CA1150454A

CA1150454A - Deep-drawn components and method of obtaining same

Info

Publication number: CA1150454A
Application number: CA000321072A
Authority: CA
Inventors: Hans-Juergen Schlinsog
Original assignee: Schmalback Lubeca AG
Current assignee: Ardagh Metal Packaging Germany GmbH
Priority date: 1978-02-08
Filing date: 1979-02-08
Publication date: 1983-07-26
Also published as: AT370649B; IT7919978A0; SE7901079L; ATA91779A; FR2416747A1; ES477567A1; NL7900853A; FR2416747B1; GB2019884A; DE2805279A1; BE874054A; IT1110965B; GB2019884B; DK50979A

Abstract

ABSTRACT OF THE DISCLOSURE

Deep-drawn components, e.g. cans, of aluminium or tin sheet metal or similar material and a method of pro-ducing such components are disclosed, wherein the com-ponents are characterized by a hydrophilic layer of, for example, isopropanol or triethanolamine; and the method comprises cooling of the forming tools, maintenance of an inert condition during the forming and electrolytic treat-ment prior to forming. The invention provides components and a method which are more economic than prior art articles and methods.

Description

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BACKGROU~D OF THE INVENTION
i) Field of the Invention This invention relates to deep-drawn or wall-ironed components of aluminium or tinned iron sheet and their manufacture particularly components that are -to be provided with an interior lacquer finish and which may be formed from a flat blank of rolled sheet by means of a die tool comprising top and bo-ttom dies; the invention is more especially concerned with such components to provide wall-ironed cans for packaging and the method of producing deep drawn cans formed from such deep-drawn components.
ii) Description of the Prior Art In the production of deep-drawn components, particularly components to be provided with an interior lacquer finish after the deep-drawing step, aluminium sheet or tin sheet, i.e., iron sheet coated with tin is frequently used. Such deep-drawn components are employed when the component is to be brought into contact, during subse~uent handling, with a fluid, particularly a corrosive fluid or other corrosive media. In the production of wall-ironed cans for packaging purposes, for example, aluminium sheet and tin sheet are employed almost exclusively.
When an alurninium sheet is used, protective coat-ing on the sheet is not normally required to ensure corrosion resistance. However, when iron sheet is used, it is necessary to provide a coating, for example, a tin or copper coating; which coating acts to reduce the resistance, due to solidification of the material during drawing, which resistance increases with the reduction of the wall thickness of the shee-t or component during deep-drawing, and s:imultaneously functlons as a glide layer.

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In aluminium sheets, the surface layer of the aluminium provides a glide layer. It is necessary to provide an oleophilic film, before or duriny the deep-drawing step, of the aluminium and tin sheets in order to avoid the formation of cracks and further reduction of the resistance which reduction arises from the solidification of the material during drawing.
When using -tin sheet, it has hitherto been considered necessary to carry out a thermal treatment after the rolling and the cleaning of the sheet as well as the tinning thereof, in order to produce an alloy layer of iron and tin in the region of the transition to the tin layer.
Furthermore, in a further step, the upper or exposed surface of the tin layer has been passlvated so as to avoid oxidation of the tin at the upper surface. This has yenerally been achieved by application of a very thin chromium-chromium oxide layer which is destroyed on sub-sequent deep-drawing so that the upper surface of the finished production piece is again provided substantially by the tin.
Prior to interior lacquer finishing of the drawn or wall-ironed components, it is necessary to remove the oleophilic film since this prevents the adhesion of -the lacquer on the metal surface or at least adversely affects the adhesion, such that a reliable lacquer coating of the component is not attainable. It is, accordingly, necessary to subject the deep-drawn or wall-ironed components made of the aforementioned sheet metals to an intensive washing step.
The base regions of the deep-drawn components, for example, the base regions of wall-ironed cans, are not subjected, duriny the deep-dr~winy or wall-ironing operations to appreciable mechanical loads, so that these components of tin sheet or post-treated iron sheet metal are provided with a passivating layer, while, in the case of aluminium sheet metal, the bottom regions exhibit an aluminium oxide layer. Due to the variations in the surfaces of the drawn or wall-ironed wall portions of the components and the variations in the base regions, there arises a variation in the adhesion effectiveness of the interior lacquer finish which presents considerable problems, particularly in the case of the production of wall-ironed cans for packaging purposes.
SUMMARY OF THE INVENTION
It is the aim of the present invention to form a component of aluminium or tin sheet metal that can be produced more economically and particularly without the necessity of an oleophilic glide layer during deep-drawing and which is thus furnished with a surface layer which has, in the base regions and in the wall regions, a substantially homogeneous water wetting ability and lacquer wetting ability.
According to the invention there is p~ovided a deep-drawn or wall-ironed metal component comprising a sheet of aluminium or tinned ferrous metal having a hydro-philic surface layer containing free hydroxyl groups.
The ferrous metal may be iron or steel.
The hydrophilic surface may be considered as being represented as:
Me-Rl-R2 in which Me is aluminium or tin, Rl is a hydroxide or oxyhydrate group, and R2 is at least one organic compound containing at least one of a hydroxyl group and an active nitrogen group.

