US3616309A - Method of producing colored coatings on aluminum - Google Patents

Method of producing colored coatings on aluminum Download PDF

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Publication number
US3616309A
US3616309A US773935A US3616309DA US3616309A US 3616309 A US3616309 A US 3616309A US 773935 A US773935 A US 773935A US 3616309D A US3616309D A US 3616309DA US 3616309 A US3616309 A US 3616309A
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Prior art keywords
bath
ions
magnesium
alternating current
metal ions
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US773935A
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Tehei Asada
William Ernest Cooke
Paul John Sajben
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Alcan Research and Development Ltd
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Alcan Research and Development Ltd
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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

  • the present invention relates to a process for producing colored coatings on aluminum, and more particularly relates to the production of inorganic-colored coatings on aluminum articles.
  • References to aluminum herein will be understood to include aluminum of ordinary commercial purity and aluminum-base alloys that are suitable for conventional anodizing treatments.
  • the term aluminum article as used herein is intended to include semifabricated products, such as rolled aluminum sheet and aluminum extruded sections.
  • the present invention relates to improvements in a previously described two-stage process for producing a colored coating which comprises anodically oxidizing an aluminum article and thereafter treating the anodized article by passing an alternating current between such aluminum article and a counterelectrode, while such aluminum article and electrode are immersed in a bath that contains a dissolved compound of a selected metal in an aqueous acidic medium. Under these circumstances the anodic oxide coating on the aluminum article becomes colored. More particularly, the invention is concerned with such process wherein the acidic bath of the alternating current treatment contains metal ions selected from the group consisting of the following cations and anions: Ni, Co, Cu, Ag, Pb, and anions consisting of oxygen combined with one ofthe metals Se, Te and Mn. Procedures of this sort are included in the description of U.S. Pat. No. 3,3 82,l60, granted May 7, I968 to Tahei Asada.
  • the counterelectrode in the alternating current step may be a material, such as graphite (i.e. carbon), which is inert to the electrolyte, or may be formed of other conductive composition, e.g.
  • metal which may advantageously be selected among metals having a solution potential more noble than aluminum in the conventional series of electrode potentials, and which can preferably be the same metal, if available, as constituted by the selected ions in solution in the electrolyte, all as explained in the previous disclosure.
  • a nickel counterelectrode may be very effectively employed.
  • a chief object of the present invention is to reduce the incidence of spalling.
  • a further and more specific object is to improve the operation of the above process utilizing metal ions selected from the stated group, notably the second or alternating current treatment stage of such process, so that a full range of tones or shades may be obtained by employing a given bath, including the darker tones that are achieved with higher voltages or longer times or both, while in all cases there is desirable avoidance of deterioration of the colored coating as by spalling or the like.
  • the complete procedure includes first anodizing the aluminum surface to produce the anodic coating thereon, and then subjecting the coated surface to alternating current in an aqueous bath containing the selected metal ions, such bath also containing magnesium ions, as for example in amount represented by at least about one gram per liter of magnesium sulfate (calculated as MgSO,.7I-I,O), or more generally stated at least about p.p.m. Mg ions.
  • a typical bath may constitute the salt of the metal selected for coloring function, appropriate acidic and related constituents, and a magnesium compound which in dissolved form is in effect a magnesium salt, advantageously containing an anion otherwise present in the electrolyte.
  • a special advantage of the present invention is that a given electrolyte can be employed to provide a wide range of shades or tones, notably up to the darkest values, without difficulty, so that the process has improved flexibility in practice, to accommodate a wide variety of color requirements.
  • a given electrolyte can be employed to provide a wide range of shades or tones, notably up to the darkest values, without difficulty, so that the process has improved flexibility in practice, to accommodate a wide variety of color requirements.
  • the complete process of producing a colored coating on an aluminum surface of an article involves first anodizing the surface in conventional manner to produce an anodic oxide coating, e.g. of a type customarily applied for protective or like purposes.
  • any of a number of known operations may be employed, notably with electrolytes of a group which may be defined as consisting of aqueous solutions of sulfuric acid, chromic acid, or a sulfonic acid such as sulfosalicylic acid, and suitable mixtures of these with other acids or compounds, and while in some cases AC anodizing treatment may be feasible, effective results are obtained by anodizing the work with direct current, as for periods of 20 minutes to 60 minutes, in an aqueous solution of sulfuric acid, e.g. 15 percent acid by weight.
