Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
  • C25D11/02—Anodisation
  • C25D11/04—Anodisation of aluminium or alloys based thereon
  • C25D11/18—After-treatment, e.g. pore-sealing
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
  • C25D11/02—Anodisation
  • C25D11/04—Anodisation of aluminium or alloys based thereon
  • C25D11/18—After-treatment, e.g. pore-sealing
  • C25D11/24—Chemical after-treatment
  • C25D11/246—Chemical after-treatment for sealing layers

Definitions

• the invention relates to an improved method for compacting decorative anodized oxide layers on aluminum and aluminum alloys in aqueous solutions at elevated temperatures.
• the addition of certain phosphonic acids prevents the formation of disruptive aluminum hydroxide coatings (sealing coatings) on the surfaces.
• anodically produced oxide layers are applied for the purpose of corrosion protection, which protect them from the effects of weather and other corrosive media. Furthermore, the anodized oxide layers are also applied in order to obtain a harder surface and thus to achieve increased wear resistance of the aluminum. Due to the intrinsic color of the oxide layers and their easy coloring, particularly decorative effects can be achieved.
• the oxide layer is generated with direct current in solutions of sulfuric acid.
• solutions of organic acids such as, for example, are also common Sulfophthalic acid or sulfanilic acid or mixtures thereof with sulfuric acid are used.
• anodized oxide layers applied in this way do not meet all the requirements with regard to corrosion protection, since they have a very porous structure. For this reason, it is necessary to compact the oxide layers. This compression is often carried out with hot or boiling water and referred to as "sealing". This closes the pores and increases the protection against corrosion.
• the surface pores in particular are closed, the oxide layer being restructured at the same time.
• a more or less velvety, disruptive coating of hydrated aluminum oxide the so-called sealing coating, also forms on the entire surface. This is not touch-resistant, which greatly affects the decorative effect of the layer.
• the sealing coating reduces the adhesive strength of the bonding of such aluminum parts and, due to the enlarged effective surface, promotes later contamination and corrosion.
• DE-OS 22 11 553 describes a method for treating the surfaces of aluminum or aluminum alloys by anodic generation of oxide layers with subsequent densification in aqueous solutions at elevated temperatures.
• the addition of certain phosphonic acids in conjunction with further additions of calcium ions largely prevents the formation of disruptive aluminum hydroxide deposits on the surfaces and avoids difficulties caused by hardness salts of the water.
• the compression is carried out at temperatures between 90 ° C and the boiling temperature and a pH of 5.5 to 6.5.
• Such phosphonic acids or their water-soluble salts which form complexes with divalent metals come into consideration for this process for example, 1-hydroxyethane-1,1-diphosphonic acid, 1-hydroxyhexane-1,1-diphosphonic acid, 1-hydroxypropane-1,1-diphosphonic acid, 1-aminoethane-1,1-diphosphonic acid, dimethylaminomethane-1,1-diphosphonic acid, ethylenediaminetetramethylenephosphonic acid , Aminotrimethylenephosphonic acid, 2-phosphonobutane-1,2,4-tricarboxylic acid or 1-phosphono-1-methylsuccinic acid.
• an optimal surface finish that meets decorative requirements cannot always be achieved on dark colored surfaces.
• EP-0S 122 129 describes a process for compacting anodized aluminum surfaces with aqueous solutions with a pH of at least 7 in the presence of sealing deposit inhibitors.
• Possible sealing coating inhibitors are: dextrins, acrylic acid, methacrylic acid, water-soluble polymers of acrylic or methacrylic acid lignin sulfonates, cycloaliphatic or aromatic polycarboxylic acids and cyclohexane-hexacarboxylic acid, water-soluble phosphonic acids complexing with divalent metals, reaction products with a sulfonated aromatic compound and sulfonated aromatic compounds or dimethylol urea or a mixture of formaldehyde and urea.
• phosphonic acids preferably ethylenediaminetetra (methylenephosphonic acid), hexamethylenediamine-tetra (methylenephosphonic acid), n-propyliminobis (methylenephosphonic acid), benzene hexacarboxylic acid and salts thereof and the reaction products of sulfonated aromatic compounds with an aldehyde and / or dimethylol urea a mixture of formaldehyde and urea.
• no information is given about the anodizing conditions.
• the classification of the surface layers in "Heavy Bloom” or "No Bloom” mentioned here is not suitable for adequately reproducing the finish assessment by a panel of experienced experts in the decoratively important architecture sector.
• the object of the present invention is to provide an improved method for compacting decorative anodized oxide layers on surfaces of aluminum and aluminum alloys.
• the above object is achieved with a method for compacting decorative anodized oxide layers on surfaces of aluminum and aluminum alloys in aqueous solutions containing phosphonic acids or their alkali metal salts and / or alkanolamine salts with a pH in the range from 5.5 to 8. 5 at temperatures between 80 ° C and the boiling point, characterized in that one selects the phosphonic acids from 1-phosphonopropane-1.2.3-tricarboxylic acid and / or 1.1-diphosphonopropane-2.3.-dicarboxylic acid.
• water-soluble salts such as, in particular sodium, potassium, ammonium or alkanolamine salts, can also be used.
