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EP-4735667-A1 - ALKALINE CLEANING AGENT FOR ALUMINUM SURFACES

EP4735667A1EP 4735667 A1EP4735667 A1EP 4735667A1EP-4735667-A1

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. In the method according to the invention, a high degree of gloss is achieved when using 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 being used in a method according to the invention.

Inventors

  • RIESOP, JOERG
  • KLAES, Sarah
  • Manko, Michal
  • Grabowski, Jessika

Assignees

  • Henkel AG & Co. KGaA

Dates

Publication Date
20260506
Application Date
20240620

Claims (15)

  1. 1. A process for cleaning surfaces of the metal aluminium, in which the aluminium surface to be cleaned is brought into contact with an alkaline cleaner which has a pH value 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 AlO2, and c) at least one surfactant.
  2. 2. Process according to claim 1, characterized in that the alkaline builder of the cleaner is selected from alkali metal hydroxides and/or alkali metal carbonates, preferably from alkali metal carbonates and particularly preferably from sodium carbonate.
  3. 3. Process according to claim 2, characterized in that the alkaline cleaner contains a total of at least 0.20 g/kg, preferably a total of at least 0.30 g/kg, very particularly preferably a total of at least 0.40 g/kg, but preferably a total of not more than 3.00 g/kg, particularly preferably a total of not more than 2.00 g/kg of alkali metal carbonates calculated as CO3.
  4. 4. Process according to one or more of the preceding claims, characterized in that the pH value of the cleaner is greater than 8.5, but preferably not greater than 11.0, particularly preferably not greater than 10.5 and most preferably not greater than 10.0.
  5. 5. Process according to one or more of the preceding claims, characterized in that alkali metal aluminates, preferably sodium aluminate, are contained in the alkaline cleaner as a source for the aluminates dissolved in water.
  6. 6. Process according to one or more of the preceding claims, characterized in that the alkaline cleaner contains a total of at least 0.40 g/kg, preferably a total of at least 0.60 g/kg, but preferably a total of less than 4.00 g/kg, particularly preferably a total of less than 3.00 g/kg, particularly preferably less than 2.00 g/kg of aluminates dissolved in water, calculated as AlO2.
  7. 7. Process according to one or more of the preceding claims, characterized in that the at least one surfactant contained in the alkaline cleaner is selected from nonionic surfactants, preferably from nonionic surfactants with an HLB value greater than 10.0, particularly preferably from alkylbenzyl alkoxylates with not more than 12 carbon atoms in the alkyl radical, which is preferably saturated, which contain at least 6 but not more than 14 alkoxy units, and/or from fatty alcohol alkoxylates having at least 8 but not more than 16 carbon atoms in the alkyl radical, which is preferably saturated and particularly preferably saturated and unbranched, which have at least 10 but not more than 30 alkoxy units, wherein the alkoxy units are preferably each selected from ethoxy and/or propoxy units.
  8. 8. Process according to one or more of the preceding claims, characterized in that the alkaline cleaner additionally contains organic complexing agents, which are preferably selected from α-hydroxycarboxylic acids, particularly preferably selected from α-hydroxycarboxylic acids with not more than three carboxyl groups, very particularly preferably from sugar acids, in particular aldonic acids and aldaric acids, and from citric acid and/or tartaric acid.
  9. 9. Process according to claim 8, characterized in that the molar ratio of organic complexing agents to aluminates contained in the alkaline cleaner is in the range of 1:1 to 1:10, preferably in the range of 1:2 to 1:8.
  10. 10. Process according to one or more of the preceding claims, characterized in that the alkaline cleaner contains a total of less than 100 mg/kg, preferably less than 10 mg/kg, particularly preferably less than 1 mg/kg of phosphates dissolved in water, calculated as PCM.
  11. 11. Process according to one or more of the preceding claims, characterized in that the cleaner contains a total of less than 100 mg/kg, preferably less than 10 mg/kg, particularly preferably less than 1 mg/kg of borates dissolved in water, calculated as BO3.
  12. 12. Process according to one or more of the preceding claims, characterized in that the alkaline cleaner contains a total of less than 100 mg/kg, preferably less than 10 mg/kg, particularly preferably less than 1 mg/kg of benzoic acid and benzoates dissolved in water, calculated as C7H6O2.
  13. 13. Process according to one or more of the preceding claims, characterized in that the alkaline cleaner contains a total of less than 100 mg/kg, preferably less than 10 mg/kg, particularly preferably less than 1 mg/kg of organic compounds dissolved in water with at least one nitrogen-containing heterocycle calculated as N3.
  14. 14. A method according to one or more of the preceding claims for cleaning and degreasing surfaces of the metal aluminium, which represent the surfaces of a plurality of can cylinders made of aluminium.
  15. 15. Alkaline cleaner for aluminum surfaces, which has a pH value of greater than 8.0 and preferably not greater than 11.0, containing in addition to water a) at least 0.20 g/kg, but preferably not more than 3.00 g/kg of alkali metal carbonates calculated as CO3, b) at least 0.20 g/kg, but preferably less than 4.00 g/kg of aluminates dissolved in water, preferably sodium aluminate, calculated as AlO2, c) at least one nonionic surfactant with an HLB value greater than 10.0 and d) at least one organic complexing agent, which is preferably selected from a-hydroxycarboxylic acids, particularly preferably selected from a-hydroxycarboxylic acids with not more than three carboxyl groups, very particularly preferably selected from gluconic acid and/or citric acid.

