US3616297A - Method of producing colored coatings of aluminum - Google Patents

Method of producing colored coatings of aluminum Download PDF

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Publication number
US3616297A
US3616297A US761717A US3616297DA US3616297A US 3616297 A US3616297 A US 3616297A US 761717 A US761717 A US 761717A US 3616297D A US3616297D A US 3616297DA US 3616297 A US3616297 A US 3616297A
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bath
aluminum
ions
maintaining
dissolved
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US761717A
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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

  • This invention relates to procedure for producing inorganically colored coatings on aluminum surfaces, i.e., articles of aluminum, such term including aluminum base alloys and thus generally signifying aluminum that is appropriate for anodic treatment. More particularly, this invention is concerned with colored deposits derived from nickel or cobalt ions and produced in accordance with procedure such as described in U.S. Pat. No.
  • One notably effective method of the stated character, for producing suchinorganically colored coatings involves first anodizing an aluminum article, as in sulfuric acid solution, to form an anodic coating, and then subjecting the anodized article to electrolytic treatment in an acidic bath containing metal ions selected from the group consisting of nickel ions and cobalt ions (Ni**, Co), particularly a bath having a pH substantially above 3, e.g., a pH value of at least about 4.
  • the described process effectuates a colored deposit in the anodic coating, being understood to be a deposit of the selected metal in chemical combination with oxygen, i.e., a compound of the class of oxide or hydroxide.
  • the result for example in the case of nickel, is a coating having a color that can be described as bronze, of a shade or tone ranging from a light color to a very dark bronze or brown de pending on selected conditions, the colored coating being one that can be sealed and which has good permanence. With cobalt, the coating may have a range of somewhat bronzelike colors, up to a very dark or indeed nearly black shade.
  • the anodic coating itself is advantageously such as to afford, if desired, other desirable attributes of such coatings, e.g., as in protecting the underlying metal surface from corrosion or other deterioration by weather or the like.
  • an effective coloring process involves first anodizing the aluminum article, e.g., to produce a suitable oxide coating of the so-called porous type, and then passing alternating current between the article and an electrode, for example an electrode of the selected metal of the bath (i.e., nickel, for a bath containing nickel ions), or in some cases of other suitably conductive material, such as carbon e.g., graphite), while the article and electrode are immersed in an aqueous acidic bath containing Ni or C ions.
  • a typical bath composition for instance, has comprised an aqueous solution of nickel sulfate (NiSO -7 I-I;Q), boric acid (H BQ and ammonium sulfate,
  • the bath may also include magnesium ions, e.g., supplied as magnesium sulfate (MgSO '7 H 0), functioning to reduce the incidence of certain defects, called spalling, and being the occurrence of minute uncolored spots or localities when darker shades of color are sought to be produced.
  • magnesium ions e.g., supplied as magnesium sulfate (MgSO '7 H 0)
  • spalling the incidence of certain defects
  • spalling being the occurrence of minute uncolored spots or localities when darker shades of color are sought to be produced.
  • any selected one of a range of bronze or like colors can be achieved, being understood to be effectuated by deposit in the oxide coating of nickel (or cobalt) material, presumably as the oxide.
  • This colored coating is quite permanent and may be sealed in a conventional manner, e.g., with hot water.
  • a special feature of the 28 invention is that a presently preferred mode of practicing it is of marked simplicity in that ordinarily no special account need be taken of the actual concentration of available, combined aluminum, so long as there is at least enough of it to insure saturation of the bath with dissolved aluminum ions. That is to say, in the pH range between about Sand about 6, the solubility of aluminum is so low that there cannot be enough ions present to interfere with proper realization of the entire color range, yet with the aluminum ions in saturated solution, they are always sufficiently present to obviate the grey overtone heretofore encountered in aluminum ion-free baths.
  • an unusually satisfactory mode of operation is: (a) to make up the bath originally with a deliberate addition of aluminum salt, such as aluminum sulfate, in sufficient amount to provide about 5 p.p.m., or even more, of available aluminum, meaning aluminum in combined form, i.e., combined aluminum which is capable ofoccuring as dissolved Al ions or as undissolved Al compound dependent on the pH of the bath; and (b) thereafter simply to operate the bath at the above stated, preferred pI-l, without further attention to aluminum content except referably to make sure that there is always some undissolved aluminum compound present.
  • aluminum salt such as aluminum sulfate
  • the solution will have a slightly turbid appearance and at the same time will automatically maintain a sufficient residue of dissolved aluminum ions (for instance), about 2 or 3 ppm. at about pH 5.5), to avoid any grey overtone or the like.
  • dissolved aluminum ions for instance
  • the bath is kept in the optimum pH range, all that is necessary is to keep it mildly turbid with undissolved or precipitated aiuminum compounds (possibly then appearing at least in part as hydroxide), say by simply introducing at the start sufficient soluble aluminum salt to result in such turbidity, in coaction with the necessary pH adjustment.
  • the specific concept of working in the defined pH area of the present invention i.e., above 4.75, and particularly from about 5 to about 6, and indeed most conveniently from 5.5 to 6, is of unusual value for simplicity of operation.
  • the actual amount of combined aluminum present in the bath need not be controlled to any critical maximum value, but may even rise well or far above 10 ppm, the effect of the stated pI-l being to suppress the dissolved aluminum ions, in fact to keep them at a value usually well below l0 p.p.m.
  • the bath may contain combined aluminum equivalent to as much as ppm. aluminum ions, the actual dissolved aluminum ion concentration at pH 5.5 is not more than about 2 or 3 p.p.m.
