ALUMINUM WITH CONTROLLED OXIDATION

Abstract: An aluminum which includes dopant in an amount which is effective in providing controlled oxidation of the aluminum in the presence of oxygen, thereby preventing the formation of an oxidation-resistant aluminum oxide layer (96) on the aluminum. The aluminum can be incorporated in a flexible laminar sheet material, which, in turn, can be used as a packaging material (80).

Description: ALUMINUM WITH CONTROLLED 0XIDATI0 FIELD AND BACKGROUND OF TKΞ INVENTION The present invention relates to aluminum with controlled oxidation , doped aluminum foil , flexible laminar sheet material comprising doped aluminum , as well as articles of commerce characterized by being packaged with such doped foil , or with such flexible laminar sheet material . Aluminum metal is characterized by the ready formation in air of a durable surface oxide layer , which is . generally effective in preventing further oxidation of the surface . This characteristic of alumi num is generally accepted as an advantage in many applications . Moreover , aluminum foil , and supported aluminum film , are popular packaging materials due to their cheapness , non-toxic properties , ease of working and of forming laminates with polymeric films , attractive reflective metallic appearance and durability. Their durability is in turn due in part to innate mechanical strength , and in part due to the fact that the aluminum foil or film readily forms a degradation-resistant initial surface oxide layer, as mentioned above . Many articles and products of commerce are susceptible to oxidative degradation in storage , either by direct chemical action of oxygen or by bacterial processes in which the presence of oxygen is essential . Methods have been developed for the protection of suc oxidation-susceptible articles or products from oxidative degradation, such as packaging in an inert atmosphere; hermetic sealing, e.g. with heavy or laminated polymeric films; including oxygen absorbents in the packaging or in the product; or including antioxidants, e.g. in foodstuffs or medical products. As mentioned above, the durable nature of aluminum foil or- film as a packaging material is at least in part due to the fact that it -undergoes εn initial oxidation reaction to produce a surface oxide layer which is resistant to degradation and. particularly to any further oxidation. It has surprisingly been found in accordance with the present invention, however, that there is a considerable advantage is sacrificing, at least to some extent, the durability of aluminum by making it controllably more susceptible to oxidation, so that it can prolong the shelf- life of oxidation-susceptible articles or products, by reacting with and therefore removing oxygen from the environment of such packaged commercial articles or products. Persons skilled in the- art will appreciate that aluminum foil or film packaging material in general has a much greater shelf-life than the packaged article or product; thus it will be acceptable to reduce somewhat the shelf-life of such packaging material, if simultaneously the shelf-life of the packaged article or product is extended because it is thus protected from the deleterious effects of oxygen in its immediate environment. Reduction of the shelf-life of the aluminum foil or film functioning effectively as antioxidant can of course bs 2 SUBSTITUTE SHEET countered by laminating it with a polymeric layer or layers which will maintain the integrity of the wrapping material even if the foil layer deteriorates. The use of packaging comprising aluminum foil in the effective role of oxygen-reactant or antioxidant possesses the following advantages: (1) the necessary technology, tools and experience for producing aluminum foil, or polymer fil -laminated with aluminum already exists and is very widely accepted; (2) aluminum has a very high capacity for reaction with oxygen; thus, 1 g. aluminum has the potential capacity to remove all the oxygen from 3 1. ai at N.T.P.; (3) when in accordance with the invention aluminum foil is doped to render it susceptible to continuous oxidation, i.e. oxidation is not halted after initial oxidation of the aluminum surface, oxidation of the foil will continue until all free oxygen within the packaged environment has been removed; (4) the aluminum oxide produced is chemically inert ■ and non-toxic; (5) when the protected product is used for human consumption, the doping material can be readily selected so as to be also non-toxic; (6) the invention possesses an environmental advantage, because it replaces (for example) durable aluminum cans, wrappings and bottle tops with aluminum which may be made completely degradable in the atmosphere to aluminum oxide which would readily disperse and in effect become virtually invisible. 