HK1131775A - Flexible bag having a drawtape closure - Google Patents

Description

Flexible bag with drawstring closure

Technical Field

Flexible bags of this type are commonly used for the containment and disposal of various household materials.

Background

Flexible bags, particularly those made of relatively inexpensive polymeric materials, have been widely used for the containment and disposal of various household materials such as trash, lawn clippings, leaves, and the like.

As used herein, the term "flexible" is used to refer to materials that: the materials are capable of being flexed or bent, particularly repeatedly, such that they are pliable and yieldable in response to an applied force. Thus, "flexible" has a substantially opposite meaning to the terms inflexible, rigid, or unyielding. Thus, the shape and structure of flexible materials and structures can be altered to accommodate external forces and to conform to the shape of objects with which they come into contact without losing their integrity. Commonly available flexible bags are typically formed from materials that have consistent physical properties, such as stretch, tension and/or elongation properties, throughout the bag structure.

One common method of using such bags is to line them for containers such as trash cans or bins. It is often difficult to pull the top of the bag out of the rim of the trash can or bin in order to keep the bag in place in the trash can or bin. The material is placed in the bag until the bag and/or container is filled, or until the bag is filled to a desired height. When the bag is filled or even exceeds capacity due to placement of additional material above the uppermost edge of the bag, it is often difficult for the consumer to close the opening of the bag because little, if any, free material remains to close the bag opening above the level of the contents. Another problem often encountered if the filled bag is subsequently placed on the floor by itself is the displacement of the bag contents, which causes an imbalance in the bag and correspondingly opens the closure of the bag, whereby the contents may spill.

It is therefore desirable to provide a flexible bag that is easier to place securely on the rim of a trash can or bin, that is easier to close after filling and that is not easy to reopen after closing.

Summary of The Invention

A flexible bag comprising at least one sheet of flexible sheet material, the sheet being assembled to form a semi-enclosed container having an opening defined by a periphery, the opening defining an opening plane; the bag having a drawtape closure for sealing the opening to convert the semi-closed container into a closed container, an upper region adjacent the drawtape closure, and a lower region below the upper region, wherein a sheet material of the drawtape closure exhibits an elastic-like behavior along at least one axis, the sheet material of the drawtape closure comprising: at least a first region and a second region having the same material composition and each having an unstrained projected path length; when the web material undergoes a forced elongation in a direction substantially parallel to the axis in response to an applied force applied to the sheet material of the draw tape closure, the first region undergoes a significant molecular-level deformation and the second region initially undergoes a significant geometric deformation; when the applied elongation is released, the first and second regions return substantially to their unstrained projected path lengths.

Brief description of the drawings

While the specification concludes with claims particularly pointing out and distinctly claiming the present invention, it is believed that the present invention will be better understood from the following description in conjunction with the accompanying drawings, in which like reference numerals identify like elements, and wherein:

FIG. 1 is a plan view of a flexible bag according to one embodiment of the present invention, wherein the bag is in a closed and empty state;

FIG. 2 is a perspective view of the flexible bag of FIG. 1 in a closed state with material contained therein;

FIG. 3A is a fragmentary perspective view of the polymeric film material of the flexible bag of one embodiment of the present invention in a substantially untensioned condition;

FIG. 3B is a fragmentary perspective view of the polymeric film material of the flexible bag in a partially tensioned state according to one embodiment of the present invention;

FIG. 3C is a fragmentary perspective view of the polymeric film material of the flexible bag under greater tension according to one embodiment of the present invention;

fig. 4 is a plan view of another embodiment of a sheet material suitable for use in the present invention; and

fig. 5 is a plan view of the polymeric netting material of fig. 4 in a partially tensioned state similar to that described in fig. 3B.

FIG. 6 is a side view of a portion of a draw tape according to one embodiment of the invention.

Detailed Description

Flexible bag construction：

Fig. 1 depicts one embodiment of a flexible bag 10 according to the present invention. In the embodiment depicted in fig. 1, the flexible bag 10 includes a bag body 20 formed from a sheet of flexible sheet material folded upon itself along fold line 22 and bonded to itself along side seams 24 and 26 to form a semi-enclosed container having an opening along edge 28. The flexible bag 10 also includes a drawtape closure 30 positioned adjacent the edge 28 for sealing the edge 28 to form a fully enclosed container, as shown in FIG. 1. Bags, such as the flexible bag 10 of fig. 1, may also be made from a continuous tube of sheet material, so that the side seams 24 and 26 may be eliminated and the fold line 22 may be replaced with a bottom seam. The flexible bag 10 is adapted to contain and protect a variety of materials and/or objects that may be contained within the bag body.

