Stock material or miscellaneous articles – Composite – Of silicon containing
Reexamination Certificate
1998-12-30
2001-09-11
Thibodeau, Paul (Department: 1773)
Stock material or miscellaneous articles
Composite
Of silicon containing
C428S516000, C428S457000
Reexamination Certificate
active
06287700
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to the field of polymer films containing migratory additives that can be laminated to other films and methods for forming such films. In particular, this invention relates to a film having a first outer layer containing a migratory additive, such as silicone oil, and a second outer layer containing a metallocene polyethylene that can be laminated to another film structure.
Multiple layer films are commonly used in the packaging industry for a variety of food products, such as potato chips, cookies, candies and other snack foods. These films can be formed by coextrusion methods or by laminating two or more films together. Many laminated films use oriented polypropylene (OPP) in the core layer because of its durability and strength. Different surface layers are selected for the interior and exterior layers of the package that are suitable for the particular product. For example, chips may have one type of inner layer, while wrapped candies may have a different type of inner layer. Similarly, the outer layer may be selected to enhance printability, clarity, gloss or other characteristics of the film. Frequently, additives are used to impart the desired characteristics to the outer layer.
The use of migratory additives to impart specific properties to the outer layers of multiple layer packaging films to improve specific film characteristics is well known in the art. These additives are often added to the thermoplastic resins before the film is extruded and only migrate to the surface (i.e., bloom) after the film is formed. When these migratory additives bloom to the surface of the outer layer, they promote the desired characteristics on the film surface. Often, the additive is a silicone oil. Silicone oils are added to an exterior layer of a film to improve its coefficient of friction in the heated state and reduce its slide resistance which occurs during hot plate seal by an automatic packaging machine. Examples of silicone oils which are useful for this purpose are olefin-modified silicone, polydimethylsiloxane, polymethylphenylsiloxane, polyether (e.g., polyethylene glycol, polypropylene glycol)-modified silicone, olefin/polyether-modified silicone, epoxy-modified silicone, etc.
The presence of a migratory additive on the surface of an exterior layer of a film can create problems when the film is used for an application that requires the opposing, untreated exterior surface of the film to be devoid of the additive. The untreated exterior surface is contacted by the additive when the film is rolled and subsequently unrolled. Rolling the film brings the treated exterior surface in contact with the untreated exterior surface and the additive is transferred. In order for the film to be used in an application that requires the untreated exterior layer to be devoid of the additive, the additive must first be removed. When the migratory additive is a silicone oil that has been added to improve the film's coefficient of friction and reduce its slide resistance, the characteristics that are desirable for the treated exterior surface are undesirable for the untreated exterior surface. Silicone oil on the untreated exterior surface is especially undesirable when the surface is to be laminated to another structure.
The key step in laminating is the creation of strong adhesive bonds between the films. To assure the formation of strong adhesive bonds, the adhesives must be compatible with the materials on the surfaces of the opposing films. While silicone oils impart useful properties to a film, film surfaces containing silicone oil have been found to have poor adherence when laminated to another film structure. In the past, this problem has been overcome by applying a primer (typically in the form of a solvent) to the film prior to lamination. In addition to the cost of the solvent, this method adds an additional step to the manufacturing process and is, therefore, more costly and undesirable. This has created a need for a film that does not require the application of a primer to neutralize silicone oil prior to lamination.
The films of the present invention find their principal utility as a structure that can be laminated to other film layers. However, it is to be understood that these films can also be used independently as a stand alone packaging material without adding additional layers.
SUMMARY OF THE INVENTION
The present invention provides a film structure made up of a primary web that includes a migratory additive in one outer layer and a metallocene polyethylene in a second outer layer that has an interior and an exterior surface. Unlike prior art films, the metallocene polyethylene outer layer can be laminated to a secondary web without having to treat the surface with a primer or solvent. The primary web film structure can also includes a core substrate layer disposed between the first outer layer and the second outer layer. The interior surface of the second outer layer is adjacent to the core substrate layer and the exterior surface is laminated to a secondary web.
The migratory additive used in the first outer layer is selected from the group made up of silicone oil, polydialkylsiloxanes, polydimethylsiloxane, polyalkylphenylsiloxanes, olefin-modified siloxane oils, polyether-modified silicone oils, olefin/polyether-modified silicone oils, epoxy-modified silicone oils, alcohol-modified silicone oils, antiblocking agents, antistatic agents, and slip agents. Preferred silicone oils have a viscosity of from about 350 to about 100,000 centistokes and the most preferred silicone oils have a viscosity of from about 10,000 to about 30,000 centistokes.
The first outer layer can also include a polyolefin selected from the group made up of homopolymers of polyethylene, polypropylene and polybutylene, and copolymers and terpolymers of polyethylene, polypropylene and polybutylene. The migratory additive in the first outer layer can be a silicone oil or the additive can be selected from the group made up of antiblocking agents, antistatic agents, and slip agents. In preferred embodiments, the first outer layer can include more than one migratory additive.
The films of the present invention can be laminated to other film structures without being pretreated prior to lamination. Specifically, the second outer layer of the primary web does not have to be treated with a primer to remove or neutralize the migratory additive from the surface.
The second outer layer includes a metallocene polyethylene that can be selected from the group made up of ethylene homopolymers, copolymers of ethylene and at least one C
4
-C
20
alpha-olefin polymerized using single-site metallocene catalyst, wherein the alpha olefin has a molecular weight distribution (Mw/Mn) below 5.5, preferably below 3.5 and most preferably below 3.0, and a Melt Index at 190 C. and 2160 g of from 0.3 to 20 dg/min, preferably 0.8 to 10 dg/min and most preferably from 1.2 to 7 dg min. More specifically, the metallocene polyethylene can be selected from the group made up of linear low density polyethylene, very low density polyethylene, ultra low density polyethylene, polyethylene plastomers and blends thereof In addition to the metallocene polyethylene, the second outer layer can also include a polyolefin selected from the group made up of blends of 1% to 99% metallocene-based polyethylene and 99% to 1% Ziegler-Natta catalyzed ethylene homopolymers or copolymers and homopolymers and copolymers of polypropylene and polybutylene
The metallocene polyethylene can include an additive selected from the group made up of 0.2 to 20 weight % high density polyethylene, 1 to 6,000 ppm spherical antiblock, 1 to 6,000 ppm random shape antiblock, antistatic agents and slip agents.
The core substrate layer includes a polyolefin selected from the group made up of oriented polypropylene, high density polyethylene, and blends of polypropylene and polyethylene.
The primary web of the film structures of the present invention can be laminated to a secondary web without pretreatment even though the lami
Kong Dan-Cheng
Mount, III Eldridge M.
Exxon Mobil Oil Corporation
Simmons T. Dean
Tarazano D. Lawrence
Thibodeau Paul
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