3 SUMMARY OF THE INVENTION The present invention accordingly provides in one aspect, aluminum which comprises dopant in an amount effective to provide controlled oxidation of the aluminum in presence of oxygen, and thereby to prevent formation of an oxidation- resistant aluminum oxide layer on the aluminum. In another aspect, the invention provides aluminum foil or film doped with at least one metal selected from lithium, sodium, potassium, rubidium, caesium, beryllium, magnesium, calcium, strontium and barium. Persons skilled in the art will appreciate the necessity for excluding such of the dopant- metals as are toxic (e.g. beryllium) when the doped foil or film of " the invention is intended for-use with products, e.g. foodstuffs, intended, for human use; on the other hand there may be applications where the use of relatively toxic dopants may possibly be tolerated, e.g. to remove oxygen from a sealed, chemical reaction vessel.. The invention moreover provides in another aspect, a flexible laminar sheet material which comprises doped aluminum foil or film as just described, having a polymeric layer (which in one embodiment may be a breathable layer) on one side thereof. In yet another aspect, the invention provides a flexible laminar sheet material which comprises doped aluminum as defined above having a polymeric layer on each side thereof; * in this aspect of the invention, the polymeric layer on at least one It UTE SHEET side (and if desired on each side) of the coped aluminum foil may be a breathable polymeric layer. In still another aspect, the invention provides a flexible laminar sheet material which comprises a polymeric film having on one side thereof at least one layer of doped aluminum, wherein the doped aluminum has been doped with a dopant comprising. at least one metal selected from the group consisting of lithium, sodium, potassium, rubidium, caesium, beryllium, magnesium, calcium, strontium and barium; the above remarks concerning the avoidance of relatively toxic dopants for certain applications should be noted. In one embodiment of this aspect of the invention, the polymeric film has on one side thereof a single layer of doped aluminum. In another embodiment, the polymeric film has on one side thereof at least two layers of aluminum and at least the layer of aluminum remote from said polymeric film is a doped aluminum layer; e.g. , there may be one one side of the polymeric film an undoped aluminum layer and superimposed thereon a doped aluminum layer. The flexible laminar sheet material described in the preceding paragraph may comprise additionally a breathable polymeric layer superimposed on the at least one doped alum um layer, the breathable polymeric layer being the outermost layer remote from said polymeric film. In yet another aspect, the invention provides a packaged article of commerce which is characterized by at least one of the the following features, namely: 5 SUBSTITUTE SHEET (a) at least part of the packaging comprises at least one material selected from doped aluminum foil and flexible laminar sheet material, according to the present invention as defined herein; (b) it contains internally, doped aluminum as defined herein other than in the form of packaging material, thereby serving to remove oxygen (by reaction therewith) from the internal space of the package. For purposes-— of definition, -the term "article of commerce ** in the present specification and claims is intended to include not only coherent articles, but also manufactured products such as chemical and medicinal substances, e.g. drugs, and comestibles or foodstuffs, which may exist and be marketed in substantially non-coherent form. The present invention provides for the possibility of incorporating an amount of dopant in aluminum packaging materials, which is adequate to promote the eventual conversion of all the Blnπrirmm to aluminum oxide, on prolonged exposure to air. This of course constitutes a considerable ecological advantage of the invention, since it would potentially avoid littering- the countryside with long-lasting expended aluminum packaging-. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 illustrates a method for producing an embodiment of doped aluminum materials in accordance with the present invention. Fig. 2A illustrates schematically known apparatus for 6 coating polymeric film with aluminum by evaporation in vacuum . Fig. 2B illustrates the adaptation of the high vacuum chamber of Fig. 2A for the purpose of producing an embodiment of doped aluminum materials in accordance with the invention . Fig. 2C illustrates a modification of the apparatus of Fig. 233 , for the purpose of producing a different embodiment of doped aluminum materials in accordance with the invention. Fig. 3A illustrates schematically an embodiment of a laminate according to~the invention which may be produced using the apparatus of Fig. 2C . Fig. 3B illustrates schematically an embodiment of a laminate according to the invention different from the embod ment of Fig. 3A. Figs . 