US2151302A - Tin alloy - Google Patents

Description

March 21, 19 39. E SCHELLER 2,151,302

TIN ALLOY Filed June 26, 1936 FACING LAYER OR LAY ERS (TlN INCLUDING INHlBI'TOR AGENT) BODY LAYER OF (MALLEABLE TIN'OR TIN ALLOY) Ernes i Scheller.

' camn, immfjuzzzm Patented Mar. 21, 1939 1 UNITED STATES PATENT OFFICE TIN ALLOY Application June 26, 1936, Serial No. 87,585

17 Claims. (01. 29-181) This invention relates to tin alloys for food containers, and has for its object to provide a tin alloy that is. chemically less active with certain foodstuffs than commercial tin and tin alloys now 5 employed. Alloys in conformity with the pres ent invention are susceptible to use with a wide variety of foodstufis, and in containers of a wide variety of character and construction, but they have been found to be of particular utility when employed in metal foils for food packing, especially cheese wrappers, but it is to beexpressly understood that in its broader aspects the present invention is of wider application, and may be used in the production of cans, boxes, casings, etc., or

as a lining for or as an inner facing for the walls of such containers, or wherever it is desirable to have a metal surface in contact with foodstuff. For a specific illustration of the utility of the invention, however, the invention will be described with respect to its use in foil, particularly for wrappings for cheese.

Hereto fore it has been customary to wrap cheese in tin foil, but several types of cheese have been found to have a relatively high chemical activity when in contact with such foil, causing a marked discoloration of the foil or corrosion thereof. In order to avoid such discoloration, inner paper linings have been used in conjunction with the foil, and also various resins and lacquer coatings have been applied to the foil, but such expedients have added materially to the cost of the wrapping and, moreover, they have not been found entirely satisfactory.

I have discovered that such discoloration can t be largely if not entirely prevented by alloying with the tin a relatively small percentage of what may be termed an inhibitor agent, i. e., an agent which decreases or substantially eliminates discoloration or corrosion of the tin when in contact with the foodstuff, as cheese under. the illustration being considered. I have found that certain metals which are anodic with respect to tin, and

which also are characterized by having a preferential afiinity for oxygen as respects tin, when added to commercial tin or commercial alloys of tin whose other constituents do not prevent the inhibiting action of said agent, are highly effective in preventing dicoloration or corroflon of the tin.

While not wishing to limit the present invention by the theory herein it is believed that the corrosion of the tin, which causes the discoloration, is electro-chemical in nature and due to the setting up of small galvanic cells because or the presence 01 certain impurities in commercial tin, and also perhaps because of irregular concentrations of electrolytes in the medium. Some of these impurities are cathodic with respect to tin and therefore increaseits tendency to go into solution, making it more susceptible to corrosion. By addinga small percentage of metal 5 which is anodic'with respect to tin the tendency of the tin to go into solution is decreased. Experience has demonstrated that with some cheeses the wrapper does not discolor or corrode unless exposed to air or oxygen containing com- 10 pounds. This might be accounted for by the generally accepted theory of polarization the essence of which is that hydrogen, probably in an atomic state, is deposited on the metal and prevents further action taking place. Therefore, it may be 15 that the addition of such inhibiting agents to the tin not only makes the tin cathodic but also acts as an anti-depolarizer, maintaining a state of polarization at the surface of the tin.

In conformity with the present invention, the 20 alloy used consists chiefly of tin, which term is used as generic both to commercially pure tin and alloys of tin whose other constituents, such as antimony, for example, do not interfere with the inhibiting action of metals characterized by being 25 anodic with respect to tin and having a preferential affinity for oxygen with respect to tin.

I have found that the addition to tin, as just characterized, of relatively small quantities, preferably less than three percent, of one or more 30 metals of the character above referred to, such for example as magnesium, calcium, aluminum, etc., or combinations thereof, or combinations therewith of cadmium, results in the production of an alloy which is of great utility in preventing 35 discoloration or corrosion in contact with foodstuffs. The particular inhibiting agent used varies to some extent: with the characteristics of the foodstufi which is to be in contact therewith, some alloys being better suited than others for 40 particular foodstuffs. For example, in the case of cheese, a tin alloy including .2% aluminum has been found to be better suited for a certain type of processed American cheese, while a tin alloy including .05%- magnesium and .5% cadmium has 4 been found to be better suited for processed Limburger cheese. Therefore, it is to be expressly understood that the present invention contem-" plates the selection of an inhibiting agent or agents best suited to the particular foodstuflto be 50 enclosed.

