MXPA00003079A - Method and compositions for improved oxygen scavenging - Google Patents

Abstract

A composition capable of scavenging oxygen composed of (i) a copolymer having long chain branches comprising units derived from monomers of ethylene and at least one vinyl unsaturated alicyclic monomer;(ii) a transition metal catalyst;(iii) preferably, with a photoinitiator;and (iv) optionally, a polymeric diluent.

Description

"METHOD AND COMPOSITIONS FOR IMPROVED OXYGEN PURIFICATION" FIELD OF THE INVENTION The invention is generally related to compositions, articles and methods of purifying oxygen in environments containing oxygen-sensitive products, particularly food products and beverage. More specifically, the present invention is directed to oxygen scavenger compositions composed of copolymers having long chain branching derived from ethylene monomers and an unsaturated vinyl alicyclic compound, a transition metal compound and, optionally, a compound photoinitiator The subject matter composition can be easily formed into films or mixed with other film-forming polymers to provide an improved oxygen scavenger packing material. As will be apparent from the discussion presented below, the term "oxygen scavenger" or "scavenger" refers to materials that consume, deplete or reduce the amount of oxygen in a given environment.

BACKGROUND OF THE INVENTION It is well known that limiting the exposure of oxygen sensitive products to oxygen maintains and improves the quality and "shelf life" of the product. For example, by limiting the oxygen exposure of oxygen sensitive food products in a packing system, the quality of the food product is maintained and the decomposition of the food is prevented. In addition, this packing also keeps the product in the inventory in a more prolonged manner, therefore reducing the costs incurred in waste and having to replenish. In the food packaging industry, several means have already been developed to limit the disposition to oxygen. Currently, the most commonly used media includes modified atmosphere packing (MAP), vacuum packing and oxygen barrier film gasketing. In the first two cases, the reduced oxygen environments are used in the packing, while in the latter case, oxygen is physically prevented from entering the packing environments. Another, more recent means to limit exposure to oxygen involves incorporating an oxygen scavenger into the packing structure. Incorporating a debugger into the package can provide a uniform debugging effect throughout the package. In addition, this incorporation can provide a means of intercepting and purifying oxygen as it is passing through the walls of the package (referred to herein as "active oxygen barrier"), thereby maintaining the Lowest possible oxygen level through the package. An example of an oxygen scavenger incorporated in the oxygen scavenger wall is illustrated in European Applications Nos. 301,719 and 380,319 as well as in PCT 90/00578 and 90/00504. See also United States Patent Number 5,021,515. The oxygen scavenger disclosed in these patent applications comprises transition metal / polyamide catalyst compositions. Through the filtration catalyzed by the polyamide, the wall of the package regulates the amount of oxygen that reaches the interior of the package (active oxygen barrier). However, it has been found that at the beginning of the useful oxygen purification, that is, up to about 5 cubic centimeters (ce) of oxygen per square meter per day at ambient conditions, it can occur for as long as 30 days and, therefore, Therefore, it is not acceptable for many applications. Further, with respect to the incorporation of the polyamide / catalyst system in the packing material, the polyamides are typically incompatible with the thermoplastic polymers, e.g. ethylene vinyl acetate copolymers and low density polyethylenes, typically used to make flexible packaging materials and films. Still in an additional way, when the polyamides are used by themselves to make a flexible package wall, they usually result in inappropriate rigid structures. Polyamides are more difficult to process when compared to the thermoplastic polymers typically used to make the flexible gasket. U.S. Patent No. 5,399,289 discloses oxygen scavenger compositions composed of ethylenically unsaturated hydrocarbon polymers and transition metal catalysts. The polymers are required to have a low ethylenic bond content of 0.01 to 10 equivalents per 100 grams of polymer, in order to provide a product with both debugging and physical properties retained. Various mixtures of conventional homopolymers, copolymers and polymer are disclosed. Because these polymers are amorphous materials are difficult to mix and processed with film forming semi-crystalline polymers as low density polyethylene and the like, which are conventionally used to provide flexible and similar applications packing films.

U.S. Patent No. 5,211,875 also discloses the use of ethylenically unsaturated compounds together with a transition metal as well as a photoinitiator to facilitate the initiation of the effective depuration activity. The ethylenically unsaturated polymers and copolymers suggested by this reference are also amorphous materials and, therefore, have low compatibility with conventional film-forming polymers, such as polyethylenes. Due to the limited compatibility of the scrubbing polymer with a film-forming polymer, it is required to limit the amount of the scrubbing polymer in the mixture and is usually confronted with a resulting composition that is difficult to process. It is highly desirable to have an oxygen scavenging composition that is composed of a polymeric material having a high processing capacity, while it can be formed directly into films useful in the packing field by having high compatibility with semi-crystalline polyolefins and providing a highly processable with these polymeric materials having known utility for packing application. In addition, it is highly desirable that there be a film or composition composed of an ethylenically unsaturated polymer capable of purifying oxygen that can substantially retain its physical properties after significant oxygen scavenging. Still further, it is highly desirable to provide an oxygen scavenger composition that does not provide, during oxygen scavenging, the formation of a byproduct that can deviate from the color, taste or odor of the packaged product.

