BAG WITH THERMAL WELDED BACK SEAM

Abstract

A bag having a thermal welded back seam is provided. The bag may be formed primarily of a thermoplastic material and may be in the form of a polywoven bag.

Description

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates generally to storage and transport containers such as bags. More particularly, the invention relates to a bag formed primarily from a thermoplastic material and having a thermal welded back seam. Specifically, the invention relates to such a bag which may be formed of a polywoven material.

2. Background Information

Storage devices come in many shapes, sizes and materials, many of which are configured as a bag. To create the holding volume from a single sheet of material, a manufacturing machine may fold or otherwise form material to a desired shape. Many bags are sealed to ensure proper holding of desired contents. While bags may contain a back seam, most bags require a separate and distinct external additive, such as an adhesive, a hot melt glue or stitching to close or otherwise seal the back seam of the bag. To date, known bags have not been configured to seal the back seam without the need of such a distinct and separate material additive. Thus, a need exists for an improved bag.

SUMMARY

In one aspect, the invention may provide a bag comprising a thermoplastic front panel; a thermoplastic back panel having left and right panel segments; an overlap of the left and right panel segments; and a thermal welded back seam which extends along the overlap and is free of a hot melt glue which is different from the front and back panels.

In another aspect, the invention may provide a bag comprising a tube of thermoplastic sheet material which defines an interior chamber and includes a front panel and a back panel having left and right panel segments; wherein the front panel has an inner surface which faces the interior chamber; an overlap of the left and right panel segments; a thermal welded back seam which extends along the overlap and has an inner surface which faces the interior chamber; and broken welds along the inner surface of the back seam and the inner surface of front panel.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Embodiments of the invention illustrative of the best mode in which Applicant contemplates applying the principles are set forth in the following description and are shown in the drawings and are particularly and distinctly pointed out and set forth in the appended claims.

FIG. 1A is a perspective view of a first sample embodiment of a bag having an offset thermal welded back seam.

FIG. 1B is a perspective view of a second sample embodiment of a bag having gussets and an offset thermal welded back seam.

FIG. 2 is a plan view of a bag having an offset thermal welded back seam.

FIG. 3A is a section view of the non-gusseted embodiment taken on line 3A-3A of FIG. 2.

FIG. 3B is a section view of the gusseted embodiment taken on line 3B-3B of FIG. 2.

FIG. 3C is an enlarged section view of the encircled portion of FIG. 3A showing the thermal welded back seam.

FIG. 4 is a plan view of a bag having a centered thermal welded back seam.

FIG. 5A is a section view of the non-gusseted with a centered thermal welded back seam.

FIG. 5B is a section view of the gusseted embodiment with a centered thermal welded back seam.

Similar numbers refer to similar parts throughout the drawings.

DETAILED DESCRIPTION

With primary reference to FIG. 1A, a sample embodiment of a bag is shown generally at 10. Bag 10 may be a polywoven bag and comprises a front panel 24 (FIG. 3A) and a back panel 26 and has an offset thermal welded back seam 28. Bag 10 is configured to hold a volume of bulk solid, liquid, or other material. Bag 10 is non-gusseted and has a first longitudinal or side edge 12 and an opposed second longitudinal or side edge 14 spaced apart and defining an axial or width direction 16 there between. First and second side edges 12 and 14 are defined by a folded piece of a flexible sheet of a thermoplastic material, which may be a polywoven thermoplastic material. One thermoplastic material having desirable characteristics for the construction of bag 10 is polypropylene, although other thermoplastic materials may be used to form the sheet material used to make the various panels of bag 10. First and second edges 12 and 14 may be generally parallel. Bag 10 has a first end edge 18 and an opposed second end edge 20 and defining a longitudinal direction 22 there between. End edges 18 and 20 may be generally parallel and may generally orthogonally intersect side edges 12 and 14.

