Stock material or miscellaneous articles – Composite – Of polyamide
Reexamination Certificate
2001-03-09
2002-11-12
Hampton-Hightower, P. (Department: 1711)
Stock material or miscellaneous articles
Composite
Of polyamide
C428S034600, C428S034700, C428S035400, C428S035700, C428S035900, C428S411100, C264S176100, C264S219000, C264S239000, C264S241000, C264S299000
Reexamination Certificate
active
06479160
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to oxygen barrier films. More particularly, it relates to oxygen scavenging barrier films having extremely low oxygen transmission rates (OTR) at varying relative humidity (RH) levels. Such films are particularly useful for the production of bags, pouches and liners for containers providing long shelf-life packaging of oxygen-sensitive food and beverage products, condiments, 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 including ethylene vinyl alcohol copolymers and the like 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.
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 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 polyolefin, polyvinylchloride (PVC), polyurethanes, ethylene vinyl acetate (EVA) and polyethylene terephthalate (PET).
U.S. Pat. No. 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.
Despite these advances in the art, many known oxygen barrier materials, particularly those containing nylon or EVOH, are extremely moisture sensitive and lose their oxygen barrier at high relative humidity (RH) levels. Furthermore, it is known that some oxygen scavenging materials can readily scavenge oxygen at high RH levels, but not at low RH levels. Thus, there remains a need for an oxygen barrier polymer material which can provide high oxygen scavenging capability while maintaining extremely low oxygen transmission rates at varying relative humidity levels.
Another use of oxygen barrier materials is in the retortable packages such as pouches and containers used for sterilization and storage of various food, medical and health care products. Retort is a process where the package is conditioned with steam at 121° C. for 30 minutes in order to sterilize the contents of the package. Most oxygen barrier polymers including standard EVOH cannot survive such retort conditions. The layers either become hazy, distorted or delaminated due to the severe heat history and moisture absorption. In addition, they lose their oxygen barrier property after retort due to the absorbed moisture. U.S. Pat. Nos. 5,716,715, 5,547,765 and Japan Patent No. 2000108256, 11199741, 9234833 disclose some methods to make EVOH retortable. However, the only property improved even in these retortable EVOH examples is the retention of clarity after retort. The retortable EVOH materials in these references still exhibit moisture sensitivity and a ‘retort shock’, in which the moisture trapped in EVOH layer causes a severe loss in the oxygen barrier properties. Hence the barrier retention in the film after retort is still a problem.
It would be desirable to provide films which overcome these problems.
SUMMARY OF THE INVENTION
The invention provides an oxygen barrier film which comprises:
a) a polyamide layer comprising a polyamide homopolymer, copolymer, or blends thereof;
b) an ethylene vinyl alcohol copolymer layer attached to the polyamide layer; and
c) an oxidizable polydiene and a metal salt catalyst present together in at least one of the polyamide layer and the ethylene vinyl alcohol copolymer layer.
The invention further provides a multilayer article which comprises an oxygen barrier film comprising:
A) a multilayer film comprising:
a) a polyamide layer comprising a polyamide homopolymer, copolymer, or blends thereof;
b) an ethylene vinyl alcohol copolymer layer attached to the polyamide layer;
c) an oxidizable polydiene and a metal salt catalyst present together in at least one of the polyamide layer and the ethylene vinyl alcohol copolymer layer; and
B) a thermoplastic polymer layer on one or both sides of the film.
The invention still further provides a shaped article which comprises an oxygen barrier film comprising:
a) a polyamide layer comprising a polyamide homopolymer, copolymer, or blends thereof;
b) an ethylene vinyl alcohol copolymer layer attached to the polyamide layer;
c) an oxidizable polydiene and a metal salt catalyst present together in at least one of the in at least one of the polyamide layer and the ethylene vinyl alcohol copolymer layer.
The invention also provides a process for producing an oxygen barrier film which comprises:
a) separately melting a polyamide homopolymer, copolymer, or blends thereof; and an ethylene vinyl alcohol copolymer;
b) blending an oxidizable polydiene, and a metal salt catalyst with either or both of the molten polyamide homopolymer, copolymer, or blend thereof; and the molten ethylene vinyl alcohol copolymer to thereby form an individual polyamide composition and an individual ethylene vinyl alcohol composition;
c) extruding, casting or blowing the individual compositions into an individual polyamide film layer and an individual ethylene vinyl alcohol copolymer layer;
d) cooling the polyamide layer and the ethylene vinyl alcohol copolymer layer; and
e) attaching the polyamide layer and ethylene vinyl alcohol copolymer layer to each other.
The invention yet further provides a process for producing an oxygen barrier film which comprises:
a) melting a polyamide homopolymer, copolymer, or blends thereof; and blending with an oxidizable polydiene and a metal salt catalyst therewith to form a polyamide composition and forming a polyamide film layer from the polyamide composition;
b) melting an ethylene vinyl alcohol copolymer; and blending the copolymer with an oxidizable polydiene and a metal salt catalyst to form an ethylene vinyl a
Akkapeddi Murali K.
Tsai Mingliang L.
Criss Roger H.
Hampton-Hightower P.
Honeywell International , Inc.
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