Note: Descriptions are shown in the official language in which they were submitted.
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METHOD OF FORMING POLYMERIC BAGS
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] Not applicable.
BACKGROUND OF THE INVENTION
1. Field of the Invention
[0002] The present invention relates to improvements in bags made from
polymeric film and
processes for manufacturing polymeric film bags.
2. Description of the Related Art
[0003] Thermoplastic films are used in a variety of applications. For example,
thermoplastic
films are used in sheet form for applications such as drop cloths, vapor
barriers, and protective
covers. Thermoplastic films can also be converted into plastic bags, which may
be used in a
myriad of applications. The present invention is particularly useful to trash
bags constructed
from thermoplastic film.
[0004] 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 and more particular for larger bags
used for the
collection of larger debris.
[0005] 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 collapsed tube 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.
[0006] 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.
[0007] 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.
[0008] One common method of manufacturing trash bags involves segregating the
collapsed
polymeric tube into individual trash bags by forming seals which extend
transversely across the
entire width of the tube. Typically a line of perforations is formed
immediately adjacent and
parallel to each seal to facilitate separation of the trash bags one from
another. After the trash
bags are sealed and perforated, the trash bags can be twice-folded axially
into a fractional width
configuration.
[0009] It is also known to provide wave-cut trash bags. A wave-cut trash bag
has a wave or
lobe-shaped configuration at its open end. This provides two or more lobes,
which can be used
to tie the trash bag in a closed configuration after it is filled.
[0010] Wave-cut trash bags can be manufactured by providing closely spaced,
parallel
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transversely extending seals at predetermined intervals along the collapsed
polymeric tube. A
transversely extending line of perforations is provided between the closely
spaced, parallel seals.
The collapsed polymeric tube is then separated longitudinally along a wave or
lobe-shaped line
located equidistant between the edges of the tube.
10011] The lobe-shaped features, or lobes, of a wave-cut trash bags, which may
also be
referred to as tie-flaps, provide a convenient user feature to tie and close
the opening of the bag.
The lobes are grasped and knotted to seal the bag opening. Representatives of
wave-cut or "tie
bags" can be found in the following prior art of U.S. Pat. Nos. 4,890,736,
5,041,317, 5,246,110,
5,683,340, 5,611,627, 5,709,641, and 6,565,794.
[0012] In a further publication, U.S. Pat. Appl. Pub. 2008/0292222A1 discloses
a bag having at
least two "tie flaps" with gripping features embossed on at least one surface
of the tie flaps. It is
further disclosed that the bag may formed from a tube of thermoplastic
material. However, the
publication further discloses that the gripping feature is formed in a linear
fashion along a length
of a blown film bubble that is then slit lengthwise in a wave pattern. The
bubble is then formed
into bags after being collapsed with a collapsed edge forming a bottom of the
bag.
[0013] It has been determined, however, that the lobes of prior art wave-cut
bags are often
difficult to grasp and manipulate, especially if the lobes are contaminated
with slippery trash
contamination such as oil or grease or moist organic contaminants.
Furthermore, wave-cut bags
are often manufactured with thicker film than other types of trash bags since
they often arc
intended for use with larger and heavier debris, such as yard debris and
debris from home
improvement projects. These thicker films used on larger wave-cut bags can be
as thick as 3
mils and make it challenging for a user to manipulate the lobes of a wave-cut
bag into a knot.
Hence, it would be desirable to provide a wave-cut bag that has easier to
grasp lobes that are also
thinner than the rest of the bag. The present invention represents a novel
solution to address this
need.
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SUMMARY OF THE PRESENT INVENTION
[0014] In at least one embodiment of the present invention, a bag of polymeric
film may be ,
formed. To form the polymeric bag, a collapsed tube of polymeric film may be
formed with a
machine direction. The collapsed tube may be formed from a blown film
extrusion process.
Once the collapsed tube is formed, a pair of intermeshing rollers may
intermittently engage the
collapsed tube to form a plurality of incrementally stretched sections on the
collapsed tube.
Within each incrementally stretched section may be defined a plurality of thin
and thick ribs that
extend across a width of the collapsed tube. The plurality of thin and thick
ribs may be parallel
to each other and transverse to the machine direction of the collapsed tube.