  • the operating conditions of the anodizing step do not appear to be very critical, being selected largely to suit the thickness and other characteristics of anodic coating desired; the requirements of the subsequent coloring step are satisfied over a considerable range of thicknesses of porous oxide coating on aluminum.
  • the second step of the process then involves submerging the anodized aluminum article, if desired after suitable rinsing, in an acidic bath in which a counterelectrode is likewise submerged, such bath comprising an aqueous acidic solution containing the metal selected for coloring function, specifically metal ions selected from the group consisting of the following cations and anions: Ni, Co, Cu, Ag Pb, and anions consisting of oxygen combined with one of the metals Se, Te and Mn.
  • alternating current is passed through the solution between the article and the counterelectrode, for sufficient time to effect the desired colored deposit in the oxide coating, e.g. a deposit understood to consist of metal, of the selected ions, which is in chemical combination with oxygen, such as oxide or hydroxide, conveniently herein considered to be oxide.
  • a content of magnesium ions is maintained in accordance with the present invention, preferably by adding a quantity of suitable magnesium salt (or other compound which becomes dissolved) in substantial excess so as to accommodate a slow but continuing depletion of such ions as the bath is repeatedly used, i.e. to avoid need for frequent replenishment of the Mg. content.
  • the bath should be a water solution containing the metal ions selected for coloring function, and an acidic constituent, the dissolved compounds being all in relatively low concentration.
  • the bath constituents including nonmetallic anionic constituents, may be variously selected to provide the desired solubility of metal ions and suitable acidity of the electrolyte, and supplemental or further salts and the like may be incorporated, as desired for supplemental purposes that do not interfere with the formation of the colored deposit, or as may result from initial or subsequent pH adjustment.
  • sulfate, borate, acetate, tartrate, phosphate, sulfamate and other common ions have been found appropriate for solutions of one metal or another, e.g.
  • salts of the selected metal or as forming the chosen acidic component will depend on solubility and like requirements of the metal ions, as for example in the case of lead ions, substances such as sulfamic acid and acetic acid and their salts should be utilized instead of sulfate.
  • the metal ions are of anionic nature, compounds appropriately soluble in the acidic bath should be employed, such as alkali metal selenites, selenium oxide, selenic acid, alkali metal tellurites, permanganates, and the like.
  • magnesium is preferably added to the electrolyte in the form of a salt, the anion of which is already present in the bath or is otherwise compatible as will be understood or may be readily determined.
  • a presently preferred nickel electrolyte contains nickel sulfate and boric acid, to which the magnesium may be added as magnesium sulfate or borate.
  • the magnesium can actually be supplied as a soluble form of magnesium oxide or magnesium hydroxide, then becoming a corresponding dissolved salt in the presence of acidic constitucnts. Necessary adjustments of acidity for this and other purposes are made by suitable additions such as sulfuric acid, boric acid, ammonium hydroxide and the like. While some anions, such as halides (except perhaps chlorides in small concentration) are not presently recommended, the essential requirement is to have dissolved magnesium ions present and selection ofa suitable and commonly available salt presents no problem in the light of the foregoing.
  • the amount of magnesium present should be sufficie nt to provide significant inhibition of spalling, l.e. to avoid or materially reduce the occurrence or tendency toward occurrence of minute spots or flaked-off areas, or like spots or defects in the colored product, e.g. in the darker or very dark tones, obtainable with the selected metal.
  • spalling is often represented by colorless or pale spots, it may sometimes occur otherwise, as for instance where flaking near the outset of the alternating current treatment leads to a more intense tone due to preferential flow of current to the spalled area.
  • some utility has been noted for lesser amounts, in general at least about p.p.m.
  • magnesium (measured as such, by weight) should be present for good results, and indeed preferably at least somewhat more, such as represented by about 2 grams per liter of conventional magnesium sulfate (200 p.p.m. Mg. Most preferably the magnesium compound is added in amount to provide from approximately 1,000 to 2,500 p.p.m. of Mg. as for example about 10 to 25 grams per liter of MgSO -7H O, especially to avoid unduly rapid depletion. Even considerably greater amounts, as up to 40 grams per liter of the magnesium salt (4,000 p.p.m. Mg), have shown no adverse effect, so that the upper limit appears primarily economic.
  • magnesium oxide or hydroxide is coprecipitated with the colored oxide or hydroxide of the metal of which ions are present from the above-defined group, to provide a more electrically resistant deposit
  • a present theory being that the relatively larger flow of current during that part of the AC cycle when the anodized article is the cathode results in depletion of hydrogen ions at the base of the pores, causing localized rise in pH (greater alkalinity) and consequently the desired precipitation of the metal oxide or hydroxide, and in the present process, of magnesium oxide or hydroxide as well.
