die requires an increase in the radial thickness of the die
structure. Melt can
be supplied to the die both axially and radially through multiple entry
openings. Each melt
stream then flows axially through the die along the passages, and eventually
joins into layers
where these passages join within the die, and then finally the melt exits the
die at the die lip
and is blown into film. The spiral groove that can be provided on the outer
surface of the
mandrel can assist in controlling both the direction and rate of melt flow.
Several problems have been encountered with the conventional annular die
design including deterioration of plastic melt, difficulties in controlling
and adjusting
temperature of the melt, and inability to maintain uniform film thickness. For
example, melt
residues may remain in the passages formed by the gaps between the mandrel and
the
cylinders as well as those between cylinders. These residues may contaminate
fresh melt
flow and thus deteriorate the quality of films made from the die containing
such residues.
In addition, removing such residues is extremely labor intensive, particularly
because of the
small size of the passages and the difficulty of taking the die apart. Thus,
melt that stagnates
in the die passages shortens the useful life of the die. Furthermore,
conventional extruder
design dictates that each melt delivered to a die have a separate extruder,
thus multiple
extruders take up vast amounts of space and clutter work areas.
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In addition, it is difficult to produce a laminate product containing film
layers
made of different materials because the varied temperature requirements of
different
materials are difficult to meet. Multiple streams of melts are used to produce
a laminate
product, and each stream may require a different temperature depending on the
properties of
the melt material in the stream. For example, one melt may have a higher
melting point or
different thermal properties than another melt flowing within the die. Since
the annular
cylinders are concentrically arranged in the conventional die, it is difficult
to control the
temperature of the different melts axially flowing along the cylinders,
because temperature
is controlled by applying heat in a radial direction from the outer periphery
of the die. Since
the number of concentric cylinders surrounding the core is increased to form
mufti-layered
films, the peripheral heating system makes it difficult to apply the proper
heat to plastic melt
that is flowing along the inner cylinders of the die.
Furthermore, the axial height resulting from the monolithic die design may
produce inconsistent film thickness. Producing a laminate with an increased
number of
laminate layers using a conventional die not only requires more concentric
cylinders that
increases radial thickness but also increased axial height to join the melt
passages within the
die. Inconsistencies in the thickness of extruded film may result because
increased axial
height makes the die susceptible to thermal expansion, leading to inclining of
the die.
U.S. Patent 5,076,776 issued to Yamada et al. discloses an annular
coextrusion die for a lamination product. The die consists of stacked annular
plate-like rings
with one opening in the center of the ring. Each plate-like ring has a number
of manifolds
cut into it that spiral inward. In operation, melt flows through an entry flow
area adjacent
to the center opening in each plate-like ring. A gap exists between the
manifolds, and the
melt overflows this gap to the next manifold. The center opening of the plate-
Like rings form
a gap with the core mandrel creating an axial melt passage. The melt is
thereby directed
from the melt opening on the radial periphery of the plate-like ring through
the manifolds,
across the entry flow area into the melt passage and out through the die lip.
The die disclosed in Yamada et al. still requires labor-intensive die
manufacture to produce the spiral manifolds of various thickness. In addition,
the manifolds
that are cut into plate-like rings require that these rings have a tangible
thickness, which
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contributes to the overall axial height of the die. Furthermore, the melt
residue problem
associated with the conventional annular die remains an issue with this die
design.
SUMMARY OF THE INVENTION
The present invention is directed to an extrusion die along with its extrusion
system, including a coextrusion die. In one embodiment a die for coextruding
at least one
resin material to produce a plurality of laminate layers includes a modular
disk assembly of
a plurality of cells that include a plurality of thin annular disks stacked on
top of each other
(and thus axially adjacent to each other), wherein each of the annular disks
have an inner
radius and an outer radius. Each annular disk also includes a plurality of
radially disposed
openings between the inner and outer radii. Axial alignment of these openings
form resin
passages through the modular disk assembly such that all of the resin material
can be
coplanarly supplied from the inlet end of the modular disk assembly. In a
preferred
embodiment, melts are delivered to the die with a system that operates at a
fixed ratio of
screw speed and delivers multiple melt streams to the die through sets of
inlet openings
which are spaced at 90 ° around the die.
In a preferred embodiment, the die includes a modular disk assembly that
includes at least one cell of a plurality of axially adjacent thin annular
disks. Each cell
includes at least one first cap disk that includes a plurality of cap inlet
openings, at least one
distribution disk that includes a plurality of distribution inlet openings,
one of the distribution
inlet openings also being a selection inlet port, a continuous channel
connected to the
selection inlet opening, and a plurality of distribution outlet openings
terminating the
continuous channel cavity. Each cell further includes at least one second cap
disk including
at feast one flow regulation point aligned with at least one of the
distribution inlet openings,
and a plurality of cap outlet openings that are aligned with the distribution
outlet openings.
Each cell also includes at least one spacer disk that includes a plurality of
spacer inlet ports
that are aligned with distribution inlet ports, a flow region connected to a
plurality of flow
ports, that are aligned with the cap outlet openings. In one embodiment, the
die is an
outward flow die. In another embodiment, the die is an inward flow die.
In another preferred embodiment of the invention, a unitary component
comprising the at least one distribution disk, the at least one second cap
disk and the at least
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one spacer disk is machined from a single piece of material. Other permanent
connections
may permanently join similar groups of disks to form a similar unitary
component. Only the
at least one first cap disk is added to this unitary component to complete the
cell.
In a preferred embodiment of the invention, the entire modular assembly is
disposable and can be replaced quickly by a clean preassembled assembly that
is bolted,
glued or welded together. The low cost of the modular assembly allows complete
replacement modules, thereby saving downtime caused by cleaning difficulties.
In addition,
the minimal thickness of the disks in the module lends itself to producing a
multiple layer
product with a die that is much less massive than conventional dies. In
addition, a plurality
of commonly driven extruders is preferably used to deliver the melt material
to the modular
assembly. This extruder system design takes up less space than conventional
systems.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a cross-sectional view of a coextrusion device with three
extruders employing a die of the present invention.
FIG. 2 shows a top plan view of the assembly shown in FIG. I.
FIG. 3 shows an enlarged view of the designated portion A of FIG.1.