The pair of
intermeshing rollers may stretch the collapsed tube in the machine direction.
[0015] Once the collapsed tube is incrementally stretched, a bag converting
operation may
form the collapsed tube into a plurality of bags. Each one of the plurality of
bags may have at
least a fraction of one of the plurality of incrementally stretched sections.
A wave-cutting
operation may divide each of the incrementally stretched sections into two
separate components.
Each of the two separate components may be approximately one-half of an
incrementally
stretched section. One half of an incrementally stretched section may define
an incrementally
stretched portion on a first trash bag and a second half of an incrementally
stretched section may
define an incrementally stretched portion on a second trash bag.
[0016] The bag converting operation may further comprise forming sets of
closely spaced,
parallel seals extending transversely across the entire width of the collapsed
tube. Each set of'
closely spaced parallel seals may be at equally spaced intervals from each
other. The bag
converting operation may also form perforation lines extending transversely
across the entire
width of the collapsed tube with a perforation line located between each set
of closely spaced,
parallel seals. A plurality of wave-shaped perforations may also be formed in
the collapsed tube.
A location of each wave-shaped perforation may be equidistant from adjacent
perforation lines.
Each wave-shaped perforation may be centered within one of the plurality of
incrementally
stretched sections.
[0017] The converting operation may further comprise a timing operation. The
timing
operation may detect the location of each perforation line and generate a
timing signal. The
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location of each wave-shaped perforation and perforation line may be based
upon the timing
signal. The timing operation may be a standalone operation or may be
integrated into the bag
converting operation.
109181 The pair of rollers may counter-rotate in relation to each other so
that the collapsed tube
is fed through the pair of intermeshing rollers. A rotational axis of each of
the pair of
intermeshing rollers may be perpendicular to the machine direction of the
collapsed tube. Each
roller of the pair of intermeshing rollers may include a plurality of
protruding ridges extending
completely about a circumference of each roller. The plurality of protruding
ridges may also
only extend about a partial circumference of each roller. Each of the
protruding ridges may be
parallel to each other and parallel to the axis of rotation of each roller.
Each of the protruding
ridges may have a tip protruding radially outward from the axis of rotation of
one of the pair of
intermeshing rollers. The plurality of protruding ridges of one roller may
intermesh with the
plurality of protruding ridges of the other roller. The pair of intermeshing
rollers may intermesh
with each other only over a fraction of a circumference of each roller and
only incrementally
stretch the collapsed tube when the pair of intermeshing rollers are
intermeshed. The pair of
intermeshing rollers may be separated by a gap when the rollers are not
intermeshed.
[0019] The pair of intermeshing rollers may rotate at a constant speed so that
a tangential (i.e.
circumferential) speed of the rollers matches the linear speed of the
collapsed tube. The
rotational speed of the intermeshing rollers may also oscillate so that the
tangential speed of the
rollers match the linear speed of the collapsed tube when the rollers are
intermeshed and when
the rollers are not intermeshed the tangential speed of the rollers is slower
than the linear speed
of the collapsed tube.
100201 In a further embodiment of the present invention, a bag is formed form
a collapsed tube
of polymeric film. The bag may comprise a first panel and a second panel. The
first panel and
the second panel may be joined along a first side edge, a second side edge,
and a bottom edge.
The first side edge may be formed from a first edge of the collapsed tube and
the second side
edge may be formed from a second edge of the collapsed tube. The first panel
may have a first
top edge opposite the bottom edge and the second panel may have a second top
edge opposite the
bottom edge. The first top edge and second top edge may define an opening of
the bag. A distal
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end of both the top edge and second top edge may have a wave-shaped profile
and the wave-
shaped profile may define a plurality of lobes.
