It is known that after aluminium cans have been formed and cleaned, the surface roughness is such that cans are liable to jam in the subsequent steps where they are painted since they tend to jam on the mandrel on which they are held during painting. The faster the production line, the greater is the chance of jamming and so limitation of line speed, and naturally it is desirable to increase the line speed to increase productivity if possible.

EP-A-293 820 is an example showing how the addition of a lubricant and surface conditioner to the final rinse before drying and painting can increase the mobility of the cans by reducing surface roughness. A disadvantage of this process, however, is that excess lubricant and surface conditioner may have adverse effects on painting and, since the lubricant and surface conditioner is water soluble, any excess cannot be washed off without risking

removal of all of it.

In an attempt to overcome this, US-3 332 452 proposes a composition which is added simultaneously with the application of a conversion coating and which enhances mobility of the cans. This has the advantage that, any excess material can be removed by a rinse whilst leaving the mobility aid adhered to the aluminium surface together with the conversion coating.

It is therefore an object of the present invention to provide another composition which can be added simultaneously with the conversion coating composition to give mobility, i.e. increased slipperiness, to the surfaces of the cans, particularly during the subsequent painting step.

According to the invention there is provided a composition which is soluble in acid conditions and which contains as a mobility aid a bi-functional compound, such as one which contains amine and carboxylate functions, the compound being one which does not alter the water-break free nature of a cleaned aluminium surface. Such a composition will have an acidic pH, typically from pH 2.0 to 4.0, and more preferably 3.2 to 3.6.

The invention therefore also extends to a method

of treatment of an aluminium surface with such a composition.

Such a composition is preferably added to the conversion coating composition and so a combined composition can comprise a source of zirconium ions, a source of fluoride ions, a source of phosphate ions, and a bi-functional compound such as one containing amine and carboxylate functions, which is soluble in acid conditions and which does not alter the water-- break free nature of a cleaned aluminium surface, the composition having an acidic pH.

In a typical composition there may be from about 10 to 100 ppm of zirconium ions, from about 20 to 200 ppm of fluoride ions and from about 5 to 100, and more preferably 60 to 80, ppm of phosphate ions. The composition will also contain an acid, e.g. nitric acid, preferably in an amount sufficient to adjust the pH of a working bath using the composition to from 2.0 to 4.0, and more preferably 3.2 to 3.6.

We believe that the bi-functional compound must be an organic moiety and that this should contain a carbon chain such as an alkyl group of sufficient size to give lubricity to the finished can. In that connection it appears to be desirable that the bi- functional compound contains a carbon chain of length

C8 or greater, and more preferably of C12 or greater.

It also appears that the bi-functional compound should contain a group such as an amine group between the alkyl chain and the anionic group, to ensure that the bi-functional compound is soluble under acidic conditions.

Further, it appears that the bi-functional compound should contain a weakly anionic group such that the compound will precipitate or chemisorb onto the conversion coating given to the can. If the anionic group is too strong, e.g. a sulphonate, this will not aid mobility because it does not appear to precipitate. A weakly acidic group must, however, be soluble in the acid conditions of the composition and so an acid group from a long chain fatty acid cannot be used. The anionic group should therefore be both a weakly acid group and be soluble under acid conditions. Examples of suitable anionic groups are carbonate and phosphate acid ester groups.

When a drawn aluminium can is cleaned to removed lubricant and aluminium fines after drawing, the cleaned surface will be water-break free. The bi- functional compound should be chosen such that the cleaned aluminium surface treated with the compound remains water-break free. The bi-functional compound

should therefore be water soluble.

A suitable bi-functional compound is the alkyl amine carboxylate sold under the trade name Amphionic 32B by Rhone Poulenc.

