WO2005001162A1

WO2005001162A1 - Acidic cleaning composition for aluminum and method for cleaning

Info

Publication number: WO2005001162A1
Application number: PCT/GB2004/002729
Authority: WO
Inventors: Alison Jane Hartopp; Richard Franklyn Foster
Original assignee: Natech Limited
Priority date: 2003-06-26
Filing date: 2004-06-24
Publication date: 2005-01-06
Also published as: GB0314900D0

Abstract

An acidic cleaning composition and a method usable for cleaning aluminium, where the cleaning composition comprising an aqueous acidic liquid with a pH of between 0.6 and 2.5, and the composition including for example; 0.2 grams per litre adipic acid, 0. 15 grams per litre polyglucoside, 0.006 grams per litre ferric ions, 0.035 grams per litre hydrogen peroxide; 0.285 grams per litre non ionic surfactants, and 2 grams per litre of sulphuric acid to regulate the pH.

Description

ACIDIC CLEANING COMPOSITION FOR ALUMINUM AND METHOD FOR CLEANING

This invention concerns a cleaning material, a cleaning material concentrate, and a method of cleaning, and particularly but not exclusively a material or method for cleaning the surfaces of aluminium or aluminium alloys.

Products with aluminium surfaces, e.g., beverage containers made of aluminium or aluminium alloy, are ordinarily manufactured by a moulding operation known as drawing and ironing. During this moulding operation lubricating oil is applied to the metal surface, and smut adheres to the resulting container, especially to its inner walls. The surface of this kind of container is generally protected afterwards by e.g., a conversion coating treatment or painting, and prior to this treatment it is necessary to remove the above mentioned lubricating oil and smut from the metal surface. For this purpose, one measure commonly in use is acid cleaning of the aluminium surface. Acid cleaning is done at a temperature from 50 to 80°C to remove or dissolve away aluminium powder and to take away lubricant or oil used for forming. Hydrofluoric acid cleaning agents have been proposed. For example, according to US 3728188, a cleaning agent has been proposed which consists of an acidic aqueous solution containing 0.5-2.0g per litre fluoride ion, 5-21 g per litre ferric ion, and 0.05-3. Og per litre thiourea, the pH of which is regulated to 0.1 -1.8 with a strong mineral acid such as sulphuric acid, etc. With this cleaner, satisfactory surface cleaning is accomplished due to the fact that the large quantity of fluoride ions causes a rapid rate of etching of the aluminium, while on the other hand, this etching is inhibited by the ferric ions.

However, in the case of fluoride ions, special care must be employed with respect to preventing pollution of the working environment and waste liquid treatment, due to their toxicity. This is also true, not only for the case in which hydrofluoric acid is used, but also for systems in which other fluorides are present which introduce fluoride ions into the cleaner. Cleaners with small quantities of fluoride ions, which are a problem in this respect, have also been known conventionally. For example, according to GB 1454974, a cleaner has been proposed which consists of an aqueous acidic solution containing 0.005-0.1 g per litre fluoride ions and 1 -1 Og per litre sulphuric acid, and which has a pH of 1.0-1.8. Although the fluoride ion content is reduced in this way, its toxicity can by no means be neglected. Moreover, in this cleaner the cleaning power is somewhat reduced along with the reduction in fluoride ion content. Problems may arise from the acid cleaning agents that include fluoride in that the washer equipment is subject to accelerated corrosion by the acid.

Another method is seen in Japanese Patent Publication 52-22330 (1977), wherein an acidic cleaning liquid is proposed which contains ferric ions which also can reduce the corrosion of cleaning equipment by the fluoride ions.

In the latter case of an acid cleaner containing ferric ions, a problem arises from the ferric ions which may adhere onto outer walls of the cleaning apparatus where iron rust colour develops and the apparatus becomes dirty.

Particularly in the case of a container formed from aluminium or its alloy which is used as a beverage can, the apparatus is required to be particularly clean from a hygienic point of view.

GB 2200136 describes an acidic cleaning process for aluminium beverage cans using a cleaner containing sulphuric acid, a peroxy acid or salt thereof and a source of fluoride ions. This cleaner is activated by the peroxide rather than using ferric ion, but still requires small amounts of fluoride ion for the process to be effective under the conditions of a typical can washer.

