Alkaline cleaning agent for aluminum surfaces

Abstract

The present invention relates to a method for cleaning and optionally degreasing aluminum surfaces, particularly during the continuous processing of aluminum can cylinders. In the method of the present invention, a high degree of gloss is obtained when an alkaline cleaning agent containing at least one aluminate dissolved in a certain amount of water, in addition to a builder and a surfactant, is used. The present invention also relates to an alkaline cleaning agent as an application solution, which is particularly suitable for use in the method of the present invention.

Description

Technical Field

[0001] The present invention relates to a method for cleaning and optionally degreasing the aluminum surface, particularly during the continuous processing of aluminum can cylinders. In the method of the present invention, when using an alkaline cleaning agent containing at least one aluminate dissolved in a certain amount of water in addition to a builder and a surfactant, a high degree of gloss can be obtained. The present invention also relates to an alkaline cleaning agent as an application solution, which is particularly suitable for use in the method of the present invention.

Background Art

[0002] When cleaning semi-finished products and parts made of aluminum, usually good surface cleaning and degreasing can be achieved, and in principle, the cleaning agents used for this purpose are known. However, a major challenge is to reliably provide a high-gloss surface, particularly in the continuous processing of multiple semi-finished products / parts. Especially when the part throughput is high, high levels of material waste must be tolerated due to changes in the composition of the cleaning tank due to consumption and introduction of contaminants, as well as inconsistent or temporary over-pickling, or it may mean that parts have to go through the cleaning process multiple times. This is a highly standardized and automated production process, which is particularly problematic in can manufacturing with extremely high processing speeds of hundreds to thousands of cans per minute. In addition, regarding the use of a decorative and transparent outer can lacquer when manufacturing cans, cans with low or inconsistent gloss levels are not perceived as aesthetically satisfying to the end consumer and must be discarded during the manufacturing process and sent for material recycling. Cleaning agent systems established in the prior art for aluminum materials, particularly aluminum cans, are mostly based on aqueous, acidic, fluoride-containing solutions, and for this reason, the fluoride content in the cleaning agent must be accurately monitored by optionally adding inhibitors to ensure a uniform gloss appearance during the processing of a series of components. As an example of a procedural effort, reference can be made here to US Patent No. 5,565,076, which relates to a special design of a fluoride-sensitive glass electrode for reliably measuring the fluoride content of an acidic cleaning agent bath when processing aluminum cans.

[0003] Other alkaline cleaning systems are very suitable for removing oil and grease residues from aluminum surfaces from previous manufacturing processes such as deep drawing, but they are often based on builder substances that are problematic from a health or environmental hygiene standpoint, such as borates and / or phosphates. Furthermore, alkaline builders selected from phosphates, borates and / or silicates can cause surface defects during painting, requiring rigorous monitoring of the cleaning bath composition. Finally, and most importantly, even when using alkaline cleaning agents, it is necessary to precisely configure the pickling process to achieve consistent gloss with short processing times and high processing speeds, and consequently ensure low waste, and thus high economic efficiency and environmental compatibility, for example, in can manufacturing. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] U.S. Patent No. 5565076 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] Based on the above requirements and prior art regarding cleaning and degreasing processes in the manufacturing of semi-finished products and parts made of aluminum, existing methods must be improved to enable wet chemical cleaning and degreasing of multiple semi-finished products or parts within a short processing time, thereby ensuring a high-gloss material surface even when coated with clear lacquer, and meeting high aesthetic standards without dullness on the exterior. In particular, even in high-volume processes such as can manufacturing, cleaning agents must be provided that consistently provide good characteristics in terms of cleaning results and gloss within a wide range of applicable temperatures and application times, without requiring the monitoring of complex bath parameters in the procedure. Furthermore, wet chemical cleaning and degreasing must be carried out using compositions that are as ecologically harmless as possible, and their use must not pose a health risk to workers responsible for performing and monitoring the cleaning process from an occupational hygiene perspective. [Means for solving the problem]

[0006] The present invention satisfies this requirement by establishing a method for cleaning surfaces made of metallic aluminum, which involves contacting the aluminum surface to be cleaned with an alkaline cleaning agent having a pH greater than 8.0 and containing the following in addition to water: a) At least one alkali builder b) Aluminate dissolved in water, calculated as AlO2, totaling 0.20 g / kg or more, and c) At least one surfactant. [Modes for carrying out the invention]

[0007] In the context of this invention, the specified concentrations or amounts characterizing the alkaline cleaning agent always refer to the overall composition of the alkaline cleaning agent, unless explicitly defined otherwise in each individual case.