In the configuration shown in fig. 1, the draw tape closure 30 completely surrounds the periphery of the opening formed by the edge 28. However, in some cases, a closure member formed by a lesser degree of encircling (e.g., a closure member disposed along only one edge of the rim 28) may also provide sufficient closure integrity.

According to one embodiment of the invention, the flexible bag 10 includes a region 31 adjacent the closure 30 adjacent the edge 28. The drawtape closure exhibits a lower resistance to elongation than region 31.

FIG. 1 shows a plurality of regions extending across the drawtape closure surface. Region 40 comprises rows of deep-embossed deformations in the flexible sheet material of bag body 20, while region 50 comprises undeformed regions between the deformations. As shown in fig. 1, the undeformed regions have axes that extend across the material of the bag body in a direction substantially parallel to the plane of the opening edge 28 (the axis when in the closed state), which in the illustrated configuration is also substantially parallel to the plane or axis defined by the bottom edge 22.

In one embodiment, the sheet materials are oriented such that their elongation axes in the upper portion of the bag are generally substantially perpendicular to the plane defined by the opening or opening edge of the bag. This orientation provides a defined stretch orientation of one embodiment of the present invention. In one embodiment, the sheet material is oriented such that the elongation axis of the drawtape closure is parallel to the plane defined by the opening or opening edge of the bag.

It is possible to construct substantially the entire bag body from a sheet material having the structure and characteristics of embodiments of the present invention. In some cases, it is desirable to provide such materials only in one or more portions or regions of the bag body, rather than in its entirety. For example, a band of such material having the desired stretch orientation may be provided in one region of the bag, the band forming a complete circular band around the bag body to provide more localized stretch properties. In one embodiment, the strip of material comprising the drawtape closure portion of the bag may have the structure and characteristics described herein.

In one embodiment, the first and second regions are formed only in the draw tape closure portion of the bag. This localized formation of the first and second regions may selectively allow the draw tape portion of the bag to expand circumferentially relative to the remainder of the bag 10. This relative expansion may allow a user of bag 10 to more easily envelope the perimeter of a container adapted to support bag 10 to facilitate filling of bag 10.

The selective formation of the first and second regions in the drawtape closure area may additionally produce the benefit of a closure that is less likely to open when a filled bag is closed and subsequently removed from a supporting container than a similar bag lacking the modified drawtape closure. Without being bound by theory, it is believed that there is a ratcheting effect in the mechanical interaction between the regions of the formed draw tape and the regions of the formed sheet material, and an additional ratcheting effect between the regions of the corresponding portion of the sheet material around the draw tape.

The ratcheting effect can be achieved by: the first and second regions are formed in the draw tape and the surrounding hem material, or in the draw tape only or in the surrounding hem material. Each of the draw tape and the surrounding hem material may be continuously or selectively formed into first and second regions. By selectively shaped, it is meant that discrete portions of the material may form the first and second regions, and other portions may not form such regions. Such selective shaping of the first and second regions may result in a selective ratcheting effect in which greater resistance to opening is more prevalent in certain preselected portions of the draw tape.

In one embodiment, each of the draw tape and the surrounding hem material may include first and second regions of different patterns to facilitate interaction of the regions of the draw tape with the regions of the surrounding hem material.

In one embodiment shown in FIG. 6, the draw tape 30 may further comprise one or more loop segments, wherein the draw tape is shaped as a series of peaks 32 and valleys 34, wherein each valley 36 of a loop segment is sealed to an elastomeric strip 36 corresponding to each loop segment. This allows the draw tape 30 to be extended so that the exposed portion of the draw tape 30 can be used to secure the draw tape and the top of the bag to the lip of the bag holding container.

In one embodiment, the draw tape may also include an elastomeric material, such as a thermoplastic rubber compound blended with a polyolefin.

In either embodiment, the draw tape, the surrounding hem material, or both, may be embossed such that a pattern is present in the material, but first and second regions that produce different responses to forces applied along the axis of the pattern are not formed. Bags formed with such embossed draw tape and/or hem materials may still experience a ratcheting interaction between the embossed pattern of material and other components of the draw tape closure.

The draw tape may comprise a polymer substantially similar to the polymer of the sheet material, or may comprise a dissimilar polymeric material. The sheet material may be modified to include the first and second regions before or after the draw tape is added to the bag 10. After adding the draw tape, modifying the sheet material may include modifying the draw tape to include a first region and a second region. In one embodiment, the sheet material (including the hem seal shaped to constrain the movement of the draw tape) and the draw tape may be modified simultaneously using the methods described below.

