Flexible bags – With closure – For access opening in bag bottom
Reexamination Certificate
2000-09-26
2001-10-16
Pascua, Jes F. (Department: 3727)
Flexible bags
With closure
For access opening in bag bottom
C383S107000, C383S113000, C383S117000
Reexamination Certificate
active
06302584
ABSTRACT:
TECHNICAL FIELD
This invention relates to flexible intermediate bulk containers, commonly known as bulk bags, and more particularly to bulk bags constructed from woven polypropylene fabric having polypropylene linings or liners and to processes for manufacturing the same.
BACKGROUND OF THE INVENTION
Historically, flexible intermediate bulk containers (bulk bags) have been used for receiving, storing, transporting and discharging flowable materials of all types. Bulk bags are typically constructed in square, vertically rectangular, or circular shapes with lift straps attached to each of the uppermost corners of the square, rectangle or circle.
By way of example, flexible intermediate bulk containers are used for handling flowable materials in granular or powder form such as chemicals, minerals, fertilizers, foodstuffs, grains and agricultural products, etc. The advantages of such receptacles include relatively low weight, reduced cost, versatility and, in the case of reusable receptacles, low return freight costs.
At the present time most bulk bags are manufactured from woven polypropylene fabric. Typically, such containers comprise two or more sidewalls and a bottom portion. Optionally, a top wall and lift straps or other lifting members can be added to the basic construction. The traditional method of securing the seams of the several portions of a bulk bag includes sewing or stitching.
Bulk bags are frequently provided with liners, which may be installed either during or after the manufacture of the bulk bag itself. Liners are used to prevent material contained in the bag from sifting through the woven polypropylene comprising the bag and/or through the sewn seams which are used in construction of the bag. Examples of liners for bulk bags are described in U.S. patent applications Ser. Nos. 08/417,898; 08/383,887; and 08/619,419, each assigned to the Assignee of the present application. Liners may also be used to provide bulk bags with improved anti-static, anti-corrosion and/or ant-microbial characteristics. See, for example, U.S. Patent application Ser. No. 08/474,378, filed Jun. 7, 1995 for ANTI-STATIC, ANTI-CORROSION, AND/OR ANTI-MICROBIAL FLEXIBLE COLLAPSIBLE RECEPTACLES and assigned to the Assignee of the present application.
One problem that has long been associated with the use of liners in bulk bags comprises the tendency of liners to move or shift relative to the bulk bag in which they are used. In extreme instances, the discharge of material from a bulk bag may cause a liner disposed therein to pull completely out of the bulk bag through its discharge opening. The problem of liner displacement has been addressed previously; for example, see U.S. Pat. No. 4,597,102 granted to Nattrass on Feb. 24, 1986 and U.S. Pat. No. 4,781,472 granted to La Fleur, et al. on Nov. 1, 1988. However, despite these and other attempts at preventing the displacement of liners relative to the bulk bags in which they are installed, a need exists for still further improvement in the art.
Another problem associated with prior art liners comprises the possibility of dirt and other contaminants sifting through the top or sides of the woven fabric and then collecting between the exterior bag and the impermeable liner. In prior art bags, when the liner contents are discharged the liner collapses because it is not affixed effectively to the exterior bag. As the liner collapses during discharge, the dirt and contaminants collected between the exterior bag and the interior liner may be discharged through the annular space between the bag discharge chute and the liner along with the product being discharged from the liner,. Thus, a need exists for an effective safety seal on the top of the liner to prevent contaminants from being discharged with the produce when the liner is emptied.
Yet another problem associated with prior art bulk bags and liners is their lack of conductivity. Friction that occurs as dry flowable materials are discharged from woven bags tends to cause a significant build up and retention of static electric charge within the receptacle. Discharge of the generated static electric build-up is often difficult if not impossible to control because fabrics are generally not electrically conductive materials. In an effort to address the undesirable characteristics of fabrics, prior art methods have included covering one side of the fabric with a metallic foil-like layer. While adequate in discharging static electric charge, the foil was susceptible to abrasion and tearing through use. Subsequent prior art methods include impregnating the fabric fibers with conductive elements to make the fabric itself conductive. Despite these and other attempts, a need continues to exist for a safe and cost effective solution to the problem of static electric build up in bulk bags.
SUMMARY OF THE INVENTION
Heretofore, bulk bags and the liners used therein have usually been made from different materials. Most frequently, the bulk bag is formed from woven polypropylene fabric and the liner is formed from polyethylene film. The use of different materials for the construction of bulk bags and for the construction of liners to be used therein makes difficult the task of preventing liner displacement. The result has been the above-identified Nattrass patent and Assignee's pending patent applications Ser. Nos. 08/417,898, 08/383,887, and 08/619,419, which disclose a technique of sewing the material of the liner into the sidewall seam of the bulk bag. The above-identified La Fleur patent discloses the use of connectors for securing liners within bulk bags.
In accordance with the present invention, a bulk bag and a liner to be used in the bulk bag are formed from the same polymer. For example, if the bulk bag is formed from woven polypropylene fabric, the liner is formed from polypropylene film. This allows the material of the liner to be bonded directly to the material of the fabric, thereby eliminating the step of sewing the liner material into the sidewall seam of the bulk bag as disclosed in the above-identified Nattrass patent and Assignee's pending applications and, likewise, eliminating the need of connectors secured between the liner and the bulk bag as disclosed in the above-identified La Fleur patent.
It has heretofore been known to provide bulk bags and liner formed from the same material. For example, the assignee hereof has sold woven polypropylene bulk bags having electrically conductive polypropylene liners. However, such liners could not be directly bonded to the bag fabric.
In accordance with one embodiment of the present invention, a polypropylene lining is bonded to a woven polypropylene fabric and a bulk bag is manufactured therefrom. In this manner, any possibility of displacement of the lining relative to the bulk bag is completely eliminated.
In accordance with a first variation of the first embodiment, an improved discharge chute having an exterior polypropylene woven fabric tube and an interior polypropylene film liner tube is inserted in the bulk bag. In this manner, any possibility of displacement of the discharge chute liner relative to the bulk bag and the discharge chute is completely eliminated.
In accordance with a second embodiment of the invention, a polypropylene woven fabric tube is positioned around a polypropylene film tube. The fabric tube and the film tube are heat sealed circumferentially to each other to form a tubular blank. The tubular blank is used to manufacture a bulk bag wherein the woven polypropylene fabric is on the exterior and the polypropylene tube is on the inside of the bag. The circumferential seal prevents displacement of the interior liner relative to the exterior bag and prevents contaminants from being discharged with the liner contents.
In yet another variation of the present invention, the polypropylene liner may be made conductive and thereby used to dissipate static electricity generated when discharging flowable contents from the bulk bag.
REFERENCES:
patent: 4597102 (1986-06-01), Nattrass
patent: 4781472 (1988-11-01), LaFleur et al.
Brown Bobby Glenn
Derby Norwin Ced
Nickell Craig Alan
O'Neil Michael A.
Pascua Jes F.
Super Sack Mfg. Corp.
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