REINFORCED PLASTIC BAGS

Abstract: The invention provides a method of forming plastic tubing and particularly multi-walled plastic bags wherein the seal area is strengthened by utilizing a plurality of layers of material in the seal area.

Description: The present invention relates to plastic tubing and in particular, to valve bags formed of plastic film material. Plastic bags are used for packaging a number of materials and are particularly suitable for dry fluids. These bags are made of tubing formed from plastic film material and when the plastic tubing is formed into a bag, there is often a sealing strip (generally longitudinal) which is subjected to various stresses and/or strains and which strip will ultimately become the weak part of the bag. It is at this point that the valve is formed and breakage at this point of stress or strain frequently results unless the bag is suitably reinforced. The manufacture of single and multi-walled plastic bags is, as aforementioned, well known in the art. In a single wall bag, a sheet of film is folded over longitudinally so that two edges overlap which can then be heat-sealed or glued as appropriate. The heat sealing operation utilizes conventional equipment and in the case of glueing, a band of glue is placed between the two overlapping walls or plies. When utilizing a multi-wall bag or tube, the overlapping edges of the plies or walls are offset from each other to allow for the introduction of the heat sealing or glueing equipment. This leads to a generally awkward arrangement and in most instances, an inherent weakness in the construction especially when forming a valve bag. - An object of the invention is to provide a method of making plastic bags having.edge seals- , together with apparatus suitable for the manufacture of plastic bags , and a plastic bag having reinforced areas along its edge seals offering improvements in relation to one or more of the matters identified above , or generally. According to the invention there is provided a method as defined in the accompanying claims. In an embodiment of the present invention, there is provided a method of forming a multi wall plastic tubing which includes the steps of feeding first and second layers of a suitable plastic sheet material into proximity with each other. The first and second layers have their side edges generally in alignment with each other. Subsequently, a layer of reinforcing material is placed on at least one of the layers at each side edge on facing surfaces. The facing surfaces of the side edges are then placed into juxtaposition with each other and adhered together to form a seam along the side edges. The adhered edges are then folded over on each other in a tubing operation such that the adhered edges overlap each other; they in turn are then secured together in an overlapping configuration. The plastic sheet materials utilized may be any suitable film of a plastic material, preferably thermoplastic, capable of being sealed according to the method of the invention. As will be appreciated by those skilled in the art, the preferred material is polyethylene. However, the two walls or layers forming the tube may be of a different material - i.e. since two separate plies are utilized in the double bag embodiment, the films may have different thicknesses be of different materials, and the like. One film may be preprinted such that the other film protects the printed material thereon. The thicknesses of the film will be sufficient for the end use of the product. As aforementioned, the first and second layers of thermoplastic sheet material are fed such that their side edges are generally in alignment. The thermoplastic films are then held apart and a reinforcing material is applied onto at least one of the edges of one of the films such that the edges may subsequently be secured together. As will be appreciated, the reinforcing material may be applied onto both of the facing surfaces of the films. The reinforcing material employed may be selected among those well known to those skilled in the art and in a preferred embodiment, is a hot melt adhesive such as a low density polyethylene. If the films are treated on their surfaces, it may be preferable to leave an untreated surface where the hot melt adhesive is to be applied. Subsequent to the application of the reinforcing material, the films may be then subject tQ a pressure at least at the edge portions to provide a suitable contact at the edges and adhesion thereof. Conveniently, the film may be passed between a pair of pressure rolls to thereby form a pair of seams at either side edge of the thermoplastic films. Subsequently the multi wall structure is then folded over in a tubing operation as is well known in the art. In the tubing operation, the two secured side edges are overlapped and in turn secured together. To secure the two edge seams together, different methods may be employed. Thus, one may employ heat sealing, the application of adhesive including hot melt adhesive, etc. It is also within the scope of the invention that a form of reinforcing material can be applied to the exterior surface of at least one of the layers of plastic sheet material which will then secure the multi wall structure into a multi wall tube. Utilizing the above method in a multi wall structure, it has been found that the final longitudinal seam forming the tube is stronger than the prior art seams. During production, various operations were facilitated due to the construction which appeared to be stiffer on passing through the turntable and registration section on an ender thereby facilitating these operations. One of the main advantages of the embodiment is