Front panel 24 and back panel 26 each have first side edges at or adjacent first side edges 12 and may be represented at 12, and second side edges at or adjacent second side edges 14 and may be represented at 14. In the sample embodiment, panels 24 and 26 are connected by the folded thermoplastic material at longitudinal substantially parallel folds which define side edges 12 and 14 and extend from end edge 18 to end edge 20. Front and back panels 24 and 26 define therebetween an interior chamber 40 of bag 10. The ends 18 and 20 may be open at given stage, or closed on one end and open on the other, or closed on both ends. Where both ends are open, the first end edges 18 of panels 24 and 26 define therebetween a first entrance opening of interior chamber 40 while the second end edges 20 of panels 24 and 26 define therebetween an opposed second entrance opening of interior chamber 40. When there are two entrance openings, the bag forms a flexible open-ended tube. One or both of the entrance openings may be closed off by a seam or other closure. For example, front panel 24 and back panel 26 may be connected along their respective first end edges 18 and/or along their respective second end edges 20 in conventional ways such as rolling, folding, sealing or any of various seaming methods to form a first end seam along edge 18 and/or a second end seam along edge 20.

Thermal welded back seam 28 is disposed on the back panel 26 and usually extends longitudinally from end edge 18 to end edge 20 or from adjacent end edge 18 to adjacent end edge 20, and thus from adjacent one end edge 18 and 20 toward the other of end edges 18 and 20. Back seam 28 is created by overlapping left and right back panel segments 30 and 32 (FIGS. 1A, 3) of back panel 26 and welding them directly to each other without the use of any type of hot melt glue, any adhesive, any stitching or other material which is different from the thermoplastic material from which bag 10 is formed, and thus different from the thermoplastic front and back panels 24 and 26. Back seam 28 may be formed without any material other than the thermoplastic materials forming left and right back panel segments 30 and 32. Back seam 28 may be free of any type of hot melt glue, an adhesive, stitching or any material which is different from the thermoplastic material from which bag 10 is formed, and thus different from the thermoplastic front and back panels 24 and 26.

With primary reference to FIGS. 2, 3A and 3C, front panel 24 is a continuous piece of material having a width 46 equal to or about equal to the distance between first and second side edges 12 and 14. Front panel 24 has an inner surface 24a which faces and partially defines interior chamber 40 and an outer surface 24b which faces away from chamber 40 and back panel 26. Back panel 26 has an inner surface 26a which faces and partially defines chamber 40 and outer surface 26b which faces away from chamber 40 and front panel 24. Outer surfaces 24b and 26b define an outer or exterior surface of bag 10. Right segment 32 has a first or left edge which serves as a weld edge 34. Right segment 32 is generally bound by end edge 18, end edge 20, first side edge 12 and first weld edge 34. First side edge 12 and first weld edge 34 define therebetween an axial normal right segment width 42 of right segment 32. Left segment 30 has a second or right edge which serves as a weld edge 36. Left segment 30 is generally bound by first end edge 18, second end edge 20, second side edge 14, and second weld edge 36. Second edge 14 and second weld edge 36 define therebetween an axial normal left segment width 44 of left segment 30 which is significantly less than width 42, as shown in FIG. 2.

Back seam 28 extends axially from first weld edge 34 to second weld edge 36, which define therebetween a weld width 38 (FIG. 3C) of a weld between a first welding surface 35 of a right portion of left segment 30 and a second welding surface 37 of a left portion of right segment 32. These right and left portions overlap one another, thus forming an overlap between left and right segments 30 and 32 such that weld edges 34 and 36 are spaced apart and adjacent one another and typically substantially parallel along their entire length. Although the sample embodiment shows right segment 32 overlapped atop left segment 30, back seam 28 may, for example, be created with left segment 30 overlapped atop right segment 32. Width 38 of the weld in one sample embodiment is approximately one inch, although this may vary especially depending on the strength requirements of back seam 28. In the sample embodiment, first welding surface 35 is part of outer surface 26b of left segment 30 and second welding surface 37 is part of the inner surface 26a of right segment 32. (Similarly, in the embodiment discussed below, welding surface 135 is part of outer surface 126b of left segment 130 and second welding surface 137 is part of the inner surface 126a of right segment 132.)

