Stock material or miscellaneous articles – Composite – Of addition polymer from unsaturated monomers
Reexamination Certificate
1999-08-13
2003-02-11
Tarazano, D. Lawrence (Department: 1773)
Stock material or miscellaneous articles
Composite
Of addition polymer from unsaturated monomers
C428S517000
Reexamination Certificate
active
06517950
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to multilayer films, particularly multilayer films suitable for use as packaging films. The present invention is particularly directed to multilayer films and packaged products using same, wherein the film has a relatively high modulus and a relatively high O
2
-transmission rate. The present invention is also directed to the use of such films in the packaging of O
2
-sensitive products, such as lettuce, etc.
BACKGROUND OF THE INVENTION
Multilayer films have been utilized for the packaging of “oxygen-sensitive products”, such as lettuce, i.e., products which exhibit lower shelf life in the presence of either too much oxygen in the package, or too little oxygen in the package. In such multilayer films, the O
2
-transmission rate, and even the CO
2
-transmission rate, are of primary importance, especially in the packaging of such O
2
-sensitive products as vegetables, fruits, and cheese. For example, in the packaging of precut lettuce, the presence of too much O
2
in the package results in an enzymatic browning of cut surfaces, known as pink ribbing. On the other hand, if the concentration of O
2
in the package is too low, the lettuce tends to spoil due to anaerobiosis.
One of the commercially-available multilayer films which has been used in the packaging of oxygen-sensitive products has an outer heat-resistant layer of an elastomer, such a styrene-butadiene copolymer, and an outer sealant layer of a metallocene-catalyzed ethylene/alpha-olefin copolymer. Although this multilayer film exhibits desired O
2
and CO
2
transmission rates, as well as a desirable stiffness, this multilayer film has been found to exhibit an undesirable level of “curl,” thereby exhibiting less-than-desired machinability performance. In form-fill-and-seal machinery (“FFS” machinery), curl causes film threadup problems as well as film tracking problems. Furthermore, in FFS packaging, the presence of the outer heat-resistant elastomer layer restricts package formation to a fin-type backseal, as the metallocene-catalyzed outer film layer does not seal well to the heat-resistant elastomer layer.
It has also been found that there is a pervasive belief among many skilled in the packaging of a variety of products that a heat seal cannot be made using a film having both outer layers of a low melt point polyethylene-based polymer, i.e., including both polyethylene homopolymer as well as ethylene/alpha-olefin copolymers, as it is believed that the hot bar will tend to stick to the film during sealing.
It would be desirable to provide a film which exhibits desirable O
2
and CO
2
transmission rates and a desirable stiffness, while reducing or eliminating the curl of the film, as well as providing a film which is suitable to a lap-type backseal for FFS packaging, using constant heat as opposed to impulse heating. Since fogging of the package is also a common problem in the packaging of produce and other food products, it would also be desirable that the film resist fogging, in order to provide the consumer with a clear view of the contents of the package, and in order to provide a more aesthetically appealing package, especially in retail applications where product presentation is important. However, those surface active agents which are effective antifog agents tend to interfere with ink adhesion to the film. This detrimental effect occurs because the antifog agent blooms to the outside surface of the package and interferes with the adhesion of the ink to the film. This detriment is significant for packages designed for consumer end use, as the consumer does not find such a package to be appealing if the ink is smeared or if the ink comes off onto other articles or the consumer. Thus, it would be also desirable to provide the film with an antifog agent on an outer film surface which forms the inside surface of the package, while also providing adequate adhesion for printing on an outer surface of the film, which outer surface serves as the outside surface of the package.
SUMMARY OF THE INVENTION
It has been discovered that curl can be eliminated by providing a film with outer layers of ethylene/alpha-olefin copolymer and an inner layer of elastomer, such as styrene/butadiene copolymer. Furthermore, by providing both outer layers of the film with ethylene/alpha-olefin copolymer, a lap-type backseal can be used in FFS type packaging. It has also been discovered that the homogeneous ethylene/alpha-olefin copolymers (e.g., metallocene-catalyzed ethylene/alpha-olefin copolymers) can be provided on one or both outer film layers, in order to provide the film with further enhanced sealing characteristics.
As a first aspect, the present invention pertains to a multilayer film comprising a first outer layer, a second outer layer, and an inner layer. The first outer layer comprises a first ethylene/alpha-olefin copolymer, which, in turn, comprises a homogeneous copolymer. The second outer layer comprises a second ethylene/alpha-olefin copolymer. The inner layer comprises a thermoplastic elastomer. The inner layer is between the first outer layer and the second outer layer, and the inner layer is chemically different from the first outer layer and the second outer layer. The multilayer film has an O
2
-transmission rate of from about 500 to 50,000 cc/m
2
24 hr STP; more preferably, from 1,000 to 20,000 cc/m2 24 hr STP; still more preferably, from about 2,000 to 10,000 cc/m2 24 hr STP. The multilayer film has a modulus of at least 60,000 psi; more preferably, from about 60,000 to 150,000 psi; still more preferably, from about 70,000 to 120,000 psi; and yet still more preferably, from about 80,000 to 100,000 psi.
Preferably, the first outer layer further comprises a surface-active agent component comprising at least one member selected from the group consisting of ester of aliphatic alcohol, polyether, polyhydric alcohol ester of polyhydric aliphatic alcohol, and polyethoxylated aromatic alcohol, wherein the surface-active component is present over the entire outside surface of the first outer layer.
Preferably, the first outer layer has a thickness of from about 0.3 to 0.8 mil, the inner layer has a thickness of from about 0.1 to 1 mil, the second outer layer has a thickness of from about 0.3 to 0.8 mil, and the multilayer film has a total thickness of from about 1 to 3 mils. More preferably, the inner layer has a thickness of from about 0.4 to 0.8 mil.
It has been found that the curl problem can be reduced or eliminated by providing a film having a symmetrical cross-section. That is, by providing a multilayer film having a cross section which is symmetrical in terms of layer arrangement, layer thickness, and layer chemical composition, curl is reduced or eliminated. Of course, some variation, i.e., lack of symmetry, can be present, while still substantially reducing or eliminating the amount of curl which would otherwise result without substantial symmetry. For example, one outer layer can comprise a homogeneous ethylene/alpha-olefin copolymer while the other outer layer comprises a heterogeneous ethylene/alpha-olefin copolymer. One outer layer may also contain an antifog agent, while the other layer does not. Such minor variations in the cross-sectional symmetry of the film have not been found to have a particularly detrimental effect on the curl level exhibited by the film. More severe variations are also possible, while obtaining a relatively low curl level. However, the presence of only two layers, such as a first layer comprising an ethylene/alpha-olefin copolymer and a second layer comprising a styrene/butadiene elastomeric copolymer, has been found to exhibit substantial curl, and it is believed that it is the lack of symmetry of such a film which is the cause of the undesirable level of curl.
Preferably, the homogeneous ethylene/alpha-olefin copolymer in the first outer layer is a first homogeneous ethylene/alpha-olefin copolymer, and the second outer layer comprises a second homogeneous ethylene/alpha-olefin copolymer. More preferably, the first homogeneous et
Patrick Ray Ernest
Walden Mendy Joyce
Cryovac Inc.
Tarazano D. Lawrence
LandOfFree
High modulus oxygen-permeable multilayer film, packaging... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with High modulus oxygen-permeable multilayer film, packaging..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and High modulus oxygen-permeable multilayer film, packaging... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3147193