U.S. patent application number 12/284510 was filed with the patent office on 2010-03-25 for die, system, and method for coextruding a plurality of fluid layers.
This patent application is currently assigned to Cryovac, Inc.. Invention is credited to Lawrence E. Roberts, Anton L. Timmons, Bradford E. Webster.
Application Number | 20100072655 12/284510 |
Document ID | / |
Family ID | 42036821 |
Filed Date | 2010-03-25 |
United States Patent
Application |
20100072655 |
Kind Code |
A1 |
Roberts; Lawrence E. ; et
al. |
March 25, 2010 |
Die, system, and method for coextruding a plurality of fluid
layers
Abstract
A die for coextruding a plurality of fluid layers generally
includes a primary forming stem, one or more distribution plates,
and a microlayer assembly. The microlayer assembly includes a
microlayer forming stem and a plurality of microlayer distribution
plates.
Inventors: |
Roberts; Lawrence E.;
(Spartanburg, SC) ; Timmons; Anton L.; (Mauldin,
SC) ; Webster; Bradford E.; (Moore, SC) |
Correspondence
Address: |
Sealed Air Corporation
P.O. Box 464
Duncan
SC
29334
US
|
Assignee: |
Cryovac, Inc.
|
Family ID: |
42036821 |
Appl. No.: |
12/284510 |
Filed: |
September 23, 2008 |
Current U.S.
Class: |
264/171.13 ;
425/133.5 |
Current CPC
Class: |
B29K 2023/06 20130101;
B29K 2023/086 20130101; B29K 2067/00 20130101; B29K 2023/0625
20130101; B29C 48/1472 20190201; B29K 2023/065 20130101; B29K
2025/00 20130101; B29C 48/185 20190201; B29C 2791/007 20130101;
B29C 48/304 20190201; B29K 2023/0616 20130101; B29C 48/0019
20190201; B29C 48/3363 20190201; B29C 48/10 20190201; B29C 48/18
20190201; B29K 2077/00 20130101; B29C 48/09 20190201; B29K
2023/0633 20130101; B29K 2023/083 20130101; B29C 48/08 20190201;
B29C 48/0018 20190201; B29K 2069/00 20130101; B29D 23/00 20130101;
B29K 2023/0608 20130101; B29C 48/32 20190201; B29C 48/21 20190201;
B29C 48/307 20190201; B29K 2023/12 20130101; B29C 48/49 20190201;
B29K 2023/0641 20130101 |
Class at
Publication: |
264/171.13 ;
425/133.5 |
International
Class: |
B29C 47/06 20060101
B29C047/06 |
Claims
1. A die for coextruding a plurality of fluid layers, comprising:
a. a primary forming stem; b. one or more distribution plates, each
of said plates having a fluid inlet and a fluid outlet, the fluid
outlet from each of said plates being in fluid communication with
said primary forming stem and structured to deposit a layer of
fluid onto said primary forming stem; and c. a microlayer assembly,
comprising (1) a microlayer forming stem, and (2) a plurality of
microlayer distribution plates, each of said microlayer plates
having a fluid inlet and a fluid outlet, the fluid outlet from each
of said microlayer plates being in fluid communication with said
microlayer forming stem and structured to deposit a microlayer of
fluid onto said microlayer forming stem, said microlayer plates
being arranged to provide a predetermined order in which the
microlayers are deposited onto said microlayer forming stem to form
a substantially unified, microlayered fluid mass on said microlayer
forming stem, wherein, said microlayer forming stem is in fluid
communication with said primary forming stem such that said
microlayered fluid mass flows from said microlayer forming stem and
onto said primary forming stem.
2. The die of claim 1, wherein said distribution plates have a
thickness ranging from about 0.5 to about 2 inches and said
microlayer distribution plates have a thickness ranging from about
0.1 to about 0.5 inch.
3. The die of claim 1, wherein said microlayer distribution plates
have one or more flow channels connecting said fluid inlet with
said fluid outlet, said flow channels having a spiral-shaped
configuration.
4. The die of claim 1, wherein said microlayer distribution plates
each have an orifice extending through said plate; said fluid
outlet of each of said microlayer distribution plates is positioned
adjacent to said orifice; and said microlayer forming stem extends
through the orifice of each of said microlayer distribution
plates.
5. The die of claim 1, wherein said primary forming stem and said
microlayer forming stem are substantially coaxially aligned with
one another.
6. The die of claim 5, wherein said microlayer forming stem is
external to said primary forming stem.
7. The die of claim 1, wherein said distribution plates and said
microlayer assembly are axially positioned along said primary
forming stem; and the fluids from said distribution plates and said
microlayer assembly flow in an axial direction along said primary
forming stem.
8. The die of claim 7, wherein said distribution plates are located
upstream of said microlayer assembly.
9. The die of claim 7, wherein said microlayer assembly is located
upstream of said distribution plates.
10. The die of claim 7, wherein said microlayer assembly is
positioned between one or more upstream distribution plates and one
or more downstream distribution plates.
11. The die of claim 1, wherein said microlayer assembly comprises
at least about 5 microlayer plates.
12. The die of claim 1, further including one or more additional
microlayer assemblies.
13. A system for coextruding a plurality of fluid layers,
comprising: a. a die, comprising: (1) a primary forming stem, (2)
one or more distribution plates, each of said plates having a fluid
inlet and a fluid outlet, the fluid outlet from each of said plates
being in fluid communication with said primary forming stem and
structured to deposit a layer of fluid onto said primary forming
stem, and (3) a microlayer assembly, comprising (a) a microlayer
forming stem, and (b) a plurality of microlayer distribution
plates, each of said microlayer plates having a fluid inlet and a
fluid outlet, the fluid outlet from each of said microlayer plates
being in fluid communication with said microlayer forming stem and
structured to deposit a microlayer of fluid onto said microlayer
forming stem, said microlayer plates being arranged to provide a
predetermined order in which the microlayers are deposited onto
said microlayer forming stem to form a substantially unified,
microlayered fluid mass on said microlayer forming stem, wherein,
said microlayer forming stem is in fluid communication with said
primary forming stem such that said microlayered fluid mass flows
from said microlayer forming stem and onto said primary forming
stem; and b. one or more extruders in fluid communication with said
die to supply one or more fluids to said die.
