US3773631A - Aqueous electrolytic bath for coloring anodic oxide layers on aluminum and aluminum alloy substrates and process for coloring said substrates - Google Patents

Aqueous electrolytic bath for coloring anodic oxide layers on aluminum and aluminum alloy substrates and process for coloring said substrates Download PDF

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Publication number
US3773631A
US3773631A US00189386A US3773631DA US3773631A US 3773631 A US3773631 A US 3773631A US 00189386 A US00189386 A US 00189386A US 3773631D A US3773631D A US 3773631DA US 3773631 A US3773631 A US 3773631A
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United States
Prior art keywords
coloring
liter
minutes
aluminum
bronze
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Expired - Lifetime
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US00189386A
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English (en)
Inventor
W Immel
L Laser
W Adams
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GP-CHEMIE A CORP OF GERMANY GmbH
BP PLC
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Blasberg & Co KG Friedr GmbH
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Assigned to BRITISH PETROLEUM COMPANY LIMITED reassignment BRITISH PETROLEUM COMPANY LIMITED ASSIGNMENT OF ASSIGNORS INTEREST. Assignors: WEBB, ALAN D.
Assigned to G.P.-CHEMIE GMBH A CORP OF GERMANY reassignment G.P.-CHEMIE GMBH A CORP OF GERMANY ASSIGNMENT OF ASSIGNORS INTEREST. Assignors: FRIEDR. BLASBERG GMBH & CO. KG
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    • 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
    • C25D11/20—Electrolytic after-treatment
    • C25D11/22—Electrolytic after-treatment for colouring layers

