Note: Descriptions are shown in the official language in which they were submitted.
POLYMERIC FILMS AND BAGS
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] Not applicable,
BACI:GEOUND OF THE INVENTION
1. Field of the Invention
[0002] The present invention relates to improvements in the construction and
manufacture of
polymeric film and bags. In particular, the present invention relates to
improvements in varying
the thickness of film formed from a blown film extrusion process and
constructing polymeric
bags from the resultant film.
2. Description of the Related Art
[0003] Polymeric bags are ubiquitous in modern society and are available in
countless
combinations of varying capacities, thicknesses, dimensions, and colors. The
bags are available
for numerous applications including typical consumer applications such as long-
term storage,
food storage, and trash collection. Like many other consumer products,
increased demand and
new technology have driven innovations in polymeric bags improving the utility
and
performance of such bags. The present invention is an innovation of particular
relevance to
polymeric bags used for trash collection.
[0004] Polymeric bags are manufactured from polymeric film produced using one
of several
manufacturing techniques well-known in the art. The two most common methods
for
manufacture of polymeric films are blown-film extrusion and cast-film
extrusion. In blown-film
extrusion, the resulting film is tubular while cast-film extrusion produces a
generally planar film.
The present invention is generally applicable to drawstring trash bags
manufactured from a
blown-film extrusion process resulting in tubular film stock. Manufacturing
methods for the
production of drawstring bags from a web of material are shown in numerous
prior art references
including, but not limited to, United States Patent Nos. 3,196,757 and
4,624,654.
Date Recue/Date Received 2021-04-23
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[00051 In blown film extrusion, polymeric resin is fed into an extruder where
an extrusion
screw pushes the resin through the extruder. The extrusion screw compresses
the resin, heating
the resin into a molten state under high pressure. The molten, pressurized
resin is fed through a
blown film extrusion die having an annular opening. As the molten material is
pushed into and
through the extrusion die, a polymeric film tube emerges from the outlet of
the extrusion die.
[00061 The polymeric film tube is blown or expanded to a larger diameter by
providing a
volume of air within the interior of the polymeric film tube. The combination
of the volume of
air and the polymeric film tube is commonly referred to as a bubble between
the extrusion die
and a set of nip rollers. As the polymeric film tube cools travelling upward
toward the nip
rollers, the polymeric film tube solidifies from a molten state to a solid
state after it expands to
its final diameter and thickness. Once the polymeric film tube is completely
solidified, it passes
through the set of nip rollers and is collapsed into a collapsed polymeric
tube, also referred to as
a collapsed bubble.
[00071 One common household item formed from the polymeric film produced by a
blown
film extrusion process are drawstring trash bags. Frequently, drawstring trash
bags are used to
line a rigid container, such as a trash can, for the disposal of household
trash. When used with a
rigid container, it is common to fold the upper opening of a drawstring trash
bag over the upper
rim of the container to keep the upper opening of the bag accessible. Some
rigid containers
provide retaining devices to hold the upper opening of a drawstring bag in
place while, in other
instances, the drawstring bag may provide certain features or properties that
facilitate keeping the
bag in place on the container. The use of these rigid containers is
particularly common in
connection with 13-gallon drawstring bags. Rigid containers may also be used
with larger bags,
such as those commonly used for the collection of outdoor or yard waste. When
drawstring bags
are used with supporting rigid containers, the drawstring trash bag is often
filled with trash and
other debris until the capacity of the container or trash bag is reached.
100081 After filling the drawstring bag with trash or debris, the bag and its
contents are
generally pulled out of the rigid container in one of several ways. Some
consumers may prefer
to pull the drawstrings taut, using the drawstrings to pull the bag and its
contents out of the
container. However, in many cases, consumers pull the bag out of the rigid
container before
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=
pulling the drawstrings taut. In such cases, a consumer will typically grab
the upper opening of
the bag hem or, more commonly, the area immediately below the hem. As the
consumer grabs
the bag and pulls it out of the container, significant force can result in the
area immediately
below the hem. This force on the hem is due to the weight of the bag contents
and the pulling
action by the consumer, which can cause the polymeric film to puncture or fail
in this region of
the bag--especially when the contents of the bag are particularly heavy. Thus,
there is a need to
improve the strength and puncture resistance of the hem and the area
immediately below the
hem.
[0009] Another aspect of prior art drawstring bags that may be subject to
improvement is the
tendency for the hems of drawstring bags to detach if there are even minor
manufacturing
defects. In particular, if the pressure or heat used to create the hem seal
across the width of the
drawstring trash bag is too great, the integrity of the drawstring trash bag
may be endangered due
to crystallization of the polymeric film along the hem seal. In these cases,
when the drawstring
trash bag is filled with trash or debris, the hem seal may fail causing the
entire length of the hem,
and the drawstring contained within the hem, to "zipper" or detach from the
rest of the bag.
Thus, there is a need to improve the robustness of the hem seal to ensure that
the drawstring is
retained about the opening of the trash bag.
[0010] Another further improvement of prior art drawstring trash bags may be
to reduce the
cost of producing the trash bags. A substantial cost of manufacturing trash
bags can be related to
the cost of polymeric resin used to produce a bag. One way to decrease the
cost of producing
bags is to decrease the thickness of film used in their manufacture, which
reduces the amount of
polymeric resin required to make a bag. However, reducing the thickness of
film used to
produce a bag can lead to a reduction in the strength of the bag. Thus, a need
exists to decrease
the use of resin to produce drawstring trash bags while maintaining enough
strength so that the
bags do not fail when used.
100111 One method of thinning out the material of a bag is by incrementally
stretching the
film. Stretching the film incrementally allows stretching the film in only
selected areas of the
film. Incrementally stretching also provides for a ribbed pattern to be placed
on the bag that may
serve to differentiate the appearance of the bag. The incremental stretching
can maintain the
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thickness of the bag in segments that are not stretched that can be referred
to as thick ribs. These
thick ribs may be perceived by an end user of the bag such that the bag is
perceived to be as thick
as the previously un-stretched film.
