Note: Descriptions are shown in the official language in which they were submitted.
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PAPERBOARD, PAPERBOARD CONTAINER, AND
METHOD FOR USING A PAPERBOARD ARTICLE
FIELD
[0001] This application relates to polymer coated paperboard and, more
particularly, to
polymer coated paperboard that can be converted into containers suitable for
food heating or
cooking by way of microwave radiation.
BACKGROUND
[0002] Extrusion coating of low-density polyethylene was first used to coat
butcher paper in
the 1950s, and low-density polyethylene is widely used as a barrier coating
for hot and cold
beverage cups and in a variety of other applications.
[0003] Polypropylene resin has been used in all-plastic containers for
microwave heating of
foods. Polypropylene coated paperboard can be converted into containers or
cups suitable for
food heating or cooking by way of microwave radiation. However, the extrusion
coating of
polypropylene onto paperboard and the converting of the polypropylene coated
paperboard
into containers and cups has created challenges for the paperboard industry.
To address the
challenges with extrusion coating of polypropylene onto paperboard and
converting of the
polypropylene coated paperboard, a mixture of polypropylene with 20% low-
density
polyethylene is coated on paperboard to make polymer coated paperboard that
can be
converted into containers suitable for food heating or cooking by way of
microwave
radiation.
[0004] Those skilled in the art continue with research and developments
efforts in the field
of polymer coated paperboard.
SUMMARY
[0005] In one aspect, the disclosed method for using a paperboard article
includes heating a
paperboard article by way of microwave radiation. The paperboard article
includes a
paperboard substrate having a first major side and a second major side and one
or more high-
density polyethylene layers on at least one of the first major side and the
second major side of
the paperboard substrate.
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[0006] In another aspect, the disclosed paperboard container includes a
paperboard
substrate having a first major side facing an interior of the paperboard
container and a second
major side facing an exterior of the paperboard container, and one or more
high-density
polyethylene layers directly on the first major side of the paperboard
substrate.
[0007] In another aspect, disclosed is a paperboard consisting of a paperboard
substrate
having a first major side and a second major side, one or more high-density
polyethylene
layers on one or both of the first major side and the second major side of the
paperboard
substrate, and optionally, a clay coating layer between the paperboard
substrate and the one
or more high-density polyethylene layers on one or both of the first major
side and the second
major side of the paperboard substrate.
[0008] Other aspects of the disclosed paperboard, paperboard container, and
method for
using a paperboard article will become apparent from the following
description, the
accompanying drawings and the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] Fig. 1 is a cross-section of a paperboard according to a first
embodiment;
[0010] Fig. 2 is a cross-section of a paperboard according to a second
embodiment;
[0011] Fig. 3 is a cross-section of a paperboard according to a third
embodiment;
[0012] Fig. 4 is a cross-section of a paperboard according to a fourth
embodiment;
[0013] Fig. 5 is a cross-section of a paperboard according to a fifth
embodiment;
[0014] Fig. 6 is a cross-section of a paperboard according to a sixth
embodiment;
[0015] Fig. 7 is a cross-section of a paperboard according to a seventh
embodiment;
[0016] Fig. 8 is a cross-section of a paperboard according to an eighth
embodiment;
[0017] Fig. 9 is a schematic view of an extrusion coating system for coating a
high-density
polyethylene layer onto a paperboard substrate;
[0018] Fig. 10 is a top view of an unprinted sidewall blank;
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[0019] Fig. 11 is a top view of a printed sidewall blank having indicia
printed on a major
side thereof;
[0020] Fig. 12 is a perspective view of an embodiment of an exemplary
paperboard
container;
[0021] Fig. 13 is a cross-sectional side view of the paperboard container of
Fig. 12;
[0022] Fig. 14 is a perspective view of a lid of the paperboard container of
Fig. 12;
[0023] Fig. 15 is a perspective view of another embodiment of an exemplary
paperboard
container;
[0024] Fig. 16 is a cross-sectional side view of the paperboard container of
Fig. 15;
[0025] Fig. 17 is a graph relating to a polymer extrusion coating trial
showing a melt curtain
neck-in of a paperboard having a high-density polyethylene coating compared to
a melt
curtain neck-in of a paperboard having a polypropylene/low-density
polyethylene coating;
[0026] Fig. 18 is a graph relating to a polymer extrusion coating trial
showing a corona
treatment level of a paperboard having a high-density polyethylene coating
compared to a
corona treatment level of a paperboard having a polypropylene/low-density
polyethylene
coating;
[0027] Fig. 19 is a graph relating to a polymer extrusion coating trial
showing a Coefficient
of Friction (CoF) of a paperboard having a high-density polyethylene coating
compared to a
Coefficient of Friction (CoF) of a paperboard having a polypropylene/low-
density
polyethylene coating;
[0028] Fig. 20 is a graph relating to a polymer extrusion coating trial
showing an abrasion
resistance of a paperboard having a high-density polyethylene coating compared
to an
abrasion resistance of a paperboard having a polypropylene/low-density
polyethylene
coating;
[0029] Fig. 21 is a graph relating to a polymer extrusion coating trial
showing a Water
Vapor Transmission Rate (WVTR) of a paperboard having a high-density
polyethylene
coating compared to a Water Vapor Transmission Rate (WVTR) of a paperboard
having a
polypropylene/low-density polyethylene coating; and
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[0030] Fig. 22 is a graph relating to a polymer extrusion coating trial
showing a cup
forming heat sealing profile of a paperboard having a high-density
polyethylene coating
compared to a cup forming heat sealing profile of a paperboard having a
polypropylene/low-
density polyethylene coating.
