Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
  • C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
  • C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
  • C23G1/02—Cleaning or pickling metallic material with solutions or molten salts with acid solutions
  • C23G1/12—Light metals
  • C23G1/125—Light metals aluminium
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
  • C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
  • C23G1/14—Cleaning or pickling metallic material with solutions or molten salts with alkaline solutions
  • C23G1/22—Light metals

Definitions

• the invention relates to a process for cleaning aluminum containers with the aid of alkaline cleaning solutions and subsequent rinsing with an aqueous solution, and to the use thereof as a pretreatment of aluminum containers before the application of conversion coatings.
• Aluminum containers have found widespread use and are used in particular for packaging food and beverages, such as soft drinks and beer. It is common practice in the manufacture of such containers to first punch round disks from aluminum sheet, to bring them into a preliminary cup shape with suitable devices and finally to deform them in one or more stages by pulling and smoothing them into the final can. The cans are then trimmed and subjected to various cleaning and treatment stages. The conclusion is usually the application of an inner varnish and a decorative outer coating.
• various lubricants and cooling lubricants are used which - together with fine metal particles that are formed during the shaping process - remain in certain quantities. It is essential that such lubricant residues and metal particles are removed before the containers are subjected to further treatment.
• the type and thoroughness of the rinsing after the cleaning treatment is also of crucial importance for a possible taste impairment, but also the appearance of the surface.
• the detergent solution adhering to the aluminum container and added to the rinsing stage must be practically completely removed.
• the prior art includes a process for cleaning aluminum containers using alkaline ones Detergent solutions and subsequent water rinsing, in which one works in the rinsing stage with circulating rinsing water, which is kept approximately neutral to acidic by pH control (EP - A2 - 181 673).
• this method has considerable advantages, particularly with regard to the consumption of rinsing water, the desired advantages with regard to the cleanliness of the containers and their mobility in the transport device of the treatment system and on the way from there to the further production stages, such as printing etc., cannot be achieved on a regular basis.
• EP-A-0 157 382 describes a process for cleaning aluminum surfaces with acidic, aqueous cleaning solutions or cleaning solutions suitable therefor, which contain a soluble boron compound and a soluble fluorine compound, the boron content compared to the free fluoride content being greater than the stoichiometric requirement corresponds to the formation of BF4- and which has a pH of ⁇ 3.5.
• the cleaning solution contains at least 10 ppm free fluoride, the stoichiometric excess of boron compared to the free fluoride is at least 4 ppm.
• FR-A-2 147 336 describes a process for removing oxide and dirt layers by bringing the layer to be cleaned into contact with an acidic, aqueous solution which contains between 5 and 21 g ions / l iron ions, 0.5 to 2, Contains 0 g ions / l fluoride ions and 0.05 to 3.0 g / l thiourea, the pH of the solution being between 0.1 and 1.8. After applying the solution, the treated surface is rinsed with water.
• WO 85/01302 describes a method for producing clean surfaces of aluminum and aluminum alloys before gluing or applying paint to these surfaces.
• the surface is first cleaned with alkali, washed with hot water and then etched with an acid (sulfuric acid containing fluoride ions). It is then washed again with water and then coated with a chromate-phosphate layer, after which the surface is washed again.
• an acid sulfuric acid containing fluoride ions
• US-A-3 634 262 describes a composition for the treatment of aluminum and aluminum alloy surfaces which are suitable for subsequent further treatment processes.
• the composition consists essentially of a dry mixture of 5 to 20 wt .-% of a compound selected from alkali metal peroxodiphosphate, alkaline earth metal peroxodiphosphate and ammonium peroxodiphosphate.
• the composition further consists of 77 to 95% by weight of an acidic salt of sulfuric acid and between 0 and 3.0% by weight of a water-soluble fluoride salt.
• the aluminum or aluminum alloy object is soaked in an aqueous solution of the composition for 1 to 10 minutes at a temperature of from 15.5 ° C (60 ° F) to 76.7 ° C (170 ° F) treated.
• the pH of this solution is not more than 3.
• the object of the invention is to provide a method for cleaning aluminum containers, which regularly leads to aluminum containers which have a high level of purity and which, owing to their great mobility, permit high throughputs, in particular also in a printing device which may be connected downstream.
• the object is achieved by designing the method of the type mentioned at the outset in accordance with the invention in such a way that the aluminum containers treated with alkaline cleaning solution are rinsed in at least one stage with a solution whose pH is set at ⁇ 2.5.
• a preferred development of the method according to the invention provides for rinsing with an acidic aqueous solution before treatment with alkaline cleaning solution. This measure already allows a considerable part of the contamination on the aluminum container consisting of fine aluminum particles and organic residues to be removed, so that the subsequent step of the alkaline cleaning is less stressed.
