Low migratory photoinitiators for oxygen-scavenging compositions

An improved composition and a method of scavenging oxygen using the composition which comprise oxidizable organic compounds, transition metal catalysts in combination with certain photoinitiators is disclosed. The method comprises initiating scavenging by exposing the composition to UV radiation. The present composition uses certain defined benzophenone derivatives which maintain effectiveness of photoinitiation while providing reduced migration of the photoinitiator from the resin matrix.

FIELD OF THE INVENTION
 The invention relates to compositions, articles and methods of scavenging
 oxygen in environments containing oxygen-sensitive products, particularly
 food and beverage products. It has been unexpectedly found that the
 incorporation of certain derivatives of benzophenone into an oxygen
 scavenging resin causes short initiation periods for scavenging oxygen and
 reduced migration of the initiator and its by-products from the resin
 compositions.
 BACKGROUND OF THE INVENTION
 The present invention relates to oxygen scavenging compositions, to
 polymeric compositions containing said oxygen scavenging compositions, and
 further to intermediate shaped structures, e.g., films, coatings,
 3-dimensional solids, fibers, webs, and the like, which contain such
 polymeric compositions, as well as to shaped products, into or onto, which
 such compositions or structures are incorporated or applied, respectively,
 e.g., packaging articles, having the subject compositions incorporated as
 part of or attached to the article's structure.
 It is well known that limiting the exposure of oxygen-sensitive materials
 to oxygen maintains and enhances the quality and "shelf-life" of the
 material. For instance, by limiting the oxygen exposure of oxygen
 sensitive food products in a packaging system incorporating a material or
 composition capable of scavenging oxygen, the quality of the food product
 is maintained and food spoilage is avoided for extended periods. In
 addition, such packaging systems permit keeping the product in inventory
 longer and, thereby, reduce costs incurred from waste and having to
 restock. In the food packaging industry, several means for limiting oxygen
 exposure have already been developed. At present, the most commonly used
 means are modified atmosphere packaging (MAP), and vacuum packaging
 coupled with the use of oxygen barrier films. In these instances, reduced
 oxygen environments are employed at the time of packaging and the oxygen
 barrier film physically prevents oxygen from entering the packaging
 environment during storage.
 Another, more recent means for limiting oxygen exposure involves
 incorporating an oxygen scavenger into the packaging structure. The term
 "oxygen scavenger" or "scavenger", as used in the present specification
 and appended claims refers to compounds and compositions which are capable
 of consuming, depleting or reducing the amount of oxygen from a given
 environment. Incorporation of a scavenger in a package (e.g., as part of a
 film forming the package, or at least one layer of a laminate forming the
 package or as a coating on at least a portion of the package structure)
 can provide a means of scavenging oxygen in the headspace of the package
 as well as providing uniform scavenging effect throughout the package. In
 addition, incorporation of a scavenger can provide a means of intercepting
 and scavenging oxygen as it is passing through the walls of the package
 (herein referred to as an "active oxygen barrier") to maintain the lowest
 possible oxygen level throughout the package.
 Examples of oxygen scavenger compositions incorporated into an oxygen
 scavenging wall are illustrated in European Applications 301,719 and
 380,319; PCT 90/00578 and 90/00504, and U.S. Pat. Nos. 5,021,515 and
 5,049,624. The oxygen scavenger compositions disclosed in these
 publications comprises a polyamide and a transition metal catalyst. A
 package wall containing such compositions regulate the amount of oxygen
 which reaches the interior of the package. However, the onset of useful
 oxygen scavenging activity, i.e. up to about 5 cubic centimeters (cc)
 oxygen per square meter per day at ambient conditions, by this wall may
 not occur for as long as 30 days. The delay before the onset of useful
 oxygen scavenging is hereinafter referred to as the induction period. Such
 extended induction period is not generally desired.
 Other oxygen scavenger compositions comprising a transition metal catalyst
 and an ethylenically unsaturated compound, e.g. polybutadiene,
 polyisoprene, dehydrated castor oil, etc., as described in U.S. Pat. No.
 5,346,644, also exhibit lengthy induction periods. For example, when the
 oxygen scavenger comprises a polybutadiene, the induction period can
 exceed thirty days. Scavengers comprising polyisoprene or dehydrated
 castor oil typically have induction periods of about one to fourteen days.
 The duration of the induction period depends on several factors, some of
 which are not completely understood or controllable. Accordingly, when
 using films or articles containing oxygen scavenger compositions having
 long induction periods, it is required to keep the films and articles in
 inventory for a period of time prior to use in order to provide reliable
 scavenging behavior required to protect oxygen sensitive material in a
 package. On the other hand, when using packages which incorporate films or
 articles containing scavenger compositions having short induction periods,
 the package, films and articles, as appropriate, will have to be prepared
 quickly and put to use in a short time period, sometimes immediately or
 stored in an oxygen-free atmosphere in order to attain the maximum
 effectiveness as a scavenger.
 One method described to initiate scavenging on demand in packages for
 oxygen-sensitive foods or other materials involves incorporating
 photooxidizable rubber, e.g. cis-1,4-polyisoprene, and a photosensitizing
 dye into the inner surface of a package and then exposing it to visible
 light. See Rooney, M. L., "Oxygen Scavenging: A Novel Use of Rubber
 Photo-oxidation", Chemistry and Industry, Mar. 20, 1982, pp. 197-198.
 However, while this method allows one to initiate oxygen scavenging when
 desired, it requires constant exposure of the package to light to maintain
 the scavenging effect. Such a requirement is not suitable for commercial
 application. Further, the required use of a dye makes it difficult to
 employ this method for applications which require colorless packaging,
 especially the transparent packaging commonly used commercially with food
 and beverage products.
 A method of initiating oxygen scavenging by compositions which comprise
 oxidizable organic compounds and transition metal catalysts is disclosed
 in U.S. Pat. No. 5,211,875, which is incorporated herein by reference as
 if set forth in full. The reference sets forth a method of initiating
 oxygen scavenging by administration of a dose of actinic radiation. The
 oxygen scavenging compositions are conveniently prepared by compounding a
 scavenging resin(s), transition metal catalyst and, optionally, a
 photoinitiator. The scavenging is initiated by subjecting the package,
 film or article containing the scavenging compositions to actinic
 radiation. However, the oxygen scavenging compositions prepared by this
 reference exhibit an undesirably high level of migration of the
 photoinitiator and/or its by-products from the packaging material,
 particularly when used to package fatty substances.