14. A method of coextruding a plurality of fluid layers,
comprising: a. directing a fluid through a distribution plate and
onto a primary forming stem, said distribution plate having a fluid
inlet and a fluid outlet, the fluid outlet from said plate being in
fluid communication with said primary forming stem and structured
such that said fluid is deposited onto said primary forming stem as
a layer; b. forming a substantially unified, microlayered fluid
mass on a microlayer forming stem by directing at least one
additional fluid through a microlayer assembly, said microlayer
assembly comprising a plurality of microlayer distribution plates,
each of said microlayer plates having a fluid inlet and a fluid
outlet, the fluid outlet from each of said microlayer plates being
in fluid communication with said microlayer forming stem and
structured to deposit a microlayer of fluid onto said microlayer
forming stem, said microlayer plates being arranged to provide a
predetermined order in which the microlayers are deposited onto
said microlayer forming stem; and c. directing said microlayered
fluid mass from said microlayer forming stem and onto said primary
forming stem to merge said microlayered fluid mass with said fluid
layer from said distribution plate.
15. The method of claim 14, wherein the fluid directed through said
distribution plate is substantially the same as the fluid directed
through said microlayer assembly.
16. The method of claim 14, wherein the fluid directed through said
distribution plate is different from the fluid directed through
said microlayer assembly.
17. The method of claim 14, wherein said fluid layer from said
distribution plate is deposited onto said primary forming stem
prior to the deposition of said microlayered fluid mass onto said
primary forming stem such that said fluid layer from said
distribution plate is interposed between said microlayered fluid
mass and said primary forming stem.
18. The method of claim 14, wherein said microlayered fluid mass is
deposited onto said primary forming stem prior to the deposition of
said fluid layer from said distribution plate onto said primary
forming stem such that said microlayered fluid mass is interposed
between said fluid layer from said distribution plate and said
primary forming stem.
19. The method of claim 14, wherein: each of said microlayers has a
thickness M, said fluid layer from said distribution plate has a
thickness D, and the ratio of M:D ranges from about 1:1 to about
1:8.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a coextrusion die and, more
particularly, to a coextrusion die containing both a microlayer
assembly and one or more distribution plates to produce coextruded
films having both microlayers and thicker, conventional film
layers.
[0002] Coextrusion is a technique for producing a multilayer
plastic (polymeric) film by bringing two or more molten polymers
together in a die, in which the polymers are formed into a
generally tubular or planar shape, juxtaposed in layered form, and
then pushed out of an annular- or slot-shaped opening in the die.
Once outside of the die, the still-molten multilayer film is
exposed to an environment having a temperature that is maintained
below the melting point of the component polymeric layers of the
film, which causes the layers to melt-bond together as they cool
and solidify.
[0003] Multilayer films typically have a thickness in the range of
50-200 mils upon emergence from the die, but the films are
generally stretched prior to final solidification in order to
expand their surface area and reduce their final thickness to a
range of about 0.5 to about 50 mils. Conventional multilayer films
generally have 3-10 layers; prior to stretching and thinning, i.e.,
while still in the die, each such layer generally ranges from about
20-100 mils in thickness.
[0004] Microlayer extrusion is a technique for increasing the total
number of layers in a multilayer film for a given film thickness,
by reducing the thickness of the component layers of the film.
Thus, while conventional film layers generally range from 20-100
mils inside the die (i.e., prior to stretching and thinning),
microlayers generally have an `in-die` thickness ranging from about
1-20 mils. In this manner, microlayered films may have far more
than 10 layers, e.g., 20, 30, 40, 50, or more layers. Such
microlayered films have been found to provide certain beneficial
properties relative to conventional films composed of thicker
layers that are fewer in number, e.g., improved mechanical
properties such as superior flex cracking and puncture
resistance.
[0005] For many applications, it is desirable to combine thicker,
conventional layers with microlayers. Such thicker layers are often
superior to microlayers for functions such as heat-sealing and
abuse-resistance.
[0006] Unfortunately, it has proven to be difficult to combine the
flow of thin layers, such as microlayers, with relatively thick
layers in such a way that the physical integrity and independent
properties of the thin layers are maintained. This is primarily the
result of interfacial flow instabilities, which are encountered
when microlayers are merged together with thicker layers in a die.
Such interfacial flow instabilities are caused by the more powerful
sheer forces of the thicker layers flowing against the microlayers,
which result from the higher mass flow rate of the thicker layers
relative to the microlayers. The resultant loss of the integrity
and independent characteristics of the microlayers diminishes or
even eradicates the beneficial properties thereof.
[0007] Accordingly, there is a need in the art for an improved die
that permits microlayers to be combined with conventional, thicker
layers in such a way that the integrity and independent properties
of the microlayers are maintained.
SUMMARY OF THE INVENTION
[0008] That need is met by the present invention, which, in one
aspect, provides a die for coextruding a plurality of fluid layers,
comprising:
[0009] a. a primary forming stem;
[0010] b. one or more distribution plates, each of the plates
having a fluid inlet and a fluid outlet, the fluid outlet from each
of the plates being in fluid communication with the primary forming
stem and structured to deposit a layer of fluid onto the primary
forming stem; and
[0011] c. a microlayer assembly, comprising [0012] (1) a microlayer
forming stem, and [0013] (2) a plurality of microlayer distribution
plates, each of the microlayer plates having a fluid inlet and a
fluid outlet, the fluid outlet from each of the microlayer plates
being in fluid communication with the microlayer forming stem and
structured to deposit a microlayer of fluid onto the microlayer
forming stem, the microlayer plates being arranged to provide a
predetermined order in which the microlayers are deposited onto the
microlayer forming stem to form a substantially unified,
microlayered fluid mass on the microlayer forming stem,
[0014] wherein, the microlayer forming stem is in fluid
communication with the primary forming stem such that the
microlayered fluid mass flows from the microlayer forming stem and
onto the primary forming stem.
[0015] Another aspect of the invention is directed to a system for
coextruding a plurality of fluid layers, comprising a die as
described above, and one or more extruders in fluid communication
with the die to supply one or more fluids to the die.
