Stock material or miscellaneous articles – Hollow or container type article – Nonself-supporting tubular film or bag
Patent
1996-09-19
1999-10-26
Davis, Jenna
Stock material or miscellaneous articles
Hollow or container type article
Nonself-supporting tubular film or bag
156203, 428 3691, 428349, 428355EN, 428516, B29D 2300, B32B 2732, B32B 3102
Patent
active
059724439
DESCRIPTION:
BRIEF SUMMARY
The invention relates to ethylene copolymer film of improved stiffness and clarity, to multilayer ethylene copolymer film, to pouches formed from multilayer ethylene copolymer film and especially to such pouches filled with flowable materials, e.g. liquids. In particular embodiments, the pouches are made on so-called vertical form, fill and seal apparatus.
As used herein, the term "flowable material" does not include gaseous materials, but encompasses materials which are flowable under gravity or may be pumped. Such materials include liquids e.g. milk, water, fruit juice, oil; emulsions e.g. ice cream mix, soft margarine; pastes e.g. meat pastes, peanut butter; preserves e.g. jams, pie fillings, marmalade; jellies; doughs; ground meat e.g. sausage meat; powders e.g. gelatin powders, detergents; granular solids e.g. nuts, sugar; and like materials. The invention described herein is particularly useful for flowable foods e.g. milk. In addition, as used herein "density" is determined by ASTM Procedure D1505-85, "stiffness" is understood to be tensile modulus of elasticity as measured by ASTM Procedure D882-91 (Method A) and "melt index" by ASTM Procedure D1238-90B (Condition E). The "melting point" of a polymer is measured as the peak melting point when performing differential scanning calorimetry (DSC) as described in ASTM Procedure D3417-83 (rev. 88).
Aspects of the invention relate to the packaging of flowable materials e.g. milk, in pouches using for example a so-called vertical form, fill and seal apparatus. Using such an apparatus, a flat web of synthetic thermoplastic film is unwound from a roll and formed into a continuous tube in a tube-forming section, by sealing the longitudinal edges on the film together to form a so-called lap seal or a so-called fin seal. The tube thus formed is pulled vertically downwards to a filling station. The tube is then collapsed across a transverse cross-section of the tube, the position of such cross-section being at a sealing device below the filling station. A transverse heat seal is made, by the sealing device, at the collapsed portion of the tube, thus making an air-tight seal across the tube. The material being packaged enters the tube above the transverse heat seal in a continuous or intermittent manner, thereby filling the tube upwardly from the transverse heat seal. The tube is then allowed to drop a predetermined distance usually under the influence of the weight of the material in the tube. The jaws of the sealing device are closed again, thus collapsing the tube at a second transverse section, which may be at, above or below the air/material interface in the tube, depending on the nature of the material being packaged and the mode of operation of the process. The sealing device seals and severs the tube transversely at the second transverse section. The material-filled portion of the tube is now in the form of a pillow shaped pouch. Thus, the sealing device has sealed the top of the filled pouch, sealed the bottom of the next-to-be-formed pouch and separated the filled pouch from the next-to-be-formed pouch, all in one operation.
One vertical form, fill and seal apparatus of the type described above is a Prepac.RTM. IS-6 liquid packaging apparatus.
A sealing device commonly used is a so-called impulse sealer which has a sealing element mounted in sealing jaws and electrically insulated therefrom. In operation, the sealing jaws are closed and an electrical current is caused to flow through a sealing element e.g. a wire, for a fraction of the time that the jaws are closed. The jaws remain closed while the seal forms. Once the sealing jaws are open the synthetic thermoplastic film must be able to provide a transverse seal that supports the weight of the flowable material e.g. liquid, in the next-to-be-formed pouch.
Pouches made from ethylene/butene-1 copolymer films tend to suffer from defective seals i.e. a tendency to have weak transverse end and/or longitudinal seals even though the operating conditions of the impulse sealer have been optimized. Defective se
REFERENCES:
patent: 4521437 (1985-06-01), Storms
patent: 5206075 (1993-04-01), Hodgson
Breck Alan Keith
Verdone Alana
Davis Jenna
Du Pont Canada Inc.
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