[0012] In the prior art, US Patent No. 4,116,892 to Schwarz discloses using a
pair of grooved
intermeshing rollers to incrementally stretch an orientable polymeric material
in a direction
transverse to the machine direction. In a related field, US Patent No.
5,041,255 to Zafiroglu
discloses the use of a pair of intermeshing circumferentially ribbed rollers
for stretching portions
of a fibrous web.
[0013] In a much later publication, US Pat. Appl. Pub. 2012/0088645A1
discloses use of
intermeshing rollers, each roller having a plurality of circular ridges
protruding outwards, to
stretch a portion of a polymeric web in a direction transverse to the machine
direction. The
application further discloses that the use of the aforementioned intermeshing
rollers can be used
on the film so that the panels of the trash bag are imparted with a ribbed
pattern running in a
lengthwise direction, parallel to the direction that the film is extruded.
[00141 In light of the foregoing, it would be desirable to provide a means for
reinforcing the
drawstring trash bag in the area immediately adjacent/below the hem area of
the trash bag while
also controlling the thickness of the reinforced areas. It would also be
desirable to provide
additional improvements to the manufacture of drawstrings bags by thinning out
the bags in
desirable locations to provide targeted strengthening and light weighting of
the bag. The present
invention represents a novel solution to address this needs.
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SUMMARY OF THE INVENTION
[0015] In at least one embodiment of the invention, a master roll of polymeric
film for forming
trash bags may be formed. To form the master roll, a polymeric film tube may
be formed by a
blown film extrusion process. Once the polymeric film tube is formed, it may
be collapsed by a
pair of nip rollers to form a collapsed bubble. A pre-selected partial width
of the collapsed
bubble may be ring-rolled to form an incrementally stretched collapsed bubble.
The
incrementally stretched collapsed bubble may be slit lengthwise. The slitting
of the collapsed
bubble may be proximate to a centerline of the collapsed bubble. The slit
collapsed bubble may
be separated into a first half-bubble and a second half-bubble. The pre-
selected partial width that
is incrementally stretched may be centered approximately along the centerline
of the collapsed
bubble. Each of the half-bubbles may include a fraction of the pre-selected
partial width. Each
fraction of the pre-selected partial width may extend from an edge of each
collapsed half-bubble
towards the centerline of each collapsed bubble. Each fraction of the pre-
selected partial width
may be less than one-half of the width of each half-bubble. Once stretched,
each of the half-
bubbles may be rolled onto a separate master roll. Once the master roll is
formed, it may be
placed at the head end of a bag converting line to form drawstring trash bags.
[0016] In an alternative embodiment, two separate pre-selected widths of the
above-discussed
collapsed bubble may be ring-rolled rather than a single pre-selected width.
Each of the two
separate pre-selected widths may be offset from the centerline of the
collapsed bubble and offset
from each edge of the collapsed bubble.
[0017] The ring rolling of the incrementally stretched film may include the
collapsed bubble
entering a pair of intermeshing rollers. Each of the intermeshing rollers may
include a plurality
of grooves perpendicular to the axis of the rollers. The plurality of grooves
on a first roller of the
pair of intermeshing rollers may intermesh with the plurality of grooves on a
second roller of the
pair of intermeshing rollers. An axis of the first roller may be parallel to
an axis of the second
roller and the axis of each roller may be perpendicular to the machine
direction of the collapsed
bubble. The pair of intermeshing rollers may incrementally stretch only a
section or partial
width of the collapsed bubble. The collapsed bubble may increase in overall
width after passing
through the pair of intermeshing rollers. Each intermeshing roller may rotate
in a direction that
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the collapsed bubble is moving so that the collapsed bubble is drawn through
the pair of
intermeshing rollers. The ring rolling may also include a pair of spreading
rollers downstream
from the pair of intermeshing rollers. The axis of the spreading rollers may
be parallel to each
other and perpendicular to the machine direction of the collapsed bubble. The
pair of spreading
rollers may maintain tension in the collapsed bubble and spread out the
overall width of the
collapsed bubble after being stretched by the pair of intermeshing rollers.
100181 In another embodiment of the present invention, bags may be formed from
a polymeric
film by a blown film extrusion process. The blown film extrusion process may
form a polymeric
film tube. The polymeric film tube may be collapsed to form a collapsed bubble
and the
collapsed bubble may have a collapsed bubble width extending from a first edge
to a second
edge of the collapsed bubble. The collapsed bubble may be separated into a
first half-bubble and
a second half-bubble by a slitting operation. The first half-bubble may be
rolled onto a first
master roll and the second half-bubble may be rolled onto a second master
roll. The first master
roll may be fed into the front or head end of a bag converting line. Prior to
converting the first
master roll into bags, a portion of the collapsed bubble may be ring rolled.
The ring rolling may
be centered along a centerline of the first half-bubble. The ring rolled
portion may comprise a
partial width of the first half-bubble and extend from a first edge of the
first half-bubble toward
and opposite second edge of the first half-bubble. The partial width of the
first half-bubble may
have a length that is less than half of a width of the first half-bubble.
[0019] In a further embodiment of the invention, polymeric bags may be formed
by a blown
film extrusion process. The blown film extrusion process may form a polymeric
film tube. Once
the polymeric film tube is formed, it may be collapsed by a pair of nip
rollers to form a collapsed
bubble. The collapsed bubble may have a first edge and a second edge, both
extending along a
length of the collapsed bubble, a distance between the first and the second
edge defining a width
of the collapsed bubble. The collapsed bubble may be slit along the first
edge. A portion of a
width of the collapsed bubble may be ring-rolled to form an incrementally
stretched portion. The
incrementally stretched portion may form an incrementally stretched partial
width that may be
centered along a centerline of the collapsed bubble. The incrementally
stretched partial width, in
the alternative, may extend adjacent from the first side edge of the collapsed
bubble towards the
second side edge of the collapsed bubble. The incrementally stretched partial
width may have a
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width less than half the width of the collapsed bubble. Once the collapsed
bubble is
incrementally stretched, it may feed into a bag converting operation and
formed into bags. The
ring rolling may be performed synchronously with the forming of the polymeric
film tube and
the forming of the bags.