 It is highly desired to provide an improved oxygen scavenging composition
 suitable for use in packages, films and articles. The composition should
 provide the ability to have useful oxygen scavenging activity within short
 induction periods after irradiation. Further, the composition should be
 capable of retaining the active components and the irradiation by-products
 within a polymer matrix used as a carrier for the scavenging composition.
 SUMMARY OF THE INVENTION
 It is an object of the invention to provide novel methods and compositions
 which are effective in controlling oxygen scavenging properties of a film
 or other packaging article.
 It is also an object of the invention to provide a composition capable of
 having oxygen scavenging initiated on demand, and exhibit a relatively
 short induction period.
 It is also an object of the present invention to provide a composition
 capable of retaining the active components and the irradiation by-products
 within the polymer matrix used as a carrier for the scavenging
 composition.
 It is also an object of the present invention to employ these methods and
 compositions in films, packages and articles containing oxygen-sensitive
 products.
 The above-mentioned objects are obtained from an oxygen scavenging
 composition comprising a combination of an oxidizable organic compound, a
 transition metal catalyst, and certain substituted benzophenones, as fully
 described herein below. Further, the above-mentioned objects are obtained
 by a method which employs films of single and multilayered design and
 articles which contain the subject oxygen scavenging composition,
 especially those used for packaging oxygen-sensitive products.
 The present invention provides improved oxygen scavenging compositions
 comprising (a) an oxidizable organic compound, (b) a transition metal
 catalyst, and (c) a photoinitiator which is at least one substituted
 derivative of benzophenone, as fully described herein below.
 When the composition comprising (a), (b) and (c) stated above is used with
 or in a package or as part of a film, such as at least one layer of a
 film, novel articles for packaging oxygen-sensitive products can be
 prepared. When using those articles with the method described herein, the
 article regulates the oxygen exposure by acting as an active oxygen
 barrier or means for scavenging oxygen from within the article, or both.
 The above-mentioned goals and others will be apparent from the description
 that follows.
 DESCRIPTION OF THE INVENTION
 The present invention provides a novel oxygen scavenging composition
 capable of having oxygen scavenging activity initiated on demand,
 exhibiting short induction periods, and capable of retaining the active
 components and its irradiation by-products within the polymer matrix
 acting as carrier for the scavenging composition.
 The composition comprises a combination of at least one (a) an oxidizable
 organic compound (b) at least one transition metal catalyst, and (c) a
 photoinitiator composed of at least one substituted benzophenone, as fully
 described herein below.
 The oxidizable compounds include, but are not necessarily limited to,
 benzylic, allylic and/or tertiary hydrogen containing carbon compounds.
 Specific compounds include polymers and copolymers of alpha olefins.
 Examples of such polymers are low density polyethylene, very low density
 polyethylene, and ultra low density polyethylene; polypropylene;
 polybutylene, i.e., poly(1-butene); propylene copolymers;
 ethylene/propylene copolymers ("EPC"); butylene copolymers; hydrogenated
 diene polymers; and the like.
 Suitable oxidizable compounds also include polyamides such as aromatic
 polyamides, e.g. meta-xylylene adipamide. Other suitable polyamides are
 disclosed in European Patent Application 301,719, the teachings of which
 are incorporated herein in its entirety by reference.
 It is particularly preferred to use an unsubstituted or a substituted
 ethylenically unsaturated hydrocarbon compound as the oxidizable compound
 of this invention. As defined herein, an unsubstituted ethylenically
 unsaturated hydrocarbon is any compound which possesses at least one
 aliphatic carbon-carbon double bond and comprises 100% by weight carbon
 and hydrogen. A substituted ethylenically unsaturated hydrocarbon is
 defined herein as an ethylenically unsaturated hydrocarbon which possesses
 at least one aliphatic carbon-carbon double bond and comprises about
 50%-99% by weight carbon and hydrogen. Preferable unsubstituted or
 substituted ethylenically unsaturated hydrocarbons are those having two or
 more ethylenically unsaturated groups per molecule. More preferably, it is
 a polymeric compound having three or more ethylenically unsaturated groups
 and a weight average molecular weight equal to or greater than 1,000.
 Preferred substituted ethylenically unsaturated hydrocarbons include, but
 are not limited to, those with oxygen-containing moieties, such as esters,
 carboxylic acids, aldehydes, ethers, ketones, alcohols, peroxides, and/or
 hydroperoxides. Specific examples of such hydrocarbons include, but are
 not limited to, condensation polymers such as polyesters derived from
 monomers containing carbon-carbon double bonds; unsaturated fatty acids
 such as oleic, ricinoleic, dehydrated ricinoleic, and linoleic acids and
 derivatives thereof, e.g. esters. Such hydrocarbons also include polymers
 or copolymers derived from (meth)allyl (meth)acrylates. Suitable oxygen
 scavenging polymers can be made by trans-esterification, as disclosed in
 WO 95/02616, the teachings of which is incorporated herein by reference as
 if set forth in full.
 The oxygen scavenging composition may also comprise a mixture of two or
 more oxidizable organic compounds, such as a mixture of substituted or
 unsubstituted ethylenically unsaturated hydrocarbons described above.
 While a weight average molecular weight of 1,000 or more is preferred, the
 ethylenically unsaturated hydrocarbon having a lower molecular weight may
 be used, provided it is blended with a film-forming polymer or blend of
 polymers.
 It is preferred to utilize ethylenically unsaturated hydrocarbons which are
 capable of forming solid transparent layers at room temperature when
 utilizing the composition in packaging articles. For most applications
 where transparency is necessary, a layer which allows at least 50%
 transmission of visible light is preferred.
 When making transparent oxygen-scavenging layers according to this
 invention, 1,2-polybutadiene is especially preferred as at least a portion
 of the oxidizable organic compound (a) for use at room temperature.
