U.S. patent application number 11/734235 was filed with the patent office on 2008-10-16 for apparatus and method for resisting tear propagation in polymeric products.
This patent application is currently assigned to POLY-AMERICA, L.P.. Invention is credited to George M. Hall.
Application Number | 20080253699 11/734235 |
Document ID | / |
Family ID | 39853787 |
Filed Date | 2008-10-16 |
United States Patent
Application |
20080253699 |
Kind Code |
A1 |
Hall; George M. |
October 16, 2008 |
APPARATUS AND METHOD FOR RESISTING TEAR PROPAGATION IN POLYMERIC
PRODUCTS
Abstract
A plastic bag for holding materials comprising at least one
polymeric panel defining the outer walls of the plastic bag. The at
least one polymeric panel is interconnected to form a substantially
cylindrical shape. The at least one polymeric panel defines a
machine direction and a cross direction perpendicular to the
machine direction. A plurality of substantially parallel rows on
the at least one polymeric panel wherein the plurality of
substantially parallel rows is comprised of a plurality of
curvilinear areas. The plurality of curvilinear areas having a
protrusion or an indentation in the at least one polymeric panel.
The bag further comprises a plurality of substantially parallel
neutral areas wherein each substantially parallel neutral area is
defined by an area between two adjacent rows in the plurality of
substantially parallel rows.
Inventors: |
Hall; George M.;
(Colleyville, TX) |
Correspondence
Address: |
AKIN GUMP STRAUSS HAUER & FELD, LLP
P O BOX 688
DALLAS
TX
75313-0688
US
|
Assignee: |
POLY-AMERICA, L.P.
Grand Prairie
TX
|
Family ID: |
39853787 |
Appl. No.: |
11/734235 |
Filed: |
April 11, 2007 |
Current U.S.
Class: |
383/118 ;
264/563; 428/167 |
Current CPC
Class: |
B65D 33/02 20130101;
Y10T 428/2457 20150115 |
Class at
Publication: |
383/118 ;
264/563; 428/167 |
International
Class: |
B65D 30/02 20060101
B65D030/02 |
Claims
1. A plastic bag for holding trash, debris and/or other materials
comprising: at least one polymeric panel defining the outer walls
of the plastic bag, the at least one polymeric panel interconnected
to form a substantially cylindrical shape, a first end of the
substantially cylindrical shape sealed to form a bottom of the
plastic bag and a second end forming an opening of the plastic bag,
the at least one polymeric panel defining a machine direction and a
cross direction perpendicular to the machine direction; a plurality
of substantially parallel rows on the at least one polymeric panel,
the plurality of substantially parallel rows comprised of a
plurality of curvilinear areas wherein each of the plurality of
curvilinear areas is a protrusion or an indentation in the at least
one polymeric panel; wherein each of the plurality of substantially
parallel rows extends in the cross direction of the at least one
polymeric panel.
2. The plastic bag of claim 1 further comprising a plurality of
substantially parallel neutral areas, each substantially parallel
neutral area defined by an area between two adjacent rows in the
plurality of substantially parallel rows
3. The plastic bag of claim 1 wherein the plurality of curvilinear
areas are elliptical.
4. The plastic bag of claim 1 wherein the plurality of curvilinear
areas are S-shaped.
5. The plastic bag of claim 1 wherein the plurality of curvilinear
areas are a series of alternating protrusions and indentations.
6. The plastic bag of claim 1 wherein the plurality of curvilinear
areas are substantially uniform in size and depth.
7. The plastic bag of claim 1 wherein the plurality of curvilinear
areas and plurality of substantially parallel neutral areas are not
visually distinct.