FIG. 4 shows a side-by-side line up of disks, including a first embodiment of
a distribution disk, in a seven-cell annular flow modular disk assembly in
accordance to the
present invention using three melt feeds.
FIG. 5 shows an exploded perspective view of aligned disks of the first cell
of the assembly shown in FIG. 4.
FIG. 6 shows a schematic representation of the annular exit melt flow within
the modular disk assembly shown FIG. 4.
FIG. 7 shows an inlet plate that can be connected to the assembly shown in
FIG. 4.
FIG. 8 shows a three-melt threaded attachment plate that is connected to the
inlet plate shown in FIG. 7.
FIG. 9 shows another embodiment of the distribution disk in accordance to
the present invention.
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FIG. I O shows a side-by-side line up of aligned disks in a two melt three-
cell
outward flow modular disk assembly in accordance to the present invention.
FIG. I 1 shows a partially assembled modular disk assembly of FIG. 10.
FIG. I2 shows an inlet plate that can be connected to the assembly shown in
FIG. 10.
FIG. I3 shows a three-melt threaded attachment plate that is connected to the
inlet plate shown in FIG. 12.
FIG. 14 shows a graph that illustrates the thickness of the laminate layers
extruded at various blow up ratios.
FIG. 15 shows a top view of a spiral overflow disk design that can be used
in one embodiment of the modular disk assembly.
FIG. 16 shows a top view of a composite of the disks shown in FIGS. 1 S and
FIG. 17.
FIG. I 7 shows a spiral overflow spacer that is used to define a spiral
overflow
region.
FIG. 18 shows a top view of a composite of the disks shown in FIGS. I S and
FIG. 19.
FIG. I9 shows a star-shaped overflow spacer that is used to define another
spiral overflow region.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention relates to a die including a plurality of thin disks
that can be used to extrude or coextrude resin materials. Although the
specification
specifically describes blown films, the die according to this invention may
also be used to
create a coextruded tube, such as a hose, a coextruded rod formed from
multiple continuous
layers of material to create a generally solid rod structure, or parison (a
generally elliptical
uninflated tube used in blow molding).
Referring now to FIGS. 1-2, the present invention may be used in a
coextrusion device 100 with a central extruder delivery system I02b and two
satellite
extruder delivery systems I02a, 102c and employing a die 200 of the present
invention.
Extruder delivery systems 102a, 102b, 102c are driven by a common drive.
Alternatively,
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these extruder delivery systems may be individually driven. The illustrated
three extruders
may have screw diameters of 0.75 inches, I .25 inches, and 0.75 inches
respectively, and may
operate at a fixed ratio of screw speed of I .116 to 1.0 to 1.116. As best
shown in FIG. 2, the
coextrusion device I00 forms a laminated product from three resin or melt
streams,
designated as streams a, b and c, so that extruder system 102a delivers resin
stream a,
extruder system 102b delivers resin stream b and extruder system 102c delivers
resin stream
c. Four sets of three inlet openings are spaced at 90° relative to the
adjacent sets.
As generally shown in FIG. 3 and described in more detail below, the die 200
includes an inlet plate 106, a threaded attachment plate 116 joining the
extruder extension
104 to the inlet plate 106, a disk module or modular disk assembly 202 with a
first end 208
and an opposite second end 209 and an outlet plate 118.
Die 200 also includes an inlet plate 106 that includes four die ports (not
shown) which are recessed along the axial thickness 153 of the inlet plate
106. Each die port
receives a threaded attachment plate116 disposed within each die port. An
extruder
extension 104 delivers the three resin streams a, b, c up to one inlet plate
106. As best shown
in FIG. 2, the illustrated die 200 contains four die ports and thus allow up
to twelve resin
streams to be delivered to the die 200.
As best shown in FIGS. 7-8, the inlet plate 106 directs melt streams a, b, c
through melt holes 107a, 107b, 107c to the threaded attachment plate 116.
Threaded plate
bolts 108 secure the inlet plate 106 with the threaded attachment plate 116.
Two pin holes
109 can be used to align the melt holes i07a, 107b, I07c to the extruder
extension I04. The
threaded attachment plate 116 attaches the melt streams to the modular disk
assembly 202
component of die 200 through inlet holes 117a, 117b, 117c in the inlet plate
106. Preferably,
the inlet plate 106 has an axial thickness I53 to essentially accommodate the
width 155 of
the threaded attachment plate 116. Also preferably, the inlet plate 106 has an
edge width 154
that accommodates the length 156 of the threaded attachment plate 116.
As best shown in FIG. 3, die 200 further includes the modular disk assembly
or disk module 202. The modular disk assembly 202 is an annular assembly
having an
overall inner radius 204 and an overall outer radius 206. The modular disk
assembly 202
surrounds a mandrel 114, which has a radius (not shown) that is smaller than
the overall
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inner radius 204 such that an annular resin passage 115 is formed between the
modular disk
assembly 202 and the mandrel I 14. As best shown in FIGS. 3, 7, the mandrel
114 is a
cylindrical rod with a hollow center 113. In addition, the mandrel includes a
mandrel stem
I24 and a mandrel tip I26. The die 200 further includes an outlet plate 118
with a disk end
119 that abuts the modular disk assembly 202 and an opposite exit end 117. The
mandrel
stem 124 extends through this outlet plate 118 such that it protrudes out on
the exit end 117.
The mandrel tip 126 is secured to the mandrel stem 124 adjacent to the exit
end 117 of the
outlet plate 118 such that a gap I2I is formed between the mandrel tip 126 and
the exit end
1 I7. Although the size of the mandrel 1 I4 is not crucial to the present
invention, the mandrel
tip 126 preferably has a radius of about one to five inches. The size of the
gap 121 may be
varied by using, for example a screw and lock nut design 123 on the mandrel
stem 124. As
best shown in FIGS. 2, 3, and 7, eight die bolts 1 I2 secure the inlet plate
106 with the outlet
plate 1 I8. The mandrel I I4 is held by the adjusting plate 140 and aligned
with four mandrel
bolts 141 that are pressed against the inlet plate 106. Each mandrel bolt 141
is received by
a mandrel bolt hole 142. Die bolt holes 150, which are spaced around the
outlet plate 118,
receive the die bolts I 12. Each die bolt hole permits free clearance of the
eight bolts I 12
holding the modular disk assembly. A thermocouple well 149 receives a
thermocouple for
measuring die temperature (not shown).
