METHOD OF MAKING METAL CONTAINERS

Abstract: A precoated stock material for use in forming a drawn and ironed container and a method of forming such container is disclosed herein. In the past, water soluble lubricants applied to the stock material during drawing and ironing had to be removed to produce an acceptable surface for subsequent coatings or decorations. This often involved use of harsh chemicals which, in some cases, involved potential health hazards. Recent efforts aimed at use of partially cured coatings containing lubricants applied prior to drawing and ironing have been unsuccessful in the sense that production rate is unacceptable and the coating is often removed during ironing. In this invention, the stock material initially has a layer of lubricant applied to at least one surface of the metal base with the lubricant consisting essentially of a Fatty acid ester of a mono or polyhydric alcohol and having a distribution of less than 0.5 mg./cm.<s2>s (3 mg./in.<s2>s). The method contemplates applying the layer of lubricant to a metal stock, such as aluminum, black plate or tinplate, cutting a disc from the metal stock, and transforming the disc into a drawn and ironed container without additional lubricant being applied to the tooling. In one version of the invention, a black plate stock material has a curable polymeric coating applied to one surface which is then partially cured and a layer of lubricant is applied to the other surface.

Description: METHOD OF FORMING SEAMLESS CONTAINERS Background of the Invention The present invention relates generally to containers and more particularly to an improved stock material for making containers and a method for forming seamless drawn and ironed containers from the improved stock material. The use of a two-piece container for packaging beer and/or carbonated beverages has become very popular in recent years. The two-piece container consists of a container sidewall or body that has a unitary end wall at one end thereof. The second piece for the con¬ tainer consists of an end which is seamed to the open end of the container. In the formation of drawn and ironed containers, a finished container is produced by initially cutting a disc from a sheet or coil of stock material and substan¬ tially simultaneously transforming the disc into a shallow cup in a conventional cupping machine that forms part of a can manufacturing line. The shallow cup is then converted into a drawn and ironed container in a body maker wherein the shallow cup is reformed into a cup of different dimensions and then passed through a plurality of ironing rings that cooperate with a punch to decrease the wall thickness of the reformed cup and produce a seamless container. Alternatively, the cup may initially have a diameter substantially equal to the final diameter so that the reforming or redrawing in the body maker is not necessary. In most commercial machinery utilized for forming the cups and then converting the cups to drawn and ironed containers, a lubricant-coolant is utilized in the cupper for providing the necessary lubricity between the surface of the sotck material and the tooling. The body making machinery also incorporates mechanism for flowing a lubricant-coolant to the surface of the container and to the ironing dies utilized in cooperation with the punch. Conventionally, the lubrican coolant consists of a mixture of water and an emulsified oil or emulsified synthetic lubricant, such as a com¬ mercially available Texaco 591 product. One of the difficulties with utilizing the water soluble emulsified oils in the cupping as well as the drawing and ironing tooling is subsequent cleaning of the finished con- tainers to remove the emulsified oils from the surfaces thereof. In order to produce an acceptable surface that can subsequently be coated and/or decorated, it is necessary to utilize harsh chemicals and washing tempera¬ tures as high as 72° C to remove the undesired emulsified oils. Furthermore, it has been determined that some emulsified oils may become toxic which presents a po¬ tential health hazard. Presently, most drawn and ironed containers are formed from aluminum because of the relative ease in fabric ' ability of the container. Because of the cost of aluminum, manufacturers are constantly striving to find an acceptable substitute for aluminum which can be manufactured at a competitive cost. One acceptable alternative for the drawn and ironed aluminum container is commonly referred to as tinplate. This material includes a base plate of low carbon steel, such as black plate which has both ' sur¬ faces covered with a thin layer of tin. The tin coating acts as a low friction, ductile material during the ironing process and also resists corrosion. While tinplate has been found to be an acceptable alternate for aluminum, the availability of this material is limited and the cost is high. OMP WIP Bethlehem Steel Corporation also has continued its development efforts for producing a beer and carbonated beverage container from black plate using conventional machinery by applying organic coating to the black plate which can then be drawn and ironed at a price which is competitive to the present day tinplate or aluminum container. To this end, a proposed process is disclosed in United States Patent No. 4,032,678. This process contemplates the formation of special organic coating systems that enable container manufacturers to produce drawn and ironed beer and soft- drink cans from black plate. The foregoing patent describes two coating concepts that have been developed for black plate, one of which consists of admixing a thermosetting coating and a lubricant and applying this mixture to both sides of the black plate blank and partially curing the mixture before the blank is con¬ verted into a finished container. The other concept contemplates supplying the coating-lubricant mixture to only the one side of the blank (the side forming