DETAILED DESCRIPTION
[0031] A paperboard includes a paperboard substrate having a first major side
and a second
major side, and one or more high-density polyethylene layers on at least one
of the first major
side and the second major side of the paperboard substrate. The paperboard may
further
include a clay coating layer between the paperboard substrate and the one or
more high-
density polyethylene layers on one or both of the first major side and the
second major side of
the paperboard substrate.
[0032] Fig. 1 is a cross-section of a paperboard 10 according to a first
embodiment. The
paperboard 10 includes a paperboard substrate 11 having a first major side 12
and a second
major side 13 and a high-density polyethylene layer 15 on the first major side
12 of the
paperboard substrate 11. The high-density polyethylene layer 15 may be
directly, i.e. with no
intervening layer, disposed on the first major side 12 of the paperboard
substrate 11. The
high-density polyethylene layer 15 may be disposed at an outermost surface of
the
paperboard 10 at the first major side 12. The paperboard substrate 11 may be
disposed at an
outermost surface of the paperboard 10 at the second major side 13.
[0033] Fig. 2 is a cross-section of a paperboard 20 according to a second
embodiment. The
paperboard 20 includes a paperboard substrate 21 having a first major side 22
and a second
major side 23, a clay coating layer 24 on the first major side 22 of the
paperboard substrate
21, and a high-density polyethylene layer 25 on the clay coating layer 24. The
clay coating
layer 24 may be directly, i.e. with no intervening layer, disposed on the
first major side 22 of
the paperboard substrate 21. The high-density polyethylene layer 25 may be
directly, i.e.
with no intervening layer, disposed on the clay coating layer 24. The high-
density
polyethylene layer 25 may be disposed at an outermost surface of the
paperboard 20 at the
first major side 22. The paperboard substrate 21 may be disposed at an
outermost surface of
the paperboard 20 at the second major side 23.
[0034] Fig. 3 is a cross-section of a paperboard 30 according to a third
embodiment. The
paperboard 30 includes a paperboard substrate 31 having a first major side 32
and a second
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major side 33, a high-density polyethylene layer 35 on the first major side 32
of the
paperboard substrate 31, and a clay coating layer 36 on the second major side
33 of the
paperboard substrate 31. The high-density polyethylene layer 35 may be
directly, i.e. with no
intervening layer, disposed on the first major side 32 of the paperboard
substrate 31. The
clay coating layer 36 may be directly, i.e. with no intervening layer,
disposed on the second
major side 33 of the paperboard substrate 31. The high-density polyethylene
layer 35 may be
disposed at an outermost surface of the paperboard 30 at the first major side
32. The clay
coating layer 36 may be disposed at an outermost surface of the paperboard 30
at the second
major side 33.
[0035] Fig. 4 is a cross-section of a paperboard 40 according to a fourth
embodiment. The
paperboard 40 includes a paperboard substrate 41 having a first major side 42
and a second
major side 43, a first clay coating layer 44 on the first major side 42 of the
paperboard
substrate 41, and high-density polyethylene layer 45 on the first clay coating
layer 44, and a
second clay coating layer 46 on the second major side 43 of the paperboard
substrate 41. The
first clay coating layer 44 may be directly, i.e. with no intervening layer,
disposed on the first
major side 42 of the paperboard substrate 41. The high-density polyethylene
layer 45 may be
directly, i.e. with no intervening layer, disposed on the first clay coating
layer 44. The
second clay coating layer 46 may be directly, i.e. with no intervening layer,
disposed on the
second major side 43 of the paperboard substrate 41. The high-density
polyethylene layer 45
may be disposed at an outermost surface of the paperboard 40 at the first
major side 42. The
second clay coating layer 46 may be disposed at an outermost surface of the
paperboard 40 at
the second major side 43.