[0016] A further aspect of the invention pertains to a method of
coextruding a plurality of fluid layers, comprising:
[0017] a. directing a fluid through a distribution plate and onto a
primary forming stem, the distribution plate having a fluid inlet
and a fluid outlet, the fluid outlet from the plate being in fluid
communication with the primary forming stem and structured such
that the fluid is deposited onto the primary forming stem as a
layer;
[0018] b. forming a substantially unified, microlayered fluid mass
on a microlayer forming stem by directing at least one additional
fluid through a microlayer assembly, the microlayer assembly
comprising a plurality of microlayer distribution plates, each of
the microlayer plates having a fluid inlet and a fluid outlet, the
fluid outlet from each of the microlayer plates being in fluid
communication with the microlayer forming stem and structured to
deposit a microlayer of fluid onto the microlayer forming stem, the
microlayer plates being arranged to provide a predetermined order
in which the microlayers are deposited onto the microlayer forming
stem; and
[0019] c. directing the microlayered fluid mass from the microlayer
forming stem and onto the primary forming stem to merge the
microlayered fluid mass with the fluid layer from the distribution
plate.
[0020] These and other aspects and features of the invention may be
better understood with reference to the following description and
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWING
[0021] FIG. 1 is a schematic view of a system 10 in accordance with
the present invention for coextruding a plurality of fluid layers,
including a die 12;
[0022] FIG. 2 is a cross-sectional view of the die 12 shown in FIG.
1;
[0023] FIG. 3 is a plan view one of the microlayer plates 48 in die
12;
[0024] FIG. 4 is a cross-sectional view of the microlayer plate 48
shown in FIG. 3; and
[0025] FIG. 5 is a magnified, cross-sectional view of die 12,
showing the combined flows from the microlayer plates 48 and
distribution plates 32.
DETAILED DESCRIPTION OF THE INVENTION
[0026] FIG. 1 schematically illustrates a system 10 in accordance
with the present invention for coextruding a plurality of fluid
layers. System 10 generally includes a die 12 and one or more
extruders 14a and 14b in fluid communication with the die 12 to
supply one or more fluids to the die.
[0027] In a typical application, the fluid layers coextruded by die
12 may comprise one or more molten thermoplastic polymers. Examples
of such polymers include polyolefins, polyesters (e.g., PET),
polystyrenes, polyamide homopolymers and copolymers (e.g. PA6,
PA12, PA6/12, etc.), polycarbonates, etc. Within the family of
polyolefins, various polyethylene homopolymers and copolymers may
be used, as well as polypropylene homopolymers and copolymers
(e.g., propylene/ethylene copolymer). Polyethylene homopolymers may
include low density polyethylene (LDPE) and high density
polyethylene (HDPE). Suitable polyethylene copolymers may include a
wide variety of polymers, such as, e.g., ionomers, ethylene/vinyl
acetate (EVA), ethylene/vinyl alcohol (EVOH), and
ethylene/alpha-olefins, including heterogeneous (Zeigler-Natta
catalyzed) and homogeneous (metallocene, single-cite catalyzed)
ethylene/alpha-olefin copolymers. Ethylene/alpha-olefin copolymers
are copolymers of ethylene with one or more comonomers selected
from C.sub.3 to C.sub.20 alpha-olefins, such as 1-butene,
1-pentene, 1-hexene, 1-octene, methyl pentene and the like,
including linear low density polyethylene (LLDPE), linear medium
density polyethylene (LMDPE), very low density polyethylene
(VLDPE), and ultra-low density polyethylene (ULDPE).
[0028] As is conventional, the polymeric materials may be supplied
to the extruders 14a, b in the solid-state, e.g., in the form of
pellets or flakes, via respective hoppers 16a, b. Extruders 14a, b
are maintained at a temperature sufficient to convert the
solid-state polymer to a molten state, and internal screws within
the extruders (not shown) move the molten polymer into and through
die 12 via respective pipes 18a, b. As will be explained in further
detail below, within die 12, the molten polymer is converted into
thin film layers, and each of the layers are superimposed, combined
together, and expelled from the die at discharge end 20, i.e.,
"coextruded," to form a tubular, multilayer film 22. Upon emergence
from the die 12 at discharge end 20, the tubular, multilayer film
22 is exposed to ambient air or a similar environment having a
temperature sufficiently low to cause the molten polymer from which
the film is formed to transition from a liquid state to a solid
state. Additional cooling/quenching of the film may be achieved by
providing a liquid quench bath (not shown), and then directing the
film through such bath.
[0029] The solidified tubular film 22 is then collapsed by a
convergence device 24, e.g., a V-shaped guide as shown, which may
contain an array of rollers to facilitate the passage of film 22
therethrough. A pair of counter-rotating drive rollers 25a, b may
be employed as shown to pull the film 22 through the convergence
device 24. The resultant collapsed tubular film 22 may then be
wound into a roll 26 by a film winding device 28 as shown. The film
22 on roll 26 may subsequently be unwound for use, e.g., for
packaging, or for further processing, e.g., stretch-orientation,
irradiation, or other conventional film-processing techniques,
which are used to impart desired properties as necessary for the
intended end-use applications for the film.
[0030] Referring now to FIG. 2, die 12 will be described in further
detail. As noted above, die 12 is adapted to coextrude a plurality
of fluid layers, and generally includes a primary forming stem 30,
one or more distribution plates 32, and a microlayer assembly 34.
In the presently illustrated die, five distribution plates 32 are
included, as individually indicated by the reference numerals
32a-e. A greater or lesser number of distribution plates 32 may be
included as desired. The number of distribution plates in die 12
may range, e.g., from one to twenty, or even more then twenty if
desired.
[0031] Each of the distribution plates 32 has a fluid inlet 36 and
a fluid outlet 38 (the fluid inlet is not shown in plate 32b). The
fluid outlet 38 from each of the distribution plates 32 is in fluid
communication with the primary forming stem 30, and also is
structured to deposit a layer of fluid onto the primary forming
stem. The distribution plates 32 may be constructed as described in
U.S. Pat. No. 5,076,776, the entire disclosure of which is hereby
incorporated herein by reference thereto. As described in the '776
patent, the distribution plates 32 may have one or more
spiral-shaped fluid-flow channels 40 to direct fluid from the fluid
inlet 36 and onto the primary forming stem 30 via the fluid outlet
38. As the fluid proceeds along the channel 40, the channel becomes
progressively shallower such that the fluid is forced to assume a
progressively thinner profile. The fluid outlet 38 generally
provides a relatively narrow fluid-flow passage such that the fluid
flowing out of the plate has a final desired thickness
corresponding to the thickness of the fluid outlet 38. Other
channel configurations may also be employed, e.g., a toroid-shaped
channel; an asymmetrical toroid, e.g., as disclosed in U.S. Pat.