Definitions

  • This invention relates to a bath for coloring oxide layers on aluminum substrates and a process for producing light-fast colored oxide layers on aluminum substrates, more particularly to electrolytic baths for producing light fast colored anodic coatings of alumina on aluminum and aluminum alloys, especially with the use of metal salts as coloring component under the action of alternating current.
  • oxide layers produced anodically in acidic baths on metals, especially aluminum can be colored by alternating-current treatment in electrolytic solutions which contain metal salts. Depending upon the metal salt solution used, it is possibleto obtain various colors.
  • the processes are operated in two stages, Inthe first stage, the surface of the aluminum article is anodized in a manner known per se to coat it with an oxide layer. Processes for forming satisfactory uncolored oxide layers by such anodization are generally known in the art and are widely used. After this oxide layer has been formed, the aluminum workpiece is then subjected to the electrolytic coloring process. according to the present invention. This process involves an alternating-current treatment of the workpiece in a metal salt bath which is weakly acidic in most cases thereby coloring the oxide layer formed in the first stage.
  • German Patent 741,753 describes a process in which salts of copper, nickel, lead and-silver are used for coloring alumina surfaces and in which an electrode consisting of the same metal dissolved as salt in the electrolyte is used as counterelectrode of the aluminum article having an oxidized surface.
  • the prior art electrolytic baths offer a number of considerable difficulties and disadvantages-for the process step of coloring the oxide layer.
  • Known disadvantages are, for example, the poor penetration in the coloring process and the scaling-off of the anodic oxide layers after the electrolytic coloring by means of alternating current.
  • the proposed processes do not permit the development of reproducible colors in many cases and "are applicable only to a restricted color scale.
  • the present invention to make the second process step ofithe two-stage process described above, i.e. the coloring of a preformed alumina layer so safe and reliable that the difficulties encountered up to the present are overcome thereby permitting the reliable and reproducible coloring of preformed colorless oxide layers on aluminum and aluminum alloy substrates.
  • this object is achieved by the concom'ittant use of a specific class of materials in the coloring electrolytic bath used in the stage of alternating-current treatment. It has been found surprisingly that the difficulties mentioned above are overcome by using aqueous electrolytes which contain aliphatic aminocarboxylic acids and/or their salts in solution in addition to the coloring metal salts.
  • the invention relates to an aqueous electrolyte bath which contains coloring metal salts to color anodic oxide layers on aluminum and aluminum alloy substrates by alternating-current treatment, the novel baths being characterized in that the electrolytic baths contain aliphatic aminocarboxylic acids and/or salts-thereof in solution in addition to the metal salts.
  • the electrolytic baths according to the invention may contain other known additives in addition to the coloring metal salts and the aliphatic aminocarboxylic acids and/or salts thereof.
  • aliphatic aminocarboxylic acids which contain not more than one amino group per carboxyl group.
  • those aminocarboxylic acids the isoelectric point of'which is not in excess of pH 7 and preferably does not exceed about pH 6.5.
  • Aminocarboxylic acids containing more than one carboxyl group, e.g. two carboxyl groups per amino group are useful for the electrolytic bath and the process of the invention.
  • the aminocarboxylic acids to be used in accordance with the invention preferably are members of the group of what is known as neutral or acidic amino acids asbeing described, for example, by L.F. Fieser and M. Fieser in Lehrbuch der organischen Chemie, 4th German edition (-1960), page 501.
  • aminocarboxylic acids which are readily available in practice are particularly useful for carrying outthe process of this invention in practice.
  • these aminocarboxylic acids are those which'have a limited number'of carbon atoms, e.g. aminocarboxylic acids having :not more than '1 0 carbon atomsQ
  • the aminocarboxylic acids may be present in the electrolytic baths of the invention and'in' the process of the invention with free, i.e. unsubstituted amino groupbut also with a substituted amino group provided that they have sufficient solubilityin the electrolytic solution.'lt may be advantageous to use the aminocarboxylic acids in the form of salts because salts may bemore readily soluble.
  • substituted amino groups include alkyl-substituted amino groups.
  • the alkyl-substituted aminocarboxylic acids may, for example, be monoand/or dialkyl-substituted aminocarboxylic acids having alkyl groups containing up to five carbon atoms. Particularly useful from this group are, for example, aminocarboxylic acids containing methylor ethyl-substituted amino groups.
  • amino acid as used within this specification and within the claims includes the corresponding compounds having a free amino group and a substituted amino group.
  • water-soluble amino acid salts may also be employed or used in addition to the aminocarboxylic acids.
  • suitable salts of aminocarboxylic acids include, for example, the alkali metal and/or ammonium salts. However, it is also possible to use corresponding salts of the aminocarboxylic acids which form coloring cations in aqueous electrolytic solutions. These cations include especially the cations of the coloring metal salts described in the prior art literature.
  • the process may be carried out in the neutral to strongly acidic pH range.
  • use is made of baths having a neutral to slightly acidic pH range of about pH 3 to 7.
  • the more strongly acidic pH range e.g. around or below pH 1
  • coloring metal salts such as tin salts are used which necessitate such more strongly acidic pH values due to their degree of solubility in the electrolyte.
  • the electrodeposition bath solutions of the invention may be acidifed with mineral acids such as hydrochloric acid, sulfuric acid and phosphoric acid if bath solutions having an acidic or, if desired, strongly acid pH range are desired.
  • the concentration of the concentrated mineral acids may, for example, be as high as 100 grams per liter of electrolyte solution.
  • the electrolyte baths used according to the invention for the second step of the coloring process described above contain substantially no further constituents in addition to the coloring metal salt and the amino acid. In particular, it is, therefore, generally unnecessary to use also acids or buffer systems although the additional use of such constituents in the coloring electrolytic baths is not precluded according to the invention.
  • Substantially no upper limit is set to the concentration of the aliphatic aminocarboxylic acid.
