Stock material or miscellaneous articles – Composite – Of wax or waxy material
Reexamination Certificate
1998-09-21
2001-11-06
Thibodeau, Paul (Department: 1773)
Stock material or miscellaneous articles
Composite
Of wax or waxy material
C428S516000, C428S520000, C428S910000, C264S173150
Reexamination Certificate
active
06312825
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to multi layer packaging films having enhanced barrier characteristics, and which are particularly useful as packaging films for food products, and are successful in laminating, printing or coating operations.
BACKGROUND OF THE INVENTION
Plastic materials such as polymeric films have been widely used for packaging various food and non-food products. In order to insure proper preservation of products packaged in such polymeric films, it is necessary to provide the films with barriers against transmission of air, moisture, deleterious flavors, etc. No single unmodified polymeric film, however, has sufficient gas and moisture barrier characteristics needed for proper packaging requirements. For example, polyolefin films such as polypropylene films are particularly preferred in the manufacture of packaging films due to their low cost and ease of manufacture. Such polypropylene films, however, inherently permit the transmission of oxygen and water vapor from the outside of the film to the inside of the package made up of the film. When such films are used as food packagings, oxygen and water vapor transmitted therethrough promote rapid deterioration of foods packaged therein.
In order to provide acceptable barrier properties, multi layer polymeric films have been developed having improved water vapor transmission rates (WVTR). For example, polyvinylidene chloride (PvdC) coatings have been used to impart gas and moisture barrier properties to thermoplastic films. PVdC, however, tends to degrade rapidly under typical film reprocessing temperatures, resulting in poor quality recycle products. Further, incorporating wax into film structures has been known to improve water vapor transmission rates. It is believed that the wax migrates or blooms to the outside surface of the film structure and becomes crystalline, thus imparting superior WVTR and improved oxygen barrier properties. In this approach, however, the wax on the surface is susceptible to removal, thereby presenting difficulty in maintaining such WTVR and oxygen barrier properties, particularly when such films are used in laminating, printing and coating operations.
In order to provide a film having improved barrier properties, U.S. Pat. Nos. 5,141,801 and 5,155,160 disclose incorporating a wax into a polyolefin surface layer of a co-extruded film. To prevent migration of the wax to a surface which is to be used in lamination and printing, these patents suggest incorporating a barrier layer of polymeric material such as a polyamide or an ethylene vinyl alcohol copolymer (EVOH). Such polyamide and EVOH barrier layers, however, are expensive and difficult to manufacture, and are very sensitive to moisture. Thus, while the prior art discloses various useful films, such films are typically susceptible to removal of the wax during subsequent laminating, printing and coating processes, and are difficult and expensive to manufacture.
Accordingly, a need exists for a packaging film which is simple and inexpensive to manufacture, which is capable of providing enhanced barrier properties to oxygen and water vapor transmission, and which is capable of subsequent laminating, printing or coating procedures.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a packaging film having improved oxygen and water vapor barrier properties.
It is a further object of the present invention to provide a packaging film which is efficient in laminating, printing or coating operations.
These and other objects are achieved in the present invention which provides a multi layer film having a polyolefin core layer incorporating a wax therein; a first surface layer including a polyolefin copolymer or terpolymer layer; and a second surface layer including a polar layer having ester functionality. The polyolefin core layer is preferably polypropylene including a Fischer Tropsch wax which is preferably present in an amount of about 4% to about 8% by weight of said polyolefin core layer.
The first surface layer is preferably an ethylene/propylene copolymer or an ethylene/propylene/butene terpolymer. The second surface layer is preferably selected from the group consisting of ethylene vinyl acetate copolymer and anhydride-grafted polypropylene. Most preferably, the film is a three layer biaxially oriented film having a polyolefin core layer including a first surface and a second surface and incorporating a wax therein; a first surface layer of a polyolefin copolymer or terpolymer layer adjacent the first surface of the polyolefin core layer which forms a moisture barrier surface of the film; and a second surface layer of a polar layer having ester functionality adjacent the second surface of the polyolefin core layer which forms an oxygen barrier surface of the film.
The present invention also provides for a method or preparing such a multilayer film, which method involves co-extruding a first polyolefin resin incorporating a wax therein, a second polyolefin copolymer or terpolymer resin, and a third polyolefin resin of a polar material having ester functionality to form a multi layer base film having a polyolefin core layer including the wax, a copolymer or terpolymer surface layer on a first surface of the polyolefin core layer, and a polar surface layer having ester functionality on the second surface layer of the polyolefin core layer. The method further involves biaxially orienting the multilayer base film at conditions sufficient to cause the wax to migrate from the polyolefin core layer to the copolymer or terpolymer surface layer of the film.
Thus, it has been discovered herein that a multi layer film incorporating a polyolefin core layer having a wax therein, a first surface layer including a polyolefin copolymer or terpolymer layer, and a second surface layer including a polar layer having ester functionality, provides excellent WVTR and oxygen barrier properties and provides an excellent surface for film laminating, printing and coating processes.
REFERENCES:
patent: 4377616 (1983-03-01), Ashcraft et al.
patent: 4590125 (1986-05-01), Balloni et al.
patent: 5141801 (1992-08-01), Takeshita et al.
patent: 5155160 (1992-10-01), Yeh et al.
patent: 5302327 (1994-04-01), Chu et al.
patent: 5759648 (1998-06-01), Idlas
patent: 5858552 (1999-01-01), Bader et al.
patent: 6033771 (2000-03-01), Heffelinger
Chu Shaw-Chang
Keung Jay K.
Su Tien-Kuei
ExxonMobil Oil Corporation
Santini Dennis P.
Tarazano D. Lawrence
Thibodeau Paul
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