Flexible bags – End structure – Overlapping extensions of opposed walls
Patent
1996-10-16
1998-12-08
Garbe, Stephen P.
Flexible bags
End structure
Overlapping extensions of opposed walls
383117, 383121, 383908, 493218, 493219, B65D 3018
Patent
active
058459952
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a sack made of fabric consisting of monoaxially drawn, desirably single-layer, tapes of polymer, in particular polyolefine, preferably polypropylene, which fabric may be coated on one or both sides with thermoplastics, in particular polyolefine, wherein the fabric is either seamless tubular fabric or flat fabric combined to form a tube, and wherein at least one end of the sack having in particular the shape of a box or right parallelepiped is formed by folding the fabric ends to a preferably rectangular bottom surface, as well as to a process for producing such a sack.
2. Description of the Related Art
A variety of sacks is used to pack goods such as bulk material. Sacks can be roughly divided into pillow- and box- or block-shaped types. A pillow shape is usually created by manufacturing the bottoms with seams. A box or block shape is created by folding and bonding the bottom. It will be appreciated that a box shape allows for optimal use of the material surface, good stackability and an improved utilization of volume due to its brick shape. There is also the quasi-box shape which is a pillow sack on one side and a box sack on the other. Typically, sacks have a capacity of 10, 25, 100, 500 and 1000 kg. Suitable materials include natural fiber fabric such as jute, paper, plastic sheets and plastic fabric; within the last decades sacks made of natural fiber fabric have been replaced by sacks made of paper and plastic sheets and plastic fabric, because these are cheaper and offer technical advantages.
Paper does not have great strength. For this reason sacks often include various layers of paper, which increases material consumption. A paper sack is not watertight and partly non-resistant to chemicals. However, it can be produced at low cost and by using cheap adhesives.
Plastic sheets have no great strength either and therefore require a considerable thickness of the material used. Due to their high Young's modulus (elongation capability) they are not dimensionally stable and, what is more, sensitive to heat. The sack can be readily seam welded to a pillow shape, but is it not easily bonded so as to form a box- or block-shaped sack.
Plastic fabric consisting of monoaxially drawn tapes has the highest strength and is dimensionally stable, particularly when being coated. Compared to plastic sheets material consumption is much lower, yet the load-bearing capacity is the same. Sacks made of plastic fabric are usually made in pillow shapes with seams.
SUMMARY OF THE INVENTION
In order to produce a woven box sack the folded bottom is conventionally subjected to a quite elaborate bonding process by using a multi-component adhesive, since polypropylene and polyethylene materials which normally form the fabric can only be bonded with difficulty. Apart from the complex bonding process well-known adhesives have further drawbacks, such as low durability, brittleness due to temperature variations and loss of adhesiveness due to moisture. Further, these adhesives are insufficiently resistant to chemicals; typically, the material to be bonded has to undergo a surface treatment, such as a corona treatment, before being bonded. Considering the fact that every year billions of sacks are produced all over the world and that the sacks produced according to state-of-the-art methods have more or less pronounced drawbacks, it becomes clear that huge economic gains could be achieved if sacks or their manufacturing processes were improved. This invention aims at providing a sack which dramatically decreases piece costs as compared to conventional sacks while maintaining their load-bearing capacity, and which has even further positive characteristics.
The sack of the present invention consists of fabric of monoaxially drawn polyolefine tapes. These tapes are produced by stretching polyolefine sheets to four to ten times their original length, whereby the molecule chains in the tapes' longitudinal direction are oriented and thus have a strength in this
REFERENCES:
patent: 3195801 (1965-07-01), Symons et al.
patent: 3397622 (1968-08-01), Goodwin
patent: 3448666 (1969-06-01), Kappelhoff et al.
patent: 3570749 (1971-03-01), Sato et al.
patent: 3660150 (1972-05-01), Cooper
patent: 3736219 (1973-05-01), McTaggart
patent: 3979049 (1976-09-01), Achelpohl
Garbe Stephen P.
Starlinger & Co. Gesellschaft mbH
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