Bottles and jars – Closures – Cap type
Reexamination Certificate
1997-12-24
2002-04-16
Pyon, Harold (Department: 1772)
Bottles and jars
Closures
Cap type
C215S349000, C428S035700, C428S036600, C428S036800, C428S066300, C428S066400
Reexamination Certificate
active
06371318
ABSTRACT:
The present invention is directed to plastic container closures for beverage, food, juice, pharmaceutical and like applications, and more particularly an improved process for providing closures with sealing liners having resistance to transmission of gases, water vapor and/or flavorants (flavor scalping).
Reference is made to concurrently filed application Ser. No. 08/997,871 filed Dec. 24, 1997 (Docket 17138) entitled “Plastic Closure with Compression Molded Barrier Liner” and assigned to the assignee hereof.
BACKGROUND AND OBJECTS OF THE INVENTION
It has heretofore been proposed to provide a plastic closure for a container that comprises a plastic cap with an interior liner for sealing engagement with the sealing surface of the container. For example, U.S. Pat. No. 4,984,703 discloses a plastic closure that comprises a cap having a base with a peripheral skirt and threads for securing the cap to a container, and a sealing liner compression molded in situ to the interior of the cap base. The sealing liner comprises a blend of ethylene vinyl acetate (EVA) and a thermoplastic elastomeric material such as olefin or styrene-butadiene-styrene. U.S. Pat. No. 5,451,360 discloses a method and apparatus for compression molding the liner in situ within the caps.
Although the closures and methods of manufacture disclosed in the noted patents address problems theretofore extant in the art, further improvements remain desirable. For example, although soft olefin copolymers such as EVA are sufficiently resilient to provide good sealing against the sealing surface of a container when the closure is fastened to the container, these materials do not provide an acceptable barrier against transmission of gases such as oxygen and carbon dioxide that can deleteriously affect the product within the container. It has heretofore been proposed to employ a barrier material such as ethylene vinyl alcohol (EVOH) as a gas transmission barrier layer. However, materials of this character tend to be expensive and brittle, and are not well suited to function as a seal. It is therefore a general object of the present invention to provide a liner for a plastic closure that combines the functions of a seal for engagement with the container sealing surface and an improved barrier against gas transmission, flavor absorption (flavor scalping) and/or water vapor permeation. Another and more specific object of the present invention is to provide a liner of the described character that is of readily moldable and inexpensive composition. Yet another object of the invention is to provide a liner that satisfies the foregoing objectives and is of clear or translucent construction to permit reading through the liner of printing on the closure. A further object of the present invention is to provide a method of fabricating such a liner, and a plastic closure embodying such a liner.
SUMMARY OF THE INVENTION
A plastic closure in accordance with one aspect of the present invention comprises a plastic cap having a base with a peripheral skirt defining the interior of the cap and threads or other suitable means on the skirt for securing the closure to a container. A liner is secured to the interior of the base. The linear consists essentially of a multiplicity of alternating layers of a matrix polymer and a barrier material to resist transmission of gas through the liner parallel to the plane of the liner. The liner in the preferred embodiment of the invention is compression molded in situ within the cap, and includes at least nine alternating layers of matrix polymer and barrier materials, preferably at least thirty-three alternating layers, and most preferably one hundred twenty-nine alternating layers.
The “matrix polymer” is a thermoplastic elastomer, a soft olefin polymer, or a combination thereof. A thermoplastic elastomer is a synthetic polymer having the processability of a thermoplastic material and the functional performance and properties of a conventional thermoset rubber. There are six generic classes of thermoplastic elastomer commercially available, including styrenic block, copolymers (SBC), polyolefin blends (TPO), elastomeric alloys, thermoplastic polyurethanes (TPU), thermoplastic copolyesters and thermoplastic polyamides. Thermoplastic elastomers are described beginning at page 64 in
Modern Plastics Encyclopedia Handbook,
published by McGraw-Hill, 1994, the disclosure of which is incorporated by reference. Examples of thermoplastic elastomers are styrene block copolymers as manufactured by Shell Chemical under the trademark KRATON. These synthetic polymers consist of three discrete blocks of the linear or A-B-A type: styrene. An elastomeric alloy is ethylene-propylene-diene terpolymer (EPDM). Another elastomeric alloy consists of compounds of EPDM/PP and butyl rubber/PP as manufactured by Advanced Elastomer Systems under the tradenames SANTOPRENE and TREFSIN and disclosed in U.S. Pat. Nos. 4,130,535, 4,311,628, 4,130,534 and 4,607,074. In general, thermoplastic elastomers are characterized by a Shore A hardness of 45 to 95 and a flexural modulus of 30,000 to 100,000 psi.
Soft olefin polymers are thermoplastic olefins, homopolymers and copolymers which are flexible, elastic with a Shore A hardness of less than about 100. Typical soft olefin polymers are: metallocene made polyethylene, ethylene-propylene rubbers, ethylene copolymers and blends thereof, ethylene copolymers such as ethylene vinyl acetate, ethylene methyl acrylate copolymers and ionomers and combinations thereof. Examples of soft olefin polymers are alpha olefin substituted polyethylenes manufactured using single site catalyst technology (these materials are known in the art as metellocene made polyethylenes); ethylene vinyl acetate (EVA) such as manufactured by DuPont under the trademark ELVAX; polypropylene made with single site catalyst technology known in the art as metellocene made polypropylenes; syndiotactic polypropylenes as marketed by Fina Oil and Chemical; ethylene/propylene copolymers and styrene-ethylene interpolymers as marketed by Dow Chemical; and ionomers such as DuPont's SURLYN product line.
The matrix polymer is typically compounded with anti-oxidants, lubricants and other stabilizing materials, as known in the art.
A “compatibilizer” is a thermoplastic that ties two other thermoplastics together by a reactive (covalent or dipole—dipole) bond or a non-reactive (chain entanglement) means. Examples includes maleic anhydride grafted polymers or ethylene vinyl acetate grafted polymers such as Quantum Chemical's PLEXAR (trademark), Mitsui Petrochemical's ADMER (trademark) and DuPont's BYNEL (trademark) product lines, ethylene methyl acrylate, and ionomers.
A “barrier material” is a thermoplastic material that has a low gas and/or water vapor transmission rate and a high barrier to odorants and essential oils. The following materials have gas transmission rates lower than EVA, which is an industry standard liner material: EVOH (ethylene vinyl alcohol) such as Nippon Goshei's SOARNOL (trademark) product line and Evalca's EVAL (trademark) product line, nylons such as DuPont's SELAR (trademark) PA, EMS's G21 and Mitsubishi Gas' MXD6 product lines, British Petroleum's BAREX (trademark) acrylonitrile product line, blends of EVOH and amorphous nylon, blends of EVOH and an ionomer such as SURLYN (DuPont), and cyclic olefin copolymers such as marketed by Ticona. Other suitable barrier materials are blends as disclosed in U.S. Pat. Nos. 4,977,004 and 5,064,716, and nanocomposites of EVOH or nylon and clay as disclosed in U.S. Pat. Nos. 4,472,538 and 5,552,469, the disclosures of which are incorporated herein by reference.
It is currently preferred that the liner also include an additive for reducing the coefficient of friction between the liner and the sealing surface of the container. Friction reducing additives include metal stearates, microcrystalline waxes, polyethylene glycols, fatty acid esters and amides. These are known as “lubricants” in the art. The preferred lubricant is a low mo
Nolan Sandra M.
Owens-Illinois Closure Inc.
Pyon Harold
LandOfFree
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