GB2340420A - Aerosol container - Google Patents

Abstract

An aerosol container is produced from a feedstock comprising steel strip coated on one or each of its surfaces with a coherent laminated coating, the process including the steps of:- <SL> <LI>(a) drawing the feedstock into a cup; <LI>(b) redrawing, and optionally ironing, the drawn cup to produce a cylindrical body in which the side walls are of reduced thickness; <LI>(c) shaping the open end of the cylindrical body </SL> <SL> <LI>(i) to form on its rim a flange to accommodate a separate pre-formed steel crown for receiving a valve cup, thereby producing a two-piece steel aerosol container; or, <LI>(ii) to form a neck for receiving a valve cup, thereby producing a one-piece aerosol container. </SL> Preferably, the feedstock comprises a low carbon steel strip, for example, steel strip with a carbon level of less than or equal to 0.04% by weight.

Description

2340420 1 AEROSOL CONTAINER This invention relates to a method of

producing steel aerosol containers from laminated steel feedstock and to aerosol containers produced by this method. More especially, but not exclusively, the invention relates to containers produced from only one or two polymer laminated steel blanks.

Steel aerosols are conventionally manufactured from three separate components. These comprise a welded cylinder to form the aerosol body, a pressed domed base secured to the lower rim of the cylinder by a seam, and a pressed conical top secured to the upper rim of the cylinder by a seam. The manufacturing process utilises high speed presses to form the base and top components and a conventional resistance welding machine to form the body cylinder. The raw material is predominantly externally decorated tinplate which is often lacquered internally to resist corrosion.

Although this type of aerosol container is relatively economical to manufacture and may be produced at high rates, it suffers from several major disadvantages. The seams at the top and base of the can are areas prone to corrosion, especially at the junctions of the seams and the weld of the can body. The body weld is also potentially an area of weakness.

Moreover, the body weld and the seams by which the top and base are joined to the body are considered to detract from the appearance of steel aerosol container. This is especially the case with small diz 16-sols (for example, less than 45mm diameter).

2 It is known to produce aluminiurn aerosols, known as monoblocs, from a single blank. In this known process, a thick aluminium disc is impact extruded to form a cylindrical body and integral base, the body then being decorated and lacquered. The diameter of the upper part of the body is then reduced (necked-in) prior to being filled and sealed using a standard (25mm diameter) "valve cup". Generally, aluminium aerosols are more expensive than the steel counterpart.

It is an object of the present invention to provide a steel aerosol container which is relatively economical to produce and which offers a high corrosion resistance to a variety of fillings.

According to the present invention in one aspect, there is provided a process for producing an aerosol container from a feedstock comprising steel strip coated on one or each of its surfaces with a coherent laminated coating, the process including the steps of:- (a) drawing the feedstock into a cup; (b) redrawing, and optionally ironing, the drawn cup to produce a cylindrical body in which the side walls are of reduced thickness; (C) shaping the open end of the cylindrical body W to form on its rim a flange to accommodate a separate preformed steel crown for receiving a valve cup, thereby producing a two-piece steel aerosol container; or, (ii) to form a neck for receiving a valve cup, thereby producing a one-piece aerosol container.

Preferably, the feedstock comprises a low carbon steel strip, for example, steel strip with a carbon level of less than or equal to 0.04% by weight.

In another aspect, the invention provides a process for producing an aerosol container from a feedstock of low carbon steel strip comprising less 3 than or equal to 0.04% by weight carbon, wherein the steel strip is coated on each of its surfaces with a coherent laminated coating, the process including the steps of:- (a) drawing the feedstock into a cup; (b) redrawing and optionally ironing the drawn cup, to produce a cylindrical body in which the side walls are reduced in thickness by a stretching operation; (C) shaping the free end of the cylindrical body whereby, 0) its side is flanged to accommodate a separate pre-formed steel crown for receiving a valve cup, thereby producing a two-piece steel aerosol container; or, (ii) its side is fully necked for receiving a valve cup, thereby producing a one-piece aerosol container.

Typically, the aspect ratio (i.e. ratio of the length of the sides to the diameter of the base of the aerosol container) is greater than or equal to 3: 1, preferably greater than or equal to 4:1.

