Compositions – Reductive bleachant – deoxidant – reductant – or generative – Deoxidant or oxygen scavenging
Reexamination Certificate
1999-04-21
2001-04-03
Anthony, Joseph D. (Department: 1714)
Compositions
Reductive bleachant, deoxidant, reductant, or generative
Deoxidant or oxygen scavenging
C252S188210
Reexamination Certificate
active
06210601
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of making an oxygen scavenging sealant composition that can be utilized to improve the shelf life of packaged materials, such as oxygen sensitive foods. As used herein, the term sealant is as known to those skilled in the art for forming an hermetic seal with a packaging container. It includes, for example, gaskets (bonded) and liners (non-bonded).
2. Description of Related Art
In packaging oxygen sensitive materials such as food, beverages and pharmaceuticals (collectively “foodstuffs”) oxygen contamination can be particularly troublesome. Care is generally taken to minimize the introduction of oxygen, to exclude the oxygen from the package when initially sealed or to otherwise reduce the detrimental or unwanted effects of oxygen on foodstuffs.
It is known to package foodstuffs in containers wherein the walls contain an oxidizable component which reacts with oxygen that is trapped in the package or permeates through the wall of the package. These systems are described, for example, in U.S. Pat. Nos. 4,536,409 and 4,702,966.
When the container wall is formed of a glass or metal body and is provided with a metal closure, oxygen does not permeate through the container walls due to the impermeable materials used to make the container walls or closure. However, it has long been recognized that conventional containers employed for the storage of oxidizable materials may be permeable through the seams at the juncture between glass or metal components, often through sealants used to fill these seams. In addition, oxygen may remain within the container from the closing operation.
To extend the shelf life of foodstuffs while continuing to utilize conventional materials, attempts have been made to incorporate oxygen scavenging systems in the container crown or closure. For example, U.S. Pat. No. 4,279,350 discloses a closure liner which incorporates a catalyst disposed between an oxygen permeable barrier and a water absorbent backing layer.
U.S. Pat. No. 4,510,162 describes an oxygen adsorbent composition containing iron particles, yeast and moisture, which is mounted on a suitable carrier and adapted to be mounted in a closable container for removing oxygen therefrom.
U.S. Pat. Nos. 4,756,436 and 5,106,886 disclose an oxygen scavenging composition to be installed as a gasket between the cap and the container. Particularly, U.S. Pat. No. 5,106,886, discloses a sealant that incorporates a sodium ascorbate oxygen scavenger in a plasticized polyvinyl chloride.
A disadvantage associated with the prior art oxygen scavenging sealant compositions is their inability to maintain a hermetic seal over a prolonged shelf life.
To overcome this disadvantage, it is an object of this invention to provide a method for compounding an oxygen scavenging sealant composition having improved long term sealing ability, thereby preventing the oxidation of the foodstuff and prolonging the shelf-life of the package.
Another object of the invention is to provide a method of compounding an oxygen scavenging sealant composition that has an improved oxygen uptake.
Other objects and aspects of the present invention will become apparent to one skilled in the art on a review of the specification and claims appended hereto.
SUMMARY OF THE INVENTION
According to a first aspect of the invention, a method of making a sealant composition is provided. Oxygen scavenger particles are pre-dispersed in a plasticizer to form a paste. The paste is processed to the point where at least about 99.5 percent by weight of said oxygen scavenger particles are less than 125 microns in size and, preferably less than 76.20 microns, and more preferably less than 50.80 microns. The processed paste is introduced into a plastisol formulation.
According to another aspect of the invention, a method for making a sealant composition is provided. The method includes processing oxygen scavenger particles to the point where at least about 99.5 percent by weight of particles are less than 125 microns in size preferably less than 76.20 microns, and more preferably less than 50.80 microns. The particles are dispersed into a plasticizer and the plasticizer, comprising the processed oxygen scavenger particles, is introduced into a plastisol formulation.
In a further embodiment of the present invention, a method for compounding a sealant composition is provided. The method includes pre-dispersing oxygen scavenger particles in a plasticizer to form a paste and processing said paste to the point where at least about 99.5 percent by weight of said oxygen scavenger particles are less than about 55.88 microns in size. The processed paste is then introduced into a plastisol formulation.
According to yet another aspect of the present invention, a method for making an oxygen scavenging composition for a closure is provided. The method includes pre-dispersing oxygen scavenging particles in a liquid carrier. As herein utilized, the term liquid carrier includes plasticizers or melts. The carrier comprising the dispersed particles therein is milled to the point where substantially all of the particles are less than about 76.20 microns in size and is added to a polymeric matrix to form the composition. As used herein, the term “substantially all” means at least about 99.5 percent by weight.
In another aspect of the invention, a method of making an oxygen-scavenging composition for use in closures is provided. The method includes providing an oxygen scavenging powder wherein all of the particles are less than about 76.20 microns in size, and adding said powder directly or indirectly to a polymeric matrix to form the composition.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
The present invention provides a method of forming sealing compositions suitable for fabricating closures or gaskets to effect and maintain a hermetic seal. The compositions provided by the disclosed method improves the lifespan of closure materials and improves their efficiency in oxygen scavenging. The composition of the invention can be formulated in a convenient fluid form, such as a plastisol, melt, organic solution or dispersion. In a plasticizer sealant composition, a liquid plastisol system is utilized.
One embodiment of the present invention involves a sealant composition formed from a plastisol formulation having oxygen scavenging properties necessary to protect oxygen sensitive food. By plastisol formulation, it is herein meant a dispersion of finely divided resin in a plasticizer. A particular application is to hermetically seal a glass container by means of a metal closure wherein the plastisol is utilized as a gasket. As will be appreciated by those skilled in the art, the formed plastisol gasket on a container closure device provides an adhesive agent impervious to outside interference, particularly from oxygen. Additionally, the gasket provides improved uptake of oxygen in the headspace of the package. The term, headspace as used herein, is meant to describe the volume inside the sealed package not occupied by the foodstuff. Further, it should be clear that the inventive concepts described hereinbelow are in no way limited, and can be readily applied to other forms of packaging containers.
In a preferred embodiment, the plastisol includes polyvinyl chloride resin particles dispersed in a liquid plasticizer and an oxygen scavenging agent. Additionally, the composition might contain fillers, pigments, stabilizers, lubricants, chemical blowing agents, activators, and other conventional additives in conventional amounts, depending on the nature and intended application of the composition. Suitable compositions for this invention includes Daraseal 3287 from W.R. Grace; Svelith TOS 350-7 from D S Chemie; and AH-10983, AH-10982, AH-10923 from Crown Cork and Seal Company, Inc.
The polymeric matrix material can be selected with reference to the nature of the composition (e.g., plastisol, solution, or melt). Suitable materials for use when the composition is a plastisol include vin
Hottle Larry A.
Ryall Graham
Anthony Joseph D.
Burns Doane Swecker & Mathis L.L.P.
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