  • the beneficial effects of this invention have been abundantly demonstrated and it is not to be understood as dependent on the above or any other theories.
  • aluminum articles were first anodized by conventional anodic treatment with direct current, e.g. for periods upwards of 20 minutes in the l5 percent aqueous sulfuric acid solution at an ordinary temperature, for example selected in the range of 20 C. to 25 C., conveniently 21 C. it will be understood that other strengths of acid solution, or indeed solutions of other acids as mentioned above, and likewise other modifications of condition as to suit the protective or like requirements of the coating may be employed.
  • the anodized article is then suitably rinsed and submerged in the selected acidic bath which contains the appropriate counterelectrode.
  • the alternating current is passed, between the article and the electrode, at a conveniently moderate voltage, say from 5 to 20 volts, for a correspondingly appropriate time, e.g. from a few minutes up to l0 to 15 minutes, sometimes with increasing voltage or other suitable electrical control.
  • the shade of color achieved depends on the time of treatment and on electrical conditions; for instance, lighter shades are produced by relatively brief treatment with lower voltages, whereas darker or stronger or very dark colors require a longer time or greater electrical values.
  • EXAMPLE 1 Aluminum articles, e.g. aluminum sheets, were first anodized in the conventional 15 percent sulfuric acid solution and after rinsing were then subjected to the alternating current treatment, with a counterelectrode of metallic nickel in a bath (adjusted to pH 4.0 to 4.5) having the following composition:
  • the treated articles were preferably subjected to conventional sealing treatment, as in very hot or boiling water, for usual purposes.
  • the AC treatment in the stated bath for 5 minutes yielded light and medium bronze tones at AC voltages of and 12 respectively
  • a dark bronze was achieved at volts.
  • EXAMPLE 2 Anodized articles treated with alternating current in baths comprising copper sulfate and sulfuric acid in aqueous solution having a pH of about 1.3, and containing magnesium sulfate addition of about grams per liter yielded a range of colored coatings, including pink, light maroon, dark maroon and black, depending on voltage and treatment time.
  • Copper sulfate (CuSO -5H O) was used, for example, in various concentrations from to 50 grams per liter, and sulfuric acid in amounts of 5 to 6 g.p.l.
  • the electrolyte contained 25 g.p.l. copper sulfate, sulfuric acid as last noted and from 1 to 3 g.p.l.
  • magnesium sulfate (MgSO -7 H O). Using a graphite counterelectrode an operation was effected at 8 volts AC for 3 minutes, followed by 12 volts AC for 9 minutes. A uniform, essentially black color was produced, whereas comparable treatment without magnesium sulfate addition generally resulted in spalling defects.
  • EXAMPLE 3 in this instance a sheet of uniformly oxide coated aluminum (anodized in 15 percent sulfuric acid for 40 minutes), was submerged, with a nickel counterelectrode, in a bath of 2.5 percent boric acid solution, containing 4.0 percent nickel ammonium sulfate and 3.5 percent magnesium sulfate, this bath being at a pH of 4.5. With the bath at room temperature alternating current was passed for 10 minutes at a potential of 15 volts. The product was sealed in boiling water for about minutes and had a very dark brown color, free of coating defects.
  • EXAMPLE 4 A sheet of aluminum anodized as in example 3 was similarly treated with alternating current, except for the use of a graphite counterelectrode and the use of 2.5 percent magnesium sulfate in the electrolyte. After passage of the alternating current for l3 minutes at a potential ofabout 16 volts, and sealing as before, the aluminum sheet was found to have a permanent oxide coating characterized by a uniform, essentially black color.
  • EXAMPLE 5 In this instance aluminum articles were first anodized by conventional treatment as indicated in other examples, and then subjected to the alternating current treatment, with a graphite counterelectrode, in a bath containing from 25 to 30 g.p.l. oflead acetate, 20 to 25 g.p.l. of acetic acid and 20 g.p.l. of magnesium acetate (Mg[C H O,],.4H,0). Alternating current was passed at 23 volts for about 5 minutes. A uniform black coating was produced, whereas similar operation without the magnesium addition tended to exhibit some spalling or like difficulty.
  • metal ions are Ni ions or Cu ions.
  • a method as defined in claim 1, in which said step of adding the magnesium compound consists in adding a magnesium salt to the bath in amount of at least about 2 grams per liter.
  • the procedure comprising adding to said bath a magnesium compound in an amount to provide in solution in said bath at least about 200 p.p.m. of magnesium ions and efi'ecting said alternating current treatment while maintaining magnesium ions in said bath in amount of at least about 200 ppm.
  • a method as defined in claim 9, which includes the step of first anodizing said aluminum surface of the article with direct current between said article as anode and a cathode in an aqueous solution of sulfuric acid to produce said anodic coating, and in which in the bath through which alternating current is passed to said anodized surface the metal ions selected from said group consist essentially of Ni ions and said treatment in the bath is effected by passing said alternating current between said anodized aluminum surface and an electrode of nickel.
  • said alternating current treatment bath consists essentially of nickel sulfate, ammonium sulfate, boric acid and magnesium sulfate, said bath being maintained at a pH of at least about 4.