the outside of the can) , and applying a coating lubricant alone to the other side of the blank (the side that forms the inside of the can) , However, while such process is acceptable in laboratory trials at slow speeds, actual tests have shown that the partially-cured coating having the lubricant mixed therein, while allowing drawing and ironing of the container, is not acceptable for making cans at commercial production rates and most of the coating is removed during the ironing process when containers are manufactured at rates of more than 150 containers per minute. It was also determined that the coating was removed in the form of large flakes or long narrow strips which would be introduced into the coolant and would rapidly clog up the filtering system for the coolant. These flakes or strips would also be carried by the container to downstream areas of the container processing line which disrupted the proper processing of the containers. Summary of the Invention It has been determined that all lubricants in the cooling fluid can be eliminated by applying a thin layer of an organic ester to the stock material before the cupping operation is initiated. According to the present invention, a metal base of stock material that is to be used for forming a drawn and ironed seamless container first has a thin layer of lubricant applied to at least one surface of the metal stock or blank and 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 to produce a seamless container which again is done without the use of any additional lubricant in the liquid coolant, such as water, in the drawing and ironing machine. More specifically, the thin layer of lubri¬ cant consists essentially of a fatty acid ester of a mono or polyhydric alcohol and the layer has a distribu- tion or thickness preferably less than 0.5 mg./cm. 2 (3 mg./in. ) . It has been determined that applying a single 2 layer of less than 0.5 mg./cm. of an organic ester to one surface only of black plate, tinplate or aluminum by a commercial lubricator eliminates the need for any subsequent lubrication in the cupping machine as well as the body maker. According to another aspect of the invention, a black plate container can be formed by initially applying a layer of curable polymeric coating on a surface of the black plate which will become the external surface of a container, partially curing the coating within certain critical limits, and applying the lubri- cant to the other surface of the black plate. The curable polymeric coating is applied in 2 an amount of about 0.2 (1) to about 0.7 mg./cm. (4 mg./ 2 in. ) of blank area. It has also been determined that the optimum thickness of the coating should be about 0.3 (2) to about 0.5 mg./cm. 2 (3 mg./in.2) on the surface of the metal plate. The coating can be cured to the desired degree by continuously feeding the coated stock through an oven to achieve a temperature for the metal portion of the strip of more than about 204 degrees C • but less than the degradation temperature for the applied coating and maintaining the strip within the oven for a time period of approximately one minute. The partial curing may also be accomplished by baking the coated blank at a temperature of approximately 177 degrees C for a period of approximately- 10 minutes. The present process is particularly well suited for the manufacture of containers from pure ferrous metal such as black plate of tin-free steel stock. Description of the Invention In its broadest aspect, the present inven¬ tion contemplates precoating a metal sheet or coil with , a thin layer of lubricant to one surface only of the metal sheet or coil, cutting a disc from the metal sheet or coil with the lubricant applied to one sur- face, forming a shallow cup from the disc subsequently ΪΛJR E AIΓ OMPI < WIPO Λ> redrawing and ironing the shallow cup into a full sized container. Stated another way, a stock material, such as an aluminum, black plate, or tinplate metal sheet or 5 coil, has a layer.of lubricant consisting essentially of a fatty acid ester of a mono or polyhydric alcohol applied to one surface of the stock material to a thick- ness of less than 0.5 mg./cm. 2 (3 mg./in, _>) and pref- erably about 0.2 mg./cm. (1 mg./in. ) and the pre- 10 treated stock material is then utilized in forming a seamless drawn and ironed container that has a bottom wall and an integral sidewall in conventional cupping and body making machinery that is presently utilized for making such containers. By applying the lubricant 15 to the stock material before a disc is cut therefrom, 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 rust inhibitor therein to maintain 20 the tooling below a predetermined temperature. One lubricant that is suitable for carrying out the present invention is a fatty acid ester of a mono or polyhydric alcohol. A commercially available lubricant of this type is produced by Mobil Chemical '25 Company under the designation S-6661-003. More specifically, this ester is made from a monomeric polyhydric alcohol having three to six hydroxyls and a 14 to 20 carbon fatty acid. The Mobil lubricant was successfully applied 30 to one surface of black plate, tinplate and aluminum plate by a lubricator to produce a thin layer of lubricant having a thickness or distribution of less than 0.5 mg./cm. ~ (3 mg./in.2). on the surface of the stock material that ultimately becomes the inside OMPI . W1P0 of the container. If necessary, to produce the desired thickness of the layer, it may be necessary to either thin, the fatty acid ester with a solvent before it is applied to the surface of the stock material, or simply by heating the material before it is applied by the lubricator. A further alternative form of heating would be to heat the rollers that form part of the lubricator. When black plate is used as the base mate- rial, it is preferably pretreated by applying an organic or polymeric coating to at least one surface thereof