[0008] For the purposes of this invention, "alkali builder" refers to an alkali-reactive compound or a mixture of such compounds, wherein at least one alkali-reactive compound must be a component of the builder at a concentration of 1 mmol / kg or more, and the equilibrium reaction that produces alkalinity is pK B The value is in the range of 3.0 to 6.0. Therefore, suitable builders in the context of the present invention are carbonates, borates, silicates and / or phosphates, as well as mixtures of these compounds with hydroxides.

[0009] In the context of the present invention, the alkali builder is preferably selected from alkali metal carbonates and / or alkali metal carbonates, particularly preferably from alkali metal carbonates, and most preferably from sodium carbonate.

[0010] To effectively remove pressing oils and greases commonly used in metalworking from the surface of the parts to be cleaned, the cleaning agent preferably contains alkali metal carbonates, calculated as CO3, in a total amount of 0.20 g / kg or more, particularly preferably 0.30 g / kg or more, and especially preferably 0.40 g / kg or more. Cleaning and degreasing can also be supported by pickling the aluminum substrate, but a high pickling rate is detrimental to the surface gloss because it significantly increases surface roughness, even with a short processing time. To prevent dulling of the aluminum surface, the cleaning agent used according to the present invention preferably has a total alkali metal carbonate content, calculated as CO3, not exceeding 3.00 g / kg in any case, and particularly preferably not exceeding 2.00 g / kg.

[0011] For similar reasons, the pH of the alkaline cleaning agent must be greater than 8.0, preferably greater than 8.5, in order to ensure proper cleaning and optionally remove excess oil and grease. However, in order to prevent as much as possible over-pickling of the aluminum surface treated by the method of the present invention without the use of inhibitors, the pH of the alkaline cleaning agent is preferably 11.0 or less, particularly preferably 10.5 or less, and even more preferably 10.0 or less.

[0012] For sufficient pH stability and a consistent but not excessive pickling action, the total alkalinity (points) of the alkaline detergent should be 1.5 or higher, particularly preferably 1.8 or higher, preferably not exceeding 4.0 points, particularly preferably not exceeding 3.0 points, and very preferably not exceeding 2.4 points. Here, total alkalinity is defined as the alkalinity of 50 ml of deionized water (κ < 1 μS cm). -1 This corresponds to the amount of 0.1N hydrochloric acid consumed (in milliliters) after titrating a 10 ml sample volume of washing agent, diluted with ( ), to a pH of 3.6 at 25°C.

[0013] During the method according to the present invention, for a mild pickling action, the free alkalinity (points) of the alkaline detergent is preferably not greater than 1.5, more preferably not greater than 1.0 point, particularly preferably not greater than 0.8 point, preferably 0.2 point or more, and particularly preferably 0.3 point. Here, free alkalinity is defined as the alkalinity of 50 ml of deionized water (κ < 1 μS cm). -1 This corresponds to the amount of 0.1N hydrochloric acid consumed (in milliliters) after titrating a 10 ml sample volume of washing agent, diluted with ) at a temperature of 25°C until the pH reaches 3.6.

[0014] The presence of aluminate dissolved in water, existing as a complex, hydroxoaluminate ions, provides a glossy surface and is essential for maintaining gloss during the cleaning step of the method of the present invention. All water-soluble aluminates are suitable as sources of water-soluble aluminates, preferably alkali metal aluminates, such as sodium aluminate and / or potassium aluminate, but particularly preferably sodium aluminate.

[0015] In the presence of aluminates, excessive pickling of aluminum substrates is prevented, making the cleaning and degreasing process in alkaline media highly efficient without impairing gloss properties. For this purpose, a total content of aluminates dissolved in water of 0.20 g / kg or more, preferably 0.40 g / kg or more, and particularly preferably 0.60 g / kg or more, calculated as AlO2, is required in all cases. Significantly higher content of aluminates can be obtained in the cleaning agent without impairing performance, particularly gloss, but for economic reasons, the content of aluminates dissolved in water should be limited, and the alkaline cleaning agent contains aluminates dissolved in water of less than 4.00 g / kg, particularly preferably less than 3.00 g / kg in total, and particularly preferably less than 2.00 g / kg, calculated as AlO2. Overall, there is a wide range of applicability regarding the content of aluminates dissolved in water, which opens up the possibility of a high degree of procedural flexibility.

