Patent Application
20180290424
Pelletized pet food and animal feed, and other granular products such as fertilizer, grain and industrial raw materials, are transported and stored in large bags, known as back seam laminated or circular laminated bags. Such bags may contain, for example, 20 pounds to 60 pounds or more of the product. It is thus important that the bag material have high tensile strength, in order to resist tearing or bursting of the bags during transport, and that it be possible to safely stack a large number of the bags without the bags sliding off of one another.
Traditionally, these bags were formed of a multi-layer laminate that included one or more paper layers. More recently, such paper-based laminates have been replaced by polymeric laminates. For example, some bags include a polymer film layer laminated to a woven layer by an extruded polymer “adhesive” layer. In some cases, these polymeric bags are formed of polypropylene for recyclability.
The present disclosure features laminated bags, e.g., back seam or circular laminated bags, having an inner woven layer laminated to an outer nonwoven layer. These bags are strong, resisting ripping and bursting during transport and storage. The bags also have a surface that is less slippery than that of film bags—making for easier and safer stacking of the bags back to back in warehouses and at retailers. Since the contents of laminated bags are often very heavy, the non-slip quality of the bags disclosed herein provides an important safety benefit by preventing injuries that could result from the collapse of a stack of bags. The bag surface is also easily printed on using a wide variety of printers. In some implementations, the bag is fully recyclable and/or biodegradable.
In one aspect, the disclosure features a bag for storing granular material, the bag comprising an inner woven polymeric layer, an outer nonwoven polymeric layer, and an adhesive layer bonding the inner layer to the outer layer.
In some implementations, the bag may include one or more of the following features.
The nonwoven layer may comprise a spunbonded material. The nonwoven layer may have a basis weight of from about 15 to 80 gsm (grams per square meter), for example from about 20 to 55 gsm, or from about 20 to 40 gsm (ASTM D3776). In some cases, the nonwoven layer has a grab tensile strength of at least 20 lb/in (ASTM D5034.) The nonwoven layer may be, for example, a polypropylene or polyethylene nonwoven.
The bag may have a volume of at least 3 gallons, for example at least 6 gallons or even 10 gallons or more. In some cases, the bag has a volume of from about 3 gallons to 30 gallons. In some implementations, the bag is perforated to provide breathability.
The three layers may be of the same material, e.g., all of polypropylene or all of polyethylene.
The inner woven layer may have a fabric weight of from about 27 to 135 gsm, e.g., from about 50 to 100 gsm. In some cases, the woven material is formed of fibers having a denier of about 500 to 1500, e.g., about 750 to 1250.
The adhesive layer may be an extruded polymer film, and may be present in an amount of about 15-25 gsm.
In another aspect, the disclosure features a method of making a laminated bag, the method comprising forming a laminated material by laminating a nonwoven layer to a woven layer using an extruded polymer layer, and forming the laminated material into a bag having the nonwoven layer as its outer surface.
In some implementations, forming the material into a bag includes forming the laminated material into a cylindrical shape with the nonwoven layer exposed, cutting the cylindrical shape to bag length, and sewing the laminated material to form individual bags. In some cases, the method further includes printing the laminated material and/or perforating the laminated material to provide air holes for breathability. The sewing step may include applying a finishing tape to the material edges in seam areas and stitching through the finishing tape.
As discussed above, the disclosure features back seam or circular laminated bags that are formed of a laminated material that includes an outer nonwoven layer and an inner woven layer, joined together by a laminating adhesive layer.
Referring to
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We will first discuss below methods of manufacturing the laminate, followed by examples of materials that may be used, and lastly examples of methods by which the bag may be manufactured.
Laminate Manufacture
Layers 11 and 12 are laminated together using adhesive layer 21, which is preferably a polymer film. Lamination may be performed, for example, by passing the three layers through a pair of nip rolls, with heat and pressure being applied to the layers at the nip. In some implementations, the laminating temperature would be from about 250 to 325 degrees Celcius, e.g., from about 270 to 300 degrees Celcius. Standard laminating pressures are applied.
Materials
It is generally preferred that the laminate be formed entirely of recyclable polymers, for example polypropylene and polyethylene, e.g., low density polyethylene (LDPE). It is also generally preferred, in order to obtain good adhesion between the layers, that the three layers be formed of the same polymer.
The nonwoven layer may be a spunbonded material. In order to provide the bag with the desired non-slip surface characteristics, it is important that the nonwoven layer have a basis weight that provides it with a relatively rough surface. In some implementations, the basis weight (ASTM D3776) is at least about 15 gsm, e.g., at least about 20 gsm. It is also preferred that the basis weight be as low as possible without unacceptably compromising non-slip characteristics, so as to minimize the cost of the bag and transportation costs. Thus, it is generally preferred that the nonwoven layer have a basis weight of from about 15 to 80 gsm (grams per square meter), for example from about 20 to 55 gsm, or from about 20 to 40 gsm.
It is also preferred that the nonwoven layer have relatively high tensile strength, so that the nonwoven layer can contribute to the strength of the bag. In some cases, the nonwoven layer has a grab tensile strength of at least 20 lb/in (ASTM D5034.)
The adhesive layer is preferably an extruded polymer film, for example a LDPE or polypropylene adhesive grade extruded film. The polymer used is generally selected to be the same as the polymer of the woven fabric layer. The adhesive layer is of a thickness selected to provide enough of the polymer to securely bond the woven and nonwoven layers. Generally, this corresponds to the adhesive layer having a weight of from about 15 to 25 gsm.
The woven layer may have a fabric weight of from about 27 to 135 gsm, e.g., from about 50 to 100 gsm. In some cases, the woven material is formed of fibers having a denier of about 500 to 1500, e.g., about 750 to 1250.
Because of the strength imparted by the nonwoven, in some implementations a relatively low tensile strength woven layer may be used while still maintaining a desired level of overall bag strength. Using a thinner woven layer can help to reduce both the cost of the bag and shipping costs.
Bag Manufacture
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In some embodiments, e.g., when it is desired that the bag be porous to air and moisture but still impervious to water, very fine perforations are formed in the laminated material prior to the initial bag formation step. The number and size of perforations will depend on the particular application, for example the intended bag contents and degree of breathability that is needed.
It is generally preferred that the bag be printed, for example with images and or lettering denoting the contents of the bag, the manufacturer of the product, etc. Printing may be performed with, for example, digital printers, ink jet printers, offset printers or flexographic printers. The nonwoven layer 12 provides good ink receptivity and allows clear and vivid printed images to be obtained. Printing can be performed prior to or after bag formation. In some cases, a coating is applied to the nonwoven layer prior to printing to enhance print quality and/or increase the ink receptivity of the nonwoven. Such coatings are well known in the printing art.
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A number of embodiments have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the disclosure, and that other embodiments are within the scope of the following claims.