 1,2-polybutadiene can exhibit transparency, mechanical properties and
 processing characteristics similar to those of polyethylene. In addition,
 this polymer is found to retain its transparency and mechanical integrity
 even after most or all of its oxygen capacity has been consumed, and even
 when little or no diluent resin (as described below) is present. Even
 further, 1,2-polybutadiene exhibits a relatively high oxygen capacity and,
 once it has begun to scavenge, it exhibits a relatively high rate of
 scavenging as well.
 When oxygen scavenging at low temperatures is desired, 1,4-polybutadiene,
 and copolymers of both styrene with butadiene and styrene with isoprene
 are preferred. Such compositions are disclosed in U.S. Pat. No. 5,310,497,
 the teachings of which are incorporated herein by reference as if set
 forth in full. In many cases it may be desirable to blend the
 aforementioned polymers with a polymer or copolymer of ethylene.
 As indicated above, the oxidizable organic compound(s) is combined with a
 transition metal catalyst. While not being bound by any particular theory,
 the inventors observe that suitable metal catalysts are those which can
 readily interconvert between at least two oxidation states. See Sheldon,
 R. A.; Kochi, J. K.; "Metal-Catalyzed Oxidations of Organic Compounds"
 Academic Press, New York 1981.
 Preferably, the catalyst is in the form of a transition metal salt, with
 the metal selected from the first, second or third transition series of
 the Periodic Table. Suitable metals include, but are not limited to,
 manganese II or III, iron II or III, cobalt II or III, nickel II or III,
 copper I or II, rhodium II, III or IV, and ruthenium. The oxidation state
 of the metal when introduced is not necessarily that of the active form.
 The metal is preferably iron, nickel or copper, more preferably manganese
 and most preferably cobalt. Suitable counterions for the metal include,
 but are not limited to, chloride, acetate, stearate, palmitate, caprylate,
 linoleate, tallate, 2-ethylhexanoate, neodecanoate, oleate or naphthenate.
 Particularly preferable salts include cobalt (II) 2-ethylhexanoate and
 cobalt (II) neodecanoate. The metal salt may also be an ionomer, in which
 a polymeric counterion is employed. Such ionomers are well known in the
 art.
 The present composition further contains a photoinitiator composed of at
 least one substituted derivative of benzophenone. The derivatized
 benzophenones found useful in the present composition can be represented
 by the following structural formula:
 ##STR1##
 wherein:
 i) at least one R.sup.1, R.sup.2, R.sup.3, R.sup.4 or R.sup.5 is
 independently selected from C.sub.2 -C.sub.18 alkyl, C.sub.2 -C.sub.18
 alkoxy, a phenoxy, C.sub.5 -C.sub.7 alicyclic hydrocarbon, an alkaryl or a
 C.sub.2 -C.sub.18 ester group, and the remainder of said R.sup.1, R.sup.2,
 R.sup.3, R.sup.4 and R.sup.5 are hydrogen atoms; and each R.sup.6,
 R.sup.7, R.sup.8, R.sup.9 and R.sup.10 is a halogen or hydrogen atom; or
 ii) at least one R.sup.1, R.sup.2, R.sup.3, R.sup.4 or R.sup.5 and at least
 one R.sup.6, R.sup.7, R.sup.8, R.sup.9 or R.sup.10 are each independently
 selected from a C.sub.1 -C.sub.18 alkyl, C.sub.1 -C.sub.18 alkoxy, a
 phenoxy, C.sub.5 -C.sub.7 alicyclic, an alkaryl or a C.sub.1 -C.sub.18
 ester group and the remainder of said groups are each halogen or hydrogen
 atoms.
 Thus, the subject benzophenone derivatives of the present oxygen scavenging
 composition must be at least a C.sub.15 benzophenone derivative requiring
 having at least one hydrocarbon pendent group capable of fulfilling this
 requirement pendent from one of the benzylic groups, or preferably, from
 each of the benzylic groups, of the benzophenone. Each pendent group can
 be selected from hydrocarbon containing groups selected from those
 described above. It is preferred to have at least one such group on each
 benzylic group as provided by subparagraph (ii) above. The alkyl groups
 suitable are, for example, methyl (for embodiment (ii)), ethyl, propyl,
 isopropyl, butyl, t-butyl, pentyl, dodecyl, hexadecyl, octadecyl and the
 like; a C.sub.1 -C.sub.18 alkoxy group, as for example methoxy (for
 embodiment (ii)), ethyoxy, propoxy, butoxy, dodecyloxy and the like; a
 C.sub.5 -C.sub.7 alicyclic groups, as for example, cyclopentyl cyclohexyl,
 cycloheptyl and the like; alkaryl having C.sub.1 -C.sub.6 alkyl pendent
 group such as, for example, toluenyl and the like; or an ester which may
 be either --C(O)OR.sup.7 or --OC(O)R.sup.7 wherein R.sup.7 is a C.sub.1
 -C.sub.18 hydrocarbon (for embodiment (ii) above) or C.sub.2 -C.sub.18
 hydrocarbon. Each of the above hydrocarbon groups may be fully saturated
 or may contain ethylenic unsaturation within the hydrocarbon chain as, for
 example, a propyl group may also be viewed as an allyl group, a C.sub.18
 group may be also viewed as stearate or oleate and so forth. The halogen
 atom substitution, (applicable for embodiment (I)) can be chloride,
 bromide, or the like.
 Derivatives of benzophenone which are suitable for the present improved
 oxygen scavenging composition include, for example, 4,4'-dimethyl
 benzophenone, 4,4'-dimethyoxybenzophenone, 2,2'-diethylbenzophenone,
 4,4'-diphenoxybenzophenone, 4-allyloxybenzophenone,
 4,4'-diallyloxybenzophenone, 4-dodecylbenzophenone,
 4,4'-dicyclohexylbenzophenone, 4,4'-diacetylbenzophenone,
 4-tolylbenzophenone, and the like. The subject benzophenone derivatives
 found useful in the present invention must be compatible with the
 oxidizable organic compound, and exhibit a degree of migration of about
 500 ppb or less when subjected to a food simultant under food simulation
 conditions, as proposed by the U.S. Food and Drug Administration (FDA) or
 other applicable governmental agency.