[0021] A plurality of ribs may be defined in the plurality of lobes. The
plurality of ribs may be
generally parallel to each other and each rib may extend from the first side
edge towards the
second side edge of the bag. Each rib may extend perpendicularly from the
first side edge to the
second side edge. A closure of the bottom edge may be formed from a seal
extending
transversely across the entire width of the collapsed tube. The wave-shaped
profile may define a
profile height and the plurality of ribs may extend below a bottom of the wave-
shaped profile
approximately one-half length of the profile height. The plurality of ribs may
also extend below
the bottom of the wave-shaped profile no more than a length of the profile
height, or more than a
length of the profile height. The plurality of ribs may result from
incremental stretching of the
polymeric film in the machine direction. The incremental stretching may be due
to a pair of
intermeshing rollers that intermittently incrementally stretch the collapsed
tube. The pair of
intermeshing rollers may have at least two rotational speeds. The pair of
intermeshing rollers
may rotate slower when incrementally stretching the collapsed tube than when
not incrementally
stretching the collapsed tube.
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BRIEF DESCRIPTION OF THE RELATED DRAWINGS
[0022] 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.
[0023] Fig. 1 depicts a perspective view of a first embodiment of the
present invention.
[0024] Fig. 2 depicts a partial perspective view of the first embodiment of
the present
invention.
[0025] Fig. 3a depicts a perspective view of an incremental stretching
operation of the first
embodiment.
[0026] Fig. 3b depicts a secondary perspective view of the incremental
stretching operation of
the first embodiment.
[0027] Fig. 4a depicts a perspective view of an incremental stretching
operation of a second
embodiment of the present invention.
[0028] Fig. 4b depicts a perspective view of an incremental stretching
operation of a third
embodiment of the present invention.
[0029] Fig. 5 depicts a front view of a fourth embodiment of the present
invention.
[0030] Fig. 6 depicts another front view of the fourth embodiment of the
present invention.
[0031] Fig. 7 depicts a front view of a fifth embodiment of the present
invention.
[0032] Fig. 8 depicts another front view of the fifth embodiment of the
present invention.
[0033] Fig. 9 depicts a top planar view of an intermeshing roller of a sixth
embodiment of the
present invention.
[0034] Fig. 10 depicts a front view of a trash bag of the sixth embodiment of
the present
invention.
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DETAILED DESCRIPTION OF THE INVENTION
[0035] 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.
[0036] Referring initially to Fig. 1 and Fig. 2, a process for forming wave-
cut trash bags with
incrementally stretched tie flaps or lobes is shown. The trash bags may be
formed by a blown
film extrusion process. The blown film extrusion process begins by molten
polymeric resin
being extruded through an annular die of an extruder 102 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 (MD). 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 (CD). The
blown film extrusion
process is well known in the art and is further explained in U.S. Patent No.
7,753,666.
[0037] 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
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%
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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. The film utilized to form polymeric bags may also comprise multiple
layers of blown
film resin. The resultant multi-layer film may be formed by coextrusion, a
lamination process, or
other methods of forming a multi-layer film known in the art. In each layer,
one or more of the
above-discussed polymers may be used.
[00381 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 tube 110.
The collapsed tube 110 includes two opposing interconnected surfaces of film
extending
continuously in a lengthwise direction. This continuously extending surface of
film may be
referred to as a web. 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.
[0039] As shown in Fig. 2, once collapsed, the collapsed tube 110 has a first
edge 112 and
second edge 114 defined in the opposing edges of the collapsed tube 110
extending the length of
the collapsed tube 110. The distance from the first edge 112 to the second
edge 114 of the
collapsed tube 110 can define a width of the collapsed bubble. Once the
collapsed tube 110
returns from the cooling tower (not shown), the collapsed tube 110 can feed
directly into an
incremental stretching operation 120; hence the incremental stretching can be
performed as an
in-line process, synchronously, with the blown film extrusion. As shown in
Fig. 1 and more
clearly in Fig. 2, the incremental stretching operation 120 can be configured
to only
intermittently stretch the collapsed tube 110, leading to incrementally
stretched partial lengths of
the collapsed tube 110.
[0040] As shown in Figs. 3a ¨ 4b, the incremental stretching operation 120 can
include a pair
of intermeshing rollers 122a, 122b. The diameter and length of each
intermeshing roller 122a,
122b are equal in a preferred embodiment but may vary. As best shown in Fig.