8. A plastic sheet with increased resistance to tear propagation
comprising: a plastic sheet having an upper surface, a lower
surface, and a plurality of edges, wherein the plastic sheet has an
ordinary elasticity and the plastic sheet defines a machine
direction and a cross direction perpendicular to the machine
direction; a plurality of substantially parallel rows defined on
the plastic sheet, the plurality of substantially parallel rows
traversing the plastic sheet generally in the cross direction, the
plurality of substantially parallel rows comprised of a plurality
of curvilinear areas wherein each of the plurality of curvilinear
areas is a protrusion or an indentation in the plastic sheet
9. The plastic sheet of claim 8 further comprising a plurality of
substantially parallel neutral areas, each substantially parallel
neutral area defined by an area between two adjacent rows in the
plurality of substantially parallel rows.
10. The plastic sheet of claim 8 wherein the plurality of
curvilinear areas are elliptical.
11. The plastic sheet of claim 8 wherein the plurality of
curvilinear areas are S-shaped.
12. The plastic sheet of claim 8 wherein the plurality of
curvilinear areas and plurality of substantially parallel neutral
areas are not visually distinct.
13. A method of manufacturing plastic film having increased
resistance to tear propagation comprising the steps of: providing a
blown-film polymeric tube, a machine direction defined by the
longitudinal axis of the blown-film polymeric tube and a cross
direction defined by an axis perpendicular to the longitudinal axis
of the blown-film polymeric tube; flattening the blown-film
polymeric tube; embossing the blown-film polymeric tube with a
plurality of curvilinear areas, each curvilinear area being either
a protrusion or an indentation;
14. The method of claim 13 wherein the plurality of curvilinear
areas are arranged into a plurality of substantially parallel rows
extending in the cross direction of the blown-film polymeric
tube.
15. The method of claim 14, wherein the plurality of substantially
parallel rows further define a plurality of substantially parallel
neutral areas, each substantially parallel neutral area defined by
an area between two adjacent rows in the plurality of substantially
parallel rows.
16. The method of claim 13, further comprises the steps of forming
a plurality of plastic bags from the blown-film polymeric tube.
17. The method of claim 13, wherein embossing the blown-film
polymeric tube comprises the step of passing the blown-film
polymeric tube through a pair of complementary embossing
rollers.
18. The method of claim 13, further comprising the step of:
redirecting a tear propagating through the blown-film polymeric
tube when the tear encounters one of the plurality of curvilinear
areas.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] Not applicable.
REFERENCE TO SEQUENCE LISTING, A TABLE, OR A COMPUTER PROGRAM
LISTING COMPACT DISC APPENDIX
[0002] Not applicable.
FIELD OF THE INVENTION
[0003] The present invention relates to products constructed from
plastic sheets, in particular plastic bags, the products having
indentions and protrusions configured in such a way as to provide
enhanced resistance to tear propagation without effectively
altering the elasticity of the plastic sheets.
DESCRIPTION OF THE RELATED ART
[0004] Plastic bags are utilized throughout the world for refuse
collection, storage, and numerous other purposes. Plastic bags are
generally manufactured using a blown-film extrusion process which
comprises forming a blown-film tube from polyethylene or other
polymeric materials, flattening the blown-film tube, and forming a
set of seals and/or cuts to the blown-film tube to form a plurality
of plastic bags from the blown-film tube.
[0005] In manufacturing bags using the blown-film extrusion
process, a tubular film is formed with air that blows through the
center of the tube as heated molten plastic is extruded through a
die on the extrusion machine. The resulting tubular film is of
substantially uniform thickness around the entire circumference of
the film. A pair of nip rollers pulls the blown-film up and the
film cools as it continues to be pulled upward. As the film cools,
it can be eventually be flattened and processed into various types
of bags or other plastic products.
[0006] One method of manufacturing plastic bags is by first
providing sets of closely spaced, parallel transverse seals at
predetermined intervals along the length of a flattened blown-film
polymeric tube. A transversely extending line of perforations is
provided between the closely spaced, parallel seals. These
perforations form the sides of the plastic bags. The bottom of the
plastic bag is usually formed from the fold of the blown-film tube
as it is flattened. Subsequently, another cut is provided along the
central, longitudinal axis of the flattened blown-film polymeric
tube to form the top openings of these bags.