[0020] In an additional embodiment of the invention, a bag may be formed from
polymeric
film from a collapsed polymeric bubble formed from a blown film extrusion
process. The bag
may include a front panel and a back panel. The front panel and back panel may
be generally
joined along a first side edge, a second side edge, and a bottom edge of the
respective front panel
and back panel. The front panel may have a distal edge opposite the bottom
edge. The distal
edge of the front panel may result from the folded over portion of the front
panel. The distal
edge of the front panel may provide a first hem and a first overlap area
immediately below the
first hem. A drawstring may be encapsulated within the first hem. The top of
the hem may
define an upper opening of the polymeric bag. The first overlap area may
comprise at least two
layers of polymeric film below the first hem. The at least two layers of
polymeric film of the
first overlap area may be sealed together by a lower seal. The first overlap
area may fail to
include a drawstring. The first hem and the first overlap area may comprise an
incrementally
stretched partial width of the collapsed bubble. The incrementally stretched
partial width of the
collapsed bubble may be incrementally stretched synchronously with the blown
film extrusion
process that forms the collapsed bubble. The at least two layers of polymeric
film of the first
overlap area immediately adjacent or proximate to the first lower seal may
comprise un-stretched
polymeric film.
BRIEF DESCRIPTION OF THE RELATED DRAWINGS
[0021] A full and complete understanding of the present invention may be
obtained by
reference to the detailed description of the present invention and certain
embodiments when
viewed with reference to the accompanying drawings. The drawings can be
briefly described as
follows.
100221 Fig. 1 provides a side view of a first embodiment of the present
invention
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[0023] Fig. 2 provides a partial perspective view of the first embodiment
shown in Fig. 1.
[0024] Fig. 3 provides a perspective view of a pair of intermeshing rollers
utilized in the first
embodiment.
[0025] Fig. 4 is a cross-sectional view of the intermeshing rollers taken
along circle 4-4 of Fig.
3.
[0026] Fig. 5 is a partial perspective view of a second embodiment of the
present invention.
[0027] Fig. 6 is a perspective view of a third embodiment of the present
invention.
[0028] Fig. 7 is a perspective view of a fourth embodiment of the present
invention.
[0029] Fig. 8 is a perspective view of a fifth embodiment of the present
invention.
[0030] Fig. 9 is a partial top view of a ring rolled collapsed bubble of the
present invention.
[0031] Fig. 10 is a perspective view of a sixth embodiment of the present
invention.
[0032] Fig. 11 is a partial cross-sectional view of the sixth embodiment as
shown in Fig. 10.
[0033] Fig. 12 is front view of the embodiment shown in Fig. 10 and Fig. 11.
[0034] Fig. 13 is a partial detailed front view of a seventh embodiment of the
present
invention.
[0035] Fig. 14 is a front view of an eighth embodiment of the present
invention.
[0036] Fig. 15 is a front view of a ninth embodiment of the present invention.
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DETAILED DESCRIPTION OF THE INVENTION
[0037] The present disclosure illustrates several embodiments of the present
invention. It is
not intended to provide an illustration or encompass all embodiments
contemplated by the
present invention. In view of the disclosure of the present invention
contained herein, a person
having ordinary skill in the art will recognize that innumerable modifications
and insubstantial
changes may be incorporated or otherwise included within the present invention
without
diverging from the spirit of the invention. Therefore, it is understood that
the present invention
is not limited to those embodiments disclosed herein. The appended claims are
intended to more
fully and accurately encompass the invention to the fullest extent possible,
but it is fully
appreciated that certain limitations on the use of particular terms are not
intended to conclusively
limit the scope of protection.
[0038] Fig. 1 provides a side view of a first embodiment of the present
invention while Fig. 2
provides a perspective partial view of the same embodiment. The first
embodiment is a process
for forming two sections of an incrementally stretched split polymeric film
tube. The polymeric
tube is divided lengthwise into two sections and rolled onto two master rolls.
The polymeric
film tube, which may also be referred to as a bubble, is formed by a blown
film extrusion
process.
[0039] The blown film extrusion process begins by molten polymeric resin being
extruded
through an annular die to form a bubble or tube of molten polymeric film 104.
The direction that
the film is extruded out of the die is commonly referred to as the machine
direction. The
direction of extrusion may also be referred to as the lengthwise direction of
the bubble or
polymeric film tube 104. Hence, the length of the polymeric tube 104 extends
parallel with the
machine direction. The direction transverse to the machine direction is
commonly referred to as
the cross direction. The blown film extrusion process is well known in the art
and is further
explained in U.S. Patent No. 7,753,666, which is hereby incorporated by
reference in its entirety.
[0040] The polymeric resin used in the blown film extrusion process may vary.
However, for
forming polymeric bags, a polyethylene resin is commonly used. In the current
state of the art
for polymeric bags, a blend of various polyethylene polymers may be used. A
polymer blend can
have linear low-density polyethylene (LLDPE) as the primary component, but
other polymers
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may be utilized including, but not limited to, other polyethylene resins such
as high-density
polyethylene (HDPE) or low-density polyethylene (LDPE). Typically, the primary
component of
the polymer blend, such as linear low-density polyethylene (LLDPE), will
comprise at least 75%
of the polymer blend. The remaining portion of the polymer blend may include
additives
including, but not limited to, coloring additives, anti-blocking agents,
and/or odor control
additives.
[0041] As shown in Fig. 1, once the bubble 104, or polymeric tube, of molten
film solidifies,
the bubble 104 is collapsed by a pair of nip rollers 108, which results in a
collapsed bubble 110.