No. 4,832,589; a heart-shaped channel; a helical-shaped channel,
e.g., on a conical-shaped plate as disclosed in U.S. Pat. No.
6,409,953, etc. The channel(s) may have a semi-circular or
semi-oval cross-section as shown, or may have a fuller shape, such
as an oval or circular cross-sectional shape.
[0032] In some embodiments, distribution plates 32 may have a
generally annular shape such that the fluid outlet 38 forms a
generally ring-like structure, which forces fluid flowing through
the plate to assume a ring-like form. Such ring-like structure of
fluid outlet 38, in combination with its proximity to the primary
forming stem 30, causes the fluid flowing through the plate 32 to
assume a cylindrical shape as the fluid is deposited onto the stem
30. Each flow of fluid from each of the distribution plates 32 thus
forms a distinct cylindrical layer on the primary forming stem
30.
[0033] The fluid outlets 38 of the distribution plates 32 are
spaced from the primary forming stem 30 to form an annular passage
42. The extent of such spacing is sufficient to accommodate the
volume of the concentric fluid layers flowing along the forming
stem 30.
[0034] The order in which the distribution plates 32 are arranged
in die 12 determines the order in which the fluid layers are
deposited onto the primary forming stem 30. For example, if all
five distribution plates 32a-e are supplied with fluid, fluid from
plate 32a will be the first to be deposited onto primary forming
stem 30 such that such fluid will be in direct contact with the
stem 30. The next layer to be deposited onto the forming stem would
be from distribution plate 32b. This layer will be deposited onto
the fluid layer from plate 32a. Next, fluid from plate 32c will be
deposited on top of the fluid from plate 32b. If microlayer
assembly 34 were not present in the die, the next layer to be
deposited would be from distribution plate 32d, which would be
layered on top of the fluid layer from plate 32c. Finally, the last
and, therefore, outermost layer to be deposited would be from plate
32e. In this example (again, ignoring the microlayer assembly 34),
the resultant tubular film 22 that would emerge from the die would
have five distinct layers, which would be arranged as five
concentric cylinders bonded together.
[0035] Accordingly, it may be appreciated that the fluid layers
from the distribution plates 32 are deposited onto the primary
forming stem 30 either directly (first layer to be deposited, e.g.,
from distribution plate 32a) or indirectly (second and subsequent
layers, e.g., from plates 32b-e).
[0036] As noted above, the tubular, multilayer film 22 emerges from
die 12 at discharge end 20. The discharge end 20 may thus include
an annular discharge opening 44 to allow the passage of the tubular
film 22 out of the die. Such annular discharge opening is commonly
referred to as a "die lip." As illustrated, the diameter of the
annular discharge opening 44 may be greater than that of the
annular passage 42, e.g., to increase the diameter of the tubular
film 22 to a desired extent. This has the effect of decreasing the
thickness of each of the concentric layers that make up the tubular
film 22, i.e., relative to the thickness of such layers during
their residence time within the annular passage 42. Alternatively,
the diameter of the annular discharge opening 44 may be smaller
than that of the annular passage 42.
[0037] Microlayer assembly 34 generally comprises a microlayer
forming stem 46 and a plurality of microlayer distribution plates
48. In the presently illustrated embodiment, fifteen microlayer
distribution plates 48a-o are shown. A greater or lesser number of
microlayer distribution plates 48 may be included as desired. The
number of microlayer distribution plates 48 in microlayer assembly
34 may range, e.g., from one to fifty, or even more then fifty if
desired. In many embodiments of the present invention, the number
of microlayer distribution plates 48 in microlayer assembly 34 will
be at least about 5, e.g., 10, 15, 20, 25, 30, 35, 40, 45, 50,
etc., or any number of plates in between the foregoing numbers.
[0038] Each of the microlayer plates 48 has a fluid inlet 50 and a
fluid outlet 52. The fluid outlet 52 from each of the microlayer
plates 48 is in fluid communication with microlayer forming stem
46, and is structured to deposit a microlayer of fluid onto the
microlayer forming stem. Similar to the distribution plates 32, the
microlayer plates 48 may also be constructed as described in the
above-incorporated U.S. Pat. No. 5,076,776.
[0039] For example, as shown in FIG. 3, the microlayer plates 48
may have a spiral-shaped fluid-flow channel 54, which is supplied
with fluid via fluid inlet 50. Alternatively, two more fluid-flow
channels may be employed in plate 48, which may be fed from
separate fluid inlets or a single fluid inlet. Other channel
configurations may also be employed, e.g., a toroid-shaped channel;
an asymmetrical toroid, e.g., as disclosed in U.S. Pat. No.
4,832,589; a heart-shaped channel; a helical-shaped channel, e.g.,
on a conical-shaped plate as disclosed in U.S. Pat. No. 6,409,953;
etc. The channel(s) may have a semi-circular or semi-oval
cross-section as shown, or may have a fuller shape, such as an oval
or circular cross-sectional shape.