  • the undissolved aluminum in combined form, remains as turbidity in the electrolyte or of course may even in part settle as sediment at the bottom of the tank. At least within reasonable limits such accumulation of undissolved aluminous material does not appear deleterious, yet in the pH range of 5 to 6 the automatic control of dissolved aluminum ions to a concentration of about 3 ppm. or less, and of course below about 10 p.p.m. has a two-fold advantage: there cannot be sufficient dissolved aluminum to cause spelling or otherwise to interfere with attainment of dark shades of color, yet there is enough dissolved aluminum, as now appears necessary, to prevent occurrence of undesirable grey overtone or the like.
  • the complete process of producing a colored coating on an aluminum surface of an article, whether sheet or other fabricated piece or structure involves first anodizing the surface of the work in a conventional manner to produce an anodic oxide coating, for example of the so-called porous type customarily applied for protective or like purposes.
  • anodic oxide coating for example of the so-called porous type customarily applied for protective or like purposes.
  • 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 A.C.
  • 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., 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 con siderable range of thicknesses of porous oxide coating on aluminum.
  • the second step of the process then involves submerging the anodizing aluminum article, if desired after suitable rinsing, in a nickel-containing acidic bath, in which a counterelectrode is likewise submerged, whereupon 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 colored oxide or equivalent deposit of nickel.
  • the bath may be prepared in appropriate fashion as set forth in the above cited U.S. Pat. No.
  • the bath should be a water solution of a suitable nickel salt and an acidic constituent, all in relatively low concentration.
  • the anionic constituents of the bath may be variously selected to provide the desired solubility of nickel ions and suitable acidity of the electrolyte, and supplemental salts or the like may be incorporated, as desired for purposes of stability, buffering or other function which does not interfere with the formation of the colored deposit, and may include salts or the like that result from initial or subsequent pH adjustment.
  • sulfate, borate, acetate and other common anions are appropriate, as will be apparent from the cited patent.
  • a particularly suitable composition for the nickel bath is made up with nickel sulfate and boric acid, each in amounts of the order of l5 to 40 g.p.l. (grams per liter), usually with some ammonium sulfate (say 10 to g.p.l.), and also very preferably, in accordance with another invention as mentioned above, some content of magnesium sulfate, e,g., from 2 to 20 g.p.l. of the conventional hydrated salt.
  • Addition of a small amount of combined aluminum to the bath in accordance with the present invention may be in the form of any suitable aluminum compound, such as any of a variety of aluminum salts, for instance sulfate, acetate or others, commonly regarded as water soluble e.g., such as used alone would assume a pH in a high solubility range), or conceivably a compound such as aluminum hydroxide, meaning hydroxide recognized as soluble in acidic conditions.
  • a salt of aluminum with an anion that is otherwise present in the bath is generally convenient for the purpose, i.e., sulfate for the baths here exemplified.
  • the counterelectrode is made of suitable electrically conductive material as also explained in the cited patent, presently preferred operation being achieved with a graphite electrode, or most advantageously with an electrode of the same metal as in the bath, e.g., metallic nickel for Ni ions or cobalt for Co ions.
  • Operation with baths of this character, in treatment ofa suitably anodized article, involves passage ofalternating current at a conveniently moderate voltage, say from 5 to 20 volts, for a correspondingly appropriate time, e.g.,
  • the shade of color achieved depends on the time of treatment and on electrical conditions; for instance, light shades are produced by relatively brief treatment with lower voltages, whereas very dark bronze colors require a longer time or greater electrical values.
  • the drawing indicates the manner in which the solubility of aluminum ions in a nickel sulfateboric acid-ammonium sulfate electrolyte of the sort here described (taken at 25 C.) varies with pH in the range from 4 to 6.
  • the solubility in p.p.m. Al ions
  • the solubility is relatively high as the pH falls to 4.0, and correspondingly decreases as the pH rises to 6, being of the order of 70 ppm. in the region of pH 4.5, and dropping to and below 10 p.p.m. above pH 4.7, e.g., about 4 ppm. at pH 4.75.
  • alkaline ranges i.e., above pH 7
  • combined aluminum becomes more soluble, e.g., rising from the low point of the illustrated curve, but this characteristic is of no significance in the present invention, which is related to acidic baths.
  • an aqueous bath (balance, water) is made up to have the following initial composition in grams per liter:
  • NiSO 7Hg0 25 g.p.l.
  • an amount of an aluminum compound equivalent to 5 to 10 ppm. Al ions e.g., 0.06 to 0.12 g.p.l. of aluminum sulfate (AI SO 'I8H O).
  • the pH is adjusted (usually upward) to the range of 5 to 6, as for example a target value of 5.75.
  • no more than a few ppm. of aluminum ions remain in solution, and the excess combined aluminum is precipitated, e.g., as hydroxide, and will impart a somewhat clouded or turbid appearance to the bath.
  • the pH adjustment, and subsequent maintenance of pH in the desired range can be achieved by additions of ammonium hydroxide or dilute sulfuric acid as necessary.
  • Aluminum articles to be colored first have their surfaces anodized by conventional anodic treatment with direct current, e.g., for periods upwards of 20 minutes in a 15 percent sulfuric acid solution. Thereafter the anodically coated article, suitably rinsed, is immersed in the stated nickel-ion-containing bath, with a counterelectrode made of nickel sheet, bars, rods, or the like. Upon passage of alternating current, for a selected length of time, a desired surface of the article. For instance, at voltages of 10 to 15 and with treatment times of 5 minutes or more, bronze shades from light to dark are achieved.
  • the treatment can be continued for an additional 5 minutes at a higher voltage, e.g., 17 volts.
  • These permanently colored oxide coatings can be sealed in a conventional manner, e.g., using water at or near l00 C. Over repeated use of the bath, replenishment of Ni ions may occur by consumption of the nickel electrode if employed, which is then is then replaced at intervals, or additional nickel compound can be added as necessary.
  • the process is unusually effective for its desired purpose, namely the achievement of an alternating current coloring step, of certain types, with a minimum need for chemical or other analytical determinations, and especially, in preferred operation, with an automatic control of the aluminum ions, to keep their dissolved concentration at or below the indicated levels.

