The present invention relates to a cleaning formulation, to its use in cleaning a surface comprised of aluminium or an aluminium alloy, and to a concentrate for preparing the formulation. The invention relates particularly, but by no means ^" exclusively, to such a formulation and method for use in the production of an aluminium or aluminium alloy container (e.g. a can) for holding a beverage such as beer or a soft drink. This invention may or may not be used to prepare such a container for either a pasteurisation or retortable process.

For convenience, the term "aluminium" as used in the remainder of this specification is intended to cover both aluminium metal and aluminium alloys.

Aluminium cans for holding beverages are produced by a process in which an opened-top cylindrical can body (including an integral base) is formed by a moulding operation known in the art as drawing and ironing. (The upper end cap is formed separately and applied to construct the "closed" can at a separate stage in the process). The surface of the can body is then protected by application of a coating thereto, e.g. of the type known as a "conversion coating".

It is however generally not possible simply to apply the coating to the can body immediately after it has been formed in the drawing and ironing operation. This is because the operation involves the use of lubricants that must be removed from the can body before a satisfactory coating can then be applied. Additionally the can body resulting from the drawing and ironing operation would include surface aluminium oxide which must likewise be removed before a satisfactory coating can be applied.

Consequently the can bodies must be cleaned to remove lubricating oils and surface oxides before they are passed to the coating process.

Many prior art formulations for cleaning aluminium (e.g. in the production of beverage cans) incorporate fluoride ions (e.g. in the form of hydrofluoric acid).

However such formulations have disadvantages from the safety and environmental point of view. As a result, various "fluoride-free" formulations have been proposed. Generally such formulations have a pH of 0.5 to 3 and incorporate ferric ions and hydrogen peroxide.

Thus, for example, US-A-4 980 076 (Nihon Parkerizing) proposes a fluoride- free etchant rinse for aluminium containing a phosphoric acid component, a further acid component (e.g. sulphuric acid), ferric ions, an oxidising agent (such as hydrogen peroxide) to maintain a required concentration of ferric ions, an aluminium ion sequestrant (e.g. a polybasic and/or hydroxy acid) and at least one surface active agent.

PCT-GB2004/002729 (Natech Ltd) discloses a cleaning formulation intended particularly for use in cleaning aluminium can bodies which comprises a carboxylic acid (e.g. a di-basic acid), a peroxide (e.g. hydrogen peroxide), ferric ions, surface active agents and a polysaccharide compound (such as a polyglucoside) which is preferably alkylated, ethoxylated or propoxylated.

The above described cleaning formulation may be produced from concentrates which are diluted to end-use concentration for the purpose of the cleaning operation.

We have however found that the cleaning of aluminium can bodies (produced by a drawing and ironing operation) using formulations containing ferric ions and a peroxide (such as hydrogen peroxide) does not achieve sufficient removal of aluminium oxide to provide a good coating. In particular, pasteurisation of the filled cans gives "dome staining" on the (externally visible) concave under-surface of the can. Such "dome staining" is regarded as aesthetically undesirable and may lead (potential) purchasers of the cans to believe that the beverage therein has somehow deteriorated, although this is not the case. We believe that this disadvantage is caused by the fact that the peroxide is unstable under the acid conditions and breaks down so that a satisfactory cleaning process is not achieved.

It is an object of the present invention to obviate or mitigate the above- mentioned disadvantages.

According to a first aspect of the present invention there is provided a cleaning formulation for cleaning aluminium surfaces, the formulation having a pH of 0.5 to 5 and incorporating sulphuric acid at least one aluminium sequestrant, at least one surface active agent and ions of at least one d-block transition metal characterised in that the formulation also incorporates substituted or unsubstituted hydroxyl ammonium ions or hydrazine ions.

According to a second aspect of the present invention there is provided a method of cleaning aluminium surfaces in which the aluminium surface is treated with a cleaning formulation as defined in the previous paragraph.

The invention has been based on our finding that the use of substituted or unsubstituted hydroxyl ammonium or hydrazine ions provides significantly improved results in the cleaning of aluminium as compared to similar formulations which incorporate peroxide as an oxidising agent. More particularly, the use of such ions provides significantly improved removal of aluminium oxide from the surface of the aluminium. As such, cleaning formulations in accordance with the invention are particularly useful for the cleaning of aluminium can bodies produced by a drawing and ironing operation to effect removable thereof so that a good quality conversion coat may subsequently be applied. Such coated cans are not prone to dome-staining when subjected to a pasteurising operation. Whilst not wishing to be bound by theory, we believe that the significantly improved results are due to the effective removal of both organic and inorganic contaminants thus ensuring effective bonding of the conversion coating through elimination of a "de-wetting" or "masking" effect. This process is enhanced by the catalytic effect of the substituted or unsubstituted hydroxyl ammonium or hydrazine ions at the surface of the aluminium hydroxide. This enhancement allows the sulphuric acid in the formulation to etch the oxide layer. This etching effect also enhances the aesthetic appearance of the inside of containers by affecting the "grey scale" or "lightness" of the surface.