  • a natural limit is set to it by the saturation concentration of the particular aminocarboxylic acid used in the metal salt solution.
  • very small amounts of the aminocarboxylic acid give the effect to be achieved in accordance with the invention with respect to improve ment in coloring.
  • the aminocarboxylic acid is supposed to have an action like that of a complexing agent. As the metal is anchored in the alumina layer, the aminocarboxylic acid is liberated and is capable of becoming active again. It is desirable, however, to adapt the content of aminocarboxylic acid to some extent to the metal salt content of the electrolyte bath. If noble metal salts, e.g. gold salts are used as the coloring component, low concentrations of metal salt ranging, for example, between 1 and grams per liter will be used in practice. In this case, very small amounts of the aminocarboxylic acid are sufficient, the lower limit being, for example, 0.l gJliter or preferably at least 0.5 g./liter.
  • metal salt content ranges between 50 and g./liter, it is desirable to use at least 5 grams and preferably at least 10 g./liter of the aminocarboxylic acid together with the metal salt.
  • metal salt concentrations of at least about 2 g./liter.
  • the ranges which are particularly important in practice are those from 2 to 300 g./liter and preferably 2 to g./liter dependent, of course, on the solubility of the particular metal salt.
  • the metal salts used are salts of various metals or metalloids which have been described in the prior art literature.
  • the anions of the salts may be inorganic and/or organic acids. Chlorides are known to be not particularly desirable and tend to pitting in alumina layers so that these salts are not used in general in anodizing technique.
  • the concentration of the aminocarboxylic acids in the electrolytes of the invention is preferably 2 to 200 g. per liter and more preferably 5 100 g. per liter.
  • the other conditions of the coloring electrolysis step correspond to the conventional operating directions of comparable processes.
  • the second, i.e. coloring electrolysis is carried out under the influence of alternating current using current densities which preferably do not exceed 2 A/sq.dm. and more preferably are lower than 1 A/sq.dm.
  • the voltage desirably ranges between about 5 and 30 v.
  • Suitable counterelectrodes include carbon, graphite, a metal which is insoluble in the electrolyte and/or metals which are soluble in the electrolyte and which give the same ions into solution which are used in the particular electrolyte as coloring components.
  • the temperature of the bath preferably ranges from about 10 to 60C, the range from room temperature to about 50C. being particularly preferred. Agitation of the electrolytic bath during the electrolysis may be desirable to ensure a uniform composition of the bath.
  • the time of the electrolytic treatment determines the intensity of color or shade.
  • a treatment for 0.5 to 15 minutes and preferably 1 to 12 minutes is sufficient to adjust the achievable shades from delicate to intense coloring.
  • each metal salt gives a characteristic shade.
  • some of the metal salts, e.g. the iron, cobalt and nickel salts give similar gradations of shades.
  • coloring water-soluble heavy metal salts of organic and/or inorganic acids for the electrolytic baths of the invention, use may be made, for example, of coloring water-soluble heavy metal salts of organic and/or inorganic acids, heavy metals having atomic numbers of 22 to 30, 34, 47 and 48, 50, 52, 79, and 82 being preferred as coloring metal compounds.
  • use may also be made, for example, of metal salt compounds which, in aqueous solutions, form anions which contain the coloring metal such as vanadates, titanates, tellurites, selenites, permanganates, and iron cyanates.
  • the electrolytes of the present invention have excellent penetration or throwing power.
  • the known edge effect i.e. discoloration at points or spots promoting the current, does no longer occur.
  • the deposits are homogeneously colored and no break-through of the preformed oxide layer occurs.
  • An increase in the electrolyte temperature within the range specified above generally results in a further improvement of depth penetration, which can be utilized for particularly heavily structured or profilated surfaces.
  • colors and shades within a wide range are obtainable. For example, it is possible to obtain colors from nickel silver to black with one electrolyte.
  • a particular advantage of the invention is the simple composition of the coloring electrolytic baths. Measures which are necessary in the prior art processes in many cases such as addition of various ingredients (ammonium sulfate, aluminum sulfate, magnesium sulfate or magnesium borate) can be dispensed'with.
  • various ingredients ammonium sulfate, aluminum sulfate, magnesium sulfate or magnesium borate
  • boric acid to the electrolytic bath of the invention.
  • up to about 70 to 80% of the aminocarboxylic acid and/or salts thereof may be replaced by boric acid.
  • Preferably 30 to 65% by weight of the aminocarboxylic acid may be replaced by boric acid.
  • the sole use of boric acid results in a much lesser penetration or throwing power, and the range of shades which can be achieved has no shades which are deeper than dark bronze or dark brown.
  • aluminum sheet is subjected to alternating current coloring by means of the electrolytic bath of the invention.
  • the oxide layer on the aluminum sheets has been formed as follows:
  • Aluminum sheets of the grades A1 99.7 or 99.9 or AlMgSi 0.5 are anodized by means of direct current in a 20% aqueous sulfuric acid solution at room temperature for 30 to 50' minutes.
  • EXAMPLE 1 To color the surface, the aluminum sheet having been superficially anodized in the manner described above is subjected to an alternating current treatment with a counterelectrode of carbon or a metal which is insoluble in the electrolyte and with the use ofa soluble anode which gives the same ions into solution of which the coloring electrolyte consists. In all examples, approximately the same conditions were used. It is desirable, as generally known for anodizing baths, to use voltage and/or current regulators which may be controlled by a timer.
  • the bath contained the following constituents:
  • the bath voltage was 12 v., the current density 0.3 to 0.5 A/sq.dm., and the bath temperature C.
  • the anodized aluminum sheet was treated in this bath for different periods of time.
  • the following range of shades or colors was obtained in dependence upon the time:
  • aminocarboxylic acid has an isoelectric point not in excess of pH 7.
  • coloring metal salts are water soluble coloring heavy metal salts of an organic or inorganic acid.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Electroplating And Plating Baths Therefor (AREA)
US00189386A 1970-10-16 1971-10-14 Aqueous electrolytic bath for coloring anodic oxide layers on aluminum and aluminum alloy substrates and process for coloring said substrates Expired - Lifetime US3773631A (en)

