U.S. patent application number 14/861580 was filed with the patent office on 2016-03-24 for insulated container and methods of making and assembling.
The applicant listed for this patent is DART CONTAINER CORPORATION. Invention is credited to TIM E. ACKLEY, MARK S. DECKER, ERIK J. DURFEE, TOBIN L. EMRICK, ALEX C. FENKER, RYAN P. GINGRAS, MICHAEL HARVEY, JAMES W. HUERTA, CHENGTAO LI, STEVE K. MAKELA, PETER MATYSIAK, RICK L. MEIRNDORF, WAYNE J. MYER, KEVIN R. SMITH, CARL E. STEVENS, GARY R. WILKES, WILLIAM I. WOLFE.
Application Number | 20160082621 14/861580 |
Document ID | / |
Family ID | 55524910 |
Filed Date | 2016-03-24 |
United States Patent
Application |
20160082621 |
Kind Code |
A1 |
LI; CHENGTAO ; et
al. |
March 24, 2016 |
INSULATED CONTAINER AND METHODS OF MAKING AND ASSEMBLING
Abstract
A process for forming a multi-layer sheet for forming an
expanded foam container, the process comprising: extruding a first
layer comprising a first polyolefin-based material comprising at
least one polypropylene-based polymer and at least one blowing
agent; providing a second layer comprising a second
polyolefin-based material comprising at least one
polypropylene-based polymer onto a first side of the first layer;
and expanding the first layer to form the multi-layer sheet
comprising an expanded first layer and an unexpanded second
layer.
Inventors: |
LI; CHENGTAO; (NOVI, MI)
; WILKES; GARY R.; (MASON, MI) ; MYER; WAYNE
J.; (MASON, MI) ; ACKLEY; TIM E.; (HOLT,
MI) ; STEVENS; CARL E.; (CORUNNA, MI) ; WOLFE;
WILLIAM I.; (HASLETT, MI) ; HARVEY; MICHAEL;
(HASLETT, MI) ; DECKER; MARK S.; (PERRY, MI)
; GINGRAS; RYAN P.; (CHARLOTTE, MI) ; SMITH; KEVIN
R.; (LESLIE, MI) ; MATYSIAK; PETER;
(DANSVILLE, MI) ; EMRICK; TOBIN L.; (MASON,
MI) ; MAKELA; STEVE K.; (LESLIE, MI) ;
MEIRNDORF; RICK L.; (HOWELL, MI) ; DURFEE; ERIK
J.; (LANSING, MI) ; HUERTA; JAMES W.; (MEQUON,
WI) ; FENKER; ALEX C.; (LANSING, MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
DART CONTAINER CORPORATION |
MASON |
MI |
US |
|
|
Family ID: |
55524910 |
Appl. No.: |
14/861580 |
Filed: |
September 22, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62054142 |
Sep 23, 2014 |
|
|
|
62189527 |
Jul 7, 2015 |
|
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|
Current U.S.
Class: |
156/229 ;
264/129; 264/148; 264/173.17; 264/37.32 |
Current CPC
Class: |
B32B 2307/718 20130101;
B29L 2009/00 20130101; B65D 3/12 20130101; B29C 2948/92285
20190201; B29C 2948/92904 20190201; B32B 2250/242 20130101; B32B
2307/546 20130101; B29C 48/49 20190201; B32B 2266/025 20130101;
B32B 2439/00 20130101; B65D 81/3874 20130101; B29C 48/0022
20190201; B32B 2307/72 20130101; B65D 21/0233 20130101; B65D 3/16
20130101; B29C 48/21 20190201; B32B 27/065 20130101; B29C 48/0021
20190201; B65D 81/3867 20130101; B29C 48/0018 20190201; B29C
48/0023 20190201; B29K 2623/12 20130101; B29K 2995/0015 20130101;
B29C 48/0014 20190201; B32B 2307/31 20130101; B29C 2948/92247
20190201; B29L 2009/005 20130101; B29C 48/09 20190201; B29C 48/92
20190201; B32B 5/18 20130101; B32B 2439/70 20130101; B29C 2948/922
20190201; B29C 48/307 20190201; B65D 21/0209 20130101; B29C 48/336
20190201; B29L 2031/7132 20130101; B32B 2307/304 20130101; B29C
48/0012 20190201; B29B 17/0026 20130101; B29C 48/08 20190201; B32B
27/32 20130101; B32B 27/18 20130101; B32B 2266/08 20130101; B29B
17/0005 20130101 |
International
Class: |
B29B 17/00 20060101
B29B017/00; B29C 47/00 20060101 B29C047/00 |
Claims
1. A process for forming a multi-layer sheet for forming an
expanded foam container, the process comprising: extruding a first
layer comprising a first polyolefin-based material comprising at
least one polypropylene-based polymer and at least one blowing
agent; providing a second layer comprising a second
polyolefin-based material comprising at least one
polypropylene-based polymer onto a first side of the first layer;
and expanding the first layer to form the multi-layer sheet
comprising an expanded first layer and an unexpanded second layer;
wherein an exterior surface of the second layer has a gloss level
of 18 gloss units or less.
2. The process of claim 1 wherein the second layer has a melt
tangent delta in the range of 1 to 6 and a melt complex viscosity
in the range of 1980 to 12,000 Pa.sec.
3. The process of claim 2 wherein the melt tangent delta is in the
range of 1.5 to 3.5.
4. The process of claim 2 wherein the melt complex viscosity is in
the range of 2000 to 6500 Pa.sec.
5. The process of claim 1, further comprising cutting a body blank
from the multi-layer sheet and forming at least a portion of the
container from the body blank.
6. The process of claim 5 wherein the container is a container and
the body blank comprises a sleeve blank, a bottom element blank, or
both.
7. The process of claim 5 wherein the cutting a body blank from the
multi-layer sheet generates scrap from a portion of the multi-layer
sheet remaining after the cutting of the body blank, the process
further comprising regrinding the scrap to form a polyolefin-based
regrind.
8. The process of claim 5, further comprising printing on the
multi-layer sheet prior to or subsequent to the cutting a body
blank and wherein scrap and/or waste generated during the printing
is recycled to produce a regrind material.
9. The process of claim 5 wherein the body blank comprises a sleeve
blank and the process further comprises assembling the sleeve blank
with a bottom element blank comprising a single layer of expanded
material to form the container.
10. The process of claim 1 further comprising printing on the
multi-layer sheet prior to or subsequent to forming the
container.
11. The process of claim 1 wherein the first polyolefin-based
material, the second polyolefin-based material, or both are
selected from the group consisting of a high melt strength
polypropylene having long chain branching, a blend of a high melt
strength polypropylene having long chain branching and a
polypropylene homopolymer or copolymer, a blend of a polypropylene
copolymer or homopolymer and a polyethylene polymer, and a blend of
a high melt strength polypropylene and a polyolefin having long
chain branching.
12. The process of claim 1 wherein the first and second
polyolefin-based materials are the same.
13. The process of claim 1 wherein the second layer has a thickness
of 1 to 3 mils.
14. The process of claim 1 wherein the first polyolefin-based
material, the second polyolefin-based material, or both have a
cross over point of melt elasticity modulus and loss modulus
located between a frequency of 30-150 radians/second (rad/s) and
9,000-23,000 MPa.
15. The process of claim 1 wherein the first polyolefin-based
material, the second polyolefin-based material, or both have a
flexural modulus of at least 1200 MPa.
16. The process of claim 1 wherein the first polyolefin-based
material, the second polyolefin-based material, or both have a melt
flow rate in the range of 1-13 g/10 min. at 230.degree. C. and 2.16
kg load.
17. The process of claim 1 wherein the first polyolefin-based
material, the second polyolefin-based material, or both have a melt
strength as measured by Rheotens Force at 30 bar is in the range of
6 to 40 cN.
18. The process of claim 1, further comprising providing a third
layer comprising a third polyolefin-based material comprising at
least one polypropylene-based polymer onto a second side of the
first layer, opposite the first side, wherein an exterior surface
of the third layer has a gloss level of 18 gloss units or less.
19. The process of claim 18 wherein the third polyolefin-based
material is the same as the second polyolefin-based material.
20. The process of claim 19 wherein at least a portion of the first
polyolefin-based material, the second polyolefin-based material, or
both comprises a regrind material.
21. The process of claim 20 wherein the first polyolefin-based
material, the second polyolefin-based material, or both comprise 30
wt. % or less of the regrind material.
22. The process of claim 1 wherein the providing the second layer
comprises co-extruding, extrusion coating, or laminating the second
layer onto the first layer.
23. The process of claim 1 wherein the expanding the first layer is
prior to or subsequent to the providing a second layer.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application No. 62/054,142, filed Sep. 23, 2014, and U.S.
Provisional Application No. 62/189,527, filed Jul. 7, 2015, both of
which are herein incorporated by reference in their entirety.
BACKGROUND
[0002] Insulated containers, such as cups, can be used to store hot
or cold beverages or food while providing a consumer holding the
container with some protection from the temperature of the items
stored in the container. Containers made from expanded foam
materials are beneficial due to their thermal insulating properties
and light weight. A common expanded material used in making
containers is expanded polystyrene. However, expanded polystyrene
can be challenging to recycle, dissuading some consumers from
purchasing products made from expanded polystyrene. In the United
States, an increasing number of municipalities are banning the use
of expanded polystyrene containers due to poor public
perception.
BRIEF SUMMARY
[0003] According to an embodiment of the invention, a process for
forming a multi-layer sheet for forming an expanded foam container,
the process comprising: extruding a first layer comprising a first
polyolefin-based material comprising at least one
polypropylene-based polymer and at least one blowing agent;
providing a second layer comprising a second polyolefin-based
material comprising at least one polypropylene-based polymer onto a
first side of the first layer; and expanding the first layer to
form the multi-layer sheet comprising an expanded first layer and
an unexpanded second layer; wherein an exterior surface of the
second layer has a gloss level of 18 gloss units or less.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] In the drawings:
[0005] FIG. 1 is a perspective view of a container according to an
embodiment of the invention.
[0006] FIG. 2 is a cross-sectional view of the container of FIG.
1.
[0007] FIGS. 3A and 3B are a perspective view of a container bottom
element in a pre-formed and formed state, respectively, according
to an embodiment of the invention.
[0008] FIGS. 4A and 4B are a perspective view of a container sleeve
in a pre-formed and formed state, respectively, according to an
embodiment of the invention.
[0009] FIG. 5 is a flow chart illustrating a process for forming a
container according to an embodiment of the invention.
[0010] FIG. 6 is a cross-sectional view of a portion of the
container of FIG. 1.
[0011] FIG. 7 is a flow chart illustrating a process for forming a
container according to an embodiment of the invention.
[0012] FIG. 8 is a cross-sectional view of a pair of nested
containers according to an embodiment of the invention.
[0013] FIGS. 9A and 9B illustrate a multi-layer material for use in
forming a container according to an embodiment of the
invention.
[0014] FIG. 10 is a flow chart illustrating a process for forming a
multi-layer sheet for use in forming a container according to an
embodiment of the invention.
[0015] FIGS. 11A and 11B illustrate a multi-layer material for use
in forming a container according to an embodiment of the
invention.
[0016] FIG. 12 illustrates a chart of melt tangent delta and
complex melt viscosity for exemplary unexpanded skin layers
according to an embodiment of the invention.
[0017] FIG. 13 is a flow chart illustrating a process for forming a
multi-layer sheet for use in forming a container according to an
embodiment of the invention.
[0018] FIG. 14 is a cross-sectional view of a container according
to an embodiment of the invention.
[0019] FIG. 15 is a perspective view of a container sleeve blank
according to an embodiment of the invention.
[0020] FIG. 16 is a perspective view of a container bottom element
blank according to an embodiment of the invention.
[0021] FIG. 17 is a flow chart illustrating a process for forming a
container according to an embodiment of the invention.
DETAILED DESCRIPTION
[0022] FIGS. 1 and 2 illustrate a container 10 defining an interior
volume or cavity 12 for holding liquid or other items placed
therein. In this embodiment, the container 10 is in the form of a
cup having a sleeve 13 comprising a peripheral wall 14 that
includes an interior surface 16, an exterior surface 18, an upper
end 20 and a lower end 22. The upper end 20 may terminate in an
upper rim or lip 24 that circumscribes an opening 26 of the
container 10.
[0023] As can best be seen in FIG. 2, the container 10 includes a
bottom element 30 for closing off a lower end of the container 10
opposite the opening 26. The bottom element 30 includes a floor 32
having a lower surface 34 facing away from the cavity 12 and an
upper surface 36 facing the cavity 12, with the floor 32 providing
the bottom element 30 with a slightly upwardly bowed cross-section
(shown) or a generally flat cross-section. The bottom element 30
also includes at least one stacking element 38 within the cavity 12
and extending vertically towards the upper end 20. The stacking
element 38 may include a plurality of spaced tabs, as illustrated,
which may be regularly or irregularly spaced around the periphery
of the bottom element 30. Alternatively, the stacking element 38
may comprise a non-continuous ring extending around the periphery
of the bottom element 30.
