GB2098630A - Acidic aqueous solution for cleaning aluminium surfaces - Google Patents

Abstract

Solution comprises from 1 to 10 g/litre of sulphuric acid, from 0.005 to 0.1 g/litre of hydrofluoric acid, and from 0.1 to 10 g/litre of alkali metal 2- butoxyethoxyacetate. It has high tolerance of lubricants and forming oils removed from the aluminium surfaces, with low foaming. Concentrates of sulphuric acid containing the surfactant are colourless, stable at low temperatures and do not discolour at above ambient temperature.

Description

SPECIFICATION Methods and compositions for the acid cleaning of aluminium surfaces This invention relates to cleaning aluminium surfaces.

In the manufacture of containers composed of aluminium (which term includes aluminium alloys in this specification), a drawing and forming operation is employed (commonly referred to as drawing and ironing). This operation results in the deposition of lubricants and forming oils on the surfaces of the aluminium containers. In addition, residual aluminium fines, i.e. small particles of aluminium, are deposited on both the interior and exterior surfaces. Ordinarily, the exterior surface of the container will have smaller quantities of aluminium fines than the interior surface since during the drawing and ironing step the exterior surface is not subjected to as much abrasion from the die as the interior surface.

Prior to any processing steps, such as conversion coating and sanitary lacquer deposition, the surfaces of the aluminium containers must be clean and water-break-free, i.e. free of contaminants that interfere with further processing and render the containers unacceptable for use.

Compositions and methods for the low temperature cleaning of aluminium surfaces are disclosed in U.S. Patents No. 4,009,1 15; 4,1 16,853; 4,124,407; and 3,969,135. These patents disclose cleaning compositions containing sulphuric acid, hydrofluoric acid or a fluoride salt, and a surfactant.

Compositions falling within the disclosures of these patents are commercially successful and are in fact used extensively in the cleaning of aluminium (including aluminium alloy) containers. Such commercial compositions typically utilize a combination of two non-ionic surfactants to enhance the cleaning performance and minimize foaming.

One of the problems in utilizing the prior art acid cleaning compositions is caused by the build-up of lubricants and forming oils used in the drawing and forming of aluminium containers as these containers are treated with the cleaning solutions. The cleaning solutions must be replenished with fresh solutions from time to time to keep the oil level down. When the oil levels become excessive in the cleaning bath, containers cleaned in the bath exhibit significant water breaks after the cleaning solution has been rinsed off. Water breaks are an indication that the surface of the aluminium is not clean and that oils or other foreign deposits are present. Such containers must be discarded or recleaned since they are not suitable for further processing as containers for beverages and other comestibles.

It has now been discovered that an aqueous sulphuric acid/hydrofluoric acid cleaning composition containing a particular anionic surfactant, viz an alkali metal 2-butoxyethoxyacetate, is surprisingly advantageous.

Accordingly, the invention provides an aqueous cleaning solution for removing and dissolving aluminium fines and cleaning lubricating oils from aluminium surfaces, which solution comprises from 1 to 10 g/litre of sulphuric acid, from 0.005 to 0.1 g/litre of hydrofluoric acid, and from 0.1 to 10 g/litre of alkali metal 2-butoxyethoxyacetate.

The invention also provides an aqueous solution concentrate for forming the aqueous cleaning solution, which concentrate comprises from 200 to 600 g/litre of sulphuric acid and from 0.01 to 10 parts by weight alkali metal 2-butoxyethoxyacetate per part by weight of sulphuric acid.

The invention provides also a process for cleaning an aluminium surface, which process comprises (a) contacting said surface with the aqueous cleaning solution, and (b) rinsing the aluminium surface to remove the cleaning solution.

It has been found that the cleaning solutions of the invention can tolerate relatively high concentrations of lubricants and forming oils without any water breaks occurring on the containers cleaned by such solutions. Hence, significant economies are realized since large numbers of containers can be processed before the operation must be shut down in order to replenish all or part of the cleaning solution.

