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
  • C25D11/14—Producing integrally coloured layers

Definitions

• ABSTRACT The invention is addressed to the coloring of aluminum and alloys'of aluminum by anodization wherein the aluminum article is immersed as the anode in an electrolytic bath formulated of an aqueous solution of a naphthalene sulphonic acid or alkali metal salt thereof and sulphuric acid, with or without an aliphatic acid of carbon atoms.
• This invention relates to the production of colored aluminum oxide layers by electrolytic treatment of aluminum or alloys of aluminum and it relates to the formulation of the electrolytic bath and toproducts produced thereby.
• colored layers have been produced on aluminum and alloys of aluminum by a two stage process in which a colorless oxide of aluminum is first formed on the surface by anodic oxidation in an electrolyte containing sulphuric acid. Thereafter the formed anodized layer of aluminum oxide is colored by the use of suitable colored pigments. From the architectural standpoint, the process described is insufficient by reason of the instability and non-uniformity of the formed colored layer.
• Colored layers have also been formed on aluminum and alloys of aluminum in a one stage process wherein use is made of an electrolytic bath formulated to contain an organic acid or salt thereof, when certain conditions are maintained during the electrolysis. For example, additions of oxalic acid to the electrolyte and the use of high current densities will operate to produce an oxide layer having a gold tint when use is made of direct current and a brownish layer when use is made of alternating current. The color intensity is sufficient only if very thick layers on the order of 50 to 600 microns are produced and the layers are generally non-uniform in color.
• Electrolytes formulated to contain other organic compounds have also been proposed, such as sulphosalicylic acid in German Pat. No. 657,902, but the colors obtained are weak unless layers of substantial thickness are produced.
• the composition and conditions can be varied over fairly wide limits.
• the naphthalene sulphonic acid component can be employed in solution in the aqueous electrolytic bath in an amount within the range of l-200 grams per liter and preferably within the range of 20-200 grams per liter.
• the amount of sulphuric acid should not exceed 50 grams per liter and it is preferred to formulate the aqueous electrolytic bath with an amount of sulphuric acid within the range of 3-10 grams per liter.
• Gold layers of greater harness can be obtained when the amount of sulphuric acid is maintained within the range of -10 grams per liter.
• the anodic oxidation of the aluminum or alloy of aluminum in the electrolytic bath can be carried out with direct current or with alternating current or by superimposing an alternating current on a direct current, in a system generally referred to as pulsating current.
• Current densities can be used ranging from table,
• the temperature of the electrolyte can be varied during operation within the range of 0 to 70 C. but it is preferred to make use of a temperature within the range of 15 to 30 C.
• a suitable coating can be obtained within a time ranging from 1 to 120 minutes depending somewhat upon the thickness of the coating desired and the current density.
• the electrolytic treatment should be preceded by the usual steps for preparation of the sheet or shaped metal product such as by the processing steps of polishing, degreasing and pickling, and the electrolytic treatment should be followed by the usual procedures of rinsing, sealing and perhaps brightening.
• the resulting product will have a layer of uniform color overthe entire exposed surface and in which a color of sufficient intensity will be available in a layer having a thickness in the order of about 10 microns but in which the intensity of color can be further increased in proportion to the increased thickness of the color layer which may be as great as 30 microns or more.
• EXAMPLE 1 in this series of examples the sheets or shaped elements of aluminum or alloys of aluminum, as indicated in the following were polished mechanically, degreased with trichlorethylene, and pickled by soaking for 10 minutes in a 20 to 25 C. bath containing, per liter, 300 cc. of nitric acid, 10 grams of sodium fluoride and 1 cc. of a surface active agent such as an alkyl sulphonate, commercially known as CELANOL A. After rinsing, the elements were immersed in the electrolyte in the form of an aqueous solution containing 5 grams of sulphuric acid per liter and :1 grams of chromotropic acid per liter in which n 5, 20 and grams.
• a surface active agent such as an alkyl sulphonate
• the current density was kept constant at the beginning at 2.5 A/dm while the voltage at the terminals was progressively raised to 60 volts and thereafter a constant voltage of 60 volts was employed.
• the temperature was maintained at 20 C.
• the operation was carried out on three identical samples in which the first was withdrawn after 20 minutes, the second after 30 minutes, and the last after 45 minutes of electrolysis with the result that an average thickness of an oxide layer of 5 to 8 microns was produced on the first sample, 12 to 15 microns on the second sample, and 20 to 30 microns on the third sample.
• EXAMPLE 2 Sheets of aluminum alloy containing 3 percent magnesium, previously degreased with trichlorethylene and then cleaned for minutes at 10 to 25 C. in a bath containing, per liter, 300 cc. of nitric acid, 10 grams of sodium fluoride and 1 cc. of alkyl sulphonate, followed by rinsing, are anodized in an aqueous bath containing the following ingredients and under the following conditions:
• EXAMPLE 3 Sheets of the same alloy as in Example 2 were subjected to the same surface preparation and then were anodized in an aqueous bath containing 50 grams per liter of G acid and 7 grams per liter of sulphuric acid and operated at 4 A/dm up to 60 volts and then at a constant voltage of 60 volts with a bath temperature at 20 C. After anodizing for minutes, a deep brown oxide layer of 15 microns was obtained.