Y I have iound that the addition of as little as .01% of magnesium or aluminum largely inhibits the discoloration resulting from food corrosion.

Inthecaseoimagnesiumeveninanamountas 66:

low as .01%, excellent results are obtained by adding .5 to 1% of cadmium. Cadmium may also be used as the sole alloying agent, in amounts from .1 to 3%, but less satisfactory results have been obtained therefrom. Other metals. characnesium or aluminum impairs the malleability or ductility of the resulting alloy, depending upon the concentration. This may be of little or no significance in the production of containers wherein the layer of alloy is relatively thick or does not have to be subjected to rolling, drawing or other operations to such an extent that reduced malleability or ductility is disadvantageous.

malleability or ductility becomes important, and therefore the concentration of the inhibiting agent or agents is limited by the workability of the resulting alloy for the purpose intended.

In the production of foil, I have accordingly found it'desirable to produce a composite 6r laminated foil including a lamination of the improved alloy of the present invention for contact with the foodstuff and one or more laminations which facilitate rolling of the foil to the desired thickness, and which latter may be composed of or include commercially pure tin and alloys thereof,

as an alloy of tin with antimony ranging from one to three percent thereof, which is highly malleable and ductile.

In producing such a composite laminated foil, the preferred procedure is as follows: An alloy comprising tin and an inhibiting agent as aforesaid is rolled into sheets or heavy foil, preferably on the order of .15" thick, and such sheet or foil is then used as a casing upon one or both sides of a core, say about three fourths inch thick, which may be formed of commercially pure tin or alloys thereof, such as an alloy of 98% tin and 2% antimony which alloy is of increased strength as respects tin and has good rolling qualities. The combined alloy casing and core car. then be rolled to foil of commercial thickness as on the order of .0003" or less. Rolling the casing and core under pressure welds thetwo metals together, and the core metal gives suflicient body and support to the resultant foil so that the effects of brittleness in the casing metal, due to the presence of such inhibiting agents as aluminum and magnesium, are largely avoided. It is to be expressly understood that the relative thickness of the alloy casing to the core may be varied as determined by the thickness of the foil ultimately required, it being preferred that the casing comprise between fifteen and thirty percent of the thickness of the composite metal.

The accompanying drawing illustrates diagrammatically and with greatly increased size an example of a prefer ed foil for use in wrapping cheese, wherein .th ,casing lamination Ill, here shown as applied to'both faces of the body layer, though that is not essential, is composed of 2% aluminum or magnesium with the remainder commercially pure tin, and such lamination co nstitutes between fifteen and thirty percent of the thickness of a foil, the remainder or body layer I ofwhich is composed of an alloy of ninety eight percent tin and two percent antimony.

In the case of foil, however, this impairment of Such a foil has been found to substantially prevent discoloration or' corrosion whenin contact with certain types of cheese, but as before noted a foil whose casing layer is composed of .5% cadmiumand .05% magnesium, with the remainder commercially pure tin, has been found preferable for other types of cheeses,

Various modifications and combinations of the several features of the present invention may be used, as will now be apparent .to those skilled in the art, the essence of the invention being the addition to tin of small quantities of one or more metals tending to reduce its discoloration or corrodibility in contact with foodstuffs. Other metals which are characterized by being anodic with respect to tin and by having a preferential aflinity for oxygen with respect to tin than those specifically hereinbefore referred to may also be used. It is also to be expressly understood that various proportions and combinations of the inhibiting metals as characterizedmay be used depending upon the foodstuif to be enclosed, the workability of the alloyrequired, etc. procedures described may be replaced by equivalent procedures, and certain features used without other features, without departing from the spirit of the invention. Furthermore, although the invention has been particularly described in connection with its application to the production of foil, and especially foils for use as cheese wrappings, the invention is not restricted thereto, as in its broader aspects the alloy of this-invention may be used as a lining or facing for other metals and for other types of containers, or it may be used as the material for the wall, or a lamination of the wall, of any suitable container or for Certain contact with any suitable foodstuff. Reference is 2. A cheese wrapping foil which is substantially non-discolorable from contact with the cheese and which has a malleable tin alloy body layer and at least its cheese contacting surface composed of tin containing a.,relatively small percentage of an inhibiting agent including one or more metals from the group composed of aluminum, magnesium and calcium.

3. A cheese wrapping foil which is substantially non-discolorable from contact with the cheese and which has a malleable tin alloy body layer and at least its cheese contacting surface composed of tin containing a relatively small percentage of cadmium and a relatively small percentage of one or more of the group of metals composed of magnesium, aluminum and calcium.