As described below, it is believed that materials suitable for use in embodiments of the present invention may provide additional benefits in that they may reduce the contact area with a trash can or other container, thereby facilitating removal of the bag after the contents are placed therein. The three-dimensional nature of the sheet material, along with its elongation characteristics, may also provide enhanced tear and puncture resistance as well as enhanced visual, audible, and tactile impressions. The elongation properties also allow for bags having a greater capacity (capacity per unit of material used), thereby improving the "mileage" of such bags. Thus, a smaller bag than conventionally constructed bags may be used for a given application. The bag may also have any desired shape and configuration, including bags having a handle or a particular design geometry.

To better illustrate the structural features and performance advantages of a flexible bag according to embodiments of the present invention, fig. 3A provides an extremely enlarged partial perspective view of a segment 52 of sheet material suitable for forming the bag body 20 as described in fig. 1-2. Materials such as those shown and described herein that are suitable for use in accordance with embodiments of the present invention, as well as methods for making and characterizing such materials, are described in more detail in commonly assigned U.S. patent No. 5,518,801 to Chappell et al, 1996, day 5, 21.

Referring now to fig. 3A, sheet material 52 comprises a "strainable network" of distinct areas. As used herein, the term "strainable network" refers to an interconnected and related set of regions capable of extending in a predetermined direction to a useful degree to provide elastic-like behavior to a sheet material in response to an applied and subsequently released elongation. The strainable network includes at least a first region 64 and a second region 66. Sheet material 52 includes transition areas 65 at the interface between first areas 64 and second areas 66. The transition region 65 will exhibit a complex combination of the behavior of the two regions, the first region and the second region. It should be recognized that each embodiment of such sheet materials suitable for use in the present invention will have transition regions, however such materials are defined by the behavior of the sheet material in the first 64 and second 66 regions. The following description will therefore focus on the behaviour of the sheet material in the first and second areas, simply because the behaviour is not dependent on the complex behaviour of the sheet material in the transition areas 65.

Sheet material 52 has a first surface 52a and an opposing second surface 52 b. In the embodiment shown in fig. 3A, the strainable network includes a plurality of first regions 64 and a plurality of second regions 66. The first region 64 has a first axis 68 and a second axis 69, wherein the first axis 68 is preferably longer than the second axis 69. First axis 68 of first regions 64 is substantially parallel to longitudinal axis "L" of sheet material 52 and second axis 69 is substantially parallel to transverse axis "T" of sheet material 52. Preferably, the second axis of the first region (i.e., the width of the first region) is about 0.01 inches to about 0.5 inches, and more preferably about 0.03 inches to about 0.25 inches. The second region 66 has a first axis 70 and a second axis 71. First axis 70 is substantially parallel to the longitudinal axis of sheet material 52 and second axis 71 is substantially parallel to the transverse axis of sheet material 52. Preferably, the second axis of the second region (i.e., the width of the second region) is about 0.01 inches to about 2.0 inches, and more preferably about 0.125 inches to about 1.0 inches. In the embodiment of fig. 3A, first areas 64 and second areas 66 are substantially linear, extending continuously in a direction substantially parallel to the longitudinal axis of sheet material 52.

The first region 64 has a modulus of elasticity E1 and a cross-sectional area A1. Second region 66 has a modulus E2 and a cross-sectional area A2.

In the illustrated embodiment, the sheet material 52 has been "formed" such that, when subjected to a force of axial elongation in a direction substantially parallel to the longitudinal axis, the sheet material 52 exhibits a resistive force along the axis, which in the case of the illustrated embodiment is substantially parallel to the longitudinal axis of the web. As used herein, the term "formed" refers to the formation of a desired structure or geometry on a sheet material that will substantially retain the desired structure or geometry when it is not subjected to any applied elongation or applied force. The sheet materials of the embodiments of the present invention are comprised of at least a first area and a second area, wherein the first area is visually distinct from the second area. As used herein, the term "visually distinct" refers to the characteristics of the sheet material. The features are readily discernible by the normal naked eye when the sheet material or object embodying the sheet material is subjected to normal use. As used herein, the term "surface path length" refers to a measurement taken along the contoured surface of the area in question in a direction substantially parallel to the axis. Methods for determining the surface path length of the respective regions can be found in the "test methods" section of Chappell et al, referenced above.