[0007] Plastic bags may also be produced by providing a pair of
closely spaced, parallel seals extending transversely at
predetermined intervals along the length of a flattened blown-film
polymeric tube. A line of perforations extending transversely
across the flattened blown-film polymeric tube is introduced
between the pair of seals. In this case, each seal forms the bottom
of the bag, and another perforation line is introduced at a point
somewhere between successive pairs of closely spaced, parallel
seals to form the opening, or top, of the bags. These bags
typically result from the use of the entire circumference of the
blown-film polymeric tube.
[0008] The blown film extrusion process results in bags that
generally have a uniform thickness. There is an inherent
relationship between the strength and thickness of the plastic bag.
As the thickness of the bag is reduced, it becomes lighter and
generally less expensive to manufacture.
[0009] One of the most significant limitations in offering thinner
bags is that thinner bags are generally more prone to ripping and
tearing. It is known that plastic bags formed from the blown-film
extrusion process tend to offer differing levels of resistance to
tear propagation depending on the direction of the tear. In
particular, the blown-film polymeric tube is more susceptible to
tearing in the machine direction, which is the longitudinal axis of
the blown-film polymeric tube, than in the cross direction, which
extends across the width of the blown-film polymeric tube,
perpendicular to the machine direction. This is primarily due to
the molecular orientation of the film resulting from the blown-film
process.
[0010] Plastic sheet products are susceptible to stretching because
of the natural elastic properties of plastics in general,
especially when considering the thin plastic used to manufacture
bags. When an object within a bag forces the walls of the bag to
stretch to a point where they can no longer resist the force of the
object, a tear or puncture is formed. One method to attempt to
address this problem used in the prior art is to modify the bags so
that they controllably stretch in a manner that exceeds their
natural elastic properties. In such cases, when a protruding object
inside or outside of a plastic bag comes into contact with the
walls, it causes the walls of the bag to stretch "controllably." As
a result, the amount of plastic material in the wall of the bag
stays constant while the surface area of the bag increases, causing
the thickness of the walls to be significantly reduced. Therefore,
even though a tear has not formed in the bag, the structural
integrity of the bag has been significantly diminished. As an
alternative to "controlled stretching," it would be desirable to
offer a plastic bag that offers properties of increased resistance
to tear propagation without increased stretching of the plastic
bags and without diminishing the structural integrity of the
bag.
[0011] One of the problems with tears in plastic bags, or when any
other type of puncture is introduced to a plastic sheet, is that
even a small tear or puncture in the bag has a tendency to
propagate along the machine direction of the bag, which, as
discussed previously, is typically markedly weaker than the
cross-direction. As noted above, bags manufactured with a
perforation forming the side of the bag have the weaker machine
direction running across the width of the bag, while the stronger
cross direction runs from the bottom of the bag to the top of the
bag. In such bags, it would be desirable to redirect a tear
propagating in the weaker machine direction to turn in the
cross-direction, which is stronger and therefore more resistant to
tear propagation.
[0012] With bags that are manufactured using the entire
circumference of the blown-film polymeric tube, the width of the
bag tends to be the stronger cross direction and the machine
direction tends to run in the vertical direction from the top of
the bag to the bottom of the bag. In these bags, tears have a
tendency to propagate in the vertical direction, which is the
weaker machine direction. In these bags, it is desirable to
redirect this tear into the horizontal, cross direction of the bag,
which is stronger and more resistant to tear propagation. Doing so
would effectively result in increased tear resistance of the bag as
a whole.
[0013] In previous methods, attempts to control tear propagation
were made by introducing, through an embossing process, a plurality
of connected diagonal lines into the wall of the bag, i.e. a linear
direction. The lines have the effect of redirecting a tear
propagating in the machine direction along one of the diagonal
lines. Redirecting the tear in a direction that is roughly oriented
at a 45 degree angle to both machine direction and cross direction
of the bag can result in an increased resistance to tear
propagation. However, in the event a tear is naturally propagating
in the cross-direction, the lines can actually and undesirably
encourage the tear to propagate into the weaker diagonal machine
direction.