 The subject oxygen scavenging composition may be further combined with one
 or more polymeric diluent, such as thermoplastic polymers which are
 typically used to form film layers in plastic packaging articles. In the
 manufacture of certain packaging articles well known thermosets can also
 be used as the polymeric diluent.
 Antioxidants may be incorporated into the subject composition as well as
 films and articles containing the composition of this invention to control
 scavenging initiation. An antioxidant, as defined herein, is any material
 which inhibits oxidative degradation or cross-linking of polymers.
 Typically, such antioxidants are added to facilitate the processing of
 polymeric materials and/or prolong their useful lifetime. In relation to
 this invention, such additives inhibit the initiation of the induction
 period for oxygen scavenging in the absence of irradiation. Then when the
 layer's or article's scavenging properties are required, the layer or
 article having the subject composition and incorporated photoinitiator can
 be exposed to radiation.
 When an antioxidant is incorporated into the composition (either directly
 or via a polymer diluent or the like forming a part of the polymer matrix
 containing the oxygen scavenging composition), it should be used in an
 amount effective to permit processing and desired storage life without
 significant oxidation, while not interfering in activation by irradiation.
 The exact amount will depend on the particular oxidizable organic
 compound, the processing conditions, the desired length of storage prior
 to use and the amount of photoinitiator present in the composition. The
 exact amount for a particular situation can be readily determined by
 simple experimentation. Examples of antioxidants suitable for use are, for
 example, hindered phenolics, such as, 2,6-di(t-butyl)4-methyl-phenol(BHT),
 2,2'-methylene-bis(6-t-butyl-p-cresol); phosphites, such as,
 triphenylphosphite, tris-(nonylphenyl)phosphite; and thiols, such as,
 dilaurylthiodipropionate and the like.
 The composition of this invention can be used as an oxygen scavenging film
 or layer, per se, or in combination with film-forming diluent polymers.
 Such polymers are thermoplastic and render the film more adaptable for use
 as packaging layers. They also may be, to some extent, oxidizable, and
 thus factored into the oxygen scavenger formulation as an oxidizable
 organic compound. Suitable diluents include, but are not limited to,
 polyethylene, low density polyethylene, very low density polyethylene,
 ultra-low density polyethylene, high density polyethylene, polyethylene
 terephthalate (PET), polyvinyl chloride, and ethylene copolymers such as
 ethylene-vinyl acetate, ethylene-alkyl (meth)acrylates,
 ethylene-(meth)acrylic acid and ethylene-(meth)acrylic acid ionomers. In
 rigid articles such as beverage containers PET is often used. Blends of
 different diluents may also be used. However, the selection of the
 polymeric diluent largely depends on the article to be manufactured and
 the end use thereof. Such selection factors are well known in the art. For
 instance, the clarity, cleanliness, effectiveness as an oxygen scavenger,
 barrier properties, mechanical properties and/or texture of the article
 can be adversely affected by a blend containing a diluent polymer which is
 incompatible with the oxidizable organic compound.
 Other additives which may also be included in oxygen scavenger layers
 include, but are not necessarily limited to, fillers, pigments, dyestuffs,
 stabilizers, processing aids, plasticizers, fire retardants, anti-fog
 agents, and the like.
 The subject oxygen scavenging composition has been found to be
 substantially non-migratory in the film or packaging article during normal
 use. Thus, the presently used photoinitiator component and the by-products
 formed after subjecting the composition to irradiation to initiate
 oxidation have been unexpectedly found to remain within the oxygen
 scavenging composition or layer containing same. Thus, a film having a
 plurality of layers, one of which is an oxygen scavenging layer, does not
 show significant migration of the photoinitiator from the oxygen
 scavenging layer to the other layers of the film. The resultant film can,
 thereby, be stored prior to subjection to irradiation and use as a
 packaging material without loss of potential activity associated to the
 initiator. Further, the subject compositions have been found to be readily
 activated by subjection to ultraviolet radiation and to provide oxygen
 scavenging properties without having the residual initiator or the
 by-products formed within the oxygen scavenging layer migrate into the
 food material, especially fatty material, during normal use.
 To prepare oxygen scavenging layers and articles, the desired components
 thereof are preferably melt-blended at a temperature in the range of
 50.degree. C. to 300.degree. C. However, alternatives, such as the use of
 a solvent followed by evaporation, may also be employed. The blending may
 immediately precede the formation of the finished article or preform or
 precede the formation of a feedstock or masterbatch for later use in the
 production of finished packaging articles. When the blended composition is
 used to make film layers or articles, (co)extrusion, solvent casting,
 injection molding, stretch blow molding, orientation, thermoforming,
 extrusion coating, coating and curing, lamination, extrusion lamination or
 combinations thereof would typically follow the blending.
 The amounts of the components which are used in the oxygen scavenging
 compositions, or layers have an effect on the use, effectiveness and
 results of this method. Thus, the amounts of oxidizable organic compound,
 transition metal catalyst and photoinitiator, as well as any antioxidant,
 polymeric diluents or additives, can vary depending on the article and its
 end use.
 For instance, the primary function of an oxidizable organic compound of the
 oxygen scavenger composition is to react irreversibly with oxygen during
 the scavenging process, while the primary function of the transition metal
 catalyst is to facilitate this process. Thus, to a large extent, the
 amount of oxidizable organic compound will affect the oxygen capacity of
 the composition, i.e., affect the amount of oxygen that the composition
 can consume. The amount of transition metal catalyst will affect the rate
 at which oxygen is consumed. Because it primarily affects the scavenging
 rate, the amount of transition metal catalyst may also affect the
 induction period.
 The amount of oxidizable organic compound may range from 1 to 99%,
 preferably from 10 to 99%, by weight of the film, layer or article
 containing the oxygen scavenging composition of the present invention. For
 example, in a coextruded film, the scavenging layer would comprise the
 particular layer(s) in which both oxidizable organic compound, transition
 metal catalyst and photoinitiator are present together. A film, layer, or
 article containing said composition is herein after referred to as a
 scavenging component.
