ALKALINE CLEANING AGENT FOR ALUMINUM SURFACES

Abstract

The present invention relates to a method for cleaning and optionally degreasing aluminum surfaces, in particular during serial treatment of can cylinders made of aluminum, which provides a high degree of gloss, the method comprising contacting the aluminum surfaces with an alkaline cleaning agent containing, in addition to a builder and a surfactant, a quantity of at least one aluminate dissolved in water; the invention also relates to an alkaline cleaning agent as an application solution, which agent is especially suitable for use in a method according to the invention.

Claims

1. A method for cleaning surfaces of the metal aluminum, in which an aluminum surface to be cleaned is brought into contact with an alkaline cleaning agent which has a pH of greater than 8.0 and contains, in addition to water, a) at least one alkaline builder, b) a total of at least 0.20 g/kg of aluminates dissolved in water, calculated as AlO.sub.2, and c) at least one surfactant.

2. The method according to claim 1, wherein the alkaline builder of the cleaning agent is selected from alkali metal hydroxides and/or alkali metal carbonates.

3. The method according to claim 2, wherein the alkaline cleaning agent contains a total of at least 0.20 g/kg and no more than 3.00 g/kg, of alkali metal carbonates, calculated as CO.sub.3.

4. The method according to claim 1, wherein the pH of the cleaning agent is greater than 8.5, but no greater than 11.0.

5. The method according to claim 1, wherein the alkaline cleaning agent contains alkali metal aluminates as a source of the aluminates dissolved in water.

6. The method according to claim 1, wherein the alkaline cleaning agent contains a total of at least 0.40 g/kg but less than 4.00 g/kg, of aluminates dissolved in water, calculated as AlO.sub.2.

7. The method according to claim 1, wherein the at least one surfactant in the alkaline cleaning agent is selected from nonionic surfactants comprising alkyl benzyl alkoxylates that have no more than 12 carbon atoms in the alkyl group, and have at least 6 but no more than 14 alkoxy units.

8. The method according to claim 1, wherein the alkaline cleaning agent additionally contains organic complexing agents, which are selected from -hydroxycarboxylic acids with no more than three carboxyl groups.

9. The method according to claim 8, wherein the molar ratio of organic complexing agents to aluminates in the alkaline cleaning agent ranges from 1:1 to 1:10.

10. The method according to claim 9, wherein the at least one surfactant in the alkaline cleaning agent is selected from fatty alcohol alkoxylates that have saturated alkyl groups comprising at least 8 but no more than 16 carbon atoms in the alkyl groups, and have at least 10 but no more than 30 alkoxy units, the alkoxy units each being selected from ethoxy and/or propoxy units.

11. The method according to claim 1, wherein the alkaline cleaning agent additionally contains organic complexing agents, which are selected from gluconic acid, citric acid, tartaric acid and salts thereof.

12. The method according to claim 1, wherein the alkaline cleaning agent contains a total of less than 100 mg/kg of phosphates dissolved in water, calculated as PO.sub.4.

13. The method according to claim 1, wherein the cleaning agent contains a total of less than 100 mg/kg of borates dissolved in water, calculated as BO.sub.3.

14. The method according to claim 1, wherein the alkaline cleaning agent contains a total of less than 100 mg/kg of benzoic acid and benzoates dissolved in water, calculated as C.sub.7H.sub.6O.sub.2.

15. The method according to claim 1, wherein the alkaline cleaning agent contains a total of less than 100 mg/kg of organic compounds dissolved in water that have at least one nitrogen-containing heterocyclic compound, calculated as N.sub.3.

16. The method according to claim 1 for cleaning and degreasing surfaces of the metal aluminum, which represent the surfaces of a plurality of can cylinders made of aluminum.

17. An alkaline cleaning agent for aluminum surfaces, which has a pH of greater than 8.0 and containing, in addition to water, a) at least 0.20 g/kg of alkali metal carbonates calculated as CO.sub.3, b) at least 0.20 g/kg of aluminates dissolved in water, calculated as AlO.sub.2, c) at least one nonionic surfactant with an HLB value greater than 10.0, and d) at least one organic complexing agent, which is selected from -hydroxycarboxylic acids.

Description

EXAMPLES

[0039] To illustrate the cleaning and degreasing performance of alkaline cleaning agents according to the invention, beverage cans made of Al3004 that were open on one side were cleaned using different formulations by spraying. The cleaning agents were applied by spraying at 1.0 bar. After spraying on the cleaning agent, cleaning agent residues were removed from the semi-finished products by briefly immersing them in deionized water (<1 Scm.sup.1) and the degree of gloss was determined after removing and blowing off the surfaces. To determine the degree of gloss, the reflectance of each substrate surface was measured and compared with the reflectance of a surface of each semi-finished product degreased using a mixture of n-hexane/ethanol (1:1 by volume). The corresponding results are shown in Table 1. The application solution according to the invention contains the following components as a 1 wt. % solution of the cleaning agent concentrate (see B1, Table 1):

TABLE-US-00001 Sodium aluminate 0.90 g/kg Na.sub.2CO.sub.3 0.47 g/kg Non-ionic surfactants 0.26 g/kg (HLB value 10-12) Sodium gluconate 0.26 g/kg Citric acid 0.30 g/kg

TABLE-US-00002 TABLE 1 Amount in Duration T Degree wt. % pH in s in C. of gloss.sup.# B1 1.0 9.6 40 60 95 B1 1.0 9.6 180 60 94 B2 1.5 9.6 40 60 94 B2 1.5 9.8 180 55 95 VB1 1.5 9.8 40 60 70 VB1 1.5 9.8 180 60 20 VB2 1.5 2.1 40 60 98 VB2 1.5 2.1 180 60 50 .sup.#determined at an angle of 60 with Picogloss Model 503 from Erichsen B1/B2 alkaline cleaning agents according to the invention based on the same concentrate VB1 Comparative Example 1: commercial alkaline cleaning agent based on NaOH/borate (Bonderite C-AK 60036 from Henkel AG) VB2 Comparative Example 2: commercial fluoride-containing cleaning agent based on H.sub.2SO.sub.4/HF (Bonderite C-IC 740 E from Henkel AG).