DESCRIPTION Reference to Related Application This application is a continuation-in-part of U.S. Serial No. 149,850, filed May 14, 1980.

Technical Field

Our present invention relates to an improved stock material for making aluminum containers and to a method for forming seamless drawn and ironed aluminum containers from the improved stock material.

Background Prior Art

The use of a two-piece container for packaging products such as beer and/or carbonated beverages has become very popular in recent years. The two-piece container generally is a container sidewall or body with a unitary end wall at one end thereof. The second piece of the container comprises an end seamed to the open end of the container in a fluid-tight manner. Typically, a two-piece aluminum container may be produced by initially cutting a disc from a sheet or coil of stock aluminum, and substantially simultaneously transforming the disc into a shallow cup in a conven¬ tional cupping machine forming a part of a can manufac- turing line. The shallow cup is then converted into

a drawn and ironed container of desired dimensions in a body maker by ramming the cup through a plural¬ ity of forming die rings on a punch in a known manner to progressively decrease the wall thickness of the reformed cup and produce a seamless container as described in detail in an article appearing in the November, 1973 AEROSOL AGE magazine entitled "The Drawn and Ironed Can - Understanding the Technology". In general, conventional commercial machin- ery which form the cups for conversion to drawn and ironed aluminum containers utilizes a lubricant- coolant in the cup making device or cupper to provide the necessary lubricity between the surface of the stock material and the tooling. The can body making machinery also incorporates a mechanism for flowing a lubricant-coolant onto the surface of the container and to the ironing dies utilized in cooperation with the punch. Typically, th lubricant-coolant is a mixture of water and an emulsified oil-blend lubricant, such as a commercially available Texaco brand 591 product. Criteria which such lubricants must meet to be commercially acceptable include the following qualties: good lubricity at high pressure and tempera¬ ture, good emulsion stability, easily washable from the can surface, good availability and inexpensiveness.

Considerable effort has gone into finding and developing lubricants which meet the exacting requirements for optimal use in the manufacture and production of two-piece aluminum containers, and illustrative of such efforts are numbers of patents. Thus, as shown in U.S. Patents Nos. 3,298,954; 3,478,554 and 3,873,458, various resin coatings containing lubricants have been suggested for use. Mixtures of polymers, mineral oil and f tty acids

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are disclosed in U.S. Patent No. 4,027,070. Others have taught the application of a pretreatment pro¬ cedure wherein a phosphate coating is applied prior to the application of a fatty acid as is disclosed in U.S. Patents Nos. 3,313,728 and 3,525,651. The special requirements for lubricating aluminum sheet are discussed in U.S. Patents Nos. 3,783,644 and 3,832,962, where an oil-water emulsion and a thermo- setting resin are used respectively. U.S. Patent No. 3,826,675 lists some of the more important characteristics of an entirely satisfactory lubri¬ cant for metallic container stocks such as tinplate, blackplate and aluminum, and then discloses numbers of lubricants which were previously proposed for such use. Among the latter have been naturally occurring vegetable oils and synthetic esters of carboxylic acids, stated examples of which are cottonseed oil, palm oil, and synthetic esters of sebacic acid such as dioctyl sebacate. The aforesaid vegetable oils are stated to have the objection that they have a tendency to oxidize to a solid film which is no longer a good lubricant after a relatively short period of storage. The disadvantages or deficiencies of syn¬ thetic ester lubricants, even the stated best of them, dioctyl sebacate are described in said U.S.

Patent No. 3,826,675, and it is stated therein that an entirely satisfactory lubricant was not available prior to the invention of the said patent. The inven¬ tion of U.S. Patent No. 3,826,675 resides in the use of a lubricant in the form of a citric acid ester of an alcohol containing from 1 to 10 carbon atoms in an amount of about 0-05 to 1 gram for each 67,720 square inches of lubricated surface area, illus¬ trative examples of said citric acid ester lubricant being triethyl citrate, acetyl triethyl citrate and tributyl citrate.

Summary of the Invention

We have discovered, surprisingly, that, when forming seamless, drawn and ironed containers from aluminum stock, which containers have a bottom wall and an integral sidewall, all lubricants in the cool¬ ing fluid can be eliminated by applying a thin layer or coating of peanut oil to the stock material before " the cupping operation is initiated. We have also dis¬ covered that peanut oil does not solidify on the can forming machine, thus avoiding the necessit . for fre¬ quent or constant cleaning. Peanut oil also cleans off the can surface readily using mild detergents, and it is readily available and relatively inexpensive. It is particularly surprising that peanut oil is so satisfactory since, as noted above, U.S. Patent No.

3,826,675 states that a number of naturally occurring vegetable oils, such as cottonseed oil and palm oil, tend to oxidize to a solid film which is no longer a good lubricant after a relatively short period of storage.