In operation, resin streams a, b, c are fed to the die 200 through extrusion
extension 104 and is directed to inlet plate 106, as best shown in FIG. 3. The
resin streams
are then directed to the modular disk assembly 202 via the threaded attachment
plate 1 I6 and
inlet plate 106. The melt streams a, b, c are thus fed in a coplanar fashion
to the modular
disk assembly and directed through the modular disk assembly 202 in the axial
direction 151
as well as the radial direction 152, depending upon the flow path provided by
the disk
components, described in greater detail below, that make up the modular disk
assembly 202.
The modular disk assembly 202 forms one or more layers of blown f lm I20 from
each melt
stream. As illustrated and described in greater detail below, the illustrated
modular disk
assembly 202 forms seven layers of blown film 120 from the three melt streams
a, b, c. In
general, the modular disk assembly 202 forms these layers by sequentially
selecting a melt
stream one or more times as the melt streams a, b, c travel in the axial
direction 151 through
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the modular disk assembly 202. Melt from a selected melt stream (not shown) is
then
directed to the annular resin passage 1 I5. Melts flowing in the annular resin
passage are
hereinafter referred to as exit melts 161. The pattern of seven exit melt
flows 161 from the
modular disk assembly 202 to the annular resin passage 115 is best shown in
FIG. 6. The
annular resin passage 115 directs the melt out of the modular disk assembly
202. The
annular exit die tube 300 directs the exit melt out of the die 200. Blown film
I20 is formed
as it exits die 200 and is cooled by air rings 122. The form of the blown film
120 is
maintained by air blown through the hollow center 113 of the mandrel 114. In
another
preferred embodiment of this invention, a tube or a rod may be formed from
multiple layers
of material directed out of the die 200.
The modular disk assembly 202 will now be described in greater detail. As
best shown in FIG. 4, the modular disk assembly 202 is made up of seven cells
2I0, 220,
230, 240, 250, 260, 270. Each cell produces one laminate layer. Each cell is
preferably
made up of four thin annular disks: a first cap disk 212, a distribution disk
214, a second cap
disk 216 and a spacer disk 218. Each disk has an axial thickness (not shown)
of preferably
less than one inch. These disks are stacked in the axial direction 151 of the
modular disk
assembly 202.
In another embodiment of the invention, a unitary component (not shown)
comprising the distribution disk 214, the second cap disk 216 and the spacer
disk 218 is
machined from a single piece of material. Only the first cap disk 212 is added
to this unitary
component to complete the cell.
As best shown in FIGS. 4-5, the first cap disk 2I2 can have 24 inlet openings
49 arranged in eight sets of three openings 50a, 50b, 50c. In the embodiment
shown, only
one set of three is used. Each set is disposed at an angle relative to the
adjacent sets. As
explained in greater detail below, resin streams are supplied to the die 200
through these sets
of cap disk inlet openings 50a, 50b, 50c that extend through the first cap
disk 212. Thus, the
illustrated design allows three, six, twelve, or even twenty-four resin
streams to be supplied
to die 200 depending on how many sets are used. In other embodiments (not
shown), each
set may contain fewer or more than three inlet openings, and each cap disk may
contain more
or less than eight sets. For example, a cap disk may contain two sets of six
inlet openings
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in rows of three so that up to 24 melt streams can be delivered to the die.
For illustration
purposes, the design of modular disk assembly 202 is shown to produce a seven-
layer
laminate product using three resin streams, designated as streams a, b and c.
Thus, for
. example, as used herein, inlet opening SOa is an inlet opening for resin
stream a, while inlet
opening SOb is an inlet opening for resin stream b and inlet opening SOc is an
inlet opening
for resin stream c. These stream designations also apply to openings in the
remaining
annular disks described below. Thus, the modular disk assembly 202 is shown
with all but
three of the inlet openings 49 being unused.
The distribution disk 214 is axially adjacent to the first cap disk 2I2. When
a first disk is "axially adjacent" to a second disk, it is meant that the
first disk is axially or
vertically closest to the second disk, as shown in FIG. 3. The distribution
disk 214 of the
first cell Z I O includes distribution inlet openings 52a, 52c, that extend
through the
distribution disk 2I4 and are axially aligned with the respective cap disk
inlet openings SOa,
SOc. Cap disk inlet opening SOb of the first cell 2I0 is axially aligned with
selection port
60b, that extends through the distribution disk 214. Selection port 60b is
connected to a
continuous channel 62 that also extends through the distribution disk 214.
This continuous
channel terminates at a plurality of distribution outlet openings 64x, 64y. By
the terms
"port" or "channel," it is meant that the described portion is an opening in
the disk such that
the portion penetrates or extends through the entire axial thickness of the
disk.
The illustrated distribution disk 214 in FIGS. 3-4 contains eight distribution
outlet openings 64x, 64y, that extend through the distribution disk 214. Each
opening 64x,
64y is disposed at an angle, for example, of 45°, relative to the
adjacent distribution outlet
openings. The axial alignment of the selection port with respect to the cap
inlet openings
SOa, SOb, SOc determines the resin stream from which a laminate layer is
formed by that
particular cell. Thus, for example, the distribution disk 214 of the first
cell 210 is aligned so
that a laminate layer is formed with resin stream b. Similarly, because
selection port 60a in
the third cell 230 is aligned with cap inlet opening SOa, third cell 230 is
aligned to form a
laminate layer from stream a. Therefore, the modular disk assembly 202 is made
up of cells
that form seven laminate layers from resin streams a, b and c in the following
order: b, b,
a, c, a, b, b. It should be understood that, as with the first cap disk 2I2,
the distribution disk
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214 can have four sets of distribution inlet openings, each disposed at
90° relative to the
adjacent sets. As best shown in FIG. 5, channel 62 may include a first split
channel 59, a
second split channel 61, a relief zone 63, and a third split channel 65.