Methods for forming such sheet materials suitable for use in embodiments of the present invention include, but are not limited to, embossing by twin plate or roll, thermoforming, high pressure hydroforming, or casting. While the entire portion of web 52 has been subjected to the forming operation, the present invention may also be practiced with only a portion thereof (e.g., the portion of the material making up bag body 20) being subjected to forming, as described in detail below.

In the embodiment shown in fig. 3A, the first region 64 is substantially planar. In other words, the material within first region 64 is in substantially the same state before and after web 52 undergoes the forming step. The second region 66 includes a plurality of raised rib-like elements 74. The rib-like elements may be embossed, have a pattern of indentations, or a combination thereof. The rib-like elements 74 have a first or major axis 76 that is substantially parallel to the transverse axis of the web 52 and a second or minor axis 77 that is substantially parallel to the longitudinal axis of the web 52. The length parallel to the first axis 76 of the rib-like elements 74 is at least equal to, and preferably greater than, the length parallel to the second axis 77. Preferably, the ratio of the first axis 76 to the second axis 77 is at least about 1: 1 or greater, and more preferably at least about 2: 1 or greater.

The rib-like elements 74 in the second regions 66 may be separated from one another by unformed regions. Preferably, the rib-like elements 74 are adjacent to each other and separated by unformed areas of less than 0.10 inches, measured perpendicular to the major axis 76 of the rib-like elements 74, and more preferably, the rib-like elements 74 are contiguous with substantially no unformed areas therebetween.

The first region 64 and the second region 66 each have a "projected path length". As used herein, the term "projection path length" refers to the length of the shadow cast by an area under illumination by parallel light. The projected path length of the first region 64 is equal to the projected path length of the second region 66.

The first regions 64 have a surface-path length L1 that is less than the surface-path length L2 of the second regions 66, measured in profile in a direction parallel to the longitudinal axis of the web 52 when the web is in an untensioned condition. Preferably, the surface pathlength of the second region 66 is at least about 15% greater than the surface pathlength of the first region 64, more preferably at least about 30% greater than the surface pathlength of the first region, and most preferably at least about 70% greater than the surface pathlength of the first region. Generally, the greater the surface pathlength of the second region, the greater the elongation of the web before encountering the force wall. Suitable techniques for measuring the surface path length of such materials are described in the Chappell et al patent referenced above.

Sheet material 52 exhibits an improved "poisson lateral contraction effect" that is substantially less than that of an otherwise identical base web of similar material composition. Methods for determining the poisson lateral contraction effect of a material can be found in the "test methods" section of the Chappell et al patent referenced above. Preferably, webs suitable for use in the present invention have a poisson lateral contraction effect of less than about 0.4 when the web is subjected to an elongation of about 20%. Preferably, the web exhibits a poisson lateral contraction effect of less than about 0.4 when the web is subjected to an elongation of about 40%, 50% or even 60%. More preferably, the poisson lateral contraction effect is less than about 0.3 when the web is subjected to 20%, 40%, 50% or 60% elongation. The poisson lateral contraction effect of such a web is determined by the amount of web material occupied by the first and second regions, respectively. As the area of the sheet material occupied by the first region increases, the poisson lateral contraction effect also increases. Conversely, the poisson lateral contraction effect decreases as the area of the sheet material occupied by the second region increases. Preferably, the area percentage of the sheet material occupied by the first regions is from about 2% to about 90%, and more preferably from about 5% to about 50%.

Prior art sheet materials having at least one layer of elastomeric material will generally have a greater poisson lateral contraction effect, i.e., they will "neck in" as they elongate in response to an applied force. Web materials suitable for use in the present invention can be designed to mitigate, if not substantially eliminate, the poisson lateral contraction effect.

For sheet material 52, the direction of applied axial elongation D (indicated by arrow 80 in fig. 3A) is substantially perpendicular to first axis 76 of rib-like elements 74. The rib-like elements 74 are capable of straightening or geometrically deforming in a direction substantially perpendicular to their first axis 76 to allow extension to occur in the web 52.

Referring now to fig. 3B, when the web of sheet material 52 is subjected to applied axial elongation D (indicated by arrow 80 in fig. 3B), first regions 64 having a shorter surface path length L1 provide the majority of the initial resistive force P1 to the applied elongation due to molecular-level deformation. In this stage, the rib-like elements 74 of the second regions 66 undergo geometric deformation or unbending, thus providing minimal resistance to applied elongation. In the course of transitioning to the next stage, the rib-like elements 74 will gradually become aligned with (i.e., coplanar with) the applied elongation. In other words, the second region will gradually exhibit a change from geometric deformation to molecular-level deformation. This is the beginning of the force wall. In the stage shown in fig. 3C, the rib-like elements 74 in the second regions 66 have become substantially aligned with (i.e., coplanar with) the plane of applied elongation (i.e., the second regions have reached their limits of geometric deformation) and begin to resist further elongation by molecular-level deformation. Due to the molecular level deformation, the second region 66 now provides a second resistance P2 to further applied elongation. The resistive force to elongation provided by the molecular-level deformation of the first regions 64 and the molecular-level deformation of the second regions 66 forms a total resistive force PT that is greater than the resistive force provided by the molecular-level deformation of the first regions 64 and the geometric deformation of the second regions 66.