Peanut oil is a triglyceride of a mixture of fatty acids or aliphatic carboxylic acids, the contents of said acids being somewhat variable. An illustrative example of the mixture of acids and the proportions thereof in the triglycerides which comprise peanut oil is primarily oleic acid, approximately 55 to 60%.;. linoleic ac±d, approximately 22 to 26%; palmitic acid, approximately 6 to 8%; stearic acid, approximately 3 to 5%; behenic acid, approximately 3%; and arachidic acid, approximately 2 to 2.5%. In place of peanut oil, one can utilize what may be characterized as a synthetic peanut oil which would result from esterifying a mixture of the foregoing fatty or aliphatic carboxylic acids, or their acyl

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chlorides or bromides or their methyl esters, in the approximately above stated ratios with an amount of glycerol to produce the triglycerides, although this approach would be uneconomical. The term "peanut oil" will be understood to include such synthetically produced peanut oils and which would possess a low solidification temperature, similar to that of peanut oil, which is around 0°C or slightly below.

While, as stated, peanut oil has been discovered to be exceptionally satisfactory as a lubricant in the forming of seamless, drawn and ironed containers from aluminum stock, which contain¬ ers have a bottom wall and an integral sidewall, and its use represents the best and most important embodi- ment of our invention, it has, further, been discovered that certain synthetically produced oleic acid esters of aliphatic polyhydric alcohols containing at least three hydroxyl groups are also very satisfactory as lubricants for the same purposes which have described above in regard to the use of peanut oil as the lubri¬ cant. Such synthetically produced oleic acid esters which are useful as lubricants in accordance with the present invention are, particularly, the predominately trioleic acid esters of said aliphatic polyhydric alcohols; but, where the aliphatic polyhydric alcohol contains four or more hydroxyl groups, as in pe t- aerythritol and in aliphatic hexahydric alcohols such as sorbitol, mannitol and dulcitol, the tetra-and hexa- oleic acid esters can be used. It is, however, espe- cially desirable, in regard to the synthetically pro¬ duced oleic acid esters of said polyhydric alcohols, that the trioleic acid esters be utilized or said esters which contain predominately trioleic acid esters of the said aliphatic polyhydric alcohols. Commercial

sources of oleic acid can be used in preparing the aforesaid esters such as Red Oil and so-called White Oleic Acid; but crude oleic acid containing unduly high contents of acids with two or more double bonds, such as are prepared from tall oil, should generally not be used if optimal results are to be obtained.

The aliphatic polyhydric alcohols of which said synthetically produced oleic acid esters are useful in the practice of our present invention in- elude, by way of examples, glycerol, pentaerythritol, and aliphatic hexahydric alcohols of which sorbitol, annitol and dulcitol are illustrative and of which aliphatic hexahydric alcohols sorbitol is preferred. Illustrative examples of the synthetically produced oleic acid esters of the polyhydric alcohols which are useful as lubricants in the practice of our present invention are glycerol trioleate, pentaery¬ thritol tetraoleate, sorbitol trioleate, mannitol trioleate, sorbitol tetraoleate and mannitol tetra- oleate, particularly glycerol trioleate and sorbitol trioleate.

The aforesaid synthetically produced oleic acid esters of the polyhydric alcohols can be pro¬ duced by reacting the polyhydric alcohols with oleic acid in the requisite proportions to produce said esters, or with oleyl chloride or bromide, or with the methyl ester of oleic acid, in the presence or absence of catalysts, in accordance with esterifica- tion procedures which are well known to the art. When reference is made herein and in the claims to oleic acid esters of aliphatic polyhydric alcohols con¬ taining at least three hydroxyl groups and wherein three or more of said hydroxyl groups of said aliphatic polyhydric alcohols are esterified with

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oleic acid, or, for example, to glycerol trioleate or to sorbitol trioleate, it will be understood that it is intended to cover such esters which are produced synthetically and by the procedures generally, described above-

It will also be understood that mixtures of peanut oil and one or more of said oleic acid esters, in various proportions in relation to each other, can also effectively be used; and, further, that mixtures of two or more of said oleic acid esters, in various proportions in relation to each other, can also be utilized, it being understood that, where the foregoing mixtures are used, they are in the form of homogeneous compositions or solutions. Except as otherwise indicated hereafter, the invention will, for convenience as well as because the use of peanut oil represents the best embodiment of the present invention of which we are presently aware, be described in terms of the use of peanut oil as the lubricant.

In accordance with the best manner of the practice of our invention, aluminum stock material that is to be used for forming a drawn and ironed seamless container first has a thin layer of peanut oil applied to at least one surface, and preferably both surfaces. A disc is cut from the metal blank and formed into a shallow cup without the use of any additional lubricant or coolant. The shallow cup is then further drawn and ironed, as described above, to produce a seamless container which again is done without the use of any additional lubricant in the drawing and ironing machine.

More specifically, according to one embodiment of our invention, the thin layer of peanut- oil has a generally uniform distribution or thickness

2 on the aluminum stock surface, desirably 0-5-3 g./in. .