Preferably, the split
channels symmetrically divide the melt selected by the selection port 60b
("selected melt")
(not shown). More particularly, each first split channel 59 preferably directs
about one-half
of the amount of the selected melt from the selection port 60b to its adjacent
two second split
channels 61. Similarly, each second split channel 61 directs one-half of the
amount of
selected melt from the first split channel 59 to its adjacent third split
channels 65. A relief
zone 63 is preferably provided to allow a momentary rest of the selected melt
flow before
it flows into the third split channels 65. As previously described, one of
eight distribution
outlet openings 64 terminates each end of the third split channels 65. The
split channels thus
preferably split the selected melt stream until its flow geometry becomes
annular. Although
not wishing to be bound by theory, it is postulated that, the geometry of the
selected melt
stream may govern actual thickness and uniformity of thickness of the extruded
layer.
The second cap disk 216 is axially adjacent to the distribution disk 214. The
second cap disk 216 includes flow regulation points 66a, 66b, 66c, which, in
the first cell
210, are axially aligned with the respective distribution inlet openings 52a,
52c and selection
port 60b. The second cap disk 216 also includes cap outlet openings 68x, 68y,
which are
axially aligned with the respective distribution outlet openings 64x, 64y. The
second cap
disk 216 is designed to direct the selected resin stream to the spacer disk
218. In addition,
the second cap disk 216 also directs the unselected resin streams) to the next
cell.
Moreover, the second cap disk 2I6 may terminate a resin passage. For example,
the second
cap disk 216 of the first cell 210 directs stream b to the spacer disk 218 via
the cap outlet
openings 68x, 68y. In addition, the flow regulation points 66a, 66b, 66c in
the first cell 210
are inlet openings to the second cell 220, so that the second cap disk 216 of
the first cell 210
directs all three resin streams to the second cell 220. In contrast, the flow
regulation point
that is aligned with selection port 60c in the fourth cell 240 is a
termination point 70c that
terminates the resin passage of resin stream c. Similarly, the resin passage
of resin stream
a is terminated in the fifth cell 250 by termination point 70a, and the resin
passage of resin
stream b is terminated in the seventh cell 270 by termination point 70b.
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The spacer disk 218 is axially adjacent to the second cap disk 216. The spacer
disk 218 includes spacer inlet openings 72a, 72b, 72c that are axially aligned
with the
respective flow regulation points 66a, 66b, 66c. The spacer disk 2I 8
additionally includes
flow ports 76x, 76y that are axially aligned with the respective cap outlet
openings 68x, 68y.
A flow region 74 is shown to have a configuration of an eight-point star. The
flow region
74 is connected to the flow ports 76x, 76y, which are the eight points of the
eight-point star.
In FIGS. 3-4, the illustrated flow region 74 is a cavity that extends through
the entire axial
thickness of the spacer disk 218. The spacer disk 218 is designed to receive
the selected melt
from the second cap disk 216 at flow ports 76x, 76y, allow the selected melt
to fill the flow
region 74 and direct the selected melt to the annular passage 130.
In another preferred embodiment of the subject invention, a composite spacer
disk 218' may comprise a spiral overflow design as shown in FIG. 1G. The
composite spacer
disk 2I 8' may replace the spacer disk 218 shown in FIG. 4. The composite
spacer disk 2I8'
includes spacer inlet openings 72a', 72b', 72c' that are axially aligned with
the respective
flow regulation points 66a, 66b, 66c (shown in FIG. 4). The spacer disk 218'
additionally
includes flow ports 76x', 76y' that are axially aligned with the respective
cap outlet openings
68x, 68y (shown in FIG. 4). An overflow region 74' is shown in addition to a
deeper channel
of a spiral flow region 75. The overflow region 74' and a spiral flow region
75 are connected
to the flow ports 76x', 76y', which are the starting flow points of each of
eight spiral flow
regions 75 formed with respect to the composite spacer disk 218'. In FIG. 16,
the illustrated
flow region 74' is a cavity defined by the inner diameters of the spiral disk
2I 7 shown in
FIG. 15 and the overflow spacer 219 shown in FIG. 17. The spiral disk 217 may
combine
with the overflow spacer 219 to form the flow region 74' shown in the
composite spacer disk
218' in FIG. 16. The composite spacer disk 218', like the spacer disk 218
shown in FIG. 4,
is designed to receive the selected melt from the second cap disk 216 (shown
in FIG. 4) at
flow ports 76x', 76y', allow the selected melt to fill the spiral channels 75
and into overflow
region 74' and direct the selected melt to the annular passage 130. Such a
spiral overflow
design assists in spreading out melt join lines over a broader area than the
star configuration
of the spacer disk 218, shown in FIG. 4. The composite spacer disk 218' could
also be
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machined from a single piece of material or welded from a group of disks such
as those
shown in FIGS. 15 and 17.
In another, similar, preferred embodiment of the subject invention, a
composite spacer disk 218" may comprise a spiral overflow design as shown in
FIG. 18.
The composite spacer disk 218" may replace the spacer disk 218 shown in FIG.
4. In FIG.
18, the illustrated flow region 74' is a cavity defined by the inner diameter
of the spiral disk
217 shown in FIG. 15 and the inner region defined by the eight-point star in
the overflow
spacer 219' shown in FIG. 19. The configuration of the overflow spacer 219'
shown in FIG.
19 is very similar to the spacer disk 218 shown in FIG. 4. However, in this
embodiment, the
spiral disk 217 combines with the overflow spacer 219' to form the flow region
74' shown
in the composite spacer disk 218" in FIG. 18.
As best shown in FIG. 4, the disks 212, 214, 216 may have an inner radius
170 and an outer radius 175 that is equal to the overall inner 204 and outer
206 radii of the
modular disk assembly 202. Similarly, the spacer disk 218, 218' in each cell
may have an
outer radius 185 that is equal to the overall outer radius 206. The modular
disk assembly 202
also includes a third cap disk 280 adjacent to the spacer disk 218 in the last
cell 270. Cap
disk 280 provides an end plate to the cells so that the entire assembly 202
may be secured
together to act as a self contained and replaceable unit within the die 200.