The collapsed bubble 110 includes two opposing interconnected surfaces of film
extending
continuously in a lengthwise direction. As shown in Fig. 2, once collapsed,
the collapsed bubble
110 has a first edge 112 and second edge 114 defined in the opposing edges of
the collapsed
bubble 110 extending the length of the collapsed bubble 110. The distance from
the first edge
112 to the second edge 114 of the collapsed bubble 110 can define a width of
the collapsed
bubble. The nip rollers 108 are commonly elevated above the extruder 106 a
considerable
distance, since the molten bubble 104 is air-cooled and requires a relatively
large vertical
distance to cool and solidify before the bubble 104 is collapsed. Once the
collapsed bubble 110
returns from the cooling tower (not shown), the collapsed bubble 110 can feed
directly into a
ring-rolling operation 120. As shown in Fig. 1 and more clearly in Fig. 2, the
ring rolling
operation 120 can be configured to stretch only a portion of the width of the
collapsed bubble
110. The ring rolling operation can include a pair of intermeshing rollers
122a, 122b and a pair
of spreading rollers 124a, 124b.
100421 As shown in Figs. 3 and 4, the pair of intermeshing rollers 122a, 122b
has a plurality of
grooves 128a, 128b and corresponding concentric rings formed perpendicular in
relation to the
axis of the intermeshing rollers 122a, 122b. The pair of intermeshing rollers
122a, 122b can be
arranged with the axis of each roller parallel to each other and perpendicular
to the machine
direction of the collapsed bubble 110. The pair of intermeshing rollers 122a,
122b rotates in
opposite directions from each other, as shown in Fig. 3, so that the collapsed
bubble 110 is drawn
through the pair of intermeshing rollers I22a, 122b. The tension in the
collapsed bubble 110 is
maintained after passing through the intermeshing rollers 122a, 122b by a pair
of spreading
rollers 124 as shown in Figs. 1 and 2. The spreading rollers 124 ensure that
the collapsed bubble
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110 spreads evenly over its width and maintains the appropriate amount of
tension in the
collapsed bubble 110. The spreading rollers 124 are typically arranged with
each axis parallel to
each other and perpendicular to the machine direction of the collapsed bubble
110.
[0043] As shown in Figs. 1 and 2, once the collapsed bubble 110 passes into
the nip 126 of the
pair of intermeshing rollers 122a, 122b, the collapsed bubble 110 is deformed
by the plurality of
grooves 128a, 128b and is stretched by a factor of a draw ratio. The draw
ratio is a ratio between
the path-length that the plurality of grooves 128a, 128b causes the film to
take versus the
original length of the film width passed through the plurality of grooves
128a, 128b, as
illustrated in Fig. 4. Since the collapsed bubble 110 enters the intermeshing
rollers 122a, 122b
travelling in the machine direction, the intermeshing rollers 122a, 122b
incrementally stretch the
collapsed bubble 110 in the cross direction ¨ transverse to the machine
direction.
[0044] As shown in Fig. 4, the film of the collapsed bubble 110 is stretched
in between each
groove of the plurality of grooves 128a, 128b, which results in a pattern of
stretched and un-
stretched lengths extending along the length of the collapsed bubble 110.
Examined closely, this
pattern of stretched and un-stretched lengths results in a pattern of parallel
thick ribs (un-
stretched lengths) and thin ribs (stretched lengths) extending in the machine
direction of the
collapsed bubble 110. In one particular embodiment, the spacing of the grooves
can be 20
grooves per inch, with each groove leading to a matching thin rib/thick rib
extending along the
length of the collapsed bubble 110. The spacing of the ribs in the film after
stretching is greater
than the groove spacing of the intermeshing rollers 122a, 122b, since the
stretching causes each
rib to spread away from each other. The pattern of thick and thin ribs is
represented by a pattern
of parallel and adjacent lines in the figures. The spacing between ribs is
exaggerated for ease of
illustration.
[0045] Once the collapsed bubble 110 has been incrementally stretched in the
cross direction,
the collapsed bubble 110 can be slit to form two separate partial collapsed
bubbles 110a and
110b. As shown in Figs. 1 and 2, the slitting operation 140 of the collapsed
bubble 110 can
occur approximately at a location between the first edge 112 and second edge
114 of the
collapsed bubble 110. A centerline can be defined to extend parallel to the
length of the
collapsed bubble and at the center of the collapsed bubble 110, relative to
the first edge 112 and
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second edge 114. The centerline of the collapsed bubble 110 is also parallel
to the first edge 112
and second edge 114. The slitting operation 140 can be located approximately
at the centerline
of the collapsed bubble 110. Once the collapsed bubble 110 is slit at the
centerline, it can be
separated into two half-bubbles 110a, 110b and each half-bubble can be rolled
onto separate
master rolls 134a, 134b. The first half-bubble 110a can have a first edge 112a
and a second edge
112b, the second edge 112b formed from the splitting operation 140. The second
half-bubble
110b can have a first edge 114a and a second edge 114b, the second edge 114b
formed from the
splitting operation 140.
100461 As shown in Fig. 2 and 3, the plurality of grooves 128a, 128b, can be
centered along
the centerline of the collapsed bubble 110. Hence, the ring rolling operation
120 results in a first
incrementally stretched partial width 116 centered about the width of the
collapsed bubble 110.
After the collapsed bubble 110 is split into a first and second half bubbles
110a, 110b, the first
incrementally stretched partial width 116 of the collapsed bubble 110 results
in a second
incrementally stretched partial width 116a of the first half-bubble 110a and a
third incrementally
stretched partial width 116b of the second half-bubble 110b. The second and
third incrementally
stretched partial widths 116a, 116b extend from one of the second edges 112b,
114b of each half-
bubble 110a, 110b, towards one of the first edges 112a, 114a of each half-
bubble 110a, 110b. In
at least one embodiment, the second and third incrementally stretched partial
widths 116a, 11613,
can have a width that is less than half the width of each half-bubble 110a,
110b.