[0016] For effective cleaning and degreasing, the presence of at least one surfactant is necessary. In principle, all surfactants known in the prior art that can emulsify nonpolar components in a continuous aqueous phase are suitable. These include anionic surfactants such as the fatty acids mentioned above, and especially nonionic surfactants. In a preferred embodiment of the method of the present invention, the alkaline cleaning agent thus comprises at least one nonionic surfactant having an HLB value greater than 10.0, preferably greater than 11.0, and particularly preferably greater than 12.0. In the context of the present invention, the HLB value is an experimentally determined amount and is calculated as follows: HLB = 20 (1-M L / M) Here, M L : Molar mass of the lipophilic group of a nonionic surfactant; M: Molar mass of nonionic surfactant.

[0017] Preferred nonionic surfactants having an HLB value greater than 10.0 are selected from alkylbenzyl alkoxylates having 12 or fewer carbon atoms in the alkyl group, wherein the alkyl group is preferably saturated, where the alkylbenzyl alkoxylate has from 6 to 14 alkoxy units.

[0018] Similarly suitable and equally preferred within this range are nonionic surfactants having an HLB value greater than 10.0. These are selected from fatty alcohol alkoxylates having 8 to 16 carbon atoms in the alkyl group, wherein the alkyl group is preferably saturated, particularly preferably saturated and unbranched, and having from 10 to 30 alkoxy units, where the alkoxy units are preferably each selected from ethoxy units and / or propoxy units.

[0019] Due to the increased introduction of aluminum ions at high processing speeds of semi-finished products and parts made of aluminum or during long-term operation of the cleaning bath according to the method of the invention, precipitation of aluminum salts can become a problem. The microcrystalline deposits that occur together with the deposits on the semi-finished products and parts correspond to surface defects that can impair the gloss properties of the aluminum surface and also lead to insufficient adhesion to subsequently applied paint systems. To prevent this, the alkaline cleaning agent preferably also contains an organic complexing agent, which is preferably selected from α-hydroxycarboxylic acids, particularly preferably from α-hydroxycarboxylic acids having 3 or fewer carboxyl groups, very particularly preferably from sugar acids, particularly preferably from aldonic acids and aldaric acids, and particularly preferably from citric acid and / or tartaric acid. For sufficient measurement, it is generally advantageous when the molar ratio of the organic complexing agent to the aluminate in the cleaning agent is from 1:1 to 1:10, particularly preferably from 1:2 to 1:8.

[0020] One advantage of the alkaline cleaning agent used in the method of the present invention is that it can be formulated without fluoride and without adding inhibitors. Furthermore, it is possible to avoid builder substances such as phosphates and / or borates that may be harmful to health and the environment.

[0021] According to the present invention, therefore, a method is preferred in which the alkaline cleaning agent contains phosphates dissolved in water calculated as PO4, borates dissolved in water calculated as BO3, or silicates dissolved in water calculated as SiO4, in total less than 100 mg / kg, particularly preferably less than 10 mg / kg, and particularly preferably less than 1 mg / kg.

[0022] Also preferred according to the present invention is a method in which the alkaline cleaning agent contains fluorides dissolved in water, calculated as total fluoride content, in total less than 100 mg / kg, particularly preferably less than 10 mg / kg, and particularly preferably less than 1 mg / kg. The total proportion of fluoride (total fluoride content) is measured in an aliquot part of the alkaline cleaning agent buffered with TISAB using a fluoride-sensitive electrode at 20 °C (TISAB: "Total Ion Strength Adjustment Buffer Solution"), and the mixing ratio of the volume of the buffer solution to the volume of the aliquot part of the cleaning agent is 1:1. The TISAB buffer solution is prepared by dissolving 58 g of NaCl, 1 g of sodium citrate, and 50 ml of glacial acetic acid in 500 ml of deionized water (κ < 1 μS cm -1 ), adjusting the pH to 5.3 using 5N NaOH, and filling up to a total volume of 1000 ml with deionized water (κ < 1 μS cm -1 ). <照

[0023] Also preferred is that there is no common corrosion inhibitor for aluminum, and therefore the alkaline cleaning agent contains benzoic acid and benzoates dissolved in water calculated as C7H6O2, or organic compounds dissolved in water having at least one nitrogen-containing heterocyclic compound calculated as N3, in total less than 100 mg / kg, preferably less than 10 mg / kg, and particularly preferably less than 1 mg / kg.