 The amount of transition metal catalyst may range from 0.001 to 1% (10 to
 10,000 ppm) of the scavenging component, based on the metal content only
 (excluding ligands, counterions, etc.). In the event the amount of
 transition metal catalyst is less than 1%, it follows that the oxidizable
 organic compound, and benzophenone derivative as well as any diluent
 and/or other additives, will comprise substantially all of the scavenging
 component, i.e. more than 99% as indicated above for the oxidizable
 organic compound.
 The subject benzophenone derivatives act as a photoinitiator which has a
 primary function of enhancing and facilitating the initiation of oxygen
 scavenging upon exposure to radiation. The amount of photoinitiator can
 vary. In many instances, the amount will depend on the oxidizable
 compounds used, the wavelength and intensity of radiation used, the nature
 and amount of antioxidants used, as well as the particular photoinitiator
 used. The amount of photoinitiator also depends on how the scavenging
 component is used. For instance, if the photoinitiator-containing
 component is placed underneath a layer which is somewhat opaque to the
 radiation used, more initiator may be needed. For most purposes, however,
 the amount of photoinitiator will be in the range of 0.01 to 10%, more
 preferably in the range of 0.1 to 1%, by weight of the total composition.
 The exact amount required can be readily determined by the artisan and
 should be sufficient to provide an induction period of less than five
 days, preferably less than three days and most preferably less than one
 day.
 The total amount of antioxidant which may be present in the composition may
 affect the results achieved. As mentioned earlier, such antioxident
 materials are usually present in oxidizable organic compounds or diluent
 polymers to prevent oxidation and/or gelation of the polymers prior to the
 induction period. Typically, they are present in about 0.01 to 1% by
 weight. However, additional amounts of antioxidant may also be added if it
 is desired to tailor the induction period as described above.
 When one or more diluent polymers are used, those polymers can comprise, in
 total, as much as 99% by weight of the scavenging component.
 Any further additives employed normally will not comprise more than 10% of
 the scavenging component, with preferable amounts being less than 5% by
 weight of the scavenging component.
 The method of this invention can be used with packaging articles used in a
 variety of fields. Packaging articles typically come in several forms
 including rigid containers, flexible bags, combinations of both, etc.
 Typical rigid or semi-rigid articles include plastic, paper of cardboard
 cartons or bottles such as juice containers, soft drink containers,
 thermoformed trays or cups which have wall thicknesses in the range of 100
 to 1000 micrometers. Typical flexible bags include those used to package
 many food items, and will likely have thicknesses of 5 to 250 micrometers.
 The walls of such articles either comprise single or multiple layers of
 material.
 The scavenging component of the present invention can be used as a single
 scavenging layer or a scavenging layer as part of a multilayer article
 such as those described in. U.S. Pat. No. 5,350,622, which teaching is
 incorporated herein by reference, as if setforth in full. Single layered
 articles can be prepared by solvent casting or by extrusion. Multilayered
 articles are typically prepared using coextrusion, coating, lamination or
 extrusion lamination. The additional layers of a multilayered article may
 include "oxygen barrier" layers, i.e. those layers of material having an
 oxygen transmission rate equal to or less than 500 cubic centimeters per
 square meter per day per atmosphere (cc/(m.sup.2.multidot.d.multidot.atm))
 at room temperature, i.e. about 25.degree. C. Typical oxygen barriers
 comprise poly(ethylene vinylalcohol), poly(vinylalcohol),
 polyacrylonitrile, polyvinyl chloride, poly(vinylidene dichloride),
 polyethylene terephthalate, silica, and polyamides such as Nylon 6, MXD6,
 and Nylon 6,6. Copolymers of certain materials described above, and metal
 foil layers, can also be employed.
 Other additional layers may include one or more layers which are permeable
 to oxygen. In one preferred packaging construction, especially for
 flexible packaging for food, the layers include, in order starting from
 the outside of the package to the innermost layer (that exposed to the
 cavity within a formed package suitable for containing a packaged
 material) of the package, (i) an oxygen barrier layer, (ii) a scavenging
 layer, i.e. the scavenging component as defined earlier, and optionally,
 (iii) an oxygen permeable layer. Control of the oxygen barrier property of
 (i) allows a means to regulate the scavenging life of the package by
 limiting the rate of oxygen entry to the scavenging component (ii), and
 thus limiting the rate of consumption of scavenging capacity. Control of
 the oxygen permeability of layer (iii) allows a means to set an upper
 limit on the rate of oxygen scavenging for the overall structure
 independent of the composition of the scavenging component (ii). This can
 serve the purpose of extending the handling lifetime of the films in the
 presence of air prior to sealing of the package. Furthermore, layer (iii)
 can provide a barrier to migration of the individual components in the
 scavenging films or by-products of scavenging into the package interior.
 Even further, layer (iii) also improves the heat-sealability, clarity
 and/or resistance to blocking (the tendency of film to cling to itself,
 especially during storage and handling) of the multilayer film. Thus,
 layer (ii) can be either directly or indirectly exposed to the cavity of
 the formed package.
 Further additional layers such as adhesive layers may also be used.
 Compositions typically used for adhesive layers include anhydride
 functionalized polyolefins and other well-known adhesive layers.
 Once the components have been chosen and formulated for the desired
 scavenging composition, layer or article, the method of this invention
 employs exposing the composition, layer or article to radiation in order
 to initiate oxygen scavenging. The initiation of oxygen scavenging of an
 oxygen scavenger composition is defined herein as facilitating scavenging
 such that the induction period of oxygen scavenging is significantly
 reduced or eliminated. As indicated above, the induction period is the
 period of time before the scavenging composition exhibits useful
 scavenging properties.
 The radiation used in this method should be ultraviolet light having a
 wavelength of from about 200 to 450 nanometers (nm) and preferably has a
 wavelength of about 200 to 400 nm. It is preferred to use UV radiation in
 the UVA, UVB or UVC ranges. As used herein, UVA means radiation having a
 wavelength of about 315-400 nm; UVB has a range of about 280-315 nm, and
 UVC has a range of about 200-280 nm. When employing this method, it is
 preferable to expose the oxygen scavenger composition to at least 0.1
 Joules per gram of scavenging component. A typical amount of exposure is
 in the range of 10 to 200 Joules per gram. The radiation can also be an
 electron beam at a dosage of about 0.2 to 20 megarads, preferably about 1
 to 10 megarads. Other sources of radiation include ionizing radiation,
 such as gamma, x-rays or corona discharge. The radiation exposure is
 preferably conducted in the presence of oxygen. The duration of exposure
 depends on several factors including, but not limited to, the amount and
 specific photoinitiator compound present, thickness of the layers to be
 exposed, amount of any antioxidant present, and the wavelength and
 intensity of the radiation source.