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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)
  • Water Treatment By Electricity Or Magnetism (AREA)
  • Chemical Treatment Of Metals (AREA)
  • Electroplating And Plating Baths Therefor (AREA)
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US773935A 1967-11-24 1968-11-06 Method of producing colored coatings on aluminum Expired - Lifetime US3616309A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB53699/67A GB1241296A (en) 1967-11-24 1967-11-24 Process for colouring anodised aluminium by electrolytic deposition
GB5369867 1967-11-24

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US (2) US3616309A (enrdf_load_stackoverflow)
AT (1) AT305721B (enrdf_load_stackoverflow)
BE (1) BE724327A (enrdf_load_stackoverflow)
CH (1) CH495431A (enrdf_load_stackoverflow)
DE (1) DE1809741C3 (enrdf_load_stackoverflow)
DK (1) DK131794C (enrdf_load_stackoverflow)
ES (1) ES360607A1 (enrdf_load_stackoverflow)
FI (1) FI47115C (enrdf_load_stackoverflow)
FR (1) FR1592472A (enrdf_load_stackoverflow)
GB (1) GB1241296A (enrdf_load_stackoverflow)
IE (1) IE32543B1 (enrdf_load_stackoverflow)
IL (1) IL31135A (enrdf_load_stackoverflow)
LU (1) LU57373A1 (enrdf_load_stackoverflow)
NL (1) NL141579B (enrdf_load_stackoverflow)
NO (1) NO120098B (enrdf_load_stackoverflow)
SE (1) SE337972B (enrdf_load_stackoverflow)
YU (1) YU34438B (enrdf_load_stackoverflow)

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3909367A (en) * 1973-02-23 1975-09-30 Pechiney Aluminium Method for creating a polychrome motif on an object made of aluminum or aluminum alloy
US3912602A (en) * 1973-11-09 1975-10-14 Alusuisse Process for colouring aluminum electrolytically
US4177299A (en) * 1978-01-27 1979-12-04 Swiss Aluminium Ltd. Aluminum or aluminum alloy article and process
US4431489A (en) * 1983-03-31 1984-02-14 Kaiser Aluminum & Chemical Corporation Coloring process for anodized aluminum products
US4931151A (en) * 1989-04-11 1990-06-05 Novamax Technologies Holdings Inc. Method for two step electrolytic coloring of anodized aluminum
WO2010039937A1 (en) * 2008-10-01 2010-04-08 Lorin Industries Outdoor-suitable antique copper color aluminum material and process
US20130154061A1 (en) * 2011-11-30 2013-06-20 Solexel, Inc. Anodizing apparatus, an anodizing system having the same, and a semiconductor wafer
US20130153427A1 (en) * 2011-12-20 2013-06-20 Apple Inc. Metal Surface and Process for Treating a Metal Surface
CN107190299A (zh) * 2017-06-14 2017-09-22 江苏昊科汽车空调有限公司 用于空调压缩机旋转压缩盘铝合金的硬质氧化方法