and partially curing the coating. Curable organic or polymeric coatings suitable for the purposes of the present invention are exemplified by the curable epoxy resins, e.g., the glycidyl poly- ethers of polyhydric phenols, the epoxy novolac resins, the glycidyl ethers of aliphatic polyols, the cycloaliphatic epoxy resins, and the like, the curable vinyl resins, the curable epoxy-urea-formaldehyde resins, and similar curable polymers. Preferred for the present purposes are the curable epoxy resins having a chain of alternating glycidyl and divalent phenolic units united through an ether oxygen and having glycidyl units in the terminal positions of the chain. The ether oxygen (as distinguished from the oxirane or hydroxy oxygen) is linked to the primary carbon atoms of the glycidyl units. These particular epoxy resins are glycidyl polyethers of polyhydric phenols. Exemplary are the reaction products of epichlorohydrin with a dihydric phenol represented by the general formula as follows: wherein n can have a value of 1 to about'20, wherein R can be wherein R 1 can be 10 Suitable dihydric phenols for reaction with "epichlorohydrin to produce the aforementioned resins are 20 -resorcinol, catechol, the polynuclear phenols such as 1,1-bis (4-hydroxyphenyl)ethane, 1,1-bis (4-hydroxyphenyl)propane, 2,2-bis (4-hydroxyphenyl)propane, 25 2,2-bis (4-hydroxyphenyl)butane, 1,1-bis (4-hydroxyphenyl)butane, 1,1-bis (4-hydroxyphenyl)-2-methylpropane, 3,3-bis (4-hydroxyphenyl)pentane, and the like. Preparation of the foregoing products is well 30 known in the art and generally involves heating the dihydric phenol with epichlorohydrin at a temperature of about 49 degrees C to about 199 degrees C in a basic reaction medium. The desired molecular weight -BUR OMP W1P of the reaction product is obtained by varying the relative amounts of the phenol and epichlorohydrin. In addition, a portion of the foregoing reaction product can be combined with a reactive modifier to increase toughness, flexibility, elonσa- tion and/or adhesive peel strength. A particularly preferred modifier is a xylene-formaldehyde resin condensed with the aforementioned reaction product. A particular preferred curable polymeric composition for the practice of the present invention comprises a 4,4'- isopropylidene-diphenol-epichloro- hydrin resin having a portion of the resin condensed with a xylene-formaldehyde resin. A curable polymeric composition of this type is available commercially from Mobil Chemical Company under the designation S-9019-001. The degree of cure of the applied curable coating for drawing and ironing is very important. The applied coating should be about 50 to about 75% cured before drawing and ironing, and preferably about 60 to about 70% cured. Stated in another way, the coating should be cured to a degree so that about 25% to about 50% of the coating constituents are extractable, preferably about 30 to about 40% of the constituents are extractable by methylene chloride In the extraction test, the coating was extracted in the following manner: 1) Each coated metal disc was weighed and the total weight was recorded. 2) Each coated disc was then soaked in methylene chloride for thirty minutes. 3) The discs were dried in an oven at 107 degrees C for thirty minutes . 4) Each disc was again weighed. 'BUREATJ' OMPI . fa W1PO . 5) The total weight loss for each disc was determined, ie, step 1-4, 6) The percent extraction was then determine using the following formula: Percent Extracted = weight loss in (5) x 100 total weight of coating Actual comparisons were made between black plate that was coated on one side only with a partially cured organic coating, with and without having an internal lubricant mixed with the organic coating. Contrary to the teachings of the above Bethlehem patent, actual tests snowed that containers formed from black plate coated with the organic coating, but without having an internal lubricant mixed with the coating, retained substantially more coating on the finished container than when the internal lubricant was present in the organic coating. Furthermore, production formability was enhanced by applying a thin layer of lubricant to the other surface of the blank. Example I Laboratory tests were conducted by applying a layer of approximately 0.2 mg./cm. 2 (1.25 mg./in. 2 ) of the above Mobil lubricant on one surface of a sheet of tinplate stock material. The sheet of stock mate¬ rial was then cut and formed into a shallow cup in a conventional manner without the addition of any further lubricant or without any water. The cups with the layer of lubricant on the inner surface, were then reformed into finished containers in a conventiona body maker where only water alone or water with 0.05% rust inhibitor was circulated through the tooling used in producing the finished container. Some containers were made using " a water-emulsion oil mixture for the coolant. 'B J OM Container ' s made from the organic ester pre- applied sheets or coils consistently showed better cleanability when water alone was used as the coolant. In all instances the containers made without the emulsion oil lubricant had a smooth and uniform surface appearance. Example II Aluminum stock material in the form of plates was coated on one side with an organic ester, such as the Mobil lubricant, to produce a layer on one surface 2 having a distribution of approximately 0.2 mg./cm. (1.25 mg./in. ). These plates were then converted into cups and subsequently cans utilizing a commercially available cupper and body maker. In converting the plates into cups, the plates were positioned so that the lubricated surface became the internal surface of the cup and no additional lubricant or water was needed to produce satisfactory cups from the plates. The cups were then converted to finished containers in the body maker utilizing -only tap water. Several thousand of such cups and containers were produced and inspection of