[0024] In the method of the present invention, contact with the alkaline aqueous cleaning agent can be carried out using any of the application methods established in the prior art, including immersion, pouring, spraying, and fine spraying of the aluminum surface, with immersion and spraying being particularly preferred, the latter of which is established in high-volume processes such as can manufacturing. The contact time is preferably in the range of 5 to 180 seconds, and usually, and therefore particularly preferably, less than 60 seconds, and especially preferably 10 to 30 seconds.

[0025] The temperature range in which contact with an alkaline aqueous cleaning agent occurs and cleaning is particularly effective is 30 to 65°C, particularly preferably 40 to 60°C, and especially preferably 45 to 55°C, as the temperature of the cleaning agent at the time of contact.

[0026] The surfaces of metallic aluminum treated by the cleaning method of the present invention are preferably surfaces of semi-finished products and parts made of aluminum material or aluminum plated. Since the aluminum plating and aluminum material forming the surface of metallic aluminum in the sense of the present invention consists of more than 50 at.%, preferably more than 80 at.%, and particularly preferably more than 90 at.%, aluminum alloys can also be cleaned by the method of the present invention. Other alloying components can be selected from, for example, manganese, magnesium, iron, copper, zinc, chromium, zirconium, and / or silicon. Particularly preferred aluminum materials that can be cleaned very reliably by the method of the present invention are the 3xxx alloy series, particularly the 3004 alloy used for the manufacture of beverage cans.

[0027] In principle, all semi-finished products and parts made of the aforementioned materials can be cleaned and degreased by the method of the present invention. Of particular note here are flat products, such as sheets, and semi-finished products formed therefrom, for example by deep drawing, such as cans with one side open. However, as stated at the beginning, since this method is particularly suitable for cleaning and degreasing between the continuous production of multiple semi-finished products and parts at high processing speeds, the present invention focuses on cleaning and degreasing can cylinders for the manufacture of beverage cans or aerosol cans, which corresponds to a preferred application example of the method of the present invention.

[0028] In the method of the present invention, the metallic aluminum surfaces corresponding to the surfaces of multiple can cylinders made of aluminum and its alloys are therefore particularly preferably cleaned and degreased.

[0029] In a second aspect, the present invention relates to a composition particularly suitable for use as an aqueous alkaline cleaning agent in the method of the present invention. This composition of the present invention is an alkaline cleaning agent for aluminum surfaces having a pH greater than 8.0, preferably 11.0 or less, and comprising the following in addition to water: a) Alkali metal carbonate calculated as CO3, in an amount of 0.20 g / kg or more, preferably 3.00 g / kg or less. b) 0.20 g / kg or more, preferably less than 4.00 g / kg, of aluminate 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, preferably selected from α-hydroxycarboxylic acids, particularly preferably selected from α-hydroxycarboxylic acids having 3 or fewer carboxyl groups, and very particularly preferably selected from gluconic acid and / or citric acid.

[0030] Further preferred embodiments of the alkaline cleaning agent can be carried out in the same manner as those described with respect to the alkaline cleaning agent used in the method of the present invention. [Examples]

[0031] To illustrate the cleaning and degreasing performance of the alkaline cleaning agent of the present invention, an Al3004 beverage can with one end open was cleaned by spraying with various formulations. The cleaning agent was applied by spraying at 1.0 bar. After spraying the cleaning agent, deionized water (κ < 1 μS cm) was used. -1 The semi-finished products were briefly immersed in the solution to remove detergent residue, and after removing and blowing away the surface, the gloss was measured. To measure the gloss, the reflectance of the surface of each substrate was measured and compared with the reflectance of the surface of each semi-finished product that had been degreased using a mixture of n-hexane / ethanol (volume ratio 1:1). The corresponding results are shown in Table 1. The application solution of the present invention contains the following components as a 1 wt% solution of the detergent concentrate (B1, see Table 1): Sodium aluminate 0.90 g / kg Na2CO3 0.47g / kg Nonionic surfactant (HLB value 10-12) 0.26 g / kg Sodium gluconate 0.26 g / kg Citric acid 0.30 g / kg

[0032] [Table 1]

Claims

1. A method for cleaning the surface of metallic aluminum, comprising contacting the aluminum surface to be cleaned with an alkaline cleaning agent having a pH greater than 8.0 and containing the following in addition to water: a) At least one alkali builder b) AlO2 totaling 0.20 g / kg or more ２ Aluminate dissolved in water, which is calculated as, and c) At least one surfactant.

2. The method according to claim 1, characterized in that the alkali builder of the cleaning agent is selected from alkali metal hydroxides and / or alkali metal carbonates, preferably from alkali metal carbonates, and particularly preferably from sodium carbonate.