Another significant advantage of the present cleaning compositions is the almost complete absence of foam in the cleaning bath and in the rinsing cycle following the cleaning step. Many of the acid cleaning compositions currently on the market exhibit problems with foam to a greater or lesser extent. Such compositions are mixtures of a high foaming non-ionic surfactant to achieve good cleaning action with a low foaming anionic surfactant to try to contain the quantity of foam that would otherwise result. Foaming often results in overflow or dropping of the foam onto the floor of the facility containing the operation, resulting in slippery and unsafe conditions. Also, appearance of foam may lead to an operator concluding that the cleaning solution is not satisfactory due to the risks of foam overflow.

Consequently, the container cleaning operations are shut down while the foam is skimmed off or the cleaning solution is replenished, leading to lost time and decreased flow-through of containers.

A further advantage of the present cleaning compositions is that the alkali metal 2butoxyethoxyacetate can be utilized effectively in relatively small quantities, and this factor, combined with the inexpensive cost of this surfactant (as the sodium salt) compared with the non-ionic surfactants currently in use, results in great economic savings over the present commercial compositions.

Significant cost savings are also realized even when a low foaming non-ionic surfactant or a combination of such surfactants is also present in the cleaning composition of the invention, since the non-ionic surfactant(s) can also be present in relatively small quantities.

Typically, concentrates containing the sulphuric acid and the surfactant are prepared by the manufacturer and sold to container processing companies who make up cleaning solutions by diluting such concentrates with water and adding hydrofluoric acid to the solutions. Concentrates currently on the market tend to be rather highly coloured, due to decomposition products formed from the action of concentrated sulphuric acid on the surfactants and/or from interactions between the surfactants and impurities in the commercial sulphuric acid which is commonly used in formulating the concentrates.

Surprisingly, concentrates formed with an alkali metal 2-butoxyethoxyacetate as the sole surfactant are colourless or only slightly yellow in colour. Such concentrates are stable at very low temperatures, e.g.

no precipitation occurs even at the temperature of a dry ice-acetone bath. Also, the concentrates are stable and do not discolour even when subjected to temperatures at 500C for periods of three weeks or more. Most concentrates currently in use discolour even at room temperature, and precipitates form in some when containers of the concentrates are placed in dry ice-acetone baths. The great stability of the present compositions permits their shipment and storage under adverse temperature conditions without problems, a further significant economic advantage.

Another advantage of the present invention is the high level of cleanliness produced in the containers, particularly when low foaming non-ionic surfactant is also present, providing for unusually uniform conversion coating and lacquer deposition on the containers during their further processing.

Interestingly, when the only anionic surfactant disclosed in U.S. Patents No. 4,009,1 15, 4,116,853 and 4,124,407, viz Tergitol Anionic 08 (sodium 2-ethyl hexyl sulphate), was tested in the acid cleaning compositions of these patents, water breaks occurred on the aluminium containers cleaned with such compositions after the addition of only small quantities of forming oils. Hence, the surprising advantages afforded by the particular anionic surfactant of the present invention appear to be unique and clearly are not advantages common to anionic surfactants in general.

The compositions and processes of the invention provide improvements over the compositions and processes disclosed in U.S. Patents No. 4,009,1 15, 4,1 16,853 and 4,124,407, and the disclosures of such patents are specifically incorporated herein by reference. The procedures and methods used therein in carrying out cleaning operations and in forming concentrates and cleaning solutions are appiicable to the present invention unless otherwise indicated herein.

The aqueous cleaning solution of the invention comprises from 1 to 10 g/litre, preferably from 3 to 5 g/litre of sulphuric acid; from 0.005 to 0.1 g/litre, preferably from 0.01 to 0.03 g/litre of hydrofluoric acid; and from 0.1 to 10 g/litre, preferably from 0.2 to 0.8 g/litre of alkali metal 2-butoxyethoxyacetate.

The alkali metal 2-butoxyethoxyacetate is preferably sodium 2-butoxyethoxyacetate

this is available commercially under the trademark "MIRAWET B" from the Miranol Chemical Company, Inc. as an aqueous solution containing 49.0% sodium 2-butoxyethoxyacetate. Other alkali metal salts can be employed, e.g. potassium 2-butoxyethoxyacetate or lithium 2-butoxyethoxyacetate.