3a, the collapsed
tube 110 can enter a nip 124 defined by the pair of intermeshing rollers 122a,
122b. The
rotational axes 128a, 128b of each roller 122a, 122b can be parallel to each
other and transverse
to the machine direction (MD) of the collapsed tube 110. Each of the rollers
122a, 122b can
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have a plurality of protruding ridges 126 parallel to the axis of each roller
128a, 128b that extend
around the entire circumference of each roller 122a, 122b at a constant
spacing. The protruding
ridges 126 of the rollers 122a, 122b can be configured to intermesh like
gears. As the collapsed
tube 110 enters the nip of the intermeshing rollers 122a, 122b, the film of
the collapsed tube 110
is stretched based upon the depth and spacing of the grooves 126.
[0041] As best shown in Fig. 3a, the film of the collapsed tube 110 is
stretched by each groove
of the plurality of protruding ridges 126 in the machine direction, which
results in a pattern of
stretched and un-stretched lengths with each length extending along the width
or cross-direction
of the collapsed tube 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 cross-direction of the collapsed tube 110 for each
incrementally stretched
section 116.
[0042] The preferred actual size and spacing of each of the plurality of
protruding ridges 126
in relation to each of the rollers 122a, 122b is substantially exaggerated for
ease of illustration in
the figures. In one preferred embodiment, the spacing of the grooves can be 20
grooves per inch
about the circumference of each roller 122a, 122b, with each groove leading to
a matching thin
rib/thick rib extending along the width of the collapsed tube 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 the ribs 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.
[0043] Once again examining Fig. 3a and Fig. 3b, the incremental stretching
operation 120
can be configured to only engage, and hence only incrementally stretch, the
collapsed tube 110
intermittently. This intermittent engagement of the collapsed tube 110 leads
to lengths of un-
stretched sections 118 and lengths of incrementally stretched sections 116. As
illustrated in Fig.
3b, the intermittent engagement of the collapsed tube 110 can be accomplished
by the pair of
intermeshing rollers 122a, 122b moving away from each other a certain distance
G allowing the
collapsed tube 110 to move past the incremental stretching operation 120
without being stretched
by the intermeshing rollers 122a, 122b. The gap G, as shown in Fig. 3b, must
be large enough
to allow the collapsed tube 110 to pass through the nip 124 without
interference from the
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intermeshing rollers 122a, 122b.
[0044] Shown in Fig. 4a is an alternative method of intermittently
incrementally stretching the
collapsed tube 110. Unlike the previous embodiment of the incremental
stretching operation 120
shown in Figs. 3a and 3b, the rotational axes 128c, 128d of the pair of
intermeshing rollers 122a,
122b are mounted stationary in relation to each other. However, the protruding
ridges 126a,
126b extend only partially around the circumference of each roller 122a, 122b
rather than about
the entire circumference. The locations of the protruding ridges 126a, 126b on
each roller 122a,
122b are spaced appropriately so that the protruding ridges 126a, 126b
intermesh when the pair
of rollers 122a, 122b revolve. Thus, the collapsed tube 110 is incrementally
stretched only when
the protruding ridges 126a, 126b intelinesh and engage the collapsed tube 110.
The geometry of
each roller 122a, 122b can be configured so that the collapsed tube 110 is not
in contact with
either of the rollers 122a, 122b when not engaged with the protruding ridges
126a, 126b. In the
alternative, the diameter of each roller 122a, 122b, can be configured such
that the surface of one
or more of the rollers 122a, 122b is in contact with the collapsed tube 110
while the protruding
ridges 126a, 126b are not intermeshed. One or more of the rollers 122a, 122b
in contact with
the collapsed tube 110, when the protruding ridges 126a, 126b are not engaging
the collapsed
tube 110, may assist in maintaining the desired tension in the collapsed tube
110.
[0045] The rollers of Fig. 4a may rotate at a speed so that a tangential speed
of each roller
122a, 122b matches a linear speed of the collapsed tube 110 passing through
the nip 124. In the
alternative, the tangential speed of the rollers 122a, 122b may only match the
speed of the
collapsed tube 110 when the collapsed tube 110 is engaged by the protruding
ridges 126a, 126b.