[0014] By using diagonal lines to attempt to direct the propagation
of a tear, the diagonal lines are interconnected so that after a
short distance a line runs into another perpendicular diagonal
line. Ideally, the tear would immediately turn and follow the
perpendicular diagonal line. However, in practice the hard angle
between the two lines rarely results in such, and generally results
in a tear that breaks free of the diagonal path because the force
is concentrated into the apex formed by the junction angle of the
two lines, allowing tearing in the machine direction until it
encounters another diagonal. Therefore, it would be desirable to
introduce more gradual transitions and turns in plastic sheets,
such as a plastic bag, to encourage a propagating tear to follow a
curved and tortuous path instead of one comprised of diagonal
lines.
SUMMARY OF THE INVENTION
[0015] The present disclosure introduces a novel way of addressing
the problems and issues involved in providing increased resistance
to tear propagation while not effectively altering the stretching
or elastic properties of the plastic bag. In particular, the
present disclosure does not induce properties in the bag or plastic
sheet that would cause the bag to be more likely to stretch when a
force is applied against one of its walls.
[0016] The present disclosure generally relates to the introduction
of a plurality of indentions and protrusions into a plastic bag,
which as previously mentioned is typically formed using a
blown-film extrusion process. The plurality of indentions and
protrusions are curvilinear in shape, such as elliptical or
S-shaped. The curvilinear shapes lack sharp corners, thereby
providing increased resistance to force concentration and resulting
in increased tear propagation resistance as more fully described in
the drawings and figures. The curvilinear shapes are generally
configured so as to be adjacent to one another with a series of
curvilinear shapes forming a row of curvilinear shapes in the cross
direction of the plastic bag or plastic sheet.
[0017] While the present disclosure is directed primarily toward
plastic bags, it is contemplated that novel techniques and
structures disclosed herein have uses outside the realm of plastic
bags. In particular, other types of plastic sheeting products
manufactured using a blown-film extrusion process may benefit from
the novel features discussed herein. This is especially true since
the plastic bags of the present invention are essentially
constructed from a plastic sheet, albeit one tubular in nature.
[0018] Another aspect of the present disclosure is a method of
manufacturing plastic film having increased resistance to tear
propagation without effectively altering the stretching properties
of the plastic film. In particular, the method entails using a
blown-film polymeric tube having a machine direction along the
longitudinal axis of the polymeric tube that is less resistant to
tear propagation than the cross direction which is perpendicular to
the machine direction. After flattening the blown-film polymeric
tube, the tube is embossed with a plurality of curvilinear
indentations and protrusions, the plurality of curvilinear
indentations and protrusions defining a plurality of substantially
parallel rows extending in the cross direction.
[0019] The present disclosure is described primarily with reference
to plastic bags; however, it is recognized that numerous other
types of plastic sheeting products would benefit from the methods
described herein. Therefore, the present disclosure is not limited
to the embodiments described herein. The embodiments described
herein illustrate the preferred methods and ways of practicing the
invention, but these techniques can be applied to other types of
plastic sheeting having properties similar to bags. The claims
herein are intended to more fully encompass the scope of invention
as contemplated.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] A full and complete understanding of the present disclosure
may be obtained by reference to the detailed description of the
invention when viewed with reference the accompanying drawings. The
drawings can be briefly described as follows:
[0021] FIG. 1A provides a plan view of a side seal plastic bag as
known in the prior art, highlighting the machine direction and
cross direction of that plastic bag.
[0022] FIG. 1B provides a plan view of a bottom seal plastic bag as
known in the prior art, highlighting the machine direction and
cross direction of that plastic bag.
[0023] FIG. 2 illustrates a particular pattern used on panels of
plastic bags as known in the prior art.
[0024] FIG. 3 illustrates a novel tear-resistant pattern according
to one embodiment of the present invention.