A preferred solution comprises from 3 to 5 g/litre of sulphuric acid, from 0.01 to 0.03 g/litre of hydrofluoric acid and from 0.2 to 0.8 g/litre of sodium 2-butoxyethoxyacetate.

The present solution preferably contains from 0.1 to 10 g/litre, preferably from 0.2 to 0.8 g/litre of low foaming non-ionic surfactant. The surfactant can be one or a combination of two or more low foaming non-ionic surfactants. Advantageously, a weight ratio of alkali metal 2-butoxyethoxyacetate to non-ionic surfactant of about 1:1 is used.

The term "low foaming non-ionic surfactant" means that the non-ionic surfactant or combination of non-ionic surfactants give less than 20 mm of foam after five minutes standing in the well known Ross-Miles Foam Test at 500C. Examples of such low foaming non-ionic surfactants that can be used alone or in combination in the practice of the invention include the following:: TRITON DF-16 (Rohm 8 Haas Co.), believed to be a modified polyethoxylated straight chain alcohol; POLYTERGENT S-505 LF (Olin Corp.), believed to be a modified polyethoxylated straight chain alcohol; SURFONIC LF-17 (Jefferson Chemical Co.), believed to be an alkyl polyethoxylated ether; ANTAROX BL 330 (GAF Corp.), believed to be an alkyl poly(ethyleneoxy) ethanol; TRITON CF-10 (Rohm S Haas Co.), believed to be an alkylaryl polyether having a carbon chain of about 14 carbon atoms and approximately 16 moles of ethoxylation; PLURONIC L061 (BASF Wyandotte, Inc.), believed to be a condensate containing only ethylene oxide and propylene oxide chains; ANTAROX LF-330 (GAF Corp.), believed to be an alkyl poly(ethyleneoxy) ethanol; and MIN-FOAM 1X (Union Carbide Corp.), believed to be alkyloxy(polyethyleneoxypropyleneoxyiso- propanol) having a molecular weight of about 706.

The pH of the cleaning compositions of the invention is usually from 0.6 to 2.0. Preferably it is maintained in the range 1.0 to 1.8 and most preferably in the range 1.2 to 1.5.

The concentrates of the present invention comprise from 200 to 600 g/litre of sulphuric acid and from 0.01 to 10 parts, preferably from 0.04 to 0.27 parts, of alkali metal 2-butoxyethoxyacetate per part of sulphuric acid. Parts in this specification are by weight. A suitable quantity of alkali metal 2-butoxyethoxyacetate in a particular concentrate can be determined by using these ratios and the quantity of sulphuric acid desired in the cleaning solution, so that the desired quantity of alkali metal 2-butoxyethoxyacetate is present in the cleaning solution when the concentrate is diluted with an appropriate quantity of water.For example, if 1 g/litre of sulphuric acid is desired in the cleaning solution, then from 0.1 g to 10 g of alkali metal 2-butoxyethoxyacetate is present in the concentrate per g of sulphuric acid; and if 10 g/litre of sulphuric acid is desired in the cleaning solution, then from 0.1 g to 1 g of alkali metal 2-butoxyethoxyacetate is present in the concentrate per 9 of sulphuric acid.

Optionally, from 0.01 to 10 parts, preferably from 0.04 to 0.27 parts of low foaming non-ionic surfactant is also present in the concentrate.

The present concentrate can be added to water in controlled amounts sufficient to produce a cleaning solution having the desired concentrations of sulphuric acid and alkali metal 2-butoxyethoxyacetate. Hydrofluoric acid in quantities sufficient to give its desired concentration is usually added separately. While the hydrofluoric acid can be added to the concentrate in quantities sufficient to produce the requisite amounts in the cleaning solution when the concentrate is added to water, it is much preferred to add the hydrofluoric acid separately to the cleaning solution in carefully metered quantities on a continuing controlled basis. Separate monitored addition of hydrofluoric acid is preferred because the cleaning solution continually loses hydrofluoric acid as etching of the aluminium surfaces takes place during the cleaning stage.

