Abstract:
A bag ( 100 ) is disclosed as including an opening at an open end ( 102 ) and a seal ( 108 ) adjacent to a closed end ( 104 ), in which the bag is movable between a collapsed configuration in which the bag is flat and an expanded configuration in which the opening is closed and the bag is fully inflated, and the seal is non-straight when the bag is in the collapsed configuration, and the seal is straight when the bag is in the expanded configuration.

Description:
[0001]    This invention relates to a bag, e.g. a bag made of a synthetic material, which may be used for containing refuse.  
         BACKGROUND OF THE INVENTION  
         [0002]    [0002]FIGS. 1A to  1 C show various views of a conventional bag  10  made of a sheet of plastic material. FIG. 1A shows a view of the plastic bag  10  in a fully collapsed configuration, and  
           [0003]    [0003]FIG. 1B shows a sectional view of the plastic bag  10  taken along a line P-P in FIG. 1A. During the production of the plastic bag  10 , a width of the sheet of plastic material is folded inward of a respective designed lateral edge of the bags  10 , each forming a gusset, and a straight seal  12  is then formed near the intended bottom end and transverse to the length of the bag  10 , by heat sealing at a temperature of 200 to 350° C. in the conventional manner. It is however found in practice that the region between two points, namely M and N shown in FIGS. 1A and 1B, where the seal  12  meets the gussets is the weakest in terms of loading capacity. This usually results in leakage of the contents in the bag  10  through or around this region, or the bag  10  is torn apart around the region between the points M and N, on the weight of the contents.  
           [0004]    This phenomenon can be more clearly explained with reference to FIG. 1B. In particular, it is found that when such a conventional plastic bag  10  is fully expanded, i.e. fully inflated and closed at its mouth in an airtight manner, the seal  12  is bent with its mid portion, i.e. the region between the points M and N, nearer to the mouth of the bag  10  than the rest of the seal  12 . In this way, the region between the points M and N will have to bear a higher proportion of the pressure exerted by the contents in the bag  10  on the seal  12  than the rest of the seal  12 . Put another way, the pressure exerted by contents in the bag  10  on the seal  12  is not even, thus causing some part of the seal, namely the region between the points M and N in the bag  10  shown in FIG. 1B, to bear a higher pressure than other part of the seal  12 .  
           [0005]    It is thus an object of the present invention to provide a bag in which the aforesaid shortcomings are mitigated, or at least to provide a useful alternative to the public.  
           [0006]    It is a further object of the present invention to provide a bag with a higher loading capacity, as compared with a conventional bag made of the same type and amount of material.  
         SUMMARY OF THE INVENTION  
         [0007]    according to the present invention, there is provided a bag with an opening at a first end and at least a seal adjacent to a second end, wherein said bag is movable between a collapsed configuration in which said bag is substantially flat and an expanded configuration in which said bag is fully inflated and said opening is closed, characterized in that said seal is non-straight when said bag is in said collapsed configuration. 
       
    
    