 When using oxygen scavenging layers or articles, the exposure to radiation
 can be during or after the layer or article is prepared. If the resulting
 layer or article is to be used to package an oxygen sensitive product,
 exposure can be just prior to, during, or after packaging. However, in any
 event, radiation exposure is required prior to using the layer or article
 as an oxygen scavenger. For best uniformity of radiation, the exposure
 should be conducted at a processing stage where the layer or article is in
 the form of a flat sheet.
 In order to use the method of this invention in the most efficient manner,
 it is preferable to determine the oxygen scavenging capabilities, e.g.
 rate and capacity, of the oxygen scavenger. To determine the rate of
 oxygen scavenging, the time elapsed before the scavenger depletes a
 certain amount of oxygen from a sealed container can be readily measured.
 In some instances the scavenger's rate can be adequately determined by
 placing a film comprising the desired scavenger in an air-tight, sealed
 container of a certain oxygen containing atmosphere, e.g. air which
 typically contains 20.6% oxygen by volume. Then, over a period of time,
 samples of the atmosphere inside the container are removed to determine
 the percentage of oxygen remaining. Usually, the specific rates obtained
 will vary under different temperature and atmospheric conditions. Unless
 otherwise noted, the rates indicated in the Examples are at room
 temperature and one atmosphere of air.
 When an active oxygen barrier is needed, a useful scavenging rate can be as
 low as 0.05 cc oxygen (O.sub.2) per gram of oxidizable organic compound in
 the scavenging component per day in air at 25.degree. C. and at 1
 atmosphere pressure. However, certain compositions, e.g. those containing
 the ethylenically unsaturated oxidizable organic compounds, have the
 capability of rates equal to or greater than 0.5 cc oxygen per gram per
 day, thus making such compositions suitable for scavenging oxygen from
 within a package, as well as suitable for active oxygen barrier
 applications. The scavengers comprising ethylenically unsaturated
 hydrocarbons are capable of more preferable rates equal to or greater than
 5.0 cc O.sub.2 per gram per day.
 Oxygen scavenging films initiated in accordance with the present invention
 exhibit oxygen scavenging rates, depending upon the formulation and type
 of package to which the film is applied, of between about 1 cc/m.sup.2
 /day to about 100 cc/m.sup.2 /day at temperatures of about 4.degree. C.
 when measured 4 days after triggering. For modified atmosphere packages
 (MAP) having a modified atmosphere headspace, (MAP, 1-2% O.sub.2), oxygen
 scavenging film triggered as set forth above exhibits an oxygen scavenging
 rate of between about 20 cc/m.sup.2 day to about 66 cc/m.sup.2 /day at
 about 4.degree. C. when measured 4 days after initiation, thereby
 advantageously removing oxygen from the head space of such a package so as
 to reduce or eliminate adverse effects upon the product or article
 packaged therein.
 When it is desired to use this method with an active oxygen barrier
 application, the initiated oxygen scavenging activity, in combination with
 any oxygen barriers, should create an overall oxygen transmission rate of
 less than about 1.0 cubic centimeters per square meter per day per
 atmosphere at 25.degree. C. The oxygen scavenging capacity should be such
 that this transmission rate is not exceeded for at least two days. For
 many commercial applications, it is expected that the scavenging rates be
 able to establish an internal oxygen level of less than 0.1% in as soon as
 possible, preferably less than about four weeks' time.
 Once scavenging has been initiated, the scavenger, layer or article
 prepared therefrom, should be able to scavenge up to its capacity, i.e.
 the amount of oxygen which the scavenger is capable of consuming before it
 becomes ineffective. In actual use, the capacity required for a given
 application depends on:
 (1) the quantity of oxygen initially present in the package,
 (2) the rate of oxygen entry into the package in the absence of the
 scavenging property,
 (3) the amount of oxygen which might be generated or absorbed by the
 package contents, and
 (4) the intended shelf life for the package.
 When using scavengers comprising ethylenically unsaturated compounds, the
 capacity can be as low as 1 cc oxygen per gram, but can be at least 50 cc
 oxygen per gram. When such scavengers are in a layer, the layer will
 preferably have an oxygen capacity of at least 250 cc oxygen per square
 meter per mil thickness and more preferably at least 1200 cc oxygen per
 square meter per mil thickness.
 As stated above, the present oxygen scavenging composition has unexpectedly
 been found to be readily activated by subjection to ultraviolet radiation,
 provide good oxygen scavenging properties and to do the above without
 having residual initiator or by-products migrate into the food material,
 especially fatty foods, during normal use.
 For the purposes of this application, substantially non-migratory means
 that no more than about 500 parts per billion (ppb), preferably no more
 than about 100 ppb, and even more preferably no more than 50 ppb,
 initiator is extracted by a food simulant from the article under food
 simulation conditions. The U.S. Food and Drug Administration has developed
 test procedures for determining the ability of a substance to migrate into
 various food substances.
 A migration test is an analysis to detect the presence of one material
 mixed in another. The test results are properly reported as some non-zero
 number. Where no migrating material has been found, the results are
 properly reported as "not more than" or "less than" the least amount of
 material that the test can reliably detect (the threshold level of
 detection). Amounts in the low parts per billion (ppb) range are generally
 recognized as insignificant in most instances. Although some products,
 such as purified oils, may be readily analyzed for migratory materials,
 many other products present substantial practical problems. For that
 reason, a food-simulating solvent can be used to help establish the nature
 and amount of migration of a material from an article into a product.
 The food simulant for a fatty food may be a liquid food oil or 95% ethanol
 in water. The liquid food oil may be a natural product, such as olive oil
 or corn oil, a derivative of a natural oil, such as a fractionated coconut
 oil composed of saturated (30-70%) C.sub.8 and (30-50%) C.sub.10
 triglycerides commercially available as Miglyol 812.TM., or a mixture of
 synthetic triglycerides, primarily C.sub.10, C.sub.12, and C.sub.14
 (commercially available as HB307). For low-and high-alcoholic foods, the
 food simulant is 10% or 50% solution of ethanol in water. For aqueous and
 acidic foods, the typical solvent is 10% solution of ethanol in water,
 although water and acetic acid may also be used.