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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)
  • Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
  • Chemical Treatment Of Metals (AREA)
  • Printing Plates And Materials Therefor (AREA)
  • Electrochemical Coating By Surface Reaction (AREA)
US761717A 1968-09-23 1968-09-23 Method of producing colored coatings of aluminum Expired - Lifetime US3616297A (en)

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US (1) US3616297A (enrdf_load_stackoverflow)
JP (1) JPS4824139B1 (enrdf_load_stackoverflow)
AT (1) AT288106B (enrdf_load_stackoverflow)
BE (1) BE738912A (enrdf_load_stackoverflow)
BR (1) BR6912589D0 (enrdf_load_stackoverflow)
CH (1) CH514685A (enrdf_load_stackoverflow)
CS (1) CS177018B2 (enrdf_load_stackoverflow)
DE (1) DE1947671C3 (enrdf_load_stackoverflow)
DK (1) DK132767C (enrdf_load_stackoverflow)
ES (1) ES371568A1 (enrdf_load_stackoverflow)
FI (1) FI47117C (enrdf_load_stackoverflow)
FR (1) FR2018630A1 (enrdf_load_stackoverflow)
GB (1) GB1216440A (enrdf_load_stackoverflow)
IE (1) IE33554B1 (enrdf_load_stackoverflow)
IL (1) IL32946A (enrdf_load_stackoverflow)
LU (1) LU59436A1 (enrdf_load_stackoverflow)
NL (1) NL146543B (enrdf_load_stackoverflow)
NO (1) NO123953C (enrdf_load_stackoverflow)
SE (1) SE346124C (enrdf_load_stackoverflow)