When (L1+ D) is less than L2, drag P1 is significantly greater than drag P2. When (L1+ D) is less than L2, the first region provides an initial resistance P1, generally satisfying the formula: p1 ═ (a1 × E1 × D) L1

When (L1+ D) is greater than L2, the first and second regions provide a combined total resistive force PT for the applied elongation D, generally satisfying the formula: PT (a1 × E1 × D) L1+ (a2 × E2 × □ L1+ D-L2 □) L2 +

The maximum elongation that occurs in the stage corresponding to fig. 3A and 3B is the "available stretch" of the formed web material before the stage described in fig. 3C is reached. The available stretch corresponds to the distance that the second region travels when undergoing geometric deformation. The variable range of available stretch is about 10% to 100% or more, and may be controlled primarily by the extent to which the surface path length L2 in the second region exceeds the surface path length L1 in the first region and the composition of the base film. The term "available stretch" is not intended to imply a limit to the elongation that the web of the present invention can withstand, as there are applications: where elongation beyond the available stretch is desirable.

When a sheet material is subjected to an applied elongation, the sheet material exhibits an elastic-like behavior in that it extends in the direction of the applied elongation and returns to its substantially untensioned condition once the applied elongation is removed, unless the sheet material is extended beyond the yield point. The sheet material is capable of undergoing multiple cycles of stressed elongation without losing its ability to substantially recover. Thus, once the applied elongation is removed, the web is able to return to its substantially untensioned state.

While the sheet material can easily and reversibly extend in a direction substantially perpendicular to the first axis of the rib-like elements in the direction of applied axial elongation, the web material cannot as easily extend in a direction substantially parallel to the first axis of the rib-like elements. The formation of the rib-like elements allows the rib-like elements to be geometrically deformed in a direction substantially perpendicular to a first or major axis of the rib-like elements while requiring significant molecular-level deformation to extend in a direction substantially parallel to the first axis of the rib-like elements.

The amount of applied force required to extend the web depends on the composition and cross-sectional area of the sheet material as well as the width and spacing of the first regions. For a given composition and cross-sectional area, narrower and widely spaced first regions require a lower applied extension force to achieve the desired elongation. The first axis (i.e., length) of the first region is preferably greater than the second axis (i.e., width) of the first region, wherein the ratio of length to width is about 5: 1 or greater.

The depth and frequency of the rib-like elements can also be varied to control the available stretch of the sheet web material suitable for use in the present invention. If the height or degree of formation imparted on the rib-like elements is increased for a given rib-like element frequency, the available stretch is increased. Similarly, if the frequency of rib-like elements is increased for a given forming height or extent, the available stretch is increased.

There are several functional properties that can be controlled by applying such materials to the flexible bags of the present invention. These functional characteristics are the resistive force exerted by the sheet material against the applied elongation and the available stretch of the sheet material before it encounters the force wall. The resistive force exerted by the sheet material against an applied elongation depends on the material (e.g., composition, molecular structure and orientation, etc.) and cross-sectional area as well as the percentage of the projected surface area of the sheet material occupied by the first regions. For a given material composition and cross-sectional area, the higher the percent area coverage of the sheet material by the first region, the higher the resistive force that the web will exert against the applied elongation. The percentage of coverage of the sheet material by the first areas is determined in part (or in whole) by the width of the first areas and the spacing between adjacent first areas.

The available stretch of the web material is determined by the surface pathlength of the second region. The surface pathlength of the second region is determined at least in part by the rib element spacing, the rib element frequency, and the rib element forming depth, measured perpendicular to the plane of the web material. Generally, the greater the surface pathlength of the second region, the greater the available stretch of the web material.

As described above with respect to fig. 3A-3C, sheet material 52 initially exhibits some resistance to elongation provided by first regions 64, while rib-like elements 74 of second regions 66 undergo geometric movement. When the rib-like elements transition into the plane of the first region of material, increased resistance to elongation may be exhibited as the entire sheet material now undergoes molecular-level deformation. Accordingly, sheet materials of the type described in fig. 3A through 3C and described in the Chappell et al patent referenced above may provide the performance advantages of the present invention when formed into closed containers such as the flexible bags of the present invention.

