Abstract:
A method for producing a roll of stretch film comprises the steps of passing a stretch film web over a first roller, and winding the stretch film web around a second roller against the first roller, where the first roller has a surface for enabling the introduction of air into the wound stretch film web.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates generally to packaging and in particular, to a stretch film and a method of fabrication therefor. 
       BACKGROUND OF THE INVENTION 
       [0002]    Stretch film is widely used in the wrapping and securing of pallet loads for shipping. It is known that such plastic films, which are commonly made from low density polyethylene (LLDPE), gain significantly in ultimate tensile strength when stretched above their yield point. This is due to the fact that such plastic films have a “memory”. For example, film that is stretched to such a degree so as to create a 10% memory will shrink 10% of its stretched length. This “memory” assists in the holding of pallet loads wrapped with stretch film, as the “memory” or the tendency to shrink assists in securing the palletized articles together under compression. 
         [0003]    Stretch film is commonly fabricated by stretching the web of plastic film prior to rolling. This pre-stretching facilitates the process of manually applying of the product to a pallet load, as the end user is required to apply less manual tensile force during the wrapping process. Such pre-stretched rolled stretch film webs are fabricated in the form of rolls  20 , as illustrated in  FIG. 1 , and provide a compact product that may be either applied to a pallet load manually or loaded into an automated wrapping machine. 
         [0004]    A number of methods of fabricating pre-stretched stretch film have previously been disclosed. For example, U.S. Pat. No. 5,967,437 to Martin-Cocher, et al. discloses a method of manufacturing rolls of pre-stretched film that comprises importing oscillation to the film with a component perpendicular to the film axis. For example, during pre-stretching and winding of the film on a take-up roll, a feed roll, i.e. a spool from which the stretchable film for stretching is taken, is caused to oscillate, and/or the take-up core is caused to oscillate. This ensures that successive layers of film are offset, in particular at the margins of the film. Rolls of film obtained in this way do not have portions of extra thickness and lower tension at the margins. 
         [0005]    U.S. Pat. No. 6,592,699 to Mehta, et al. discloses a highly stretched film that has permanently heat-sealed edges which are nearly invisible. A folding apparatus folds the edge portions of a film to form folded edges. The folded film then is passed through a bridle mechanism having two heated rolls. A series of nips apply pressure to the folded film as it is heated by the heated rolls. The nip pressure, combined with the heat imparted by the heated rolls, causes thermal welding of the folded edges resulting in permanent heat-sealed edges. Because the film edges are folded prior to the hot-stretching, the hot stretch process performs dual functions of stretching the film and heat sealing the folded edges. The resulting stretched film has permanently heat-sealed edges that do no separate, and which prevent tearing of the film edges during subsequent processing and use. 
         [0006]    Stretch film has a tendency to retain a “memory” after rolling, which tends to cause the stretch film to contract into its original length as the film recovers, and which in turn can cause adjacent layers of rolled, pre-stretched film tend to fuse together. This can make it difficult to unroll pre-stretched film without tearing the film. Additionally, rolls of stretch film made by conventional fabrication methods are tightly wound, and are dense, solid items. Such stretch film rolls are typically not tolerant to mishandling such as accidental dropping, and can suffer damage such as denting. Denting can cause the film to tear during use (i.e. during the wrapping of a pallet load) which effectively terminates the usage lifetime of the roll and results in waste. 
         [0007]    It is an object of this invention to provide an improved roll of stretch film that has a high tolerance to mishandling, and a method of fabricating the same. 
       SUMMARY OF THE INVENTION 
       [0008]    Accordingly, in one aspect there is provided an apparatus for rolling a stretch film web comprising: 
         [0009]    a first roller having a surface engaging the stretch film web, the surface being shaped to cause the web to wrinkle as it passes over the surface; 
         [0010]    a second roller for winding the wrinkled stretch film so as to trap air in the rolled film; and 
         [0011]    an assembly for rotatably driving the second roller. 
         [0012]    In still another aspect, there is provided a method for producing a roll of stretch film comprising the steps of: 
         [0013]    passing a stretch film web over a first roller, the roller having a surface shaped to wrinkle the stretch film web; and 
         [0014]    winding the stretch film web in a wrinkled state around a second roller so as to trap air within the rolled film. 
         [0015]    In yet another aspect, there is provided an apparatus for rolling a stretch film web comprising: 
         [0016]    a surface engaging a stretch film web, the surface being shaped to cause the web to wrinkle as it passes over the surface; 
         [0017]    a roller for winding the wrinkled stretch film so as to trap air in the rolled film; and 
         [0018]    an assembly for rotatably driving the roller. 