The aluminium (including aluminium alloy) surface to be cleaned with the aqueous cleaning composition of the invention can be contacted with the solution by any of the contacting techniques known to the art, such as conventional spray or immersion methods. The temperature of the cleaning composition is usually at least 900F (32 OC). Preferably it is maintained in the range 11 50F to 1450F (460C to 630C) for maximum cleaning effect. Treatment times with the cleaning solutions are usually in the range 1 5 seconds to 2 minutes. Desirably, the hydrofluoric acid content of the cleaning solution and the contact time with the aluminium surface is adjusted to give an aluminium dissolution of from 8 to 25 mg, preferably from 9 to 20 mg, per square foot (90 to 280 mg, preferably 100 to 220 mg, per square metre) of aluminium surface treated.Thus the amount of hydrofluoric acid in the cleaning solution is preferably such that the aluminium dissolution rate is from 8 to 25 mg per square foot (90 to 280 mg per square metre) of aluminium surface treated at a temperature of 1300F (540C) and a contact time of one minute. Preferably aluminium cans are treated by the present process.

The invention is illustrated by the following Examples, in which the 3004 alloy referred to is the conventional alluminium alloy known by this name and containing about 1.2% by weight manganese and 1.0% by weight magnesium, with the remainder being aluminium and normal impurities.

EXAMPLE 1 A litre of concentrate was prepared containing the following quantities of ingredients: per litre H2SO4 (660 BaumB) 467.2 g (256 ml) H20 - 709.6g(711 ml) MIRAWET B - 88.6 g (80 ml) The concentrate was clear and substantially colourless. 60.0 ml of the concentrate was added to 5.940 litres of water to form six litres of solution containing 4.67 g/litre of H2SO4 (660 BaumB) and 0.434 g/litre of sodium 2-butoxyethoxyacetate (0.886 g/l of MIRAWET B). 20 Parts per million (ppm) of hydrofluoric acid was added to form a cleaning solution, and the cleaning solution was stirred to render it uniform in composition.

Aluminium cans of 3004 alloy drawn into single piece containers were employed in this procedure. The cans had a covering of aluminium fines and drawing oils.

Test specimens were treated as follows: (a) Sprayed with the above-mentioned cleaning solution maintained at 1 300F (54 C) for one minute; (b) Rinsed with water by immersion in cold water for 30 seconds; (c) Allowed to stand for 30 seconds, after which they were examined for water breaks on both the inside and outside; and (d) The inside wiped with a clean white cloth and the cloth examined for aluminium fines.

A can was tested as described above and the results noted. Then 5 ml of a cooling oil emulsion as used by Reynolds Aluminum Company in the drawing and forming of aluminium cans was added to the cleaning solution and another can tested and the results noted. Another 5 ml of cooling oil was then added to the bath and another can was tested and the results noted. Additional 5 ml increments of cooling oil were added and a can tested after each addition until water breaks were obtained. Upon each addition of cooling oil, the amount of foam in the bath was noted.

The results of these tests are given in Table I below: TABLE I Addition of Cooling Extent of Water Aluminium Fines Foam in Oil Emulsion Breaks on Cloth Bath O None None None 5 ml None None Very slight* 10 ml None None Very slight 1 5 ml None None Very slight 20 ml None None Very slight 25 ml None None Very slight 30 ml Slight None Very slight * "Very slight" means no greater than 4 inch (0.6 cm) of foam.

EXAMPLE 2 Six litres of cleaning solution were prepared by adding to water 28.02 g of H2SO4 (660 Baume'), 1.30 g of sodium 2-butoxyethoxyacetate, and 20 ppm of hydrofluoric acid. This cleaning solution contains 4.67 g/litre of H2SO4 (660 Barm6) and 0.21 7 g/litre of spdium 2-butoxyethoxyacetate (i.e. half the amount present in the cleaning solution of Example 1).