[0025] FIG. 4A depicts a visual diagram of one method of
manufacturing plastic film according to an embodiment of the
present invention utilizing a stamping press and complementary
anvil.
[0026] FIG. 4B is a visual diagram of an alternative method of
manufacturing plastic film according to another embodiment of the
present invention by utilizing a set of complementary embossing
rollers.
[0027] FIG. 5A is an illustration of one alternative configuration
for arranging the curvilinear protrusions and indentations
according to the present invention.
[0028] FIG. 5B is an illustration of another alternative
configuration for arranging the curvilinear protrusions and
indentations according to the present invention.
[0029] FIG. 5C is an illustration of yet another alternative
configuration for arranging the curvilinear protrusions and
indentations according to the present invention.
[0030] FIG. 5D is an illustration of a non-uniform alternative
configuration for arranging the curvilinear protrusions and
indentations according to the present invention.
[0031] FIG. 5E is an illustration of another alternative
configuration for arranging irregularly shaped curvilinear
protrusions and indentations according to the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0032] The present disclosure illustrates embodiments of the
present invention. In view of the disclosure of the 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. Furthermore, the
appended claims are intended to encompass the invention to the
fullest extent possible, but it is fully appreciated that
limitations on the use of particular terms is not intended to
conclusively limit the scope of protection for a particular
application.
[0033] Referring now to FIG. 1A, a perspective view of a side seal
plastic bag 100 is provided. The bag has an open top 110 and has a
bottom 112 formed by the folded longitudinal edge of the blown-film
tube and sealed sides 116. The front and back of the bag 100 is
comprised of polymeric panels 114. Bags manufactured in this way
have a machine direction 40 that runs horizontally across the bag
as depicted and a cross direction 50 that runs vertically across
the length of the bag. The cross direction 50 of the polymeric
panels 114 is markedly stronger than the machine direction 40;
therefore, the plastic bag has a tendency to resist tearing in the
vertical cross direction 50 to a much greater extent than in the
horizontal machine direction 40.
[0034] Referring now to FIG. 1B, a perspective view of a bottom
seal plastic bag 150 is provided. The bag 150 has an open top 110
and a single sealed bottom 112. The entire tubular material of a
blown-film polymeric tube is used to form this plastic bag as
previously described, so there is a single continuous polymeric
panel 114 that forms the outer wall of the bag 150. In these types
of constructions, the bags 150 have a machine direction 40 that
runs in the vertical direction from the top 110 of the bag 150 to
the sealed bottom 112. The cross direction 50 of the bag 150 runs
horizontally around the circumference of the bag 150. As with the
side seal bags 100, the cross direction 50 of the polymeric panel
114 is markedly stronger, and more tear-resistant, than the machine
direction 40. Accordingly, this bag 150 has a tendency to resist
tearing in the horizontal cross direction 50 much more so than in
the vertical machine direction 40.
[0035] Referring now to FIG. 2, an example of a prior art attempt
to resist tear propagation is illustrated. The prior art
straight-line system 200 consists of a plurality of first diagonal
lines 210 and a plurality of second diagonal lines 214 running in a
perpendicular fashion to the plurality of first diagonal lines 210.
In this particular illustration the machine direction 40 runs from
left to right while the cross direction 50 runs top to bottom.
However, because of the symmetry of the prior art straight-line
system 200, if the cross direction 50 and machine direction 40 were
reversed, the prior art straight-line system 200 would function in
basically the same manner. This can best be seen by rotating FIG. 2
in the clockwise or counter-clockwise directions. Each of the first
diagonal lines 210 has a finite length and runs between a pair of
perpendicular second diagonal lines 214. In this particular prior
art straight-line system 200 the plurality of first diagonal lines
210 and the plurality of second diagonal lines 214 terminate when
they intersect, never forming a four-way junction. Each
intersection of a first diagonal line 210 with a perpendicular
second diagonal line 214 forms a T-shaped intersection 212.