         [0019]    In still another aspect, there is provided a method for producing a roll of stretch film comprising the steps of: 
         [0020]    passing a stretch film web over a surface shaped to wrinkle the stretch film web; and 
         [0021]    winding the stretch film web in a wrinkled state around a roller so as to trap air within the rolled film. 
         [0022]    In yet another aspect, there is provided a roll of stretch film, the stretch film being rolled in a deliberately wrinkled state so as to trap air within the roll. 
         [0023]    In still another aspect, there is provided a roll of stretch film, the stretch film being wound against a surface shaped for enabling the introduction of air into the roll of film. 
         [0024]    In another aspect, there is provided an apparatus for rolling a stretch film web comprising: 
         [0025]    a first roller having a surface engaging the stretch film web; 
         [0026]    a second roller for winding the stretch film against the first roller, the surface of the first roller being shaped for enabling the introduction of air into the wound stretch film web; and 
         [0027]    an assembly for rotatably driving the second roller. 
         [0028]    In still another aspect, there is provided a method for producing a roll of stretch film comprising the steps of: 
         [0029]    passing a stretch film web over a first roller; and 
         [0030]    winding the stretch film web around a second roller against the first roller, the first roller having a surface for enabling the introduction of air into the wound stretch film web. 
         [0031]    In yet another aspect, there is provided an apparatus for rolling a stretch film web comprising: 
         [0032]    a surface engaging a stretch film web; 
         [0033]    a roller for winding the stretch film web against the surface, the surface being shaped for enabling the introduction of air into the wound stretch film web; and 
         [0034]    an assembly for rotatably driving the roller. 
         [0035]    In still another aspect, there is provided a method for producing a roll of stretch film comprising the steps of: 
         [0036]    passing a stretch film web over a surface; and 
         [0037]    winding the stretch film web around a roller against the surface, the surface being shaped for enabling the introduction of air into the wound stretch film web. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0038]    Embodiments will now be described more fully with reference to the accompanying drawings in which: 
           [0039]      FIG. 1  is a perspective view of a prior art roll of stretch film; 
           [0040]      FIG. 2  is a perspective view of a roll of stretch film; 
           [0041]      FIG. 3  is a side view of an apparatus for the production of the roll of stretch film of  FIG. 2 ; 
           [0042]      FIG. 4  is a plan view of a set of rollers for use with the apparatus of  FIG. 3 ; 
           [0043]      FIGS. 5   a  to  5   d  are photographic views of the set of rollers of  FIG. 4 ; 
           [0044]      FIG. 6  is a cross-sectional view of another embodiment of a set of rollers for use with the apparatus of  FIG. 3 ; 
           [0045]      FIG. 7  is a perspective view of the set of rollers of  FIG. 6 ; and 
           [0046]      FIG. 8  is a side elevation view of the set of rollers  FIG. 6 . 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0047]    Turning now to  FIG. 2 , a roll of stretch film is shown, and is generally indicated by reference numeral  30 . Roll  30  comprises a rolled stretch film web  32  that has been oriented prior to rolling, and which also has wrinkles  34  that have been deliberately formed in the stretch film web  32  prior to rolling. As will be appreciated, wrinkles  34  allow air to be trapped within the roll  30 , such that the roll  30  is softer, spongier and less dense than would otherwise be obtained by rolling the stretch film web  32  without wrinkles. Wrinkles  34  therefore enable the roll  30  to be more resilient to handling errors such as, for example, the dropping of roll  30  during the manual wrapping of pallet loads, or during the manual loading of roll  30  into an automated wrapping machine. In the embodiment shown, wrinkles  34  are oriented generally longitudinally with respect to the stretch film web  32 , and are distributed generally evenly across the width of the stretch film web  32 . However, as will be appreciated, wrinkles  34  need not be limited to this orientation or this distribution in order for air to be trapped within roll  30 . 
         [0048]      FIGS. 3 ,  4  and  5   a  to  5   d  illustrate a production apparatus used for fabricating roll  30 , generally indicated using reference numeral  40 . Production apparatus  40  comprises an extruder  42  that dispenses a continuous sheet of plastic film onto a surface of a rotating first drum  44  so as to form a stretch film web  32 , as is known in the art. Stretch film web  32  is fed from first drum  44  to pass between second drum  46  and second drum counter-roller  47 , and is then fed through a first series  48  of guiding rollers. A third drum  50  and a third drum counter-roller  52  are positioned downstream from the series  48  of guiding rollers. The stretch film web  32  is stretched or “oriented” as it passes through this portion of the production apparatus  40 . This stretching or orienting is accomplished by controlling the rotation speeds (i.e. rpm) of second drum  44  and third drum  50 , and such that the speed of the surface of third drum  50  is greater than that of second drum  44 . By controlling this difference of speeds, the stretching or orienting may be controlled over a range of from 5% to 30%. As is known in the art, the stretch film web generally moves through production apparatus  40  at speeds ranging from 1500 ft/min to 3000 ft/min. 