4A and - B illustrate a package utilizing doped aluminum in accordance with the present invention . DETAILED DESCRIPTION OF THE INVENTION While , in general , the doping ingredient in accordance with the invention may be preferably selected .from among lithium, sodium, potassium, rubidium, caesium, beryllium, magnesium , calcium, strontium and barium, persons skilled in the art will be aware that a narrower selection will be necessary where the protected product is e.g. a foodstuff or medicament intended for human consumption, so that toxic materials are not introduced . Without prejudice to the generality of the invention, the presently preferred doping metal is calcium . Calcium is the basis of many compounds essential to life and will obviously give rise to non-toxic products ; moreover , it is on the one hand SUBSTITUTE SHEET sufficiently active to provide controlled oxidation and thus prevent the formation of a hard aluminu oxide layer which prevents further reaction, while on the other hand, its moderate activity in this respect is such as to obviate the necessity for developing new technologies for producing the aluminum foil- or film-based packaging material. In the flexible laminar sheet material of the invention, the undoped aluminum " layer (s) "and the aluminum layers comprising dopant, and/or the dopant itself, may be deposited on the polymeric film by any method known to persons skilled in the art. However, it is presently preferred to effect deposition of at least one of the following materials, namely said aluminum and said dopant, by evaporation in vacuum. Fig. 1 depicts schematically a laboratory arrangement of items in the space 1Θ of a high vacuum chamber of which the boundaries are not shown, for producing doped aluminum materials in accordance with the ' present invention. Evaporation vessels 2, 4 ' contain respectively aluminum and calcium (or other doping metals in accordance with the invention) , which are evaporated by respective heaters 6, 8, which may be e.g. resistance heaters . The depicted arrangement may be part of an Edwards (trademark) 306 coating system. The high vacuum may be of the order of e.g. 10~° millibar. The support 12 may be e.g. , glass , polyethylene or polypropylene. In the course of evaporation, a film of doped aluminum collects on the underside of the support at 14. It may be determined that the amount of each metal deposited at 14 is a δ SUBSTITUTE SHEET function of the current applied to heaters 6 and 8 , over a fixed time period , such as 40 seconds . Subsequently , the appropriate current may be applied to each heater in order that the different metals deposit simultaneously on support 12 in the desired proportions . After preparation in this manner , samples were exposed to room temperature and atmospheric pressure until oxidation was complete . The .inverse of the time for complete oxidation was used as a measure of the rate of oxidation; this rate was found to be approximately proportional to the dopant concentration at concentrations of up to a few atomic percent . At these concentrations , it was found that a polymeric film coated with doped aluminum containing Ca:Al in a weight ratio of 5 : 1Θ0 reduced the concentration of oxygen from an initial 21 * .' to less than Θ .012 after 4 days at room temperature , when tested in a closed glass vessel of 120 ml . capacity. Fig. 2A depicts schematically known apparatus for coating polymeric film as it is unwound from bobbin 22 which rotates in an anticlockwise direction about axle 24 and simultaneously wound onto bobbin 26 as it rotates anticlockwise about axle 28. Bobbins 22, 26 are located in respective vacuum chambers 3Θ , 32, the polymeric film passing into high vacuum chamber 3 through opening 38 and exiting from high vacuum chamber 3 via opening 40. The polymeric film is coated with aluminum by evaporation from vessel 36 , heated by resistance heater 42. SUBSTITUTE SHEET Fig. 2B (in which reference numerals repeated from Fig. 2A have the same meaning as before) shows the adaptation of high vacuum chamber 34, of the apparatus described with reference to Fig. 2A, for purposes of the present invention by .inserting additionally therein an evaporation vessel for evaporation of dopant onto the polymeric film 20 by use of resistance heater 46. The thickness of the aluminum layer is controlled by the temperature of heater 42 and the percentage of dopant therein wϋl be controlled-by-the temperature of- resistance heater 46. It will be appreciated .that the product in the form of a wound roll of doped aluminum film on a polymeric film support is protected against oxidation in storage by superimposed windings of the same doped aluminum/polymer laminate, and that the outer layer may be protected from oxidation by a tightly wound*wrapping impervious to air. In the modification of Fig. 2B depicted in Fig. 2C, the two evaporation vessels 36, 44, with respective heaters 42, 46, are spaced apart and partially separated by screen 48 which is effective to enable a mixture of aluminum and dopant in preselected proportions to be superimposed on an initial aluminum layer deposited on film 20, insofar as under vacuum the dopant particles (as also the aluminum particles) travel substantially linearly from the evaporation vessels to film 2Θ. A consequence of the arrangement depicted in Fig. 2C is that a thin layer of the deposited aluminum film remote from the evaporation vessels wϋl be dopant free and thus protect the aluminum film from oxidation at that remote surface, as well as enhancing the decorative appearance of the product. 