Abstract:
A double fold seal having an ultrasonic stitch is provided as a closure means for a bag formed from synthetic resin material, and especially a woven synthetic resin material. A transverse heat seal is created using an ultrasonic welder, for example, and at least two flaps formed outboard from the seal. The flaps are folded over one of the bag panels and ultimately over the heat seal so as to create a bag closure that is strong and leak resistant.

Description:
RELATED APPLICATION 
       [0001]    The present application claims the benefit of U.S. Provisional Patent Application No. 61/089,826, filed Aug. 18, 2008, and is incorporated by reference herein in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention is generally directed toward a strong, durable seal at the end of a single-wall polywoven bag. Particularly, the seal comprises a double fold seal with an ultrasonic stitch. This method of bag closure assists in stopping leaks in the corners of the bag folded areas, reduces stress placed on the ultrasonic stitch, and is readily automated. 
         [0004]    2. Description of the Prior Art 
         [0005]    The use of bags made from synthetic resin material, and particularly woven synthetic resin material (i.e. “polywoven” material), has become increasingly popular. However, providing an effective, yet cost efficient, closure for these types of bags has proven a challenge. Polywoven bags can be manufactured that exhibit excellent tensile strength qualities making them very suitable for containing a wide variety of materials. However, the pliability of these bags does not readily lend itself to conventional types of closures such as might be used with conventional paper or non-woven bags. Conventional folded closures are prone to develop leaks in the corners of the bag folds. Another common closure for polywoven bags is a sewn closure. These closures can be strong, but are can be expensive and time consuming to create. Further, if the sewing is not done properly, leaks can occur at the closure edges. 
         [0006]    U.S. Pat. No. 4,498,192 discloses a bag having an overlapped closure and method of fabricating the same. However, the disclosure is limited to bags comprising at least one paper ply, and no mention is made regarding the use of polywoven bags. 
         [0007]    U.S. Patent Application Publication No. 2007/0274614 discloses a polywoven bag having a double fold closure. However, the double fold closure described can be prone to leaking near the corners of the bag folds, especially when fine particulate matter is being placed in the bag. 
       SUMMARY OF THE INVENTION 
       [0008]    In one embodiment of the present invention there is provided a bag comprising opposed first and second panels made from a synthetic resin material. Each of the panels has an inner face, an outer face, opposed end margins, and opposed side margins. The side margins of the first panel are interconnected with the adjacent side margins of the second panel by at least a pair of longitudinally extending segments. The bag further comprises a first bag closure including a transversely extending seal securing together respective portions of the inner faces of the panels. The seal defines a fillable portion and a closure portion of the bag. A pair of slits are located in the longitudinally extending segments on the closure portion. Each of the slits begin adjacent one end margin of one of the panels and extend toward the seal. The slits define first and second marginal flaps in the closure portion. Each of the flaps have inner and outer faces corresponding with the inner and outer faces of the panels. The first flap is double-folded upon the first panel such that the outer face of the first flap engages the first panel at a first region within the closure portion and the inner face of the first flap engages the first panel at a second region within the fillable portion. The second flap is folded over the first flap and secured to the first panel such that the inner face of the second flap engages the first panel at a third region within the fillable portion. 
         [0009]    In another embodiment according to the present invention there is provided a method of forming a bag. A tubular body is provided comprising a synthetic resin material and includes opposed first and second panels. Each of the panels has an inner face, an outer face, opposed end margins, and opposed side margins. The side margins of the first panel being interconnected with the adjacent side margins of the second panel by at least a pair of longitudinally extending segments. A seal is created between the inner faces of the panels. The seal extends transversely across both panels between respective panel side margins. The seal defines a fillable portion and a closure portion of the bag. A pair of slits are formed in the longitudinally extending segments of the closure portion. Each of the slits begin adjacent one end margin of one of the panels and extend toward the seal. The slits define first and second marginal flaps within the closure portion. Each of the flaps have inner and outer faces corresponding with the inner and outer faces of the panels. The first flap is folded upon the first panel such that the outer face of the first flap engages the first panel at a first region within the closure portion. The second flap is folded over the first flap such that the inner face of the first flap engages the first panel at a second region within the fillable portion, and such that the inner face of the second flap engages the first panel at a third region within the fillable portion. The second flap is secured to the first panel at the third region. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a view of an exemplary polywoven bag comprising closures made in accordance with the present invention; 
           [0011]      FIG. 2  is a view of a tubular polywoven body having gussets formed therein and the creation of a heat seal proximate one end thereof; 
           [0012]      FIG. 3  is a view of the creation of a first fold in the bag closure; 
           [0013]      FIG. 4  is a view of the bag closure following the first fold and beginning of the second fold; 
           [0014]      FIG. 5  is a view of the bag closure following the second fold; and 
           [0015]      FIG. 6  is a view of the bag closure following securing of the second flap to the bag panel. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0016]    Turning now to  FIG. 1 , a bag  10  made in accordance with the present invention is shown. Bag  10  is shown sealed at both ends with a pair of closures  12 ,  14  that are described in greater detail below. Note that is within the scope of the present invention for bag  10  to comprise only one closure made as described hereunder with the second closure being of a conventional type, such as a sewn closure, a folded closure, or the like. In certain embodiments, bag  10  comprises a woven, synthetic resin material, such as polypropylene, and is referred to herein as a “polywoven” bag. In particular embodiments, the polywoven bag is of a single-wall construction, however, it is within the scope of the present invention to construct bags having multi-ply walls and walls comprising materials other than the woven synthetic resin material. 