,~ - 4 -~5~54 The hydrophilic surface may similarly be considered as being represented as: MRn in which M is aluminum or tin;
R is selected from the group consisting of: a) OH, b) O and OH, with the surface concentration of oxygen (O) directly bonded to a metal atom (M) being smaller than the surface concentration of hydroxyl (OH) directly bonded to a metal atom (M), and c) a hydrophil-ic organic group containing at least one hydroxyl (OH) group, and n is a suitable positive -num~er for rendering the surface layer electrically neutral.
In thisrepresentation, when R is c), it may suit-ably be a complex, for example, a combined alkanolamine, especially a trialkanolamine, for example, of the triethanol amine class, or it may suitably be an oxalic acid ester or glycerol ester.
In accordance with a particular embodiment of the invention there is provided a constructive part of a deep drawn, rolled aluminum or tinplate blank, suitably produced by deep drawing the rolled blank using punch and ring like tools, in which the plate material employed for the blank has a hydrophilic surface layer represented as MRn, wherein M, R and n are as defined above.
More especially the blank may be a drawn and wall ironed can body for packaging purposes, which is to be internally lacquered.

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DESCRIPTIOM OF PREFERRED EMBODIl~ENTS
It has been found that the presence of metal oxides on the surface of the aluminium and tin sheet, particularly aluminium oxide and tin oxide, is hazardous to the metal forming operation, causing build-up of material on the forming tools which scars the surface of the sheet and modifies the pressure and pulling forces produced in the forming operation D
In the invention surface metal oxides which are hydrophobic are converted to metal hydroxides or oxy-hydrates which are hydrophilic.
The metal hydroxide or oxyhydrate or a peroxide of the metal may form the hydrophilic layer.
The metal hydroxides are not, however, especially stable and they are converted, in time, back to the me-tal oxides. In the invention the metal hydroxides are maintained and the hydrophilic nature of the surface of the sheet is maintained by means of an organic coating which is held or bound firmly to the suxface metal hydroxide.
This organic coating functions as a temporary protective film.
The organic coating may comprise an organic com-pound containing at least one hydroxyl group, for example, an alkanol, for exarnple, isopropanol or a polyol, for example, glycol or glycerol, the organic compound may comprise at least one active nitrogen group, for example, an amino group, for exarnple, triethylammonium hydroxide, or the organic compound may contain both one or more hydroxyl groups an~ one or more active nitrogen groups, for example, amino groups, particularly there may be mentioned alkanol-amines for example, triethanolamine.

The organic coating may also comprise a mixture of an organic hydroxyl group containing compound and an active nitrogen group containing compound. Still further the organic coating may comprise a reaction product of a hydroxyl group containing compound, for example, an ester of a carboxylic acid and a mono- or poly-alcohol, for example, glycerine or an alkanolamine, for example, tri-ethanolamine, or a reaction product of an alkanolamine, for example, triethanolamine, with salicylic acid.
The coating may further be composed of a mixture of oxalic acid and glycerine or an ester reaction product thereof.
The temporary organic coating should be compatible with the metal hydroxide surface and suitably provides a liquid volatile, water-soluble or lacquer compatible pro-tective coating which will permit the maintenance of the metal hydroxide or oxyhydrate surface during the metal forming operation.
The organic coating may react with the metal hydroxide surface by a condensation or addition reaction.
It is found that cooling of the coa~ed components with water during the forming operation is facilitated by the organic hydrophilic surface film, and the residual film remaining after the forming operation is compatible with the lacquer subsequently applied.
Insoluble organic coatings may also be possible based on the reaction of an organic compound of the time indicate~ above with salicylic acid.
It is especially preferred that the temporary organic coating be formed at an alkaline pH, although an acid pH is also possible. The alkaline pH may be achieve~
when the coating composition is not inherently alkaline, 5~
by including a small amoun-t of a basic material, for example, an amine, in the organic coating. It has been found that when an alkanol, for example, isopropanol is employed as the organic coating, as little as 0.05 to 0.15%, particularly about 0.1%, by weigh-t, of an amine, for example, trimethylamine produces a sufficiently alkaline environment.
It has been discovered that a hydrophilic upper surface layer not only takes over the function of the oleophilic layer during the deep-drawing or wall-ironing operations, but in addition has a reduced affinity for contaminating matter, for example, fats and oils, and on the other hand, it favorably improves the lacquer ad-hesion and permits a homogeneous distribution of lacquer over the surface, irrespective of whether a surface of a deep-drawn or wall-ironed wall part is treated or the surface of the bottom of a component or wall-ironed can.
Further the cleaning operation prior to interior lacquer finishing can be carried out far more simply than with the use of oleophilic substances durlng the deep-drawing or wall-ironing operations.
The radicals mentioned in the foregoing structural formula are selected so that substances are used on which polar H20 can deposit itself.
The formation of hydrophilic upper surface layers of the aforementioned structural formula can ~e achieved on aluminium or tin sheet metals in various ways.
Thus, components with these surface layers can be produced from aluminium sheet, after rolling and cleaning and from tin sheet, after rolling, cleaning and tinning by subjecting the sheet to the influence of an inert gas immediately up to the deep-drawing operation.