that when the tubing is used as a valve bag, the valve seat is reinforced. In other words, the area or edge where the valve is attached to the tube and is stressed when the filling bag is inserted is a lot stronger than conventional bags and this is particularly true when the bag is used at lower temperature. In the manufacture of a valve bag, valve components may be inserted to provide a valve structure during the tubing operation. Thus, in one particular embodiment, one or more envelopes or tubes of a suitable material may be interposed between the two secured side edges during the tubing operation. This would then provide an entry into the interior of the bag which is formed by transverse cutting and sealing of the tubes. In one particular embodiment, a pair of valve tubes may be provided; a first one of a relatively short length of a relatively thick material to be secured to the overlapped edges with a longer more flexible inner portion providing the valve entrance per se. The apparatus adapted to practice the present invention may consist of substantially conventional bag-forming machinery. Thus, there will be provided means for supplying a pair of films, means for guiding the same into proximity with each other, means for extruding a layer of hot melt adhesive between the edges of the films, means for securing the films together and conventional tubing means. The method of the invention can also be applied to single wall bags. In such a case, one would lay down a band or seam of a reinforcing material on each side of the film. The film is then passed over conventional tubing machinery such that the two bands or seams of reinforcing material overlap each other and a layer of hot melt adhesive may be extruded between the two bands or seams to form a single wall tube or bag. The bag is then reinforced at its critical points. The means for securing the seams together can be made from various types of adhesives - e.g. isocyanate solvent glue, pure polyethylene hot melt, and other hot melt temperature adhesives. If desired, in some circumstances, heat sealing may be utilized between the reinforced seams or edges for securing the bag together. Having thus generally described the invention, reference will be made to the accompanying drawings illustrating embodiments thereof in which: FIGURE 1 is a cross-sectional view of the seam area of a conventional multi walled tube or bag; FIGURE 2 is a cross-sectional view of the seam area of a multi-wall tube or bag according to the present invention; FIGURE 3 is a cross-sectional view of the valve area of a multi-wall bag; FIGURE 4 is a perspective view of an apparatus for forming the multi wall tube or bag of the present invention; FIGURE 5 is a perspective view of an apparatus used for forming a single walled tube; FIGURE 6 is a sectional view taken along the lines 6-6 of Figure 5; and FIGURE 7 is a cross-sectional view of the single walled film used in the embodiment of Figures 5 and 6. Referring to the drawings in greater detail and by reference characters thereto, Figure 1 illustrates a prior art sealing arrangement for a double wall tubed bag. In this arrangement, a first panel 12 having walls or layers 14 or 16 is overlapped with a second panel 18 having walls or layers 20 and 22. As may be seen from Figure 1, the sealing arrangement is such that plies 20 and 22 are offset with respect to each other as are plies 14 and 16. The upper surface of ply 20 is secured to the lower surface of ply 16 by hot melt adhesive 24. Similarly, a strip of hot melt adhesive 26 secures the upper surface of ply 22 to the lower surface of ply 14. Thus, two separate seals are provided in the making of a double wall tubed bag. As shown in Figure 4, a first film layer 30 is provided from a source of the same, is passed over guide roller 34 journalled on shaft 36. A second film layer 32 is similarly passed over guide roll 38 which is journalled on shaft 40. Layers 30 and 32 then converge to pass over roll 46 as may be seen in Figure 3. Before the point of convergement of layers 30 and 32 extruder nozzles 42, 42' are provided on each side of the sheet material 30, 32 and a layer of a suitable reinforcing material is applied to the facing surfaces of layers 30, 32. Pressure rolls 44, 44' are situated at either side of the sheet material. Thus, at either side of sheet material 30, 32 a reinforced area generally designated by reference numerals 50 and 52 is provided1 at which reinforced area the films are subsequently secured together. The double walled material is passed over guide roller 48 to a tuber as designated by arrow 54. At the tuber (not shown), the side edges or reinforced areas of the double walled material are overlapped in a conventional manner and are secured together, preferably by a suitable adhesive. Thus, one obtains the structure shown in Figure 2 wherein at the seam of the tube or bag, an extremely strong structure is obtained with adhesive 56 joining the double walled structure together. When forming a valve bag, valve components are inserted between the reinforced areas of the double walled material prior to securing the reinforced areas together in the tuber. Thus, having reference to Figure 3 illustrating the valve structure, a first outer valve component 51 is inserted between reinforced areas 50 and 52 and which component 51 is secured to the reinforced areas. In turn there is an inner valve component 53 secured to outer valve component 51. In practice, it is preferred that inner valve component 53 be of a thinner slightly more flexible material than outer valve component 51 and it will at the same time, extend into the interior of the tube or bag further than outer