Stock material or miscellaneous articles – Hollow or container type article – Shrinkable or shrunk
Reexamination Certificate
2000-06-09
2004-08-03
Pyon, Harold (Department: 1772)
Stock material or miscellaneous articles
Hollow or container type article
Shrinkable or shrunk
C428S034100, C428S515000, C428S516000, C428S520000, C428S910000
Reexamination Certificate
active
06770338
ABSTRACT:
BACKGROUND OF THE INVENTION
Heat shrinkable polymer films have gained substantial acceptance for use in meat packaging. This description will detail the usage of films for packaging meat, it being understood that these films are also suitable for packaging other products. The films embodying this invention are useful as heat shrinkable bags supplied to the meat packer with one open end, to be closed and sealed after insertion of the meat. After the product is inserted, air is normally evacuated, the open end of the bag is closed, such as by heat sealing, or applying a metal clip, and finally heat is applied, such as by hot water, to initiate film shrinkage about the meat.
In subsequent processing of the meat, the bag may be opened and the meat removed for further cutting of the meat into user cuts, for retail sale, for example, or for institutional use.
Successful shrink bags must satisfy a multiplicity of requirements imposed by both the bag producer and the bag user. Of primary importance to the bag user is the capability of the bag to survive physically intact the process of being filled, evacuated, sealed closed, and heat shrunk. The bag must also be strong enough to survive the meat handling involved in moving the contained meat, which may weigh 50 pounds or more, along the distribution system to the next processor, or to the user. Thus, the bag must physically protect the meat.
It is also highly desirable to the bag user that the bag serve as a barrier to infusion of gaseous materials from the surrounding environment. Of particular importance is provision of an effective barrier to infusion of oxygen, since oxygen is well known to cause spoilage of meat.
The bag producer requires a product which can be produced competitively while meeting the performance requirements of the user. Thus the bag material should be readily extrudable, and susceptible to orientation, with sufficient leeway in process parameters as to allow for efficient film production. The process should also be susceptible to efficient extended production operations. In the orientation process, the film must be tough enough to withstand the stretching. The orientation temperature should be a temperature which is economically achieved by the producer, and which provides for use of economical shrink processes by the bag user.
Conventional shrink bags have generally been constructed with ethylene vinyl acetate copolymers (EVA). In some cases the bags contain a layer of a Saran copolymer to serve as an oxygen barrier. Ethylene vinyl alcohol copolymer (EVOH) has also been suggested as the barrier layer.
Notwithstanding the advantages, shrink-bag packaging of meat is not without its difficulties, many of which are attributable to limitations in the film. As will be appreciated, the processes of stretching the film, and later shrinking it, expose the film to rather severe conditions, due to the nature of the operations.
It is especially important to appreciate that the film is particularly vulnerable to failure at conditions of operation, due to the relatively high temperatures to which it is exposed in the orientation and shrinking process.
The film must be susceptible to orientation without distortion, or separation of the multiple layers which are normally present in films of this nature. The film must be strong enough, at the orientation temperature to withstand the stretching without creation of holes, tears, or non-uniform zones of stretching.
In the case of blown tubular film, the film must be capable of supporting the stretching bubble during the orientation process. Finally, each of the layers of the film should be susceptible to orientation without fracture, separation, or creation of holes in the layer.
In packaging use, the film must respond to heat rapidly enough for commercial practicability, and yet must not exhibit such a level of shrink energy as would cause the film to pull apart or delaminate during shrinkage, under its own internal forces.
In U.S. Pat. No. 4,457,960 oriented multiple layer polymeric films comprise a barrier layer having two opposing surfaces; a second layer adheres to one surface of the first layer, said second layer being 10% to 90% linear low density polyethylene and 90% to 10% ethylene vinyl acetate copolymer; and a third layer adheres to the other surface of the first layer, the composition of said third layer being an ethylene vinyl acetate or a blend of 10% to 90% linear low density polyethylene with 90% to 10% of ethylene vinyl acetate. The '960 patent further discloses a five layer film structure having a barrier layer; a second and third layer having essentially the same composition and a fourth and fifth layer having essentially the same composition with at least one of said pairs having at least 50% of an ethylene vinyl acetate copolymer, the remainder being linear low density polyethylene and at least one of the pairs comprises at least 10% linear low density polyethylene, the remainder being ethylene vinyl acetate copolymer.
In U.S. Pat. No. 4,853,265 the heat-shrinkable, oriented, multi-layer packaging film has at least two layers comprising an ethylene vinyl acetate copolymer. One of the ethylene vinyl acetate copolymer layers has a melt index difference of about 0.3 dg/minute from the melt index of the other ethylene vinyl acetate copolymer layer.
In U.S. Pat. No. 4,894,107 a process for making multiple layer polymeric films is disclosed. The films have a layer of vinylidene chloride copolymer between at least two other layers which contain ethylene vinyl acetate and optionally, linear low density polyethylene.
In U.S. Pat. No. 5,030,511 films are made from vinylidene chloride copolymer compositions comprising about 0.01% to 6% by weight of a processing aid wherein said processing aid has a molecular weight of less than about 700. The films also have a first and second layer wherein each of the first and second layers comprises an ethylene vinyl acetate copolymer having a melt index greater than about 1.2.
In U.S. Pat. No.'5,538,770 the polymeric film comprises first and second surface layers wherein said first and second surface comprise an olefinic polymer or copolymer and a vinylidene chloride polymeric layer disposed between said first and second layers wherein said vinylidene chloride polymeric layer comprises 100 parts by weight of at least one vinylidene chloride copolymer; between 4 and 15 parts by weight of a plasticizer and between 4 and 15 parts by weight of an acrylate/styrene copolymer.
Despite the known technology surrounding heat-shrinkable films, there is still a need to improve the film in order to meet the demands of the meat packaging industry.
Thus, it is an object of the invention to provide improved film structures for use in shrink bags wherein the shrink bags are capable of withstanding production and shrink processes.
SUMMARY OF THE INVENTION
The present invention provides an oriented multiple layer polymeric film useful in the packaging of meat. The present invention also provides for a process for manufacturing the oriented multiple layer polymeric film of the present invention. The present invention still further provides for heat shrinkable bags which are made of the oriented multiple layer polymeric film of the invention and are useful in the packaging of meat.
In one embodiment of the present invention the oriented multiple layer polymeric film has a first barrier layer, the first layer having two opposing surfaces; a second layer is adhered to one of the surfaces of the first layer; a third layer is adhered to the other surface of the first layer, a fourth layer is adhered to one of said second or said third layer; and a fifth layer is adhered to the other of said second or third layer.
In this embodiment the barrier layer comprises a polyvinylidene chloride methyl acrylate blend, the second and third layers independently comprise a blend of two ethylene vinyl copolymers wherein the melt index of the blend for each of the second and third layers are the same; the fourth layer comprises a blend of two ethylene vinyl copo
Hon Sow-Fun
McDermott & Will & Emery
Pechiney Emballage Flexible Europe
Pyon Harold
LandOfFree
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