WO2025090349A1 - Steel can construct - Google Patents

Abstract

A can construct is provided with an interior polymeric lining layer and an exterior zinc layer on a carbon steel cylindrical wall. The resulting can is amenable to usage as an aerosol can. A base and a lid of the can are formed as separate pieces that are joined to the cylindrical wall, or a each independently formed integral therewith. The lid and the base are also readily formed with an interior polymeric lining layer and an exterior zinc layer.

Description

STEEL CAN CONSTRUCT

FIELD OF THE INVENTION

[0001] The present invention in general relates to containers, and more particularly to a galvanized steel based can.

BACKGROUND OF THE INVENTION

[0002] Cans are the most commonly used metal packaging and are made from steel or aluminum. Steel-containing cans are made from electrolytic tinplate or electrolytic chromium/chromium oxide-coated steel, also known as tin-free steel (TFS). Metal based packaging provides an excellent barrier to light, gas and moisture, recyclability, easy conversion into various shapes, ability to withstand high heating temperatures, rigid structure, transportation to long distances, and unique decorating possibilities. However, health and product safety concerns of metal packaging include migration of bisphenol A, lead, cadmium, mercury, aluminum, iron, nickel, bulging of cans, tin dissolution, blackening, and corrosion. Metals are not inert to food products, hence are coated with protective lacquers to prevent metal-food interaction and migration of metal components.

[0003] Several alloys of iron are referred to as steels, with all of the alloys having carbon content ranging between 0.2 and 2%. The carbon binds the iron atoms in a rigid lattice and contributes to mechanical properties of steels, especially exceptional tensile strength. The alloys of iron used for food packaging applications can be categorized as ‘carbon steel' with carbon content not exceeding 1%. Tin plate, tin free steel, and polymer coated steels are the three majorly used coated steel for food packaging applications.

[0004] Tin plate usually refers to steel (base steel) coated with tin on each side. Historically, dipping was used for coating and was known as hot-dipped tin plate, but currently electroplating is most commonly used (know n as electrolytic tin plate) because of its ability to have coatings of different thickness on both sides. The process of tin plate production includes: tinning which involves covering of steel base plate with thin layer of tin; flow melting that incudes thermal treatment above tin’s melting point (260-270 °C) and rapid quenching in water leading to formation of tin iron compound (FeSm); chemical passivation in a sodium dichromate electrolyte generating tin and chromium oxides on the surface thus providing more stability' and resistance to the atmosphere; coatings with oily lubricant such as dioctyl sebacate and acetyl tributyl citrate for resistance against scratch, environmental corrosion, and finally passage of tin plate sheets through container forming machines.

[0005] Tin free steel (TFS) or electrolytically chromium/chromium oxide coated steel (ECCS) is similar to tin plate except non-involvement of flow melting and chemical passivation during its production. The production process involves dual electroplating of chromium and chromium sesquioxide, and finally coating with an oil such as butyl stearate oil. ECCS is slightly less expensive as compared to tin plate and more susceptible to corrosion in acidic environments because of absence of a sacrificial tin layer and is therefore usually coated. Conversely, TFS/ECCS is more acceptable for protective enamel coatings than tin plate because of a low melting point (232 °C). The use of TFS is less common as compared to tin plate and mainly utilized for food can ends, crown caps, and vacuum closures for glass containers. Removal of coatings as a prerequisite for welding of TFS hinders its extensive usage for single use containers and recyclability. Moreover, TFS lower cost over tinplate makes it the best choice for drums used in bulk storing and transportation of finished products.

[0006] Polymer coated steel utilizes conductive polymers to passivate steel against corrosion. Conducting polymers used for passivation include polyaniline, polythiopen, and polypyrrole for coating steel cans. Similarly, thermally sprayed coatings of synthetic fluoropolymer including polyvinylidene fluoride (PVDF), ethylene chlorotrifluoroethylene (ECTFE), perfluoroalkoxy alkane (PF A), and fluorinated perfluoroethylenepropylene (FEP) have employed for avoidance of corrosion using optical microscope, liquid immersion, and salt spray. Utilization of polyethylene terephthalate (PET) and polypropylene (PP) as coatings on deep drawn cans have proven effective. Polymer coated steels are highly abrasion and corrosion resistant with outstanding appearance and moisture barrier properties.

[0007] Stainless steel is an iron alloy which possesses extensive corrosion resistance and chemical inertness due to chromium content (normally above 11%). Although chromium is a highly active metal but in contact with atmospheric oxygen, chromium forms an inert layer of chromium oxide (C O?) on surfaces of the steel leading to its auto-passivation against corrosion. Stainless steel, owing to its corrosion resistance and inertness, is used in the food industry as a packaging material and for development of food processing and storage equipment. Austenitic, ferritic, and martensitic are the three major t pes of stainless steel based on their crystalline structure. Austenitic types are considered as food grade and most commonly used for packaging applications. Stainless steel is costly as compared to aluminum and tin therefore it is mainly used for returnable containers in food packaging (kegs for beer, wine, and soft drinks).