An additional benefit realized by the use of the aforementioned sheet materials in the construction of flexible bags according to the present invention is the enhancement of the visual and tactile appeal of such materials. The polymeric films typically used to form such flexible polymeric bags are typically thin in nature and often have a smooth, shiny surface finish. While some manufacturers may emboss or otherwise texture the surface of the film to a lesser degree, bags made from such materials still tend to exhibit a slippery and crunchy tactile impression on at least the outward facing side of the finished bag. The thinner materials of such flexible polymeric bags, along with the substantially two-dimensional surface geometry, also tend to leave consumers with an exaggerated impression of thinness and may be perceived as lacking durability.

In contrast, sheet materials suitable for use in the present invention, such as those depicted in fig. 3A-3C, exhibit a three-dimensional cross-sectional profile in which the sheet material is deformed (in an untensioned state) to project out of the major plane of the sheet material. This may provide additional surface area for gripping and may dissipate glare typically associated with substantially planar, smooth surfaces. The three-dimensional rib-like elements may also provide a "soft, cushion-like" tactile impression when the pouch is held in the hand, while also providing a desirable tactile impression as opposed to conventional pouch materials, and may enhance the perception of thickness and durability. The additional texture may also reduce noise associated with certain types of film materials, resulting in an enhanced auditory impression.

Suitable mechanical methods of forming the matrix material into a sheet web material suitable for use in the present invention are well known in the art and are disclosed in the aforementioned Chappell et al patent and commonly assigned U.S. patent 5,650,214 issued in 1997, 7, 22, in the name of Anderson et al.

Another method of forming the base material into a sheet web material suitable for use in the present invention is vacuum forming. An example of a vacuum forming process is disclosed in commonly assigned U.S. Pat. No. 4,342,314 to Radel et al, 8/3, 1982. Alternatively, the formed sheet web material may be hydroformed in accordance with the teachings of commonly assigned U.S. Pat. No. 4,609,518 to Curro et al, 9/2, 1986.

The forming process may be implemented in a static mode, in which only one discrete portion of the base film is deformed at a time. Alternatively, the forming process may be accomplished using continuous dynamic pressing for intermittently contacting a moving web and forming the matrix material into the formed web material of the present invention. These and other suitable methods for forming the web material of the present invention are more fully described in the above-referenced Chappell et al patent. The flexible bag may be made from a formed sheet material, or alternatively, the flexible bag may be made first and then subjected to the process for forming the sheet material.

Referring now to fig. 4, other patterns for the first and second regions may also be used as sheet material 52 suitable for the uses described herein. Fig. 4 shows sheet material 52 in its substantially untensioned condition. Sheet material 52 has two centerlines: a longitudinal centerline, which is also referred to hereinafter as an axis, line, or direction "L"; and a transverse or direction-finding centerline, which is also referred to hereinafter as an axis, line, or direction "T". The transverse centerline "T" is generally perpendicular to the longitudinal centerline "L". Materials of the type described in fig. 4 are described in more detail in the aforementioned Anderson et al patent.

As described above with respect to fig. 3A-3C, sheet material 52 includes a "strainable network" of distinct areas. The strainable network includes a plurality of first regions 60 and a plurality of second regions 66 that are visually distinct from one another. Sheet material 52 also includes transition regions 65 at the interface between first regions 60 and second regions 66. The transition region 65 will exhibit a complex combination of the behavior of the two regions, the first region and the second region, as described above.

Sheet material 52 has a first surface (facing the viewer in fig. 4) and an opposing second surface (not shown). In the embodiment shown in fig. 4, the strainable network comprises a plurality of first regions 60 and a plurality of second regions 66. A portion of the first region 60, generally indicated at 61, is substantially linear and extends in a first direction. The remainder of the first region 60, generally indicated at 62, is substantially linear and extends in a second direction substantially perpendicular to the first direction. The first direction may be perpendicular to the second direction. Other angular relationships between the first and second directions may also be suitable, as long as the first regions 61 and 62 intersect each other. The angle between the first and second directions ranges from about 45 ° to about 135 °. In one embodiment, the angle is about 90 °. The intersection of the first regions 61 and 62 forms a boundary (indicated by phantom line 63 in fig. 4) that completely surrounds the second region 66.