 Because a product may contact many foods with different processing
 conditions and shelf lives, testing is done under the most sever
 temperature and time conditions to which a food-contact article containing
 the material of interest will be exposed. For high temperature, heat
 sterilized or retorted packaging processes, the package is heated to
 121.degree. C. (250.degree. F.) for two hours followed by holding at
 40.degree. C. (104.degree. F.) for 238 hours, and analyzed periodically
 for a total holding time of 10 days.
 The same testing protocol is used for boiling water sterilized processes,
 except that the highest temperature is 100.degree. C. (212.degree. F.).
 For hot-filled processes, food simulants are added to test samples at
 100.degree. C. (212.degree. F.), held for 30 minutes, and then allowed to
 cool to 40.degree. C. (104.degree. F.). For room temperature applications,
 a test temperature of 40.degree. C. (120.degree. F.) for 10 days has been
 recommended, and for refrigerated or frozen food applications, the test
 temperature is 20.degree. C. (68.degree. F.).
 Results are reported in terms of milligrams of substance extracted per
 square inch (mg/in.sup.2) of surface area, for ease of conversion to
 concentration in food. If ten grams of food are in contact with one square
 inch of packaging surface, migration of 0.01 mg/in.sup.2 corresponds to a
 concentration in food of 1 ppm.
 In order to determine the accuracy and precision of a given test method,
 migration test solutions (not pure solvents) are spiked with the material
 of interest at known levels to serve as controls. Generally, the spiked
 solutions contain about 1/2, 1 and 2 times the analyzed concentration of
 the material of interest. Unless otherwise noted, control samples are
 polymer films or placques formulated without the material of interest.

The following examples illustrate the practice of the present invention
 without limiting its scope or the scope of the claims which are appended
 hereto. All parts and percentages indicated in the examples are by weight,
 unless indicated otherwise.
 EXAMPLE 1
 Photoinitiators were screened for their ability to initiate oxygen
 absorption and cause oxygen scavenging by melt blending scavenging resin
 composed of 1,2-poly(butadiene) (RB830 available from Japan Synthetic
 Rubber) with sufficient cobalt neodecanoate (Ten-Cem.RTM. available from
 OMG, Inc.) to give 350 ppm dosage of cobalt metal, and 0.5% by weight of a
 photoinitiator under study in a Brabender batch mixture. Each formulation
 was then pressed into films (usually 10-25 mils thick). The films were
 then cut into squares (200 cm.sup.2) and exposed to UV irradiation which
 were then sealed in oxygen barrier bags and inflated with 300 cc of air
 and retained at 25.degree. C. Portions of the headspace gas were
 periodically withdrawn and analyzed for oxygen with a Mocon LC 700.degree.
 F. oxygen analyzer. Table 1 provides results of films irradiated with a
 Fusion Systems lamp equipped with an H bulb, at a dose of 0.25 to 0.5
 J/cm.sup.2 measured at 365 nm. Table 2 provides results of films
 irradiated with an Amergraph.RTM. UV unit (low intensity UVA) at a dosage
 of about 1 J/cm.sup.2 measured at 365 nm. The average rate is calculated
 by considering only the end points, with the following formula: Average
 Rate=cc O.sub.2 scavenged/(m.sup.2.multidot.day), and in this example was
 calculated after 30 days. The peak instantaneous rate is the highest
 scavenging rate observed during any sampling period and is calculated by
 the change in volume (cc) of oxygen scavenged per m.sup.2 over incremental
 time (days) change.
 The results of Table 1 and 2 below show that each of the derivatives of
 benzophenone including those of the instant invention provide short
 induction periods and good average rates of oxygen scavenging. Further,
 the samples which illustrate the present invention provide superior peak
 oxygen scavenging rates to those formed with comparative initiators (c).
 TABLE 1
 Summary of Photoinitiators
 Fusion H-bulb Triggering
 Induc-
 tion
 Period Average Rate Peak Ins. Rate
 Photoinitiator (days) (cc O.sub.2 /m.sup.2.multidot.day) (cc
 O.sub.2 /m.sup.2.multidot.day)
 4-allyloxybenzophenone &lt;3 174 343(4)
 4,4'-diallyloxybenzophenone &gt; 1 &lt; 4 102 195(4)
 4-dodecycloxybenzophenone &gt; 1 &lt; 4 106 134(11)
 4,4'-diphenoxybenzophenone &gt; 1 &lt; 5 132 225(15)
 4-benzoylbiphenyl &gt; 1 &lt; 2 133 184(13)
 (4-phenylbenzophenone) (c)
 Benzophenone (c) &lt;3 90 200
 2-methoxybenzophenone (c) &lt;1 137 210(16)
 4-methoxybenzophenone (c) &gt; 1 &lt; 3 115 160(2)
 TABLE 2
 Summary of Photoinitiators
 UVA Triggering
 Average Peak
 Induction Rate Ins. Rate
 Period (cc O.sub.2 / (cc O.sub.2 /
 Photoinitiator (days) m.sup.2.multidot.day)
 m.sup.2.multidot.day)
 Benzophenone (c) &lt;1 171 874(2)
 4-allyloxybenzophenone &lt;1 137 369(5)
 4-4'-diallyloxybenzophenone &lt;1 147 1,155(1)
 4,4'-diphenoxybenzophenone &gt; 1 &lt; 5 141 323(12)
 Benzophenone (c) &lt;1 171 874(2)
 4,4'-bis(benzoyl)diphenylether (c) &gt; 1 &lt; 5 163 348(8)
 EXAMPLE 2
 Several photoinitiators were evaluated for oxygen scavenging at low
 temperature conditions by forming compositions having initiators at a
 constant loading of 0.5% by weight which were compounded into a blend of
 polyethylene and polybutadiene consisting of 60% by weight low density
 polyethylene (LDPE) (PE1017 resin available from Chevron Chemical Company,
 Houston, Tex.) and 40% 1,4-polybutadiene (Taktene 1202 available from
 Bayer) along with 680 ppm cobalt neodecanoate (Ten-Cem.RTM. from OMG,
 Inc., Cleveland, Ohio). The blends were used as the oxygen scavenging
 layer ("OSL") in film structures having linear low density polyethylene
 (LLDPE) outer layers. Three-layer films were made comprising
 LLDPE/OSL/LLDPE on a Randcastle micro-extrusion unit, and films were
 triggered with a 1-minute dose of UVC from UVC lamps (Anderson-Vreeland,
 Bryan, Ohio). Samples were tested in the same manner as described in
 Example 1, except that air was replaced with 1% oxygen in nitrogen and
 samples were stored under refrigerated conditions (4.degree. C.). The
 results are shown in Table 3 below.