[0024] Still referring to FIG. 2, the sleeve 13 includes a flange
40 extending from the lower end 22 of the peripheral wall 14 which
extends inward towards the bottom element 30 and may be attached to
the lower surface 34 of the bottom element 30. The flange 40 may be
attached to the lower surface 34 in any suitable manner,
non-limiting examples of which include a heat seal and/or an
adhesive.
[0025] FIGS. 3A and 3B illustrate the bottom element 30 in a
pre-formed and formed state, respectively. As illustrated in FIG.
3A, the bottom element 30 is made from a bottom element blank 50
which is cut from a sheet of expanded foam polymeric material. The
bottom element blank 50 includes the floor 32 with the stacking
elements 38 extending radially outward from the floor 32 in an
unfolded, pre-formed condition. As illustrated in FIG. 3B, the
stacking elements 38 can be folded vertically to form the bottom
element 30.
[0026] FIGS. 4A and 4B illustrate the sleeve 13 in a pre-formed and
formed state, respectively. As illustrated in FIG. 4A, the sleeve
13 is made from a sleeve blank 54 which is made from a strip cut
from a sheet of expanded polymeric material. The sleeve blank 54
can have a curved profile and include a portion corresponding to
the peripheral wall 14 and a portion corresponding to the flange
40. As illustrated in FIG. 4B, the sleeve blank 54 can be wrapped
to abut or overlap side edges 56 and 58 of the sleeve blank 54 and
the flange 40 can be folded inward to form the sleeve 13.
[0027] FIG. 5 illustrates a thermoforming process 100 for forming
the container 10. The sequence of steps depicted for this process
is for illustrative purposes only, and is not meant to limit the
method in any way as it is understood that the steps may proceed in
a different logical order or additional or intervening steps may be
included without detracting from the invention.
[0028] The process 100 may begin at 102 and 104 with forming the
bottom element blank 50 and the sleeve blank 54, respectively. The
bottom element blank 50 and peripheral wall blank 54 may be formed
by cutting the blanks 50, 54 from a sheet of expanded or partially
expanded polymeric material. Depending on the material used to form
the blanks 50, 54, there may be some additional expansion of the
material during the forming process when heat is involved. For
example, for a polypropylene-based material, the sheet used to form
the blanks 50, 54 may be fully or mostly expanded prior to cutting
the blanks 50, 54. An additional, secondary expansion of the sheet
forming the blanks 50, 54, such as 5-10% or less, may occur during
steps of the container forming process which may include the
application of heat to the material. The bottom element blank 50
and sleeve blank 54 are preferably from a polypropylene-based
expanded polymeric material, however, it is also within the scope
of the invention for the bottom element blank 50 and sleeve blank
54, and thus the container 10, to be made from any suitable
expanded polymeric material, such as a polystyrene-based material,
for example.
[0029] At 106, the bottom element blank 50 can be shaped to form
the bottom element 30 by folding the stacking elements 38 (see FIG.
3B). The stacking elements 38 can be folded by placing the bottom
element blank 50 on the end of a male mold and applying a vacuum to
hold the bottom element blank 50 in place. The male mold can then
be inserted into a corresponding bottom-forming female mold to fold
the stacking elements 38 vertically about the side of the male
mold. Heat can be applied before or during insertion of the bottom
element blank 50 into the bottom-forming female mold to facilitate
folding the stacking elements 38 against the sides of the male
mold.
[0030] After the bottom element 30 is formed at 106, at 108 the
sleeve blank 54 can be shaped around the bottom element 30 to form
the sleeve 13. The bottom-forming female mold used at 106 can be
removed and the sleeve blank 54 can be wrapped around the bottom
element 30, which is held in place on the male mold by vacuum,
until the side edges 56, 58 overlap or abut (see FIG. 4B). The
sleeve blank 54 can be wrapped around the male mold such that at
least a portion of the sleeve blank 54 is wrapped around the folded
stacking elements 38 with a portion of the sleeve blank 54
corresponding to the flange 40 extending past the bottom element
30.
[0031] At 110, the side edges 56, 58 can be sealed to form a
liquid-tight peripheral wall seam. The side edges 56, 58 can be
sealed using heat and/or pressure by inserting the male mold with
the sleeve blank 54 into a female mold and applying heat and/or
pressure. Alternatively, heat and/or pressure can be applied to
just the side edges 56, 58 to form the side wall seam using a seam
clamp to provide localized pressure to the side edges 56, 58.
[0032] Before, after or concurrently with the formation of the
peripheral wall seam at 110, the flange 40 can be folded under the
bottom element 30 and sealed to the lower surface 34 of the bottom
element 30 to form a liquid-tight bottom seal using heat and/or
pressure at 112. In one example, heat can be applied to the flange
40 to facilitate folding of the flange 40 and then a bottom-forming
mold can be used to compress the flange 40 against the floor 32 to
form a liquid-tight bottom seal.
[0033] As illustrated in FIG. 6, the bottom-forming mold can press
the flange 40 and the floor 32 against a bottom wall of the male
mold until a thickness of a portion of the floor 32 which overlaps
with the flange 40 is about the same as a thickness of a portion of
the floor 32 which does not overlap with the flange 40. In this
manner, the flange 40 and the bottom element 30 can be compressed
during the formation of the liquid-tight seal such that there is a
generally smooth transition between an exterior surface of the
flange 40 and the lower surface 34 of the bottom element 30.
[0034] In addition to forming a bottom seal between the floor 32
and the flange 40, a liquid-tight heat seal can also be formed
between the stacking elements 38 and the interior surface 16 of the
peripheral wall 14 adjacent the stacking elements 38. The interior
surface 16 of the peripheral wall 14 and/or an exterior surface of
the stacking elements 38 can be provided with a coating, such as
polyethylene, for example, which can be heated to form a heat seal
between the interior surface 16 of the peripheral wall 14 and the
stacking elements 38.
[0035] The thus formed container can then undergo additional
processing, such as rolling of the upper edge 20 to form the lip
24.
[0036] FIG. 7 illustrates an alternative thermoforming process 200
that is similar to the process 100 of FIG. 5 except for the order
of forming and assembling the bottom element 30 and sleeve 13. The
bottom element blank 50 and sleeve blank 54 can be formed at 202
and 204, respectively, in the same manner as described above for
the process 100.
[0037] At 206, the sleeve blank 54 can be wrapped until the side
edges 56, 58 overlap or abut to form the sleeve 13 and the side
edges 56, 58 can be sealed using heat and/or pressure to form a
liquid-tight peripheral wall seam at 208. The sleeve blank 54 can
be wrapped around a male mold and inserted into a female mold where
heat and pressure between the male and female mold can be used to
form the side wall seam, in a manner similar to that described
above at 108 for the process 100. Alternatively, heat and/or
pressure can be applied to just the side edges 56, 58 to form the
side wall seam using a seam clamp to provide localized pressure to
the side edges 56, 58. The liquid-tight peripheral wall seam can be
formed prior to assembling the sleeve 13 and bottom element 30 at
208 or after the assembling of the sleeve 13 and the bottom element
30 at 210.
[0038] The sleeve 13 can be assembled with the bottom element 30 in
its formed or pre-formed condition at 210. In one example, the
bottom element blank 50 can be formed into the bottom element 30 by
folding the stacking elements 38 using a male and female mold in a
manner similar to that described above at 106 of the process 100.
The thus formed bottom element 30 can then be inserted into the
formed sleeve 13. Alternatively, the bottom element blank 50 can be
inserted into the formed sleeve 13 and the process of inserting the
bottom blank 50 into the formed sleeve 13 can fold the stacking
elements 38 to form the bottom element 30 within the sleeve 13.
[0039] For example, the sleeve blank 54 or the formed sleeve 13 can
be inserted into a female mold and the unformed bottom element
blank 50 can be inserted into the sleeve 13 through the open upper
end 20. As the bottom element blank 50 is inserted into the sleeve
13, interaction between the stacking elements 38 and the peripheral
wall 14 folds the stacking elements 38 due to a difference in a
diameter of the bottom element blank 50 and a diameter of portions
of the sleeve 13, which tapers from the upper end 20 to the lower
end 22. The bottom element blank 50 can be heated prior to
insertion to facilitate folding of the stacking elements. A male
mold can be inserted into the sleeve 13 adjacent the lower end 22
to act as a stop to limit insertion of the bottom element blank 50
within the sleeve 13.
[0040] At 212, the flange 40 can be folded under the bottom element
30 and sealed to the lower surface 34 of the bottom element 30 to
form a liquid-tight bottom seal using heat and/or pressure in a
manner similar to that described above at 110 for the process 100.
If the sleeve 13 was formed using a female mold and not formed
around a male mold, a male mold can be inserted into the sleeve and
the female mold removed. A bottom-forming mold can be used to
compress the flange 40 against the floor 32 to form a liquid-tight
bottom seal. The bottom-forming mold can press the flange 40 and
the floor 32 against a bottom wall of the male mold until a
thickness of a portion of the floor 32 which overlaps with the
flange 40 is about the same as a thickness of a portion of the
floor 32 which does not overlap with the flange 40.
[0041] The thus formed container can then undergo additional
processing, such as rolling of the upper edge 20 to form the lip
24. As described above for the process 100, in addition to forming
a bottom seal between the floor 32 and the flange 40, a
liquid-tight heat seal can also be formed between the stacking
elements 38 and the interior surface 16 of the peripheral wall 14
adjacent the stacking elements 38.
[0042] As illustrated in FIG. 8, the stacking elements 38 are
configured to abut the lower end 22' of a similar container 10'
that is inserted into the cavity 12 of the container 10 to limit
the insertion of the container 10' into the cavity 12. The number
and dimensions of the stacking elements 38 can be configured to
support the similar container 10' that is inserted into the
container 10 to facilitate nesting and de-nesting the stacked
containers 10 and 10'. The stacking elements 38 limit the insertion
of one container 10 into another container 10 to facilitate removal
or de-nesting of a container 10 from a stack of similar nested
containers 10.
[0043] The sleeve 13 and the bottom element 30 can be made from the
same or different material and preferably are made from an expanded
polymeric material, such as an expanded polypropylene. The expanded
polymeric material can include one or more polypropylene materials
as a base material. In an exemplary embodiment, the expanded
polymeric material comprises a high melt strength
polypropylene-based resin, at least one nucleating agent, and a
blowing agent. The expanded polymeric material can be a single
layer of material or part of a multi-layered material comprising at
least two layers of material in which the expanded polymeric
material forms the core layer and one or more additional skin
layers are provided on one or both sides of the expanded polymeric
material.
[0044] The material used to form the container 10 can be printed on
prior to forming the container 10 or after the container 10 is
formed. In one example, the expanded polymeric material used to
form the sheets for the sleeve blank 52 and/or the bottom element
blank 50 can be printed on prior to cutting the blanks 50, 52. The
sheets can be fed into a flexographic printer where each color
station of the flexographic printer can print a specific color onto
the sheet according to the print design. If ultraviolet (UV)
flexographic ink is used, the ink can be cured between each color
station using a UV light source. If the ink is water-based, all of
the colors can be printed onto the sheet and forced air can be used
to dry the ink. The thus printed sheet can then be used immediately
to for the bottom element and sleeve blanks 50, 52 or wound onto a
roll for storage.
[0045] Alternatively, after the container 10 is formed, the
container 10 can be fed into a conical container printer using a
feed screw system that places the container 10 on print mandrels.
Each print mandrel is indexed to a pretreat system for surface
treatment of the side wall 14 and then indexed into the print
position. At the print position, the side wall 14 can be printed on
using a dry offset printing process with UV paste ink, for example.
After printing, the container 10 is indexed into a curing position
where the print mandrels are rotated in front of a UV light source
to cure the ink. Once cured, the mandrels are indexed to an
out-feed position and the containers 10 can be nested into stacks
for storage.
[0046] Referring now to FIGS. 9A and 9B, the material used to form
a body blank for a container, such as the bottom element blank 50
and the sleeve blank 52, can be a multi-layer material 300 that
includes an expanded polymeric layer as a core layer 302 and at
least one unexpanded polymeric layer that forms a skin layer 304,
which may be laminated, extrusion coated, or co-extruded with the
core layer 302. It is also within the scope of the invention for
the bottom element blank 50 to be made from a single, core layer
302, while the sleeve blank 52 is made from the multi-layer
material 300. The multi-layer material 300 can include a single
skin layer 304 on one side of the core layer 302, as illustrated in
FIG. 9A, or alternatively, as illustrated in FIG. 9B, the
multi-layer material 300 can include the core layer 302 and first
and second unexpanded polymeric skin layers 304a and 304b,
laminated, extrusion coated, or co-extruded on both sides of the
expanded core layer 302.
[0047] The terms laminated, extrusion coated, and co-extruded are
used herein in accordance with the normal meaning ascribed to such
terms in the art of polymeric expanded materials. Extrusion coating
as used herein refers to a process in which a first layer is
extruded from a die onto a second, already extruded, and optionally
already expanded, layer and pulled into a nip between a pressure
roll and a chill roll with the pressure between the pressure roll
and the chill roll forcing the first layer onto the second layer.