Peroxide is not stable in acidic solutions that contain small amounts of metal ions, especially ferric ions which catalyse the decomposition of peroxide.

It is desirable to reduce the coefficient of friction on the exterior surface of aluminium cans, to aid in the efficient movement of the cans through either metal forming or end product packaging equipment.

US 5139586 describes the conventional method of reducing the coefficient friction on the exterior surface of the metal containers such as aluminium cans, by coating the cans with an invisible layer of lubricating agent.

According to the present invention there is provided a cleaning material usable for cleaning aluminium, the material comprising an aqueous acidic liquid with a pH of between 0.6 and 2.5, the material including:

0.1 - 10g per litre carboxylic acid; 0.1 - 10g per litre peroxide; 0.0001 - 1 g per litre ferric ions; 0.05 - 10g per litre polysaccharide; 0.05 - 10g per litre surface active agents; and nitric and/or sulphuric acid to regulate the pH.

The material is preferably substantially free from fluoride ions. The ferric ions can be obtained from water soluble ferric salts such as

Fe₂(S0₄)₃, Fe(NO₃)_s, FeCO4₃.

Alternatively, the ferric ions can be obtained from ferrous salts, such as FeS0₄ or Fe(N0₃)₂ Where ferrous salts are used, an equivalent quantity of oxidant such as hydrogen peroxide, may be added to oxidise the ferrous ions to ferric ions.

The carboxylic acid may be a dicarboxylic acid, and may be succinic acid or adipic acid. The polysaccharide may be polyglucoside. The polyglucoside is preferably derived from any of starch, pectins, alginates and gums from plants, trees and seaweed by hydrolysis using acid or enzymes, either synthetic or those produced by yeasts and bacteria.

The polysaccharide is preferably alkylated, ethoxylated or propoxylated. Between 0.05 and 10g per litre surface active agents may be provided in the material. The surface active agents may be any of non-ionic, cationic, anionic or amphoteric agents. The surface active agents may be non ionic surfactants. The peroxide preferably includes one or more of hydrogen peroxide, a peroxy acid or a peroxy acid salt.

The invention also provides a concentrate which can be made into a cleaning material according to any of the preceding ten paragraphs.

The concentrate may include: 0.5 - 25g per litre carboxylic acid; 0.5 - 15g per litre peroxide; 0.5 - 25g per litre ferric ions; 0.5 - 50g per litre polysaccharide; 0.5 - 50g per litre surface active agents;

The invention further provides a method of cleaning the surface of aluminium or aluminium alloys, the method comprising using a cleaning material according to any of the said ten paragraphs. The material may be made from a concentrate as previously defined, and nitric and/or sulphuric acid may be added to the concentrate to regulate the pH.

The cleaning may be carried out by immersion or spraying. The cleaning may take place at a temperature of between 20 and 80°C, and preferably between 50 and 70°C. The cleaning may take place for a period of between 10 and 120 seconds. The surface may be washed with water following cleaning with the cleaning material, and thereafter phosphated.

An embodiment of the present invention will now be described by way of example only.

Five compositions with the contents as per Table 1 below were used to spray wash drawn and ironed aluminium cans, which cans were subsequently rinsed with cold tap water and then cold deionised water. The washing took place for 50 seconds at 54°C at a spray pressure of 1.5bar. Following washing the cans were dried at a temperature of 180°C for 2 minutes. Composition 1 is according to the present invention whilst compositions 2 to 5 are provided for reference. At least composition 1 was made up by appropriate dilution of a concentrate.

Where the rows refer to the composition number and the columns are as follows:

A) Sulphuric acid grams per litre

B) Adipic acid grams per litre

C) Polyglucoside grams per litre

D) Ferric ions grams per litre E) Hydrogen peroxide grams per litre F) Non ionic surfactants grams per litre. Table 1

The dried cans were then subjected to the tests outlined below, and the results obtained are provided in Table 2 below.

The following four tests were carried ou - Water Wettability Test

Immediately after the water spray washing, the container was shaken three times to remove the water, after which the container was set down upright, and after 30 sec. the amount of outer surface area of the container wetted with water was measured.