100471 In one particular example, the collapsed bubble 110 may have a width
prior to
stretching of 60 inches. The plurality of grooves 128a, 128b of the
intermeshing rollers 122a,
122b may have a width of approximately 16 inches and a depth of engagement so
that the 16
inches of the collapsed bubble 110 that is engaged by the intermeshing rollers
122a, 122b is
stretched to approximately 20 inches. Thus, once stretched, the width of the
collapsed bubble
110 is approximately 64 inches. Once the collapsed bubble 110 is separated
into a first half-
bubble 110a and a second half-bubble 110b, each half bubble 110a, 110b has an
overall width of
approximately 32 inches with an incrementally stretched partial width 116a,
116b of
approximately 10 inches.
100481 As shown
in Figs. 1 and 2, each operation, including the blown film extrusion and
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incremental stretching of the collapsed bubble 110 can be performed
synchronously. For
example, at the same time a portion of the bubble 104 is being formed by the
extruder 106, the
same bubble 104, in the form of a collapsed bubble 110, can be incrementally
stretched by the
intermeshing rollers 122a, 122b.
[0049] Once each incrementally stretched collapsed half-bubble 110a, 110b has
been rolled
onto a master roll, each master roll 134a, 134b can then be used to
manufacture polymeric bags,
including drawstring trash bags. One particular type of drawstring trash bag
that the present
invention is particularly well suited for use is an extended hem drawstring
trash bag, which is
explained in greater detail below.
[0050] The collapsed bubble 110 can be stretched in other locations other than
about the
centerline of the collapsed bubble 110 as shown in Fig. 2. Fig. 5 shows use of
incremental
stretching to form two discrete widths, a first incrementally stretched
partial width 118a, and a
second incrementally stretched partial width 118b of the collapsed bubble 110.
Each
incrementally stretched partial width 118a, 118b extends adjacent from the
centerline of the
collapsed bubble 110 towards one of the two edges 112, 114 of the collapsed
bubble 110.
[0051] As further shown in Fig. 5, after being incrementally stretched, the
collapsed bubble
110 can be separated by splitting operation 140 into a first half-bubble 110a
and a second half
bubble 110b. The first half-bubble 110a has a first edge 112a and a second
edge 112b. The
second half-bubble 110b also has a first edge 114a and a second edge 114b. The
splitting
operation 140 results in the first incrementally stretched partial width 118a
on the first half-
bubble 110a and the second incrementally stretched partial width 118b on the
second half-bubble
110b. Each incrementally stretched partial width 118a, 118b is bounded by un-
stretched material
on both the first edge 112a, 114a and the second edge 112b, 114b. Each half-
bubble 110a, 110b
can be rolled onto a separate master roll 134a, 134b.
[0052] In one particular example, each incrementally stretched partial width
118a, 118b can be
incrementally stretched approximately 14 inches wide after stretching, and
have approximately a
12 inch width prior to stretching. The width of each half-bubble 110a, 110b,
can be
approximately 29 inches prior to stretching and 31 inches after stretching.
The un-stretched
material that bounds each side of each incrementally stretched partial width
118a, 118b can vary
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considerably, but in one particular example, the width of each un-stretched
area can be
approximately 8.5 inches.
[0053] As shown in Fig. 6, in another embodiment of the present invention, a
collapsed bubble
110 is incrementally stretched a partial width synchronously with the
extrusion of the bubble 104
and the converting of the collapsed bubble 110 into polymeric bags 200.
Polymeric resin is first
extruded from extruder 106 to form a polymeric tube or bubble 104. After being
collapsed by
nip rollers 108, the collapsed bubble 110 can be slit on a first edge 112 of
the collapsed bubble
110 by a slitting operation 150. In an alternative embodiment, the slitting
operation 150 can be
performed further downstream after the collapsed bubble 110 has been
incrementally stretched.
The slitting mechanism cuts a first edge 112 of the collapsed bubble 110 so
that the collapsed
bubble is open at the first edge 112. The slitting operation 150 results in a
first panel and a
second panel from the two opposing faces of the collapsed bubble 110 with each
panel having a
distal end at the first edge 112 and an interconnected end at the second edge
114 of the collapsed
bubble 110.
100541 After being slit along the first edge 112, the collapsed bubble 110 can
enter a pair of
intermeshing rollers 122a, 122b through the nip 126. The intermeshing rollers
122a, 122b can
have intermeshing grooves 128a, 128b along only a partial width of the
rollers, so that the
collapsed bubble 110 is incrementally stretched only along a portion of its
width to form an
incrementally stretched partial width 116. The intermeshing rollers 122a, 122b
can engage the
collapsed bubble 110 from the first edge 112 to a certain distance inward from
the first edge 112.
Once the collapsed bubble 110 is incrementally stretched, it can enter a bag
converting operation
130 that converts the incrementally stretched collapsed bubble 110 into a
plurality of trash bags
200. The bag converting operation 130 can separate each panel of the collapsed
bubble 110 and
fold in half the incrementally stretch partial width 116 of each panel towards
the second edge 114
to form a pair incrementally stretched extended hems 246, 248 on each trash
bag 200.
100551 In one particular embodiment, the entire width of the collapsed bubble
110 of Fig. 6
may be approximately 30 inches and the incrementally stretched partial width
116 may be
approximately eight inches before the ring rolling operation completes. After
stretching, the
incrementally stretched partial width 116 may grow to approximately 10 inches
so that the
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overall width of the collapsed bubble 110 increases to approximately 32
inches. After folding
one-half of the incrementally stretched partial width 116 to form the pair of
extended hems 246,
248, trash bags 200 may be formed with each trash bag having a final length of
approximately 27
inches and each extended hem 246, 248 having a length of approximately 5
inches.
[0056] In a further embodiment as shown in Fig. 7, a method of forming
polymeric bags can
begin with a previously slit collapsed half-bubble 110a rolled onto a master
roll 136. The
collapsed half-bubble 110a on the master roll 136 can have previously been
formed in a blown
film extrusion process. In this embodiment, the collapsed half-bubble 110a is
not incrementally
stretched prior to being rolled onto the master roll 136. The collapsed half-
bubble 110a is
unrolled from the master roll 136 and enters the nip 126 of the pair of
intermeshing rollers 122a,
122b. The intermeshing rollers 122a, 122b incrementally stretch the collapsed
half-bubble 110a.