[0040] Regardless of the particular configuration or pattern that
is selected for the flow channel(s) 54, its function is to connect
the fluid inlet(s) 50 with the fluid outlet 52 in such a manner
that the flow of fluid through the microlayer assembly 34 is
converted from a generally stream-like, axial flow to a generally
film-like, convergent radial flow towards the microlayer forming
stem 46. Microlayer plate 48 as shown in FIG. 3 may accomplish this
in two ways. First, the channel 54 spirals inwards towards the
center of the plate, and thus directs fluid from the fluid inlet
50, located near the periphery of the plate, towards the fluid
outlet 52, which is located near the center of the plate. Secondly,
the channel 54 may be fashioned with a progressively shallower
depth as the channel approaches the fluid outlet 52. This has the
effect of causing some of the fluid flowing through the channel 54
to overflow the channel and proceed radially-inward toward the
fluid outlet 52 in a relatively flat, film-like flow. Such
radial-inward flow may occur in overflow regions 53, which may be
located between the spaced-apart spiral sections of channel 54. As
shown in FIG. 4, the overflow regions 53 may be formed as recessed
sections in plate 48, i.e., recessed relative to the thicker,
non-recessed region 55 at the periphery of the plate. As shown in
FIG. 3, overflow regions 53 may begin at step-down 57 and, e.g.,
spiral inwards towards fluid outlet 52 between the spirals of
channel 54. The non-recessed, peripheral region 55 abuts against
the plate or other structure above the plate, e.g., as shown in
FIGS. 2 and 5, and thus prevents fluid from flowing outside the
periphery of the plate. In this manner, the non-recessed,
peripheral region 55 forces fluid entering the plate to flow
radially inward toward fluid outlet 52. Step-down 57 thus
represents a line or zone of demarcation between the `no-flow`
peripheral region 55 and the `flow` regions 53 and 54. The fluid
that remains in the channel 54 and reaches the end 56 of the
channel flows directly into the fluid outlet 52.
[0041] The fluid outlet 52 generally provides a relatively narrow
fluid-flow passage and generally determines the thickness of the
microlayer flowing out of the microlayer plate 48. The thickness of
the fluid outlet 52, and therefore the thickness of the microlayer
flowing therethrough, may be determined, e.g., by the spacing
between the plate surface at outlet 52 and the bottom of the plate
or other structure (e.g., manifold 76 or 78) immediately above the
plate surface at outlet 52.
[0042] With continuing reference to FIGS. 2-3, each of the
microlayer distribution plates 48 may have an orifice 58 extending
through the plate. The orifice 58 may be located substantially in
the center of each microlayer plate 48, with the fluid outlet 52 of
each plate positioned adjacent to such orifice 58. In this manner,
the microlayer forming stem 46 may extend through the orifice 58 of
each of the microlayer distribution plates 48. With such a
configuration, the microlayer distribution plates 48 may have a
generally annular shape such that the fluid outlet 52 forms a
generally ring-like structure, which forces fluid flowing through
the plate to exit the plate in a radially-convergent, ring-like
flow pattern. Such ring-like structure of fluid outlet 52, in
combination with its proximity to the microlayer forming stem 46,
causes the fluid exiting the microlayer plates 48 to assume a
cylindrical shape as the fluid is deposited onto the microlayer
stem 46. Each flow of fluid from each of the microlayer
distribution plates 48 thus deposits a distinct cylindrical
microlayer on the microlayer forming stem 46.
[0043] The microlayer plates 48 may be arranged to provide a
predetermined order in which the microlayers are deposited onto the
microlayer forming stem 46. For example, if all fifteen microlayer
distribution plates 48a-o are supplied with fluid, a microlayer of
fluid from plate 48a will be the first to be deposited onto
microlayer forming stem 46 such that such microlayer will be in
direct contact with the stem 46. The next microlayer to be
deposited onto the forming stem would be from microlayer plate 48b.
This microlayer will be deposited onto the microlayer from plate
48a. Next, fluid from microlayer plate 48c will be deposited on top
of the microlayer from plate 48b, etc. The last and, therefore,
outermost microlayer to be deposited is from plate 48o. In this
manner, the microlayers are deposited onto the microlayer forming
stem 46 in the form of a substantially unified, microlayered fluid
mass 60 (see FIG. 5). In the present example, such microlayered
fluid mass 60 would comprise up to fifteen distinct microlayers (at
the downstream end of stem 46), arranged as fifteen concentric
cylindrical microlayers bonded and flowing together in a
predetermined order (based on the ordering of the microlayer plates
48a-o) on microlayer forming stem 46.
[0044] It may thus be appreciated that the fluid layers from the
microlayer distribution plates 48 are deposited onto the microlayer
forming stem 46 either directly (the first layer to be deposited,
e.g., from microlayer plate 48a) or indirectly (the second and
subsequent layers, e.g., from microlayer plates 48b-o). The
orifices 58 in each of the microlayer plates 48 are preferably
large enough in diameter to space the fluid outlets 52 of the
microlayer plates 48 sufficiently from the microlayer forming stem
46 to form an annular passage 62 for the microlayers (FIG. 2). The
extent of such spacing is preferably sufficient to accommodate the
volume of the concentric microlayers flowing along the microlayer
stem 46.
[0045] In accordance with the present invention, microlayer forming
stem 46 is in fluid communication with primary forming stem 30 such
that the microlayered fluid mass 60 flows from the microlayer
forming stem 46 and onto the primary forming stem 30. This may be
seen in FIG. 5, wherein microlayered fluid mass 60 from microlayer
assembly 34 is shown flowing from microlayer forming stem 46 and
onto primary forming stem 30. Fluid communication between the
microlayer stem 46 and primary stem 30 may be achieved by including
in die 12 an annular transfer gap 64 between the annular passage 62
for the microlayer stem 46 and the annular passage 42 for the
primary stem 30 (see also FIG. 2). Such transfer gap 64 allows the
microlayered fluid mass 60 to flow out of the annular passage 62
and into the annular passage 42 for the primary forming stem 30. In
this manner, the microlayers from microlayer plates 48 are
introduced as a unified mass into the generally larger volumetric
flow of the thicker fluid layers from the distribution plates
32.
[0046] The inventors have discovered that combining the flows of
the microlayers with the thicker fluid layers in this fashion
minimizes the deleterious effects of interfacial flow
instabilities, which generally make it difficult to combine the
flow of thin layers with relatively thick layers in such a way that
the physical integrity and independent properties of the thin
layers are maintained. The microlayer forming stem 46 allows the
microlayers from the microlayer plates 48 to assemble into the
microlayered fluid mass 60 in relative calm, i.e., without being
subjected to the more powerful sheer forces of the thicker layers
flowing from the distribution plates 32. As the microlayers
assemble into the unified fluid mass 60 on stem 46, the interfacial
flow instabilities created by the merger of each layer onto the
fluid mass 60 are minimized because all the microlayers have a
similar degree of thickness, i.e., relative to the larger degree of
thickness of the fluid layers from distribution plates 32. When
fully assembled, the microlayered fluid mass 60 enters the flow of
the thicker layers from distribution plates 32 on primary stem 30
with a mass flow rate that more closely approximates that of such
thicker layers, thereby increasing the ability of the microlayers
in fluid mass 60 to retain their physical integrity and independent
physical properties.