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The upper surface layers of the alumlnium and tin sheets form merely due to a transient atmospheric infl~lence, a hydrophilic sur~ace layer, which, however, on prolonged exposure to the atmosphere will oxidize and will then be predominantly present as an oxidized layer which does not exhibit -the required hydrophilic properties.
~ccordingly, oxidation of the surface of the sheets is prevented by the influence of the inert gas up to the deep-drawing or wall-ironing operations and there~y the hydrophilic layer remains intact, and this produces the advantageous influence described, during deep-drawing or wall-ironing and upon subsequent lacquer finishing.
The coating of the surface with a glide layer and the re-moval and cleaning thereof after deep-drawing or wall-ironing operations can be dispensed with. This provides a considerable simplification of the production process which is accompanied by a considerable advantage with respect to the economics of the process and environmental aspects thereof.
It is particularly useful when the aluminium or tin sheet metal is provided immediately prior to the deep-drawing with a film of the hydrophilic organic material.
This procedural measure can be employed on tin sheet metal as long as the tin of the upper surface layer is present in divalent form, i.e., also when the tin sheet metal has been subjected to atmospheric oxidation for a period of time to provide a more advanced oxidation. The film provides a hydrophilic surface coating having an oleo-philic character, which affords particularly favorable conditions for deep-drawing and wall-ironing, as well as ~or subsequent interior lacquer finishing.

While the application of the hydrophilic film is generally carried out when the sheet is worked on in normal ambient air, the film application can be dispensed with when in the production method the component to be deep-drawn or wall-ironed is subjected to the influence of an inert gas until completion of the deep-drawing.
The production may comprise passing the sheet after rolling and cleaning, and in the case of tin sheet after tinning, through a tunnel containing an inert gas and immediately thereafter, winding the sheet into a coil in an inert gas containing zone and retaining the coil airtight until further treatment, The aforementioned further treatment can be carried out either after application of the film of the named substances, or, under the influence of the inert gas, up to the completion of the deep-drawing or wall-ironing.
It has been determined that particularly favor-able results are obtained when the aluminium sheet or the tin sheet are maintained, during deep-drawing by means of cooled tools and/or by means of the inert gas, at temperatures below room temperature, preferably below 0C
to -15C. When further treating the she~ts at the afore-~entioned temperatures, particularly advantageous upper surface characteristics are attained for the deep-drawn or wall-ironed, respectively components, which characterist,ics will allow a very thin, homogeneous lacquer application on the inner upper surface of the component, so that a considerable saving is achieved, not only with respect to the amount of lacquer, but also with respect to energy consumption for the suhsequent drying of the lacquer.

EXAMPLES
1. Production of Wall-Ironed Tin Plate (Sheet Metal) Immediately after passing through a tinning bath, a tin sheet strip is passed, in counter current direction with the exclusion of atmospheric oxygen, through a wetting chamber and in the chamber is wetted with a 0.05%, by weight, solution of triethanolamine in isopropanol, rolled over a set of rubber rollers and wound in moist condition into a coil.
The sheet rernains thereby hydrophilic at the sur-face. By the addition of triethanolamine to form an alkaline environment, any possible corrosion due to tramp water is prevented.
Immediately prior to forming of a cup shape, the coil is passed, via a reel, to a deep-drawing press, in which the tin sheet is again passed through the wetting chamber so that on shut-down of the line for more than 30 minutes, the evaporated alcoholic mixture is replenished.
After deep-drawing, the cup is passed, over the shortest distance to the wall-ironing press.
The cooling of the tools is carried out with a triethanolamine-containing isopropanol solution. The cool-ing medium is made up in a cooling aggregate and in small amounts of, for example, 10 liter/min. is applied, at a temperature of -5C, between the wall-ironing rings primarily onto the die.
The application of the cooling medium is con-trolled such that in intervals, for example, 140 cycles per minute, the tool in the reverse stroke is cooled by the admitted cooling medium and during the down working stroke only is cooled by the remaining cooling medium.