When the protruding ridges 126a, 126b are not engaged, the rotational speed,
and hence the
tangential speed, of the pair of rollers 122a, 1221) can be decreased. In this
instance, the
diameter of each roller 122a, 122b must be configured such that the collapsed
tube 110 is not in
contact with the rollers 122a, 122b when not engaged with the protruding
ridges 126a, 126b,
since the linear speed of the collapsed tube 110 is typically constant.
Decreasing the speed of the
rollers 122a, 122b when not engaged with the web has the advantage of allowing
smaller
diameter rollers than would be required if the rollers rotated at a constant
speed.
100461 In one particular example, the incremental stretching operation 120 may
be configured
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such that each incrementally stretched section 116 of the collapsed tube 110
is 15 inches in
length after being stretched and each un-stretched section 118 is 85 inches in
length. For rollers
that rotate at a constant speed, the intermeshing rollers can be configured to
stretch the collapsed
tube approximately 15 percent such that the protruding ridges would extend
about the
circumference of each roller approximately 13 inches, stretching a length of
13 inches of the
collapsed tube 110, which results in a length of 15 inches after being
stretched. The remaining
smooth circumference of 85 inches would then be devoid of the protruding
ridges, which results
in a total circumference of approximately 98 inches and a diameter of
approximately 31.2 inches
for each roller 122a, 122b.
[0047] Unlike rollers that rotate at a constant speed, rollers 122a, 122b
configured to run at an
oscillating speed could have a smaller circumference and hence a smaller
overall size. For
instance, when not engaged, the rollers 122a, 122b could rotate with an
average tangential speed
of 50 percent of the linear speed of the web. The speed of the rollers 122a,
122b would not step
down instantly to 50 percent. Thus, the rollers 122a, 122b would first
decelerate, then rotate at a
speed of less than 50 percent, and then accelerate prior to engaging the
collapsed tube 110 again.
This arrangement would only require a smooth partial circumference of one-half
the previous
smooth circumference of approximately 42.5 inches and a 13-inch partial
circumference having
protruding ridges 126a, 126b for a total circumference of approximately 55.5
inches and a
diameter of approximately 17.7 inches for each roller 122a, 122b. It also
foreseeable that the
rollers could rotate at an average tangential speed of much less than 50
percent when not
engaged with the collapsed tube, such as 25 percent.
[0048] Decreasing the diameter and hence the overall size of the rollers 122a,
122b offers
several advantages. First, the cost to produce the rollers is decreased with
rollers of decreased
size. In addition, with smaller rollers, the time to manufacture the rollers
may also be reduced.
Smaller rollers lead to lighter weight rollers, which can lead to a mounting
system for the rollers
to be proportionally smaller and less expensive to construct. Lighter rollers
may also lead to
smaller, less expensive motors for driving the rollers. The use of smaller
drive motors may also
lead to less energy consumption.
[0049] As shown in Fig. 4a, the axes 128a, 128b of the rollers 122a, 122b can
be located
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relative to the collapsed tube 110 so that the collapsed tube 110 passes
equidistant from both
rollers 122a, 122b. However, in an alternative embodiment shown in Fig. 4b,
the collapsed tube
110 can be located slightly further away from the bottom roller 122b so that
protruding ridges
126 may extend completely about the entire circumference of the bottom roller
122b. In such an
embodiment, the collapsed tube 110 passes over the lower protruding ridges 126
when not
engaged by the upper protruding ridges 126a. When the collapsed tube 110 is
engaged by the
upper protruding ridges 126a, the collapsed tube 110 is pushed down into the
lower protruding
ridges 126 by the upper protruding ridges 126a.
[0050] In an alternative embodiment, the above-described incremental
stretching operation 120
can be performed on a single layer web of polymeric film. For instance, the
collapsed tube 110
may be slit along the first edge 112 so that the tube is open along the first
edge 112. The
collapsed tube may then be spread out so that the two opposing layers of the
collapsed tube 110
lie in the same plane adjacent to each other. The single layer web may then be
intermittently
incrementally stretched as described above. Once the stretching is complete,
the web may be
folded so that the two layers of the collapsed tube 110 once again oppose each
other. The two
layers of film adjacent to the first edge 112 may then be sealed together so
that the collapsed tube
100 may still be used to form wave-cut trash bags. Performing the incremental
stretching on one
layer of film may prevent undesired binding of the two layers of film.