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3772166A (en) * 1972-07-21 1973-11-13 Perma Technological Ind Inc Electrolytic process for slating a curvilinear aluminum workpiece
US8050831B2 (en) 2006-04-07 2011-11-01 Ford Global Technologies, Llc Vehicle engine speed control for a continuously variable transmission

Cited By (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3909367A (en) * 1973-02-23 1975-09-30 Pechiney Aluminium Method for creating a polychrome motif on an object made of aluminum or aluminum alloy
US3912602A (en) * 1973-11-09 1975-10-14 Alusuisse Process for colouring aluminum electrolytically
US4177299A (en) * 1978-01-27 1979-12-04 Swiss Aluminium Ltd. Aluminum or aluminum alloy article and process
US4431489A (en) * 1983-03-31 1984-02-14 Kaiser Aluminum & Chemical Corporation Coloring process for anodized aluminum products
US4931151A (en) * 1989-04-11 1990-06-05 Novamax Technologies Holdings Inc. Method for two step electrolytic coloring of anodized aluminum
US20100092797A1 (en) * 2008-10-01 2010-04-15 Lorin Industries Outdoor-Suitable Antique Copper Color Aluminum Material and Process
WO2010039937A1 (en) * 2008-10-01 2010-04-08 Lorin Industries Outdoor-suitable antique copper color aluminum material and process
US8580101B2 (en) * 2008-10-01 2013-11-12 Lorin Industries Outdoor-suitable antique copper color aluminum material and process
US20140061052A1 (en) * 2008-10-01 2014-03-06 Lorin Industries, Inc. Outdoor suitable antique copper color aluminum material and process
US20130154061A1 (en) * 2011-11-30 2013-06-20 Solexel, Inc. Anodizing apparatus, an anodizing system having the same, and a semiconductor wafer
US20130153427A1 (en) * 2011-12-20 2013-06-20 Apple Inc. Metal Surface and Process for Treating a Metal Surface
CN107190299A (zh) * 2017-06-14 2017-09-22 江苏昊科汽车空调有限公司 用于空调压缩机旋转压缩盘铝合金的硬质氧化方法
CN107190299B (zh) * 2017-06-14 2023-07-04 江苏昊科汽车空调有限公司 用于空调压缩机旋转压缩盘铝合金的硬质氧化方法

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IE32543L (en) 1969-05-24
AT305721B (de) 1973-03-12
FI47115C (fi) 1973-09-10
IL31135A0 (en) 1969-01-29
IL31135A (en) 1972-10-29
DE1809741A1 (de) 1969-11-06
ES360607A1 (es) 1970-07-16
DE1809741C3 (de) 1975-10-23
SE337972B (enrdf_load_stackoverflow) 1971-08-23
YU273068A (en) 1978-12-31
GB1241296A (en) 1971-08-04
NL6816721A (enrdf_load_stackoverflow) 1969-05-28
NO120098B (enrdf_load_stackoverflow) 1970-08-24
FI47115B (enrdf_load_stackoverflow) 1973-05-31
FR1592472A (enrdf_load_stackoverflow) 1970-05-11
DE1809741B2 (enrdf_load_stackoverflow) 1971-02-04
YU34438B (en) 1979-07-10
IE32543B1 (en) 1973-09-05
CH495431A (fr) 1970-08-31
DK131794B (da) 1975-09-01
DK131794C (da) 1976-02-02
US3616308A (en) 1971-10-26
LU57373A1 (enrdf_load_stackoverflow) 1969-03-03
NL141579B (nl) 1974-03-15
BE724327A (enrdf_load_stackoverflow) 1969-05-22

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