the finished containers showed that the containers had a shiny outside surface and a scratch-free inside sur¬ face. The containers were then cleaned using several standard cleaners with less than the present standard recommended concentration to remove all of the lubri¬ cants from the container surfaces. Example III A coil of black plate stock material was cut into sheets and each of the sheets was coated on one surface with Mobil S-9019-001 organic coating to 2 produce a layer of approximately 0.5 mg./cm. (3 mg./ in. 2 ) and the plate was baked at 177 degrees C for five minutes to partially cure the coating. A Mobil S-6661-003 lubricant was then roll-coated with a thin layer (0.4 mg./cm. ) on the other surface of the sheets to produce a thin layer of lubricant. The sheets were then stacked and delivered to a cupping machine and during this process some of the lubricant was transferred to the coated, partially-cured surface of the sheets. Discs were then cut from the " sheets and con¬ verted into shallow cups using commercial cupping equipment without the use of any water or additional lubricant. The shallow cups had the layer of lubricant on the inner surface and the organic coating on the outer surface. The cups were then converted into drawn and ironed containers in a commercial body maker. Some containers were formed from cups using only water aa the cooling agent while other containers were formed using a lubricant-coolant. This lubricant-coolant ' was a water and emulsified oil mixture which included about 15% of a Texaco 591 emulsified oil. In all instances, the containers formed with water alone had as good or better surface appearance then those formed using the lubricant-coolant mixture. Example IV A coil of dry black plate was coated with a Mobil S-9019-001 organic coating to produce a layer of approximately 0.55 mg./cm. ~ (3.25 mg./in.2). The coated coil was passed through an oven that had three temperature zones so that the metal surface temperature reached approximately 216 degrees C to partially cure the coating. The coil with partially- cured coating was then subjectee to an extraction test and it was determined that 34% of the coating was extracted, ie, the coating was about 66% cured. The other surface was roll-coated with Mobi_l S-6661-003 lubricant to provide a coating thickness car less than 0.3 mg./cm. 2 (2 mg./in,?), The material was then cupped without the use of any water or additional lubricant. The cups were then drawn and ironed using water only as a coolant in the body make r. The cups were converted into containers without difficulty, and the containers were run through the remainder of a can making line without difficulty. The cure of the partially-cured organic coating was completed after the drawing and ironing step, as the containers were passed through the remainder of the container processing line. The above tests establish that drawn and ironed containers can be formed from coated black plate, aluminum or tinplate by precoating the stock material with a thin layer of an organic ester lubricant and the drawn and ironed containers can be formed without the use of water or emulsifiable oils in the cupper and using only water as a coolant in the body maker or drawing and ironing machine. It is believed that elimination of the water emulsion oils from the process and substitution of the organic ester results in a cost savings of approximately 50% in the lubricant alone and also provides additional savings in the use of milder cleaners and lower cleaning temperatures. It has also been established that the organic ester lubricant provides better lubrication for the tooling than the water-lubricant mixture. This is believed to result from the fact that the lubricant is initially located directly between the tooling and the container surface interface and also from the fact that the organic ester lubricants withstand the high .temperatures encountered during ironin of the metal body without deterioration. Also, applying the layer of lubricant to the surface which becomes the inner surface of the container is believed to aid in stripping the ironed container from the punch. Of course, if desired, both surfaces of the stock material could be coated with a lubricant and/or the distribution or thickness of the layer or layers could be increased. However, tests have shown that increasing the thickness of the coating on one surface only will not increase the efficiency of the opera¬ tion but will increase the cost without any addi¬ tional benefits. Respecting the two-sided coating with lubricant, it was determined that the additional coating on the second side increased the costs without deriving any benefits from the increased cost. In other words, tests showed that one side coated mate¬ rial would have enough lubricant transferred to the other side- during the processing of the stock material and in the cupper and body maker to eliminate the need for applying lubricant to the second side. While the manner of applying the lubricant to the stock material is not critical in carrying out the present invention, the lubricant is pref¬ erably applied as the stock material is fed to the cupping machine. When the lubricant is applied to a stock material which also has an organic coating applied to one side, such as Example III, the coating and lubricant could simultaneously be applied to opposite sides of the stock material with a lubricator and the material could then be passed through an oven to partially cure the organic coating. It has been determined that the heating of the lubricant in the JUR OM oven has no deleterious affect on the lubricant. Of course, the lubricant could also be applied in other ways. For example, ' it would be possible to apply the lubricant to the stock material in the cupping machine as the discs are being severed from the stock: material and the appended claims are intended to cover such alternate method of application.