In a further aspect, the invention provides a one- or two-piece aerosol container made from a feedstock comprising steel strip coated on each of its surfaces with a coherent laminated coating, the process including the steps of:- (a) drawing the feedstock into a cup; (b) exposing the cup to redrawing, and optionally ironing, to produce a cylindrical body whose side walls are reduced in thickness by a stretching operation; and, (C) shaping the free end of the sides of the cylindrical body wherein, W its sides are flanged to accommodate a separate pre-formed steel crown for receiving a valve cup, thereby producing a twopiece steel aerosol container; or, 0i) its sides are fully necked for receiving a valve cup, thereby producing a one-piece aerosol container.

4 Preferably, the feedstock comprises a low carbon steel strip, for example, steel strip with a carbon level of less than or equal to 0.04% by weight.

In a yet further aspect, the invention provides a one- or two-piece aerosol container made from a feedstock of low carbon steel strip comprising less than or equal to 0.04% by weight carbon, wherein the steel strip is coated on each of its surfaces with a coherent laminated coating, the process including the steps of:- (a) drawing the feedstock into a cup; (b) exposing the cup to redrawing, and optionally ironing, to produce a cylindrical body whose side walls are reduced in thickness by a stretching operation; (C) shaping the free end of the side of the body whereby, M its side is flanged to accommodate a separate pre-formed steel crown for receiving a valve cup, thereby producing a two-piece steel aerosol container; or, (ii) its side is fully necked for receiving a valve cup, thereby producing a one-piece aerosol container.

Typically, the proof strength of the feedstock lies in the range 500670N/mm'.

Preferably, the steel is of a minimum earing quality and is cast to conventional draw and wall ironed (DWI) steel cleanliness rules.

Typically, the steel is a high strength ductile steel known as TENFORM DR (RTM).

It is preferable to use feedstock with a thickness range between 0.2mm and 0.26mm.

The steel strip feedstock may be exposed to an electrolytic coating process. In this process, the steel strip is cleaned and pickled before being passed through a plating bath in which it is coated with a thin layer of chromium metal (typically of 0.01/im thickness) followed by a thin layer of chromium oxide (again typically of 0.01/im thickness). Alternatively, tinplate, blackplate, chemically treated blackplate or other suitable substrate could be employed.

The strip is then laminated with a polymer material, typically that known under the name "Ferrolite" (RTM). The standard Ferrolite process bonds a film of PET (polyethylene terephthalate) and/or PP (polypropylene) and/or nylon, to the surface of the metallic coated steel using heat and pressure. The films are co-extruded so that a bonding layer of about 2/im first makes contact with the steel and forms a strong bond. The bonding layer is typically 10-20% of total film thickness. After the bond is formed with the substrate the polymer films are melted and held above the recrystallisation temperatures for a few seconds before being rapidly quenched to below their softening temperatures. This produces an amorphous structure in the PET and a minimal crystalline structure in the PP.

Laminating processes and polymer films of a different structure and composition other than those discussed may be employed.

For high aspect ratio applications (e.g. 4:1 and above) the adhesion of standard Ferrolite (Trade Mark) coatings may be insufficient at the top of the cup wall after redrawing. To achieve good adhesion it may be necessary to modify the polymer coating.

In one embodiment, a bonding layer based on a non-recrystallising PET (PETG) may be used as an alternative bonding layer for the PET film. The ratio of this layer to the remainder of the film may be varied to constitute from 10-90% of total film thickness in order to improve adhesion and 6 formability.

Alternatively, or in addition, polyethylene iso-phthalate (PEI) may be added to the layer of PET to reduce crystallisation. Typically, PEI is added to constitute less than or equal to 20% of the total PET layer.

In one example in accordance with this invention, an aerosol container with dimensions 45 x 195mm bodies comprises a 25/im thick external coating of PET based coating consisting of 80-90% white pigmented PET and 10-20% PETG bonding layer, and an internal 201im thick PET based coating consisting of 80-90% clear (unpigmented) PET with 18% PIT and 10-20% PETG bonding layer.