 TABLE 3
 Survey of Photoinitiators
 1 Minute UVC, Refrigerated, MAP
 Randcastle 3-layer Films: LLDPE/OSL/LLDPE (target 1/1/1 mil)
 Ave. Ins.
 Rate a Rate
 Photoinitiator Induction (cc O.sub.2 / (cc O.sub.2 /
 Sample (0.5% by wt. in OSL) Period m.sup.2.multidot.d)
 m.sup.2.multidot.d)
 A 4-allyloxybenzophenone &lt;1 35 55(1)
 B 4,4'-diallyoxybenzophenone &lt;1 27 50(1)
 C 4-dodecyloxybenzophenone &lt;1 36 63(2)
 D 4,4'-diphenoxybenzophenone &lt;1 34 61(1)
 E benzophenone (c) &lt;1 23 19(2)
 F 4,4'-bis(benzoyl)-diphenylether &lt;1 13 22(1)
 (c)
 a. Average rate calculated after 3 days.
 The above results show that under low temperature application each sample
 A, B, C and D exhibited higher rates of oxygen absorption and peak
 absorption rates than provided by the comparative samples E and F formed
 with non-derivatized benzophenone and diphenyl ether, respectively.
 Each of the films made above were tested for migration of the
 photoinititator and/or by-product material using an approved FDA
 procedure. Each sample was subjected to an FDA approved food simulant
 composed of a mixture of caprylic and capric triglycerides (MiglyolTm 812
 of Huls America, Piscataway, N.J.) to provide 10 g of simulant per square
 inch of film surface. The extraction was conducted at room temperature
 (25.degree. C.) for 10 days. The simulant was then analyzed by high
 performance liquid chromatography for the presence of photoinitiator
 and/or by-product.
 The results, shown in Table 4 below, show that only very low amounts of
 derivitized benzophenone photoinitiators migrate while each of the
 comparative photoinitators (included herein was a sample having
 4-benzoylbiphenyl: Sample G) show undesirable high levels of migration.
 TABLE 4
 Migration Test Results for Benzophenone Derivatives
 Migration.sup.b
 Sample Photoinitiator ppb
 A 4-allyloxybenzophenone.sup.a &lt;16
 B 4,4'-diallyloxybenzophenone &lt;47
 C 4-dodecyloxybenzophenone.sup.a &lt;47
 D 4,4'-diphenoxybenzo- &lt;47
 phenone
 E Benzophenone (c) 150
 F 4,4'-bis(benzoyl)diphenyl 1,125
 ether (c)
 G 4-benzoylbiphenyl (c) 1,015
 .sup.a 4-Hydroxybenzophenone, a possible degradation by-product of these
 photoinitiators, was not detected.
 .sup.b Assuming 10 g of food simulant per square inch of film surface.
 (c) comparative
 EXAMPLE 3
 Three layers blown films consisting of poly(ethylene-vinyl acetate) (EVA),
 an Oxygen Scavenging Layer (OSL) and Linear Low Density Poly(ethylene)
 (LLDPE) were prepared. The OSL was formed with 10% of a masterbatch
 indicated below and 90% diluent composed of 60% low density polyethylene
 and 40% 1,4-polybutadiene. In each case the materials were blended
 together using a twin screw extruder. Each masterbatch contained 1% of
 photoinitiator and 6,800 ppm cobalt as neodecanoate.
 The film samples were irradiated with UVC light (254 nm) for one minute and
 were tested using the standard refrigerated Modified Atmosphere (MAP)
 Headspace Scavenging Test (HST). Each film was tested in triplicate and
 the Average and peak Instantaneous Rates are presented in Table 5 below as
 the means of three replicates. The number in parenthesis after the mean
 peak Instantaneous Rate is the number of days after triggering required to
 reach that rate.
 Film samples which were subjected to oxygen atmosphere for 12 days using
 the standard refrigerated Headspace Scavenging Test were cut into
 (circular) test specimens, placed over the opening of individual aluminum
 test cells, and exposed to corn oil (FDA-approved fatty food simulant) for
 10 days at room temperature. Each film was tested in triplicate. An
 aliquot of the corn oil that had been in contact with each film was then
 collected and analyzed by reverse-phase High Pressure Liquid
 Chromatography (HPLC) for the presence of photoinitiator. A sample of the
 virgin corn oil was similarly analyzed as a negative control and, as
 expected, showed no evidence for the compounds being determined.
 The results of both the induction scavenging up-take and migration tests
 are given in Table 5 below.
 TABLE 5
 Average
 Induc- Ave. Ins. Migration
 tion Rate Rate (10 g corn oil/
 Masterbatch Period (cc O.sub.2 / (cc O.sub.2 / in.sup.2 film)
 Sample (10% in OSL) (days) m.sup.2.multidot.d) m.sup.2.multidot.d)
 ppb
 A (4,4'-dimethyl- &lt;1 24 73(1) &lt;25
 benzophenone)
 B (4,4'-dimethoxy- &lt;1 34 64(1) &lt;36
 benzophenone)
 C Benzophenone &lt;1 33 78(1) 625
 The above results show that the derivatized benzophenones of the present
 invention provide short induction periods, good rates of oxygen scavenging
 while not exhibiting undesired migration properties. When subjected to a
 food simulant for fatty foods (worst case scenario). In comparison,
 unsubstituted benzophenone exhibited undesirable high levels of migration.