[00511 In another alternative embodiment, rather than the incremental
stretching operation 120
performed in-line and synchronously, as described above, with the blown film
extrusion 102, the
incremental stretching 120 can be performed off-line from the blown film
extrusion. For
instance, once the polymeric bubble 104 is collapsed by the nip rollers 108,
the collapsed tube
110 can be rolled onto a master roll. The master roll can then be placed at a
lead end of the
incremental stretching operation 110 and the collapsed tube can be unrolled
from the master roll.
The collapsed tube 110 can then be fed into the incremental stretching
operation 120.
100521 Returning now to Figs. 1 and 2, once the incremental stretching is
complete, the
collapsed tube 110 can enter a bag converter 140. The bag converter 140 can
form sets of closely
spaced, parallel seals 142. The sets of closely spaced parallel seals 142 can
extend transversely
to the machine direction and across the entire width of the collapsed tube
110. As shown in Figs.
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and 6, one seal of each set 142 can define a bottom seal 142a for each bag
154a. As shown in
Fig. 2, between each set of the closely spaced parallel seals 142, the bag
converter 140 can form
perforation lines 144. The perforation lines 144 can extend transversely to
the machine
direction, the cross direction, and across the entire width of the collapsed
tube 110. Each
perforation line 144 can define the bag bottom 144a (shown in Fig. 5) and
separation point of
adjoining bags 154.
[0053] Once again examining Fig. 2, once the sets of closely spaced parallel
seals 142 and
perforation lines 144 are formed, the bag converter 140 can fold the collapsed
tube 110 one or
more times, with each fold extending along the length of the collapsed tube
110 and parallel to
the machine direction. In at least one particular embodiment, the collapsed
tube 110 can be
folded twice such that a width of the folded collapsed tube 110a is one-fourth
the width of the
un-folded collapsed tube 110. Once folded, a first folded edge 112a and second
folded edge
114a can be defined in opposing edges of each bag 154.
[0054] Once the
collapsed tube 110 is folded, it can proceed into a wave-cutter 150. The
wave-cutter 150, which may also be referred to as a wave-cutting operation,
creates wave-cuts
152. Wave-cuts 152 are wave-shaped perforations, extending across the width of
the folded
collapsed tube 110a. The wave-cuts 152 can perforate the folded collapsed tube
110a in the
shape of a one-half sine wave extending across the width of the folded
collapsed tube 110a. In
one particular embodiment, the amplitude of the sine wave can be approximately
5 inches but
may vary considerably. Due to the collapsed tube 110a being folded twice when
each wave-cut
152 is made, when un-folded each wave-cut can have, in general, a shape of two
full sine waves
extending across the width of the collapsed tube 110.
[0055] The location of the wave-cut 152 in relation to the perforation line
144 can be
controlled by a timing operation 160. The timing operation 160 can detect the
location of each
perforation line 144. The timing operation 160 can rely upon a laser beam,
infrared light, a spark
generator, or another form of an electromagnetic signal to detect each
perforation line 144. The
detected location of each perforation line 144, along with the fixed position
of the timing
operation 160 and the collapsed tube 110 traveling at a steady state, can be
used to time the
incremental stretching operation 120 and wave-cutting operation 150 so that
each wave-cut 152
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CA 02927799 2016-04-25
and incrementally stretched section 116 are placed at predetermined locations.
The timing
operation 160 may be a standalone operation or may be integrated into the bag
converter 150.