Lamination refers to a process by which a first and second layer
are formed separately and then adhered together using heat,
pressure, and/or adhesives. Co-extrusion refers to a process by
which a first extrudate and a second extrudate are coupled with a
single die head and the first and second extrudates are extruded
together through the die to form a multi-layer material.
[0048] The polypropylene-based resin used for the base material for
the expanded core layer 302 may be a high melt strength homopolymer
or copolymer that is not cross-linked and does not include long
chain branching. A polypropylene homopolymer is typically
characterized by a high isotactic index, resulting in a high
melting point. Copolymers of polypropylene can include copolymers
in which the polymer is derived from polypropylene monomers and at
least one other species of monomer or a block copolymer derived
from blocks of polypropylene monomers and blocks derived from at
least one other species of monomer, non-limiting examples of which
include ethylene, propylene, or a combination of ethylene and
propylene. In an exemplary embodiment, the base material is an
ethylene-propylene block copolymer.
[0049] Suitable high melt strength polypropylenes have a strain
hardening behavior based on the elongational viscosity that imparts
cell nucleating and growth properties that lead to fine, closed
cells and a low density expanded material. Suitable high melt
strength polypropylenes will also have high crystallinity and a
high flexural modulus. An illustrative example of a high melt
strength polypropylene has a melting point in the range of about
155-170.degree. C., preferably 160-165.degree. C., and a flexural
modulus of at least 1400 MPa, preferably at least 1600 MPa, more
preferably at least 1700 MPa. The melt flow rate (MFR) at
230.degree. C. and 2.16 kg load is in the range of 0.1-18 g/10
min., preferably 1-13 g/10 min. Additionally, or alternatively, the
high melt strength polypropylene has a die swell ratio (the ratio
of extrudate diameter versus die diameter) of at least 1.55 as
measured during extrusion from a 1 mm diameter orifice at an
extrusion speed of 0.1 g/min. at 190.degree. C. In another example,
the high melt strength polypropylene has a melt tension of at least
0.5 grams, preferably 1.5 grams or greater, as characterized by
capillary rheometer (measurements conducted at 230.degree. C.,
strand length 40 mm, strand diameter 2 mm, piston speed 20 mm/min.,
drawing speed 4 m/min.).
[0050] Additional suitable high melt strength polypropylenes are
ethylene-propylene block copolymers having high isotacicity, a
broad molecular weight distribution and a high molecular weight. An
exemplary high melt strength polypropylene has a weight average
molecular weight (Mw) or number average molecular weight (Mn) of at
least 300,000 g/mol and a polydispersity index (PDI) of at least
5.6. In another exemplary embodiment, the high melt strength
polypropylene has a weight average molecular weight (Mw) or number
average molecular weight (Mn) of at least 400,000 g/mol and a
polydispersity index (PDI) of at least 8.4. The ethylene-propylene
block copolymer may include an isotactic polypropylene segment with
a crystalline polyethylene segment. In a further embodiment, the
ethylene-propylene block copolymer has high elongation or tensile
strain that is 70% or greater, preferably about 70-80%, at room
temperature. The tensile strain can be measured according to ISO
method 527 or ASTM method D638. As used herein, "ISO" refers to
International Organization for Standardization and "ASTM" refers to
ASTM International, formerly American Society for Testing and
Materials; the year of the method is either designated by a suffix
in the method number following a hyphen or colon, or, in the
absence of such a designation, is the most current year prior to
the filing date of this application.
[0051] An exemplary high melt strength homopolymer or copolymer
that is not cross-linked and does not include long chain branching
has a melting point in the range of about 155-170.degree. C., more
preferably 160-165.degree. C., a flexural modulus of at least 1400
MPa, preferably at least 1600 MPa, more preferably at least 1700
MPa, a melt flow rate within the range of 0.1-18 g/10 min.,
preferably 1-13 g/10 min., at 230.degree. C. and 2.16 kg load, a
weight average molecular weight (Mw) or number average molecular
weight (Mn) of at least 300,000 g/mol, a polydispersity index (PDI)
of at least 5.6, and combinations thereof. Preferably, the
exemplary high melt strength homopolymer or copolymer is an
ethylene-propylene block copolymer. In another preferred
embodiment, the exemplary high melt strength homopolymer or
copolymer is an ethylene-propylene block copolymer having a high
elongation or tensile strain that is 70% or greater, preferably
about 70-80%, at room temperature.
[0052] An exemplary high melt strength polypropylene, which is not
cross-linked and does not include long chain branching, is BC3BRF,
available from Japan Polypropylene Corp., which is a linear
ethylene-propylene block copolymer containing 8% ethylene that does
not include long or short chain branching. Additional examples
include an extrusion grade ethylene-propylene block copolymer
having a higher melt strength than BC3BRF, such as FT3000 and
FT6000, also available from Japan Polypropylene Corp.
[0053] The base material can be a single polypropylene-based resin
having the above identified properties or a blend of two or more
polypropylene-based resins. When the base material comprises a
blend of polypropylene-based resins, all of the resins in the blend
can have the above identified properties. Alternatively, at least
one of the polypropylene-based resins used in the blend will be a
high melt strength homopolymer or copolymer that is not
cross-linked and does not include long chain branching having the
above identified properties while one or more of the other
polypropylene-based resins in the blend may have different
properties.
[0054] In one example, the base material can include a blend of a
first resin that is a high melt strength homopolymer or copolymer
that is not cross-linked and does not include long chain branching
having the above identified properties, such as BC3BRF, with a
second resin having a high melt strength and long-chain branching
and/or cross-linking Non-limiting examples of such a second resin
include DAPLOY.TM. WB140, available from Borealis A/S, Denmark, or
Pro-fax PF814 or X11844-30, available from Lyondell-Basell Montell,
U.S.A. In yet another example, the base material can include a
blend of a first resin that is a high melt strength homopolymer or
copolymer that is not cross-linked and does not include long chain
branching having the above identified properties, such as BC3BRF,
with a second resin that is the same as the first resin, but which
has been previously used and re-processed for additional use.
[0055] In another embodiment, the polypropylene-based resin used
for the base material for the expanded core layer 302 may be a high
melt strength polypropylene homopolymer which includes long chain
branching. The long chain branched polypropylene can be
characterized by a melt strength of at least 20 cN, and preferably
in the range of 25-30 cN or greater (as determined according to ISO
method 16790:2005). Illustrative examples of suitable long chain
branched high melt strength polypropylenes have a melting point in
the range of about 155-175.degree. C. and a flexural modulus of at
least 1400 MPa, preferably 1600 MPa or greater. The melt flow rate
at 230.degree. C. and 2.16 kg load is preferably in the range of
0.1-6 g/10 min., more preferably 1-3 g/10 min. The long chain
branched polypropylene can be characterized by a melt tension of at
least 3-15 g, preferably 5-12 g, as characterized by capillary
rheometer (measurements conducted at 230.degree. C., strand length
40 mm, strand diameter 2 mm, piston speed 20 mm/min., drawing speed
4 m/min.). The long chain branched polypropylene can also be
characterized by a PDI of at least 8.
[0056] DAPLOY.TM. WB140, available from Borealis A/S, is an example
of an exemplary long chain branched polypropylene suitable for use
according to the embodiments of the invention. DAPLOY.TM. WB140 is
characterized by the manufacturer as having a melting point in the
range of 163-164.degree. C., a crystallization temperature in the
range of 127-128.degree. C., a flexural modulus of 1900 MPa, a melt
strength of 32-40 cN (as determined according to ISO method
16790:2005), an MFR of around 1.9-2.3 g/10 min., and a PDI of
around 9. Additional long chain branched polypropylenes having one
or more similar characteristics can also be used. In another
example, long chain branched polypropylenes having a melt strength
in the range of 20-25 cN can be used, such as X5259, which has a
melt tension of 3 g at 230.degree. C., or X5261, which has a melt
tension of 13 g at 230.degree. C., both available from Japan
Polypropylene Corp.
[0057] In another embodiment, the polypropylene-based resin of the
expanded core layer 302 may be a blend of the long chain branched
high melt strength polypropylene and a second polypropylene. In one
example, the second polypropylene is a high melt strength
polypropylene block co-polymer, such as described above, that does
not include long chain branching and is not cross-linked. An
exemplary high melt strength polypropylene block co-polymer is
BC3BRF, available from Japan Polypropylene Corp., or BC3BRF-MT,
also available from Japan Polypropylene Corp., which has a higher
melt strength than BC3BRF and is characterized by a melt tension of
0.9 g at 230.degree. C. Additional examples of suitable high melt
strength polypropylenes include STX0807, also available from Japan
Polypropylene Corp., which has a melt tension of 1.5 g at
230.degree. C., and STX0806, which has a melt tension of 1.3 g at
230.degree. C., both of which are available from Z. The
polypropylene block co-polymer can be present in the base resin at
20 to 25 wt. %.
[0058] In another embodiment, the second polypropylene can be a
high melt strength polypropylene homopolymer that does not include
long chain branching and is not cross-linked. The polypropylene
homopolymer can have a melt strength of at least 15-18 cN and
preferably in the range of 20-30 cN or greater, and a high
molecular weight distribution, as characterized by a PDI greater
than 8. An exemplary polypropylene homopolymer is further
characterized by a melting point of 163-164.degree. C., a
crystallization temperature of 120-121.degree. C., a melt flow rate
in the range of 1-4 g/10 min. at 230.degree. C. and 2.16 kg load,
and a flexural modulus in the range of 2000-2200 MPa, such as
PDH002, available from ExxonMobil.TM., U.S.A. The polypropylene
homopolymer can be present in the base resin at 20 to 25 wt. %.
[0059] In another embodiment, the second polymer can be a
thermoforming or blow molding grade polypropylene homopolymer, such
as Inspire 6025 or Inspire 6021, available from Braskem, which have
a melt flow rate in the range of 2-3.5 g/10 min. at 230.degree. C.
and 2.16 kg load, and a flexural modulus in the range of 1900-2000
MPa or greater to increase the strength of the expanded core layer
302.
[0060] In addition to the polypropylene-based base material, the
expanded core layer 302 can also include at least one nucleating
agent to provide nucleation sites to facilitate bubble formation in
the molten resin during an extrusion process and control the size
and morphology of cell formation in forming the expanded material.
Non-limiting examples of suitable nucleating agents that may be
included in the expanded polymeric material include organic sodium
phosphates, sodium benzoate, carboxylic aromatic or aliphatic
acids, silicates or alumino-silicates of an alkali or alkaline
earth metal, mixtures of citric acid and sodium bicarbonate or
other alkali metal bicarbonate, talc, silicon dioxide, diatomaceous
earth, kaolin, polycarboxylic acids and their salts, and titanium
dioxide. The type and amount of nucleating agent can be selected to
provide the desired cell size and morphology. The amount of
nucleating agent can be defined in terms of weight percent (wt. %)
of the nucleating agent based on the total weight of the mixture of
the base resin and any additional components that form the polymer
melt. As used herein, wt. % refers to the amount by weight of a
given material as a percentage of the total weight of the mixture
of the base resin and any additional components that form the
polymer melt. The amount of nucleating agent added to the base
resin may correspond to an amount of a nucleating agent composition
that includes one or more nucleating agents and optionally
additional additives that may or may not facilitate cell formation.
Alternatively, the amount of nucleating agent added to the base
resin may correspond directly to an amount of the material that
provides the properties of a nucleating agent regardless of whether
additional materials are mixed with the nucleating agent.
[0061] The expanded polymeric material of the expanded core layer
302 can also include at least one blowing agent. A blowing agent
introduces gas into the resin mixture to form an expanded structure
within the resin and reduce the density of the extrudate. The
blowing agent can be a physical or a chemical blowing agent.
Chemical blowing agents can be organic or inorganic materials that
release gas upon thermal decomposition. Physical blowing agents
facilitate cell formation within the resin through the expansion of
a compressed gas, evaporation of a liquid or the dissolving of a
solid. Non-limiting examples of suitable blowing agents include
nitrogen, carbon dioxide and other inert gases and agents that
undergo phase change from liquid to gas during the expanding
process, chlorofluorocarbons (CFC), hydrochlorofluorocarbons
(HCFC), hydrofluorocarbons (HFC), low boiling alcohols, ketones,
hydrocarbons such as propane, butane, cyclobutane, cyclopentane,
pentane, n-butane, n-pentane, isopentane, and isobutene,
azodicarbonamide, azodiisobutyro-nitrile, n-propanol, isopropanol,
sodium bicarbonate, sodium carbonate, ammonium bicarbonate,
ammonium carbonate, and ammonium nitrite. The type and amount of
blowing agent can be selected to provide the desired expanded
structure and density of the extrudate.