Formulations in accordance with the invention can be essentially fluoride-free. Additionally the formulations need not contain a peroxide, although we do not preclude the possibility of incorporating either compound (e.g. hydrogen peroxide or a fluoride).

Each component of the formulation, as defined for the first aspect of the invention, is preferably present in the amount indicated in the following table, with more preferred amounts for each component being given in the following description:

The amount of the substituted or unsubstituted hydroxyl ammonium or hydrazine ions present in the formulation is preferably in the range 0.0004 to 0.05%, more preferably 0.0004 to 0.02% and even more preferably 0.004 to 0.008% by weight of the formulation.

The substituted or unsubstituted hydroxyl ammonium or hydrazine ions may be introduced into the cleaning formulation in the form of salts or in the form of the corresponding free base, which is converted in situ in the acid conditions prevailing in the bath to the corresponding substituted or unsubstituted hydroxyl ammonium or hydrazine ions.

The hydroxyl ammonium or hydrazine ions may be of the formula H ₃ XN ⁺ where X is -OH, -NH ₂ or -NH ₃ ⁺ .

Preferably X is -OH, i.e. H ₃ XN ⁺ represents the hydroxyl ammonium ion. The formulation may, for example, be prepared from a hydroxyl ammonium salt which can incorporate a wide variety of anions, e.g. sulphate, phosphate, chloride, nitrate or bromide. It is however also possible to prepare the formulation from NH ₂ OH which (as indicated above) is converted in situ in the acid conditions of the formulation to the hydroxyl ammonium ion.

It is preferred that the formulation is prepared from hydroxyl ammonium sulphate.

Substituted or unsubstituted hydrazine ions may be provided by sulphate, nitrate, nitro or chloride salts. Particular examples include phenyl hydrazine sulphate, p-nitro phenyl hydrazine, benzyl phenyl hydrazine, maleic hydrazine, hydrazine sulphate, hydrazine di-mono hydrochloride, 2,4-dinitrophenyl hydrazine, anthrone, dithizone, 1,2,3,4-tetrahydrocarbazole, dimethylglyoxime, and hydrazine nitrate.

The d-block transition metal ion is preferably present in the formulation in an amount 0.0001-0.015%, more preferably 0.003-0.006%.

The d-block transition metal ion may for example be provided by salts of iron, platinum, silver, gold, manganese, nickel or molybdenum.

The d-block transition metal ion is preferably the ferric ion (Fe ³⁺ ).

Most conveniently, the ferric ion is provided by a ferric salt such as Fe ₂ (SO ₄ ) ₃ , Fe(NO ₃ ) ₂ orFe ₂ (CO ₄ ) ₃ .

Alternatively the ferric ions may be produced in situ from ferrous salts which are converted under the oxidising conditions of the cleaning formulation to provide the ferric ions.

The amount of aluminium sequestrant present in the formulation is preferably 0.005-0.25% by weight, more preferably 0.05-0.1%.

The aluminium sequestrant is preferably provided by at least one carboxylic acid. The carboxylic may be provided at least partly by a di- or higher- basic carboxylic acid. The acid may, for example, be of the formula HOOC (CEb) _n COOH with n preferably being from 0 to 4 so that the acid has a maximum of 6 carbon atoms, this being preferred to ensure that the di-basic acid (of the indicated formula) is water-soluble. It is however also possible to use di-basic acids that also incorporate at least one hydroxyl group to improve water solubility, in which case the acid may contain more than 6 carbon atoms.

The di-basic acid may be malonic acid, succinic acid or adipic acid. For preference, malonic or succinic acid are used.

We have also found that improved results for the cleaning formulation can be obtained if the sequestrant comprises a mixture of a di-basic acid of the formula HOOC(CH ₂ ) _n COOH (where n is as defined above) and a carboxylic acid (preferably a poly-basic carboxylic acid) containing a hydroxyl group. This latter acid may be a di- or higher- basic carboxylic acid (also containing a hydroxyl group) and is most preferably citric acid. The improved results obtained by the combination of these two acids reside in an improvement in the brightness of the interior of the can body after conversion coating.

Preferably the amount of acid of the formula HOOC(CH ₂ ) _n COOH in the formulation is in the range 0.02-0.06% as also is the amount of the hydroxycarboxylic acid (e.g. citric acid). It is particularly preferred that the amount of acid of the formula HOOC(CH ₂ ) _n COOH is in the range 0.02-0.04% whereas the amount of the hydroxycarboxylic acid is in the range 0.03-0.06%.

The cleaning formulation contains a total amount of 0.004-0.25% (more preferably 0.04-0.1%) of surface active agents. The surface active agents may be cationic, anionic, non-anionic or amphoteric agents, suitable examples of which are

disclosed in US-A-4 980 076 (Nihon Parkerizing). It is however particularly preferred that the surface active agents are non-ionic agents.