Back seam 28 may provide a watertight seal and may be made entirely from the thermoplastic material which may form all or essentially all of bag 10 in that no external substances need be added to create the bond of back seam 28. Back seam 28 is typically thermally welded together using only heat and compression pressure (which may, for example, be applied with pinch rollers). Heating in the area where back seam 28 is to be formed melts the thermoplastic material in this area, particularly along overlapping surfaces 35 and 37. Welding surfaces 35 and 37 are typically heated in a range of about 100° F. to about 1450° F. although this may vary depending on the thermoplastic material used. In particular, the weld is created by positioning first welding surface 35 and second welding surface 37 in an overlapping manner, heating welding surfaces 35 and 37 of the overlap so that they melt, compressing the heated overlapping portions of segments 30 and 32 together, and cooling (actively or passively) the melted portions until they solidify, which typically occurs fairly rapidly. Preferably, the weld is continuous along the entire length and width of the weld of back seam 28.

Formation of back seam 28 makes panel segments 30 and 32 become one continuous piece of material in the form of back panel 26, so that bag 10 is a tube with open ends prior to being seamed along either end edge 18 and 20. When welded properly, back panel 26 with the welded back seam 28 will be as strong as a similarly sized continuous piece of the sheet material. Thermal coalescence (that is, melting and cooling of thermoplastic material to form seam 28) provides a back seam having the same chemical properties as a solid piece of the sheet material.

Back seam 28 may be formed as described in the US patent application entitled “BACK SEAM WELDER AND METHOD OF OPERATION” which is filed on the same date as the present application and is incorporated herein by reference. As detailed in said patent application, undesired incidental welds may be formed between the back seam and the front panel during formation of the back seam. Thus, the back seam welder of said application uses a weld breaker to break these incidental welds, thus forming broken welds 45 (FIGS. 3A, 3B, 3C, 5A, 5B) along inner surface 26a of back seam 28 and inner surface 24a of front panel 24 directly opposite back seam 28, or in the embodiment discussed further below, along inner surface 126a of back seam 28 (panel segment 30) and inner surface 124a of front panel 124 directly opposite back seam 28. The incidental welds created during the formation of back seam 28 are formed of the same thermoplastic material of which the present bag is formed, including the front and back panels (and any gusset panels such as shown in the later embodiment). Thus, broken welds 45 are likewise formed of the same thermoplastic material of which the present bag is formed, including the front and back panels (and any gusset panels such as shown in the later embodiment).

Broken welds 45 extend inwardly respectively from inner surface 26a, 126a of seam 28 (panel segment 30, 130) and inner surface 24a, 124a of the portion of front panel 24, 124 directly opposite seam 28. The broken welds 45 which extend inwardly from the inner surface of seam 28 thus extend inwardly toward the broken welds 45 which extend inwardly from the inner surface of the portion of the front panel directly opposite seam 28. A portion of interior chamber 40 is directly between the broken welds 45 which extend inwardly from inner surface 26a, 126a of seam 28 and the broken welds 45 which extend inwardly from inner surface 24a, 124a of the portion of the front panel directly opposite seam 28.

A seam may be formed along first end edge 18, for instance, by a bottomer device as conventionally known in the art. First end edge 18 may be thermally welded or otherwise closed or sealed through other known conventional means. The seam along first end edge 18 may define what becomes the bottom of the bag in a manner sufficient to support the contents within interior chamber 40. Similarly, the seam along second end edge 20 may be heat welded, sealed or seamed with an adhesive, stitching or other means known in the art to form a seam along second end edge 20 which may define what becomes the top of the bag and which may thus provide a sealed closure for the contents of chamber 40.

FIGS. 4 and 5A show back seam 28 generally centered along back panel 26, thus illustrating that back seam 28 may be disposed longitudinally along the back panel 26 at any position. The location of back seam 28 may relate to the contents to be contained by the bag and the desired strength properties of the bag. When back seam 28 is generally centered, left and right segments 30, 32 are generally equal in width (widths 42 and 44 in FIG. 4) and each of widths 42 and 44 is generally slightly wider than one-half the width of front panel 24.