The collapsed half-bubble 110a is incrementally stretched only a partial width
of the collapsed
half-bubble 110a. In this embodiment, the incrementally stretched partial
width 116 extends
from the second edge 112b of the collapsed half-bubble 110a towards the center
of the collapsed
half-bubble 110a with a length less than half of the width of the collapsed
half-bubble 110a.
Once the collapsed half-bubble 110a passes through the stretching rollers 124,
it enters the bag
converting operation 130.
[0057] During the bag converting operation 130 shown in Fig. 7, the slit on
the second edge
112b of the collapsed half-bubble 110a provides a first panel and second panel
from the
collapsed half-bubble 110a, each panel having a distal edge at the second edge
112b. Each distal
edge of each panel is folded inwards towards itself. The length of each fold
is approximately
half of each incrementally stretched partial width 116. After being folded, an
extended hem 246,
248 is defined in the collapsed half-bubble 110a with the extended hem 246,
248 comprised of
the incrementally stretched partial width 116. Prior to or during the folding
operation, a
drawstring can be inserted adjacent to the fold within the folded area. To
complete the bag
converting operation 130, side seals and perforations are formed at pre-
defined lengths extending
along the width of the collapsed half-bubble 110a.
[0058] In one particular example of the Fig. 7 embodiment, the entire width of
the collapsed
half-bubble 110a may be approximately 30 inches and the incrementally
stretched partial width
CA 02927815 2016-04-25
116 may be approximately eight inches before being stretched. After
stretching, the
incrementally stretched partial width 116 may grow to approximately 10 inches
so that the
overall width of the collapsed bubble 110a increases to approximately 32
inches. When
converted to trash bags 200, these dimensions results in trash bags 200 with a
length of
approximately 27 inches and having approximately 5 inch long extended hems
246, 248.
[0059] In another embodiment shown in Fig. 8, a method of forming polymeric
bags can begin
with a previously slit collapsed half-bubble 110a rolled onto a master roll
136 as previously
described regarding Fig. 7. Rather than incrementally stretching the collapsed
bubble 110a
proximate to the second edge 112b, a partial width 118 of the half-bubble 110a
can be
incrementally stretched about the centerline of the half-bubble 110a. As shown
in Fig. 8, the
incrementally stretched partial width 118 is bounded on both sides by a
partial width of un-
stretched material of the half-bubble 110a.
[0060] In one particular example, the incrementally stretched partial width
118 can be
approximately 17 inches prior to stretching and approximately 21 inches after
stretching. The
un-stretched width adjacent to the second edge 112b can be approximately 6
inches and the un-
stretched width adjacent to the first edge 112a can be approximately 2 inches.
The entire width
of collapsed half-bubble 110a can be approximately 26 inches prior to
stretching and
approximately 29 inches after stretching.
[0061] After being incrementally stretched, the collapsed half-bubble 110a can
then enter a bag
converting operation 130. In the bag converting operation 130, the collapsed
bubble can be
converted into a plurality of drawstring trash bags 200 as previously
discussed. However, for the
embodiment shown in Fig. 8, the hem of each drawstring trash bag is not formed
from
incrementally stretched material but rather un-stretched material.
Furthermore, the hem can be
formed from less width of the collapsed bubble than the embodiment of Fig. 7.
For instance, in
one particular embodiment, four inches of the collapsed bubble along the
second edge 112b can
be used to form a resulting hem with a two-inch length after being folded.
[0062] Shown in Fig. 9 is an alternative embodiment of a partially
incrementally stretched
collapsed half-bubble 110a. The half-bubble 110a can be formed in the same
manner as
described for the embodiments shown in either Fig. 5 or Fig. 8 but with the
location of where the
16
CA 02927815 2016-04-25
plurality of grooves 128a, 128b of the intermeshing rollers 122a, 122b engage
the collapsed
bubble offset from the previous embodiments. As shown in Fig. 9, the
incrementally stretched
partial width 138 is located adjacent to the second edge 112b of the half-
bubble 110a with a
partial width of un-stretched film 142 separating the incrementally stretched
partial width 138
from the second edge 112b. The width of the incrementally stretched partial
width 138 can be
limited so that more than half of a width un-stretched material of the half-
bubble 110a separates
the incrementally stretched partial width 138 from the first edge 112a. The
partial width of un-
stretched film 142 can have a width that is a fraction, less than one-half, of
the width of the
incrementally stretched partial width 138.
[0063] In a particular embodiment of the Fig. 9 embodiment, after stretching,
the entire width
of the collapsed bubble 110 or half-bubble 110a can be approximately 32
inches. The
incrementally stretched partial width 138 can be approximately nine inches
after stretching, the
un-stretched region between the incrementally stretched partial width 138 and
first edge 112 can
be approximately one inch, and the remaining un-stretched width of the
collapsed bubble can be
approximately 22 inches.
[0064] As previously discussed, the previously disclosed embodiments of the
invention are
particularly well adapted for use in an extended hem drawstring trash bag.
Fig. 10 provides a
perspective view, Fig. 11 provides a top cross-section view, and Fig. 12
provides a front view of
such a trash bag. Looking collectively at Figs. 10-12, the extended hem
drawstring trash bag
200 is comprised of a front panel 202 and a back panel 204, the front panel
202 and back panel
204 being substantially rectangular in shape and joined along a first edge
210, a second edge
212, and a bottom edge 214 to provide the body of the bag. The front panel 202
and back panel
204 may be formed from a single piece of polymeric film, such as a section of
the collapsed
bubble 110 or collapsed half-bubble 110a, 110b. The bottom edge 114 of the
collapsed bubble
110 can form the bottom edge 214 of the trash bag 200. The section of the
collapsed bubble 110
is subsequently sealed along the first edge 210 and second edge 212 of the
trash bag.