[0062] In an exemplary embodiment, the expanded polymeric material
of the expanded core layer 302 can include a physical blowing agent
and a passive nucleating agent. A passive nucleating agent is
typically a solid material having a fine particle size, such as
talc, for example. The nucleating agent can create sites where the
physical blowing agent can come out of solution during foam
expansion, providing a starting point from which the foam cells
start to grow. Alternatively, an active nucleating agent can be
used. An active nucleating agent is a material that can act as a
chemical blowing agent by generating gas upon decomposition, and
also act as a nucleating agent. An example of a suitable active
nucleating agent is a mixture of sodium bicarbonate and citric
acid.
[0063] The expanded polymeric material of the expanded core layer
302 can also include additional materials, non-limiting examples of
which include processing aids, plasticizers, anti-static agents,
and clarifiers.
[0064] In an exemplary embodiment, the expanded core layer 302 can
include a high melt strength polypropylene having a melting point
of about 155-170.degree. C., a flexural modulus of at least 1400
MPa, and a melt flow rate in the range of 0.1-18 g/10 min.
230.degree. C. and 2.16 kg load, such as BC3BRF, as the base resin,
0.07-0.25 wt. %, more preferably 0.1-0.2 wt. %, of a nucleating
agent, and a physical blowing agent charged at about 1.2 lbs/hr. In
a preferred embodiment, the expanded core layer 302 includes a high
melt strength polypropylene having a melting point of about
160-165.degree. C., a flexural modulus of 1720 MPa, and a melt flow
rate of 12.+-.2 g/10 min. 230.degree. C. and 2.16 kg load, such as
BC3BRF, as the base resin. An exemplary physical blowing agent is a
hydrofluorocarbon, such as 1,1-difluoroethane, also known as
HFC-152a, commercially available as Formacel.RTM. Z2 from
DuPont.TM., U.S.A. An exemplary nucleating agent is commercially
available as Hydrocerol.RTM. 1604 from Clariant.TM., U.S.A., which
is described as a mixture of a chemical blowing agent, calcium
oxide and silica.
[0065] Table 1 below illustrates exemplary compositions for forming
the expanded core layer 302. In a preferred embodiment, the
nucleating agent is Hydrocerol.RTM. 1604 from Clariant.TM., U.S.A.
and the blowing agent is Formacel.RTM. Z2 from DuPont.TM., U.S.A.,
although additional or alternative nucleating agents and/or blowing
agents can be used without deviating from the scope of the
invention. In Examples 3-5 the second resin is present in an amount
in the range of 20-30 wt. %. All of the examples included a 1-2 mil
unexpanded skin layer made using BC3BRF and 3 wt. % of a white
pigment, such as CH27043 2FA masterbatch, available from Ferro
Corporation, U.S.A.
TABLE-US-00001 TABLE 1 Exemplary expanded core layer compositions.
Nucleating Blowing Agent (wt. Agent Example Base resin Second Resin
%) (lbs/hr) 1 PP block co-polymer (e.g. -- 0.07-0.25 1.2 BC3BRF) 2
Long chain branched PP -- 0.15-0.25 1.2 (e.g. DAPLOY .TM. WB140) 3
Long chain branched PP PP block co-polymer (e.g. 0.15-0.25 1.2
(e.g. DAPLOY .TM. WB140) BC3BRF) 4 Long chain branched PP PP
homopolymer 0.15-0.25 1.2 (e.g. DAPLOY .TM. WB140) 5 Long chain
branched PP Thermoforming or blow 0.15-0.25 1.2 (e.g. DAPLOY .TM.
WB140) molding grade PP (e.g. Inspire 6025 or 6021)
[0066] The unexpanded skin layer or layers 304 can include a base
resin that is the same or different than the base resin used in the
expanded core layer 302. For example, the unexpanded skin layer can
include a high melt strength homopolymer or copolymer that is not
cross-linked and does not include long chain branching, such as
BC3BRF or FTS3000, or other similar polypropylenes having a similar
or higher melt flow rate.
[0067] The polypropylene material used in the unexpanded skin layer
304 preferably has an elongation or tensile strain high enough to
stretch without breaking during the expanding of the core layer
302, but does not necessarily need to have the high melt strength
or extensional viscosity that provides strain hardening properties
that would typically be needed for expansion in a foaming process.
Thus, thermoforming grades of polypropylene which have a high melt
strength, such as a polypropylene homopolymer PP6262, available
from ExxonMobil.TM., U.S.A., or FT021N or 6025N, both available
from Braskem, U.S.A, are suitable for use in the unexpanded skin
layer 304. Film or blowing molding grade polypropylenes, such as
FB3B, available from Japan Polypropylene Corp. or any of several
polypropylene homopolymers available from Borealis A/S, Denmark,
non-limiting examples of which include HD601CF, HD905CF, HD915CF,
and HC205TF, or polypropylene copolymers, such as RD204CF, RB206MD,
RB707CF, which have a high melt strength and high tensile strain
are also suitable for use in the unexpanded skin layer 304.
[0068] Additional desirable characteristics of the material used to
form the unexpanded skin layer 304 include a material that can flow
and extrude steadily at the expanding temperature of the expanded
core layer 302. In an exemplary embodiment, the material used for
the unexpanded skin layer 304 can be a high gloss random or block
copolymer having a slightly lower melting point than the material
used in the expanded core layer 302 to minimize crystallization of
the unexpanded skin layer 304 at the expansion temperature of the
expanded core layer 302 when the layers 302 and 304 are
co-extruded. Crystallization of the unexpanded skin layer 304 can
result in undesirable solidification and shrinkage of the
unexpanded skin layer 304 too early in a co-extrusion process. In
addition, when the expanded core layer 302 and unexpanded skin
layer 304 are co-extruded, the unexpanded skin layer 304 is
preferably selected to have a viscosity suitable for merging with
the gas laden polymer melt of the expanded core layer 302 flowing
through the extrusion die to minimize instability at the interface
of the expanded core layer 302 and unexpanded skin layer 304 that
could result in poor surface quality of the unexpanded skin layer
304. The materials of the unexpanded skin layer 304 can also be
selected to provide a shrinkage rate compatible with that of the
expanded core layer 302, which decreases creases and wrinkles in
the co-extruded multi-layer sheets 300.
[0069] In an exemplary embodiment, the melt flow rate of the
material used for the unexpanded skin layer 304 is higher than the
melt flow rate of the material used for the expanded core layer
302. For example, the expanded core layer 302 can be made from a
material having melt flow rate in the range of 0.1-14 g/10 min. at
230.degree. C. and 2.16 kg load while the unexpanded skin layer 304
is made from a material having an melt flow rate in the range of
8-18 g/10 min. at 230.degree. C. and 2.16 kg load.
[0070] Additional additives may be combined with the base resin to
provide the unexpanded skin layer 304 with the desired
characteristics. In an exemplary embodiment, the base resin may be
combined with additives to provide the unexpanded skin layer 304
with the desired physical characteristics, such as opacity, color,
gloss and brightness. The type and amount of additive can be
selected to provide the desired opacity to minimize the visibility
of blotches that may occur if a colored liquid inside the container
10, such as coffee, leaches through the expanded core layer 302.
Increasing the opacity of the unexpanded skin layer 304 can also
hide defects in the cell structure on the surface of the expanded
core layer 302 which lie underneath the unexpanded skin layer
304.
[0071] An example of a suitable additive can include a mixture of
inorganic materials, such as titanium oxide and calcium carbonate,
and pigment, such as a white color concentrate commercially
available from Ferro Corporation, U.S.A, available under the trade
name CH27043 2FA masterbatch. CH27043 2FA masterbatch has typical
melt flow rate greater than 10 g/10 min. 230.degree. C. and 2.16 kg
load, 60-65% ash content, a density of 1.49 g/cm.sup.3, and a
pigment content of approximately 63%. Additional non-limiting
additives are commercially available from PolyOne.TM. under the
trade names MB D77503 or CC10197045WE, for example. In a preferred
embodiment, the unexpanded skin layer 304 can include a mixture of
a high melt strength homopolymer or copolymer that is not
cross-linked and does not include long chain branching, such as
BC3BRF, and approximately 3-5 wt. % of a pigment and opacifying
agent, such as CH27043 2FA masterbatch. The masterbatch can be
provided at a concentration configured to provide the unexpanded
skin layer 304 with the desired opacity, whiteness, brightness and
gloss as well as reduces the viscosity of the base resin to provide
the unexpanded skin layer 304 with rheological properties that are
compatible with those of the of the expanded core layer 302 at the
expansion temperature inside the die used in the co-extrusion
process of the foamed core layer 302 and the unexpanded skin layer
304.
[0072] Additional examples of opacifying additives suitable for use
with the base resin of the unexpanded skin layer 304 include zinc
sulfide, barium sulfate, and antimony oxide.
[0073] Preferably, the expanded core layer 302 and the unexpanded
skin layer 304 have comparable rheological properties (e.g. similar
or equivalent viscosity) at the extrusion foaming temperature of
the expanded core layer 302 inside the die. Compatible rheological
properties can inhibit melt fracturing or instability at an
interface of the expanded core layer 302 and the unexpanded skin
layer 304, which can provide a smooth surface that has minimal
indentations to facilitate printing high resolution graphics onto
the skin layer 304. In addition, the polypropylene of the skin
layer 304 can be selected based on its crystallization temperature
according to a temperature gradient across the skin layer 304 and
the expanded core layer 302 in the thickness direction to provide
compatible shrinkage and crystallization rates between the skin
layer 304 and the expanded core layer 302 to inhibit the formation
of wrinkles and creases in the multi-layer material 300. The skin
layer 302 can further be selected to have a high extension or
elongation and a high stretching capability to inhibit corrugation
during expansion of the core layer 302. BC3BRF, for example,
embodies both of these characteristics, having a high tensile
modulus of 1730 MPa (as determined according to ISO 527-1) with a
100% tensile yield strain (as determined according to ISO 527-1).
The skin layer 304 can also provide lacing resistance and a barrier
effect to inhibit gas leakage and permeation which can facilitate
the nucleation of uniform, fine closed cells in the expanded core
layer 302.
[0074] The multi-layer material 300 can be formed with properties
suitable for use in forming the container 10 in a thermoforming
process. The multi-layer material 300 used to form the bottom
element blank 50 can be the same or different than that used to
form the sleeve blank 52, depending on the desired characteristics
of the sleeve 13 and the bottom element 30. The multi-layer
material(s) 300 can be formed to provide the subsequently formed
bottom element blank 50 and sleeve blank 52 with properties that
facilitate subsequent container forming processes. For example, the
multi-layer sheet 300 forming the sleeve blank 52 can be
co-extruded to facilitate inward curling of the edges of the sleeve
blank 52 upon the application of heat to facilitate wrapping the
sleeve blank 52 to form the sleeve 13 and/or to facilitate folding
the bottom edge of the sleeve blank 52 around the bottom element
30. In contrast, when the assembled bottom element 30 forms a
slightly bowed (FIG. 2) or generally flat cross-section, it can be
desirable to form the bottom element blank 50 from a material which
does not curl when heat is applied.
[0075] One method for facilitating inward curling of the edges of
the sleeve blank 52 is to extrude the multi-layer material 300 in a
process which includes different cooling and shrinkage rates on the
outer surfaces of the extrudate. The difference in temperature
distribution between the two outer surfaces can provide a
difference in the stress and strain characteristics of the two
surfaces which can result in curling of the extrudate. For example,
the co-extruded multi-layer material 300 can be extruded such that
the outer surface of the unexpanded skin layer 304 is cooled by an
air ring, while the outer surface of the expanded core layer 302 is
cooled differently, such as by contact with a water chilled mandrel
and/or cooling air.
[0076] In an exemplary embodiment, the multi-layer material 300
comprising the expanded core layer 302 and a single unexpanded skin
layer 304 used to form the sleeve blank 52 can have a total
thickness of about 55-68 mils (1.397-1.727 mm), a density of less
than about 12.5 lb/ft.sup.3, a base weight of less than 0.72
g/in.sup.2 and a skin layer thickness of about 1-2 mils
(0.0254-0.0508 mm). While this same material can also be used to
form the bottom element blank 50, in a preferred embodiment, the
material used to form the bottom element blank 50, which can be the
multi-layer material 300 or a material comprising only the expanded
core layer 302, can have a thickness in the range of 55-85 mil,
more preferably 65-75 mils, and a density in the range of 9-12
lb/ft.sup.3. The use of a single, expanded core layer 302 to form
the bottom element 30 can reduce the weight of the bottom element
30 as well as facilitate the formation of the flat cross-section
bottom.
[0077] Additionally, or alternatively, to facilitate the formation
of a bottom element 30 having a slightly bowed or flat
cross-section, the material used to form the bottom element blank
50, whether it is the multi-layer material 300 or the single,
expanded core layer 302, can be formed such that there is minimal
orientation of the cells during expansion in both the machine
direction and the cross-machine direction, to minimize shrinkage of
the bottom element blank 50 upon heating. The material used to form
the bottom element blank 50 may further be expanded in a process
which provides equal stress and strain on both sides of the
material to facilitate forming a flat sheet and to minimize curling
of the sheet upon heating.