Aluminium cans from the same batch as were used in Example 1 were tested according to the conditions and procedures set forth in Example 1 with the following results: TABLE II Addition of Cooling Extent of Water Aluminium Fines Foam in Oil Emulsion Breaks on Cloth Bath O None None None 5 ml None None Very slight* 10 ml None None Very slight 15 ml None None Very slight 20 ml None None Very slight 25 ml None None Very slight 30 ml Slight None Very slight * "Very slight" means no greater than a inch (0.6 cm) of foam.

COMPARATIVE EXAMPLE 3 Six litres of an aqueous cleaning solution were prepared containing the following quantities of ingredients per litre: H2SO4 (660 Barm4) - 4.67 g Sodium 2-ethyl hexyl - 0.464 g (0.98 ml of sulphate TERGITOL ANIONIC 08) HF - 20 ppm Aluminium cans from the same batch as those used in Example 1 were tested according to the conditions and procedures set forth in Example 1 with the following results: TABLE Ill Addition of Cooling Extent of Water Aluminium Fines Foam in Oil Emulsion Breaks on Cloth Bath O Slight None None 5 ml Extensive* None None 10 ml Extensive None None * "Extensive" means commercially unacceptable.

COMPARATIVE EXAMPLE 4 Six litres of an aqueous cleaning solution were prepared containing the quantities of ingredients set forth in Example 3 except that 0.928 g/l of sodium 2-ethyl hexyl sulphate was used. Test procedures were carried out as in Example 3 with the following results: TABLE IV Addition of Cooling Extent of Water Aluminium Fines Foam in Oil Emulsion Breaks on Cloth Bath O Slight None None 5 ml Extensive* None None 10 ml Extensive None None * "Extensive" means commercially unacceptable.

COMPARATIVE EXAMPLE 5 Six litres of an aqueous cleaning composition were prepared containing the following quantities of ingredients per litre: HzSO4 (66 BaumB) - 4.70 g Ethoxylated abietic acid - 1.053 g (Hercules Surfactant AR 150)* Alkyl poly(ethyleneoxy)- - 0.673 g ethanol (ANTAROX LF-330)* HF - 20 ppm * both non-ionic surfactants.

Aluminium cans from the same batch as those used in Example 1 were treated according to the procedures and conditions set forth in Example 1 with the following results: TABLE V Addition of Cooling Extent of Water Aluminium Fines Foam in Oil Emulsion Break on Cloth Bath o None Trace Slight** 5 ml Slight Trace Slight 10 ml Extensive* Trace Slight * "Extensive" means commercially unacceptable.

** "Slight" means between 41 inch (0.6 cm) and 1 inch (2.5 cm).

COMPARATIVE EXAMPLE 6 Six litres of an aqueous cleaning solution were prepared containing the following quantities of ingredients per litre: H2SO4 (66 BaumB) - 4.67 g Modified polyethoxylated - 0.464 g straight chain alcohol (TRITON DF-16) (non-ionic surfactant) HF - 20 ppm Aluminium cans from the same batch as those used in Example 1 were treated according to the procedures and conditions set forth in Example 1 with the following results:: TABLE VI Addition of Cooling Extent of Water Aluminium Fines Foam in Oil Emulsion Breaks on Cloth Bath O None Trace Slight* 5 ml None Trace Slight 10 ml None Trace Slight 1 5 ml None Trace Slight 20 ml None Trace Slight 25 ml Slight Trace Slight * "Slight" means between inch (0.6 cm) and 1 inch (2.5 cm).