COMPENDIUM OF THE INVENTION The present invention is directed to oxygen scavenger compositions composed of (i) a copolymer having long chain branches comprising units derived from ethylene monomers and at least one unsaturated vinyl alicyclic monomer; (ii) a transition metal catalyst; (iii) preferably also with a photoinitiator; and (iv) optionally, a polymeric diluent. The present composition has been found to exhibit a high degree of processability to form film products; which is highly compatible with conventional polymers used in the formation of films such as semi-crystalline polyolefins and the like; which exhibits significant ability to purify oxygen while being part of a film or article used to form a package for oxygen sensitive products; and not to produce significant byproducts that would detract from the odor, color and / or taste of the packaged product.

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to a composite oxygen scavenger composition (i) of at least one copolymer having long chain branches comprising units derived from ethylene and at least one unsaturated vinyl alicyclic comonomer; (ii) a transition metal catalyst; (iii) preferably also with a photoinitiator; and (iv) optionally, with a polymeric diluent. The present long chain branched copolymer is semi-crystalline to a degree sufficient to make it highly compatible with polyolefins and semaks, which are conventionally used to provide packing films and laminated structures and to provide a composition or blends having high capacity of processing, eg, low susceptibility to melt fracture even under conditions of high shear stress such as those found in extrusion processing.

The novel copolymers found useful in the present invention are fully described in the co-pending North American Patent Application Serial Number (Attorney's Note Number 9380), filed concurrently with the present application. The teachings of the co-pending application are they are incorporated here by reference in their entirety. The processing capacity has been attributed to the structural particularity of the presence of long chain branching together with the copolymer object material chain as well as its low molecular weight distribution. The molecular weight or polydispersity distribution of a polymer (the ratio of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn) is an influence on the processing capacity., polymers that have a low ratio of Mw / Mn and a high melt flow index ratio (I10 / I2) that is carried out at different loads (10 kilograms and 2 kilograms), as described in method D -1238 of the American Society for the Testing of Materials are indicative of a polymer structure having long chain branching and, in turn, are known to provide desired characteristics of processability.

The present oxygen scavenging composition has, as an active scavenging agent, an ethylene copolymer containing a long chain branching (having branching chains of> 6 carbon atoms) and at least one comonomer containing an alicyclic group. unsaturated vinyl, represented by the formula: wherein c7 represents an ethylenically unsaturated alicyclic group of 6 to 12 carbon atoms which may further have one or more of its hydrogen atoms of the alicyclic group substituted by a hydrocarbon of 1 to 2 carbon atoms, as will be fully described continuation. The subject matter copolymer "must have ethylene as one of its monomeric forming groups, In addition, the subject matter copolymer must have, as one of its monomeric forming groups, at least one monomer of the formula I, mentioned above. (i) a hydrogen atom suspended from the beta-carbon and the gamma-carbon of the monomer I, (ii) a gamma-carbon alicyclic atom containing a suspended beta-carbon group, (iii) at least one double bond from carbon to non-aromatic ethyl carbon within the alicyclic group.