[0036] Fig. 5 is a cross-section of a paperboard 50 according to a fifth
embodiment. The
paperboard 50 includes a paperboard substrate 51 having a first major side 52
and a second
major side 53, a first high-density polyethylene layer 55 on the first major
side 52 of the
paperboard substrate 51, and a second high-density polyethylene layer 57 on
the second
major side 53 of the paperboard substrate 51. The first high-density
polyethylene layer 55
may be directly, i.e. with no intervening layer, disposed on the first major
side 52 of the
paperboard substrate 51. The second high-density polyethylene layer 57 may be
directly, i.e.
with no intervening layer, disposed on the second major side 53 of the
paperboard substrate
51. The first high-density polyethylene layer 55 may be disposed at an
outermost surface of
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the paperboard 50 at the first major side 52. The second high-density
polyethylene layer 57
may be disposed at an outermost surface of the paperboard 50 at the second
major side 53.
[0037] Fig. 6 is a cross-section of a paperboard 60 according to a sixth
embodiment. The
paperboard 60 includes a paperboard substrate 61 having a first major side 62
and a second
major side 63, a clay coating layer 64 on the first major side 62 of the
paperboard substrate
61, a first high-density polyethylene layer 65 on the clay coating layer 64,
and a second high-
density polyethylene layer 67 on the second major side 63 of the paperboard
substrate 61.
The clay coating layer 64 may be directly, i.e. with no intervening layer,
disposed on the first
major side 62 of the paperboard substrate 61. The first high-density
polyethylene layer 65
may be directly, i.e. with no intervening layer, disposed on the clay coating
layer 64. The
second high-density polyethylene layer 67 may be directly, i.e. with no
intervening layer,
disposed on the second major side 63 of the paperboard substrate 61. The first
high-density
polyethylene layer 65 may be disposed at an outermost surface of the
paperboard 60 at the
first major side 62. The second high-density polyethylene layer 67 may be
disposed at an
outermost surface of the paperboard 60 at the second major side 63.
[0038] Fig. 7 is a cross-section of a paperboard 70 according to a seventh
embodiment. The
paperboard 70 includes a paperboard substrate 71 having a first major side 72
and a second
major side 73, a first high-density polyethylene layer 75 on the first major
side 72 of the
paperboard substrate 71, a clay coating layer 76 on the second major side 73
of the
paperboard substrate 71, and a second high-density polyethylene layer 77 on
the clay coating
layer 76. The first high-density polyethylene layer 75 may be directly, i.e.
with no
intervening layer, disposed on the first major side 72 of the paperboard
substrate 71. The
clay coating layer 76 may be directly, i.e. with no intervening layer,
disposed on the second
major side 73 of the paperboard substrate 71. The second high-density
polyethylene layer 77
may be directly, i.e. with no intervening layer, disposed on clay coating
layer 76. The first
high-density polyethylene layer 75 may be disposed at an outermost surface of
the
paperboard 70 at the first major side 72. The second high-density polyethylene
layer 77 may
be disposed at an outermost surface of the paperboard 70 at the second major
side 73.
[0039] Fig. 8 is a cross-section of a paperboard 80 according to an eighth
embodiment. The
paperboard 80 includes a paperboard substrate 81 having a first major side 82
and a second
major side 83, a first clay coating layer 84 on the first major side 82 of the
paperboard
substrate 81, a first high-density polyethylene layer 85 on the first clay
coating layer 84, a
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second clay coating layer 86 on the second major side 83 of the paperboard
substrate 81, and
a second high-density polyethylene layer 87 on the second clay coating layer
86. The first
clay coating layer 84 may be directly, i.e. with no intervening layer,
disposed on the first
major side 82 of the paperboard substrate 81. The first high-density
polyethylene layer 85
may be directly, i.e. with no intervening layer, disposed on the first clay
coating layer 84.