Claims: WHAT IS CLAIMED IS; 1. A method of forming a seamless container having a bottom wall and an integral sidewall from a sheet of metal stock material by cutting a disc from said stock material drawing said disc into a cup and substantially reducing the sidewall of said cup to produce a drawn and ironed container, characterized by applying a thin layer of lubricant to said stock material before said disc is cut from said stock material, and forming said seamless drawn and ironed container without applying any additional lubricant to said stock material. 2. A method as defined in claim 1, character ized by said layer of lubricant being applied in an amount not exceeding 0,5 mg./cm. 2 . 3. A method as defined in claim 2, character ized by said layer of lubricant having a thickness of approximately 0.2 mg./cm. - 4. A method as defined in any one of claims 1 to 3 characterized by said lubricant consisting essentially of a fatty acid ester of a polyhydric or monohydric alcohol. 5. A method as defined in claim 4 , characte ized in that said metal is aluminum. 6. A method as defined in claim 4, character ized in that said metal stock material is tinplate. 7. A method as defined in claim 4, further characterized by applying a layer of polymeric curable OM coating free of any lubricant to the other surface of said metal stock material and heating said material to partially cure said coating before cutting said disc and subsequently heating said seamless drawn and ironed container to fully cure said coating. 8. A method as defined in claim 7, in which said metal stock material is black plate and said coating is present in an amount of about 0.2 to 0.7 mg./cm. 2 . 9. A container produced by the method defined in claims 1 through 8. 10. A metal stock material having a lubricant as defined in claims 1 through 4. "BU EAU OMPI AMENDED CLAIMS (received by the International Bureau on 9 May 1979 (09.05.79)) 1. A method of forming a seamless container having a bottom wall and an integral sidewall from a sheet of metal stock material by cutting a disc from said stock material, drawing said disc into a cup and substantially reducing the sidewall of said cup in a multistage ironing process to produce a drawn and ironed container, characterized by applying a thin layer of 2 lubricant of at least " 0.2 mg./cm. to at least one surface of said stock material before said disc is cut from said stock material, and forming said seamless drawn and ironed container, and maintaining at least some of said lubricant on said surface throughout said multi¬ stage ironing process. 2. A method as defined in claim 1, character¬ ized by said layer of lubricant being applied in an 2 amount not exceeding 0.5 mg./cm. . 3. A method as defined in claim 2 character- ized by said layer of lubricant having a thickness of 2 approximately 0.2 mg./cm. . 4. A method as defined in any one of claims 1 to 3 characterized by said lubricant consisting essentially of a fatty acid ester of a polyhydric or monohydric alcohol. 5. A method as defined in claim 4, character¬ ized in that ' said metal is aluminum. 6. A method as defined in claim 4, character¬ ized in that said metal stock material is tinplate. 7. A method as defined in claim 4, further characterized by applying a layer of polymeric curable coating free of any lubricant to the other surface of said metal stock material and heating said material to partially cure said coating before cutting said disc and subsequently heating said seamless drawn and ironed container to fully cure said coating. 8. A method as defined in claim 7, in which said metal stock material is black plate and said coating is present in an amount of about 0.2 to 0.7 2 m ./c . . 9. A container produced by the method defined in claims 1 through 8. -BUREAU OMPI STATEMENTUNDERARTICLE19 There is submitted herewith an amended set of claims in the above application comprising new pages 16 and 17. Please enter these amended claims into the above application in accordance with the rules pertaining to Patent Cooperation Treaty applications. -BUR OM

Inventors: HESSEL W, MISRA S, OPENCHOWSKI R, ZENGER R
Applicants: NAT CAN CORP, NATIONAL CAN CORP
Application year: 1978
Main classification: B21D51
IPC codes: B21D22, B21D51, C10M105