3. The alkaline detergent is present in a total amount of 0.20 g / kg or more, preferably 0.30 g / kg or more, very preferably 0.40 g / kg or more, preferably 3.00 g / kg or less, and particularly preferably 2.00 g / kg or less, CO ３ The method according to claim 2, characterized by comprising an alkali metal carbonate calculated as such.

4. The method according to one or more of the preceding claims, characterized in that the pH of the detergent is greater than 8.5, preferably 11.0 or less, particularly preferably 10.5 or less, and very particularly preferably 10.0 or less.

5. The method according to one or more of the preceding claims, characterized in that the alkaline cleaning agent contains an alkali metal aluminate, preferably sodium aluminate, as a source of the aluminate dissolved in water.

6. The alkaline detergent is present in an amount of 0.40 g / kg or more in total, preferably 0.60 g / kg or more in total, preferably less than 4.00 g / kg in total, particularly preferably less than 3.00 g / kg in total, and particularly preferably less than 2.00 g / kg in total, AlO ２ A method according to one or more of the preceding claims, characterized by containing an aluminate dissolved in water as calculated as.

7. The method according to one or more of the preceding claims, characterized in that the at least one surfactant in the alkaline detergent is selected from nonionic surfactants, preferably from nonionic surfactants with an HLB value of 10.0, particularly preferably from alkylbenzyl alkoxylates having 12 or fewer carbon atoms in an alkyl group, the alkyl group is preferably saturated, and having 6 to 14 alkoxy units, and / or fatty alcohol alkoxylates having 8 to 16 carbon atoms in an alkyl group, the alkyl group is preferably saturated, particularly preferably saturated and unbranched, and having 10 to 30 alkoxy units, wherein the alkoxy units are preferably selected from ethoxy units and / or propoxy units, respectively.

8. The method according to one or more of the preceding claims, wherein the alkaline cleaning agent further comprises an organic complexing agent, the organic complexing agent is preferably selected from α-hydroxycarboxylic acids, and more preferably selected from α-hydroxycarboxylic acids having three or fewer carboxyl groups, and very preferably selected from sugar acids, particularly aldonic acid and aldalic acid, and citric acid and / or tartaric acid.

9. The method according to claim 8, characterized in that the molar ratio of the organic complexing agent to the aluminate in the alkaline cleaning agent is in the range of 1:1 to 1:10, preferably 1:2 to 1:

8.

10. The alkaline cleaning agent is present in a total amount of less than 100 mg / kg, preferably less than 10 mg / kg, and particularly preferably less than 1 mg / kg. ４ A method according to one or more of the preceding claims, characterized by comprising a phosphate dissolved in water as calculated as.

11. The alkaline cleaning agent is present in a total amount of less than 100 mg / kg, preferably less than 10 mg / kg, and particularly preferably less than 1 mg / kg. ３ A method according to one or more of the preceding claims, characterized by containing a borate dissolved in water as calculated as

12. The alkaline cleaning agent is present in a total amount of less than 100 mg / kg, preferably less than 10 mg / kg, and particularly preferably less than 1 mg / kg, C ７ H ６ O ２ A method according to one or more of the preceding claims, characterized by comprising benzoic acid and benzoate dissolved in water as calculated.

13. The alkaline cleaning agent contains, in total, less than 100 mg / kg, preferably less than 10 mg / kg, particularly preferably less than 1 mg / kg of N ３ as calculated, an organic compound dissolved in water having at least one nitrogen-containing heterocyclic compound, characterized by the method according to one or more of the preceding claims.

14. A method according to one or more of the preceding claims for cleaning and degreasing the surface of metallic aluminum corresponding to the surface of a plurality of aluminum can cylinders.

15. An alkaline cleaning agent for aluminum surfaces having a pH greater than 8.0, preferably 11.0 or less, and containing the following in addition to water: a) CO2 0.20 g / kg or more, preferably 3.00 g / kg or less ３ Alkali metal carbonates calculated as, b) AlO2 0.20 g / kg or more, preferably less than 4.00 g / kg ２ Aluminate dissolved in water, preferably sodium aluminate, is calculated as: c) At least one nonionic surfactant with an HLB value exceeding 10.0, and d) At least one organic complexing agent, preferably selected from α-hydroxycarboxylic acids, particularly preferably selected from α-hydroxycarboxylic acids having three or fewer carboxyl groups, and very particularly preferably selected from gluconic acid and / or citric acid.

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