[0078] The bottom element blank 50 can be formed from a single
layer of expanded core layer 302 or from the multi-layer material
300 comprising an expanded core layer 302 and an unexpanded skin
layer 304 on one or both sides of the expanded core layer 302. In
one exemplary embodiment, the bottom element blank 50 can be formed
from a single expanded core layer 302 made from an expanded high
melt strength polypropylene having a thickness in the range of
52-72 mils and a density of 11.5-12.5 lb/ft.sup.3. Alternatively,
the bottom element blank 50 can be made from a multi-layer material
300 comprising an expanded core layer 302 and a single unexpanded
core layer 304, the total thickness of the bottom element blank 50
in the range of 48-60 mils and having a density of 11.5-12.5
lb/ft.sup.3.
[0079] The expanded core layer 302, whether used alone as a single
layer or as part of a multi-layer material 300, preferably has a
normalized cell size, as measured by microscopy according to ASTM
method D3576-98 in the range of 300-500 micrometers, more
preferably in the range of 300-450 micrometers. Cell size in the
thickness dimension can be in the range of 150-200 micrometers
while cell size in the machine direction and the transverse (cross
direction) can be in the range of 500-980 micrometers and 350-500
micrometers, respectively. The preferred cell size aspect ratio in
the machine direction relative to the transverse direction is about
2 or less. The closed cell content as measured by pycnometer
according to ASTM method D6226-10 is at least 25%, preferably at
least 35%, more preferably at least 50% and still more preferably
at least 60%. The closed cell content can be selected based on the
intended use of the container 10. For example, if the container 10
is in the form of a hot beverage cup, such as would be used for
coffee or tea, the closed cell content is preferably at least
within the range of 35-40% to minimize leaching of the hot beverage
through the container.
[0080] The unexpanded skin layer 304 of the multi-layer material
300 which forms the exterior surface 18 of the container 10 can be
provided with properties to facilitate printing graphics on the
exterior surface 18. Preferably, the unexpanded skin layer 304
forming the exterior surface 18 has a smooth surface to facilitate
printing on as well as a gloss level in the range of 35-40 gloss
units or greater and/or an opacity of equal to or greater than
about 65%. The gloss level was determined using a gloss meter at a
60 degree measurement angle. The gloss meter was used to take a
gloss level measurement at multiple locations of the test sample
and the highest reading was recorded. The measurement values for
the gloss meter are related to the amount of reflected light from a
calibration standard for defining a standard gloss unit according
the instructions provided by the manufacturer of the gloss meter,
as is known in the art.
[0081] The multi-layer material 300 comprising a
polypropylene-based expanded core layer 302 and unexpanded skin
layer 304 can be used to form containers having stiffness and
thermal insulation characteristics comparable with a typical
expanded polystyrene foam container. In addition, forming both the
core and skin layers 302 and 304 of the multi-layer material 300
from a polypropylene-based base resin provides a material that can
provide fewer recycling challenges than a polystyrene based
material. High melt strength polypropylene-based materials which
are not cross-linked and do not include long chain branching, such
as FT3000 or BC3BRF from Japan Polypropylene Corp., can be re-used
or re-ground for repeated extrusion and expansion to provide an
expanded material having properties similar to the original
material without additional recycling additives (e.g.
anti-oxidation additives and/or thermal stabilizers). The use of a
high melt strength polypropylene-based material which is not
cross-linked and does not include long chain branching negates the
need to add recycling additives for the purposes of preventing
scission or damage of long chain branches or cross-linking during
re-grinding and pelletizing. FT3000, for example, can be re-used
multiple times to form an expanded material without recycling
additives to prevent scission or damage of long chain branches or
cross-linking. When the multi-layer material 300 includes
polypropylenes which are cross-linked and/or include long chain
branching, recycling additives (e.g. anti-oxidation additives, such
as IRGAFOS.RTM. 168, available from BASF, and/or thermal
stabilizers) can be used to prevent scission or damage of the long
chain branches or cross-linking during re-grinding and
pelletizing.
[0082] Referring now to FIG. 10, a process 400 for co-extruding the
multi-layer sheet 300 comprising an expanded core layer 302 and an
unexpanded skin layer 304 is illustrated in a tandem extrusion
line. The sequence of steps depicted for this process and any
process described herein is for illustrative purposes only, and is
not meant to limit the method in any way as it is understood that
the steps may proceed in a different logical order or additional or
intervening steps may be included without detracting from the
invention.
[0083] The process can begin at 402 by combining the base resin for
the expanded core layer 302 with the desired additives, such as a
nucleating agent, and then providing the blended resin to the
primary melting extruder 404. The blended resin is heated to form a
core layer plasticated mixture or melt that is moved through the
primary melting extruder 404. The blowing agent 406 is added to the
core layer melt to form an expandable mixture and the expandable
mixture is then transferred through a heated crossover 408 to a
secondary cooling extruder 410. When a physical blowing agent is
used, the blowing agent is mixed with the core layer melt at an
elevated pressure sufficient to prevent substantial expansion of
the melt and to disperse the blowing agent within the core layer
melt. The expandable mixture is then moved through the secondary
cooling extruder 410 to a heated die 412. A co-extruder 414 is
joined with the heated die 412 to provide a skin layer melt
comprising the base resin and the desired additives for the
unexpanded skin layer 304 to the heated die 412 for co-extrusion
with the expandable mixture from the secondary cooling extruder
410.
[0084] The expandable mixture and the skin layer melt are extruded
through the heated die 412 to form a multi-layer extrudate 416. The
heated die 412 can be a flat die that produces an extrudate sheet
or an annular die that extrudes a tube that is then slit to form a
sheet. When a physical blowing agent is used, the expandable
mixture and skin layer melt are extruded to a zone of lower
pressure sufficient to allow the blowing agent to generate a gas to
produce cells within the extruded expandable mixture to form the
expanded foam material. When a chemical blowing agent is used, the
expandable mixture and skin layer melt can be extruded to a zone of
elevated temperature such that the blowing agent can decompose and
generate a gas to produce cells within the extruded expandable
mixture to generate the expanded foam material. The multi-layer
extrudate 416 can then be cooled on a cooling mandrel 418 to form
the multi-layer sheet 300 having an expanded core layer 302 and
unexpanded skin layer 304 which can be wound on a winder at 420 for
storage and later use in forming the bottom element blank 50 and
the sleeve blank 52 for forming the container 10.
[0085] Alternatively, rather than co-extruding the expanded core
layer 302 and the unexpanded skin layer 304, the layers 302 and 304
can be formed separately and combined using a lamination or
extrusion coating process to form the multi-layer sheet 300. The
lamination process can include the use of heat, pressure and/or
adhesives to facilitate adhering the expanded core layer 302 and
the unexpanded skin layer 304 together to form the multi-layer
sheet 300.
[0086] While the co-extrusion process 400, extrusion coating
process, and lamination process are described in the context of a
multi-layer material 300 having an expanded core layer 302 and a
single unexpanded skin layer 304, it will be understood that the
co-extrusion process 400, extrusion coating process, and lamination
process can be used in a similar manner to form a multi-layer
material 300 having more than one unexpanded skin layer 304 on one
or both sides of the expanded core layer 302. The unexpanded skin
layer(s) 304 can act as a gas barrier to maintain the blowing agent
content within the expanded core layer 302 during any secondary
expansion that may occur during or after the thermoforming process.
The unexpanded skin layer(s) 304 can also increase the overall
stiffness and strength of the multi-layer material 300.
Examples
[0087] The following examples illustrate embodiments of the present
invention and are not necessarily representative of the full scope
of the present invention.
[0088] Example cups were made according to the embodiments of the
invention in a 16 fluid ounce and 20 fluid ounce size. The Example
cups had a side wall made from a multi-layer polypropylene-based
material that included an expanded core layer made using DAPLOY.TM.
WB140 and a co-extruded unexpanded skin layer made using
BC3BRF.
[0089] Comparative 16 fluid ounce and 20 fluid ounce cups are
commercially available cups and are made from an expanded
polypropylene-based material that does not include a co-extruded
unexpanded skin layer.
Methods
[0090] The weight and side wall thickness for the 16 and 20 ounce
size Example and Comparative cups was determined based on an
average of the measurements for 3 different cups for each sample.
The flush fill volume was determined for the 16 and 20 ounce
Example and Comparative cups based on the volume of water required
to fill the cup flush with the upper edge of the lip of the cup.
The average flush fill volume was determined based on the
measurements for 3 different cups for each sample.
[0091] The side wall deflection test is indicative of the strength
of the side wall of the cup. The side wall deflection test measures
the peak kilogram force during deflection of the cup side wall by
0.25 inches. The cup is filled with hot water at a temperature of
190.degree. F..+-.5.degree. F. to a fill level 1/2'' below the lip
of the cup. The cup is placed on a sliding gauge table that slides
the force gauge sensor towards the cup at 7 inches/min. A force
gauge with a 10 lb capacity was used. Deflection measurements were
determined at 120 degree intervals around the circumference of the
cup side wall below the lip of the cup for a total of 3
measurements per cup. The deflection force values increase with
increasing strength of the side wall.
TABLE-US-00002 TABLE 2 Comparison of 16 oz. cups*. Example 16 oz.
cup Comparative 16 oz. cup Average weight (g) 9.69 12.04 Side wall
thickness 0.052 0.064 (inches) Average 0.25'' deflection 0.304
0.384 force (kgF) Average flush fill volume 16.4 17.1 (oz.)
*Results based on the statistical average for 25 cup samples per
Example and Comparative group.
TABLE-US-00003 TABLE 3 Comparison of 20 oz. cups*. Example 20 oz.
cup Comparative 20 oz. cup Average weight (g) 12.59 13.73 Side wall
thickness 0.057 0.068 (inches) Average 0.25'' deflection 0.484
0.395 force (kgF) Average flush fill volume 20.6 20.5 (oz.)
*Results based on the statistical average for 25 cup samples per
Example and Comparative group.
[0092] Tables 4 and 5 below compare the insulation characteristics
for the 16 and 20 ounce Comparative cups and the 16 oz. Example
cup. The insulation characteristics are determined by measuring a
temperature of a liquid inside the cup and a temperature of an
exterior surface of a side wall of the cup at predetermined time
intervals after the cup is filled with hot water at a temperature
of 190.degree. F..+-.5.degree. F. to a fill level 1/2'' below the
lip of the cup.
TABLE-US-00004 TABLE 4 Internal temperature for Example and
Comparative cups. Elapsed time Comparative Comparative Example
(min.) 16 oz. cup 20 oz. cup 16 oz. cup 0 185.0 186.0 185.9 10
170.4 171.4 171.7 20 159.2 160.3 161.0 30 149.9 150.9 151.9 40
142.0 142.8 143.9 45 138.5 139.2 140.3
TABLE-US-00005 TABLE 5 External temperature for Example and
Comparative cups. Elapsed time Comparative Comparative Example
(min.) 16 oz. cup 20 oz. cup 16 oz. cup 0 163.8 162.8 165.1 10
154.9 153.2 155.0 20 144.9 147.3 146.6 30 138.9 138.3 139.0 40
130.9 133.1 133.0 45 129.0 130.4 129.9
[0093] As illustrated in Tables 2 and 3, the Example 16 and 20
ounce cups are lighter and have a thinner side wall than the
corresponding Comparative 16 and 20 ounce cups while the strength
of the cup side wall (as indicated by the average 0.25'' deflection
force) is equivalent between the Example and Comparative cups. In
addition, as illustrated by the temperature data in Tables 4 and 5,
the Example cup has thermal insulation properties equivalent to the
Comparative cups. The test results indicate that the Example cups
including an expanded polypropylene-based core and unexpanded
polypropylene-based skin can provide equivalent strength and
thermal insulation properties in a cup that is lighter and has a
thinner cup side wall, which can provide savings in transportation
and storage costs. The weight of the cup can directly affect the
cost of transporting the cup and the raw material cost while
thickness of the side wall can affect the number of cups that can
be packed within a given space, which can effect both storage and
transportation costs.
[0094] FIGS. 11A and 11B illustrate a multi-layer material 500 that
is similar to the multi-layer material 300 of FIGS. 9A and 9B,
respectively, except for a low gloss unexpanded skin layer 504.
Therefore, elements of the multi-layer material 500 similar to
those of the multi-layer material 300 are labeled with the prefix
500. The multi-layer material 500 includes an expanded polymeric
layer 502 that can be the same as the expanded core layer 302
described herein. The multi-layer material 500 can include one or
more layers of the low gloss unexpanded skin layer 504 that can be
laminated, extrusion coated, or co-extruded with the core layer 502
in the same manner as described above for the multi-layer material
300.
[0095] As used herein, the term "low gloss" with respect to an
unexpanded polypropylene-based layer refers to a material having a
gloss level of about 18 gloss units or less as determined as a
percent of the reflection of incident light at an angle of 60
degrees with respect to the surface being measured. In a preferred
embodiment, the low gloss unexpanded skin layer 504 can have a
gloss level of 15 gloss units or less, 13 or even 10 gloss units or
less, depending on the desired aesthetic. A low gloss level of
about 15 gloss units or less generally correlates with a matte or
paper-like finish aesthetic.