The peanut oil films can, however, be used in amounts significantly less than 0.5 mg./in. with even distri- bution, e.g. down to about 0.2 mg./in. . Coatings of greater than 3.0 mg./in. also produce acceptable com¬ mercial cans, but the cost-benefit ratio of such thicker films makes it economically unattractive. The scope of the subject invention, therefore, is intended to cover such lower and higher weight distributions.- While the manner of applying the peanut oil to the aluminum stock material is not critical in carrying out our present invention,, the peanut oil is most esirably applied to the aluminum stock material prior to the point when it is fed to the blanking and/or cupping machine. The peanut oil can, however, be applied in other ways. For example, it can be applied to blank discs before they are formed into cups in the cupping machine. Preferably the peanut oil coating is applied to each side of the aluminum stock, although it can be applied as a coating to only one side of the sheet, suf¬ ficient transfer of the peanut oil to the uncoated side occurring during the normal coiling or stacking of the aluminum stock. It is, however, more advantageous initially to apply the peanut oil to both sides of the blank discs.

It has been determined that cans can be formed very effectively from an aluminum stock material having a layer of peanut oil applied to one or both surfaces of the stock material in a layer or coating weight of

2 approximately 0.5 mg./in. or somewhat more on each surface, and such pretreated stock material is then utilized in forming a seamless drawn and ironed con¬ tainer that has a bottom wall and an integral sidewall in the general manner set forth above. By applying the peanut oil to the aluminum stock material before forming

such stock material into a can, we have found that all additional lubricants in the drawing and ironing process can be eliminated and it is only necessary to provide the body maker with a water coolant that has a small amount of a conventional rust inhibitor ^' and a conven¬ tional sequestering agent therein to maintain the tool¬ ing below a predetermined temperature. No additional lubricant is needed because a sufficient amount of the peanut oil remains on the cups after the cupping oper- ation. Furthermore, since peanut oil is water-insoluble, it is not washed off in the body maker by the water cool¬ ant of the bodymaker, and thereby remains on the can surface for lubrication during the ironing process. The peanut oil can be successfully applied to one or both surfaces of aluminum stock by commer¬ cially available lubricators to produce a thin layer or weight distribution thereof as indicated above. To produce the desired thickness of the layer, it may, in certain instances, be necessary either to thin the lubricant mixture by adding an organic solvent before it is applied to the surface of the stock material or by simply heating the aluminum stock before being con¬ tacted by the lubricator. A further alternative form of heating is to heat the rollers that form part of the lubricator.

A series of experiments was performed using three sets of sheets of aluminum stock material. The peanut oil was applied to one set of sheets to provide

2 a lubricating layer of approximately 1.25 mg./in. weight distribution on each side. On the second set of sheets, glycerol trioleate was applied to provide a layer thickness or weight distribution of 2.5 mg./in. 2 for each side. On the third set of sheets, sorbitol trioleate was applied as the lubricant to a layer thick- ness of 1.25 mg./in.2 per side. The sheets in each case

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were then converted into cups and subsequently into cans, utilizing a commercially available cupper and body maker in the manner previously discussed. The cups were converted to finished containers in the body maker without using any additional lubricant and utilizing only tap water as a coolant. Approximately a thousand of such cups and containers were produced with eac lubricant. Inspection of the finished con¬ tainers showed that they had a shiny outside surface and a scratch-free inside surface in each case. The containers were then cleaned using standard cleaning solutions with less than the present standard recom¬ mended concentration, yet commercially acceptable cleaning of the can surfaces was achieved. The elimination of the water-emulsion oils from the process and substitution of the peanut oil results in appreciable cost savings in the lubricant alone and also provides additional savings in the use of milder cleaners and lower cleaning temperatures since less cleaning agent is required. Furthermore, peanut oil provides better lubrication for the tooling than water-lubricant mixtures as currently used. This is believed to result from the fact that the peanut oil is initially located directly between the tooling and the container surface interface and also from the fact that the peanut oil permits ironing of the metal body without deterioration. Also, the presence of the peanut oil on the surface which becomes the inner surface of the container tends to aid in stripping the ironed con- tainer from the punch.

While the above description deals with the application of the peanut oil to the aluminum stock material before the cupping operation, it should be understood that the peanut oil can be applied after

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the cupping operation by spraying or otherwise applying it as the cup goes to the body maker. Alternatively, the. peanut oil can be sprayed or otherwise applied on to the cup as it goes through the body maker. It will be clear to those skilled in the art in light of the above teachings of the present invention that various modifications can be made in the details of carrying out the invention, but without departing from the principles disclosed and the scope thereof which is more clearly set forth in the appended claims.

The low rate of oxidation of peanut oil allows it to be applied to the stock material at the mill and stored for extended periods of time. It can also be applied at any point between the mill and the cupper. The peanut oil eliminates the necessity of adding any lubricant in the water coolant which is necessary to operate at commercial rates. However, it will be appreciated that it is usually necessary to add a rust inhibitor into the coolant for the tooling.