[0008] Aluminum is produced through a process that involves the conversion of alumina to aluminum hydroxide (Al(OH)?) in a solution of sodium hydroxide at 175 °C. The insolubles are filtered off and soluble Al(OH)s precipitated as white fluffy solid. The cost of aluminum is higher as compared to almost all coated steels and mostly preferred for seamless containers because of its incompetency to get welded. Aluminum is mainly used as light weight packaging material in its pure form for soft-drink cans, pet foods, etc., while addition of manganese enhances the strength of aluminum. Aluminum is considered to be the best material for recyclability.

[0009] Metal cans are classified by either a monoblock, two-piece or three-piece manufacturing method. [0010] A metal can formed with a three-piece structure consists of two end lids and a body. The body is the wall of the can and is formed from a cut to size flat metal sheet rolled with longitudinal sides joined to form a cylindrical structure with an open top and bottom. Three piece cans are easier to form in any combination of height and diameter, providing mixed specification cans with ease. Firstly, the cut sheets of metal are coated, printed, and rolled as per the requirement and longitudinal sides of the flat metal sheet are joined either by soldering or welding. However, soldering is usually avoided for food cans because of concerns related to migration of lead from tin/lead solder into foods. Welding is preferred for side seaming in food industries, which not only overcomes safety concerns of soldering but also reduces the metal usage as overlapping is a prerequisite for welding which requires less metal as compared to interlocking for soldering. After the formation of a round, hollow structure (cylindrical body) by side seaming, necking, and flanging for beverage cans and beading and flanging for food cans are performed. Necking usually refers to reducing the diameter of flat ends in perfectly cylindrical seamed body to concave ends thus offering metal usage reduction. The beading treatment of food cans gives spherical curves (corrugations) to the round structure of the can for extra strength. Flanging refers to the creation of outward flanges (hooks) for better fitting of can lids. Can ends (lids) are attached mechanically using double seaming process, involving interlocking of flange and lid’s edge.

[0011] Two piece cans were a major innovation in can making, consisting of one end (lid) and seamless body that is formed from a flat metal sheet stretched to form a cylindrical cup type structure with a closed bottom without any joint. Two piece cans are economic, hygienic, and have high printing area as compared to three piece cans because of absence of the side seam. Two piece cans are approximately 35% lighter and provide better integrity since absence of the side seam doesn’t require coatings or enamel usage. The production process for two- piece cans involves two major processes namely, drawn and wall ironed (DWI) and drawn and redrawn (DRD).

[0012] The production process for formation of a drawn and wall ironed (DWI) involves stamping of circular discs from lubricated metal sheets, a forming process punch draws circular disc to a shallow cup leading to uniform wall thickness throughout the structure; an ironing process involving passage of the shallow cup through a series of tungsten carbide dies resulting in a wall thickness reduction and increase of body height. Drawn structures are later trimmed to have the same height and cleaned for removal of lubricants. Finally, the bottom end is domed or profiled and similar to three piece cans, the DWI cans are necked or beaded and flanged. The base thickness for DWI can is more than the wall thickness as during the ironing process only side wall is stretched and thinned.

[0013] The production process for formation of a drawn and redrawn (DRD) has initial stages of stamping and forming for DRD can development that is similar to DWI cans. The ironing stage of DWI cans is replaced by multistage drawing in DRD, which is sequential stretching of the initial structure (shallow- cups) of the can. The multistage drawing leads to metal flow from base to the wall of a container and provides a similar wall and base thickness for DRD cans. The final treatments including trimming, cleaning, flanging, and lidding for DRD cans are similar to DWI cans.

[0014] While there have been many advancements in metal based can technology as outlined above for primarily food based products, there continues to be a need for improvements in aerosol can technology.

SUMMARY OF THE INVENTION

[0015] A carbon steel, two-piece aerosol can is provided as formed from a deep drawn cylinder and a stamped bottom. The steel used to form the can is lined with a PET, Epoxy or PU coating on the inside, and zinc, aluminium, or other rust resistant metals are applied on the outside of the can to form a three-layer wall.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The Figure illustrates three layers that form a wall of a can in accordance with embodiments of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0017] The present invention has utility as a carbon steel aerosol can. While the present invention is generally discussed hereafter in the context of a two-piece can, is appreciated that the present invention is also suitable for formation of a monoblock, three-piece aerosol can, a conventional cylindrical can, buckets, and paint cans may also use the structures and improvements disclosed herein.