[0096] The low gloss unexpanded skin layer 504 can be made from a
high melt strength polyolefin-based resin or resin blend having
long chain branching. Suitable high melt strength polyolefin-based
resin/blends have a melt flow rate at 230.degree. C. and 2.16 kg
load in the range of 1-13 g/10 min., preferably 2-9 g/10 min. The
melt tangent delta, as measured by dynamic mechanical analysis
using a parallel plate rheometer at 230.degree. C., 1% strain rate,
and 0.1 rad/s frequency, is in the range of 1-6, preferably
1.5-3.5. The melt tangent delta is the tangent of the phase angle
(the delay between the applied force and material response) and is
the ratio of loss to elasticity, sometimes also referred to as
damping. Unless otherwise specified, as used herein, the melt
tangent delta, is measured by dynamic mechanical analysis using a
parallel plate rheometer at 230.degree. C., 1% strain rate, and 0.1
rad/s frequency according to ASTM D4440-2015 or ISO 6721. Suitable
high melt strength polyolefin-based resin/blends further have a
melt complex viscosity, as measured by dynamic mechanical analysis
using a parallel plate rheometer at 230.degree. C., 1% strain rate,
and 0.1 rad/s frequency, in the range of 1980 to 12,000
Pascal-second (Pa.sec.), preferably 2,000-6,500 Pa.sec., even more
preferably 2,500-4,000 Pa.sec. Unless otherwise specified, the melt
complex viscosity, as used herein, is measured by dynamic
mechanical analysis using a parallel plate rheometer at 230.degree.
C., 1% strain rate, and 0.1 rad/s frequency according to ASTM
D4440-2015 or ISO 6721.
[0097] The preferred high melt strength polyolefin-based
resin/blend has a cross over point of melt elasticity modulus and
loss modulus, as measured by dynamic mechanical analysis using a
parallel plate rheometer at 230.degree. C. and 1% strain rate,
located between a frequency of 30-150 radians/second (rad/s) and
9,000-23,000 MPa, preferably located between a frequency of 35-120
rad/s and 9,500-18,000 MPa. The melt strength of the preferred high
melt strength polyolefin-based resin/blend, as measured by Rheotens
Force at 30 bar, is in the range of 6-40 cN, preferably 9-36 cN
according to ISO 16790. The preferred high melt strength
polyolefin-based resin/blend has a melting point of greater than
160.degree. C., preferably greater than 163.degree. C., more
preferably in the range of 163-168.degree. C., and a
crystallization temperature greater than 120.degree. C., preferably
greater than 125.degree. C., more preferably within the range of
127-135.degree. C. Suitable high melt strength polyolefin-based
resin/blends have a flexural modulus greater than 1200 Mpa,
preferably greater than 1700 Mpa.
[0098] An exemplary polyolefin-based resin for forming the low
gloss unexpanded skin layer 504 is DAPLOY.TM. WB140, available from
Borealis A/S, Denmark. In a preferred embodiment, the
polyolefin-based resin includes DAPLOY.TM. WB140 regrind from
previously extruded material that can include expanded and/or
unexpanded material. As used herein, regrind is a term that applies
to material that has been mechanically reduced in size to particles
that can be re-introduced into the processing stream for extrusion.
The source of the regrind can be pre-consumer waste, such as
process scrap or rejected parts, or recycled post-consumer waste.
In this example, material made from expanded and/or unexpanded
DAPLOY.TM. WB140, either pre- or post-consumer waste, can be
reground and used to co-extrude the low gloss unexpanded skin layer
504. The polyolefin-based regrind can be used in combination with
virgin material at a loading rate of up to 30 wt. % or more,
depending on the material and the desired gloss. Alternatively,
polyolefin-based resin for forming the low gloss unexpanded skin
layer 504 can be made from entirely virgin resin.
[0099] In a preferred example, the exemplary polyolefin-based resin
for forming the low gloss unexpanded skin layer 504 is a high melt
strength polypropylene with long chain branching, such as
DAPLOY.TM. WB140, that includes at least a portion of the material
from regrind of unexpanded and/or expanded DAPLOY.TM. WB140. In one
example, the polyolefin-based resin can include at least 30 wt. %
regrind of the high melt strength polypropylene with long chain
branching blended with virgin material of the same or different
resin. Regardless of the ratio of virgin high melt strength
polypropylene with long chain branching and regrind material, the
polyolefin-based resin for forming the low gloss unexpanded skin
layer 504 has a melt flow rate of 6-12 g/10 min., a tangent delta
of 2.0-4.0, and a melt complex viscosity of 2200-4200 Pa.sec.
[0100] In another example, the polyolefin-based resin for forming
the low gloss unexpanded skin layer 504 is a high melt strength
polypropylene blend of a long chain branched (LCB) polypropylene
with either a homopolymer or a co-polymer. Non-limiting examples of
such a high melt strength polypropylene blend include resins
identified by the trade name WAYMAX, available from Japan
Polypropylene Corp., such as grades MFX-3, MFX-6, or MFX-8, or
EX4000, EX6000, or EX8000, also available from Japan Polypropylene
Corp. The MFX family of materials are a long chain branched
polypropylene blended with polypropylene homopolymer, while the EX
family is a long chain branched polypropylene blended with a
polypropylene-based co-polymer. MFX-3 (also available under the
trade name X5258) has melt flow rate at 230.degree. C. and 2.16 kg
load of 8 g/10 min. and a melt tension of 5 g. MFX-6 has a melt
flow rate at 230.degree. C. and 2.16 kg load of 3 g/10 min. and a
melt tension of 13 g, while MFX-8 has a melt flow rate at
230.degree. C. and 2.16 kg load of 1 g/10 min. and a melt tension
of 24 g. EX8000 (also available under the trade name X5261) has a
melt flow rate at 230.degree. C. and 2.16 kg load of 1 g/10 min.
and a melt tension of 15 g. EX6000 (also available under the trade
name STH0817) has a melt flow rate at 230.degree. C. and 2.16 kg
load of 3 g/10 min. and a melt tension of 8 g, while EX4000 (also
available under the trade name X5259) has a melt flow rate at
230.degree. C. and 2.16 kg load of 6 g/10 min. and a melt tension
of 4 g.
[0101] In yet another example, the exemplary polyolefin-based resin
for forming the low gloss unexpanded skin layer 504 is a blend of a
polypropylene copolymer and a long chain branched low density
polyethylene (LDPE). The blend can have a melt flow rate of 6 g/10
min., a melt tangent delta of 1.6, a melt complex viscosity of 7600
Pa.sec. A suitable blend is commercially available from A.
Schulman, trade name DUL3636 DP20A, which is described as a blend
of a random polypropylene copolymer and a long chain branched LDPE.
The blend of a polypropylene copolymer and long chain branched LDPE
can be used alone or mixed with DAPLOY.TM. WB140 or another
polypropylene-based material having a high stiffness as
demonstrated by a high flexural modulus greater than 1200 Mpa.
[0102] The low gloss unexpanded skin layer 504 can include
additional additives, non-limiting examples of which include
colorants and opacifying additives. Examples of suitable opacifying
agents include 3-5 wt. % Ferro CH270432FDA masterbatch, titanium
dioxide, calcium carbonate, zinc sulfide, barium sulfate, and
antimony oxide.
[0103] Table 6 below illustrates melt tangent delta, melt complex
viscosity, and gloss level for unexpanded skin layers made from
various polyolefin-based resins. Melt tangent delta and melt
viscosity was determined as described above. The gloss level was
determined using a gloss meter at a 60 degree measurement angle.
The gloss meter was used to take a gloss level measurement at
multiple locations of the test sample and the highest reading was
recorded. The measurement values for the gloss meter are related to
the amount of reflected light from a calibration standard for
defining a standard gloss unit according the instructions provided
by the manufacturer of the gloss meter, as is known in the art. The
data in Table 6 was obtained using an Elcometer 406 60 degree micro
NOVO-GLOSS.TM. gloss meter or a BYK Gardner 60.degree. 4442
micro-gloss 60 degree gloss meter.
TABLE-US-00006 TABLE 6 Characteristics of Example Unexpanded Skin
Layers Melt Melt Complex Unexpanded Skin Polyolefin Tangent
Viscosity Gloss level Example Resin(s) Delta (Pa sec.) (gloss
units) Example 1 75% DUL3636 DP20A + 25% 1.98 5,794 6.5 Sukano
P-ma-S218.sup.1 Example 2 20% DUL3636 DP20A + 80% 3.52 2,639 7.2
DAPLOY .TM. WB140 Example 3 75% DUL3636 DP20A + 25% 2.17 6,982 7.3
HM10LC.sup.2 Example 4 DAPLOY .TM. WB140 (virgin) 3.01 3,411 7.5
Example 5 DUL3636 DP20A 1.76 6,252 7.5 Example 6 30% DUL3636 DP20A
+ 70% 3.84 2,715 8.1 WB140 Example 7 EX6000 2.10 6,804 8.4 Example
8 EX6000 (different batch than 2.95 3,327 8.8 Example 7) Example 9
30% DUL3636 DP20A + 70% 5.54 5,951 9 PP4712E1.sup.3 Example 10 40%
DUL3636 DP20A + 60% 2.92 3,048 9.6 PP4712E1.sup.3 Example 11 40%
DUL3636 DP20A + 60% 4.39 8,493 9.7 BB213CF.sup.4 Example 12 75%
DAPLOY .TM. WB140 2.92 3,497 10.5 (regrind) + 25% DUL3636 DP20A
Example 13 50% DAPLOY .TM. WB140 3.75 2,620 10.8 (regrind) + 50%
DAPLOY .TM. WB140 (virgin) Example 14 20% PP4712E1.sup.3 + 80% 3.08
4,476 11.2 DUL3636 DP20A Example 15 75% DAPLOY .TM. WB140 3.85
3,742 11.4 (regrind) + 25% PP4712E1.sup.3 Example 16 BB213CF.sup.4
3.93 11,990 12.2 Example 17 75% DAPLOY .TM. WB140 3.85 2,178 12.9
(regrind) + 25% DAPLOY .TM. WB140 (virgin) Example 18 EX4000 2.69
3,519 13.4 Example 19 30% DUL3636 DP20A + 70% 4.34 9,315 13.4
BB213CF.sup.4 Example 20 DAPLOY .TM. WB140 (regrind) 4.97 1,981
13.7 Example 21 DAPLOY .TM. WB140/DUL3636 3.98 2,535 15 DP20A
(regrind).sup.5 Example 22 90% DAPLOY .TM. WB140 4.01 2,657 15
(regrind) + 10% DAPLOY .TM. WB140 (virgin) Example 23 80% DAPLOY
.TM. WB140 3.75 2,773 15 (regrind) + 20% DAPLOY .TM. WB140 (virgin)
Example 24 70% DAPLOY .TM. WB140 3.84 2,417 15 (regrind) + 30%
DAPLOY .TM. WB140 (virgin) Example 25 20% DUL3636 DP20A + 80% 3.30
2,485 16 DAPLOY .TM. WB140 Example 26 20% DUL3636 DP20A + 80% 7.17
4,751 16 PP4712E1.sup.3 Example 27 30% DUL3636 DP20A + 70% 6.26
4,315 16 PP4712E1.sup.3 Example 28 30% DUL3636 DP20A + 70% 3.76
2,788 16.1 DAPLOY .TM. WB140 Example 29 PP4712E1.sup.3 5.54 5,962
16.7 Example 30 EX8000 2.33 4,946 16.8 Example 31 Polyone 158119
MATPP.sup.6 0.87 12,770 17.2 Example 32 40% DUL3636 DP20A + 60%
5.44 4,885 17.6 PP4712E1.sup.3 Example 33 50% DUL3636 DP20A + 50%
4.91 2,457 20.1 PP4712E1.sup.3 Example 34 PP22524E.sup.7 10.21
3,200 22.4 Example 35 C7054-07NA.sup.8 7.51 3,035 22.6 Example 36
75% DAPLOY .TM. WB140 3.59 4,915 22.9 (regrind) + 25% BB213CF.sup.4
Example 37 Exxon HMS.sup.9 2.67 9,824 23.1 Example 38
BE170CF.sup.10 (Borealis 10.76 1,342 24.2 copolymer) Example 39
BC3BRF 6.66 1,629 24.4 Example 40 DAPLOY .TM. WB140 (regrind) 4.39
2,351 26.8 Example 41 DAPLOY .TM. WB140 (foam 4.59 2,206 28.6
regrind) Example 42 Braskem D115A.sup.11 20.80 1,351 29.1 Example
43 50% DAPLOY .TM. WB140 4.43 4,730 39.3 (regrind) + 50%
PP4712E1.sup.3 Example 44 Borealis HD905CF.sup.12 6.13 3,392 49.1
Example 45 Borealis BD712CF.sup.13 7.03 2,492 58.3 .sup.1Sukano
P-ma-S218 is a talc-based masterbatch matting agent for
polypropylene available from Sukano Products Ltd., Switzerland.