The group containing the alicyclic gamma-carbon atom is selected from an unsaturated (non-aromatic) alicyclic group of 6 to 12 carbon atoms such as, for example, 2-cyclohexenyl, 3-cyclohexenyl, 2,5-cyclohexadienyl, cyclooctenyl, 3-cyclooctenyl, 4-cyclooctenyl, 2,6-cyclooctadienyl, cyclododecatrienyl and the like. The alicyclic groups, in addition to having no ethylenic saturation within the alicyclic group, may have one or more substitutions of the hydrocarbon group of 1 to 20 carbon atoms from the alicyclic ring as long as the gamma-carbon atom has a hydrogen atom discontinued. The substitution may be an aliphatic hydrocarbon such as for example methyl, ethyl, isopropyl, pentyl and the like, an alkenyl group such as for example 3-butenyl, 4-hexenyl and the like, or a saturated or unsaturated alicyclic group which may be melted or not melt in the alicyclic ring containing the gamma-carbon atom. The subject material copolymer may contain, in addition to the ethylene monomers and the monomer 1 described above, at least one additional monomer other than those previously defined. For example, the additional monomer may be an alpha-olefin of 3 to 20 carbon atoms such as propylene, 1-butene, 1-hexene, 3-methylbutene-1, 1-octene-4-methyl-pentene and above; cycloolefins such as for example cyclopentene, norbornene, tetracyclododecene and the like, and non-conjugated dienes such as for example 5-ethylidene-2-norbornene, 5-vinyl-2-norbornene, 5-methylene-2-norbornene, 2,5-norbornadiene , 1, 3-divinylcyclohexane, 1/4-divinylcyclohexane, l-allyl-5-vinylcyclooctane, dicyclopentadiene, 1,4-hexadiene, 1,7-octadiene and the like. The ethylene must be a comonomer that forms the subject matter copolymer. It may be present in from 0.01 to about 99 mole percent of the copolymer, preferably from 25 to 95 mole percent and especially preferably from 75 to 90 mole percent of the copolymer formed. The monomer I must be a comonomer that forms the subject matter copolymer. It can be selected from one or a mixture (in any proportion) of more than one monomer I. It may be present in from about 1 to about 35 mole percent of the copolymer, preferably from about 1 to 15, and more preferably from 1 to 10 mole percent of the copolymer formed. The remainder of the subject matter copolymer can be formed of other copolymerizable monomeric compounds, as described above.

The resulting copolymer has been found to have a critical molecular weight distribution and long chain branches as demonstrated by its polydispersity (Mw / Mn) and by its high melt flow index ratio (I10 / I2). Its polydispersity normally has a value of at least about 1.5 to about 5, and preferably at least from about 1.7 to about 2.5, and especially preferably from 1.9 to 2.5. In combination, in low polydispersity polymers, a long chain branched structure is shown which is present by the high values of the melt index ratio of at least about 8, and preferably of 8.5, and most preferably by at least about 10, as measured in accordance with Method D-1238 of the American Society for the Testing of Materials. Preferred copolymers of the present invention comprise units derived from ethylene comonomers and at least one vinyl alicyclic monomer wherein the alicyclic ring contains a carbon-to-carbon ethylene double bond, represented by the formula: IX where n and m are each selected independently of positive integers from 0 to 9, provided that the sum of n + m has a value of 3 to 9, and more preferably 3 to 5. The especially preferred copolymer of the present invention is formed of the vinyl ethylene and cyclohexene comonomers. This copolymer preferably has from about 1 to about 35 mole percent of vinyl cyclohexene, preferably from about 1 to 10, and especially preferably from about 2 to 8 mole percent of vinyl cyclohexene (which can be determined by Nuclear magnetic resonance analysis of carbon-13). The weight average molecular weight of the subject material copolymers will vary depending on the specific monomer I present, the amount of the monomer I present in the copolymer as well as the specific catalyst used in its formation. Normally, the weight average molecular weight will vary from about 10,000 to 1,000,000 being preferred from about 25,000 to 125,000. Molecular weight regulation can be achieved by having a hydrogen present in the polymerization reaction vessel during the formation and the branched copolymer of long chain subject material. The long chain branched copolymer has unexpectedly been found. Subject matter can be formed by solution polymerization using certain essentially non-stressed metallocene catalysts, as fully described in the copending US Patent Application.

Serial Number (Touch of Attorney Number 9380) whose teaching has been incorporated into the presence by present by reference. The solvent that forms the polymerization medium can be an inert liquid hydrocarbon (with respect to the present comonomers) which may for example be an aliphatic hydrocarbon having from 4 to 10 carbon atoms such as for example isobutane, pentane, isopentane or the like, or mixtures thereof (or an aromatic hydrocarbon, such as for example , benzene, toluene, xylene or the like Alternately, the solvent may have one or more of the monomers or, if appropriate, the third comonomer present in excess either alone or in addition with an inert diluent, such as the solvents described In the above, when a comonomer is used as a solvent for polymerization, it is preferred that it be selected from a monomer I. The purifying composition of the subject matter oxygen requires the presence of a transition metal compound as a scavenging catalyst, in combination with the long chain branched copolymer described above.