The second clay coating layer 86 may be directly, i.e. with no intervening
layer, disposed on
the second major side 83 of the paperboard substrate 81. The second high-
density
polyethylene layer 87 may be directly, i.e. with no intervening layer,
disposed on the second
clay coating layer 86. The first high-density polyethylene layer 85 may be
disposed at an
outermost surface of the paperboard 80 at the first major side 82. The second
high-density
polyethylene layer 87 may be disposed at an outermost surface of the
paperboard 80 at the
second major side 83.
[0040] Although various embodiments of the paperboard are described above with
reference to Figs. 1 to 8, modifications may occur to those skilled in the art
upon reading the
specification. For example, in any of the above Figs. 1 to 8, any of the high-
density
polyethylene layers may be substituted with multiple high-density polyethylene
layers. The
present application includes such modifications and is limited only by the
scope of the
claims.
[0041] The paperboard substrate may include any web of fibrous material that
is capable of
applying a high-density polyethylene layer thereon. The paperboard substrate
may be
bleached or unbleached. For example, the paperboard substrate may include a
coated natural
kraft board, a solid bleached sulfate board, a solid unbleached sulfate board,
a coated
recycled board, a coated white lined chipboard, or a folding boxboard.
[0042] The thickness of the paperboard substrate may depend on various
factors, such as
the density of the paperboard substrate. For example, the paperboard substrate
may have a
caliper thickness in a range of 6 points to 36 points (1 point equals 0.001
inch). As one
specific example, the paperboard substrate may have a caliper thickness of 7
points to 30
points. As another specific example, the paperboard substrate may have a
caliper thickness in
a range of 14 points to 20 points. As yet another specific example, the
paperboard substrate
may have a caliper thickness in a range of 16 points to 18 points. As used
herein, 1 point
equals 0.001 inches, which equals 25.4 micrometers (p.m).
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[0043] The weight of the paperboard substrate may depend on various factors.
For
example, the paperboard substrate may have a basis weight ranging from 60 to
350 pounds
per 3,000 square feet. As one specific example, the paperboard substrate may
have a basis
weight of 100 to 150 pounds per 3000 ft2. As another specific example, the
paperboard
substrate may have a basis weight of 150 to 180 pounds per 3000 ft2. As yet
another specific
example, the paperboard substrate may have a basis weight of 180 to 220 pounds
per 3000
ft2.
[0044] The clay coating layer may be applied to the paperboard substrate to
improve a
printing quality of a surface of the paperboard. The clay coating layer may
include a mixture
of inorganic pigment and one or more other materials, such as binders (e.g.
emulsion polymer
binders) and dispersing agents. In a specific example, the clay coating layer
may include
kaolin clay.
[0045] The clay coating layer may be applied in any manner that is capable of
applying the
clay coating layer onto a paperboard substrate. In a specific example, the
clay coating layer
may be coated onto the paperboard substrate. Examples of coaters which may be
employed
include air knife coaters, blade coaters, rod coaters, bar coaters, multi-head
coaters, roll
coaters, roll/blade coaters, cast coaters, laboratory coaters, gravure
coaters, kiss coaters,
liquid application systems, reverse roll coaters, curtain coaters, spray
coaters and extrusion
coaters.
[0046] It was surprisingly discovered by the inventors that high-density
polyethylene
protects the paperboard substrate from moisture even after heating the same by
way of
microwave radiation.
[0047] The density of the high-density polyethylene of the one or more high-
density
polyethylene layers may range from 0.93 to 0.97 g/cm3. In one example, the
density of the
high-density polyethylene ranges from 0.95 to 0.96 g/cm3. In an aspect, the
high-density
polyethylene may have a melt index of greater than 0.3 g/10 min (190 C/2.16
kg). In another
aspect, the high-density polyethylene may have a melt index of greater than 4
g/10 min
(190 C/2.16 kg). In yet another aspect, the high-density polyethylene may have
a melt index
of greater than 8 g/10 min (190 C/2.16 kg). In one aspect, a first layer of
the one or more
high-density polyethylene layers may have a first density and first melt
index, and a second
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layer of the one or more high-density polyethylene layers may have a second
density and
second melt index different from the first density and first melt index.