The disks making up the modular disk assembly can be made of any material
suitable for use in a coextrusion die. Suitable materials include, for
example, ceramic, plastic
or metallic materials that can withstand a welded attachment or the clamping
pressure of the
securing means such as the die bolts 112 and mandrel bolts 141 and that do not
chemically
or thermally react with the melts being processed. Preferably the disks
comprise a material
that facilitates easy and inexpensive manufacture of the disks themselves. A
preferred disk
may comprise, for example, metallic materials such as steel and aluminum. More
preferably,
each disk has smooth surfaces so that a surface from a disk intimately abuts a
surface from
an axially adjacent disk. Such intimate contact will ensure that melt streams
flowing through
the modular disk assembly 202 are properly directed and without leaking. Where
poor
surface quality disks are being used it is preferable that the disks are
secured together by glue
or welds to reduce leaking.
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The cells in the modular disk assembly 202 are secured by disk bolts (not
shown), these bolts can be inserted in a plurality of unused melt holes such
as those aligned
with inlet openings, if available. Alternatively, dedicated holes (not shown)
in each disk
specifically made for the disk bolts can also be provided. However, these
dedicated holes
are preferably placed such that the disk bolts would not interfere with the
melt flow, for
example, in the channels in the distribution disk 214 or the flow region 374
of the spacer disk
218. Also, as previously mentioned, other securing means such as for example,
glue, may
be used. In a preferred embodiment, each disk within each cell can be glued to
the axially
adjacent disks and finally to a cap disk 216. Any glue material suitable for
securing the
material making up the disks may be used so long as the processed melt streams
do not
chemically react with the glued materials. An example of acceptable glue
material for
metallic disks including steel and aluminum (specifically product number DK-
175-022A),
is an inorganic polymer ceramic glaze from Cerdec Corporation of Washington,
Pennsylvania.
In another preferred embodiment, disks within a cell may be permanently
joined together. One such means of permanetly joining disks within a cell
together is with
spot welds between abutting surfaces of adjacent disks. Specifically, two or
more of the
distribution disk 2I8, the second cap disk 216 and the spacer disk Z I8 may be
connected with
respect to each other with spot welds. Such welding eliminates possible errors
made during
module assembly because the disks within each cell cannot be transposed or
omitted entirely
from the modular disk assembly 202. In one embodiment wherein the distribution
disk 218
is welded to the second cap disk 2I6 and the second cap disk 216 is welded to
the spacer disk
218, only the first cap disk 212 is separable. In one preferred embodiment,
two or more
distribution disks 218 may be welded, or otherwise permanently joined,
together to increase
the overall thickness of the cell and/or distribution disk 218.
Other means of welding known to those having ordinary skill in the art, such
as braze welding, may be used to join two or more disks within a cell. A
preferred weld
would permit grinding disk surfaces smooth following placement of the weld.
Multiple cells
may also be welded together to further ensure reliable and high speed assembly
of the
modular disk assembly 202.
I3
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In yet another preferred embodiment, each cell or group of two or more disks
can be machined from a single piece of material. Like a welded group of disks,
a single-
piece machined cell creates a permanent connection among groups of disks and
would
eliminate errors made during module assembly because the single-piece machined
cell would
prevent an accidental interchange of adjacent disks.
The die of the present invention illustrated in FIGS. 1-8 is an inward flow
die,
since melts are directed radially inward towards the mandrel 114 to form the
blown films
120. Another embodiment of the inward flow die (not shown) may not employ a
mandrel
114. When the mandrel is not used the exit melt 161 is extruded into a solid
laminate rod,
whereas the use of the mandrel causes the melt to be blown into a hollow tube.
The
extrusion of a solid laminate rod (not shown) may also be useful to extrusion
coat objects
such as a wire which is passed through the hollow center 125 of the inward
flow die. This
is accomplished by removing the mandrel, inserting the object to be coated
into the hollow
center 125 from the top end such that the annular exit melt passage is formed
between the
object and the modular assembly, and passing the object through the center
125. The melt
is simultaneously delivered into the modular disk assembly and directed
through the exit
melt passage whereupon the melt contacts and coats the object as it passes
through.
FIG. 9 shows another configuration for the distribution disk 215 that can be
used in an inward flow die of the present invention. The pattern stamped into
the disk shown
in FIG. 9, facilitates a more symmetrical division of the selected melt and
thereby resulting
in more uniform layer thickness in the laminate.
Alternatively, as illustrated in FIGS. 10-13, the die of the present invention
may be configured to direct melt flow radially outward, away from the mandrel
314. As best
shown in FIG. 1 l, an outward flow die 400 includes a modular disk assembly or
modular
disk 402 with a first end 408 and an opposite second end 409, an overall inner
radius 404 and
an overall outer radius 406. The modular disk assembly 402 is disposed about a
mandrel
314, which includes a mandrel stem 324 and a mandrel tip 326. The surface (not
shown) at
the inner radius 404 of the modular disk abuts the mandrel stem 324 and the
modular disk
402. Similarly, the mandrel tip 326 abuts the second end 409 of the modular
disk assembly
402 such that no gap exists there-between. The die 400 also includes an
annular die wall 502
14
CA 02239411 2005-02-23
connected to an exit die tube 500, both of which surround the modular die
assembly such that
a peripheral resin passage 315 is formed therebetween. A screw and lock nut
design allows
for attachment of a mandrel tip with various radii. It is also understood that
the exit die tube
500 may also be replaced by one with a different radius in order to obtain a
peripheral resin
passage 3 I S with a different width. Die bolts secure the inlet plate 306,
annular die wall 500,
and exit die tube 502. Recessed holes are in the annular die wall 500 so that
the die bolts 112
do not interfere with clamping pressure.
Figure I 1 also shows that the mandrel 314 has a hollow center 313. As an
example, a screw lock nut design 323 may be provided on the mandrel stem 324.
The
mandrel is held by the adjusting plate 340 and aligned with four mandrel bolts
341.
As best shown in FIG. I 0, two melt streams a, b are introduced to a modular
die containing a first cell 410, a second cell 420 and a last cell 430.