Description

Alkaline cleaner for aluminum surfaces The present invention relates to a method for cleaning and optionally degreasing aluminum surfaces, in particular in the series treatment of can cylinders made of aluminum. A high degree of gloss is achieved in the method according to the invention when using an alkaline cleaner containing, in addition to builder and surfactant, an amount of at least one aluminate dissolved in water. The invention also includes an alkaline cleaner as an application solution, which is particularly suitable for use in a method according to the invention. When cleaning semi-finished products and components made of aluminum, good cleaning and degreasing of the surfaces can be achieved on a regular basis and the cleaners to be used for this are generally known, but a greater problem is the reliable provision of high-gloss surfaces, especially when treating a large number of semi-finished products/components in series. Especially with high component throughputs, changes in the composition of the cleaning bath due to consumption and the introduction of dirt, as well as inconsistent pickling or temporary over-pickling, can mean that a high level of material waste has to be accepted or components have to go through a cleaning step several times. This is particularly problematic in can production, a highly standardized and automated production process with extreme throughput rates of several hundred to several thousand cans per minute. In addition, in can production, insofar as transparent can outer paints are used for decoration, such cans with low or inconsistent gloss levels are perceived as unaesthetic by the end consumer and have to be sorted out in the production process and sent for material recycling. Established cleaning systems for aluminum materials and aluminum cans in particular are often based on aqueous, acidic, fluoride-containing solutions, for which the fluoride content in the cleaner must be precisely controlled during the throughput of the series of components to ensure a uniform gloss finish, if necessary by adding inhibitors. As an example of the process engineering effort, reference can be made to US 5,565,076, which deals with a special design of a fluoride-sensitive glass electrode for the reliable determination of the fluoride content in acidic cleaning baths when treating aluminum cans. Other alkaline cleaning systems, which are ideal for removing oil and grease residues from previous production steps such as deep drawing from the aluminum surfaces, are often based on builder substances such as borates and/or phosphates, which are problematic in terms of health or environmental hygiene. In addition, the alkaline builders selected from phosphates, borates and/or silicates can cause surface defects during painting, so that a technically demanding control of the composition of the cleaning bath is required. Last but not least, it is also important for alkaline Cleaners can be used to precisely adjust the pickling effect in order to achieve a consistent level of gloss with short treatment times and high throughput rates, thus ensuring, for example, in can production, that there is little waste and thus high economic efficiency and environmental compatibility. The above-mentioned requirements for a cleaning and degreasing step in the manufacture of semi-finished products and components made of aluminum and the state of the art mean that the existing processes must be improved so that wet-chemical cleaning and degreasing of a large number of semi-finished products or components is possible in short treatment times, as a result of which reliably high-gloss material surfaces are provided which, when coated with transparent paints, also meet high aesthetic standards and do not have any matting on the outer surfaces. In particular, a cleaner should be provided which, in terms of application temperature and duration, provides consistently good properties in terms of cleaning results and gloss level without complex process-related control of bath parameters, even in high-throughput processes such as can production. Furthermore, wet-chemical cleaning and degreasing should be able to be carried out with a composition that is as ecologically harmless as possible and, when used, does not cause any health risks for the workers responsible for carrying out and controlling the cleaning from an occupational hygiene perspective. The present invention solves this requirement profile by establishing a method for cleaning surfaces of the metal aluminum, in which the aluminum surface to be cleaned is brought into contact with an alkaline cleaner which has a pH value of greater than 8.0 and, in addition to water, contains a) at least one alkaline builder, b) a total of at least 0.20 g/kg of aluminates dissolved in water, calculated as AlO2, and c) at least one surfactant. The concentration or quantity specifications characterizing the alkaline cleaner in the context of the present invention al