The transition metal catalyst may be a salt of a metal that is selected from the first, second or third transition series of the Periodic Table, and preferably those from the series of scandium to zinc (ie, Se, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn) with preferably iron, nickel or copper and manganese, being especially preferred and cobalt being that one especially preferred. Suitable counter ions for the metal include, but are not limited to chloride, acetate, oleate, stearate, palmitate, 2-ethylhexanoate, neodecanoate and naphthenate. Particularly preferred salts include cobalt (II), 2-ethylhexanoate, cobalt oleate and cobalt neodecanoate (II). The metal salt can also be an ionomer in which case a polymeric counterion is employed. These ionomers are well known in the art. The composition present when used to form a packing article can be composed only of the above described long chain branched copolymer and a transition metal catalyst. However, compounds such as photoinitiators can also be added to facilitate and control the initiation of oxygen scavenging properties. For example, it is often preferred to add a photoinitiator, or a mixture of different photoinitiators to the oxygen scavenger compositions, especially when antioxidants are included to prevent premature oxidation of that composition during processing. Suitable photoinitiators are well known to those skilled in the art as exemplified by the teachings of Patent Number WO 97/07161 and the Co-pending North American Application Serial No. 08 / 857,226, filed May 16, 1997, which is incorporated herein by reference in its entirety. Specific examples include, but are not limited to, benzophenone, o-methoxy-benzophenone, acetophenone, o-methoxy-acetophenone, acenaphthenequinone, methylethyl ketone, valerophenone, hexanophenone, alpha-phenyl-butyrophenone, p-morpholinopropiophenone, dibenzosuberone, 4- morpholinobenzophenone, benzoin, benzoinmethyl ether, 4-o-morpholinodeoxibenzoin, p-diacetylbenzene, 4-aminobenzophenone, 4'-methoxyacetonophenone, substituted and unsubstituted anthraquinone, alpha-tetralone, 9-acetylphenanthrene, 2-acetyl-phenanthrene, 10-thioxanthenone , 3-acetyl-phenanthrene, 3-acetylindole, 9-fluorenone, 1-indanone, 1,3,5-triacetylbenzene, thioxanthen-9-one, xanthene-9-one, 7-H-benz [de] anthracene-7 -one, tetrahydropyranyl ether of benzoin, 4-4 'bis (dimethylamino) -benzophenone, 1'-acetonaphthone, 2'-acetonaphthone, acetonaphthone and 2,3-butanedione, benz [a] anthracene-7, 12-dione , 2, 2-dimethoxy-2-phenylacetophenone, alpha, alpha-diethoxy-acetophenone, alpha, alpha-dibutoxyacetophenone, etc. Photosensitizers that generate singlet oxygen such as Rose Bengal, methylene blue and tertrafenilporfina can also be used as photoinitiators. Polymeric initiators include poly (ethylene carbon monoxide) and oligo [2-hydroxy-methyl-1- [4- (1-methylvinyl) phenyl] propanone]. The use of a photoinitiator is preferred because it usually provides faster and more efficient initiation. When actinic radiation is used, primers also provide initiation at longer wavelengths that are less expensive to generate and less harmful. When a photoinitiator is used, its main function is to improve and facilitate the initiation of oxygen purification when exposed to radiation. The amount of the photoinitiator may vary. In many cases, the amount will depend on the amount and type of monomer and present in the present invention, the wavelength and intensity of radiation used, the nature and amount of antioxidants used as well as the type of photoinitiator used. The amount of the photoinitiator also depends on the way in which the purifying composition is used. For example, if the composition containing the photoinitiator is placed below a layer that is somewhat opaque to the radiation used, more of the initiator may be required. For most purposes, however, the amount of the initiator when used will be within the range of 0.01 percent to 10 percent by weight of the total composition. The initiation of oxygen scavenging can be achieved by exposing the packing article to actinic or electron beam radiation, as will be described below. The antioxidants can be incorporated into the purifying compositions of this invention to control the degradation of the components during the stirring and shaping. An antioxidant, as defined herein, is any material that inhibits oxidative degradation or cross-linking of polymers. Typically, these antioxidants are added to facilitate the processing of the polymeric materials and / or to prolong their useful life. Even when these additives prolong the induction period for oxygen purification activity to occur in the absence of irradiation, when depuration properties of the layer or article are required, the layer or article (and any incorporated photoinitiator) may be exposed to radiation . Antioxidants such as 2,6-di (t-butyl) -4-methyl-phenol (BHT), 2,2 '-methylene-bis (6-t-butyl-p-cresol), triphenyl phosphite, tris- (nonylphenyl) phosphite and dilaurylthiopropionate would be suitable for use with this invention. When the antioxidant is included as part of the present composition, it should be used in amounts that will prevent oxidation of the components of the purifying composition as well as other