Stock material or miscellaneous articles – Hollow or container type article – Nonself-supporting tubular film or bag
Reexamination Certificate
1998-04-22
2001-10-23
Dye, Rena L. (Department: 1772)
Stock material or miscellaneous articles
Hollow or container type article
Nonself-supporting tubular film or bag
C428S035700, C428S036700, C428S192000, C428S194000, C428S200000, C428S347000, C428S518000, C428S519000, C383S116000, C383S211000
Reexamination Certificate
active
06306472
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the packaging industry. More particularly, the invention relates to multilayer films and packages which incorporate a delamination seal feature and also have oxygen barrier properties.
BACKGROUND OF THE INVENTION
In many commercial packaging applications it is desirable to provide multilayer packaging materials in order to produce a package having multiple attributes. For instance, in the food packaging area, it is especially desirable to make consumer packages which are readily opened by digital pull-apart force. Delamination seals are particularly useful for this purpose. These seals include two or more layers and in which delamination occurs between two of the layers. Such a delamination system works on the principal that a bond is formed between structural package layers and one of the layers making up the delamination structure which has a greater bond strength than the peelable bond between the two film layers which delaminate from each other with manual force. Choice of materials determines which layers will delaminate from each other.
It is also important to place perishable foods such as meats and cheeses into packages which allow for the preservation of these foods for as long as possible. Maximizing the time in which the food remains preserved, especially between initial packaging and arrival at the retail store is especially important. Atmospheric oxygen is a common culprit in promoting food spoilage. Oxygen is reduced to a variety of free radical species which oxidize carbon-carbon double bonds in food and other perishable products. Such oxidation by free radicals adversely affects the odor and flavor of certain foods and can affect the stability of non-food products. Thus, it is desirable to incorporate oxygen barrier film layers into packaging materials. A particularly effective oxygen barrier material is ethylene vinyl alcohol (EVOH).
Providing packages having multiple attributes such as an easy opening delamination seal and oxygen barrier properties frequently necessitates bonding multiple layers of film having different properties together. Unfortunately, many film materials are not compatible with and thus, do not adequately seal to other packaging materials. It has been especially difficult to directly seal oxygen barrier film layers containing EVOH to film layers typically used in delamination seal technology. One approach to the problem is to interpose extra layers in between the EVOH layer and the layers making up the delamination seal. However, this approach does not always prove expedient or convenient.
A need therefore exists for a multilayer packaging material having an oxygen barrier layer as well as delamination layers. Furthermore, it is desirable to achieve this structure with a minimal number of film layers. It is therefore necessary to find film layer materials which bind together well and also retain their independent attributes of ease of delamination and oxygen barrier properties.
SUMMARY OF THE INVENTION
The present invention is directed to multilayer films and packaging structures having a delamination seal and an oxygen barrier layer. The delamination structure adjacent to the EVOH oxygen barrier layer binds well to the EVOH layer and also retains its ability to delaminate.
In one embodiment, the invention provides an easy open package adapted to be heat sealed closed in order to contain a product within the package. The package is easily opened by manual force. The package includes a first package wall having a multilayer film construction. The multilayer film construction includes the following layers: a first, external layer; a second, tie layer comprising a blend of an anhydride modified polyethylene and one or a mixture of polybutylene, polypropylene or a styrene-butadiene copolymer so that a peelable bond is formed between the first, external layer and the second, tie layer; a third, core layer comprising ethylene vinyl alcohol; a fourth, tie layer comprising an anhydride modified polyethylene; and a fifth, external layer. The package also includes a second package wall joined at a portion of its perimeter to the first package wall. The first, external layer of the first package wall is heat sealed to the second package wall to create a sealed pouch or package, The bond formed between the first, external layer of the first package wall and the second package wall has a greater bond strength compared to the peelable bond so that upon application of manual force, the first and second package walls will remain bonded together and delamination will occur between the peelably bonded layers.
In a preferred embodiment, the first package wall has a multilayer film construction specifically including the following layers: a first, external layer comprising an ethylene vinyl acetate copolymer; a second, tie layer comprising a blend of an anhydride modified polyethylene and a compound selected from the group consisting of polybutylene, polypropylene and a styrene-butadiene copolymer such that a peelable bond is formed between the first, external layer and said second, tie layer; a third, core layer comprising ethylene vinyl alcohol; a fourth, tie layer comprising an anhydride modified polyethylene and a fifth, external layer comprising an ethylene vinyl acetate copolymer. The package also includes a second package wall joined at a portion of its perimeter to the first package wall. The first, external layer of the first package wall is heat sealed to the second package wall to create a sealed pouch or package. The bond formed between the first, external layer of the first package wall and the second package wall has a greater bond strength compared to the peelable bond so that upon application of manual force, the first and second package walls will remain bonded together and delamination will occur between the peelably bonded layers.
In yet another preferred embodiment, the second package wall comprises a polymer which is identical to or, at least, heat seal compatible to, the first package wall.
In an especially preferred embodiment, the second, tie layer of the first package wall comprises approximately ten to thirty-five percent polybutylene by weight and between about sixty-five to ninety percent of an anhydride modified polyethylene by weight.
In a second embodiment, the present invention provides a multilayer film construction which includes the following layers: a first, external layer; a second, tie layer comprising a blend of an anhydride modified polyethylene and a compound selected from the group consisting of polybutylene, and a styrene-butadiene copolymer so that a peelable bond is formed between the first, external layer and the second, tie layer; a third, core layer comprising ethylene vinyl alcohol; a fourth, tie layer comprising an anhydride modified polyethylene and a fifth, external layer.
In a preferred embodiment, the multilayer film construction specifically includes the following layers: a first, external layer comprising an ethylene vinyl acetate copolymer; a second, tie layer comprising a blend of an anhydride modified polyethylene and a compound selected from the group consisting of polybutylene, polypropylene and a styrene-butadiene copolymer such that a peelable bond is formed between the first, external layer and said second, tie layer; a third, core layer comprising ethylene vinyl alcohol; a fourth, tie layer comprising an anhydride modified polyethylene and a fifth, external layer comprising an ethylene vinyl acetate copolymer.
In an especially preferred embodiment, the second, tie layer of the multilayer film construction comprises approximately ten to thirty-five percent polybutylene by weight and between about seventy to ninety percent of an anhydride modified polyethylene by weight.
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patent: 4712990 (1987-12-01), Kudert et al.
patent: 4759984 (1988-07-01), Hwo
patent: 4782951 (1988-11-01), Griesbach et al.
patent: 4784885 (1988-11-01), Carespodi
patent: 4944409 (1990-07-01), Busche et
Dye Rena L.
McDermott & Will & Emery
Miggins Michael C.
Pechiney Emballage Flexible Europe
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