Desmutting Ability

Transparent adhesive tape was stuck to the inner surface of the container after drying, and it was then pulled off and stuck to white cardboard. The case in which the smut was completely removed and the surface had no contamination, was considered good. The evaluation was made based on the 5 stages below according to the degree of contamination: no contamination traces of contamination very minute contamination moderate contamination great contamination

Tape Adhesion Test

The tape adhesion test was performed to measure the adhesion between a cleaned surface and an organic finish or overcoating. White ink from BASF was applied, using a rubber brayer. Water-borne, wet-ink varnish from PPG Company, was roll-coated with a #1 0 draw-down bar to achieve a coating thickness of 3gm^'2. The coated surface was cured in a forced-air oven for 90 seconds at about 177°C. The finished (i.e. painted) surface, after being cured, was immersed in boiling tap water or a 1% detergent (such as "JOY", a commercially available PROCTOR & GAMBLE product) solution for 15 minutes, rinsed in tap water, and dried. The treated surface was then cross- hatched, and SCOTCH brand transparent tape (#61 0) (commercially available from 3M) was applied to the cross-hatched area. The amount of paint removed by the tape was observed, and the results were rated as follows:

10: excellent adhesion 8-9 very slight removal 5-8 obvious removal 1-5 very obvious removal 0 complete removal.

Internal Lacquer Adhesion Test This check measures lacquer integrity. Results are given in milliamps, with 2 milliamps being the maximum reading allowed for a single can. Tests were carried out on 50 cans taken at random through the test run. The result is the number of cans that gave a reading above 2 milliamps.

Table 2

Composition 1 provided a better wettability than the other compositions and provided the best tape adhesion test. This indicates its propensity for receiving an organic finish or overcoating. Very good cleaning was demonstrated by full marks in the desmutting test and also the internal lacquer adhesion test. Therefore superior cleaning properties have been achieved in a number of different ways according to the invention.

The cleaning material according to the present invention achieves a reduction of the coefficient of friction by preventing etching of the can during the cleaning process, thus producing a very smooth, shiny can which has an intrinsically low coefficient of friction on the exterior surface.

With cleaners according to the invention the cleaning of the aluminium by the sulphuric acid is thought to be promoted by the hydrogen peroxide and the ferric ions. This promotion mechanism is suspected to be due to a combination of cathodic reaction of the ferric ion with the aluminium and the generation of free oxygen at the aluminium surface by the hydrogen peroxide. The ferric ions and dissolved aluminium ions catalyse the decomposition of the hydrogen peroxide and if this is not suppressed, the cleaner will lose some of its effectiveness over a period of time. This decomposition of the peroxide is prevented by the polyglucoside or other polysaccharide which successfully stabilises the peroxide against catalytic decomposition by ferric ions and dissolved aluminium ions. The polyglucoside also catalyses the cleaning of the lubricants from the aluminium surface in conjunction with the other non ionic surfactants used in the cleaner formulation.

The small amount of ferric ion inhibits corrosion of the washing equipment and also accelerates the cleaning of the aluminium surface whilst simultaneously inhibiting etching of the can surface, to enable the production of bright, shiny cans with optimum surface condition for further conversion coating and/or decorating with base coats, inks and varnishes. The carboxylic combines with any dissolved aluminium and prevents the latter from inhibiting the cleaning process. Avoiding using hydrofluoric acid provides for a less hazardous working environment, and reduced waste liquid treatment. Hydrofluoric acid also tends to etch the can.

The polysaccharide accelerates oil removal from the can by other surface active agents in the formulation.

Various modifications may be made without departing from the scope of the invention. For instance, a different washing technique or parameters could be used. It may be possible to use polysaccharides other than polyglucosides, and those derived from starch, pectins, alginates and gums from plants, trees and seaweed by hydrolysis using acid or enzymes, wether synthetic or those produced by yeasts and bacteria have been found to be effective. Optimal cleaning has generally been found if the polysaccharide is alkylated, ethoxylated or propoxylated.

Carboxylic acids, and in particular dicarboxylic acids, have been shown to be effective agents for complexing aluminium. This behaviour is exhibited by a wide range of carboxylic acids and in particular dicarboxylic acids. For example, it is possible to use succinic acid, adipic acid and other water soluble simple carboxylic acids. It is also possible to use more complex carboxylic acids where the carboxylic acid has been substituted onto for example aromatic rings.

Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

Claims

1. A cleaning material usable for cleaning aluminium, the material comprising an aqueous acidic liquid with a pH of between 0.6 and 2.5, the material including:

0.1 - 10g per litre carboxylic acid; 0.1 - lOg per litre peroxide; 0.0001 - 1 g per litre ferric ions; 0.05 - 10g per litre polysaccharide; 0.05 - 10g per litre surface active agents; and nitric and/or sulphuric acid to regulate the pH.

2. A cleaning material according to claim 1 , characterised in that the material is substantially free from fluoride ions.

3. A cleaning material according to claims 1 or 2, characterised in that the ferric ions are obtained from water soluble ferric salts such as Fe₂ (S0₄)₃, Fe(NO₃)_s, FeCO4₃.

4. A cleaning material according to claims 1 or 2, characterised in that the ferric ions are obtained from ferrous salts, such as FeSO₄or Fe(NO₃)₂

5. A cleaning material according to claim 4, characterised in that an equivalent quantity of oxidant such as hydrogen peroxide to that of the ferrous ions, is added to oxidise the ferrous ions to ferric ions.

6. A cleaning material according to any of the preceding claims, in which the carboxylic acid is a dicarboxylic acid.

7. A cleaning material according to claim 6, characterised in that the carboxylic acid is succinic acid or adipic acid.

8. A cleaning material according to any of the preceding claims, characterised in that the polysaccharide is polyglucoside.

9. A cleaning material according to claim 8, characterised in that the polyglucoside is derived from any of starch, pectins, alginates and gums from plants, trees and seaweed by hydrolysis using acid or enzymes, either synthetic or those produced by yeasts and bacteria.

10. A cleaning material according to any of the preceding claims, characterised in that the polysaccharide is alkylated, ethoxylated or propoxylated.

11. A cleaning material according to any of the preceding claims, characterised in that between 0.05 and 10g per litre surface active agents are provided in the material.

12. A cleaning material according to claim 11 , characterised in that the surface active agents are any of non-ionic, cationic, anionic or amphoteric agents.

13. A cleaning material according to claim 12, characterised in that the surface active agents are non ionic surfactants.

14. A cleaning material according to any of the preceding claims, characterised in that the peroxide includes one or more of hydrogen peroxide, a peroxy acid or a peroxy acid salt.

15. A concentrate characterised in that the concentrate can be made into a cleaning material according to any of the preceding claims.

16. A concentrate according to claim 15, characterised in that the concentrate includes:

0.5 - 25g per litre carboxylic acid; 0.5 - 15g per litre peroxide; 0.5 - 25g per litre ferric ions; 0.5 - 50g per litre polysaccharide; 0.5 - 50g per litre surface active agents; 17. A method of cleaning the surface of aluminium or aluminium alloys, the method comprising using a cleaning material according to any of claims 1 to 14.

18. A method according to claim ^'17, characterised in that the cleaning material is made from a concentrate according to claims 15 or 16.

19. A method according to claim 18, characterised in that nitric and/or sulphuric acid are added to the concentrate to regulate the pH.

20. A method according to any of claims 17 to 19, characterised in that the cleaning is carried out by immersion or spraying.

21. A method according to any of claims 17 to 20, characterised in that the cleaning takes place at a temperature of between 20 and 80°C.

22. A method according to claim 21 , characterised in that the cleaning - takes place at a temperature of between 50 and 70°C.

23. A cleaning material according to any of claims 17 to 22, characterised in that the cleaning takes place for a period of between 10 and 120 seconds.

24. A method according to any of claims 17 to 23, characterised in that the surface is washed with water following cleaning with the cleaning material, and thereafter phosphated.

25. A cleaning material substantially as hereinbefore described.

26. A concentrate which can be made into a ^' cleaning material, the concentrate being substantially as hereinbefore described.

27. A method of cleaning the surface of aluminium or aluminium alloys, the method, being substantially as hereinbefore described.

28. Any novel subject matter or combination including novel subject matter disclosed herein, whether or not within the scope of or relating to the same invention as any of the preceding claims.