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
  • C25D11/24—Chemical after-treatment
  • C25D11/246—Chemical after-treatment for sealing layers

Definitions

• a number of processes are known for the application of anodic oxide layers to aluminum.
• the production of the oxide layers takes place using direct current in solutions of sulfuric acid (the direct currentsulfuric acid process).
• solutions of organic acids such as in particular sulfophthalic acid or sulfanilic acid or mixtures of these organic acids with sulfuric acid, are also frequently used.
• the last named processes are particularly known as the autocolor processes.
• This velvety film is the so-called sealing coating and consists of amorphous aluminum hydroxide which is not resistant to handling, so that the decorative effect of the layer is thereby impaired. Furthermore, it reduces the adhesive strength during the bonding of such aluminum parts and, due to the increased effective surface, this sealing film promotes later soiling and corrosion. For these reasons it has previously been necessary to remove the coating by hand, mechanically or chemically.
• the invention relates to a process for the treatment of surfaces of aluminum or aluminum alloys by anodic oxidation with a subsequent sealing step in aqueous solutions at elevated temperatures. In this manner, the formation of troublesome aluminum hydroxide coat ings (sealing films) on the surfaces are prevented and difficulties caused by the salts producing hardness in the water are avoided by the addition of certain phosphonic acids.
• the present invention is further directed to a development in the process for treating the surface of aluminum or an aluminum alloy which comprises subjecting said surface to an anodic oxidation and subsequently sealing with hot water or steam, the improvement which consists essentially of sealing said surface by applying an aqueous solution containing calcium ions and from 0.001 to 0.05 gm per liter of at least one acid selected from the group consisting of (A) a water-soluble phosphonic acid which forms a complex with a divalent metal, (B) a water soluble salt of said acid of (A), and (C) the mixtures thereof at a temperature ranging from 90C to the solution boiling point temperature and at a pH of from 5 to 6.5, to the anodic oxidized surface, the molar ratio of calcium ions to phosphonic acid being at least 2:1.
• A a water-soluble phosphonic acid which forms a complex with a divalent metal
• B a water soluble salt of said acid of (A)
• C the mixtures thereof at a temperature ranging from
• R represents phenyl or alkyl of l to 5 carbon atoms
• R and R each represent hydrogen or alkyl of 1 to 4 carbon atoms, R represents hydrogen, alkyl of l to 4 carbon atoms, or phenyl;
• R represents -I O I'I or a group of the formula:
• Examples of l-hydroxyalkane-l l -diphosphonic acids of formula I which may be used are lhydroxypropanel l -diphosphonic acid, 1- hydroxybutane-l 1 -diphosphonic acid, 1- hydroxypentane-l 1 -diphosphonic acid, 1-
• aminopolymethylene phosphonic acids of the formula III include aminotrimethylenephosphonic acid, ethylenediaminotetramethylenephosphonic acid, diethylenetriaminopentamethylenephosphonic acid, aminotri(2-propylene-2 phosphonic acid).
• Suitable examples of phosphono succinic acids of formula IV include phosphonosuccinic acid, l-phosphonol -methylsuccinic acid and 2- phosphonobutanel ,2,4-tricarboxylic acid.
• the solutions containing phosphonic acids or their salts are adjusted, where necessary, to a pH in the range of from 5 to 6.5. This adjustment may be effected with ammonia or acetic acid.
• Ordinary water which is neither completely deionized or softened may be used for the solutions. If completely deionized water, distilled water, or very soft water is used for making the solutions, it is necessary to add calcium ions, and, preferably, water-soluble calcium salts such as CaCl or Ca(NO are used.
• the molar ratio of calcium ions to phosphonic acids should be at least 2:1. Generally it is advantageous to use a higher molar ratio of calcium ions to phosphonic acids of 5:1 to about 500:1.
• a preferred form of the process comprises adding from 0.1 to 5 gm/liter, preferably from 0.1 to 2 gm/liter, of a dextrin additionally to the sealing solutions.
• a dextrin for this purpose, those dextrins are specially used which have a viscosity of 50 to 400 cP in 50% solution at 20C, the viscosity being measured with a Brookfield rotary viscosimeter.
• the notation of the aluminum alloys is based upon nomenclature according to DIN 1,725.
• the quality of the oxide layers was determined by the so-called Testal value according to DIN 50,949 and by the loss factor d (Anotest apparatus) according to DIN 50,920 (design). Further, the products of the aftersealing were tested by means of the Green test according to DIN 50,146.
• DIN is the abbreviation for Manual Industrie-Norm representing a series of standard German published test procedures.
• EXAMPLE 1 Aluminum sections (AlMg degreased with an aqueous alkali metal hydroxide solution and pickled in the usual manner, were anodically oxidized in direct current-sulfuric acid process (layer thickness 22p.) and were sealed at 100C for minutes with a solution of 0.003 gm/liter of l-hydroxyethane-l,l-diphosphonic acid and 0.5 gm/liter of dextrin (viscosity I00 cP, measured in 50% solution at 20C) in water of l5dH (Gerammonia prior to the sealing. The sections showed no sealing film.
• EXAMPLE 2 Aluminum sheets (AlSi degreased in the usual manner, which had been anodically oxidized in the di rect current-sulfuric acid-oxalic acid process (layer thickness 2111.), were sealed at 100C for 60 minutes with a solution of 0.007 gm/liter of l-hydroxyethanel, l -diphosphonic acid in deionized water with the addition of mgm/liter of calcium ions, which was adjusted with ammonia to pH 5.6 prior to the sealing. The sheets showed no sealing film. The Testal value of 12 and the loss factor d of 0.49 both indicated a satisfactory sealing. The same results were obtained with di-, triand tetra-alkali metal salts or ammonium salts.
• EXAMPLE 3 Aluminum sections (AlMgSi 0.5) degreased and pickled in the usual manner, which had been anodically oxidized by an autocolor process (layer thickness 18p), were sealed at 100C for 60 minutes in a solution of 0.005 gm/liter of l-hydroxyethane-l,l-diphosphonic acid, 0.005 gm/liter of aminotrimethylenephosphonic acid and l gm/liter of dextrin (viscosity 200 cP, measured in 50% solution at 20C) in water of 35 dH (German hardness), adjusted with ammonia to pH 5.9 prior to sealing. The sections showed no sealing film. A satisfactory sealing was indicated by the Testal value of 10.5 and by the loss factor d of 0.47. The degree of water hardness was not noticeably objectionable, since the water hardness causing components were precipitated in a flocculent, easily removable, settling form.
• EXAMPLE 4 Aluminum sections (AlMgSi 0.5) which had been degreased with an aqueous alkali metal solution and pickled in the usual manner, were anodically oxidized in the direct current sulfuric acid process (layer thickness 20; ⁇ . to 22,u.). The sections were then sealed at 98C to 100C for 60 minutes in a solution which contained 0.01 gm/liter of l-hydroxyethane-l, l-diphosphonic acid and 2 gm/liter of dextrin (viscosity 150 cP, measured in 50% solution at 20C), in water of 20 dH (German hardness) which was adjusted with ammonia to a pH of 5.8 prior to the sealing. The sections showed no sealing film; and the Testal value of 9.0 and the loss factor d of 0.40 indicated a very satisfactory sealing. No difficulty resulted from the water hardness causing components of the sealing solution.