FIGS. 1B, 3B-C and 5B show a sample gusseted polywoven bag 110 having a thermal welded back seam 128. Note that FIG. 5B shows that the bag is formed with seam 128 generally centered while FIGS. 1B and 3B show seam 128 offset from center and FIG. 3C shows seam 128 regardless of position (as with seam 28). Bag 110 is substantially similar to bag 10 except for the gusseted side edges and thus for the most part will be described only to the extent that bag 110 differs from bag 10. Bag 110 has a first longitudinal or side edge 112, 115 and a generally parallel second longitudinal or side edge 114, 117 defining therebetween an axial or width direction 116.

Bag 110 has a front panel 124 and a back panel 126 defining therebetween an interior chamber 140. Front panel 124 has first and second opposed longitudinal or side edges 115 and 117 which are at or adjacent the side edges of bag 10. Likewise, back panel 126 has first and second opposed longitudinal or side edges 112 and 114 which are at or adjacent the side edges of bag 10. Front panel 124 has inner and outer surfaces 124a and 124b analogous to surfaces 24a and 24b and thus has essentially the same characteristics and relationships described above. Back panel 126 has inner and outer surfaces 126a and 126b analogous to surfaces 26a and 26b and thus has the same characteristics and relationships described above. Back panel 126 comprises a left segment 130 and a right segment 132 welded together by thermal welded back seam 128 along an overlap of left and right segments 130 and 132 to form a weld along weld surfaces 135 and 137, in the same manner as discussed above with respect to seam 28 being formed by an overlap of segment 30 and 32. Back panel 126 is bound by edges 112, 114, 118, 120. Front panel 124 is bound by edges 115, 117, 118, 120.

Back seam 128 extends axially from first weld edge 134 to second weld edge 136, which define therebetween a weld width 38 (FIG. 3C) of the weld between first welding surface 135 of a right portion of left segment 130 and second welding surface 137 of a left portion of right segment 132. These weld edges, the weld and welding surfaces are analogous to those of bag 10. Thus back seam 128 extends longitudinally and axially in the same manner described above regarding bag 10.

One of the gusseted side edges of bag 110 includes two gusset panels 123 (only one labeled) which extend inwardly respectively from side edges or longitudinal outer folds 112 and 115 to an inner fold 119 which is folded in the opposite direction from folds 112 and 115 and spaced inwardly of folds/edges 112 and 115 toward the opposite side edge 114, 117. Inner fold 119 is thus adjacent and inward of side edge 112, 115. The other of the gusseted side edges of bag 110 includes two gusset panels 125 (only one labeled) which extend inwardly respectively from side edges or longitudinal outer folds 114 and 117 to an inner fold 121 which is folded in the opposite direction from folds 114 and 117 and spaced inwardly of folds/edges 114 and 117 toward the opposite side edge 112, 115. Inner fold 121 is thus adjacent and inward of side edge 114, 117. All of folds 112, 115, 119, 114, 117 and 121 are generally parallel to one another and extend from end edge 118 to end edge 120 or from adjacent edge 118 to adjacent edge 120. While bag 110 shows only two gusset panels in each gusseted side edge, it will be understood that additional panels and folds may be formed in each gusset.

Gusset panels 123 and 125 are formed of the same polywoven thermoplastic material as front and back panels 124 and 126, and typically all of these panels 123-126 are formed from a single piece of a sheet of the polywoven material which is folded at the above-noted folds to define each of the panels. Gusset folds 119 and 121 are spaced apart a normal axial distance less than width 46 of bag 110. The cross section of each gusseted side edge of the sample embodiment has a generally inward facing “W” shape. Other gusset shapes are contemplated, as bag 110 may have multiple aligned gusseted folds and gusset panels.

Preferably, prior to thermal welding, the back seam 28, 128 is formed in a manner creating a lap joint. However, other conventionally known joints as would be understood in the art to weld two pieces of material together, such as a v-joint or butt joint, are contemplated. While back seam 28, 128 may be free from separate or different materials such as holt melt glue, stitching or an adhesive, branding or label materials may cover part of or the whole outer surface of the back panel, such as ink or paper, yet do not heat seal and may be understood to form no part of the back seam 28, 128.