[0047] As shown in FIG. 2, primary forming stem 30 and microlayer
forming stem 46 may be substantially coaxially aligned with one
another in die 12, e.g., with the microlayer forming stem 46 being
external to the primary forming stem 30. This construction provides
a relatively compact configuration for die 12, which can be highly
advantageous in view of the stringent space constraints that exist
in the operating environment of many commercial coextrusion
systems.
[0048] For example, the coaxial alignment of the primary forming
stem 30 with the microlayer forming stem 46 allows the distribution
plates 32 and the microlayer assembly 34 to be axially positioned
along the primary forming stem, as shown in FIG. 2. This reduces
the width of die 12, and also allows the fluids from both the
distribution plates 32 and the microlayer assembly 34 to flow in an
axial direction, e.g., in parallel paths along primary forming stem
30 and microlayer forming stem 46, then together along the primary
stem 30 downstream of transfer gap 64, at which the microlayered
fluid mass 60 flows from the microlayer stem 46 and onto the
primary stem 30 to merge with the fluid layers from the
distribution plates 32.
[0049] Such construction also allows die 12 to be set up in a
variety of different configurations to produce a coextruded film
having a desired combination of thick layers and microlayers. For
example, one or more distribution plates 32 may be located upstream
of the microlayer assembly 34. In this embodiment, fluid layers
from such upstream distribution plates are deposited onto primary
forming stem 30 prior to the deposition of the microlayered fluid
mass 60 onto the primary stem 30. With reference to FIG. 2, it may
be seen that distribution plates 32a-c are located upstream of
microlayer assembly 34 in die 12. Fluid layers 65 from such
upstream distribution plates 32a-c are thus interposed between the
microlayered fluid mass 60 and the primary forming stem 30 (see
FIG. 5).
[0050] Alternatively, the microlayer assembly 34 may be located
upstream of the distribution plates 32, i.e., the distribution
plates may be located downstream of the microlayer assembly 34 in
this alternative embodiment. Thus, the microlayers from the
microlayer assembly 34, i.e., the microlayered fluid mass 60, will
be deposited onto primary forming stem 30 prior to the deposition
thereon of the fluid layers from the downstream distribution plates
32. With reference to FIG. 2, it may be seen that microlayer
assembly 34 is located upstream of distribution plates 32d-e in die
12. As shown in FIG. 5, the microlayered fluid mass 60 is thus
interposed between the fluid layer(s) 70 from such distribution
plates 32d-e and the primary forming stem 30.
[0051] As illustrated in FIG. 2, the microlayer assembly 34 may
also be positioned between one or more upstream distribution
plates, e.g., plates 32a-c, and one or more downstream distribution
plates, e.g., plates 32d-e. In this embodiment, fluid(s) from
upstream plates 32a-c are deposited first onto primary stem 30,
followed by the microlayered fluid mass 60 from the microlayer
assembly 34, and then further followed by fluid(s) from downstream
plates 32d-e. In the resultant multilayered film, the microlayers
from microlayer assembly 34 are sandwiched between thicker layers
from both the upstream plates 32a-c and the downstream plates
32d-e.
[0052] As a further variation, die 12 may include one or more
additional microlayer assemblies, which may be the same as
microlayer assembly 34 or may have a different configuration, e.g.,
a different number of microlayer plates. In this embodiment, any
such additional microlayer assemblies may be coaxially aligned with
the primary forming stem 30, and may be positioned upstream and/or
downstream of the microlayer assembly 34 shown in FIG. 2. Such
additional microlayer assemblies may be used in place of or in
addition to the distribution plates 32. Thus, additional microlayer
assemblies may be positioned adjacent to the microlayer assembly
34, or may be spaced from such assembly 34 by one or more
distribution plates 32. If two or more microlayer assemblies are
included in die 12, such assemblies may also be sandwiched between
upstream and downstream distribution plates, e.g., between the
upstream plates 32a-c and downstream plates 32d-e shown in FIG.
2.
[0053] In many embodiments of the invention, most or all of the
microlayer plates 48 have a thickness that is less than that of the
distribution plates 32. Thus, for example, the distribution plates
32 may have a thickness T.sub.1 (see FIG. 5) ranging from about 0.5
to about 2 inches, e.g., greater than 0.5 inch, such as 0.501 or
more, 0.502 or more, 0.503 or more, etc., or less than 2, e.g.,
1.999 or less, 1.998 or less, etc., such as from about 0.501 to
1.999 inches, 0.502 to 1.998 inches, etc. The microlayer
distribution plates 48 may have a thickness T.sub.2 ranging from
about 0.1 to about 0.5 inch, e.g., greater than 0.1, such as 0.101
or more, 0.102 or more, etc., or less than 0.5, e.g., 0.499 or
less, 0.498 or less, etc., such as from about 0.101 to 0.499 inch,
0.102 to 0.498 inch, etc. Such thickness ranges are not intended to
be limiting in any way, but only to illustrate typical examples.
All distribution plates 32 will not necessarily have the same
thickness, nor will all of the microlayer plates 48. For example,
microlayer plate 48o, the most downstream of the microlayer plates
in the assembly 34, may be thicker than the other microlayer plates
to accommodate a sloped contact surface 66, which may be employed
to facilitate the transfer of microlayered fluid mass 60 through
the annular gap 64 and onto the primary forming stem 30.
[0054] As also shown in FIG. 5, each of the microlayers flowing out
of the plates 48 has a thickness "M" corresponding to the thickness
of the fluid outlet 52 from which each microlayer emerges. The
microlayers flowing from the microlayer plates 48 are schematically
represented in FIG. 5 by the phantom arrows 68.
[0055] Similarly, each of the relatively thick fluid layers flowing
out of the plates 32 has a thickness "D" corresponding to the
thickness of the fluid outlet 38 from which each such layer emerges
(see FIG. 5). The relatively thick fluid layers flowing from the
distribution plates 32 are schematically represented in FIG. 5 by
the phantom arrows 70.