         [0017]    As illustrated in  FIG. 2 , bag  10  comprises a tubular body  15  that may be folded so as to present a pair of opposed panels  16 ,  18  including end margins  20 ,  22 , and side margins  24 - 30 . The adjacent side margins of panels  16  and  18  are interconnected by at least a pair of longitudinally extending segments  32 ,  34 . In the embodiments illustrated, segments  32  and  34  comprise respective gusset panels  36 ,  38  each including a pair of interconnecting subpanels  40 - 46 . Subpanels  40  and  44  are secured to panel  16 , and subpanels  42  and  46  are secured to panel  18 . It is contemplated that bag  10  may be formed without gussets and that respective end margins of panels  16 ,  18  can be directly attached by a longitudinally extending segment which presents itself as a seam or line of attachment. 
         [0018]      FIGS. 2-6  illustrate the steps involved in the creation of bag bottom closure  12 , and it is understood that the same steps could be performed during the creation of a substantially identical top closure  14 . Note, the various panels and gussets are shown slightly expanded so as to more clearly illustrate these features. First, a seal  48  is created proximate one end of bag  10 , and spaced from end margins  20  and  22 . In certain embodiments, seal  48  is a heat seal or an ultrasonic seal that is created, for example, by an ultrasonic welder, that melts small co-linear portions of the inner faces  50 ,  52  of panels  16 ,  18 , respectively, thereby securing the faces of the panels together. In particular embodiments, seal  48  comprises a plurality of discreet conjoined segments  49  of the inner faces  50 ,  52  of panels  16 ,  18 . Collectively, segments  49  form what appears to be stitching, however, no actual threaded or sewn stitch is used in the present closure. Depending upon the ultrasonic welding device used, the sealing rate typically ranges from about 40 to 60 feet per minute with an average operating temperature ranging from about 175 to 350° F. Seal  48  extends transversely across panels  16 ,  18 , and in certain embodiments the entire length between respective panel end margins  24 - 30 . If a gusseted bag is being made, gusset panels  36  and  38  are also included in seal  48 , sandwiched in between portions of panels  16  and  18 . Seal  48  also defines a fillable portion  54  of the bag that can receive the desired contents to be placed therein and a closure portion  56  that will be used to create various flaps and folds which comprise closure  12 . When viewed completely laid out as in  FIG. 2 , finable portion  54  is located inboard and closure portion  56  is located outboard of seal  48 . 
         [0019]    As shown in  FIG. 3 , slits  58 ,  60  are cut in segments  32 ,  34 , respectively so as to define marginal flaps  62 ,  64 . Each slit  58 ,  60  begins adjacent end margin  22  and extends toward seal  48  a predetermined length along a portion of a corresponding juncture line  66 ,  67  between panel  18  and subpanel  42 ,  46  of gusset panel  36 ,  38 , respectively. In certain embodiments, the length of the slits  58 ,  60  is approximately half the length between end margin  22  and seal  48 . Flap  62  comprises marginal, transversely extending portions of panel  16  and gusset panels  36  and  38 , and flap  64  comprises a transversely extending portion of panel  18  and is defined at its lateral ends by slits  58 ,  60 . In a first fold, flap  62  is folded upon panel  16  such that the outer face  69  of flap  62  engages panel  16 , and particularly the outer face thereof, at a first region  68  within closure portion  56 . The first fold occurs about a transverse axis that extends substantially between the slit termination points  71 ,  73 . As shown in  FIG. 4 , end margin  20  is now positioned adjacent seal  48 . A line of adhesive  70 , such as a hot melt adhesive, is laid down on the outer face of panel  16  within fillable portion  54 . Typically, line of adhesive  70  presents a width of between about 1 to 2 inches and is located several inches inboard from seal  48 . 
         [0020]    A second fold is created by folding flap  64 , and consequently flap  62 , such that inner face  50  of flap  62  engages panel  16  at a second region  72  and the inner face  52  of flap  64  engages the outer face of panel  16  at a third region  74 , with both regions  72  and  74  being within fillable portion  54 .  FIG. 5  illustrates this final fold which occurs about an axis between seal end points  76 ,  78 . Thus, the portion of seal  48  formed in panel  16  is buried within the folds of closure  12  so as to eliminate leaks that may occur in the corners around seal  48  and reduce stress on seal  48  upon filling of bag  10 . The portion of seal  48  formed in panel  18  is visible on the exterior of bag  10 . The inner face of flap  64  is secured to line of adhesive  70  as shown in  FIG. 6  thereby completing closure  12 . 
         [0021]    Upon securing of flap  64  to line of adhesive  70 , bag  10  is ready for filling. Bag  10  may be manufactured in any number of desired dimensions such as bags having widths that range from about 8-24 inches and lengths from about 16-48 inches.