.sup.2HM10LC is a CaCO.sub.3 masterbatch for polypropylene
available from Heritage Plastics, U.S.A. .sup.3P4712E1 is an
oriented film grade polypropylene homopolymer having a melt flow
rate at 230.degree. C. and 2.16 kg load of 2.8 g/10 min., available
from ExxonMobil .TM., U.S.A. .sup.4BB213CF is a film grade
heterophasic polypropylene copolymer available from Borealis.
.sup.5A mixture of regrind from 75/25, 60/40, 45/55 DAPLOY .TM.
WB140/DUL3636 DP20A scraps. .sup.6Polyone 158119 MATPP is a matting
agent containing a talc-based mineral filler and rubber/elastomer,
available from Polyone Corp., U.S.A. .sup.7PP2252E4 is a
polypropylene homopolymer having a melt flow rate at 230.degree. C.
and 2.16 kg load of 4.2 g/10 min., available from ExxonMobil .TM.,
U.S.A. .sup.8C7054-07NA is a polypropylene-based impact copolymer
having a melt flow rate at 230.degree. C. and 2.16 kg load of 4.2
g/10 min., available from Braskem. .sup.9Exxon HMS is a high melt
strength development grade polypropylene from ExxonMobil .TM.,
U.S.A. having a melt flow rate at 230.degree. C. and 2.16 kg load
of 2 g/10 min., a melt strength as measured by Rheotens Force at 30
bar in the range of 20-25 cN, and a PDI >8. .sup.10BE170CF is a
polypropylene-based copolymer available from Borealis. .sup.11D115A
is a polypropylene homopolymer without a crystalline nucleation
additive having a melt flow rate at 230.degree. C. and 2.16 kg load
of 11 g/10 min., available from Braskem. .sup.12HD905CF is high
crystalline polypropylene homopolymer having a melt flow rate at
230.degree. C. and 2.16 kg load of 6.5 g/10 min. and high
stiffness, available from Borealis. .sup.13BD712CF is a
heterophasic polypropylene-based copolymer having a melt flow rate
at 230.degree. C. and 2.16 kg load of 13 g/10 min., available from
Borealis.
[0104] FIG. 12 illustrates the relationship between the melt
tangent delta and the melt complex viscosity of the
polyolefin-based resin for forming a low gloss unexpanded skin
layer of Examples 1-32 of Table 6 which have a gloss level of about
18 gloss units or less. As demonstrated by the data in FIG. 12,
materials having a gloss level of about 18 or less generally had a
melt tangent delta in the range of 1 to 8 and a melt complex
viscosity in the range of 1980 to 13,000 Pa.sec. Preferred
materials having a gloss level of about 16 or less generally had a
melt tangent delta in the range of 1 to 6, preferably in the range
of 1.5 to 3.5, and a melt complex viscosity in the range of 2000 to
6500 Pa.sec., preferably in the range of 2000-4000 Pa.sec.
[0105] FIG. 13 illustrates a process 700 for co-extruding the
multi-layer sheet 500 comprising an expanded core layer 502 and at
least one low gloss unexpanded skin layer 504 made using a
polyolefin-based resin comprising at least a portion of regrind
material. The process for forming the multi-layer sheet 500 is
similar to the process 400 for forming the multi-layer sheet 300
except for the formation of the low gloss unexpanded skin layer
504. Therefore, steps in the process 700 similar to those of the
process 400 are labeled with the prefix 700.
[0106] The process can begin at 702 by combining the base resin for
the expanded core layer 502 with the desired additives, such as a
nucleating agent, and then providing the blended resin to the
primary melting extruder 704. The resin supplied to the primary
melting extruder 704 can include virgin resin or a mixture of
virgin and regrind resin. As is described in more detail below,
regrind material can be provided at 722 such that at least a
portion of the blended resin provided to the primary melting
extruder 704 comprises a regrind material. The blended resin is
heated to form a core layer plasticated mixture or melt that is
moved through the primary melting extruder 704. The blowing agent
706 is added to the core layer melt to form an expandable mixture
and the expandable mixture is then transferred through a heated
crossover 708 to a secondary cooling extruder 710. When a physical
blowing agent is used, the blowing agent is mixed with the core
layer melt at an elevated pressure sufficient to prevent
substantial expansion of the melt and to disperse the blowing agent
within the core layer melt. The expandable mixture is then moved
through the secondary cooling extruder 710 to a heated die 712. A
co-extruder 714 is joined with the heated die 712 to provide a skin
layer melt comprising the base resin and the desired additives for
the low gloss unexpanded skin layer 504 to the heated die 712 for
co-extrusion with the expandable mixture from the secondary cooling
extruder 710.
[0107] The co-extruder 714 is provided with a high melt strength
polypropylene-based resin comprising at least a portion of regrind
material at 715. In a preferred embodiment, the high melt strength
polypropylene regrind is obtained from pre- or post-consumer waste
regrind from a previously formed multi-layer sheet 500 including an
expanded core layer 502 and a low gloss unexpanded skin layer 504.
Alternatively, the regrind can be from a previously formed expanded
core layer 502 that does not include a low gloss unexpanded skin
layer 504. Preferably, the material used in the regrind at 715 has
the same formulation as the layers 502 and/or 504 of the
multi-layer sheet 500 of the current process 700. However, it is
within the scope of the invention for the material used in the
regrind at 715 to have a different formulation than that of the
current process 700.
[0108] The expandable mixture and the skin layer melt are then
extruded through the heated die 712 to form a multi-layer extrudate
716. The heated die 712 can be a flat die that produces an
extrudate sheet or an annular die that extrudes a tube that is then
slit to form a sheet. The multi-layer extrudate 716 can then be
cooled on a cooling mandrel 718 to form the multi-layer sheet 500
having an expanded core layer 502 and low gloss unexpanded skin
layer 504 which can be wound on a winder at 720 for storage and
later use in forming sleeve and/or bottom element blanks for use in
forming a container. As indicated at 724, scraps and/or waste from
the co-extrusion and expansion process forming the multi-layer
sheet 500 can be collected and provided as regrind at 715 and/or
722. It is within the scope of the invention for one or both of the
expanded core layer 502 and/or low gloss unexpanded skin layer 504
to be made from material comprising at least a portion of regrind
material.
[0109] When producing a multi-layer sheet 500 for use in forming
containers, such as a cup, the low gloss unexpanded skin layer 504
has a thickness in the range of 1-3 mils, preferably 1.5-2.2 mils,
and more preferably 1.7-2 mils. The total thickness of the
multi-layer sheet 500 is typically about 55 mils or greater,
preferably 60-70 mils, and more preferably 64-68 mils for use in
forming cups and other containers. In a preferred embodiment, a
total thickness of the multi-layer sheet 500 is 66+/-4 mil. The
multi-layer sheet 500 can have a base weight of 12.48+/-1.0 g per
60 square inches and a density of about 10-13 lb/ft.sup.3.
[0110] While the process 700 is described in the context of using a
regrind material to form the low gloss unexpanded skin layer 504,
the process 700 can be used in a similar manner to form a
multi-layer sheet 500 having a low gloss unexpanded skin layer 504
made using only virgin material. For example, as described above, a
low gloss unexpanded skin layer 504 can also be formed by providing
a blend of a polypropylene copolymer and a long chain branched
LDPE, such as DUL 3636 DP20A, or virgin DAPLOY.TM. WB140 at
715.
[0111] FIG. 14 illustrates a cup 810 that is similar to the cup 10
of FIG. 1 except for the structure of the bottom element and the
stacking element. Therefore, elements of the cup 810 similar to
those of cup 10 are labeled with the prefix 800. The cup 810 is an
example of a container that can be formed using the multi-layer
sheet 500, although it is understood that the uses of the
multi-layer sheet 500 are not limited to the cup 810. It is further
understood that the cup 810 can also be formed using the
multi-layer sheet 300 or a combination of the multi-layer sheets
300 and 500.
[0112] Still referring to FIG. 14, the cup 810 includes a sleeve
813 having a peripheral wall 814 and a bottom element 830 for
closing off the lower end of the container 810. The bottom element
830 includes a floor 832 having a lower surface 834 facing away
from the cavity 812 and an upper surface 836 facing the cavity 812,
with the floor 832 providing the bottom element 830 with a slightly
upwardly bowed cross-section (shown) or a generally flat
cross-section. The sleeve 813 includes a flange 840 that extends
from the lower end 822 of the peripheral wall 814 which extends
inward and is attached to the lower surface 834 of the bottom
element 830 using a heat seal and/or an adhesive.
[0113] The cup 810 includes a stacking element 838 in an upper
portion of the cup 810 in the form of a shoulder 860 formed in the
peripheral wall 814 near the upper end 820. The dimensions of the
shoulder 860 and the taper angle of the peripheral wall 814 above
and below the shoulder 860 can be configured such that a first cup
810 can be inserted into a second cup 810 until the shoulder 860 of
the first cup abuts the lip 824 of the second cup. The shoulder 860
limits the extent to which a first cup 810 can be inserted into a
second cup 810 to facilitate removal or de-nesting of a cup 810
from a stack of similar nested cups 810.
[0114] The cup 810 can be formed from body blanks made from the
multi-layer sheet 500 in a manner similar to that described above
for forming the cup 10. Referring to FIG. 15, the cup 810 can be
formed from a sleeve blank 854 in a manner similar to that
described with respect to the sleeve blank 54 of FIGS. 4A-4B.
Similarly, the cup 810 can be formed from a bottom element blank
850 in a manner similar to that described with respect to the
bottom element blank 50 of FIGS. 3A-3B. Therefore, elements of the
bottom element blank 850 and sleeve blank 854 similar to those of
the bottom element blank 50 and sleeve blank 54 are labeled with
the prefix 800. The sleeve 813 can be formed by cutting the sleeve
blank 854 from the multi-layer sheet 500 and, optionally, the
bottom element 830 can also be formed by cutting the bottom element
blank 850 from the multi-layer sheet 500. Alternatively, as
discussed above with respect to the bottom element 30 of the cup 10
of FIGS. 1-2, the bottom element 830 can be made from a single
layer of expanded material, such as the expanded core layer 502
rather than the multi-layer sheet 500. When the bottom element 830
is made from an expanded core layer 502, the bottom element 830 can
be configured to have the same thickness and base weight as the
multi-layer sheet 500 used to form the sleeve 813. For example, the
single layer bottom element 830 and multi-layer sleeve 813 can have
a thickness of 66+/-4 mil and a base weight of 10.48+/-1.0 g per 60
square inches. The bottom element blank 850 and the sleeve blank
854 can then be assembled to form a cup according to either of the
processes 100 of FIG. 5, 200 of FIG. 7, 900 of FIG. 15, or an
alternative process.
[0115] FIG. 18 illustrates a process 900 for using the multi-layer
sheet 500 to form a container, such as the cup 810, having a low
gloss unexpanded skin layer 504 made using a blend of virgin and
regrind material. The process 900 can be used alone or in
combination with the process 700 of FIG. 13. While the process 900
is described in the context of forming the two-piece cup 810
illustrated in FIG. 14, it will be understood that the multi-layer
sheet 500 can be used in a similar manner to form any type of
container having a low gloss unexpanded skin layer, non-limiting
examples of which include the two-piece cup 10 of FIGS. 1-4. In
another example, the container may be in the form of any one or
two-piece cup known in the art, non-limiting examples of which
include: a one-piece cup, such as that disclosed in U.S. Pat. No.
3,854,583 to Amberg et al., issued Dec. 17, 1974; a two-piece
disc-bottom type cup, such as that shown in U.S. Pat. No. 3,854,583
to Amberg et al., issued Dec. 17, 1974 or PCT Application WO
86/06045 to Baker, published Oct. 23, 1986, in which the cup bottom
is in the form of a disc and the bottom edges of the cup sleeve are
folded under and sealed with an underside of the disc; and a
pot-bottom type cup in which the cup bottom is in the form of a
disc having a downwardly extending skirt about which the bottom
edges of the cup sleeve are folded around and sealed with, such as
that shown in U.S. Pat. No. 3,658,615 to Amberg, issued Apr. 25,
1972, all of which are herein incorporated by reference in their
entirety.
[0116] Still referring to FIG. 15, the process 900 for forming the
cup 810 begins at 902 with providing a multi-layer sheet 500 having
a low gloss unexpanded skin layer 504 and an expanded core layer
502 made according to the process 700 of FIG. 13. While the process
900 is described in combination with the low gloss unexpanded skin
layer 504, it will be understood that the process 900 can be used
independently of the process 700 in the context of using regrind
material in the formation of the low gloss unexpanded skin layer
504.