materials present in a resulting mixture during formation and processing, but the amount should be less than that that could interfere with the activity of the debugger of the resulting layer, film, or article after the initiation has occurred. The specific amount needed will depend on the specific components of the composition, the specific antioxidant used, the degree and amount of thermal processing used to form the shaped article and the dosage and wavelength of radition applied to initiate oxygen scavenging and can be determine by conventional means. They are typically present in from about 0.01 percent to 1 percent by weight. The present copolymer has been found to provide a film that is suitable as a packing material. The present copolymer can be used as the only polymeric material that forms at least one layer of a film (the film can be a multilayer film having for example a gas barrier layer, a sealing layer, etc.). Alternatively, the subject matter copolymer containing the composition may further comprise one or more non-oxygen scavenging diluent polymers, known to be useful in packing film forming materials. These polymers are thermoplastic and make the film more adaptable for use as packing layers. Suitable diluent polymers 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 frequently used. Mixtures of different diluent polymers can also be used. In general, these polymers are semi-crystalline materials useful for forming packing materials and films. The selection of the polymeric diluent depends greatly on the article to be manufactured and the final use thereof. These selection factors are well known in the art. For example, it is known that certain polymers provide clarity, cleanliness, barrier properties, mechanical properties and / or texture to the resulting article. Other additives that may also be included in the oxygen scavenging layers include, but are not necessarily limited to fillers or fillers, pigments, coloring materials, stabilizers, processing aids, plasticizers, flame retardants, anti-fogging agents, etc. The amounts of the components that are used in the oxygen scavenging compositions or layers have an effect during the use, effectiveness and results of this method. Therefore, the amounts of the copolymer, the transition metal catalyst and any photoinitiator, antioxidant, diluents and polymeric additives may vary depending on the article and its end use. For example, one of the main functions of the long chain branched copolymer described above is to react irreversibly with oxygen during the purification process, while the main function of the transition metal catalyst is to facilitate this process. In this way to a considerable degree, the amount of the copolymer present will affect the oxygen scavenging capacity of the composition, i.e., it will affect the amount of oxygen that the composition can consume. The amount of the transition metal catalyst will affect the rate at which oxygen is consumed. Because it mainly affects the purification regime, the amount of the transition metal catalyst can also affect the induction period. It has been found that the long-chain branched polymers present when used as part of the present composition provide oxygen scavenging properties at a desirable rate and capacity, while causing the composition to have improved processing capacity and properties of compatibility through conventional ethylenically unsaturated polymers. In this manner, the present composition can be used to provide, by itself or as a mixture with the diluent film-forming polymers, such as polyolefins and the like, a packing material or film having improved processability properties. In addition, it is believed that the present oxygen scavenging composition consumes and depletes oxygen within the package cavity without deteriorating the color, taste and / or odor of the product contained within the package cavity. The amount of the copolymer of the present composition can vary from 1 percent to 99 percent, preferably from 10 percent to 90 percent by weight of the composition or composite layer of the composition wherein both the copolymer and the metal catalyst of transition are present (which will be referred to below as the "depuration composition" eg in a co-extruded film, the depuration composition would comprise the specific layer (s) wherein the copolymer components are present together and the transition metal catalyst). Typically, the amount of the transition metal catalyst can vary from 0.001 percent to 1 percent (from 10 to 10,000 parts per million) of the depuration composition based solely on the metal content (excluding the coordinating groups, counterions, etc.). .) in the case where the amount of the transition metal is less than 1 percent, it is evident that the copolymer and any of the additives will comprise essentially all the rest of the composition. Alternatively, when one or more essentially non-scavenging diluent polymers are used as part of the composition, those polymers can comprise, in total, as much as 99 percent, preferably up to 75 percent by weight, of the scavenging composition with the copolymer present and the transition metal catalyst and, if appropriate, the photoinitiator present in the ratios described above.