In another example the standard polypropylene bonding layer is increased in thickness up to 50% of total film thickness.

In a further example, the standard polypropylene bonding layer is Corona treated to enhance adhesion.

The strip, either in sheet or coil form, is fed into the cupper either in a pre-waxed condition or it is passed through a waxer on entry to the cupping system. The wax may be edible, petroleum based and FDA approved with film weights in the range of 50-200mg/m2. At this stage, the laminate may be heated in the range 70-1 200C. Alternatively, the heating process may be carried out after the cupping or redrawing stage prior to dome formation. Pre-heating relieves stresses and ageing effects in the laminate so that subsequent forming is carried out more easily.

Discs are stamped from the strip or sheet. The cup is stretch drawn in one operation using a disc with a diameter typically in the range 120mm to 200mm. This diameter is dependent (with gauge) upon the container size and type of application. A range of feedstock gauges may be used but 7 typically lie in the range 0.20mm to 0.26mm. The draw ratio (i.e. ratio of the diameter of the disc to that of the cup) is in the range 1.2 to 2. 0: 1. The geometry of the tooling is designed in combination with the current blank holding load to give a reduction in wall thickness at the cupping stage of up to 10%. This is accomplished with a die radius range typically between 0. 5mm to 1. 5mm and a parallel land length of up to 5mm. The blankholding load is achieved by use of a boosted air pressure of up to 200psi fed into a series (typically three) of internal multiplying pistons. The punch/die gap is also critical and is controlled by the feedstock gauge and coating and gaps of 0.95-1.50 times the starting total laminate thickness are typically used. The punch nose radius is carefully controlled to achieve the required stretch whilst minimising subsequent container wall marking which could lead to laminate rupture. Punch nose radii in the range 2.5mm to 7mm are generally required.

The cupper cup is passed into the redraw press which contains tooling for the redraw operations. The cup is redrawn in a number of operations depending upon the aspect ratio of the finished container. One redraw may be used for low aspect ratio containers and as many as four or more redraws for high aspect ratio containers. Typically, three redraws are sufficient. The aspect ratio is the ratio of the container height to its diameter. Using this process, an aspect ratio of over 5 to 1 may be achieved which is far in excess of that achieved using a conventional draw wall iron process. The diameter reduction at each redraw stage is between 20%-35% with side wall thickness reductions up to 25% of the ingoing cup wall thickness. The total diameter reduction from the initial blank to the final can may be up to 80% with a total side wall thickness reduction from the starting gauge of up to 50%.

The tooling geometries for all redraw operations typically fall in the following ranges:- pressure sleeve diameter up to 0.6mm smaller than the internal 8 diameter of the preceding cup. pressure sleeve radii to be no greater than the nose radius of the preceding operation.

die radii up to 2mm with a parallel land length up to 5mm.

The blankholding load is achieved by use of air pressure of up to 90psi fed into a stack of internal multiplying pistons. The load is carefully balanced with the redraw die radius and punch/die gap of each operation to achieve the desired wall thinning.

Location of the cup on each die is achieved by means of a nest recess with a diameter matched to the cup, allowing for the thickness of the actual laminate in use. The radius of the nest diameter with the die at the base of the nest is in the range 0.10-2.Omm.

Each redraw punch may have a taper of up to 0.50mm in diameter at various positions to aid stripping. The gap between the largest punch diameter and die (per side) is controlled to between 0.5 and 1.50 times the starting laminate thickness. When this gap is at its smallest, i.e. narrower than the thickness of the laminate, then "ironing" occurs. This may be used simply to assist the stretching operation to reduce the can wall thickness but may also be used to modify the surface finish of the laminate to give it a shiny appearance. The punch nose radius is again important to achieve the required stretch whilst minimising subsequent can wall marking which could lead to laminate rupture. Punch nose radii in the range 1 mm to 3mm are typically used.

Gap control or arrested draw may be employed at all redraw stages to eliminate cup high spot clip offs or the generation of laminated "whiskers". When the gap control is used, gaps of 50% to 80% of starting laminate thickness (i.e between 0. 10 to 0. 1 5mm) between the pressure sleeve and die face are typically used.