[0048] An exemplary high-density polyethylene layer is a single layer of 100%
high-
density polyethylene resin extrusion coated on either or both sides of the
paperboard
substrate, in which the high-density polyethylene has a density of 0.950 g/cm3
per ASTM
D792 and the melt index (MI) is 12 g/10 min per ASTM D1238 testing at 2.16 kg
load and
190 C.
[0049] The one or more high-density polyethylene layers may be applied to the
paperboard
substrate using any available technique. Examples of suitable techniques for
applying the
one or more high-density polyethylene layers include extrusion coating,
extrusion laminate,
curtain coating, and adhesive lamination. In an example, multiple high-density
polyethylene
layers may be coextruded onto the paperboard substrate. In another example, a
first high-
density polyethylene layer may be laminated onto the paperboard, and then a
second high-
density polyethylene layer may be extruded onto the paperboard. In yet another
example, a
first high-density polyethylene layer may be extruded onto the paperboard, and
then a second
high-density polyethylene layer may be laminated onto the paperboard.
[0050] Fig. 9 illustrates an exemplary extrusion coating system 90 for coating
a high-
density polyethylene layer onto a paperboard substrate. As shown, a paperboard
substrate 91
may be unwound from an unwind roll 92 and passed between a nip roll 93 and a
chill roll 94
and wound to a rewind roll 95. Meanwhile, resin 96 may be extruded from a slot
die 97 at
elevated temperatures onto the moving paperboard substrate. The resin-coated
paperboard
substrate 91 may then be passed through the nip roll 93 and the chill roll 94
to cool the resin
96 and impart a desired finish. The coating thickness may be controlled by
controlling a ratio
of the speed of the moving paperboard substrate 91 and the speed at which
resin 96 is
extruded from the slot die 97.
[0051] The composition of the one or more high-density polyethylene layers may
be pure
high-density polyethylene layer or may be a mixture of high-density
polyethylene and one or
more other materials that do not inhibit the capability of the high-density
polyethylene layer
from protecting the paperboard substrate from moisture even after heating the
same by way
of microwave radiation. For example, the one or more high-density polyethylene
layers may
include high-density polyethylene in an amount of 50% or greater, such as 60%
or greater,
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70% or greater, 80% or greater, 90% or greater, 95% or greater, 99% or
greater, or 100%
high-density polyethylene layer. In an example, a first high-density
polyethylene layer may
include a first percentage of high-density polyethylene and a second high-
density
polyethylene layer may include a second percent of high-density polyethylene
different from
the first percentage of high-density polyethylene.
[0052] The disclosed paperboard may be made into a paperboard article using
any available
technique. Although various operations of making paperboard articles are
described below,
modifications may occur to those skilled in the art upon reading the
specification. The
present application includes such modifications and is limited only by the
scope of the
claims.
[0053] The disclosed paperboard may be printed with indicia, such as high-
quality
advertising text and graphics, on one or both major sides by a printing
operation. The
printing operation may include any apparatus or system capable of marking the
paperboard
with indicia. For example, the printing operation may include a printing press
capable of
printing high quality text and/or graphics (e.g., advertising text and
graphics) onto the
paperboard. Specific examples of printing techniques include offset printing,
gravure
printing, flexographic printing and digital printing.
[0054] The disclosed paperboard may be cut into blanks by way of a cutting
operation. The
cutting operation may include any apparatus or system capable of cutting
blanks from the
paperboard. For example, the cutting operation may include a die cutting
machine. The
cutting operation may provide the blanks with the desired shape. The shape of
the blanks
may depend on the intended shape and configuration of the paperboard article.
Furthermore,
in the case of cutting after a printing operation, the cutting operation may
cut the blanks such
that the printed indicia are positioned at the desired location.
[0055] The blanks may be formed into a paperboard article by a forming
operation. The
forming operation may shape and assemble one or more blanks into a paperboard
article
having the desired shape and configuration. The forming operation may include
any
apparatus or system capable of forming one or more blanks into a paperboard
article having
the desired shape and configuration. The forming operation may, for example,
include a
press mold or thermoforming mold.
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[0056] Although various operations of making paperboard articles are described
above in a
specific order and as independent operations performed by separate machines or
systems, it
will be understood that one or more operations may be performed in a different
order, that
one or more operations may be combined in a single operation, that one
operation may be
separated into multiple operations, or that one or more operations may be
performed by a
single machine or system.
[0057] An embodiment of a method for using a paperboard article may include
heating the
disclosed paperboard article by way of microwave radiation. For example, a
paperboard
article including a paperboard substrate having a first major side and a
second major side, and
one or more high-density polyethylene layers on at least one of the first
major side and the
second major side of the paperboard substrate may be heated by way of
microwave radiation,
such as by heating the paperboard article in a microwave oven. A food product
(e.g. soup,
oatmeal, coffee, water, etc.) may be on a surface of the paperboard article
during the heating
of the paperboard article.