Referring now to FIG. 11,
the first cell 410 is adjacent to the first end 408 of the modular disk
assembly 402 while the
last cell 430 is adjacent to the second end 409. As best shown in FIG. I0,
each of these cells
includes a first cap disk 412, a distribution disk 414, a second cap disk 416
and a spacer disk
418. Melt stream a is introduced to the first cell 410 through cap inlet
opening 350a while
melt stream b is introduced the modular disk 402 through cap inlet opening
350b. A selection
port 360a of the first cell 410 is aligned with cap inlet opening 350a and
thus selects melt a
for distribution in the first cell 410. A continuous channel that extends
through the distribution
disk 362 directs the selected melt material from stream a radially outward to
eight outlet
openings 364x, 364y that terminate the channel 362. Distribution inlet opening
352b in the
first cell 410 is aligned with cap inlet opening 350b and therefore directs
melt stream b to the
second cell 420 via flow regulation point 366b and spacer inlet opening 372b
of the second
cap disk 416 and spacer disk 418, respectively, in the first cell 410. The
eight cap outlet
openings 368x, 368y are aligned with the distribution outlet openings 364x,
364y, so that the
selected melt material from stream a is directed to eight flow ports 376x,
376y of the spacer
disk 418 in the first cell 410. The selected melt material is then allowed to
fill the flow region
374 that surrounds the outer periphery of the spacer disk 418. Referring now
to FIG. 1 I, the
selected melt material that fills the flow region 374 then follows the
peripheral resin passage
315 and exits the die 400 as a blown film (not shown).
As best shown in FIG. 10, the first cap disk 412 preferably has an outer
radius
515 that is greater than the outer radius 525 of the spacer disk 418 so that
the flow region 374
extends beyond the points of the eight-star configuration to allow melt
material to join in the
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flow region 374 before it enters the peripheral resin passage 315. The inner
radius 510 of
all of the disks making up the cells 410, 420, 430 are preferably equal to the
overall inner
radius 404 so that the modular disk assembly 400 snugly fits around the
central core portion
of the mandrel 3I4.
In the preferred embodiment wherein each cell or group of two or more disks
is machined from a single piece of material, another configuration may replace
the star-
shaped spacer disk 418. In this preferred embodiment, the star-shaped spacer
disk 418
shown in FIG. 10 may be replaced with a disk having a spiral overflow design
such as that
shown in FIGS 15 and 16. A spiral overflow design aids in spreading out melt
join lines
over an area rather than a discrete and narrow weld line.
The modular disk assembly 402 can be used in the device 100 illustrated in
FIG. l with the inlet plate 306 shown in FIG. 12 and the threaded attachment
plate 316
shown in FIG. 13. FIG. 13 shows the inlet plate 306 that directs melt stream a
through melt
holes 307a to the modular disk assembly 402. The illustrated stream b is
directed to the
modular disk through a separate threaded inlet plate (not shown). As best
shown in FIG. 12,
threaded plate bolts 308 secure the inlet plate 306 with the threaded
attachment plate 3I6.
Two pin holes 309 can be used to align the melt hole 307a of the inlet plate
306 to the
extruder extension 104 (of FIG. 1). The threaded attachment plate 3I6 directs
the melt
streams to the modular disk assembly 402 component of die 400 through inlet
holes 3I7a,
317b.
As with the distribution disks 214, 215 of the inward flow die 202, the melt
is preferably divided by symmetric split channels in the annular disks.
Particularly, each first
split channel 359 preferably directs about one-half of the amount of the
selected melt from
the selection port 360a to its adjacent two second split channels 361.
Similarly, each second
split channel 361 directs one-half of the amount of selected melt from the
first split channel
359 to its adjacent third split channels 365. A relief zone 363 is preferably
provided to allow
a momentary rest of the selected melt flow before its flow into the third
split channels 365.
As previously described, one of eight distribution outlet openings 364
terminates each end
of the third split channels 365.
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For both inward flow and outward flow dies of the present invention, valuing
components such as choker rods 800 can be inserted in the channel cavities of
the
distribution disk in order to facilitate uniform distribution of the melt
material. For example,
as best shown in FIG. 4, a set of choker rods 800 may be installed in each
distribution disk
214 at the third split channel closest to the selection port 260 designate
channel legs, as
shown for the seventh cell 270. These rods 800 may be made of, for example,
rubber or
metal wire. Other possible valuing components include, for example disks (not
shown) that
may be placed within one or more relief zones 363.
Because of the thinness of the disks and the cells, the die of the present
invention can produce laminate products having a greater number of laminate
layers than the
conventional die within a given amount of space for the die. In addition, the
coplanar
feeding of all of the melt streams into the die from one end of the die also
eliminates the
temperature control problem associated with the conventional die, which
requires increased
radial thickness for increased melt streams. Furthermore, the extruder
delivery design with
commonly driven extruders facilitates the ability to deliver multiple melts
without taking up
a large amount of floor space, because the inlet openings are spaced at
90° around the die
and the adapter attached to the die can deliver three or more melts. Moreover,
the die is easy
to clean because the entire module may be removed. Once removed, the module
may be
replaced with a new or cleaned module. Replacement is cost-effective, because
the disks that
make up the module are cheap to manufacture. Also, replacement is not a
problem, because
assembling the module and installing it into the system are straightforward
and simple
processes. This replacement and cleaning system enables a wide selection of
structures to be
inventoried and quickly installed (a feature not present in current
conventional dies). The
present invention also provides increased versatility to a die. For example, a
die of the
present invention can produce a first laminate, including a first number of
layers having a
first thickness as well as a second laminate having a second larger number of
layers having
the same first thickness, simply with a modular assembly containing more but
thinner disks
than the assembly used to produce the frst laminate. In addition, an inventory
of reusable
modular setups can be maintained such that, for example, the die can produce
an ABA
17
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structure with one modular setup, and an ABCD structure simply by switching to
another
modular setup.
In another preferred embodiment of this invention, a plurality of thin cells
comprising sets of thinner disks can be positioned within disks having
standard thicknesses.
This embodiment permits many thin layers of film to be positioned between two
or more
standard thicknesses of film. Such an embodiment permits multiple continuous
and
uninterrupted layers of film. An example of this embodiment would be a film
comprising
a layer of polydichloroethylene sold under the trade name Saran~ (S)
positioned between
two layers of ethylene vinyl acetate (EVA) to form a film structure of
EVA/S/EVA. A film
structure according to this preferred embodiment of the invention would
replace the single
polydiehloroethylene layer with a layer of equal thickness comprising a
structure of
S/EVA/SlEVA . . . EVA/S. One such embodiment would require cells having
approximately
.25" disks positioned among cells having 16 gauge disks.
Other advantages and characteristics of the present invention are illustrated
in the following examples.