An advantage of the invention is that the bi- functional compound will give increased mobility to the treated can so that there is less risk of jamming during later process steps in the production line, e.g. during removal from the mandril during the conversion coating step. No additional or separate treatment step is required since the bi-functional compound can be applied during the conversion coating step and any excess material can be removed during later washing steps which are conventional. Thus, the bi-functional compound seems to become incorporated into the conversion coating either by adsorption or chemisorption, so that washing will only remove an excess and not remove it completely. There is therefore less risk that too much will be present on the can to affect the adhesion of ink during the subsequent painting step. Further the bi-functional compound seem to have no detrimental effect on the conversion coating itself. No significant change is required to the production line, although if desired it is possible for the bi-functional compound to be

added in a separate step after the conversion coating.

The composition of the conversion coating can be largely conventional and for examples of particular materials, concentrations, types of treatment, etc.

reference is directed to US-5 332 452, the whole disclosure of which is deemed to be incorporated herein.

According to one embodiment of the invention, the concentration of the conversion coating compounds in the treatment bath can be reduced as compared with the conventional amounts disclosed in US-5 332 452 if one wishes to provide the resulting aluminium cans with mobility and staining of the dome in the underside of the can is not important because the contents of the filled can do not need pasteurisation.

Therefore one can reduce the concentration of the conversion coating components to the minimum necessary to hold the bi-functional compound on the surface of the cans.

Further advantages of the invention are that the addition of the bi-functional compound to the conversion coating composition does not give sludge or foam in the treatment bath, the composition is tolerant of the presence of residual oils, and the resulting cans are water-break free after their final

rinse which enhances drying. Also the compositions appear to impart no adverse taste to the liquid in the final filled cans.

The cans treated in this way have a high mobility and when subjected to a conventional slip test, slip angles of 200 are typical and angles of 170 to 180 are often possible. In that connection, an untreated can would typically have a slip angle of 50° to 600 and there would be no significant improvement in handling of the cans during painting unless the angle was less than 350. Angles of 200 are therefore regarded as very good.

According to embodiments of the invention, a treatment bath containing the conversion coating composition and bi-functional compound would operate at a temperature of about 35 to 380C, preferable about 350C, a contact time of about 10 to 30 s, preferably about 15 s, a pH of about 3.2 to 3.6, preferably about 3.2, a free acid content of about 0.6 to 1.2%.

The bi-functional compound is preferably present in the bath in an amount of from about 0.01 to 0.1%, and more preferably about 0.02 to 0.035%, by weight of the total bath weight.

The invention will now be illustrated, by way of example, with reference to the following tests taken

together with the accompanying figures.

EFFECT OF VARYING APPLICATION CONDITIONS The major variables are:- Application time Temperature Concentration of the bi-functional compound Concentration of conversion coating composition Process Conditions Drawn aluminium cans were sprayed with a cleaning composition consisting of 1% Novaclean 70 (available commercially from the Applicants) plus 15ppm fluoride.

The spraying conditions were: pressure 30psi temperature 510C time 30s Thereafter the cans were water rinsed for 20s.

They were then sprayed with a conversion coating composition according to Novamax, treatment NC 9090 (available from the Applicants) and additionally

containing as a slip agent 0.035% of the bi-functional compound Amphionic 25B.

The spraying conditions were: temperature 300C spray pressure 6psi time 10s.

Thereafter, the cans were again subject to a water rinse for 20s followed by a rinse in de-ionised water for 20s.

Temperature From Figure 1 (Slip v Temperature) it is apparent that an optimum temperature for slip occurs at 35 to 400C.

This is believed to be due to the conflicting effects of the rougher treatment which is formed at high temperatures and the absorbed slip agent (Amphionic 25B) which is less temperature dependent.

The optimum appears to be at 380C and this temperature was used in subsequent tests.

Effect of pH and concentration of bi-functional compound (Amohionic 25B

The combination of pH and concentration of Amphionic 25B application times was evaluated and the results shown in Figures 2 and 3.

From Figures 2 and 3 the slip at different concentrations of conversion coating composition and Amphionic 25B were determined. Slip angles above 24° are inconsistent and difficult to measure and so are not reported.

For both 10 and 20 second contact times 0.03 to 0.035% Amphionic 25B and pH of 3.2 to 3.4 give optimum performance. A pH of 3.6 gives acceptable results.