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• 1972
  • 1972-03-10 DE DE2211553A patent/DE2211553C3/de not_active Expired
• 1973
  • 1973-02-20 SE SE7302384A patent/SE383764B/xx unknown
  • 1973-02-20 DK DK089173A patent/DK150715C/da not_active IP Right Cessation
  • 1973-02-20 NO NO693/73A patent/NO131208C/no unknown
  • 1973-02-23 US US335065A patent/US3900370A/en not_active Expired - Lifetime
  • 1973-03-08 FR FR7308272A patent/FR2175808B1/fr not_active Expired
  • 1973-03-08 NL NLAANVRAGE7303294,A patent/NL171914C/xx not_active IP Right Cessation
  • 1973-03-09 CA CA165,719A patent/CA1005788A/en not_active Expired
  • 1973-03-09 CH CH352373A patent/CH578053A5/xx not_active IP Right Cessation
  • 1973-03-09 IT IT21387/73A patent/IT982499B/it active
  • 1973-03-09 GB GB1146573A patent/GB1419597A/en not_active Expired
  • 1973-03-09 BE BE128589A patent/BE796534A/xx not_active IP Right Cessation
  • 1973-03-09 ES ES412477A patent/ES412477A1/es not_active Expired
  • 1973-03-09 BR BR731707A patent/BR7301707D0/pt unknown
  • 1973-03-09 AT AT210573A patent/AT317627B/de not_active IP Right Cessation
  • 1973-03-09 ZA ZA731678A patent/ZA731678B/xx unknown
  • 1973-03-10 JP JP2846673A patent/JPS565835B2/ja not_active Expired

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