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS4849637A (enrdf_load_stackoverflow) * 1971-10-28 1973-07-13
US3878056A (en) * 1973-08-24 1975-04-15 Sumitomo Chemical Co Process for electrolytic coloring of the anodic oxide film on a aluminum or aluminum base alloys
US3891517A (en) * 1973-03-20 1975-06-24 Sumitomo Chemical Co Process for electrolytic coloring of aluminum cr aluminum alloy articles
US3912602A (en) * 1973-11-09 1975-10-14 Alusuisse Process for colouring aluminum electrolytically
US3929593A (en) * 1973-09-21 1975-12-30 Riken Light Metal Ind Company Method of forming colored oxide film on aluminum or aluminum alloy material
US3929612A (en) * 1973-10-20 1975-12-30 Sumitomo Chemical Co Process for electrolytically coloring the anodically oxidized coating on aluminum or aluminum base alloys
US4894127A (en) * 1989-05-24 1990-01-16 The Boeing Company Method for anodizing aluminum
US7276293B1 (en) * 2000-05-24 2007-10-02 Fujikura Ltd. Far-infrared radiator and method for producing method

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS4849637A (enrdf_load_stackoverflow) * 1971-10-28 1973-07-13
US3891517A (en) * 1973-03-20 1975-06-24 Sumitomo Chemical Co Process for electrolytic coloring of aluminum cr aluminum alloy articles
US3878056A (en) * 1973-08-24 1975-04-15 Sumitomo Chemical Co Process for electrolytic coloring of the anodic oxide film on a aluminum or aluminum base alloys
US3929593A (en) * 1973-09-21 1975-12-30 Riken Light Metal Ind Company Method of forming colored oxide film on aluminum or aluminum alloy material
US3929612A (en) * 1973-10-20 1975-12-30 Sumitomo Chemical Co Process for electrolytically coloring the anodically oxidized coating on aluminum or aluminum base alloys
US3912602A (en) * 1973-11-09 1975-10-14 Alusuisse Process for colouring aluminum electrolytically
US4894127A (en) * 1989-05-24 1990-01-16 The Boeing Company Method for anodizing aluminum
US7276293B1 (en) * 2000-05-24 2007-10-02 Fujikura Ltd. Far-infrared radiator and method for producing method

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GB1216440A (en) 1970-12-23
IE33554L (en) 1970-03-23
NL6913865A (enrdf_load_stackoverflow) 1970-03-25
DK132767B (da) 1976-02-02
IL32946A0 (en) 1969-11-30
SE346124B (enrdf_load_stackoverflow) 1972-06-26
DE1947671C3 (de) 1975-11-13
FR2018630A1 (enrdf_load_stackoverflow) 1970-06-26
NO123953C (enrdf_load_stackoverflow) 1977-02-04
DK132767C (da) 1976-07-05
CS177018B2 (enrdf_load_stackoverflow) 1977-07-29
DE1947671B2 (enrdf_load_stackoverflow) 1975-04-03
BE738912A (enrdf_load_stackoverflow) 1970-03-16
JPS4824139B1 (enrdf_load_stackoverflow) 1973-07-19
FI47117B (enrdf_load_stackoverflow) 1973-05-31
NO123953B (enrdf_load_stackoverflow) 1972-02-07
LU59436A1 (enrdf_load_stackoverflow) 1970-01-08
IL32946A (en) 1973-05-31
CH514685A (fr) 1971-10-31
FI47117C (fi) 1973-09-10
SE346124C (enrdf_load_stackoverflow) 1975-10-06
ES371568A1 (es) 1971-11-01
BR6912589D0 (pt) 1973-06-12
DE1947671A1 (de) 1970-04-23
IE33554B1 (en) 1974-08-07
AT288106B (de) 1971-02-25
NL146543B (nl) 1975-07-15

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