Any of the additional additives normally employed will not comprise more than 10 percent of the treatment composition and with preferable amounts being less than 5 weight percent of the treatment composition. The oxygen scavenging composition of the present invention may unexpectedly have improved properties not capable of being achieved by conventional compositions. First, the copolymers of the present composition can have a high non-saturation content due to the high molar content of the vinyl alicyclic units in the copolymer and / or the ability to form appropriate films for packing applications directly from the copolymer / metal composition of Transition. In addition, the present composition may have a high content of the copolymer depuration agent even when the composition contains a diluent polymer. As stated above, the long branched chain copolymer is highly compatible with known film-forming polymers such as polyolefin, and in particular, semi-crystalline polymers conventionally used in providing film packing articles. Due to the high compatibility, the copolymer and the other diluent polymer can be easily mixed in any ratio. In contrast, the amorphous ethylenically unsaturated polymers used above do not readily provide high content mixtures that are suitable for processing (e.g. extruded) into films and the like. Still further, the composition present when formed with or without a diluent polymer has been found to have great processing power and has high shear viscosity, low propensity to fracture melt, high melting stress and prolonged relaxation time. under the conditions of fusion. In this way, the present copolymer can be processed (e.g., extruded) at high rates in films having highly desirable characteristics (e.g., high clarity, reduced surface imperfections at high extrusion rates) alone or as a layer of a multilayer film. As indicated above, the composition of the present invention can be used as a single purification layer or a purification layer present in a multilayer film to form other articles for packaging or container application. The single layer articles can be easily prepared by extrusion processing. Multilayer articles are typically prepared using co-extrusion, coating, lamination or extrusion / lamination, as disclosed in U.S. Patent Nos. 5,350,622 and 5,529,833. Additional layers of a multi-layer article may include "oxygen barrier" layers, ie 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. / cra -d-atm) at room temperature, that is, at approximately 25 ° C. Typical oxygen barriers comprise poly (ethylene / vinyl alcohol), poly (vinyl alcohol), polyacrylonitrile, polyvinyl chloride, poly (vinylidene dichloride), polyethylene terephthalate, silica and polyamides such as nylon 6, meta adipamide. -xylene (MXD6) and Nylon 6, 6 as well as the copolymers thereof, as well as metal layers. Other additional layers may include one or more layers that are permeable to oxygen. In a preferred gasket construction, especially for flexible food packing, the layers include, in the order of departure from the outside of the package to the innermost layer of the package, (i) an oxygen barrier layer, (ii) a debug layer, i.e., the depuration composition as defined above, and optionally (iii) an oxygen permeable layer. The control of the oxygen barrier property of (i) allows a means to regulate the purification duration of the package by mimicking the oxygen input rate to the purification composition (ii), and in this way limiting the consumption regime of the purification capacity. The control of the oxygen permeability of layer (iii) allows a means to adjust an upper limit of the oxygen scavenging rate for the total structure irrespective of the composition of the purification composition (ii). This can be used in order to extend the duration of handling of the films in the presence of air before sealing the package. In addition, the layer (iii) may provide a barrier to the migration of the individual components in the debugging films or by-products to the interior of the package. Still additionally, layer (iii). it also improves the sealing ability, clarity and / or blocking resistance of the multilayer film. Additional layers as well as adhesive layers can also be used. The compositions typically used for adhesive layers include the functional anhydride polyolefins and other well known adhesive layers. The method of this invention comprises exposing the resulting composition to the cavity of the package having an oxygen sensitive product therein. A preferred embodiment provides for the inclusion of a photoinitiator as part of the present composition and subjecting a film, layer or article having the composition to radiation in order to initiate oxygen scavenging at the desired regimes. To initiate oxygen scavenging in an oxygen scavenging composition is defined herein as facilitating purification 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 depuration composition exhibits useful purification properties. In addition, the initiation of oxygen scavenging can also be applied to compositions that have an indeterminate induction period in the absence of radiation. The radiation used in this method must be actinic, eg, ultraviolet or visible light having a wavelength of about 200 to 750 nanometers (nm), and preferably having a wavelength of about 200 to 600 nanometers and of greater preference of approximately 200 to 400 nanometers. When this method is employed, it is preferred to expose the oxygen scavenger to at least one Julio per gram of the purification composition. A typical amount of exposure is within the range of 10 to 2000 Joules per gram. The radiation can also be an electron beam radiation at a dosage of about 2 to 200 kilograms Gray, preferably about 10 to 100 kilograms Gray. Other sources of radiation include ionization radiation such as gamma, X-rays and corona discharge. The duration of exposure depends on several factors including, but not limited to, the amount and type of photoinitiator present, the thickness of the layers to be exposed, the thickness and opacity of the intervention layers of any antioxidant present, and the wavelength and intensity of the radiation source. The radiation that is provided by heating polyolefin and similar polymers (e.g., 100 to 250 ° C) during processing, does not provide for activation to take place. When the oxygen scavenging layers or articles are used, the radiation exposure may be during or after the layer or article has been prepared. If the resulting layer or article is to be used to pack an oxygen sensitive product, the exposure may just be before, during or after the packing. However, in any case, exposure to radiation is required before using the layer or article as an oxygen scavenger. For the best radiation uniformity, the exposure must be carried out during a processing step 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 preferred to determine the oxygen scavenging capabilities, e.g., the rate and capacity of the specific oxygen scavenging composition proposed for use. To determine the oxygen scavenging rate, the time elapsed before the scavenger is depleted in a certain amount of oxygen from a sealed container is measured, of course. In some cases, the depuration rate can be conveniently determined by placing a film comprising the composition of the desired scavenger in an air-tight sealed package of a certain oxygen-containing atmosphere, e.g., air typically containing 20.6 percent oxygen by volume. Then, over a period of time, the samples of the atmosphere inside the container are removed to determine the percentage of oxygen remaining. Usually, the specific regimes obtained will vary under different temperature and atmosphere conditions. Atmospheres having a lower initial oxygen content and / or which are carried out under low temperature conditions, provide a more demanding test of a capacity and depuration regime of the composition. The regimes indicated below are at room temperature and an air atmosphere because they represent the conditions under which in many cases the oxygen scavenging composition and / or the layers of articles prepared therefrom will be used. When an active oxygen barrier is needed, a useful purification regime can be as low as 0.05 cubic centimeter of oxygen (O2) per gram of the copolymer in the purification composition per day in air at 25 ° C and pressure of 1 atmosphere. However, in most cases, it has been found useful that the present compositions have the capacity of regimes equal to or greater than 0.5 cubic centimeter and even 5 cubic centimeters or more of oxygen per gram per day. In addition, the films or layers comprising the present composition are capable of a depuration rate greater than 10 cubic centimeters of oxygen per square meter per day, and may have an oxygen scavenging rate equal to or greater than about 25 cubic centimeters of oxygen. oxygen per square meter per day under some conditions. These regimes make those layers suitable for purifying oxygen from within a package, as well as appropriate for active oxygen barrier applications. Generally, the film or layers are generally considered appropriate for use as an active oxygen barrier and can have a low purification rate as well as a cubic centimeter of oxygen per square meter per day when measured in 25 ° air. C and pressure of an atmosphere. When it is desired to use this method with an active oxygen barrier application, the oxygen scavenging activity initiated in combination with any of the oxygen barriers should create a total oxygen transmission rate of less than about 1.0 cubic centimeter per square meter per day per atmosphere at 25 ° C. The oxygen purification capacity must be such that this transmission regime is not exceeded for at least two days. Once debugging has been initiated, the debugging composition, layer or article prepared therefrom must be capable of debugging up to its capacity, that is, the amount of oxygen that the debugger is able to consume before it becomes ineffective . During current use, the capacity required for a given application depends on: (1) the amount of oxygen initially present in the package. (2) the rate of oxygen entry in the package in the absence of the purification property, and (3) the shelf life intended for the package.