• EXAMPLE 5 Shaped elements of aluminum alloy containing 1.10 percent by weight silicon, 1.00 percent by weight magnesium and 0.44 percent by weight manganese, the remainder aluminum, were subjected to the same surface treatment as in Example 2 and then anodized in an aqueous bath containing 100 grams per liter of chromotropic acid and 7 grams per liter of sulphuric acid and operated at 2.5 A/dm up to 60 volts and then at a constant voltage of 60 volts, and at a temperature of 22 C. After anodizing for 30 minutes, a black oxide layer of 12 microns in thickness was developed.
• Bath composition of the types described find excellent use when it is desired to produce aluminum and alloys of aluminum having deeply colored shades on the surfaces thereof.
• Lighter shades can be produced by modification to raise both temperatureor to reduce current density.
• Such mixtures of naphthalene sulphonicacid, aliphatic acid and sulphuricacid enables the electrolytic treatment to be carried out at lower voltage and it enables the naphthalene sulphonic acid to be used in lower concentrations in the bath.
• the amount of aliphatic acid use will depend somewhat on the nature of the acid and the effect desired to be secured but, in general, it is'desired to make use of an electrolytic bath in which the aliphatic acid is present in an amount within the range of 10-100 grams per liter.
• the amount of naphthalene sulphonic acid can be reduced to less than grams per liter and preferably within the range of 50-100 grams per liter or up to saturated solution when use is made of a naphthalene sulphonic acid containing an amino group.
• colored oxide layers having a thickness within the range of 10-30 microns should be produced.
• the colored layer that is formed is characterized by good hardness and excellent'light and weather resistance.
• EXAMPLE 7 An aluminum alloy containing about 0.6 percent by weight of silicon and 0.7 percent by weight of magnesium is anodized in an aqueous bath containing in solution:
• EXAMPLE 8 A sheet of commercial aluminum (99.5 percent Al) is anodized in an aqueous bath containing in solution:
• the anodizing is carried out at 30 C. with a current density I of 1.5 aldm After 30 minutes, an oxide layer is obtained having a thickness of 15 microns and a light bronze color. The shade is very unifonn and resistant to ultraviolet rays.
• EXAMPLE 9 Shaped elements of aluminum alloy having a composition the same as that in Example 7 are anodized for 30 minutes at 25 C. with a current density of 1.5 a/dm' in a bath containing chromotropic acid, maleic acid and sulphuric acid. Several tests were carried out in which the proportions of acids were varied as set forth in the following table:
• EXAMPLE 10 This example is intended to show the extent of the range of colors which can be obtained on aluminum or on alloys of alu- EXAMPLE I l
• a shaped element of aluminum alloy containing l percent silicon, 0.5 percent magnesium and 0.5 percent manganese (by weight) is anodized in a bath formed of an aqueous solution of:
• EXAMPLE 12 A shaped element of aluminum-magnesium-silicon alloy containing about 0.5 percent silicon and 0.5 percent magnesium (by weight) is anodized in a bath formed of an aqueous solution of:
• a shaped element of aluminum-magnesium-silicon alloy containing 0.5 percent silicon and 0.5 percent magnesium (by weight) is anodized in a bath formed of an aqueous solution of:
• EXAMPLE l4 chromotro ic acid 50 /l maleic 100 i 50 Shaped elements of alummum-magnesium-srllcon alloy havsulphuric acid 7 g/l mg the composition of Example 7 are anodized in an aqueous TABLE IV electrolysis voltage on comthickcurrent temperduration mence on comness of Nature of metal density alure "C. minment pletion the layer color 99.5% aluminum l.5 a/dm 40 33.5 V 36 V 18 very sheets. 2.5 25 20 37.5 43 16 p.
• EXAMPLE is A commercial aluminum sheet (99.2 percent aluminum) is anodized in a bath formed of an aqueous solution of:
• EXAMPLE 16 chromotropic acid 50 g/l succinic acid 65 'g/l sulphuricacid g/l
• the anodization is carried out at 20 C. with a current density of 2.5 a/dm for 45 minutes.
• An anodized layer having a thickness of microns is obtained which is black in color.
• the shade is very uniform and resistant to ultraviolet rays.
• An electrolytic bath for coloring aluminum and alloys of aluminum by anodization comprising ,an aqueous solution containing the combination of a naphthalene sulphonic acid' selected from the group consisting of 2'-naphthol-6, 8- disulphonic acid, 2-naphthol-3, o-disulphonic acid, 1,8- dihydroxynaphthalene-3, G-disulphonic acid and l-naphthol- 8-amino-3, ti-disulphonic acid, an aliphatic acid of less than five carbon atoms and sulphuric acid.
• a naphthalene sulphonic acid' selected from the group consisting of 2'-naphthol-6, 8- disulphonic acid, 2-naphthol-3, o-disulphonic acid, 1,8- dihydroxynaphthalene-3, G-disulphonic acid and l-naphthol- 8-amino-3,
• An electrolytic ath as claimed in claim 12 in which the naphthalene sulphonic acid or salt contains an amine group, and is present in the bath in an amount to saturate the solution.
• An electrolytic bath as claimed in claim 12 in which the sulphuric acid is present in an amount within the range of 3 to 10 grams per liter.
• An electrolytic bath as claimed in claim 12 in which the naphthalene sulphonic acid or its alkali metal salt is present in an amount within the range of 10 to 200 grams per liter, the aliphatic acid is present in an amount within the range of 10 to I00 grams-per liter and the sulphuric acid is present in an amount within the range of 3 to 10 grams per liter.
• an electrolytic bath as claimed in claim 12 in which the aliphatic acid is selected from the group consisting of acetic acid and a compound selected from the group consisting of 2- naphthol-6, 8-disulphonic acid, 2-naphthol-3, 6-disulphonic acid, 1, 8-dihydroxynaphthalene-3, 6-disulphonic acid and lnaphthol-8-amino-3, 6-disulphonic acid, and water soluble salts thereof in which the sulphuric acid is present in an amount within the range of l-200 grams per liter. while the disulphonic acid derivative is present in an amount within the range of 1-200 grams per liter, and passing current between the electrodes through the bath.
• the aliphatic acid is selected from the group consisting of acetic acid and a compound selected from the group consisting of 2- naphthol-6, 8-disulphonic acid, 2-naphthol-3, 6-disulphonic acid, 1, 8-dihydroxynaphthalene

