Stock material or miscellaneous articles – Hollow or container type article – Polymer or resin containing
Reexamination Certificate
2001-03-07
2004-09-21
Nolan, Sandra M. (Department: 1772)
Stock material or miscellaneous articles
Hollow or container type article
Polymer or resin containing
C428S474400, C525S168000, C525S171000, C525S177000, C525S298000, C525S445000
Reexamination Certificate
active
06793994
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to polymer compositions. More particularly, the invention relates to oxygen scavenging polymer compositions containing ethylene vinyl alcohol (EVOH) copolymers, which compositions exhibit extremely low oxygen transmission rates (OTR) at various relative humidity (RH) levels. Such compositions are useful for the production of bottles, containers, and other long shelf-life applications for packaging a variety of oxygen-sensitive food and beverage products such as beers, juices, condiments, fresh and processed meats as well as certain pharmaceutical and health care products.
2. Description of the Related Art
It is well known in the art to provide polymer based packaging articles such as films, bottles, containers, and the like, which are useful for food packaging. Many such articles are made of plastics such as ethylene vinyl alcohol copolymers in order to achieve the desired barrier properties. For example, U.S. Pat. Nos. 5,055,355 and 5,547,765 teach laminates of polyamides and ethylene vinyl alcohol copolymers which have good oxygen barrier properties.
In order to enhance freshness preservation, it is a standard practice to package food and beverage products within a packaging structure composed of laminated sheets of two or more plastics. Such packaging structures generally include a barrier plastic layer which has a low permeability to oxygen. The packaging structure can be thin, in which case it is wrapped around the item being packaged, or it can be thick enough to form a shaped container body such as a bottle.
It is known in the art to include an oxygen scavenger in the packaging structure. An oxygen scavenger reacts with oxygen that is trapped in the package or that permeates from outside into the package. This is described, for example, in U.S. Pat. Nos. 4,536,409 and 4,702,966. U.S. Pat. No. 4,536,409 describes cylindrical containers formed from such packaging plastics.
Various types of oxygen scavengers have been proposed for this purpose. U.S. Pat. No. 4,536,409 recommends potassium sulfite as an oxygen scavenger. U.S. Pat. No. 5,211,875 discloses the use of unsaturated hydrocarbons as oxygen scavengers in packaging films. It is known in the art that ascorbic acid derivatives as well as sulfites, bisulfites, phenolics, and the like can be oxidized by molecular oxygen, and can thus serve as an oxygen scavenging material. U.S. Pat. No. 5,075,362 discloses the use of ascorbate compounds in containers as oxygen scavengers. U.S. Pat. Nos. 5,202,052 and 5,364,555 describe polymeric material carriers containing oxygen scavenging material. These polymeric carriers for the oxygen scavenging material include polyolefins, polyvinylchloride (PVC), polyurethanes, ethylene vinyl acetate (EVA) and polyethylene terephthalate (PET).
U.S. Pat. Nos. 5,021,515, 5,049,624 and 5,639,815 disclose packaging materials and processes therefor which utilize a polymer composition which is capable of scavenging oxygen. Such compositions include an oxidizable organic polymer component, preferably a polyamide, such as nylon MXD6, and a metal oxidation promoter, such as a cobalt compound. These compositions can be used with PET, for example.
U.S. Pat. No. 5,529,833 describes the use of a composition comprising an ethylenically unsaturated hydrocarbon oxygen scavenger which is incorporated into a film layer, and used for making packaging for oxygen sensitive products. The oxygen scavenger is catalyzed by a transition metal catalyst and a chloride, acetate, stearate, palmitate, 2-ethylhexanoate, neodecanoate or naphthenate counterion. Preferred metal salts are selected from cobalt (II) 2-ethylhexanoate and cobalt (II) neodecanoate. Because water deactivates the oxygen scavenger composition, the composition can only be used for packaging for dry materials.
Despite these advances in the art, many known oxygen barrier materials, particularly those containing EVOH, are extremely moisture sensitive and lose their oxygen barrier at high relative humidity (RH) levels. A need exists for an oxygen barrier polymer material which can provide high oxygen scavenging capability while maintaining extremely low oxygen transmission rates at high relative humidity (RH) levels.
Another use of oxygen barrier materials is in the retort process which has been commonly employed for pouches and containers in various food applications as well as certain pharmaceutical, medical and health care products. Retorting is a process wherein a sample is conditioned at 121° C. for 30 minutes. Most oxygen barrier polymers including standard EVOH cannot survive at these retort conditions. The layers either becomes distorted/delaminated and turns hazy due to the severe heat history, or they lose their oxygen barrier property during or after retorting due to absorbed moisture. U.S. Pat. Nos. 5,716,715, 5,547,765 and Japan Patent Nos. 2000108256, 11199741, 9234833 describe methods to make EVOH retortable. Even in these examples where retortable EVOH remains clear after retort, retortable EVOH still exhibits moisture sensitivity as well as retort shock, in which the moisture is trapped in EVOH layer and thus worsens the oxygen barrier.
It would be desirable to provide a barrier material which can provide high oxygen scavenging and extremely low oxygen transmission rates (OTR) at high relative humidity (RH) levels, before and after retort, as well as provide a solution to the problems mentioned above.
SUMMARY OF THE INVENTION
The invention provides an oxygen-scavenging polymer composition which comprises:
a) at least one ethylene vinyl alcohol copolymer;
b) at least one oxidizable polydiene; and
c) at least one metal salt catalyst.
The invention further provides an oxygen barrier film comprising a layer of a polymer composition which comprises:
a) at least one ethylene vinyl alcohol copolymer;
b) at least one oxidizable polydiene; and
c) at least one metal salt catalyst.
The invention still further provides a multilayer article which comprises:
a) a polymer composition layer comprising at least one ethylene vinyl alcohol copolymer; at least one oxidizable polydiene; and at least one metal salt catalyst; and
b) a thermoplastic polymer layer on one or both sides of the polymer composition layer.
The invention still further provides a shaped article which comprises a polymer composition comprising:
a) at least one ethylene vinyl alcohol copolymer;
b) at least one oxidizable polydiene; and
c) at least one metal salt catalyst.
The invention still further provides a process for producing a polymer composition which comprises:
a) melting at least one ethylene vinyl alcohol copolymer;
b) blending the molten copolymer with at least one oxidizable polydiene and at least one metal salt catalyst to thereby form a mixture; and
c) cooling the mixture.
The invention still further provides a process for producing an oxygen barrier film which comprises:
a) melting at least one ethylene vinyl alcohol copolymer;
b) blending the molten copolymer with at least one oxidizable polydiene and at least one metal salt catalyst to thereby form a mixture;
c) extruding, casting or blowing the mixture into a film; and
d) cooling the film.
The invention still further provides a process for producing an oxygen barrier polymer film which comprises:
a) melting a composition which comprises at least one ethylene vinyl alcohol copolymer; at least one oxidizable polydiene; and at least one metal salt catalyst;
b) extruding, casting or blowing the composition into a film; and
c) cooling the film.
The invention still further provides a process for producing a multilayer article which comprises:
a) melting at least one ethylene vinyl alcohol copolymer; at least one oxidizable polydiene; and at least one metal salt catalyst to thereby form a mixture;
b) separately melting a thermoplastic polymer composition;
c) coextruding, casting, blowing, thermoforming, blow molding or coinjecting the mixture and thermoplastic polymer composition into a multilayer article; and
d) cooling the article.
The invention
Akkapeddi Murali K.
Tsai Mingliang L.
Honeywell International , Inc.
Nolan Sandra M.
Szigeti Virginia
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