When using the scrubbers comprising the composition containing the present copolymer, the capacity can be as low as 1 cubic centimeter of oxygen per gram., but it can be 50 cubic centimeters or more oxygen per gram. When these scrubbers are in a layer or a film, the layer of preference will have an oxygen capacity of at least about 250 cubic centimeters of oxygen per square meter per 25.4 microns thickness, and preferably at least 1200 cubic centimeters of oxygen. oxygen per square meter per 25.4 microns thickness of said layer. The present composition has been found to provide a film, layer or article that retains essentially its physical properties of resistance to stress and modulus even after considerable oxygen clearance has occurred. In addition, the present composition does not provide a by-product or effluent that would impart undesired taste, color and / or odor to the packaged product. The term "exposed to the interior" refers to a portion of a packing article having the present cleaning composition that is exposed, either directly or indirectly (through the layers that are permeable to O2) to the interior cavity that It has a product sensitive to oxygen.

The following examples are provided for illustrative purposes only and are not designated to be considered as a limitation of the invention as defined by the appended claims. All parts and percentages are by weight unless otherwise indicated. Example 1 Oxygen Debug with Films of Poly (ethylene-co-vinylcyclohexene) A copolymer of ethylene and 4-vinylcyclohexene (7 molar percent by Nuclear Magnetic Resonance) that has long chain branches (Tm = 83 CC, I2 = 0.67, Il? / I2 = 12.7, Mw = 74,000, Polydispersity = 2.2) was stirred by melting at 140 ° C with 680 parts per million cobalt of a commercially available cobalt neodecanoate (Ten-Cem (R) from OMG Inc.), 1000 parts per million of 4,4'-dimethylbenzophenone, and 500 parts per million of a hindered phenolic antioxidant (Irganox ') 1076 Ciba). A film of this composition was formed and a specimen of 200 square centimeters (activated) was irradiated with UVC radiation at a dose of 800 mj / square centimeter.