[0058] In an example, the paperboard article may be a paperboard container
(e.g. cup,
bowl). The paperboard container may have any desired container configuration.
[0059] It will be understood that the paperboard container may be made from a
disclosed
paperboard using any available technique. Although various operations of
making
paperboard containers are described below, modifications may occur to those
skilled in the
art upon reading the specification.
[0060] A roll of the disclosed paperboard may be printed with indicia on one
or both major
sides by a printing operation, such as by way of offset printing, gravure
printing, flexographic
printing or digital printing. The printed or unprinted paperboard may be cut
into container
blanks, such as sidewall blanks, bottom blanks, or lid blanks, by way of a
cutting operation,
such as by way of a die cutting machine. Figs. 10 and 11 illustrate exemplary
sidewall blanks
100, 110 that may be used in the manufacture of a paperboard container. Fig.
10 shows an
unprinted sidewall blank 100, and Fig. 11 shows a printed sidewall blank 110
having indicia
112 printed on a major side thereof
[0061] The printed or unprinted container blanks are then formed into a
paperboard
container by a forming operation. For example, a sidewall blank 100, 110 of
Figs. 10 or 11
may be shaped by wrapping the sidewall blank 100, 110 around a mandrel to form
a
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frustoconical-shaped sidewall. In an example, a sidewall blank may have a
caliper thickness
of 16 points. The sidewall may be completed by overlapping and sealing
longitudinal ends of
the shaped sidewall blank to form an overlapped and sealed seam. The seam may
be sealed
using any available technique. In an example, the seam may be sealed by
heating and
connecting a first high-density polyethylene layer with a second high-density
polyethylene
layer at the overlapped portion. In another example, the seam may be sealed by
folding a first
longitudinal end and heating and connecting the first high-density
polyethylene layer at the
first longitudinal end with the first high-density polyethylene layer at the
second longitudinal
end.
[0062] In a non-limiting embodiment, the container may include a bottom. The
bottom
may be made from the disclosed paperboard, a different paperboard, or a non-
paperboard
material. In an example, a bottom blank may have a caliper thickness of 13
points. The
bottom may be sealed to the sidewall using any available technique. In an
example, a lower
end of the sidewall may be shaped to form a circumferential recess. The bottom
may be
placed into the circumferential recess and sealed to the sidewall. In a
specific example, at
least one of the sidewall and the bottom have a high-density polyethylene
layer, which
facilitates excellent sealing.
[0063] In a non-limiting embodiment, the container may include a lid. The lid
may be
made from the disclosed paperboard, a different paperboard, or a non-
paperboard material,
such as a film material (e.g., polymer; metal; metal-polymer combination),
press-on lids (e.g.,
molded plastic lids) and the like. The lid may be sealed to the sidewall or
may remain an
unsealed lid. The lid may be sealed to the sidewall using any available
technique and may
depend on, among other possible factors, the type of lid being used. In a
specific example, at
least one of the sidewall and the lid have a high-density polyethylene layer,
which facilitates
excellent sealing.
[0064] During packaging, a food product (e.g. soup, oatmeal, etc.) may be
placed into the
internal volume of the paperboard container and the lid may be sealed to the
sidewall of the
paperboard container, such as with a heat-seal, an adhesive or an interference
fit.
[0065] In an example, an upper end of a sidewall may be rolled over to form a
flange and
the lid may be sealed to the flange.
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[0066] In another example, a film material may be sealed, such as by way of
lamination
onto the sidewall to seal the paperboard container. A second non-sealing lid
may be provided
to cover the film material.
[0067] Although various embodiments of paperboard containers are described
below,
modifications may occur to those skilled in the art upon reading the
specification.
[0068] An embodiment of an exemplary paperboard container 120 is illustrated
in Figs. 12-
14. A paperboard container 120 formed from the disclosed paperboard may
include a
sidewall 122, a bottom 124 and a lid 126. The sidewall 122 may be formed by,
for example,
die-cutting a sidewall blank from a sheet of the disclosed paperboard into the
desired
configuration (e.g., trapezoidal), such the sidewall blanks 100, 110 of Figs.
10 and 11. The
sidewall blank may include a first longitudinal end and a second longitudinal
end. The
sidewall 122 may be formed by overlapping both longitudinal ends to surround
an interior
cavity of the container, forming an overlapped seam 128 in which the first
longitudinal end is
positioned inside the second longitudinal end. The seam 128 may be sealed by,
for example,
connecting a high-density polyethylene layer of the first longitudinal end to
a high-density
polyethylene layer of the second longitudinal end.