10 The product of the process shown in Fig. 2C is schematically depicted in Fig. 3A and consists of a laminate 60 of polymeric film 62/undoped aluminum film 64/doped aluminum film 66. The product 60 as described with reference to Fig. 3A may be subsequently laminated by known means with a further, e.g. breathable, polymeric film, thereby to obtain the laminar product 70, schematically depicted in Fig. 3B. which consists of polymeric film 62/undoped aluminum film 64/doped aluminum film 66/breathable polymeric film 72, the breathable layer 72 preventing direct contact of the doped aluminum layer with the protected packaged product, yet nevertheless permitting reaction of the doped aluminum layer with oxygen. Figures 4A and 43 illustrate a packaged article in the invention. In both figures, a plastic container 80 is sealed by lamina -foil 82, comprising a doped aluminum layer in accordance with the present invention, along outwardly turned flange 84 which is integral with container 80. When access to the contents is desired, the laminar foil may be at least partly removed from, e.g., front left corner 86 of the foil. In Fig. 4A, the packaged article, which may contain for example foodstuffs such as soft cheese or halva, is shown before opening, and neither the contents nor the laminar structure of the foil are shown in this figure. Fig. 4B shows the now partly opened package of Fig. 4A, the opening having been achieved (e.g.) by the well known method of cutting the foil at the top front-left corner of the container 11 SUBSTITUTE SHEET and pulling the foil away from this corner to reveal foodstuff (or other content) 88. In Fig. 4B, the thickness of the foil 90 is shown greatly enlarged in order to depict its laminar structure. Illustrated in this figure is a four-layer laminate in which the outer layer is a polymeric protective film 92 which is in contact with a deposited undoped aluminum layer 94, followed by a doped aluminum layer 9 and an inner breathable polymeric layer 98. When the container 80 is originally sealed by foil 82, any oxygen which may be in the interior of the package will di fuse through breathable layer 8 and reacted with the doped ainm-fT-m-ii layer 96, thus inhibiting oxidative deterioration of the contents. It will be appreciated that the same principle applies when the whole of, rather than part of, the container is in the nature of a foil, e.g. in the case of potato chips or some ready- to-cook meals. It will further be appreciated "that the mentioned foodstuffs are only iϋustrative as to the contents ' of the package, which could of course alternatively contain other foodstuffs, or non-foodstuffs such as pharmaceutical compositions. The laminate could also of course differ from that illustrated in Fig. 4B, e.g. a single doped aluminum layer could replace layers 9 and 96- Alternatively, the four-layer laminate may be replaced by an aluminum foil, doped in accordance with the invention on the inside surface only, i.e. on the surface nearest 12 to the contents of the package; such foil may optionally have a breathable polymeric layer between the doped aluminum surface and the contents of the package. In another embodiment, not illustrated, foil 0 n y be replaced by a conventional foil sealant, and antioxidative protection of the contents of the package may be achieved by insertion into the package before sealing of a piece of aluminum (doped in accordance..with the invention) , if desired encased in breathable polymer. Persons skilled in the art will be aware of the manner in which the processes described with reference to the Figures may be adapted to the doping of aluminum foil rather than the simultaneous deposition of aluminum and dopant as has been described. Polymeric film may also be interleaved with the doped foil so as to protect it prior to use. Alternatively doped aluminum foil could be manufactured by cold or hot rolling, but it will be appreciated that hot doped sheets or liquid aluminum containing dopant, will need to be protected from oxidation by working in an inert gas atmosphere in substantial 'absence of oxygen. APPLICATIONS OF THE INVENTION It is contemplated that doped aluminum foil and the flexible laminar sheet materials (incorporated doped aluminum film or foil) according to the invention will be useful in the packaging of products such as foods, medicaments, cosmetics and semiconductors (for example) , which are sensitive to direct 13 TITUTE SHEET chemical oxidation and/or bacterial deterioration in presence of oxygen. The potential ecological advantage of aluminum packaging which after use and in the course of time is capable of complete conversion to oxide, has already been mentioned. A particular application of the invention is to dairy and meat products, which often spoil rapidly as a result of oxidation of their fat content and bacterial deterioration; such products may be packed using as packaging, the materials of the invention including doped aluminum, such that oxygen contained within the packet would react with the doped aluminum. Baked goods may be similarly wrapped. It is further contemplated that the materials of the invention may readily be printed as other aluminum foils, films and polymeric laminates. Caps containing an internal surface including doped aluminum, e.g. laminated with breathable polymeric film, could be used on bottles of sensitive liquids such as milk, beer, cosmetics or medicines. It will be apparent to persons skilled in the art that many modifications and variations may be made in relation to embodiments which have been particularly described herein; merely by way of illustration only, an aluminum film or foil can be gradiently doped. Accordingly, the invention is not", to be construed as limited to such embodiments as have been particxilarly described, rather the concept, scope and spirit of the invention will be appreciated from the claims which follow. 14 T