EXAMPLE 7A AND COMPARATIVE EXAMPLES 7B, 7C AND 7D The following concentrates were prepared: per litre A H2SO4 (66 Baumé) - 467.2 g H20 - 709.6 g Sodium 2-butoxyethoxy- - 43.4 g acetate B H2SO4 (66 Baumé) - 467.2 g H20 - 709.6 g Sodium 2-ethyl hexyl - 46.4 g sulphate C H2SO4 (660 Baumé) - 469.6 g H20 - 627.0 g Ethoxylated abietic acid - 105.3 g (Hercules Surfactant AR 150) Alkyl poly(ethyleneoxy) - 67.3 g ethanol (ANTAROX LF-330) D H2SO4 (660 Baumé) - 467.2 g H20 - 709.6 g Modified polyethoxylated - 46.4 g straight chain alcohol (TRITON DF-16) Samples of the above concentrates were treated according to the conditions shown and with the results set forth in Table VII below: TABLE VII 550for Concentrate Dry Ace/Acetone Bath OOC for 24 hours 24 hours A Slightly viscous, Clear, substantially Clear, substantially clear, substantially t colourless colourless colourless solution solution solution B* ~ ~ C Significant Significant Very dark brown precipitate precipitate discolouration, some separation into layers D Slightly viscous Lightly brown- Moderately lightly brown-coloured coloured brown-coloured solution solution solution * Homogeneous solution could not be obtained. TERGITOL 08 layered on top of the sulphuric acid solution.

Concentrate A was then placed in an oven maintained at 500C for a period of three weeks. When the solution was removed, it was clear and substantially colourless, i.e. no change in colour occurred in this period.

EXAMPLE 8 Six litres of an aqueous cleaning solution were prepared containing the following quantities of ingredients per litre: H2SO4 (660 BaumB) - 4.7 g MlRAWETB - 0.9g HF - 20 parts per million Aluminium cans of 3004 alloy drawn into single piece containers were employed in this procedure. The cans had a covering of aluminium fines and drawing oils.

Test specimens were treated as follows: (a) Sprayed with the above-mentioned cleaning solution maintained at 1250F (530C); (b) Rinsed with water by immersion in cold water for 30 seconds; and (c) Allowed to stand for 30 seconds, after which they were examined for water breaks on both the inside and outside.

A can was tested as above with a spray time in step (a) of 30 seconds, and the results noted. A second can was tested as above with a spray time in step (a) of 45 seconds and the results noted. Then 200 ppm of NALCO XL 174 (a mineral oil based coolant and lubricant for drawing and ironing aluminium cans) was added to the cleaning solution, and a third can was tested as above with a spray time in step (a) of 30 seconds, and a fourth can with a spray time in step (a) of 45 seconds.

The results of these tests are given in Table VIII below: TABLE VIII Addition of Spray Time Extent of NALCO XL 174, ppm in Seconds Water Breaks 0 30 None 0 45 None 200 30 None 200 45 None COMPARATIVE EXAMPLE 9 Six litres of cleaning solution were prepared by adding to water 4.7 g/l of H2SO4 (660 Barm6), 1.053 g/l of Hercules Surfactant AR-1 50, 0.673 g/l of SURFONIC LF 17, and 20 ppm of hydrofluoric acid.

Aluminium cans from the same batch as were used in Example 8 were tested according to the conditions and procedures set forth in Example 8 with the following results: TABLE IX Addition of Spray Time Extent of NALCO XL 174, ppm in Seconds Water Breaks 0 30 None 0 45 None 200 30 Extensive 200 45 Slight EXAMPLE 10 Six litres of an aqueous cleaning solution heavily contaminated with NALCO XL 1 74 were prepared containing the following quantities of ingredients per litre: H2SO4 (660 BaumB) - 4.7 g MIRAWETB - 0.9g HF - 20 ppm NALCO XL 174 - 500 ppm Aluminium cans of 3004 alloy drawn into single piece containers were employed in this procedure.The cans had a covering of aluminium fines and drawing oils.

Test specimens were treated as follows: (a) Washed with tap water at 1 250F (530C) for 30 seconds; (b) Sprayed with the above-mentioned cleaning solution maintained at 1250F (530C) for 40 seconds; (c) Rinsed by spraying with tap water for 20 seconds; (d) Rinsed by spraying with deionized water; and (e) Allowed to stand for 30 seconds, after which they were examined for water breaks on both the inside and outside.

A can was tested as described above and the results noted. Then to a portion of the cleaning solution contaminated as mentioned above was added 0.9 g/l of the low foaming non-ionic surfactant Plurafac RA 30, and another can tested as described above. This procedure was repeated with the addition of 0.9 g/l of the different low foaming non-ionic surfactants specified in the Table below to fresh portions of the cleaning solution contaminated as mentioned above. The results obtained are given in Table X below.