[0056] In at least one preferred embodiment, each wave-cut 152 can be centered
by the wave-
cutter 150 about a height of an incrementally stretched section 116, in
relation to the machine
direction. Thus, a distance from a bottom of a wave-cut 152 to a lower
boundary of an
incrementally stretched section 116, the lower boundary separating an
incrementally stretched
section 116 from an un-stretched section 118, can be equal to a distance from
a top of the wave-
cut 152 to an upper boundary of the incrementally stretched section 116, the
upper boundary
opposite from the lower boundary. Each centered wave-cut 152 and incrementally
stretched
section 116 can be equidistant from adjacent perforation lines 144. In this
preferred
embodiment, once the collapsed tube 110 is separated at wave-cuts 152 and
perforation lines 144
to form bags 154a, an approximate one-half length of an incrementally
stretched section 116 is
defined on each bag 154a (in relation to a mid-point or average of the
waveform of the wave-cut
152).
[0057] In a particular example of this embodiment, the perforation lines 144
can be 100 inches
away from each other. Each incrementally stretched section 116 and wave-cut
152 can also be
separated from adjacent incrementally stretched sections 116 and wave-cuts 152
by 100 inches.
Since the sections 116 and wave-cuts 152 are aligned or centered, a mid-point
of each section
116 and wave-cut 152 is located 50 inches away from adjacent perforation lines
144.
[0058] Once the collapsed tube is folded and the wave-cuts 152 are placed, the
folded
collapsed tube 110a may be separated at the perforation lines 144 and wave-
cuts 152 into
individual bags 154 with each bag having a height of approximately 50 inches.
Each bag 154
may then be overlapped with an adjoining bag and rolled into a roll of bags as
is known in the
art.
[0059] Figs. 5 and 6 show in detail the structure of the trash bags 154 that
may be formed from
the above-described processes. Fig. 5 shows that once adjacent perforation
lines 144 arc
separated, a matching pair of interconnected trash bags 154 are defined. A
boundary of each
trash bag is defined by one of the wave-cuts 152. An incrementally stretched
section 116 is
shown located on the two adjoining bags 154. Further shown is first edge 112
and second edge
CA 02927799 2016-04-25
114 of the collapsed tube 110 defining two opposing sides of the two adjoining
bags 154. Two
opposing perforation lines 144 are shown defining a bottom of each adjoining
bag 154. Once the
perforated wave-cut 152 is separated, two separate trash bags result. One of
the resultant trash
bags 154a is shown in Fig. 6.
100601 As shown in Fig. 6, each wave-cut trash bag 154a can comprise a front
panel and a rear
panel formed from opposing sides of the collapsed tube 110. The trash bag 154a
can have a first
side edge 112b defined by the first edge 112 of the collapse tube 110 and a
second side edge
114b defined by the second edge 114 of the collapsed tube 110. The trash bag
154 can further
have a bottom seal 142a defined by one seal of the closely spaced sets of
seals 142. A bag
bottom 144a can be defined by one of the perforation lines 144. The bag top
152a can be
defined by one of the wave-cuts 152. The bag top 152a can have a wave-cut
profile. The bag
top 152a can be defined on both the front panel and back panel of the bag 154a
and the bag top
152a can define a bag opening.
100611 As shown in Figs. 2, 5 and 6, an incrementally stretched portion 158 of
the trash bag
154a can be comprised of an incrementally stretched section 116 of the
collapsed tube 110. The
incrementally stretched portion 158 can be a fractional length of one of the
incrementally
stretched sections 116. Within the incrementally stretched portion 158, a
plurality of lobes 156
can be defined. The plurality of lobes 156 may also be referred to as tie-
flaps. A wave-cut
profile height H can be defined as a vertical distance from a top of the wave-
cut profile to a
bottom of the wave-cut profile, the wave-cut profile height H equal to an
amplitude of the wave
shape of the wave-cut profile. The incrementally stretched portion 158 can
extend from the bag
top 152a to at least the bottom of the wave-cut profile. However, at least in
one embodiment, the
incrementally stretched portion 158 can extend below the bottom of' the wave-
cut profile up to
one-half the wave-cut profile height H. In an alternative embodiment, the
incrementally
stretched portion 158 can extend below the bottom of the wave-cut profile at
least a distance
equal to the wave-cut profile height H. The incrementally stretched portion
158 can define a
plurality of ribs extending from the first side edge 112b to the second side
edge 114b of the bag
154a. The plurality of ribs can generally be parallel to each other and
transverse to both the first
side edge 112b and second side edge 114b.