[0065] In Fig. 11, a cross-sectional partial view of the extended hem
drawstring trash bag 200
is shown. In particular, an upper cross-section of a drawstring trash bag 200
is depicted,
although the thicknesses and dimensions are exaggerated to better illustrate
the relation between
17
CA 02927815 2016-04-25
the various parts of the bag. During manufacture of the bag, the distal edge
216 of the front
panel 202, i.e. the edge of the folded-over portion of the front panel 202
results from the fold-
over portion defining the first hem 222 in the front panel 202 and a first
drawstring 232 disposed
within the first hem 222. Similarly, the distal edge 218 of the back panel 204
results from the
fold-over portion defining the second hem 224 with a second drawstring 234
disposed in the
second hem 224. The upper boundaries of the hems 222, 224 define the upper
opening 220 of
the drawstring trash bag 200.
[0066] The drawstrings 232, 234 may be comprised of traditional high-density
polyethylene
drawstrings or, in some embodiments, elastic or elastic-like polymeric
components. The
drawstrings 232, 234 are anchored to the front panel 202 and back panel 204 at
the ends of the
respective drawstrings 232, 234 near the first side edge 210 and second side
edge 212. In
particular, the drawstrings 232, 234 are commonly anchored using short seals
236, 238 as shown
in Figs. 10 and 12, the short seals 236, 238 fusing both drawstrings 232, 234
with both the front
panel 202 and the back panel 204. Other than the anchor point, the drawstrings
232, 234 are
generally loose within the hems 222, 224 enabling the drawstrings 222, 224 to
be accessed and
pulled through the respective drawstring cutouts 226, 228 centrally located
between the first side
edge 210 and second side edge 212. Consequently, when the drawstrings 232, 234
are pulled
through the drawstring cutouts 226, 228 of the drawstring trash bag 200, the
respective upper
corners of the drawstring trash bag 200 are pulled together to facilitate
closure of the bag.
100671 Now looking at Figs. 10-12, the distal edges 216, 218 of the
respective front and back
panels 202, 204 are located a distance below the respective hems 222, 224.
Thus, the front panel
202 has an overlap area 242 that extends from the lower boundary of the first
hem 222 to the
distal edge 216 of the front panel 202. In the same manner, the back panel 204
has an overlap
area 244 that extends from the lower boundary of the second hem 224 to the
distal edge 218 of
the back panel 204.
10068] Thus, for the front panel 202, the overlap area 242 comprises two
layers of polymeric
film, and the hem overlap area 244 of the back panel 204 also comprises two
layers of polymeric
film according to the depicted embodiment. The length of the first overlap
area 242 and the
second overlap area 244 can be selected to be any length including a distance
ending only
18
CA 02927815 2016-04-25
slightly below the bottom boundaries of the respective hems 222, 224 or a
distance that extends
nearly to the bottom of the bag. The area of the first hem 222 and overlap
area 242 defines a first
extended hem area 246. In a likewise manner, the area of the second hem 224
and the overlap
area 244 defines a second extended hem area 248.
[00691 When utilizing the above-described methods of incremental stretching,
the extended
hem areas 246, 248 may be comprised of the partially incrementally stretched
width 116, 116a,
116b, or 138 of Figs. 2, 6, 7, or 9, depending upon the method utilized to
form the incrementally
stretched width.
100701 The drawstring trash bag depicted in Figs. 10-12 is illustrated as
having hem seals 262,
264 extending across the width of the drawstring trash bag 200. Additionally,
lower seals 272,
274 are provided in the respective panels 202, 204 proximate to the respective
distal edges 216,
218. By providing hem seals 262, 264 near the top of the overlap areas 242,
244 and lower seals
272, 274 near the bottom of the overlap areas 242, 244, the two layers of
polymeric film
comprising each overlap area 242, 244 are kept in close proximity, providing
effectively a two-
ply polymeric film of increased thickness in the region of the overlap areas
242, 244.
[0071] The overlap areas 242, 244, as shown in the depicted embodiments,
provide important
benefits during use of the drawstring trash bag 200. The primary benefit
offered by the overlap
areas 242, 244 is reinforcing the drawstring trash bag 200 in the areas
immediately below the
hems 222, 224 and drawtape 232, 234. As best illustrated by Fig. 11, it can be
seen that the
thickness of the polymeric film is increased substantially in the overlap
areas 242, 244 compared
to the remaining area of the front panel 202 and back panel 204 below the
overlap areas 242,
244. The thicker overlap area 242, 244 is therefore expected to be stronger
than the remainder of
the bag. Thus, in the event that a consumer is carrying the bag or gripping
the bag in one or both
of the overlap areas 242, 244, it is less likely that the drawstring trash bag
200 will puncture or
tear in that particular area. By reducing the likelihood that the drawstring
trash bag 200 will fail
when a consumer grabs the drawstring trash bag 200 in the overlap areas 242,
244, the
drawstring trash bag 200 is more useful--especially when it contains heavier
items or debris.
100721 For example, in the case of a collapsed bubble 110 or collapsed half-
bubble 110a, the
film of the bubble can have a nominal thickness of 0.7 mil. The incrementally
stretched partial
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width 116 or 116a of Fig. 2, 6, 7 can have a width of 10 inches with an
average stretch of 20
percent, which leads to approximately an average thickness of 0.56 mil for the
incrementally
stretched partial width 116 or 116a. The incrementally stretched collapsed
bubble 110 or
collapsed half-bubble 110a can be formed into extended hem trash bags 200 with
the
incrementally stretch partial width 116, 116a formed into the extended hem
areas 246, 248. The
resulting average thickness of each extended hem areas 246, 248 can be
approximately 1.12 mil,
with each extended hem area 246, 248 having a length of approximately 5
inches. Thus, the
extended hem areas 246, 248 may provide an increase in overall film thickness
and hence
strength while not utilizing as much material as would be required from film
that had not been
partially incrementally stretched.