         [0049]    Downstream from third drum  50  is positioned a second series  54  of guiding rollers, followed by a grooved roller  60  and a take-up roller  62  rotating in opposite directions. In this embodiment, and as may be more clearly seen in  FIG. 4 , grooved roller  60  comprises a surface having a plurality of radial grooves  64 . Grooved roller  60  is positioned adjacent to a take-up roller  62 , which provides a surface onto which a core  66  is removably mounted. As stretch film web  32  passes over grooved roller  60 , grooves  64  cause stretch film web  32  to become wrinkled evenly across its width. Stretch film web  32  is then wound in this wrinkled state around take-up roller  62 , and in particular around core  66  removably mounted onto take-up roller  62 , so as to form roll  30  having air trapped within. In this sense, stretch film web  32  is wound around take-up roller  62  “against” grooved roller  60 . An assembly is provided for rotatably driving take-up roller  62 . An assembly may optionally be provided for driving grooved roller  60 . 
         [0050]    As is known in the art, to increase the efficiency of the production process, a plurality of rolls  30  may be fabricated simultaneously in a side-by-side arrangement using a single roller  60  and a single roller  62 . Such an arrangement is depicted in  FIG. 5   b . Here, a plurality of adjacently-spaced stretch film webs  32  is fed into rollers  60  and  62 , wherein each stretch film web  32  is wound around a respective core  66  removably mounted onto take-up roller  62 . 
         [0051]      FIGS. 6 to 8  illustrate another embodiment of a pair of rollers  160  and  62  for use with the production apparatus  40 . Roller  160  comprises an array of single radial grooves  164 . Each groove  164  causes wrinkling across the width of a respective stretch film web  32  as it passes around roller  160 . Stretch film web  32  is then wound in this wrinkled state around roller  62 , and in particular around core  66  removably mounted onto roller  62 , so as to form roll  130 . Owing to the size of the groove  164  relative to the width of the roll  130 , roll  130  has a non-uniform profile across its width, wherein the diameter in a central portion  170  of roll  130  is greater than in each end portion  172 . This difference is attributed to a difference in the degree of wrinkling, and therefore in the quantity of trapped air, between central portion  170  and end portions  172 . 
         [0052]    Although in embodiments described above, the cross sectional profiles of the grooves are illustrated as comprising right angles, the profiles of the grooves are not limited to this configuration, and may comprise grooves having profiles of any shape. Indeed, one skilled in the art will appreciate that varying the shape of the groove profile will have an effect on the wrinkling. Similarly, one skilled in the art will also appreciate that the varying any of the spacing and the depth of the grooves will have an effect on the wrinkling. 
         [0053]    In embodiments described above, the production apparatus comprises a grooved roller that causes the stretch film web to be wrinkled as it passes over the roller. However, in other embodiments, the production apparatus may comprise a device other than a roller for causing wrinkling. For example, such a device may comprise a guide or channel having a surface shaped to cause wrinkling of the stretch film web as the web passes through the device or over the surface of the device. In this embodiment, the stretch film web would be wound in this wrinkled state around the take-up roller “against” the surface of the device. 
         [0054]    The roll of stretch film that has been rolled in a wrinkled state so as to trap air within the roll may be formed using any apparatus and/or method of the embodiments described above. Alternatively, in other embodiments, the roll of stretch film that has been rolled in a wrinkled state so as to trap air within the roll may instead be formed by unwinding a conventional roll of stretch film wound in an unwrinkled state, and rewinding the film in such a manner as to roll the film in a wrinkled state and so as to trap air within the roll. 
         [0055]    Although in embodiments described above, the grooved roller has one or more radial grooves, the orientation of the grooves are not limited to the radial orientation, and instead the grooved roller may comprise grooves that are oriented at an angle to the radial orientation. 
         [0056]    Although embodiments have been described above with reference to the accompanying drawings, those of skill in the art will appreciate that variations and modifications may be made without departing from the spirit and scope thereof as defined by the appended claims.