[0056] Generally, the thickness M of the microlayers will be less
than the thickness D of the fluid layers from the distribution
plates 32. The thinner that such microlayers are relative to the
fluid layers from the distribution plates 32, the more of such
microlayers that can be included in a multilayer film, for a given
overall film thickness. Microlayer thickness M from each microlayer
plate 48 will generally range from about 1-20 mils (1 mil=0.001
inch), e.g., greater than 1 mil, greater than 2 mils, greater than
3 mils, etc., less than 20 mils, less than 19 mils, less than 18
mils, etc., such as between 2 to 19 mils, 3 to 18 mils, 4 to 17
mils, etc. Thickness D from each distribution plate 32 will
generally range from about 20-100 mils, e.g., greater than 20 mils,
greater than 21 mils, greater than 22 mils, etc., less than 100
mils, less than 90 mils, less than 80 mils, less than 70 mils, less
than 60 mils, etc., such as between 20 to 50 mils, 21 to 49 mils,
22 to 48 mils, 23 to 47 mils, etc. The foregoing thicknesses are
not intended to be limiting of the scope of the present invention
in any way, and are provided solely for illustration purposes.
[0057] The ratio of M:D may range from about 1:1 to about 1:8,
e.g., greater than 1:1, greater than 1:1.1, greater than 1:1.2,
greater than 1:2, greater than 1:3, etc., less than 1:8, less than
1:7.9, less than 1:7.8, less than 1:7, less than 1:6, etc., such as
between 1:1.1-1:7.9; 1:1.2-1:7.8, 1:2-1:7, 1:3-1:6, 1:4-1:5,
etc.
[0058] Thickness M may be the same or different among the
microlayers 68 flowing from microlayer plates 48 to achieve a
desired distribution of layer thicknesses in the microlayer section
of the resultant film. Similarly, thickness D may be the same or
different among the thicker layers 70 flowing from the distribution
plates 32 to achieve a desired distribution of layer thicknesses in
the `thick-layer section(s)` of the resultant film. The layer
thicknesses M and D will typically change as the fluid flows
downstream through the die, e.g., if the melt tube is expanded at
annular discharge opening 44 as shown in FIG. 2, and/or upon
further downstream processing of the tubular film, e.g., by
stretching, orienting, or otherwise expanding the tube to achieve a
final desired film thickness and/or to impart desired properties
into the film. Such downstream processing techniques are well known
in the art. The flow rate of fluids through the plates will also
have an effect on the final downstream thicknesses of the
corresponding film layers.
[0059] With reference back to FIGS. 1-2, it may be appreciated that
a method of coextruding a plurality of fluid layers in accordance
with the present invention comprises the steps of:
[0060] a. directing one or more fluids through one or more
distribution plates 32 and onto primary forming stem 30 in die
12;
[0061] b. forming a substantially unified, microlayered fluid mass
60 on microlayer forming stem 46 by directing at least one
additional fluid through microlayer assembly 34; and
[0062] c. directing the microlayered fluid mass 60 from the
microlayer forming stem 46 and onto the primary forming stem 30 to
merge the microlayered fluid mass 60 with the fluid layer(s) from
the distribution plate(s) 32.
[0063] As described above, the distribution plates 32 and
microlayer plates 48 preferably have an annular configuration, such
that primary forming stem 30 and microlayer stem 46 pass through
the center of the plates to receive fluid that is directed into the
plates. The fluid may be supplied from extruders, such as extruders
14a, b. The fluid may be directed into the die 12 via vertical
supply passages 72, which receive fluid from feed pipes 18, and
direct such fluid into the die plates 32 and 48. For this purpose,
the plates may have one or more through-holes 74, e.g., near the
periphery of the plate as shown in FIG. 3, which may be aligned to
provide the vertical passages 72 through which fluid may be
directed to one or more downstream plates.
[0064] Although three through-holes 74 are shown in FIG. 3, a
greater or lesser number may be employed as necessary, e.g.,
depending upon the number of extruders that are employed. In
general, one supply passage 72 may be used for each extruder 14
that supplies fluid to die 12. The extruders 14 may be arrayed
around the circumference of the die, e.g., like the spokes of a
wheel feeding into a hub, wherein the die is located at the hub
position.
[0065] With reference to FIG. 1, die 12 may include a primary
manifold 76 to receive the flow of fluid from the extruders 14 via
feed pipes 18, and then direct such fluid into a designated
vertical supply passage 72, in order to deliver the fluid to the
intended distribution plate(s) 32 and/or microlayer plate(s) 48.
The microlayer assembly 34 may optionally include a microlayer
manifold 78 to receive fluid directly from one or more additional
extruders 80 via feed pipe 82 (shown in phantom in FIG. 1).
[0066] In the example illustrated in FIGS. 1-2, extruder 14b
delivers a fluid, e.g., a first molten polymer, directly to the
fluid inlet 36 of distribution plate 32a via pipe 18b and primary
manifold 76. In the presently illustrated embodiment, distribution
plate 32a receives all of the output from extruder 14b, i.e., such
that the remaining plates and microlayer plates in the die 12 are
supplied, if at all, from other extruders. Alternatively, the fluid
inlet 36 of distribution plate 32a may be configured to contain an
outlet port to allow a portion of the supplied fluid to pass
through to one or more additional plates, e.g., distribution plates
32 and/or microlayer plates 48, positioned downstream of
distribution plate 32a.
[0067] For example, as shown in FIGS. 3-4 with respect to the
illustrated microlayer plate 48, an outlet port 84 may be formed in
the base of the fluid inlet 50 of the plate. Such outlet port 84
allows the flow of fluid delivered to plate 48 to be split: some of
the fluid flows into channel 54 while the remainder passes through
the plate for delivery to one or more additional downstream plates
48 and/or 32. A similar outlet port can be included in the base of
the fluid inlet 36 of a distribution plate 32. Delivery of fluid
passing through the outlet port 84 (or through a similar outlet
port in a distribution plate 32) may be effected via a through-hole
74 in an adjacent plate (see FIG. 5), or via other means, e.g., a
lateral-flow supply plate, to direct the fluid in an axial, radial,
and/or tangential direction through die 12 as necessary to reach
its intended destination.
[0068] Distribution plates 32b-c are being supplied with fluid via
extruder(s) and supply pipe(s) and/or through-holes that are not
shown in FIG. 2. The fluid flow along primary forming stem 30 from
distribution plates 32a-c is shown in FIG. 5, as indicated by
reference numeral 65.