In one embodiment, the width 68 of the first region 60 may be about 0.01 inches to about 0.5 inches. In another embodiment, the width 68 of the first region 60 may be about 0.03 inches to about 0.25 inches. However, other width dimensions for the first region 60 may also be suitable. Since the first regions 61 and 62 are perpendicular to each other and equally spaced apart, the second region has a square shape. However, other shapes for the second regions 66 are also suitable and may be obtained by varying the spacing between the first regions and/or the alignment of the first regions 61 and 62 with respect to each other. The second region 66 has a first axis 70 and a second axis 71. The first axis 70 is substantially parallel to the longitudinal axis of the web material 52 and the second axis 71 is substantially parallel to the transverse axis of the web material 52. The first region 60 has a modulus of elasticity E1 and a cross-sectional area A1. Second region 66 has a modulus of elasticity E2 and a cross-sectional area A2.

In the embodiment shown in fig. 4, the first region 60 is substantially planar. In other words, the material within first region 60 is in substantially the same state before and after web 52 undergoes the forming step. The second region 66 includes a plurality of raised rib-like elements 74. The rib-like elements 74 may be embossed, have a pattern of indentations, or a combination thereof. The rib-like elements 74 have a first or major axis 76 that is substantially parallel to the longitudinal axis of the web 52 and a second or minor axis 77 that is substantially parallel to the transverse axis of the web 52.

The rib-like elements 74 in the second regions 66 may be separated from one another by unformed regions that are substantially unembossed or have a pattern of indentations, or simply formed as spaced regions. Preferably, the rib-like elements 74 are adjacent to each other and separated by unformed areas of less than 0.10 inches, measured perpendicular to the major axis 76 of the rib-like elements 74, and more preferably, the rib-like elements 74 are contiguous with substantially no unformed areas therebetween.

The first region 60 and the second region 66 each have a "projected path length". As used herein, the term "projection path length" refers to the length of the shadow cast by an area under illumination by parallel light. The projected path length of the first region 60 and the projected path length of the second region 66 are equal to each other.

The first regions 60 have a surface-path length L1 that is less than the surface-path length L2 of the second regions 66, measured in a parallel direction along the profile when the web is in an untensioned condition. Preferably, the surface pathlength of the second region 66 is at least about 15% greater than the surface pathlength of the first region 60, more preferably at least about 30% greater than the surface pathlength of the first region, and most preferably at least about 70% greater than the surface pathlength of the first region. Generally, the greater the surface pathlength of the second region, the greater the elongation of the web before encountering the force wall.

For sheet material 52, the direction of applied axial elongation D (indicated by arrow 80 in fig. 4) is substantially perpendicular to first axes 76 of rib-like elements 74. This can be attributed to the fact that: the rib-like elements 74 are capable of straightening or geometrically deforming in a direction substantially perpendicular to their first axis 76 to allow extension to occur in the web 52.

Referring now to FIG. 5, when web 52 is subjected to applied axial elongation D (indicated by arrow 80 in FIG. 5), first region 60, having a shorter surface path length L1, will provide a majority of the initial resistive force P1, due to molecular level deformation, to the applied elongation corresponding to stage I. In stage I, the rib-like elements 74 in the second regions 66 undergo geometric deformation or unbending, thus providing minimal resistance to applied elongation. In addition, the shape of the second region 66 may also change due to movement of the network formed by the intersecting first regions 61 and 62. Thus, when web 52 is subjected to a force elongation, first regions 61 and 62 undergo a geometric deformation or bending, thereby changing the shape of second region 66. The second region is extended or elongated in a direction parallel to the direction of forced elongation and is collapsed or contracted in a direction perpendicular to the direction of forced elongation.

In addition to the aforementioned elastic-like characteristics, it is believed that sheet materials of the type described in fig. 4 and 5 may also provide a softer, more cloth-like texture and appearance, and be less noisy in use.

Various compositions suitable for use in constructing flexible bags of embodiments of the present invention include substantially impermeable materials such as polyvinyl chloride (PVC), polyvinylidene chloride (PVDC), Polyethylene (PE), polypropylene (PP), aluminum foil, coated (waxed, etc.) and uncoated paper, coated nonwovens, and the like; and substantially permeable materials such as scrims, webs, wovens, nonwovens, or perforated or porous films, whether predominantly two-dimensional in nature or formed into three-dimensional structures. Such materials may comprise a single composition or layer, or may be a composite structure of multiple materials.