EXAMPLE 1
The uniformity of distribution of a selected melt was tested using an
aerosol can of whipped cream to mimic a plastic melt.
A cell containing four annular disks was assembled. The four disks had
the general configurations of the first cell shown in FIG. 4. Each annular
disk was made
of stainless steel and had a thickness of 1/8 inch, an inner radius of 1 inch
and an outer
radius of 3 inches. The diameter of the inlet openings (S0, 52, 66, 72 of FIG.
4) were 3/8
inches. The diameter of the outlet openings (64, 68 of FIG. 4) were 1/4
inches. In the
first run no choker rods were used. In the second run, the distribution disk
was fit with
two choker rods made of 0.070 mil. wire in the positions shown in FIG. 4
(component
800).
It was found that the choker rods 800 allowed for more uniform
distribution of the whipped cream.
1$
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EXAMPLE 2
Annular disks including first cap disks, distribution disks, second cap
disks and spacer disks having the respective configurations shown in FIG. 4
were
produced and assembled together. The dimensions and materials of these disks
are listed
in Table I below.
TABLE I
Disk Ref. No. Outer Inner ThicknessMaterial
(see FIG. Radius Radius of disk
4)
(inches)(inches) (inches)
first 212 3 1 0.060 steel (
cap 16 ga.)
disk
distribution214 3 1 0.060 aluminum
disk
second 216 3 1 0.060 steel (
cap 16 ga.)
disk
spacer 218 3 N/A 0.060 aluminum
disk
The diameter of the inlet openings (50, 52, 66, 72 of FIG. 4) were 3l8 inches.
The diameter of the outlet openings (64, 68 of FIG. 4) were '/4 inches. The
dimension of the
channels openings and selection port in the distribution disk are listed in
Table II below.
TABLE II
Channels and Ports on Ref. Dimension
Distribution Disk No. (inches)
(see
FIG.
4)
selection port 60 3/8 (diameter)
first split channel 59 0.25 (width)
second split channel 61 0.1875
(width)
third split channel 65 0.125 (width)
relief zone 63 3/8 (diameter)
The first 212 and second 216 cap disks were made through a stamping process
by HPL Ohio of Solon, Ohio. Male and female molds were made and then attached
to the
punch press. A metal sheet was then inserted in between the molds. Full
pressure of the
press was then exerted and a hole or other shape was cut.
The distribution 214, 215 and spacer disks 218 were produced by Versatile
Tool & Die Co. of Ft. Lauderdale, Florida. The configuration on the
distribution 214, 215
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and spacer disks 218 was produced by a water jet cutting process.
Alternatively, tooling for
the configuration can be made so that the disks can be made by a stamping
process.
It is anticipated that the thinner distribution 214, 215 and spacer disks 218
will
at least double the laminate layers that can be made from a die having the
space provide as
that in Example 1.
EXAMPLE 3
A module assembly 202 containing seven cells of the four disks described in
Example 2 was secured with bolts and installed into a die 200 as shown in FIG
3. The
module 202 was inserted into the die 200. The module 202 was clamped in
between the inlet
plate 106 and exit plate 118 of the die 200 using 8 die bolts 112. The mandrel
1 I4 and
annular resin passage I 15 were aligned using 4 mandrel bolts 141. The entire
process of
inserting the module 202 into the die 200 took approximately 1 hour.
Two melt streams were delivered to the module 202. However, it was found
that an amount of melt leaked out of the module 202, possibly due to uneven
surfacing of the
aluminum distribution 214, 21 S and spacer disks 218.
The module 202 was disassembled by removing the bolts and thereafter re-
secured by gluing according to the following steps: (1) as the module 202 was
assembled
both the aluminum distribution 2I4, 215 and spacer disks 2I 8 were coated on
both sides with
DK-175-022A, a ceramic glaze available from Cerdec Corp. of Washington,
Pennsylvania;
(2) the assembly stack was pressed in a I2-ton press and the glaze was
permitted to dry for
24 hours; (3) the dried glaze assembly was oven baked at 465~F for about five
hours to insure
complete curing of the inorganic polymer; (4) the assembled and cured module
202 was then
inserted into the die 200. The seven layer ABABABA laminate product was
successfully
produced without leaks. Therefore, gluing the module 202 imprnved the poor
surface quality
of the disks, because the ceramic coating filled in the gaps that caused
leaking.
EXAMPLE 4
A modular disk assembly 202 containing seven cells with a total of 29 annular
disks was assembled and installed in a die 200 as shown in FIG. 3. The disks
had the general
configurations shown in FIG. 4. Each annular disk was made of steel and had a
thickness
of I/8 inch, an inner radius of I inch and an outer radius of 3 inches. The
diameter of the inlet
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openings (50, 52, 66, 72 of FIG. 4) were 3/8 inches. The diameter of the
outlet openings
(64, 68 of FIG. 4) were '/4 inches. The disks were aligned and secured with
bolts. Pre-
assembly took about one hour. This pre-assembled modular disk assembly was
connected
to two 1-1/4 inch diameter screw extruders, the first containing a
polypropylene melt (A),
the second containing a low-density polyethylene melt (B). The modular disk
assembly was
connected to a mandrel 114 having a radius of 1.75 inches so that a gap is
formed between
the mandrel and the inner radius of the annular disks. This gap provides an
annular axial
flow passage 130 for the exit melt. A mandrel tip (I26 of FIG. 3) having a
diameter of 9
inches was connected to the end ofthe mandrel that is adjacent to the exit die
plate. This was
set with a 0.040 gap between the outlet plate 118 and the mandrel tip 126. A
seven-layer
laminate tube with a 9 inch diameter and having layers in the order of
A/B/A/B/A/BlA was
made. Each layer was about 0.9 mil thick, and the total film thickness was
about 6 mils.
EXAMPLE 5
The 9-inch diameter mandrel tip connected to the modular disk die of
Example 4 was replaced with a smaller mandrel tip (2 inches in diameter) and a
seven-layer
laminate with total laminate layers having a 8-mil thickness was produced. An
exit melt
tube having a diameter of 4 inches was blown to achieve the result. A set of
cooling rings
were installed, which resulted in a more controlled run. The laminate layers
were
individually inspected. The film thickness of each layer varied between a
thickness of 0.8
to 1.8 mils, the thicker portion was developed on the inlet side and the
thinner portion was
observed on the opposite side.