[0069] As shown in FIGS. 1-2, microlayer assembly 34 is being
supplied with fluid by extruders 14a and 80. Specifically,
microlayer plates 48a, c, e, g, i, k, m, and o are supplied by
extruder 14a via supply pipe 18a and vertical pipe and/or passage
72. Microlayer plates 48b, d, f, h, j, l, and n are supplied with
fluid by extruder 80 via feed pipe 82 and a vertical supply passage
86. In the illustrated embodiment, vertical passage 86 originates
in microlayer manifold 78 and delivers fluid only within the
microlayer assembly 34. In contrast, vertical passage 72 originates
in manifold 76, extends through distribution plates 32a-c (via
aligned through-holes 74 in such plates), then further extends
through manifold 78 via manifold passage 79 before finally arriving
at microlayer plate 48a.
[0070] Fluid from extruder 14a and vertical passage 72 enters
microlayer plate 48a at fluid inlet 50. Some of the fluid passes
from inlet 50 and into channel 54 (for eventual deposition on
microlayer stem 46 as the first microlayer to be deposited on stem
46), while the remainder of the fluid may pass through plate 48a
via outlet port 84. Microlayer plate 48b may be oriented, i.e.,
rotated, such that a through-hole 74 is positioned beneath the
outlet port 84 of microlayer plate 48a so that the fluid flowing
out of the outlet port 84 flows through the microlayer plate 48b,
and not into the channel 54 thereof. Microlayer plate 48c may be
positioned such that the fluid inlet 50 thereof is in the same
location as that of microlayer plate 48a so that fluid flowing out
of through-hole 74 of microlayer plate 48b flows into the inlet 50
of plate 48c. Some of this fluid flows into the channel 54 of plate
48c while some of the fluid passes through the plate via outlet
port 84, passes through a through-hole 74 in the next plate 48d,
and is received by fluid inlet 50 of the next microlayer plate 48e,
where some of the fluid flows into channel 54 and some passes out
of the plate via outlet port 84. Fluid from extruder 14a continues
to be distributed to remaining plates 48g, i, k, and m in this
manner, except for microlayer plate 48o, which has no outlet port
84 so that fluid does not pass through plate 48o, except via
channel 54 and fluid outlet 52.
[0071] In a similar manner, fluid from extruder 80 and vertical
passage 86 passes through microlayer plate 48a via a through-hole
74 and then enters microlayer plate 48b at fluid inlet 50 thereof.
Some of this fluid flows through the channel 54 and exits the plate
at outlet 52, to become the second microlayer to be deposited onto
microlayer stem 46 (on top of the microlayer from plate 48a), while
the remainder of the fluid passes through the plate via an outlet
port 84. Such fluid may pass through microlayer plate 48c via a
through-hole 74, and be delivered to plate 48d via appropriate
alignment of its inlet 50 with the through-hole 74 of plate 48c,
through which the fluid from extruder 80 passes. This
fluid-distribution process may continue for plates 48f, h, j, and
l, until the fluid reaches plate 48n, which has no outlet port 84
such that fluid does not pass through this plate except via its
fluid outlet 52.
[0072] In this manner, a series of microlayers comprising
alternating fluids from extruders 14a and 80 may be formed on
microlayer stem 46. For example, if extruder 14a supplied EVOH and
extruder 80 supplied PA6, the resultant microlayered fluid mass 60
would have the structure:
EVOH/PA6/EVOH/PA6/EVOH/PA6/EVOH/PA6/EVOH/PA6/EVOH/PA6/EVOH/PA6/EVOH
[0073] The fluids from extruders 14a and 80 may be the same or
different such that the resultant microlayers in microlayered fluid
mass 60 may have the same or a different composition. Only one
extruder may be employed to supply fluid to the entire microlayer
assembly 34, in which case all of the resultant microlayers will
have the same composition. Alternatively, three or more extruders
may be used to supply fluid to the microlayer assembly 34, e.g.,
with each supplying a different fluid such that three different
microlayer compositions are formed in microlayered fluid mass 60,
in any desired order, e.g., abcabc; abbcabbc; abacabac; etc.
[0074] Similarly, the fluid(s) directed through the distribution
plate(s) 32 may be substantially the same as the fluid(s) directed
through the microlayer assembly 34. Alternatively, the fluid(s)
directed through the distribution plate(s) 32 may be different from
the fluid(s) directed through the microlayer assembly. The
resultant tubular film may have thick layers and microlayers that
have substantially the same composition. Alternatively, some of the
thick layers from distribution plates 32 may be the same as some or
all of the microlayers from microlayer plates 48, while other thick
layers may be different from some or all of the microlayers.
[0075] In the illustrated example, the extruders and supply
passages for distribution plates 32d-e are not shown. One or both
of such plates may be supplied from extruder 14a, 14b, and/or 80 by
appropriate arrangement of vertical supply passages 72, 86,
through-holes 74, and/or outlet ports 84 of the upstream
distribution plates 32 and/or microlayer plates 48. Alternatively,
one or both distribution plates 32d-e may not be supplied at all,
or may be supplied from a separate extruder, such as an extruder in
fluid communication with primary manifold 76 and a vertical supply
passage 72 that extends through distribution plates 32a-c and
microlayer assembly 34, e.g., via appropriate alignment of the
through-holes 74 of plates 32a-c and microlayer assembly 34 to
create a fluid transport passage through die 12, leading to fluid
inlet 50 of distribution plate 32d and/or 32e.
[0076] If desired, one or more of the distribution plates 32 and/or
microlayer plates 48 may be supplied with fluid directly from one
or more extruders, i.e., by directing fluid directly into the fluid
inlet of the plate, e.g., from the side of the plate, without the
fluid being first routed through one of manifolds 76 or 78 and/or
without using a vertical supply passage 72, 86. Such direct feed of
one or more plates 32 and/or 48 may be employed as an alternative
or in addition to the use of manifolds and vertical supply passages
as shown in FIG. 2.
[0077] The foregoing description of preferred embodiments of the
invention has been presented for purposes of illustration and
description. It is not intended to be exhaustive or to limit the
invention to the precise form disclosed, and modifications and
variations are possible in light of the above teachings or may be
acquired from practice of the invention.
* * * * *