Patent Application
20150036952
The present invention relates to bulk bags manufactured from polypropylene, and more particularly to an anti-skid treatment applied to one or more outer surfaces of such bags to prevent relative movement between adjacent bags in a stack.
Bulk materials bags manufactured from polywoven materials are used the world over to package bulk items ranging from pet foods to foods for human consumption, and ingredients for processing in the food industry. There are several types of materials that are used for such polywoven bags; exemplary films include but are not limited to oriented polypropylene (“OPP”) and biaxially oriented polypropylene (“BOPP”). Each of these types of films demonstrates known and advantageous characteristics for use in manufacturing bulk bags. As a result, bags made from such films have found wide acceptance in a variety of industries.
Bags manufactured with OPP and BOPP film are extremely popular and are in widespread use. Generally described, BOPP film is a polypropylene film that has been stretched in both the machine and cross machine directions. It has excellent working properties. For example, it is resistant to oils and greases, defines a good vapor barrier, demonstrates high clarity and performs well in high speed printing operations. BOPP has an attractive high gloss finish, good puncture and crack resistance and is not affected by moisture and does not shrink with changes in the environment. And there are many closure options available for use with BOPP.
Bags made with BOPP film typically are laminates having an inner layer made out of material that has properties designed to be compatible with the bulk material that will be in the bag. For example, if the bag is being designed to accommodate a bulk food item that has high oil content, the material used for the inner layer is chosen to be compatible with the food product and with the oil content. A middle layer is biaxially oriented woven polypropylene and the outer layer is a print and bonding layer.
But both BOPP and OPP bags are notoriously slippery when stacked atop other like bags. That is, the coefficient of friction between two OPP bags is low so that stacked backs tend to slide relative to one another. When a bulk bag made of BOPP is filed with a heavy material and stacked on another BOPP bag, a number of problems arise due to the slippery nature of the material. For example, when multiple bags are stacked onto a pallet the stack is fairly unstable because the bags in the stack are prone to relative movement. Since the coefficient of friction between the adjacent bags is low, when the pallet is moved during transport the stack of bags on the pallet may become unstable and become upset. Shrink wrapping the stack can help alleviate this stability problem, but it does not eliminate it as relative movement between bags may still occur.
One known solution for stabilizing BOPP and similar bags that tend to be “slippery” when stacked on a pallet is to use so-called “palletizing adhesives.” Palletizing adhesives are applied to one or both facing surfaces of adjacent bags in a stack to effectively increase the coefficient of friction between the bags. There are a variety of such products, but generally described these products are an adhesive that is applied to the upper surface of a bulk bag as the bag is stacked onto a pallet. The adhesive on one bag then binds to the facing surface of the next bag stacked on top of the adhesive-coated bag, thereby stabilizing the stack. There are both hot melt and liquid cold palletizing adhesives and these products have found widespread usage. However, there are known limitations with these methods, including adding expense to the process of palletizing bags, undesired “stickiness” due to applied adhesive, gummy residue left on the bags, the danger of burns using hot melt adhesive (typically applied at temperatures over 250 degrees F.), and package tearing upon separation when a stack of bags is de-stacked.
There is a need therefore for an anti-skid solution that addresses these known limitations of applied palletizing adhesives.
The present invention comprises an anti-skid treatment that is applied to bulk materials bags on one or both of the major outer surfaces of the bags. The anti-skid material is deposited onto the bag surface(s) during manufacturing of the bag and when finished, filled bags are stacked atop one another, the anti-skid material on one bag is pressed against a major surface of an adjacent bag in the stack. Because the anti-skid material increases the coefficient of friction between bags in a stack, relative movement between bags is minimized or eliminated.
Since the anti-skid treatment is applied during manufacturing of the bag, the problems inherent with palletizing adhesives are avoided. The material used for the anti-skid treatment is an elastomeric polymer that is applied to the bag during forming with an extruder. The polymer is non-tacky and does not adversely affect handling of the bag either before or after filling and does not result in package tearing when a stack of bags is unstacked.
Other advantages of the invention will become clear from review of the following description and drawings.
The invention will be better understood and its numerous objects and advantages will be apparent by reference to the following detailed description of the invention when taken in conjunction with the following drawings.
The invention described herein relates to an anti-skid treatment that is applied to film that is commonly used to manufacture bulk material bags. As noted above, exemplary films with which the anti-skid treatment described herein are used include but are not limited to oriented polypropylene (“OPP”), polyolefin (“PO”), and biaxially oriented polypropylene (“BOPP”). The invention is described herein with reference to a typical bulk bag manufactured from BOPP.