One advantage of bags 10, 110 is that a bag manufacturer may increase production efficiency by thermal welding the back seam of the bag. A bag having a thermal welded back seam removes manufacturing costs associated with adhesives, hot melt glue, stitching or other materials ordinarily associated with forming/sealing the back seam on a bag.

In the foregoing description, certain terms have been used for brevity, clearness, and understanding. No unnecessary limitations are to be implied therefrom beyond the requirement of the prior art because such terms are used for descriptive purposes and are intended to be broadly construed.

Moreover, the description and illustration of the preferred embodiment of the invention are an example and the invention is not limited to the exact details shown or described.

Claims

1. A bag comprising: a thermoplastic front panel;a thermoplastic back panel having left and right panel segments;an overlap of the left and right panel segments; anda thermal welded back seam which extends along the overlap and is free of a hot melt glue which is different from the front and back panels.

2. The bag of claim 1 wherein the front and back panels define therebetween an interior chamber; the front panel has an inner surface which faces the interior chamber;the back seam has an inner surface which faces the interior chamber; and further comprising broken welds along the inner surface of the back seam and the inner surface of front panel.

3. The bag of claim 1 wherein the front panel has opposed first and second side edges and opposed first and second end edges; the back panel has opposed first and second side edges and opposed first and second end edges;the first and second side edges of the back panel are respectively adjacent the first and second side edges of the front panel;the first and second end edges of the back panel are respectively adjacent the first and second end edges of the front panel.

4. The bag of claim 3 wherein the back seam extends from adjacent one of the first and second end edges of the back panel toward the other of the first and second end edges of the back panel.

5. The bag of claim 4 wherein the back seam extends from adjacent the one of the first and second end edges of the back panel to adjacent the other of the first and second end edges of the back panel.

6. The bag of claim 5 wherein the back seam extends from the one of the first and second end edges of the back panel to the other of the first and second end edges of the back panel.

7. The bag of claim 1 further comprising a first fold extending along the first side edges; and a second fold extending along the second side edges.

8. The bag of claim 7 further comprising a third fold extending along the first side edges; and a fourth fold extending along the second side edges.

9. The bag of claim 8 further comprising a fifth fold extending along the first side edges; and a sixth fold extending along the second side edges.

10. The bag of claim 7 wherein the first fold defines the first side edges; and the second fold defines the second side edges.

11. The bag of claim 3 wherein the back seam is substantially parallel to the first side edges and the second side edges.

12. The bag of claim 1 further comprising an interior chamber defined between the front and back panels;a first entrance opening of the interior chamber adjacent the first end edges; anda second entrance opening of the interior chamber adjacent the second end edges.

13. The bag of claim 12 wherein the back seam extends from adjacent one of the first and second entrance openings toward the other of the first and second end openings.

14. The bag of claim 1 further comprising an interior chamber defined between the front and back panels;an entrance opening of the interior chamber adjacent the first end edges;an end seam extending from adjacent the first side edges to adjacent the second side edges;wherein the back seam extends from adjacent one of the entrance opening and end seam toward the other of the entrance opening and end seam.

15. The bag of claim 14 wherein the back seam extends from the entrance opening to the end seam.

16. The bag of claim 1 wherein the front and back panels are formed from a single sheet of thermoplastic material.

17. The bag of claim 16 wherein the thermoplastic material is a polywoven thermoplastic material.

18. The bag of claim 1 wherein each of the front and back panels is formed of a polywoven thermoplastic material.

19. The bag of claim 1 further comprising a first gusset extending along the first side edges; anda second gusset extending along the second side edges.

20. A bag comprising: a tube of thermoplastic sheet material which defines an interior chamber and includes a front panel and a back panel having left and right panel segments; wherein the front panel has an inner surface which faces the interior chamber;an overlap of the left and right panel segments;a thermal welded back seam which extends along the overlap and has an inner surface which faces the interior chamber; andbroken welds along the inner surface of the back seam and the inner surface of front panel.