[0036] In the prior art straight-line system 200, a tear can be
contemplated propagating in the machine direction 40, which in this
particular illustration would be a tear running from left to right.
Ideally, the tear would follow one of the first diagonal lines 210
or second diagonal lines 214. Assuming it propagates along one of
the first diagonal lines 210, when the tear reaches a T-shaped
intersection 212 with a perpendicular second diagonal line 214, it
is hoped that the tear will continue propagating down the second
diagonal line 214. However, even in this case, that is not what
occurs.
[0037] FIG. 3 illustrates one embodiment of the present invention.
In particular, it shows a magnified view of one configuration for a
portion of the plastic sheet 114 used in the manufacture of the
bags 150, 100 illustrated in FIG. 1A and FIG. 1B. In this
embodiment, a row embodiment of ellipses 300, the plastic sheet 114
of the bag is configured with a plurality of curvilinear areas,
particularly, raised elliptical areas 310 and recessed elliptical
areas 312. The process used to introduce the raised elliptical
areas 310 and recessed elliptical areas 312 can be an embossing
process, a debossing process, a combination of the two, or any
other method known in the art. These methods will be better
illustrated with reference to FIG. 4A and FIG. 4B. Referring back
to FIG. 3, the raised elliptical areas 310 and recessed elliptical
areas 312 form a plurality of rows 330, 332, 334. Each row 330,
332, 334 extends in the cross direction 50 of the plastic sheet
114. Between two adjacent rows 330, 332, 334 is a neutral area 320,
322 that also extends in the cross direction 50 of the plastic
sheet 114
[0038] With specific reference to elliptical row embodiment 300 of
FIG. 3, it is readily determined that a tear, depicted as 70,
propagating in the machine direction 40, i.e. from the top to the
bottom of the figure, will encounter the raised elliptical areas
310 or recessed elliptical areas 312. Testing has shown that a tear
70 has a tendency to attempt to propagate along the perimeters of
the raised elliptical areas 310 or recessed elliptical areas 312.
As the tear 70 attempts to propagate across a first row 330 it will
follow along the curved edge of the raised elliptical area 310 or
recessed elliptical area 312. Eventually, the tear 70 will have a
tendency to diverge from the raised elliptical area 310 or recessed
elliptical area 312.
[0039] However, as the tear has a tendency to attempt to propagate
around the edges of the elliptical areas 310, 312, the tear is now
redirected generally in the cross direction 50 of the plastic sheet
114 rather than the machine direction 40. At this point, the tear
has a natural tendency to try to revert back to the path of least
resistance, i.e., the machine direction 40. However, as the tear
attempts to revert back to the machine direction 40, it encounters
another row 332 of raised elliptical areas 310 and recessed
elliptical areas 312. This process continues and frustrates the
attempts of the tear to propagate. Tests show that this
configuration can increase the resistance to tear propagation by
15% or more.
[0040] Regarding the scale of FIG. 3, the size and depth of the
raised elliptical areas 310 and recessed elliptical areas 312 are
extremely small. In fact, in some embodiments, the elliptical areas
310, 312 have major axis lengths, or row 330, 332, 334 widths, of 1
mm or less. The net result is that it is extremely difficult to
distinguish the individual rows 330, 332, and 334, and neutral
areas 320 and 322 during normal observation. In fact, a person must
make a very close inspection to even recognize the raised
elliptical areas 310 or recessed elliptical areas 312 and the scale
makes the neutral areas 320, 322 almost indiscernible with the
naked eye in normal use. The resulting plastic sheet 114 has a
unique textured appearance.
[0041] Referring now to FIG. 4, one method of embossing by stamping
400 is illustrated. In this particular illustration, a roll of
polymeric material 410 to be embossed is oriented by a roller 402
to position the polymeric material 410 between a stamping press 420
and an anvil 422. With a combination of heat and pressure, the
stamping press 420 is extended downward (as illustrated by arrow
421) to force the polymeric material 410 into the anvil 422 under
the stamping press 420. The stamping press 420 and anvil 422 have
complementary configurations that result in the patterns such as
those in the present disclosure. Embossing/debossing of patterns
with a stamping press 420 is generally well-understood as is its
implementation. However, one disadvantage is that the polymeric
material 410 must be halted to allow the stamping press 420 and
anvil 422 to operate.