component 51. The practice of the present invention can also be utilized in a single wall bag to provide greater strength characteristics than conventional bags or tubes. When or if required, bags of more than two walls can also be made in accordance with this invention. Figure 5 illustrates the use of the method as it is applied to a single wall bag. In this method, sheet material 60 is passed over a back-up roll' 62 journalled on shaft 64 which is driven by means of belt 66. Back-up roll 62 rotates in the direction indicated by arrow 68. At either side of continuous film 60, are a pair of extruders 70, 70' extruding a reinforcing material 82, 82' on an upper surface of the film 60. A cooling roll generally designated by reference numeral 72 rotates in the direction indicated by arrow 76 to drive belt 78 rotating shaft 74. Means generally designated by reference character 80 are utilized to provide a cooling fluid to the interior of cooling roll 72. As will be appreciated, suitable inlet and outlet means for the cooling fluid are provided. Following placement of reinforcing material 82, 82' on the side edges of film 60, the material is advanced to a conventional tuber (not shown) wherein the edges are overlapped and secured together. As in the case of the double wall tube or bag, a layer of adhesive may be utilized or a heat sealing operation may be utilized. Utilizing the present invention, it is possible to use the reinforced tubing as a plastic pipe conduit or gas pocket with the seams or reinforced edges being used to support the conduit or pocket such that nails, screws or other fasteners could be inserted in or attached to these seams whereby they can function as lugs. A double wall construction may be used in greenhouse construction wherein the space between the two walls can be filled with air for insulation purposes or alternatively for heating. Still further, the tube could be suitably inflated to provide cushioning or other effects where desired. The bags of the present invention were thin tested in comparison to bags manufactured according to the prior art teachings. In test No. 1 double wall machine made gusseted bags (355 mm x 100 mm x 615 mm) were filled with 25 kgs of material and cooled in a deep freeze to the temperature indicated. The bags were then dropped 4 feet as per the type of drop indicated in Table I. Bags 1 to 6 were gusseted bags of 5.7 mil thickness and manufactured according to the present invention; bags 7 and 8 were gusseted bags of 6 mil thickness manufactured according to the prior art. The results are as follows: TABLE I Bag Flat Edge Valve Bottom Temp. Bag Failed at: - Drop Drop Drop Drop OF 1 2 4 1 1 +2 Did not break 2 4 6 1 1 +4- n n n 3 4 4 2 4 -4 II II 4 4 4 2 4 -4 n U 5 4 4 2 3 -2 n u n 6 4 4 - - -2 Bottom seal 7 4 1 - - +4 Bottom seal 8 4 1 - - -4 Top seal In a second test, the prior art bags and bags according to the present invention were filled with 25 kg of material, frozen and were dropped a distance of 4 feet at temperatures varying between -30F to +60F until they failed. The types of drops were varied. Gusseted bags (15-1/8" x 25") formed of 3 mil material and being double wall according to the prior art failed after an average of 1.63 drops. Gusseted bags (12-V2''x 4" x 28") formed of 3 mil material and being double walled according to the present invention averaged 5.0 drops prior to failure. It will be understood that the above described embodiments are for purposes of illustration only and that changes and modifications may be made thereto without departing from the spirit and scope of the invention. In addition to the invention defined in the preamble of this specification and in the claims , there is also provided a method of forming multi-walled tubing a method for the manufacture of plastic bags having edge seals , apparatus suitable for the manufacture of plastic bags , and a plastic bag having reinforced areas along its edge seals , comprising any novel feature or step or novel combination of features or steps disclosed in the documents of this application.

Claims: CLAIMS 1. A method of forming multi walled tubing comprising feeding first and second layers of a plastic sheet material into proximity to each other, said first and second layers having their side edges generally in alignment, placing a layer of reinforcing material on at least one facing surface of at least one film at each side edge, juxtaposing and adhering side edges together such that said first and second sheet materials form a double wall structure, folding one of said pair of adhered edges over to form a double wall tube with said secured edges overlapping each other, and securing said overlapped edges together. 2. The method of claim 1 further including the step of placing adhesive material on a facing surface of one of said overlapped edges to thereby secure said overlapped edges together. 3. The method of claim 2 wherein the step of placing a layer of adhesive on said films comprises the step of placing a hot melt adhesive thereon. 4. The method of claim 3 wherein said first and second layers of plastic material are a polyethylene material. 5. The method of claim 2 further including the step of passing said side edges between a pair of pressure rolls to adhere the first and second layers together. 6. In a method of forming a single wall tube, the improvement comprising the step of placing a strip of adhesive material on each of the side edges of a film material to thereby form a reinforced area thereon.

Inventors: AUBRY PAUL E., POKLUKAR, JOSEF
Applicants: TWINPAK INC.
Application year: 1985
Main classification: B31B39
IPC codes: B31B1, B31B39, B29C53, B32B1, B29C65, B31B19