[0073] If the extended hem areas 246 and 248 were composed of un-stretched
film, then the
thickness of the extended hem areas would be double in relation to the
remaining body of the
bag. Although this would be expected to provide for a substantial increase in
the strength of the
extended hem area of the bag, it also would substantially increase the amount
of polymeric resin
used to manufacture the bag. By forming the extended hem areas 246, 248 of the
bag from film
that has been incrementally stretched, a substantial increase in strength is
imparted to this area of
the bag while decreasing the amount of material required to manufacture each
bag in comparison
to an extended hem bag not utilizing film that has been partially
incrementally stretched.
[0074] The collapsed half-bubble 110a of Fig. 9 can also be used to form an
extended hem
drawstring trash bag as shown in Figs. 10-12. A detailed sectional view of
this bag is shown in
Fig. 13. To form the extended hem areas 246 and 248 of the trash bag, each
panel of the
collapsed bubble 110 can be folded into itself a slight distance below a
middle of the
incrementally stretched partial width 138. Thus, the incrementally stretched
partial width 138
encompasses a substantial portion of the extended hem areas 246 and 248.
However, a bottom
area of the extended hem area 246 extending from the distal edge 216 and
encompassing the
location of the lower seal 272 is comprised of the partial width of un-
stretched film 142 of Fig. 9.
This partial width of un-stretched film 142 of Fig. 9 is shown in Fig. 13
extending from the distal
edge 216 to the border of the incrementally stretched partial width 276. In
one particular
example, a width of the un-stretched film 142 can be approximately one inch.
CA 02927815 2016-04-25
[0075] Use of the incrementally stretched partial width 138 of Fig. 9 offers
additional
advantages from other methods disclosed to form an incrementally stretched
partial width. For
instance, there is a risk that incremental stretching of the film of the
collapsed bubble could
interfere with the sealing of the trash bag, such as for the lower seal 272 of
Fig. 13. Use of the
incrementally stretched half-bubble 110a of Fig. 9 limits this risk since the
film is not stretched
at the location of the lower seal 272. Thus, a more secure lower seal 272 may
result from this
embodiment and lead to a stronger and more reliable trash bag.
100761 Fig. 14 illustrates another extended hem drawstring trash bag utilizing
an incrementally
stretched partial width created via the methods previously described. The
trash bag 200 shares
many of the same features as the trash bag illustrated in Figs. 10-12. Hence,
likewise features
share the same identifiers as the previous figures. However, the bag
illustrated by Fig. 14
utilizes incremental stretching in a different area of the bag from the
previously illustrated bag of
Figs. 10-12. Rather than utilizing incremental stretching on the extended hem
drawstring trash
bag in the extended hem areas 246, 248 of the trash bag, the bag body 250 is
incrementally
stretched. The processes discussed and shown for Figs. 5 and 8 may be utilized
to manufacture
the bag shown in Fig. 14. This embodiment allows use of film with a thinner
average gauge to
be present in the bag body 250 for circumstances where it is desirable for the
extended hem areas
246, 248 to have greater than twice the thickness of the bag body. The bag
body 250 can be
defined to be the section of the front and back panel 202, 204 located below
the lower seals 272,
274 and above the bottom edge 214.
[00771 In one particularly example for Fig. 14, the processes described above
can form a
collapsed bubble 110 or collapsed half-bubble 110a having a film thickness of
approximately 0.8
mil. Thus, the total thickness of each extended hem area 246, 248 will be
approximately 1.6 mil.
However, if the 0.8 mil film is stretched on average 15 percent, the resultant
average thickness of
the incrementally stretched region of the bag body will be approximately 0.68
mils. In a
particular embodiment, the length of the incrementally stretched region of the
bag body 250 can
be approximately 18 inches with two inches of the bag body 250 on each side of
the
incrementally stretched region left un-stretched. Thus, the entire length of
the bag body 250 can
be 22 inches. The extended hem area of the bag can have a length of 5 inches
so that the entire
length of the bag 200 is approximately 27 inches.
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[0078] A further embodiment of a drawstring trash bag is shown in Fig. 15 that
may utilize the
previously discussed methods of partial incremental stretching of a collapsed
bubble. The
embodiment of Fig. 15 fails to include overlap areas 242, 244 and hence does
not include an
extended hem area 246/248 as shown in Fig. 11. In this instance, the bag body
250 is
incrementally stretched to reduce the amount of film used in the bag body 250.
The processes
discussed and shown for Figs. 5 and 8 may be utilized to manufacture the bag
shown in Fig. 15.
[0079] The amount of film used is limited in this embodiment since the hem is
not extended,
relative to the embodiment shown in Fig. 14. The embodiment of Fig. 15 allows
the use of a
thicker film than normally would be used to increase the strength of the
bottom of the bag and
the hems 222, 224 of the bag. By utilizing one of the incremental stretching
methods described
above, the bag body 250 can be incrementally stretched while the hems 222, 224
and the film
immediately below the hems 222, 224 can be left un-stretched so that the area
proximate to the
hems 222, 224 has greater strength than the remaining area of the bag.
[0080] In one particular embodiment, the collapsed bubble film thickness can
be a nominal
thickness of one mil. A partial width of the collapsed bubble 110 or collapsed
half-bubble 110a
can be stretched approximately 20 percent so that when the collapsed bubble
110 or collapsed
half-bubble 110a is converted into bags, the bag body 250 comprises the
incrementally stretched
film. The resultant average thickness of the bag body 250 that has been
incrementally stretched
can be approximately 0.8 mil. For a trash bag with an overall length of
approximately 27 inches,
approximately 21 inches of the bag body can be incrementally stretched with
approximately two
inches of the bag bottom un-stretched, leaving approximately a two-inch un-
stretched hem, and
approximately two inches below the hem un-stretched. Thus, the bag 200 should
have targeted
increased strength in the bag bottom and hem area, in comparison to a bag made
exclusively out
of tin-stretched 0.8 mil film.
100811 As previously noted, the specific embodiments depicted herein are not
intended to limit
the scope of the present invention. Indeed, it is contemplated that any number
of different
embodiments may be utilized without diverging from the spirit of the
invention. Therefore, the
appended claims are intended to more fully encompass the full scope of the
present invention.
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