Once the desired sheet material is manufactured in any desirable and suitable manner (including all or a portion of the material intended for the bag body), the bag may be constructed in any known and suitable pattern, including those patterns such as those known in the art for manufacturing bags of such commercially available forms. The various components or elements of the bag may be joined to themselves or to one another using heat sealing, mechanical sealing, or adhesive sealing techniques. In addition, the bag body can also be thermoformed, blown, or otherwise molded rather than relying on folding and bonding techniques to construct the bag body from a web or sheet of material. Two recent U.S. patents that illustrate the state of the art regarding flexible storage bags similar in overall structure to those depicted in fig. 1 and 2, but of the type currently available, are U.S. patent 5,554,093 issued to Porchia et al at 9/10 1996 and 5,575,747 issued to Dais et al at 11/19/1996.

The dimensions and values disclosed herein are not to be understood as being strictly limited to the exact numerical values recited. Rather, unless otherwise specified, each such dimension is intended to mean both the recited value and a functionally equivalent range surrounding that value. For example, a dimension disclosed as "40 mm" is intended to mean "about 40 mm".

All documents cited in the detailed description of the invention are incorporated herein by reference in relevant part. The citation of any document is not to be construed as an admission that it is prior art with respect to the present invention. To the extent that any meaning or definition of a term in this document conflicts with any meaning or definition of the same term in a document incorporated by reference, the meaning or definition assigned to that term in this document shall govern.

While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.

Claims (7)

1. A flexible bag comprising at least one sheet of flexible sheet material, the sheets being assembled to form a semi-enclosed container having an opening defined by a periphery, the opening defining an opening plane; the bag having a drawtape closure for sealing the opening to convert the semi-closed container to a closed container, an upper region adjacent the drawtape closure, and a lower region below the upper region, wherein the flexible bag is characterized in that a sheet material of the drawtape closure exhibits an elastic-like behavior along at least one axis, the sheet material of the drawtape closure comprising: at least a first region and a second region having the same material composition and each having an unstrained projected path length; when the sheet material is subjected to a forced elongation in a direction substantially parallel to the axis in response to an applied force applied to the sheet material of the draw tape closure, the first region undergoes a significant molecular-level deformation and the second region initially undergoes a significant geometric deformation.

2. The flexible bag of claim 1, wherein said sheet material, when formed into a closed container, exhibits at least two significantly different stages of resistive forces to applied axial elongation along at least one axis when subjected to said applied elongation in a direction parallel to said axis in response to an applied force applied to said flexible storage bag, said sheet material comprising: a strainable network comprising at least two visually distinct regions, one of said regions being configured such that it will exhibit a resistive force in response to a forced axial elongation in a direction parallel to said axis before a significant portion of the other of said regions produces a significant resistive force to said forced axial elongation; at least one of the areas has a surface path length greater than the other of the areas, the length being measured parallel to the axis when the sheet material is in an untensioned condition; the region exhibiting the longer surface pathlength comprises one or more rib-like elements; the sheet material exhibits a first resistance to said applied elongation until a substantial portion of said region of said sheet material elongated sufficiently to have a longer surface pathlength falls into the plane of said applied axial elongation, whereupon said sheet material exhibits a second resistance to further applied axial elongation, said sheet material exhibiting a total resistance greater than the resistance of said first region.

3. The flexible bag of claim 1, wherein said sheet material, when formed into a closed container, exhibits at least two stages of resistive forces to applied axial elongation D along at least one axis when subjected to applied axial elongation along said axis in response to an applied force applied to said flexible storage bag, said sheet material comprising: a strainable network of visually distinct regions, the strainable network comprising at least a first region and a second region; the first areas have a first surface path length L1 measured parallel to the axis when the sheet material is in an untensioned condition; the second region has a second surface path length L2 measured parallel to the axis when the web material is in an untensioned condition; the first surface path length L1 is less than the second surface path length L2; said first region independently generating resistive force P1 in response to applied axial elongation D, said second region independently generating resistive force P2 in response to applied axial elongation D, said resistive force P1 being substantially greater than said resistive force P2 when (L1+ D) is less than L2.

4. A flexible bag according to any one of claims 1 to 3, wherein said sheet material comprises a plurality of first areas and a plurality of second areas having the same material composition, a portion of said first areas extending in a first direction and the remainder of said first areas extending in a direction perpendicular to said first direction so as to intersect one another, said first areas forming a boundary completely surrounding said second areas.

5. The flexible bag of claim 1, wherein said drawtape closure comprises a drawtape and a hem, wherein the sheet material of at least one of said drawtape and said hem comprises a pattern of embossed regions.

6. A flexible bag according to any one of claims 1 to 5, wherein said sheet material comprises a polymeric film material.

7. The flexible bag of any one of claims 1-6, wherein the bag comprises a trash bag.