9 Depending upon the stroke length and configuration of the press, a reverse redraw operation may be used.

In the final redraw operation, a concave dome may be drawn into the bottom of the container. The dome is formed in a separate doming operation to achieve the pressure resisting requirements of the particular container required, that is, typically, 12, 15 or 18 bar. Dome design to achieve these requirements is conditional on the use of FEA (finite element analysis) techniques. Of particular importance is the need for tight radii at the stand diameter position combined with a steep reverse chime angle. This may also be achieved by the use of a separate reforming operation. The side walls of the container display a burst pressure of typically at least 20% greater than the reversal pressure requirement of the dome.

The geometry of the dome of the container of the present invention is not restricted by the need to spray lacquer on the internal surface of the dome, as in the aluminium monobloc aerosol. The flexibility and abrasion resistance of the laminate allows for such an off-line dome reforming operation.

The container may be trimmed after the final redraw operation and may be decorated in a variety of ways. A printed plastic label or sleeve may be applied which may be manufactured from a plastic which shrinks above a given temperature. Thereafter, the container pass through a conventional oven to shrink the label or sleeve tightly onto the container. There is no need to remove the petroleum wax lubricant.

Alternatively, the container may be printed with thermal curing inks. in this case, the petroleum wax is removed from the external surface of the container to permit good application and adhesion of printing inks. The wax may be removed by washing the container (typically with chemical solutions and high quality water), passing the container through an oven at 190- 2200C for 1-3 minutes, or by rapidly passing the container through a gas flame whilst it is rotating. Printing may be carried out using conventional machinery using low or high temperature curing inks. The inks may be cured in a conventional tunnel oven.

Alternatively, the container may be printed with ultra violet (UV) curable inks. Once again, the wax needs to be removed and the inks can be applied using conventional machinery. After printing, the containers are typically passed, whilst rotating, under UV lamps.

The container may be necked using either die necking or spin flow necking techniques. The type of neck varies according to the fillers requirement. In one embodiment, the container may be necked, flanged and then seamed with a conventional aerosol cone. Alternatively, the container may be necked down and the flange rolled to directly accommodate a 25mm diameter aerosol valve cup. Using specially designed necking dies or spin flow necking tools, the shape of the neck may be tailored to the individual fillers requirements (usually for aesthetic appeal).

Container fillers are continually seeking methods of product differentiation in various forms. To date, this has mainly been achieved by the use of various decorations and decorating techniques. Another method of product differentiation being sought is by the use of shaped containers. The shaping of three-piece containers, particularly in the speciality packaging market, has been used for many years, but the shaping of two-piece cans has hitherto been unknown. The key to the solution of container shaping is the formability inherent in the container wall presented to the shaping machine. There are various methods of achieving the desired shape, but all rely on a measure of formability, given by a combination of container wall thickness and ductility. Three-piece containers may have can walls with mechanical properties and thickness essentially the same as the ingoing plate. Two- piece containers have walls that are thinner than the starting 11 material and hence, due to strain hardening effects, stronger and less ductile than the starting material.

Different methods of can shaping require differing levels of formability and hence, the level of formability left in a container wall will dictate the method of shaping that is likely to prove successful.

The shaping possibilities of the aerosol containers made from the raw materials discussed above are superior. This is because of the increased formability of the aerosol container wall which results from the special steel and production route used which is designed to increase ductility with little reduction in strength. This property, coupled with the strain hardening property of the steel, results in the formation of a shaped container with relatively high axial crush strength.

If either an aluminium or steel draw wall ironed aerosol container is shaped, coating is particularly difficult due to the problems of internal lacquer damage and the difficulty of internally spraying a shaped container. Therefore, a further advantage of the aerosol container of the present invention is that these difficulties are avoided.

It will be appreciated that the foregoing is merely exemplary of an embodiment according to the present invention and that modifications may be made thereto without departing from the true scope of the invention.