4. A cheese wrapping foil which is substantially non-discolorable from contact with the cheese and which has a malleable tin alloy body layer and at least its cheese contacting surface composed of tin containing a relatively small percentage of an inhibiting agent comprising not more than three tenths percent of a metal from the group composed of aluminum, magnesium and calcium.

' 5. A cheese wrapping foil'which is substantially non-discolorable from contact with the U memos cheese and which has a malleable tin alloy body layer and at least its cheese contacting surface composed of tin containing an inhibiting agent comprising a relatively small percentage of cadmium and an amount not exceeding three tenths percent of a metal from the group composed of aluminum, magnesium and calcium.

6. A composite sheet metal or foil for contact with foodstuff which is substantially non-discolorable or. non-corrodible from contact with the foodstufl and having a body layer of tin-antimony alloy and a surface layer composed of tin containing a relatively small percentage of an inhibiting agent which is anodic with respect to tin and adapted to maintain the tin polarized.

7. A composite sheet metal or foil for contact with foodstuff which is substantially non-discolorable or non-corrodible from contact with the foodstufl and having a body layer of tin-antimony alloy and a surface layer composed of. tin containing a relatively small percentage of an inhibiting agent including one or more metals from the group composed of aluminum, magnesium and calcium. a

8. A composite sheet metal or foil for contact with foodstuff which is substantially non-discolorable or non-corrodible from contact with the foodstuff and having a body layer of tin-antimony alloy and a surface layer composed of tin containing a relatively small percentage of one or more metals fromthe group composed of aluminum, magnesium and calcium and a relatively small percentage of cadmium.

9. A composite sheet metal or foil for contact with foodstuff which is substantially non-dis-v colorable or non-corrodible from contact with the foodstuii' and having a body layer of malleable tin alloy and a surface layer composed of tin containing a relatively small percentage of an :nhltgting agent which is anodic with respect 10. A composite sheet metal or foil for contact with foodstuff which is substantially non-discolorable or non-corrodible from contact with the foodstuff and having a body layer of malleable tin alloy and a surface layer composed of tin,

containing a relatively small percentage of an inhibiting agent which includes one or more metals from the group composed of aluminum, magnesium and calcium.

11. A composite sheet metal or foil for contact with ioodstufl' which is substantially non-dis- 'colorable or non-corrodible from contact with the foodstuff and having a body layer of malleable tin alloy and a surface layer composed of tin containing a relatively small percentage of one or more metals from the group composed of aluminum, magnesium and calcium and a relatively small percentage of. cadmium.

12. A non-ferrous sheet metal or foil for contact with foodstuff which is substantially non-discolorable or non-corrodible from contact with the foodstuff and having at least the food contacting surface thereof composed of tin containing a relatively small percentage of an inhibiting agent which includes one or more metals from the group composed of aluminum, magnesium and calcium.

13. A non-ferrous sheet metal or foil for contact with foodstuff which is substantially non-discolorable or non-corrodible from contact with the foodstufi and having at least the food contacting surface thereof composed of tin containing a relatively small percentage of an inhibiting agent which includes a small percentage of cadmium and a relatively small percentage of one or more metals from the group composed of aluminum, calcium and magnesium.

14. A non-ferrous sheet metal or foil for con tact with foodstuff which is substantially non-discolorable or non-corrodible from contact with the I foodstuff and having at least the food contacting surface thereof composed of tin containing a relatively small percentage of an inhibiting agent which is adapted to maintain the tin polarized and which comprises not more than three tenths percent of one or more metals from the group composed of aluminum, calcium and magnesium.

15. A non-ferrous sheet metal or foil for contact with foodstuff which is substantially non-discolorable or non-corrodible from contact with the foodstuff and having a body layer of malleable tin and at least the ,food contacting surface thereof composed of tin containing a relatively small percentage of an inhibiting agent which is anodic with respect to tin and which has a preferential affinity for oxygen with respect to tin.

16. A non-ferrous sheet metal or foil for contact with foodstuff which is substantially non-discoiorabie or non-corrodible from contact with the foodstuff and having a body layer of malleable tin and at least the food contacting surface thereof composed of tin containing a relatively small percentage of an inhibiting agent which is adapted to maintain tin polarized.

17. A non-ferrous sheet metal or foil for contact with foodstuff which is substantially non-discolorable or non-corrodible from contact with the foodstuff and having at least the food contacting surface thereof composed of tin containing arelatively small percentage of an inhibiting agent which is adapted to maintain the tin polarized and which comprises not more than three percent of cadmium and not more than three tenths percent of one or more of the group of metals composed of aluminum, calcium and magnesium.

ERNEST SCHELLER.

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