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The can is nearly dry after wall-ironing and can be finished by dipping, spraying or sprinkling with lacquer interiorly and exteriorly.

2. Production of Wall-Ironed Aluminium Cans After a final rolling, aluminium sheet is cleaned in a conventional manner, such that the cleaning medium and the measurable pH result in a neutral surface. Analogously as in the treatment of the tin sheet, the aluminium sheet is treated, in the absence of atmospheric oxygen, in a reducing atmosphere with a solution of triethanolamine in isopropanol and is coiled while in moist condition.
The production of the components in accordance with the invention is not limited to sheets which are handled so as to prevent surface oxidation, imrnediately or shortly a-Eter rolling and cleaning, or cleaning and tinning, respectively, by means of inert gases, but is also possible with sheets of the kind here under consideration having an already o~idized surface to convert this surface into a hydrophilic condition. Also, sheets can be used which are stored after production in the usual manner under the influence of normal atmosphere, for example, in the form of wound coils. For this, it is envisioned in accordance with the invention, that the sheet immediately prior to the deformation be electrolytically treated in an acidic or alkaline bath with preferably an anodic voltage (plate or anode voltage) and be subsequently dried.
It has been shown in practice that it is appro-priate to subject the sheet in the bath to the influence of an electrolyte of aqueous tetrapotassiurnphosphate, triethanolamine or NaOH, at a bath temperature of about 20C
and a current density of 200 - 300 A/m2 for a period of time J

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of 1 to 2 seconds and subsequently to pass the sheet through a pair of wetting rollers, wetted with butylglycol/
propyl alcohol.
A further advantage o-f the components produced in accordance with the invention and formed in accordance with the invention resides therein that -the desired and achieved hydrophilic surface appreciably enhances the adhesion o~ a coating to be applied thereon, parti-cularly of a lacquer as generally used, so that not only the advantages described with respect to the forming, but also with respect to the application of the mentioned protective coating are realized, when it is ensured that during the duration of the hydrophilic condition of the surface of the component the application of the lacquer, or similar protective coating is accomplished.

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:-

1. A component which has been deep-drawn or wall-ironed from aluminium or tinned iron sheet from a flat blank or rolled sheet metal with the aid of a tool in the form of a lower and upper die, wherein the sheets have a hydrophilic surface layer according to the formula:
Sn(R) or Al(R) where R=OH, R=O + OH with O smaller than OH, or R - a hydrophilic organic group having a free OH
group, said group being derived from an alkanol amine, an ester or an oxalic acid glycerin.

2. A component according to claim 1, wherein R is a rest of triethanolamine.

3. A component according to claim 1, wherein said component comprises a deep-drawn or wall-ironed container intended for packaging purposes.

4. A method of manufacturing the component claimed in claim 1, wherein to produce the hydrophilic surface layer, the aluminum sheet is subjected to the action of an inert gas after rolling and cleaning or the tinned iron sheet is subjected to the action of an inert gas after rolling, cleaning and tin plating until immediately before it is deep-drawn or wall-ironed.

5. A method according to claim 4, wherein the aluminium or tinned iron sheet is provided with a film of an alkanol amine immediately before being deep-drawn or wall-ironed.

6. A method according to claim 5, wherein the alkanol amine comprises a 0.1% triethanolamine, an ester or an oxalic acid glycerin.

7. A method according to claim 4, wherein the aluminium or tinned iron sheet is subjected to the action of inert gas before being deep-drawn or wall-ironed until deep-drawing or ironing has been terminated.

8. A method according to claim 4, wherein the aluminium or tinned iron sheet is kept at temperatures below room temperature during deep-drawing or wall-ironing.

9. A method according to claim 8, wherein the aluminium or tinned iron sheet is kept at temperatures between 0°C and -15°C during deep-drawing or wall-ironing.

10. A method according to claim 8 or 9, wherein the aluminium or tinned iron sheet is kept at said temperature by means of cooled tools and/or the inert gas.

11. A method of manufacturing the component claimed in claim 1, wherein the aluminium or tinned iron sheet has an oxidized surface and wherein the sheet is treated electroly-tically in an acidic or alkaline liquid immediately before forming to form a hydrophilic surface layer and is sub-sequently dried.