EXAMPLE 6
Two 0.065 inch diameter copper choker rods 800 were inserted into each
distribution disk in the system described in Example 5. The position of these
rods were as
shown in FIG. 4 in the cell 270. The above variation obtained in Example 5 was
reduced to
a maximum of plus 22.5% and minus 26.5%. Thus, it appears that the greater
thickness
variation obtained in Example 5 resulted from the nonuniform distribution of
the selected
melt in the distribution disk of each cell.
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EXAMPLE 7
The thickness and uniformity of film produced by the present invention were
evaluated. A modular disk assembly of seven cells was assembled. Each cell
contained five
disks, including two distribution disks placed next to each other. The
dimensions and
material of these disks are described in Table III below.
TABLE III
Disk Ref. No. Outer Inner Thickness Material
(see FIG. Radius Radius of each of each
4) disk disk
(inches)(inches)(inches)
first 212 3" 2" 0.120 steel (
cap 10 ga.)
disk
distribution215 3" 2" 0.060 aluminum
disks(2)
second 216 3" 2" 0. i 20 steel (
cap 10 ga.)
disk
spacer 218 3" N/A 0.120 steel (
disk 10 ga)
The assembly utilized the distribution disk shown in FIG. 9. The cells were
stacked so that
five cells consecutively ran ethylene vinyl acetate (EVA) (2 MI) as a first
layer and two cells
consecutively ran polypropylene (PP) (12 MF) as an opposing second layer.
Laminate film
was blown from a 2-inch mandrel tip with a 0.090 inch gap between the mandrel
tip 126 and
the outlet plate 1 I 8 at approximately a mandrel tip 126 diameter to air
inflated tube diameter
ratio of about 1.75:1. The circumferences produced are shown in FIG. 14. The
total
thickness was measured every '/Z inch with a Federal 22P-10 gauge. The two
layers were
then separated and measured individually.
The graph in FIG. 14 depicts the maximum thickness variation of all the
measurements. The vertical axis of the graph represents thickness 600 in mils,
while the
horizontal axis represents circumference 610 in inches. The horizontal line
620 represents
the average thickness of the PP layer. The line 630 above the f rst horizontal
line 620
represents the average thickness of the EVA layer 630. The line 640 on FIG. 14
represents
the average thickness of all 7 layers. The percentage indications, such as
+10.2% on the
EVA line 650, indicate maximum deviations and are not averages. The 5 tol5%
maximum
22
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WO 98!17459 PCTlUS97l17735
thickness deviation of the average shows that the performance of the
distribution disk shown
in FIG. 9 is commercially acceptable.
EXAMPLE 8
A modular die assembly containing 100 cells will be preassembled. Each cell
will contain four disks, each disk will be made of a 22 Ga steel having a
thickness of 0.030
inches. Thus, the complete assembly will have a height of 12.030 inches. A
modular die
assembly including 100 cells of four disks with the configuration shown in
FIG. 4 using up
to 12 melt streams will produce a laminate product containing 100 laminate
layers.
EXAMPLE 9
A coextrusion "lab" die with a 2 inch mandrel tip with the disk configuration
shown in FIG. 4 will be converted to a "production" die with a 9-inch mandrel
tip.
Assuming a maximum delivery of 50 pounds per hour through 3/8 inch melt holes
in a 2-inch
lab die, a modular 9-inch production die will be assembled using larger melt
passageways.
Melt will be delivered to the die at a rate of 600 pounds per hour and the
melt will flow
through 12-3l8 inch inlet openings. Thus, the present invention allows a 2
inch coextrusion
lab die to be readily converted into a 9 inch production die.
EXAMPLE 10
The cells were stacked so that twenty seven cells consecutively ran ethylene
vinyl acetate (ES%VA) and polypropylene (PP) (12 MFR) as alternating layers.
Two 1.25"
extruders fed the module with inlets alternating from the sources which were
180° opposed.
The annular axial flow passage was .030". This configuration resulted in 27
layer film but
with some melt instability. The film had the configuration (EVA/PP),3/EVA.
EXAMPLE 11
The cells were stacked so that twenty seven cells consecutively ran ethylene
vinyl acetate (ES%VA) and ethylene vinyl alcohol (EVOH) as alternating layers.
Two 1.25"
extruders fed the module with inlets alternating from the sources which were
180° opposed.
The annular axial flow passage was .030". This configuration resulted in 27
layer film with
only slight melt instability. The film had the configuration (EVA/EVOH),3/EVA.
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EXAMPLE 12
The annular axial flow passage was enlarged from .030" to .050" to reduce
exit shear. Polypropylene (PP) was run against the metal parts of the die to
reduce friction
since some of the polypropylene degrades to an oil and ethylene vinyl acetate
does not. The
cells were stacked so that twenty seven cells consecutively ran polypropylene
(PP) ( 121VIFR)
and ethylene vinyl acetate (E5%VA) as alternating layers. Two 1.25" extruders
fed the
module with inlets alternating from the sources which were 180 °
opposed. This
configuration resulted in 27 layer film without any observed melt instability.
The layer of
film were continuous and uninterrupted. The film had the configuration
(PP/EVA),3/EVA.
Therefore, the die of the present invention has the ability to produce
coextruded blown film laminate products containing large numbers of layers
(e.g. 12, 13, 14,
15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27 and more) as well as
products made up of
more than eight separate materials. Such products have not been obtained from
an extrusion
process before. Additionally, the die has the ability to produce Laminate
products of various
configurations including hollow tubes, solid rods and parisons having large
numbers of
layers (e.g. 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27,
and more) as well as
such products containing more than eight separate materials. These products of
the present
invention can be made of any melt material that can be extruded. Suitable
materials include
thermoplastic materials such as, fvr example, polyethylene, polypropylene,
ethylene vinyl
acetate, as well as elastomer materials such as, for example, copolymers of
alkenes having
from 2 to about 30 carbons in the alkyl chain.
Of course, it should be understood that a wide range of changes and
modifications can be made to the embodiments described above. It is therefore
intended that
the foregoing description illustrates rather than limits this invention, and
that it is the
following claims, including all equivalents, which define this invention.
24