[0069] The bottom 124 may formed from the disclosed paperboard. Various
techniques
may be used to seal the bottom 124 to the sidewall 122. As one example, a
lower end of the
sidewall 122 may be shaped to form a circumferential recess 130. The bottom
124 may be
placed into the recess 130 and sealed to the sidewall 122. Suitable techniques
for sealing the
bottom 124 to the sidewall 122 include hot air heat seal and ultrasound
sealing.
[0070] The lid 126 may be an unsealed plastic lid 126. The lid 126 may attach
to the
sidewall 122 by way of, for example, an interference fit. An upper end of the
sidewall 122
may be rolled over to form a bead 132. The lid 126 may be made to form an
interference fit
with the bead 132 at the upper end of the sidewall 122, such that the lid 126
may be
repeatedly removed and attached to cover the paperboard container 120.
[0071] Another embodiment of an exemplary paperboard container 140 is
illustrated in
Figs. 15 and 16. A paperboard container 140 formed from the disclosed
paperboard may
include a sidewall 142, a bottom 144 and a lid 146. The sidewall 142 may be
formed by, for
example, die-cutting a sidewall blank from a sheet of the disclosed paperboard
into the
desired configuration (e.g., trapezoidal), such the sidewall blanks 100, 110
of Figs. 10 and 11.
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The sidewall blank may include a first longitudinal end and a second
longitudinal end. The
sidewall 142 may be formed by overlapping both longitudinal ends to surround
an interior
cavity of the container, forming an overlapped seam (not shown) in which the
first
longitudinal end is positioned inside the second longitudinal end. The seam
may be sealed
by, for example, connecting and heating a high-density polyethylene layer of
the first
longitudinal end to a high-density polyethylene layer of the second
longitudinal end.
[0072] The bottom 144 may formed from the disclosed paperboard. Various
techniques
may be used to seal the bottom 144 to the sidewall 142. As one example, a
lower end of the
sidewall 142 may be shaped to form a circumferential recess 150. The bottom
144 may be
placed into the recess 150 and sealed to the sidewall 142. Suitable techniques
for sealing the
bottom 144 to the sidewall 142 include hot air heat seal and ultrasound
sealing.
[0073] The lid may be sealed to the sidewall 142. The paperboard lid 146 may
be made
from the disclosed paperboard, a different paperboard or a different material
such as a film
material (e.g., polymer; metal; metal-polymer combination). Various techniques
may be used
to seal the lid 146 to the sidewall 142. As one example, an upper end of the
sidewall may be
rolled over to form a flange 152 and the lid 146 may be sealed to the flange
152. The lid 146
may be sealed to the flange 152 by, for example, connecting and heating a high-
density
polyethylene layer of a paperboard lid 146 to a high-density polyethylene
layer of the flange
152. As another example, a film lid 146 may be sealed to the flange 152, by,
for example, a
heat-seal or an adhesive, and a second lid may be provided to cover the film
lid 146.
[0074] Another embodiment of an exemplary paperboard container may include a
food
product contained in an internal volume of the paperboard container and a lid
sealing the
internal volume of the paperboard container. The lid may be sealed using any
available
technique and may depend on, among other possible factors, the type of lid
being used.
Indicia may include instructions for heating the food product by way of
microwave radiation.
The instructions may be included with the paperboard container in any manner,
such as by
printing on an exterior of the paperboard container or by way of an additional
packaging
material attached with the paperboard container. Accordingly, the paperboard
container
containing the food product may be purchased by a consumer and the food
product may be
heated by way of microwave radiation according to the instructions while the
food product is
contained in the paperboard container. Additional steps may be included
without departing
from the scope of the present disclosure.
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[0075] Figures 17-22 show comparative results of a high-density polyethylene
(HDPE)
coating on a paperboard substrate relative to a conventional polypropylene
with 20% low-
density polyethylene (PP/LDPE) coating on a paperboard substrate.
[0076] Fig. 17 relates to a polymer extrusion coating trial conducted on a
solid bleached
sulfate paperboard substrate. A die width for the polymer extrusion coating
trial was 19
inches. A width of the polymer coating on the paperboard was measured after
the extrusion
coating process. A difference between the die width (19 inches) and the width
of the polymer
coating on the paperboard is referred to as a total neck-in. Reduced neck-in
is favorable for a
polymer extrusion process to increase material utilization by reducing trim
waste. In the trial,
the HDPE extrusion coating showed much less total neck-in (1.5 inches) than
PP/LDPE (3.6
inches). The HDPE extrusion coating shows better process performance by
increasing material utilization than the PP/LDPE extrusion coating.