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DE19702050870 DE2050870C (de) 1970-10-16 Wässriges Bad zum elektrolytischen Farben von anodischen Oxidschichten auf Aluminium und Aluminiumlegierungen

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Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3892636A (en) * 1972-06-06 1975-07-01 Riken Light Metal Ind Co Method for producing a colored oxide film on an aluminum or aluminum alloy
US3912602A (en) * 1973-11-09 1975-10-14 Alusuisse Process for colouring aluminum electrolytically
US3935084A (en) * 1974-03-28 1976-01-27 Sumitomo Light Metal Industries, Ltd. Anodizing process
US4042471A (en) * 1975-03-05 1977-08-16 Yoshida Kogyo Kabushiki Kaisha Process for electrolytically coloring aluminum and aluminum alloys
US4070255A (en) * 1975-03-06 1978-01-24 Yoshida Kogyo K.K. Process for electrolytically coloring aluminum and aluminum alloys
US4196060A (en) * 1975-01-22 1980-04-01 Societe De Vente De L'aluminium Pechiney Method of surface treating an aluminum wire for electrical use
GB2156852A (en) * 1984-04-02 1985-10-16 Sprague Electric Co Electrolyte for anodisation of aluminium or for electrolytic capacitors
GB2237817A (en) * 1989-11-08 1991-05-15 Sandoz Ltd Electrolytic colouring of anodized aluminium
US5849169A (en) * 1996-11-18 1998-12-15 Ykk Corporation Method for electrically coloring aluminum material and gray-colored aluminum material obtained thereby
US20090220806A1 (en) * 2005-10-27 2009-09-03 Clariant International Ltd. Method for Improving the Corrosion Resistance and Lightfastness of Painted Aluminum Oxide Layers
EP3553208A1 (de) * 2018-04-09 2019-10-16 DURA Operating, LLC Verfahren zum herstellen eines aluminiumbauteils mit einer farbigen oberfläche

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0289459A1 (de) * 1987-04-30 1988-11-02 Schweizerische Aluminium Ag Verfahren zur elektrolytischen Graufärbung von anodischen Oxidschichten auf Aluminium oder Aluminiumlegierungen

Cited By (14)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3892636A (en) * 1972-06-06 1975-07-01 Riken Light Metal Ind Co Method for producing a colored oxide film on an aluminum or aluminum alloy
US3912602A (en) * 1973-11-09 1975-10-14 Alusuisse Process for colouring aluminum electrolytically
US3935084A (en) * 1974-03-28 1976-01-27 Sumitomo Light Metal Industries, Ltd. Anodizing process
US4196060A (en) * 1975-01-22 1980-04-01 Societe De Vente De L'aluminium Pechiney Method of surface treating an aluminum wire for electrical use
US4042471A (en) * 1975-03-05 1977-08-16 Yoshida Kogyo Kabushiki Kaisha Process for electrolytically coloring aluminum and aluminum alloys
US4070255A (en) * 1975-03-06 1978-01-24 Yoshida Kogyo K.K. Process for electrolytically coloring aluminum and aluminum alloys
GB2156852A (en) * 1984-04-02 1985-10-16 Sprague Electric Co Electrolyte for anodisation of aluminium or for electrolytic capacitors
GB2237817A (en) * 1989-11-08 1991-05-15 Sandoz Ltd Electrolytic colouring of anodized aluminium
GB2237817B (en) * 1989-11-08 1994-03-02 Sandoz Ltd Process for electrolytically treating aluminium and aluminium alloys
US5849169A (en) * 1996-11-18 1998-12-15 Ykk Corporation Method for electrically coloring aluminum material and gray-colored aluminum material obtained thereby
US20090220806A1 (en) * 2005-10-27 2009-09-03 Clariant International Ltd. Method for Improving the Corrosion Resistance and Lightfastness of Painted Aluminum Oxide Layers
US8057858B2 (en) * 2005-10-27 2011-11-15 Clariant Finance (Bvi) Limited Method for improving the corrosion resistance and lightfastness of painted aluminum oxide layers
EP3553208A1 (de) * 2018-04-09 2019-10-16 DURA Operating, LLC Verfahren zum herstellen eines aluminiumbauteils mit einer farbigen oberfläche
CN110359072A (zh) * 2018-04-09 2019-10-22 德韧营运有限责任公司 生产具有着色表面的铝部件的方法

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FR2111674B1 (enrdf_load_stackoverflow) 1974-08-19
FR2111674A1 (enrdf_load_stackoverflow) 1972-06-09

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