[0018] Currently, it is convention to make aerosol cans with tin plated steel. Older versions of aerosol cans are formed as a three-piece can wi th a dome that is made of stamped steel that has a crimp joint to a cylinder. The cylinder is produced by resistance welding, with a bottom that is also stamped and crimped to complete the can. More recent aerosol cans may employ a two-piece design that has previously been made with tin coated steel for historical reasons owing to the fact that tin is both food compatible and functions as a flux for high speed resistance welding. However, owing to the increasing cost of materials, there is now a growing need to go to a lighter gauge steel for cost saving purposes. The use of lighter gauge steel lessens the amount of material used for each can, and also lightens the weight of the can. Lower weight cans also lessen transportation costs as less fuel is needed to distribute the products held in the cans.

[0019] Embodiments of the invention involve switching from tin plated steel to galvanized steel. In a specific inventive embodiment, a two-piece aerosol can construction has an electrodeposited zinc outer layer (galvanization layer) on a carbon steel substrate, with a polymeric coating on the inside layer that is in contact with the contents of the can. Representative polymers illustratively include polytetraethylene (PTE), polytetrafluoroethylene (PTFE), polyethylene terephthalate (PET, PETE), epoxy, and polyurethane (PU). An optional set of intermediate layers may include a rust inhibitor, an adhesion promoter, or a combination thereof intermediate betw een the steel and the polymeric coating. The thicknesses of these \ layers are those conventional to the art.

[0020] Numerical ranges cited herein are intended to recite not only the end values of such ranges but the individual values encompassed within the range and vary ing in single units of the last significant figure. By way of example, a range of from 0.1 to 1.0 in arbitrary units according to the present invention also encompasses 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, and 0.9; each independently as low er and upper bounding values for the range.

[0021] Referring now to the Figure, three layers (14, 16, 18) are illustrated that form a cylindrical w all 12 of an embodiment of an inventive can 10. The cylindrical wall 12 is joined to a base 11 to define an interior volume, V. A lid 13 terminates the cylindrical wall 12. The outer layer 16 is an electrodeposited zinc outer layer (galvanization layer) that is deposited on a carbon steel 14. The inner layer 18 is a polymeric coating. Layer 18 may also have an optional set of intermediate layers that may include a rust inhibitor intermediate between the steel substrate 14 and the polymeric coating 18. The layers 16 and 18 are also readily applied to the base 11, the lid 13, or both. The layers 16 and 18 are each independently readily applied to the flat stock steel substrate prior to cutting and forming to form the can 10. thereafter, or at intermediate stages of forming the construct. The can 10 is a two-piece aerosol can, a monoblock aerosol can, three-piece aerosol can, depending on if the lid is integral, both the base and lid are integral, or neither are integral relative to the wall 12; respectively. The can 10 is also formed as a conventional cylindrical can, bucket, or friction ring lidded can. [0022] Patent documents and publications mentioned in the specification are indicative of the levels of those skilled in the art to which the invention pertains. These documents and publications are incorporated herein by reference to the same extent as if each individual document or publication was specifically and individually incorporated herein by reference [0023] The foregoing description is illustrative of particular embodiments of the invention but is not meant to be a limitation upon the practice thereof. The following claims, including all equivalents thereof are intended to define the scope of the invention.

Claims

1. A can comprising: a cylindrical wall formed of carbon steel with an outer zinc layer and an inner polymeric coating and joined to a base to define an interior volume; a lid that terminates the cylindrical wall.

2. The can of claim 1 wherein the cylindrical wall is integral with at least one of the base or the lid.

3. The can of claim 1 wherein the polymeric coatings comprise polytetraethylene (PTE), polytetrafluoroethylene (PTFE), polyethylene terephthalate (PET, PETE), epoxy, and polyurethane (PU).

4. The can of claim 1 further comprising one or more intermediate layers intermediate between the carbon steel and the polymeric coating.

5. The can of claim 4 wherein the intermediate layer is a rust inhibitor, an adhesion layer, or a combination thereof.

6. The can of any one of claims 1 to 5 wherein the zinc outer layer is electrodeposited on the outer layer of the carbon steel.

7. The can of claim 1 wherein the can is an aerosol can.

8. The can of claim 7 wherein the aerosol can is a two-piece can.

9. The can of claim 7 wherein the aerosol can is a monoblock can.

10. The can of claim 7 wherein the aerosol can is a three-piece can.

11. The can of any one of claims 1 to 5 wherein the base comprises an outer zinc base layer and an inner base polymeric coating.

12. The can of any one of claims 1 to 5 wherein the lid comprises an outer zinc lid layer and an inner lid polymeric coating.