Claims: CLAIMS 1. Aluminum which comprises dopant in an amount effective to provide controlled oxidation of the aluminum in presence of oxygen and thereby to prevent formation of an oxidation-resistant aluminum oxide layer on the aluminum. 2. Aluminum according to claim 1, wherein said dopant comprises at least one metal selected from the group consisting of lithium, sodium, -potassium, rubidium, caesium, ' beryllium, magnesium, calcium, strontium and barium. 3• Aluminum in a form selected from foils and films, which comprises in at least an outer surface layer thereof, dopant in an amount effective to provide controlled damage of the aluminum surface oxide layer which forms on exposure of the aluminum ■ surface to air. 4. Aluminum according to claim 3. wherein said dopant comprises at least one metal selected from the group consisting of lithium, sodium, potassium, rubidium, caesium, beryllium, magnesium, calcium, strontium and barium. 5. A flexible laminar sheet material which comprises aluminum ' in a form selected from foils and films, as defined in claim 3 t and having a polymeric layer on one side thereof. 6. A flexible laminar sheet.material according to claim 5- wherein said polymeric layer is a breathable polymeric layer. 15 7- A flexible laminar sheet material which comprises aluminum in a form selected from foils and films, as defined in claim ι and having a polymeric layer on each side thereof. 8. A flexible laminar sheet material according to claim 7t. wherein the polymeric layer on at least one side of the doped aluminum foil is a breathable polymeric layer. 9. A flexible laminar sheet material which comprises aliim-inum in a form selected from foils and films, as defined in claim 4, and having a polymeric layer on one side thereof. 10. A flexible laminar sheet material according to claim » wherein said polymeric layer is a breathable polymeric layer. 11. A flexible laminar sheet material which " comprises aluminum in a form selected from foils and films, as defined in claim , and having a polymeric layer on each side thereof. 12. A flexible laminar sheet material according to claim 11, wherein the polymeric layer on at least one side, of the doped r-πuTirirmm " foil is a breathable polymeric layer. 13- A flexible laminar sheet material which comprises polymeric film having on one side thereof at least one layer of doped aluminum, wherein said doped aluminum has been doped with a dopant comprising at least one metal selected from the group consisting of lithium, sodium, potassium, rubidium, caesium, beryllium, magnesium, calcium, strontium and barium. 16 SUBSTITUTE SHEET 46 14. A flexible laminar sheet material according to claim 13, wherein said polymeric film has on one side thereof a single layer of doped aluminum. 15- A flexible laminar sheet material according to claim 13, wherein said polymeric film has on one side thereof at least two layers of aluminum and at least the layer of aluminum remote from said polymeric film is a doped aluminum layer. 16. A flexible laminar sheet material according to claim 15 1 wherein said polymeric film has one one side thereof an undoped aluminum layer and superimposed on said undoped layer a doped aluminum layer. 17. A flexible laminar sheet material according to claim 13, which comprises additionally a breathable polymeric layer superimposed on the at least one doped aluminum layer, said breathable polymeric layer being the outermost layer remote from said polymeric film. 18. A packaged article of commerce which is characterized by at least one of the the following features (a) and (b) , namely: (a) at least part of the packaging comprises at least one material selected from doped aluminum foil and flexible laminar sheet material incorporating doped aluminum; (b) it contains internally, doped aluminum, said doped aluminum being aluminum doped with a dopant which comprises at least one metal selected from the group consisting of lithium, sodium, potassium, rubidium, caesium, beryllium, magnesium, calcium, strontium and barium. 17 19 - An article according to claim 18 which comprises a product selected from cometstibles and drugs for human use, wherein said dopant is restricted to non-toxic dopant metals selected " from said group . 18 SUBSTITUTE SHEET

Inventors: KUSTANOVICH JOSEPH, KUSTANOVICH, JOSEPH
Applicants: GOLDMUNTZ LAWRENCE, SHIRAT ENTERPRISES LTD, GOLDMUNTZ, LAWRENCE, SHIRAT ENTERPRISES LTD.
Application year: 1992
Main classification: B32B15
IPC codes: B32B15, B65D65, B65D77, B65D81, C22C21, C23C14