Claims (1)

12 CLAIMS

1 A process for producing an aerosol container from a feedstock comprising steel strip coated on one or each of its surfaces with a coherent laminated coating, the process including the steps of:- (a) drawing the feedstock into a cup; (b) redrawing, and optionally ironing, the drawn cup to produce a cylindrical body in which the side walls are of reduced thickness; (c) shaping the open end of the cylindrical body W to form on its rim a flange to accommodate a separate pre-formed steel crown for receiving a valve cup, thereby producing a two-piece steel aerosol container; or, (ii) to form a neck for receiving a valve cup, thereby producing a one-piece aerosol container.

2. A process as claimed in Claim 1 wherein the feedstock comprises a low carbon steel strip whose composition includes carbon of less than or equal to 0.04% by weight.

3. A process for producing an aerosol container from a feedstock of low carbon steel strip comprising less than or equal to 0.04% by weight carbon, wherein the steel strip is coated on each of its surfaces with a coherent laminated coating, the process including the steps of:- (a) drawing the feedstock into a cup; (b) redrawing and optionally ironing the drawn cup, to produce a cylindrical body in which the side walls are reduced in thickness by a stretching operation; (c) shaping the free end of the cylindrical body whereby, (i) its side is flanged to accommodate a separate preformed steel crown for receiving a valv6 cup, thereby 13 producing a two-piece steel aerosol container; or, (ii) its side is fully necked for receiving a valve cup, thereby producing a one-piece aerosol container.

4. A process as claimed in Claim 3 wherein the aspect ratio (i.e. ratio of the length of the sides to the diameter of the base of the aerosol container) is greater than or equal to 3:1.

5. A process as claimed in Claim 4 wherein the aspect ratio is greater than or equal to 4: 1.

6. A one- or two-piece aerosol container made from a feedstock comprising steel strip coated on each of its surfaces with a coherent laminated coating, the process including the steps of:- (a) drawing the feedstock into a cup; (b) exposing the cup to redrawing, and optionally ironing, to produce a cylindrical body whose side walls are reduced in thickness by a stretching operation; and, (c) shaping the free end of the sides of the cylindrical body wherein, W its sides are flanged to accommodate a separate preformed steel crown for receiving a valve cup, thereby producing a two-piece steel aerosol container; or, (ii) its sides are fully necked for receiving a valve cup, thereby producing a one-piece aerosol container.

7. An aerosol container as claimed in Claim 6 wherein the feedstock comprises a low carbon steel strip whose carbon content is less than or equal to 0.04% by weight.

8. A one- or two-piece aerosol container made from a feedstock of low carbon steel strip comprising less than or equal to 0.04% by weight 14 carbon, wherein the steel strip is coated on each of its surfaces with a coherent laminated coating, the process including the steps of:- (a) drawing the feedstock into a cup; (b) exposing the cup to redrawing, and optionally ironing, to produce a cylindrical body whose side walls are reduced in thickness by a stretching operation; (c) shaping the free end of the side of the body whereby, W its side is flanged to accommodate a separate preformed steel crown for receiving a valve cup, thereby producing a two-piece steel aerosol container; or, 0 0 its side is fully necked for receiving a valve cup, thereby producing a one-piece aerosol container.

9. An aerosol container as claimed in Claim 8 wherein the proof strength of the feedstock lies in the range 500-67ON /MM2.

10. An aerosol container as claimed in Claim 8 or Claim 9 wherein the steel is a high strength ductile steel known as TENFORM DR (RTM).

11. An aerosol container as claimed in any one of Claims 8 to 10 wherein the feedstock is of a thickness range between 0.2mm and 0.26mm.

An aerosol container as claimed in any one of Claims 8 to 11 in which the steel strip feedstock is exposed to an electrolytic coating process.

13. An aerosol container as claimed in Claim 12 wherein the steel strip is cleaned and pickled before being passed through a plating bath in which it is coated with a thin layer of chromium metal (typically of 0. 01jim thickness) followed by a thin layer of chromium oxide (again typically of 0.011im thickness).

14. An aerosol container as claimed in any one of Claims 8 to 11 wherein tinplate, blackplate, chemically treated blackplate is employed as a feedstock.

15. An aerosol container and a method of producing the same substantially as herein described.