The invention will now be described in detail with reference to the drawings. Relative directional terms are used at times to describe components of the invention and relative positions of parts of the invention and equipment for manufacturing bags incorporating the invention. As a naming convention, the plane of the floor in a manufacturing or work space is considered to be a generally horizontal surface. Other relative directional terms correspond to this convention: “upper” refers to the direction above and away from the ground plane; “lower” is generally in the opposite direction, “inward” is the direction from the exterior toward the interior of a bulk bag and “outward” is the opposite direction. “Vertical” is the direction normal to the horizontal ground plane, and so on.
Turning now to the drawings, a first embodiment of a bag 5 incorporating the anti-skid treatment 10 according to the present invention is shown. It will be understood that bag 5 may be any type of bulk bag and is described herein as a typically bulk bag manufactured from BOPP. The bag 5 shown in the drawings is typical of the type of bulk bags that are shipped from the bag manufacturer to the users in a flattened condition with one end of the bag closed and the opposite end open. In the present description, the closed end 12 of bag 10 is sometimes referred to as the “manufactured” end. The open end 14 is sometimes referred to as the “consumer” end because the open end is closed by the consumer after the bag is filled. There are a variety of closure types that may be used to close both the manufactured end 12 and the consumer end 14. In
Bags such as bag 5 according to the present invention may be manufactured with gusseted side edges 18 as illustrated herein, or may just as well be made with flat sides. In either case, the bag 5 has a first major surface 20 and an opposite major surface 22. For reference purposes, the bag axis is defined as the axis extending in the direction of arrow A in FIG. 1—that is, the axis that extends along the longitudinal axis of the formed bag. The cross-bag axis is transverse to the bag axis—arrow B in
Bag 5 includes an anti-skid treatment 10 applied to major surface 20 of the bag and extending along the surface in along the bag axis. Anti-skid treatment 10 is defined by plural strips 30 of an elastomeric polymer material 32 that is applied to the bag according to the process described below. The elastomeric polymer is applied to the bag with a modified extrusion machine during formation of the bag. The material is applied in heated liquid form and dries quickly so that it is not tacky and the strips are bonded onto the major surface 20 and cannot easily be removed therefrom. The anti-skid material when applied to the bag defines an area of the bag that has a higher coefficient of friction (between stacked bags) relative to stacked bags that are untreated. As a result, when plural bags 5 having anti-skid treatment 10 are stacked atop one another, relative movement between the bags is eliminated or minimized so that the stack is stable.
One preferred polymeric material 32 suitable for use with the present invention is a propylene-based, olefinic elastomer that is flexible, elastic and transparent. The polymer must be suitable for thermoplastic application with an extruder and should have excellent adhesion properties for application to BOPP. A propylene-based elastomer meeting these criteria and found to perform well for use with the present invention is currently available from ExxonMobil Chemical and is offered under the brand name VISTAMAXX 6202.
With reference to
The polymeric material 32 that is used for the strips 30 causes the coefficient of friction between bags 5a and 5b, and between 5b and 5c to be higher than the coefficient of friction between adjacent bags that do not include strips 30. As such, bags according to the present invention that include the anti-skid treatment 10 define more stable stacks in which the bags are resistant to relative movement to a greater degree. Thus, if we assume that the coefficient of kinetic friction between two BOPP bags that do not include anti-skid treatment 10 is equal to μb, and that that the coefficient of kinetic friction between two BOPP bags that do incorporate anti-skid treatment 10 described herein is μa, then the invention defined herein results in the following: μa>μb.
The strips 30 illustrated in
It will be understood that the strips 30 may be relatively wider or narrower than those shown in the drawings and may be greater or fewer in number than shown in the drawings. Finally, those of skill in the art will appreciate that the strips may be arranged and placed differently on the major surface(s) of the bag. Thus, it is possible to have a group of one or more strips 30 near one lateral edge of the bag 5 and a group of one or more strips 30 near the opposite edge of the bag. Similarly, the strips 30 described herein extend along the bag axis. The strips could be applied along the cross bag axis and the strips could be applied in intermittent patches rather than continuous strips.
The manufacturing process used to apply anti-skid treatment 10 to bags 5 will now be described with reference to
A bag making machine 50 is illustrated in
Downstream of extruder 60 the bag stock 54 with strips 30 applied thereto continues over various other turn rolls in the downstream direction (arrow A) until the elastomeric polymer 32 is sufficiently dry and the stock 54 passes through a cutter 70. Cutter 70 is largely conventional and includes a cutter roll 72 that has a knife 74 that extends across the cutter roll in the cross bag axis. Individual bags 76 are formed each time the cutter roll 72 makes a complete rotation and the individual bags 76 are formed into a stack 78 for further processing—i.e., closing the manufactured end, shipment to the consumer, etc.
While the present invention has been described in terms of preferred and illustrated embodiments, it will be appreciated by those of ordinary skill that the spirit and scope of the invention is not limited to those embodiments, but extend to the various modifications and equivalents as defined in the appended claims.