The specimen was vacuum sealed in a barrier bag (Cryovac (R) P640B) and the bag was inflated with 300 cubic centimeters of 1 percent oxygen in nitrogen (this oxygen plus the residual air in the bag provided the initial oxygen content) and was stored at 4 ° C through of the duration of the test. The samples of the atmosphere (4 cubic centimeters) were periodically removed for oxygen analysis using a MOCON gas analyzer model LC 700F with the following results: Oxygen Percentage Time (days after activation) 0 1.17 1 1.10 2 1.01 5 0.78 8 0.62 14 0.30 22 0.24 The data clearly show that the semi-crystalline long chain branched EVCH is suitable for purifying oxygen even under low temperature conditions and low initial oxygen content. The effects of depuration at room temperature and a higher initial oxygen content would be even more dramatic. Example 2 A sample of the ethylene-4-vinylcyclohexene copolymer compound (6.5 mole percent by Nuclear Magnetic Resonance) having long chain branches (Tm = 88 ° C, I2 = 0.06, I10 / I2 = 21.4, Mw = 97,000 , Polydispersity = 2.2) was formulated by melting as described in Example 1, with the exception that the hindered phenolic level was 1360 parts per million. The sample was irradiated and tested as described in Example 1 with the following results: Oxygen Percentage Time (days after activation) 0 1. 12 1 0. 91 4 0. 43 7 0. 23 14 0. 10 21 0. 06 These data further show that the semi-crystalline long chain branched EVCH can be prepared in a film and is suitable for purifying oxygen even under conditions of low temperature and low initial oxygen content.

Claims (23)

CLAIMS:

1. A composition suitable for purifying oxygen comprising a mixture of: (a) at least one copolymer having long chain branches, the copolymer comprises units derived from (i) ethylene and (ii) at least one unsaturated alicyclic monomer of vinyl represented by the formula:. __ _. wherein _J represents a substituted unsaturated alicyclic non-aromatic alicyclic group of 6 to 12 carbon atoms; and (b) a transition metal catalyst.

2. The composition of claim 1, wherein the copolymer further comprises units derived from a monomer selected from an alpha-olefin of 3 to 20 carbon atoms, cycloolefin, non-conjugated dienes and mixtures thereof.

3. The composition of claim 1, wherein the mixture further contains at least one photoinitiator compound.

4. The composition of claim 2, wherein the mixture further contains at least one photoinitiator compound.

The composition of claim 1, wherein the mixture further comprises at least one diluent polymer.

The composition of claim 2, wherein the mixture further comprises at least one diluent polymer.

The composition of claim 3, wherein the mixture further comprises at least one diluent polymer.

The composition of claim 4, wherein the mixture further comprises at least one diluent polymer.

The composition of claims 1, 2, 3, 4, 5, 6, 7 or 8, wherein at least one unit derived from unsaturated vinyl alicyclic is present in the copolymer in 1 to 15 mole percent of the copolymer.

The composition of claim 9 wherein at least one of the unsaturated vinyl alicyclic units of the copolymer has an ethylene group of carbon to carbon within the alicyclic group.

11. The composition of claim 9, wherein the copolymer is derived from ethylene and vinyl cyclohexene.

The composition of claim 11, wherein the vinyl cyclohexene is present from 1 to 15 mole percent.

The composition of claim 9, wherein the copolymer has a polydispersity of at least about 1.5 to 5 and a melt flow rate ratio (I10 / I2) ^ e By -10 minus about 8.

14. The method of purifying oxygen by a composition in the form of a film or packing material comprising forming the composition of claims 1, 2, 3, 4 or 5; configure the composition to form at least a part of a package or film material. exposing the packaged material or film for actinic radiation having a wavelength of between 200 and 750 nanometers or to electron beam radiation of at least about 2 kilo Gray.

The method of claim 14, wherein at least one unsaturated vinyl unsaturated alicyclic unit is present in the copolymer in 1 to 15 molar percent of the copolymer.

16. The method of claim 14, wherein at least one of the unsaturated vinyl alicyclic units of the copolymer has only one carbon to carbon ethylene group within the alicyclic group.

The method of claim 14, wherein the copolymer is derived from ethylene and vinyl cyclohexene.

18. The method of claim 14, wherein the vinyl cyclohexene is present in 1 to 10 mole percent.

The method of claim 14, wherein the copolymer has a polydispersity of at least about 1.5 to 5 and a melt flow index ratio (I ^ g / ^) of at least about 8.

20. A packing article in the form of a rigid, semi-rigid or flexible article having at least one layer, wherein at least one layer is exposed to the internal cavity of the packing article and comprising the composition of claims 1 , 2, 3, 4, 5, 6, 7 or 8.

21. A packing article in the form of a rigid, semi-rigid article or film having at least one layer, wherein at least one layer is left. exposed to the internal cavity of the packing article and comprises the composition of claim 9.

22. A packing article in the form of a rigid, semi-rigid article or film having at least one layer, wherein at least one layer is exposed to the internal cavity of the packing article and comprises the composition of claim 10

23. A packing article in the form of a rigid, semi-rigid article or film having at least one layer, wherein at least one layer is exposed to the internal cavity of the packing article and comprises the composition of claim 11.