• Normal water that is neither fully desalinated nor softened can be used to prepare the solutions. If demineralized or distilled or very soft water is used to prepare the solutions, it is not necessary, in contrast to the prior art known to date, to add calcium ions.
• the process for compacting anodically produced oxide layers on aluminum and aluminum alloys in aqueous solutions containing phosphonic acids or their salt can be carried out at a pH of 5.5 to 8.5 at a temperature between 80 ° C. and the boiling point.
• acids and / or alkalis can be used to adjust the pH of the solutions, which the person skilled in the art usually uses in such processes.
• preferred are: acetic acid, sulfuric acid, ammonia, potassium hydroxide and triethanolamine.
• Technical triethanolamine which usually contains small amounts of diethanolamine and monoethanolamine, can also be used.
• the addition of strong acids is usually unnecessary, since the previous anodizing process usually leads to the introduction of sulfuric acid or acid sulfates into the compression bath.
• the desired pH is usually stabilized by adding a buffer system, which is known to consist of the salt of a weak base and a strong acid, or a strong base and a weak acid, to the solutions.
• solutions which have a pH in the range from 5.5 to 6.5.
• the solutions acetic acid and ammonia and / or acetic acid and potassium hydroxide are added.
• the buffer salts ammonium acetate and / or potassium acetate which are formed can also be added to the solutions as such.
• solutions are used which have a pH in the range from above 6.5 to 8.5, particularly preferably in the range from 7.0 to 7.5.
• solutions acetic acid and potassium hydroxide and / or acetic acid and triethanolamine are added.
• the buffer salts potassium acetate and / or triethanolammonium acetate which are formed are additionally added to the solutions as such.
• solutions used according to the invention must contain the PPT and / or DPD in a certain minimum amount. A certain maximum amount of phosphonic acid must also be observed, otherwise the surface quality will deteriorate.
• the method for compacting anodically produced oxide layers on aluminum and aluminum alloys is characterized in that the solutions contain 0.003 to 0.1 g / l PPT and / or DPD.
• the method is carried out with solutions which contain 0.005 to 0.025 g / l PPT and / or DPD.
• At least about 1 ppm of aluminum ions in the form of a water-soluble aluminum compound are added to the solutions at the start of the compression process.
• Suitable water-soluble aluminum compounds are in particular those aluminum salts whose anions can be present in the compression solutions anyway, for example aluminum sulfate or aluminum acetate.
• the amount of aluminum ions added is preferably 1 to 20 ppm, in particular 1 ppm. Such an addition significantly reduces the formation of iridescent phenomena on the surfaces.
• the method according to the invention results in a significant improvement in the appearance of the treated surfaces, no traces of drainage remain visible.
• the name of the aluminum alloy is given according to DIN 1725; a profile AlMgSi 0.5 was used.
• the profiles were degreased in an aqueous solution consisting of 5% P3-Almeco R 18 (alkaline cleaner containing borates, carbonates, phosphates and nonionic surfactants) at a temperature of 70 ° C. It was then pickled in a long-term pickle using 112 g / l of dissolved aluminum and 80 g / l of NaOH using P3-Almeco R 46 (pickling agent containing alkali, alcohols and salts of inorganic acids). P3-Almeco R 46 was dosed in a ratio of 1: 6 to NaOH. Pickling was carried out at 65 ° C. for about 15 minutes.
• the subsequent anodization was carried out using the direct current sulfuric acid method; Bath composition: 200 g / l sulfuric acid, 10 g / l aluminum; Air injection 8 m3 / m. H; Temperature 20 ° C; DC voltage 15 V.
• the anosidization time was about 3 min / ⁇ m layer build-up; ie the total anodizing times for the oxide layers of approximately 20 ⁇ m given in the examples below were approximately 45 to 55 minutes.
• the profiles that were to be subjected to a visual inspection of the surface finish were still colored black. This was done in an electrolyte containing 18 g / l tin (II) sulfate, 25 g / l P3-Almecolor R S (iron (II) salts and organic sulfonic acids) and 20 g / l sulfuric acid with an alternating current of 16 V at 20 ° C in 10 min.
• the profiles for the comparative examples were pretreated in an analogous manner and also compacted as described below.
• the sealing layer preventers were used in concentrations of 2 g / l and compacted at temperatures of about 96 to 98 ° C.
• the quality of the surface layer was determined by the so-called paint drop test with previous acid treatment in accordance with ISO standard 2143.
• a removal test according to ISO 3210 was carried out.
• the Y value was carried out in accordance with ISO standard 3913 using an anotest device Y-D from Fischer. The percentages below represent percentages by weight.
• Examples 1 to 4 according to the invention were repeated, with sufficient aqueous aluminum sulfate solution being added to the solutions at the start of the compression process to give a concentration of 1 ppm of aluminum ions. In this way, iridescence of the surfaces treated in this way was effectively prevented.
• the table shows that the compaction formulations according to the invention had an extremely good surface quality. It is also important that improved surface quality could be achieved with a shorter compaction time. This results in a large energy saving, since the compression was carried out in practically boiling aqueous solutions.