TABLEX Addition of 0.9 g/l of Extent of non-ionic surfactant Water Breaks None Extensive PLURAFAC RA 30 Slight TRITON DF 16 None SURFONIC LF 7 None SURFONIC LF 17 None ANTAROX LF 330 Moderate As can be seen from this Example, even when very heavy contamination of a commercially used coolant is present in the composition of the invention, the presence of a small quantity of a low foaming non-ionic surfactant in addition to the alkali metal 2-butoxy-ethoxyacetate significantly increases the cleaning ability of the composition.

Claims (24)

1. An aqueous cleaning solution for removing and dissolving aluminium fines and cleaning lubricating oils from aluminium surfaces, which solution comprises from 1 to 10 g/litre of sulphuric acid, from 0.005 to 0.1 g/litre of hydrofluoric acid, and from 0.1 to 10 g/litre of alkali metal 2-butoxyethoxyacetate.

2. A solution according to claim 1 wherein the alkali metal 2-butoxyethoxyacetate is sodium 2-butoxyethoxyacetate.

3. A solution according to claim 2 wherein the sodium 2-butoxyethoxyacetate is present in amount from 0.2 to 0.8 litre.

4. A solution according to any one of claims 1-3 whose pH is from 1.0 to 1.8.

5. A solution according to any one of the preceding claims wherein the sulphuric acid is present in amount of from 3 to 5 litre.

6. A solution according to any one of the preceding claims wherein the hydrofluoric acid is present in amount from 0.01 to 0.03 g/litre.

7. A solution according to any one of claims 1-5 wherein the hydrofluoric acid is present in an amount such that the solution has an aluminium dissolution rate of from 90 to 280 mg per square metre of aluminium surface treated at a temperature of 540C and a contact time of one minute.

8. A solution according to any one of the preceding claims which contains from 0.1 to 10 g/iitre of low foaming non-ionic surfactant.

9. A solution according to claim 8 which contains from 0.2 to 0.8 g/litre of low foaming non-ionic surfactant.

1 0. A solution according to claim 1 substantially as described herein.

11. A solution according to claim 1 substantially as described herein in any one of the Examples.

12. An aqueous solution concentrate for forming the aqueous cleaning solution claimed in any one of the preceding claims, which concentrate comprises from 200 to 600 g/litre of sulphuric acid and from 0.01 to 10 parts by weight alkali metal 2-butoxyethoxyacetate per part by weight of sulphuric acid.

13. A concentrate according to claim 12 wherein the alkali metal 2-butoxyethoxyacetate is sodium 2-butoxyethoxyacetate and this is present in from 0.04 to 0.27 parts by weight per part by weight of sulphuric acid.

14. A concentrate according to claim 12 or 13 which contains low foaming non-ionic surfactant in amount from 0.01 to 10 parts by weight per part by weight of sulphuric acid.

1 5. A concentrate according to claim 14 wherein the amount of the low foaming non-ionic surfactant is from 0.04 to 0.27 parts by weight per part by weight of sulphuric acid.

1 6. A concentrate according to claim 12 substantially as described herein.

1 7. A concentrate according to claim 12 substantially as described herein in any one of the Examples.

1 8. A process for cleaning an aluminium surface, which process comprises (a) contacting said surface with an aqueous cleaning solution claimed in any one of claims 1-11 1 and (b) rinsing the aluminium surface to remove the cleaning solution.

1 9. A process according to claim 1 8 wherein the aqueous cleaning solution is contacted with the aluminium surface by spraying the solution onto the surface.

20. A process according to claim 18 or 19 wherein the solution is maintained at 46 to 630C.

21. A process according to any one of claims 18-20 wherein in step (a) 90 to 280 mg of aluminium dissolve per square metre of the surface.

22. A process according to any one of claims 18-21 wherein the aluminium surface is on an aluminium can.

23. A process according to claim 1 8 performed substantially as hereinbefore described.

24. A process according to claim 1 8 performed substantially as hereinbefore described in any one of the Examples.