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[0062] In one particular example of the wave-cut trash bag 154a, a height of
the bag from the
bag bottom 144a to the upper extent of the bag top 152a may be 50 inches. A
width of the bag
from the first side edge 112b to the second side edge 114b may be
approximately 33 inches. The
wave-cut profile height H may be 5 inches with the incrementally stretched
portion 158
extending 2.5 inches below the bottom of the wave-cut profile. Thus, the
incrementally stretched
portion 158 may have a height of approximately 7.5 inches, resulting in the
remaining 42.5
inches of bag height un-stretched. The incrementally stretched portion 158 may
be stretched
approximately 15%. Thus, if the film of the collapsed tube is formed with a
thickness of 3 mil,
the incrementally stretched portion 158 may have an average thickness of
approximately 2.5 mil
with the remaining portions of the bag having a thickness of 3 mil.
[0063) Shown in Figs. 7 and 8 is an alternative embodiment of the invention.
Rather than each
incrementally stretched section 116 aligned with one of the wave-cuts 152,
each incrementally
stretched section 116 can be offset from each wave-cut 152. In this
embodiment, each
incrementally stretched section 116 is between adjacent perforation lines 140
and wave-cuts 152
so that a bag body 160 of each resultant bag 154 is incrementally stretched.
The bag body 160
can be located between the lower extent of the bag top 152a and the bag bottom
144a.
100641 In one particular example of the embodiment shown in Figs. 7 and 8, the
intermeshing
rollers 122a, 122b can engage the collapsed tube 110 approximately 2.5 inches
away from each
side of each perforation line 142. Each incrementally stretched section 116
can be approximately
40 inches long, which results in a length of approximately 7.5 inches of un-
stretched film from
the upper extent of the bag top 152a to a top of the incrementally stretched
bag body 160 for a
bag having a total length of 50 inches. The bag body 160 can be stretched
approximately 17
percent so that an initial film thickness of 3 mil is stretched to
approximately 2.5 mil within the
bag body 160. This embodiment allows less film to be used than an un-stretched
bag.
100651 The embodiment shown in Figs. 7 and 8 may also be implemented on a wave-
cut trash
bag having typical dimensions of a kitchen trash bag. The bag body 160 can be
stretched
approximately 16 percent so that an initial film thickness of 0.7 mil is
stretched to approximately
0.6 mil within the bag body 160.
10066] Fig. 9 illustrates yet another embodiment of the incremental stretching
operation
17
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Shown in Fig. 9 is a top planar view of an alternate embodiment of the outer
surface of upper
intermeshing roller 122a. The closely spaced parallel lines of Fig. 9
represent edges of each
protruding ridge 126a. Although not to the same extend as previous
illustrations, the spacing
between adjacent ridges is exaggerated for ease of illustration. For
reference, shown in dashed
lines is the outline of the intended corresponding placement of a wave-cut
152. Within the
plurality of protruding ridges 126a is shown a plurality of ridge voids 132.
Each ridge void 132
is a location from which a length of protruding ridges has been removed from
the intermeshing
roller 122a. Each ridge void 132 defines a location where the intermeshing
roller 122a will fail
to stretch the collapsed tube 110 within each incrementally stretched section
116. The ridge
voids 132 are located about the intermeshing roller 122a such that an upper
region of each lobe
156 of each bag 154 is left un-stretched.
100671 Fig. 10 illustrates the structure of bag 154a formed by the alternate
embodiment of the
incremental stretching operation as illustrated by Fig. 9. As a result of the
plurality of ridge
voids 132, defined in an upper region of each lobe 156 is an un-stretched tip
132a that is devoid
of any ribs that otherwise would have been formed by the incremental
stretching operation. As
shown in Fig. 10, a plurality of un-stretched tips 132 is defined on the bag
154. In a likewise
manner, the incrementally stretched portion 158 of the bag does not extend to
the upper extent of
the bag top 152a. The remaining features of bag 154a remain unchanged from the
embodiment
illustrated in Figs. 5 and 6. The un-stretched tips 132a may further improve
the ease of tying the
wave-cut trash bag versus the previously described embodiments.
[0068] 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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