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• Chemical & Material Sciences (AREA)
• Metallurgy (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Organic Chemistry (AREA)
• Engineering & Computer Science (AREA)
• General Chemical & Material Sciences (AREA)
• Chemical Treatment Of Metals (AREA)
• Liquid Crystal (AREA)
• Catalysts (AREA)
• Laminated Bodies (AREA)
• Detergent Compositions (AREA)
• Sealing Material Composition (AREA)
• Preventing Corrosion Or Incrustation Of Metals (AREA)

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• 1988
  • 1988-06-18 DE DE3820650A patent/DE3820650A1/de not_active Withdrawn
• 1989
  • 1989-06-06 TR TR47889A patent/TR23838A/xx unknown
  • 1989-06-09 ES ES89110451T patent/ES2058394T3/es not_active Expired - Lifetime
  • 1989-06-09 AT AT89110451T patent/ATE93281T1/de not_active IP Right Cessation
  • 1989-06-09 EP EP89110451A patent/EP0347663B1/fr not_active Expired - Lifetime
  • 1989-06-09 DE DE8989110451T patent/DE58905303D1/de not_active Expired - Fee Related
  • 1989-06-14 US US07/365,869 patent/US4939001A/en not_active Expired - Fee Related
  • 1989-06-15 NZ NZ229570A patent/NZ229570A/xx unknown
  • 1989-06-16 AU AU36478/89A patent/AU609313B2/en not_active Ceased
  • 1989-06-16 CA CA000603114A patent/CA1338442C/fr not_active Expired - Fee Related
  • 1989-06-16 NO NO892509A patent/NO176928C/no unknown
  • 1989-06-16 ZA ZA894616A patent/ZA894616B/xx unknown
  • 1989-06-17 KR KR1019890008388A patent/KR900000509A/ko not_active Application Discontinuation
  • 1989-06-19 JP JP1158118A patent/JPH0243397A/ja active Pending

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