Triggered active packaging material

Details Triggered active packaging material Triggered active packaging material

2000-09-20

2004-11-23

McKane, E. Leigh (Department: 1744)

Chemical apparatus and process disinfecting, deodorizing, preser

Process disinfecting, preserving, deodorizing, or sterilizing

Process of storage or protection

C422S041000, C428S327000, C428S328000

Reexamination Certificate

active

06821482

ABSTRACT:

This invention relates to methods and materials for reducing the oxygen concentration present in an atmosphere, solid, semi-solid or liquid (often referred to as oxygen scavenging).
A wide variety of foods and other materials are susceptible to loss in quality during storage under atmospheric levels of oxygen. The damage can arise from chemical oxidation of the product from microbial growth, and from attack by vermin—much of which may be avoided by reducing the oxygen availability in the environment of the materials. In the field of packaging, relatively low-oxygen atmospheres have traditionally been generated by vacuum packaging and inert gas flushing. However, chemical techniques for generating low-oxygen atmospheres and deoxygenating liquid or semi-liquid foods have also been proposed (see, for example U.S. Pat. No. 5,211,875 and our co-pending application No. PCT/AU93/00598 published as WO 94/12590). The disclosure of both of these patent specifications is to be considered as incorporated herein by reference.
The compositions and packaging materials described in WO 94/12590 may be activated to their oxygen scavenging form when it is most convenient or desirable. This means that activation may be carried out just prior to application and thereby avoids the necessity of storing the activated composition or packaging material in an inert atmosphere or vacuum. However, there are situations and applications where it would be preferred to activate the composition or packaging material at a site remote from where the composition/package is to be used.
Thus, in a first aspect the present invention provides an oxygen scavenging material comprising at least one compound oxidizable by molecular oxygen, wherein said at least one compound is contained within an oxygen impermeable compartment(s) or microcapsule(s) which may, as required, be broken or otherwise rendered oxygen permeable by application of heat, electromagnetic radiation, mechanical pressure or stress, or by hydration.
The at least one compound oxidizable by molecular oxygen may be any of those described in WO 94/12590. However, it is preferred that the at least one oxidizable compound is a compound produced from the photoreduction of an oxidized precursor compound and is oxidizable under conditions independent of both constant illumination and the presence of a transition metal catalyst. More preferably, the at least one oxidizable compound is selected from the group consisting of the reduced forms of quinones, such as benzoquinone, anthraquinone (e.g. 9,10-anthraquinone) and napthoquinone (e.g. 1,4-napthoquinone); photoreducible dyes (e.g. methylene blue); and carbonyl compounds which have absorbance in the UV spectrum, such as azo, thiazine, indigoid and triarylmethane compounds. However, iron powder and oxidisable MXD-6 nylon or 1,2-polybutadiene in the presence of a transition metal salt catalyst, may also be suitable.
Most preferably, the at least one oxidizable compound is a reduced form of a substituted anthraquinone such as 2-methylanthraquinone, 2-ethylanthraquinone and 2-amylanthraquinone.
In some applications of the invention, particularly food packaging, it is also preferred that the at least one oxidation compound be present in a polymerised or oligomerised form. The preparation of oxidized polymeric and oligomeric precursor compounds is described in WO 94/12590.
The at least one oxidizable compound may be used in substantially pure form, however, it is preferred that it be present as a component of a composition according to the invention described in WO 94/12590.
Where the at least one oxidizable compound is present as a component of a composition, the composition may further comprise an activated oxygen scavenging component reactive to activated oxygen species (e.g. peroxide) which may be generated during the scavenging of molecular oxygen. Preferred examples of the activated oxygen scavenging component include antioxidants such as alkylated phenols and bisphenols, alkylidene bis-, tris- and polyphenols, thio- and bis-, tris- and polyalkylated phenols, phenol condensation products, amines, sulfur-containing esters, organic phosphines, organic phosphites, organic phosphates, hydroquinone and substituted hydroquinones; inorganic compounds such as sulphates, sulfites, phosphites and nitrites of metals, particularly those of groups 1 and 2 of the periodic table and first row transition metals, zinc and tin; sulfur-containing compounds such as thiodipropionic acid and its esters and salts, thio-bis (ethylene glycol &bgr;-aminocrotonate), as well as the amino acids cysteine, cystine and methionine; and nitrogen-containing compounds capable of reacting with activated forms of oxygen include primary, secondary and tertiary amines and their derivatives including polymers.
Preferably, the activated oxygen scavenging component is selected from the group consisting of triphenylphospine, triethylphosphite, triisopropylphosphite, triphenylphosphite, tris(nonylphenyl)phosphite, tris(mixed mono- and bis-nonylphenyl)phosphite, butylated hydroxytoluene, butylated hydroxyanisole, tris(2,4-di-tert-butylphenyl)phosphite, dilaurylthiodipropionate, 2,2-methylene-bis-(6-t-butyl-p-cresol), tetrakis(2,4-d-tert-butylphenyl) 4,4′-biphenylene diphosphonine, poly(4-vinylpyridine) and mixtures thereof.
The activated oxygen scavenging component may also be present in a polymerised or oligomerised form.
Breakage of the compartment(s) or microcapsule(s) may be achieved by application of heat (e.g. melting of waxes or low melting point polymers such as polyethylene or ethylene vinyl acetate), electromagnetic radiation (e.g. UV light) or mechanical pressure or stress (e.g. crushing through rollers, and stirring). Alternatively, the compartment(s) or microcapsule(s) may be rendered oxygen permeable by hydration (e.g. by application of water or water vapour).
The at least one oxidizable compound or composition may be present in the oxygen scavenging material, for example, in the form of a layer within a multi-layer polymeric film. Additionally or alternatively, the at least one oxidizable compound or composition may be contained in compartment(s) or microcapsule(s) incorporated into a film material (e.g. a polymeric film material) where they may be broken by for example, crushing between rollers.
The compartment(s) may be constructed from film materials such as silica-coated films, and may include or consist of hydrophilic agents such as polyvinyl alcohol and gelatine, and cellulose esters and ethers. The polymers used may also be cross-linked and may include or consist of cross-linked proteins.
Microcapsules may be prepared from, for example, hydrophilic and/or brittle polymers. Preferred materials include polysaccharides, modified polysaccharides, and hydrophilic polymers such as polyvinyl alcohol and polyethyleneimmine. These materials may also be cross-linked or combined with proteins. Mixtures of these materials may also be used.
Methods for producing microcapsules are described in Agis F. Kydonieus, (Ed), Controlled Release Technologies: Methods, Theory and Applications, CRC Press Inc. Cleveland (1980). The preferred size range for microcapsules is 0.1 to 100 &mgr;m in diameter.
Where the at least one oxidizable compound is present as a component of a composition, it may also be preferred to include within the composition a source of labile hydrogen or electrons to assist photoreduction of a photoreducible precursor compound (i.e. to prepare an oxidizable compound).
The compartment(s) or microcapsule(s) may also be a source of electrons or hydrogen atoms for photoreduction of a photoreducible precursor compound. Alternatively, the compartment(s) or microcapsule(s) may merely serve as an oxygen barrier to protect the oxidizable compound from premature exposure and oxidation by molecular oxygen.
The oxygen scavenging material may be used independently or as components of blends. The material may take the form of a cross-linked polymeric matrix, as in a can lacquer, or be bonded to or absorbed onto an inorganic polymer such as silica

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