[0117] At 904, die punches can be used to punch the sleeve blank
854 and the bottom element blank 850 from a suitable sheet of
material. The sleeve blank 854 and the bottom element blank 850 can
both be punched from the multi-layer sheet 500. Alternatively, it
is also within the scope of the invention for the sleeve blank 854
to be punch from the multi-layer sheet 500 and for the bottom
element blank 850 to be punched from a different material, such as
a single layer of expanded material. In a preferred embodiment, the
bottom element blank 850 can be punch from a single layer of
expanded material that is the same as the expanded core layer 502
of the multi-layer sheet 500 used to form the sleeve blank 854. In
this embodiment, although the bottom element blank 850 is formed
from a different sheet than the sleeve blank 854, the blanks 850,
854 include the same expanded core layer 502 and thus scrap and/or
waste from the process 900 can still be used to form regrind
material for use in producing the expanded core layer 502 alone or
in combination with the unexpanded skin layer 504 to form the
multi-layer sheet 500.
[0118] The body blanks can be provided to a suitable cup forming
apparatus for forming the cup 810 from the sleeve blank 854 and the
bottom element blank 850 at 906. In one embodiment, the cup forming
apparatus can include a plurality of turrets to move the body
blanks through a series of stations to form the cup 810. For
example, the sleeve blank 854 is provided on a transfer turret and
the bottom element blank 850 is provided on a main turret and both
the transfer and main turrets are indexed into position under a
seam heater(s) to heat the side edges 856, 858 of the sleeve blank
854. Both turrets are then indexed to a folding wing station in
which the sleeve blank 854 is folded around the mandrel on the main
turret and a seam clamp is used to apply localized pressure to the
overlapping side edges 856, 858 of the sleeve blank 854 to form a
liquid-tight peripheral wall seam. The main turret with the sleeve
blank 854 and bottom element blank 850 is then indexed into
position with a first bottom heater to heat the edges of the bottom
element blank 850. The main turret is then moved into position with
a second bottom heater and two additional heaters placed above and
below the sleeve blank 854. The main turret is then indexed into
position in a bottom forming station where a spinning tool strokes
in and folds the bottom edge 840 of the sleeve blank 854 inward
over the bottom element blank 850. The main turret indexes again
into position with a second bottom forming station in which a tool
strokes in and sets the bottom of the cup 810 by applying pressure
to the overlapping bottom edge 840 of the sleeve blank 854 and the
bottom element 850 to form a shell.
[0119] The main turret can index to a transfer station to transfer
the formed shell from the main turret to a pocket turret using air
for subjecting the shell to additional process steps to form the
final cup structure, such as brim forming at 908, stacking feature
formation at 910, and printing at 912. For example, at 908, the
pocket turret can index to a tamp/lube station where the shell is
seated into the pocket and a lubricant or slipping agent,
non-limiting examples of which include mineral oil and silicon oil,
is applied around the upper edge 820 of the shell. The pocket
turret then indexes to a pre-curling station in which a pre-curler
to initiate the curl in the upper edge 820 of the shell. The pocket
turret indexes again to a pre-curling heating station where heat is
applied to the upper edge 820 of the shell in preparation for the
final curling process. The pocket turret then indexes to a top curl
station where the upper edge curl is finished to form the final
rolled lip 824.
[0120] An example of a stacking feature that can be formed at 910
is the stacking element 838 formed in the peripheral wall 814. The
shell can be inserted into a heated mold using air cylinders to
tamp the shell into place and held in position within the mold by
vacuum. A heated plug can then be lowered inside the opening 826 of
the cup 810 to thermoform the shoulder 860 into the area of the
peripheral wall 814 below the lip 824. The cup bottom 830 can be
heated and ironed while the cup 810 is in the heated mold to
flatten and smooth the surface.
[0121] At 912, the multi-layer sheet 500 used to form the container
810 can be printed on prior to forming the container 810 or after
the container 810 is formed in a manner similar to that described
above for the sleeve blank 52 and bottom element blank 50 used to
form the container 10 of FIGS. 1-2. When the multi-layer sheet 500
is printed on prior to forming the body blanks at 904, the thus
printed sheet can be used immediately to form the sleeve blank 854
and/or bottom element blank 850 or wound onto a roll for storage.
Generally only the multi-layer sheet 500 used to form the sleeve
blank 854 is printed on, however, it is within the scope of the
invention for the material used to form the bottom element blank
850, whether it be the multi-layer sheet 500 or a sheet of a single
layer of the expanded core 502, to also be printed on prior to
cutting the blanks at 904.
[0122] Alternatively, after the container 810 is formed, the
container 810 can be fed into a conical container printer using a
feed screw system that places the container 810 on print mandrels.
Each print mandrel is indexed to a pretreat system for surface
treatment of the peripheral wall 814 and then indexed into the
print position. At the print position, the side wall 14 can be
printed on using a dry offset printing process with UV paste ink,
for example. After printing, the container 810 is indexed into a
curing position where the print mandrels are rotated in front of a
UV light source to cure the ink. Once cured, the mandrels are
indexed to an out-feed position and the containers 810 can be
nested into stacks for storage.
[0123] At 914, any scrap or waste generated during the process 900
can be collected and used to form regrind material at 916 for use
in forming a new multi-layer sheet 500 by providing the regrind
material to steps 715 and/or 722 of the process 700 of FIG. 13. The
material collected during the process 900 can be used alone or in
combination with material collected from the process 700 to form
regrind material for use in forming the multi-layer sheet 500. For
example, scrap left over from cutting the body blanks at 904, scrap
or waste left over from the printing process at 903 or 910, and/or
defective body blanks formed at 904 can be collected at 914 for use
in forming the regrind material 916. Defective cups from any of the
steps 908, 910, and/or 912 can also optionally be collected and
used to form the regrind material at 916. The process 900 of
forming a cup from a material formed according to the process 700
and then providing scrap and/or waste collected during the cup
forming process of 900 back to the process 700 for use in forming
the low gloss unexpanded skin layer 504 and/or the expanded core
layer 502 can be repeated one or more times.
[0124] The low gloss unexpanded skin layer 504 described herein
provides a surface having a finish which can satisfy the desire for
a low gloss or matte finish in the container industry and in
particularly with respect to containers used in food service. When
the low gloss unexpanded skin layer 504 has a gloss level of about
18 gloss units or less, the article is provided with a "paper-like"
finish that has sufficient smoothness for printing on. The low
gloss unexpanded skin layer 504 based on polyolefin resins as
described herein can also provide sufficient strength and stiffness
suitable for use in hot food service applications (such as hot
beverages like tea and coffee), as well as provide the benefits of
a low density and light weight material which provides good
insulation.
[0125] One alternative method for providing a low gloss surface is
to incorporate a filler, such as talc, calcium carbonate, or mica,
for example. In general, as the amount of filler is increased, the
gloss level decreases. However, increasing the filler loading can
undesirably increase the density and/or weight of the final
product. In addition, when the low gloss material is used to
produce regrind that is used to form an expanded material, the
increased filler loading can negatively effect the foam nucleation
process, resulting in an expanded material that does not have the
desired characteristics. Another alternative is to incorporate an
elastomeric rubber material. However, this can reduce the flexural
modulus and heat distortion temperature of a polypropylene-based
expanded material, which can negatively effect the applicability of
the material in hot food service applications. Alternative
processes for decreasing the gloss of polymeric surfaces, such as
texturizing the surface of the mold used to form an article are not
applicable in the present case because the extrusion expansion
process is a free surface process in which the skin layer is not in
contact with a hard or cold surface.
[0126] In contrast, the embodiments of the present invention
provide materials and processes for forming a multi-layer article
having an unexpanded skin layer having a desired low gloss level
that is useful for forming containers and in particular containers
used in the food service industry, including both hot and cold
materials. The materials useful in forming a low gloss unexpanded
skin layer having a gloss level of about 18 gloss units or less are
polypropylene-based resins which either alone or when blended with
another polymeric material have a melt tangent delta in the range
of 1-6 in combination with a melt complex viscosity in the range of
1980-12,000 Pa.sec. Suitable materials are further defined as
having a melt flow rate of 2-10 g/10 min., a cross over point of
melt elasticity modulus and loss modulus located between a
frequency of 30-150 radians/second (rad/s) and 9,000-23,000 MPa, a
flexural modulus greater than 1200 Mpa, and/or a melt strength of
6-40 cN.
[0127] The embodiments of the invention can provide a low gloss
unexpanded skin layer with little to no filler or elastomeric
rubber material provided in the skin layer, thus avoiding or
minimizing the impact these materials can have on the skin layer,
such as an increase in the density and/or weight of the layer and
reductions in the flexural modulus and/or heat distortion
temperature of the skin layer. In addition, increasing the amount
of filler in the low gloss layer can negatively impact process
control and product quality when the low gloss layer is used to
form a regrind material that is used in a subsequent foaming
process. For example, the regrind material having a high filler
content can be difficult to use in forming an expanded material due
to over nucleation and lack of uniformity in cell structure. The
embodiments of the invention can avoid or minimize these effects by
using little to no filler in the low gloss unexpanded skin
layer.
[0128] In addition, the embodiments of the present invention can
take advantage of using scrap and/or waste regrind in forming the
low gloss unexpanded skin layer as well as when forming the
multi-layer sheet having both an unexpanded and expanded layer made
at least in part from regrind materials. As discussed above, both
the unexpanded skin layer 504 and the expanded core layer 502 can
be based on the same polyolefin resin, such as high melt strength
polypropylene having long chain branching, an example of which is
DAPLOY.TM. WB140, scrap and/or waste from the multi-layer sheet and
any article formed from the multi-layer sheet, can be used to
produce regrind that can subsequently be used to form an unexpanded
and/or expanded layer of a new multi-layer sheet. As illustrated in
Table 6, virgin and regrind material can be combined to form a low
gloss unexpanded layer. See for example, Examples 17 and 22-24 of
Table 6.
[0129] The embodiments of the invention described herein provide an
expanded polypropylene container which can be used as an
alternative to traditional expanded polystyrene containers. The
multi-layer materials 300, 500 comprising an expanded core layer
302, 502 and at least one unexpanded skin layer 304, 504 can be
used to form a container having the desirable characteristics
typically associated with expanded polystyrene containers, such as
uniform closed cells, flexibility and a cell size and density in
the thickness direction that is similar to expanded polystyrene to
minimize liquid leaching through the container walls.
[0130] Another potential feature of a container formed from the
multi-layer materials 300, 500 described herein is that the article
can be recycled. Recyclable means that a material can be added back
into an extrusion or other process without segregation of
components of the material, meaning that a container formed of the
material does not have to be manipulated to remove one or more
materials or components prior to re-entering the extrusion process.
Because both the expanded core layer 302, 502 and unexpanded skin
layer(s) 304, 504 of the multi-layer material 300, 500 are made
from polypropylene-based materials, the containers made from such
materials can be recycled and used to form regrind for use in
forming new expanded core and/or unexpanded skin layers without
having to segregate the components of the layers. In addition,
containers made from the exemplary multi-layer materials can be
recycled in existing polypropylene recycling facilities, which can
often be more readily accessible to consumers than polystyrene
recycling facilities.
[0131] The combination of the unexpanded skin layer 304, 504
co-extruded with the expanded core layer 302, 502 provides a
container having an exterior surface (the unexpanded skin layer
304, 504) which can be directly printed on without the use of
additional films or laminates which can separate from the container
over time or under certain conditions. The co-extruded skin layer
304, 504 improves the strength of the container as well as provides
an exterior surface layer that does not separate from the rest of
the container. In addition, printing directly onto the co-extruded
skin layer can save time and money by avoiding additional film and
laminating steps. Avoiding the use of adhesive or tie layers
between the unexpanded skin layer 304, 504 and expanded core layer
302, 502 can also reduce the risk of contamination during the
polypropylene recycling process of the containers made from the
multi-layer materials described herein.
[0132] The multi-layer materials 300, 500 described herein can also
be used to form a two-piece cup having a stacking element 38 to
facilitate de-nesting of stacked containers. Methods for providing
a stacking feature in the lower portion of an expanded polystyrene
cup typically include thermoforming or mechanically forming lugs in
the peripheral wall of the container. These processes can damage
the expanded polypropylene material used in the embodiments of the
invention, which could result in leakage through the walls and
seams of the container. The embodiments of the invention described
herein use the bottom element 30 to provide the stacking element
38, without deforming or damaging the container peripheral wall 14.
In addition, the use of a flat bottom-type design, in which the
bottom element 30 has a slightly bowed or generally flat
cross-section, instead of a pot-type or wet bottom design in which
the cup bottom has a downward extending flange about which the
bottom edge of the peripheral wall wraps around provides material
and assembly cost savings.
[0133] To the extent not already described, the different features
and structures of the various embodiments of the invention may be
used in combination with each other as desired. That one feature
may not be illustrated in all of the embodiments is not meant to be
construed that it cannot be, but is done for brevity of
description. Thus, the various features of the different
embodiments may be mixed and matched as desired to form new
embodiments, whether or not the new embodiments are expressly
described.
[0134] While the invention has been specifically described in
connection with certain specific embodiments thereof, it is to be
understood that this is by way of illustration and not of
limitation. Reasonable variation and modification are possible
within the scope of the forgoing disclosure and drawings without
departing from the spirit of the invention which is defined in the
appended claims.
* * * * *