[0077] Fig. 18 relates to polymer extrusion coating trial conducted on a solid
bleached
sulfate paperboard substrate. Corona treatment was imparted onto the polymer
coating
surface after extrusion. Polymer surface energy measured by dyne level was
monitored over a
period of 28 days (4 weeks). A higher dyne level is favorable for a polymer
coating surface
to ensure easy printability on the polymer surface. In this example, the HDPE
surface can be
Corona-treated initially at a higher dyne level than the PP/LDPE surface. The
dyne level also
decays slower for the HDPE surface than the PP/LDPE surface. The HDPE coating
shows
better printability characteristics than the PP/LDPE coating.
[0078] Fig. 19 relates to a polymer extrusion coating trial conducted on a
solid bleached
sulfate paperboard substrate. Coefficient of Friction (CoF) was measured as a
frictional force
to slide two surfaces, i.e. the polymer coating and a polymer coating of the
same type. A
lower CoF is favorable to reduce a force required to facilitate slide two
polymer surfaces
against each other. Static CoF is a measure of the initial force required to
begin the sliding
movement. Kinetic CoF is a measure of force required to maintain the movement.
In this
example, the HDPE surface shows a lower static CoF and a lower kinetic CoF
than the
PP/LDPE surface. This implies that HDPE surface would be more favorable in
converting
and packaging processes.
[0079] Fig. 20 relates to a polymer extrusion coating trial conducted on a
solid bleached
sulfate paperboard substrate. The abrasion resistance of a polymer coating
surface was tested
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by subjecting the polymer surface to a 2-lb weight sled sliding and rubbing
reciprocally 999
times. In this trial, the high-density polyethylene surface showed better
abrasion resistant than
the polypropylene/low-density polyethylene surface as less material was lost
due to rubbing.
[0080] Fig. 21 relates to a polymer extrusion coating trial conducted on a
solid bleached
sulfate paperboard substrate. Water Vapor Transmission Rate (WVTR) also known
as
Moisture Vapor Transmission Rate (MVTR) of the polymer coated paperboard was
measured
at 100 F (37.8 C) and 90% RH (Relative Humidity) conditions. WVTR is a
measure of
water vapor transmission though a substrate. In this example, high-density
polyethylene
shows lower WVTR than polypropylene/low-density polyethylene. This implies
that high-
density polyethylene has better moisture resistance or water vapor barrier
property than
polypropylene/low-density polyethylene.
[0081] Fig. 22 relates to a polymer extrusion coating trial conducted on solid
bleached
sulfate paperboard substrates. The polymer coated paperboards were then cut
into sidewall
blanks and bottom blanks suitable for 16-oz beverage cup forming. The cup
converting trial
was conducted on a PMC-1250 cup forming machine at a speed of 165 cups per
minute. The
sidewall temperature settings were varied. The fiber tear of cup side-seam
sealing was
measured as an indication of side-seam heat seal performance. In this example,
high-density
polyethylene coated paperboard can heat-seal at lower temperature and shows
better fiber tear
than polypropylene/low-density polyethylene coated paperboard at the same cup
converting
speed.
[0082] Tables 1 and 2 relates to polymer extrusion coating trial conducted on
a one-side
kaolin clay coated paperboard for sidewall stock and solid bleached sulfate
paperboard for
bottom stock. The sidewall and bottom stock rolls were cut to proper sizes
suitable for
forming 12-oz and 17-oz cups. In both examples, high-density polyethylene
coated
paperboard formed and sealed at lower sidewall temperatures and faster
converting speeds.
TABLE 1
Cup Forming Heat Sealing Conditions (12 oz cup)
Settings 1Conditions PP/LDPE Conditions HDPE Conditions
Cup Speed (cups/min) 180 210
Sidewall Temperature (F) 1075 1025
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TABLE 2
Cup Forming Heat Sealing Conditions (17 oz cup)
Settings Conditions PP/LDPE Conditions HDPE Conditions
Cup Speed (cups/min) 125 135
Sidewall Temperature (F) 950 900
[0083] Although various embodiments of the disclosed paperboard, paperboard
containers,
and methods for using the same have been shown and described, modifications
may occur to
those skilled in the art upon reading the specification. The present
application includes such
modifications and is limited only by the scope of the claims.
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