12. A method according to claim 11, wherein the sheet is treated electrolytically with anodic voltage in said acidic or alkaline liquid.

13. A method according to claim 11 or 12, wherein the sheet is subjected to the action of an electrolyte comprising aqueous tetrapotassium phosphate, trimethylamine or NaOH at a temperature of the liquid of approximately 20°C and a current density of 200 - 300 A/m2 for a duration of 1 - 2 seconds in the liquid and is subsequently passed through a pair of wet rolls moistened with butylglycol propyl alcohol.

14. A method according to claim 11, wherein the aluminium or tinned iron sheet is provided with a film of an alkanol amine to produce a hydrophilic surface layer immediately before being deep-drawn or wall-ironed.

15. A method according to claim 14, wherein the alkanol amine comprises a 0.1% triethanolamine, an ester or an oxalic acid glycerin.

16. A deep-drawn or wall-ironed metal component com-prising a sheet of aluminium or tinned ferrous metal having a hydrophilic surface layer containing free hydroxyl groups.

17. A component as defined in claim 16, wherein said surface layer is represented as Me-R1-R2 in which Me is aluminium or tin, R1 is a hydroxide or oxyhydrate group and R2 is at least one organic compound containing at least one of a hydroxyl group and an active nitrogen group.

18. A component as defined in claim 16, wherein said hydrophilic surface layer comprises isopropanol containing 0.05 to 0.15%, by weight, of triethanolamine.

19. A component as defined in claim 16, wherein said hydrophilic surface layer comprises triethanolamine.

20. A component according to claim 16, 17 or 18, in the form of a wall-ironed can having a coating of lacquer over said hydrophilic surface layer.

21. A constructive part made of a deep-drawn, rolled aluminium or tinplate blank formed from a plate material having a hydrophilic surface layer represented as:

MRn in which M is a metal selected from the group consisting of Sn and Al;
R is selected from the group consisting of a) OH, b) O and OH, with the surface concentration of oxygen directly bonded to metal M being smaller than the surface concentration of OH directly bonded to metal M, and c) a hydrophilic organic group containing at least one OH radical; and n is a suitable positive number for rendering the surface layer electrically neutral.

22. A constructive part according to claim 21, wherein R is c) and said group is selected from the group consisting of alkanolamines, oxalic acid esters and glycerol esters.

23. A constructive part according to claim 22, wherein R is a triethanolamine.

24. A constructive part according to claim 21, having been formed by deep-drawing the rolled aluminium or tin-plate blank.

25. A constructive part according to claim 24, wherein said deep-drawing is carried out with punch and ring like tools.

26. A constructive part according to claim 21, 22 or 23, in the form of a drawn and wall ironed can body for packaging, adapted to be internally lacquered.

27. A process for manufacturing a deep-drawn or wall-ironed component of aluminium or tinned ferrous metal sheet comprising applying a hydrophilic layer containing free hydroxyl groups on the surface of an aluminium or tinned ferrous metal sheet and thereafter deep-drawing or wall-ironing said sheet.

28. A process according to claim 27, comprising wall-ironing said sheet to form a can and applying a lacquer to the can interior on the hydrophilic layer.

29. A process according to claim 27, wherein said sheet is a rolled, cleaned aluminium sheet and is maintained in an inert atmosphere until immediately prior to said deep-drawing or wall-ironing.

30. A process according to claim 27, wherein said sheet is a rolled, cleaned, tinned ferrous metal sheet and is maintained in an inert atmosphere until immediately prior to said deep-drawing or wall-ironing.

31. A process according to claim 28, wherein said sheet is maintained in an inert atmosphere until immediately prior to deep-drawing or wall-ironing and said deep-drawing or wall-ironing is carried out at a temperature of 0°C to -15°C.

32. A process according to claim 27, wherein said sheet has an oxidized surface, said sheet being subjected to an electrolytic treatment in an acid or alkaline bath followed by drying, prior to said deep-drawing or wall-ironing.

33. A process according to claim 32, wherein said bath comprises an electrolyte comprising an aqueous tetrapotassium phosphate, triethanolamine or sodium hydroxide at a bath temperature of about 20°C, and said electrolytic treatment is carried out at a current density of 200 to 300 A/m2, for a period of 1 to 2 seconds, and the sheet is subsequently passed through a pair of damping rollers wetted with butylglycol/propyl alcohol.

34. A process according to claim 29, wherein said hydrophilic layer comprises isopropanol containing tri-ethanolamine.

35. A process according to claim 27, wherein said hydrophilic layer is represented as Me-R1 in which Me is aluminium or tin and R1 is a hydroxide or oxyhydrate group.