It is preferred that the surface active agent comprises at least one fatty alcohol ethoxylate. The or each such surfacactant may have an alcohol residue containing 8- 15 carbon atoms and may incorporate 4-15 moles of ethylene oxide (per mole of fatty alcohol residue). Preferably the surface active agent system comprises 0.01-0.04% by weight (based on the total weight of the cleaning formulation) of each of:

(i) a fatty alcohol (C ₁₃ ) ethoxylate with 8 moles of ethylene oxide (e.g. as available under the names Caflon TD0900 or Lutensol T08); and

(ii) a fatty alcohol (C ₁₀ ) ethoxylate with 4 moles of ethylene oxide (e.g. as available under the names Rhodaclean MSC or Lutensol XL40).

The surface active agent system preferably also includes a surface active agent incorporating polysaccharide (e.g. polyglucoside) residues. Such a surface active agent is preferably present in an amount 0.005-0.02% by weight of the formulation. Suitable surface active agents in this category are alkylated, ethoxylated or propoxylated polyglucosides. Alkyl polyglucosides are particularly preferred, in particular those in which the alkyl residue has a carbon chain length of C ₁₂ -C ₁₆ . The formulation may incorporate a defoamer, e.g. Pluronic PE6100.

The cleaning formulation further incorporates sulphuric acid, preferably in an amount of 0.05 to 1%, more preferably 0.1% to 0.5%, by weight (expressed as H ₂ SO ₄ ) of the formulation.

The cleaning formulation of the invention has a pH of 0.5 to 5, more preferably 0.5 to 3.0, even more preferably 0.5 to 2.5.

Therefore, in summary, a preferred and even more preferred amounts for components of the cleaning formulation are as shown in the following table:

The cleaning operation (in accordance with the second aspect of the invention) may be carried out by immersing the can bodies in the cleaning formulation or alternatively by spraying the bodies with the formulation. Generally the cleaning formulation will be at a temperature of 20-80°C, more preferably 50-70°C. Generally the cleaning operation will be effected for a period of 10 to 120 seconds.

After being treated with the cleaning formulation, the aluminium may be washed with water.

A cleaning formulation in accordance with the invention may be prepared by admixing the individual components in the required amounts in water. Conveniently however a cleaning formulation in accordance with the invention is obtained by dilution of a pre-prepared concentrate. A typical concentrate formulation is as shown below:

As an alternative the above concentrate may be prepared without the sulphuric acid, in which case the concentrate and sulphuric acid are added separately to water to produce the final cleaning formulation. If the concentrate contains sulphuric acid then the amount is preferably in the range 15% to 25% by weight of the concentrate.

The aluminium sequestrant preferably comprises 1-5% by weight of a di-basic carboxylic acid of the formula HOOC(CH ₂ ) _n COOH, where n is 0 to 4 and 1-5% of a poly-basic acid containing a hydroxyl group. The sequestrant preferably comprises succinic or adipic acid and citric acid.

The surface active agent preferably comprises 0.5 to 2.5% by weight of each of:

(a) an alkyl polyglucoside;

(b) a fatty alcohol (C ₁₃ ) ethoxylate with 8 moles of ethylene oxide (e.g. as available under the names Caflon TD0900 or Lutensol T08); and

(c) a fatty alcohol (C _1O ) ethoxylate with 4 moles of ethylene oxide (e.g. as available under the names Rhodaclean MSC or Lutensol XL40).

The invention will be illustrated by reference to the following non-limiting Example and accompanying drawings which illustrate the results of the Example.

Example

A concentrate was prepared from the following components:

The concentrate was prepared by heating the water to 25 ⁰ C and adding the succinic acid with thorough mixing. The remaining components were then added in the order listed with thorough mixing between additions and for one hour after addition of the final component.

The diluted concentrate was used for cleaning aluminium can bodies that had been produced by a standard drawing and ironing operation. Cleaning was effected by washing the cans (using the wash solution detailed above) in a household dishwasher for 3 minutes at 55°C to 60°C (low pressure). Sufficient amount of the concentrate was added to produce an approximately 1% solution of the cleaning formulation.

The cleaned cans were then subjected to a washing operation with water.

One can was then subjected to a "dome staining" test in which the can was immersed in a solution of borax (0.3 g I ^"1 ) at 80 ⁰ C for 20 minutes.

A further (cleaned) can was given a "conversion coat" using Houghto-Coat NC900 at a pH 2.9 for 40 seconds at 40 ⁰ C. The coated can was then subjected to the "dome-staining" test described above.

The results are shown in Fig 1 in which the left hand photograph is for the coated can.

Comparative Example

The procedure of Example 1 was repeated but using a peroxide-based cleaning formulation of the type described in PCT/GB 2004/002729 (Natech Ltd). The results are shown in Fig 2 in which the coated can is on the right hand side.

The improvements obtained by the present invention are evident from a comparison of Figs 1 and 2.