Ammunition and explosives – Blasting – Contained blasting charge
Reexamination Certificate
1998-06-25
2001-10-16
Nelson, Peter A. (Department: 3641)
Ammunition and explosives
Blasting
Contained blasting charge
C102S324000
Reexamination Certificate
active
06302027
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the packaging of various products, especially products which are packaged using vertical-form-fill-and-seal (VFFS) packaging machinery. The present invention is particularly concerned with the packaging of explosive products in thermoplastic film. The present invention also relates to packaged products in which the packaging material comprises a thermoplastic film, especially to such packaged products in which the product is an explosive.
BACKGROUND OF THE INVENTION
For some time many flowable liquid and flowable solid products have been packaged in thermoplastic packaging films, such a polyethylene, polypropylene, etc, using vertical-form-fill-and-seal packaging equipment. The packaging of explosive compositions, such as ammonium nitrate, has used vertical-form-fill-and-seal equipment, in which the explosive ammonium nitrate composition has the viscosity of a soft putty, and hence is flowable.
In the past, vertical-form-fill-and-seal packaging of ammonium nitrate has utilized a high strength flexible film packaging material marketed by Van Leer Flexibles, Inc. of Houston, Tex., i.e., VALERON® strength film. VALERON® strength film is made from high density oriented and cross-laminated polyethylene, and is stated as being puncture-resistant, tear-resistant, and chemical-resistant. VALERON® strength film is also stated as being strong, with a smooth surface, balanced tear-resistance, of uniform thickness, and is printable with solvent-based and water-based inks, and is laminatable to paper, film, and other substrates. VALERON® strength film is also stated as maintaining its properties in harsh environments and as having a temperature operating range of from −70° F. to over 200° F., and as being useful in the flexible packaging, shipping, construction, agricultural, photographic, and tag & label industries. VALERON® strength film is stated as having much better tear-resistance than single-ply film of the same overall thickness and of the same polymer which has been biaxially oriented. VALERON® strength film has also been stated to provide improvements over even other cross-laminated films because it is annealed, i.e., subjected to an elevated temperature (i.e., from 35° C. to below the lowest melting point of the thermoplastic material present, excluding any adhesive or bonding layer). The annealing process reportedly provides VALERON® strength film with a higher impact strength relative to corresponding unannealed films.
In the packaging of explosive products in VALERON® strength film using vertical-form-fill-and-seal equipment, at least one bead, and preferably two beads, of a molten thermoplastic material, such as polyethylene homopolymer or copolymer, especially ethylene/vinyl acetate copolymer, or NOVACOR® SC7250 SCLAIRCOAT polyethylene, obtained from Nova Chemical, of Alberta, Canada, have been used in order to form a lap seal along the length of the resulting package, which contains a “chub” of the explosive product. It is important that the resulting package does not burst when dropped onto a hard surface (or water) from a distance of from 10 to 50 or more feet. The use of the molten plastic adhesive is apparently needed to ensure adequate seal strength and adequate water resistance. If the film bursts, the explosive composition could be exposed to water or other contamination which impairs its ability to explode.
Thus, it is necessary to provide a packaging film for explosives which can be sealed using vertical form fill and seal equipment, so that the resulting packaging material, when sealed around the explosive article, does not burst when it is dropped onto a hard surface (or water) from a significant height. Although VALERON® strength film has been used for this purpose, is a relatively expensive product, i.e., compared with other packaging films. This expense is undoubtedly associated with the costs of cross-laminating and annealing. It would be desirable to provide high strength, flexible film packaging which can be sealed using vertical form fill and seal packaging equipment in a manner which yields performance characteristics comparable to VALERON® strength film, but which is less complex to manufacture.
SUMMARY OF THE INVENTION
An initial attempt to use a commercially available packaging film on a vertical form fill and seal apparatus failed to provide a satisfactory package for the packaging of an explosive article, because the film exhibited too much shrink upon exposure to the molten thermoplastic adhesive. That is, the hot thermoplastic adhesive used to make the lap seal running the length of the chub was found to cause the overlapping portions of the film to shrink back and away from one another, thereby destroying the ability of the film to form the desired lap seal. However, this problem has been solved through the use of a non-crosslaminated, high strength film which has a level of free shrink at 185° F. which is low enough to avoid the shrink-back problem encountered in the formation of the lap seal using a film having a higher free shrink.
As a first aspect, the present invention is directed to a packaged product comprising a non-crosslaminated film surrounding a product. The non-crosslaminated film comprises at least one member selected from the group consisting of linear low density polyethylene, high density polyethylene, homogeneous ethylene/alpha-olefin copolymer, polycarbonate, polyester homopolymer, polyamide, ethylene/acid copolymer, ethylene/ester copolymer, ethylene/vinyl acetate copolymer, ionomer, ethylene/carbon monoxide, very low density polyethylene, low density polyethylene, polyolefin, ethylene/propylene copolymer, ethylene
orbornene copolymer, and ethylene/styrene copolymer. The non-crosslaminated film having a total free shrink at 185° F. of less than about 5 percent (preferably, a total free shrink at 185° F. of from about 0 to 4 percent; still more preferably, a total free shrink at 185° F. of from about 0 to 3 percent). The product comprises an explosive composition. The non-crosslaminated film is sealed to itself. Preferably, the non-crosslaminated film is sealed to itself in a lap seal comprising a thermoplastic adhesive.
Preferably, the explosive composition comprises at least one member selected from the group consisting of ammonium nitrate, nitroglycerine, diethylene glycol dinitrate, nitroglycerin, trinitrotoluene, nitrocellulose, mercury fulminate, lead azide, silver acetylide, diazodinitrophenol, nitrosoguanidine, lead styphnate, and pentaerythritol tetranitrate, and a mixture of potassium nitrate, charcoal, and sulfur, more preferably, ammonium nitrate.
Preferably, the explosive composition has a shape of a chub, i.e., an elongated article having a circular cross-section, with the film being sealed at each end (preferably gathered and sealed with a metal clip at each end).
One preferred non-crosslaminated film comprises: (A) a first layer comprising at least one member selected from the group consisting of polyethylene homopolymer, ethylene/alpha-olefin copolymer, ethylene/ester copolymer, ionomer, polyamide, and polyester; (B) a second layer comprising at least one member selected from the group consisting of ethylene/ester copolymer, modified polyolefin, ionomer, ethylene acrylate copolymer, ethylene acrylic acid, polyamide, and polyurethane; (C) a third layer comprising at least one member selected from the group consisting of ethylene/ester copolymer, modified polyolefin, ionomer, ethylene acrylate copolymer, ethylene acrylic acid, polyamide, and polyurethane; (D) a fourth layer comprising at least one member selected from the group consisting of polyethylene homopolymer, ethylene/alpha-olefin copolymer, ethylene/ester copolymer, ionomer, polyamide, and polyester; and, (E) a fifth layer comprising at least one member selected from the group consisting of high density polyethylene, polypropylene, polyester, polystyrene, and polyamide. In this film, the second layer is between the first layer and the third layer, the third layer is between the second layer
Compton Stephen Floyd
Vadhar Parimal M.
Cryovac Inc.
Hurley Jr. Rupert B.
Nelson Peter A.
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