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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)
• Printing Plates And Materials Therefor (AREA)
• Electrochemical Coating By Surface Reaction (AREA)
• Chemical Treatment Of Metals (AREA)

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Citations (3)

• 1966
  • 1966-07-13 FR FR69304A patent/FR1493055A/fr not_active Expired
• 1967
  • 1967-06-30 SE SE09956/67*A patent/SE329310B/xx unknown
  • 1967-07-06 OA OA53001A patent/OA02469A/xx unknown
  • 1967-07-10 GR GR670133981A patent/GR33981B/el unknown
  • 1967-07-11 ES ES342899A patent/ES342899A1/es not_active Expired
  • 1967-07-11 AT AT648367A patent/AT268808B/de active
  • 1967-07-11 NL NL6709585A patent/NL6709585A/xx unknown
  • 1967-07-11 LU LU54074D patent/LU54074A1/xx unknown
  • 1967-07-12 CH CH991967A patent/CH464641A/fr unknown
  • 1967-07-12 DE DE1967P0042577 patent/DE1621144B1/de active Pending
  • 1967-07-12 BE BE701290D patent/BE701290A/xx unknown
  • 1967-07-13 GB GB32350/67A patent/GB1197501A/en not_active Expired
• 1969
  • 1969-04-15 US US816420A patent/US3658665A/en not_active Expired - Lifetime

Patent Citations (3)

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