     BRIEF DESCRIPTION OF THE INVENTION A preferred embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:  
       [0008]    [0008]FIG. 1A is a side view of a prior art plastic bag in a fully collapsed configuration;  
         [0009]    [0009]FIG. 1B is a side view of the plastic bag shown in FIG. 1A, in a fully expanded configuration;  
         [0010]    [0010]FIG. 1C is a sectional view of the prior art plastic bag taken along the line P-P in FIG. 1A;  
         [0011]    [0011]FIG. 2 is a side view of a plastic bag according to the present invention in a fully collapsed configuration; and  
         [0012]    [0012]FIG. 3 is a side view of the plastic bag shown in FIG. 2, in a fully expanded configuration. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0013]    [0013]FIG. 2 shows a side view of a plastic bag according to a preferred embodiment of the present invention, generally designated as  100 , in a fully collapsed configuration. The bag  100  has an open end  102 , and a closed end  104 . The open end  102  may be closed in a substantially airtight manner by strings (not shown) or such other conventional closure means. The bag  100  may be made of such plastic material as low density or high density polyethylene.  
         [0014]    The bag  100  is shown here as formed with two seals, namely a straight seal  106 , represented by a straight line ST in FIG. 2, and a non-straight seal  108 , represented by a non-straight line AG, both close to the closed end  104 . In this connection, although the seal  106  is of the same structure as the seal  12  of the bag  10  shown in FIG. 1A, it is in fact only of cosmetic purpose in the bag  100 , for the reasons to be discussed below.  
         [0015]    Referring to FIG. 2, it can be seen that, when the bag  100  is in this fully collapsed configuration, the seal  108  is non-straight. In particular, the seal  108  is made up of a straight line segment AB starting from one lateral edge of the bag  100  leading downwardly towards the closed end  104 , joined by an arc BC with a centre of curvature O 2  downward of the seal  108 , followed by an arc CDE with a centre of curvature O 1  upward of the seal  108 , followed by an arc EF with a centre of curvature O 3  downward of the seal  108 , then a straight line segment FG ending at the other lateral edge of the bag  100 . It can be seen that the centre of curvature O 1  is on the longitudinal centre line L-L of the bag  100 . The arcs BC and EF are thus curved towards the open end  102 , and the arc CDE is curved towards the bottom end  104 . The line ABCD is symmetrical to the line GFED about the longitudinal centre line L-L. It can also be seen that the line segments AB and FG, when extended when the bag  100  is in the fully collapsed configuration, will intersect an angle e, which is an obtuse angle.  
         [0016]    The width of the bag  100  may be from 300 mm to 1,000 mm, depending on customer requirements, and the width of the seals  106  and  108  may be from 0.8 mm to 2 mm. The ranges of other dimensions are as follows:  
         [0017]    R 1 : 100 mm to 300 mm;  
         [0018]    f: 3 mm to 15 mm;  
         [0019]    a: 10 to 100 mm;  
         [0020]    b: 130 mm to 340 mm.  
         [0021]    As to the value of R 2 , such can be determined by reference to the value off and b, since the circle of which the arc BC forms a part only touches the circle of which the arc CD forms a part, and the line segment AB, when extended, is tangent to the arc CD.  
         [0022]    It can be seen that the distance between the points A and G to the open end  102  is shorter than the distance between the point D (where the seal  108  intersects the longitudinal centre line L-L of the bag) and the open end  102 .  
         [0023]    When the bag  100  according to the present invention is in its fully expanded configuration, i.e. fully inflated and substantially airtightly closed adjacent to the open end  102 , although the seal  106  will still be bent upwardly towards the mouth of the bag  100 , the seal  108  will however constitute a straight line, as can be seen in FIG. 3. By reason of such a change in the shape of the seal  108 , the whole of the seal  108  will contribute equally to bearing the loading of the content in the bag  100 , thus increasing the loading capacity of the bag  100 , when the bag  100  is in its fully expanded configuration. It is found in experiments that the loading capacity of a bag made in accordance with the present invention can be as much as eight times that of a conventional bag, i.e. one with the conventional seal  12  only, made of the same type and amount of material.  
         [0024]    As the weight of the contents in the bag  100  will be borne by the seal  108  only, the seal  106  is only of cosmetic purpose only, i.e. to enhance the aesthetic appearance of the bag  100 , but does not contribute to the load-bearing capacity of the bag  100 . The seal  108  may or may not touch the seal  106 , and if the seal  108  is designed not to touch the seal  106 , their distance is at the discretion of the manufacturer.  
         [0025]    It should be understood that the above only illustrates and describes an example whereby the present invention may be carried out, and that modifications and/or alterations may be made thereto without departing from the spirit of the invention.  
         [0026]    It should also be understood that various features of the invention which are, for brevity, described in the context of a single embodiment, may be provided separately or in any suitable sub-combination.