• the method according to the invention can be used with particular advantage if the aluminum containers are cleaned with a cleaning solution which, in addition to alkaline components, contains a complexing agent and at least one surfactant with an HLB number of at least 12 and a pH of at least 10.
• the alkaline reaction can occur in this cleaning solution Part of alkali or alkaline earth borate, carbonate, hydroxide or phosphate and mixtures thereof.
• Alkali hydroxide and carbonate are the preferred ingredients.
• concentration must be sufficient to remove the aluminum particles on the container surface, but on the other hand it must not cause excessive etching of the aluminum surface. The result must be a clean, shiny appearance of the surface.
• the pH value which is limited to 10, can go up to around 13 depending on the nature of the container surface. It is preferably in the range from 11.5 to 12.5.
• the concentration is usually between 0.05 and 10 g / l, preferably between 0.4 and 3.5 g / l.
• the complexing agent must be soluble in the cleaning solution and compatible with the other components. He must also be able to complexly bind the ions in the solution to the extent that the formation of troublesome precipitates is avoided.
• Sugar acids such as gluconic acid or glucoheptanoic acid, citric acid, ethylenediaminetetraacetic acid, tartaric acid or salts of these acids and sodium tripolyphosphate are particularly suitable as complexing agents.
• the concentration of the complexing agents is usually in the range from 0.01 to 5 g / l, preferably in the range from 0.05 to 1 g / l.
• the HLB number of the surfactant is a measure of the size and strength of the hydrophilic surfactant component in relation to the lipophilic surfactant component (cf. Römpps Chemie-Lexikon, Franckh'sche Verlagsbuch Kunststoff, Stuttgart, 8th edition, page 1715).
• All of the aforementioned surfactants can be used individually or in combination. Their concentration should usually be 0.003 to 5 g / l, preferably 0.02 to 1.0 g / l.
• This cleaning solution is applied as usual by e.g. Flooding, dipping or spraying at temperatures of about 15 to 65 ° C, preferably 32 to 54 ° C, for a period of time that ensures the purity of the aluminum surface.
• Another advantageous embodiment of the invention provides for rinsing the aluminum containers treated with alkaline cleaning solution in several stages.
• the second stage should then be operated with an aqueous solution adjusted to a pH ⁇ 2.5.
• a water rinse which can be multi-stage and equipped with countercurrent flow of the rinse water.
• the final rinse is carried out regularly with deionized water.
• the conditions with which the water rinse is carried out should correspond to those of the acid rinse with regard to the type and temperature of treatment. Flushing in the syringe is particularly advantageous.
• Common organic or inorganic acids are suitable for adjusting the pH of the acidic rinsing solution. It is particularly expedient to use sulfuric acid and / or hydrofluoric acid.
• the presence of fluoride ions in sufficient quantities has the advantage that the mobility of the aluminum containers is further increased and the suppression or removal of any discoloration is promoted.
• a further advantageous embodiment of the invention consists in rinsing with an aqueous acidic solution which contains fluoride ions.
• the fluoride levels can be up to 1000 ppm. Under special circumstances, if the concentrations are too high, caustic phenomena can occur, so that 200 ppm should not be exceeded. It is particularly expedient to keep the fluoride concentration below 100 ppm. In general, 40 ppm or less is sufficient.
• the aforementioned fluoride contents or concentrations refer to free fluoride.
• the fluoride can also be introduced via soluble simple or complex Fluoride compounds are made.
• the required pH value may then be adjusted with other acids, for example with sulfuric acid.
• the aluminum containers are dried after the rinsing treatment, usually also painted, printed or otherwise provided with decorative coatings.
• Conversion coatings greatly improve the mobility of the containers (rotation, sliding against each other) as they pass through the treatment plant and through the subsequent production stages and also increase the corrosion resistance.
• Conversion coatings of this type can be produced, for example, from solutions based on chromium phosphate or titanium, zirconium and hafnium fluoride with or without additional tannin content. Examples of processes for forming such conversion coatings are given in US Pat. Nos. 4,017,334, 4,054,466 and 4,338,140.
• the aforementioned drying, painting, etc. usually follows, depending on the type of process, after a previous rinsing treatment.
• the printing device could be operated with full performance and a perfect result.
• the pH of the aqueous washing-up liquid was increased from 2.5 to 5 in the third stage, the mobility of the aluminum cans was reduced, so that the performance of the printing device had to be reduced to 710 cans per minute if its perfect operation was ensured should.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)
• Detergent Compositions (AREA)
• Application Of Or Painting With Fluid Materials (AREA)

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Applications Claiming Priority (2)

Publications (3)

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ID=25231936

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• 1987
  • 1987-01-09 JP JP62003087A patent/JP2719612B2/ja not_active Expired - Lifetime
  • 1987-01-14 EP EP87100373A patent/EP0230903B1/de not_active Expired - Lifetime
  • 1987-01-14 DE DE8787100373T patent/DE3778715D1/de not_active Expired - Fee Related
  • 1987-01-14 AT AT87100373T patent/ATE75783T1/de active
  • 1987-01-14 DE DE19873700842 patent/DE3700842A1/de not_active Withdrawn

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