[0042] An alternative to the method of FIG. 4A is the rolling
embossing system 450 illustrated in FIG. 4B. In the rolling
embosser system 450, the polymeric material 410 is oriented by a
roller 402 to travel between an upper embossing roller 460 and a
lower embossing roller 462. The upper embossing roller 460 and the
lower embossing roller 462 have complementary configurations, i.e.
an indentation on the upper embossing roller 460 matches a
protrusion on the lower embossing roller 462 which will form a
raised area, such as a raised elliptical area 310 disclosed in FIG.
3. The pressure applied by the upper embossing roller 460 and lower
embossing roller 462 will allow any of the patterns disclosed
herein to be introduced into the polymeric material.
[0043] Referring now to FIGS. 5A, 5B, 5C, 5D, and 5E, other
embodiments that are contemplated by the present invention are
disclosed. In particular FIG. 5A discloses an angled ellipses
configuration 510 as opposed to the configuration disclosed in FIG.
3. The primary performance difference between FIG. 3 and FIG. 5A is
that the angled ellipses configuration 510 has a tendency to force
the propagating tear 70 in the direction of the angled ellipses,
which in FIG. 5A is from left-to-right assuming the tear 70 is
propagating in the general direction from top to bottom.
[0044] A similar alternating angled ellipses configuration 520 is
shown in FIG. 5B. However, in this configuration, adjacent rows,
for example rows 330 and 332, have elliptical areas that are
oriented in opposite directions as shown. In this case, the
propagating tear 70 has a tendency to travel a more tortuous path
than either the basic configuration 300 of FIG. 3 or the angled
ellipses configuration 510 of FIG. 5A
[0045] Referring now to FIG. 5C, an offset ellipses configuration
530 is depicted. In this offset ellipses configuration 530, the
rows 330, 332, 334 are offset from one another. As with the angled
ellipses configurations 520, 510, the offset between adjacent rows
may be altered to achieve varying degrees of offset, such as rows
330 and 332, depending on the width of the neutral areas 320, 322
and the size of the raised and recessed elliptical areas 310,
312.
[0046] FIG. 5D shows yet another configuration, in particular a
non-uniform configuration 540. In particular each row, 330, 332,
334, 336 is formed from a plurality of alternating raised
elliptical areas 310 and recessed circular areas 512. In this
non-uniform configuration 540, it may even be possible to have the
neutral areas 320, 322, 324 run in a slight zigzag pattern if the
raised elliptical areas 310 of adjacent rows, for example 330 and
332, extend far enough into the neutral areas 320, 322, 324 that
the neutral areas 320, 322, 324 become somewhat S-shaped.
[0047] Referring now to FIG. 5E, a plurality of irregular S-shaped
raised areas 552 and a plurality of irregular S-shaped recessed
areas 554 are depicted forming rows 330, 332, 334, 336 in an
example S-shaped configuration 550. The propagation of a tear 70
can be even more tortuous in the depicted S-shaped configuration
550 than in some of the previous configurations. Although not
shown, it may be desirable to reverse the configuration of
alternating rows, for example reversing the orientation of rows 332
and 336, similar to the reversed orientation of FIG. 5B. As
illustrated by the numerous potential configurations of elliptical
areas 310, 312 and S-shaped areas 552, 554, a person having skill
in the art could mix and match features of the varying depicted
configurations without departing from the scope of the present
invention. Accordingly, based on the embodiments of the present
invention that have been illustrated in the accompanying figures
and described within this written description, it will be
understood that the invention is not limited to the embodiments
disclosed herein, but is capable of other rearrangements,
modifications, and substitutes of parts and elements without
departing from the spirit of the invention.
* * * * *