US3634214A - Electrolytic bath to be used for electrolytically anodizing aluminum or aluminum alloy to form a colored oxide coating and method for anodizing said metal - Google Patents

Electrolytic bath to be used for electrolytically anodizing aluminum or aluminum alloy to form a colored oxide coating and method for anodizing said metal Download PDF

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US3634214A
US3634214A US842959A US3634214DA US3634214A US 3634214 A US3634214 A US 3634214A US 842959 A US842959 A US 842959A US 3634214D A US3634214D A US 3634214DA US 3634214 A US3634214 A US 3634214A
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oxide coating
aluminum
weight
acid
anodizing
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US842959A
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Hiroshi Nakazato
Masayoshi Yokoyama
Toshihiro Nagano
Kazuyoshi Kaneda
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RIKEN DENKA KOGYO CO Ltd
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RIKEN DENKA KOGYO CO 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
    • C25D11/14—Producing integrally coloured layers

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  • the present invention relates to electrolytic baths to be used for electrolytically anodizing aluminum or aluminum alloy to form a colored oxide coating and also to methods for anodizing said aluminous substrate by means of the electrolytic bath to form a colored oxide coating having excellent abrasion resistance and weather resistance on said substrate.
  • a method for forming a colored oxide coating on one of the surfaces of an aluminous material by subjecting the aluminous material to electrolyse in an electrolytic bath to color the aluminous material, said material serving as an anode, that is, an anodizing process,
  • the color tone of the oxide coating is usually gray and therefore, in order to color in the desired color tone, the above oxide coating is further colored by an organic or inorganic dyestuff.
  • an organic or inorganic dyestuff in order to color in the same color tone it is necessary to strictly control the thickness of the oxide coating, the temperature and concentration of the dyestuff solution, the immersing time and the like in order to maintain them constant.
  • a method for forming a rigid, tight oxide coating comprises maintaining the temperature of the electrolytic bath at a low temperature, lower than room temperature, when using an electrolytic bath which is an aqueous solution of sulfuric acid, to prevent dissolution of the aluminous substrate, but in this case an expensive cooling installation is necessary.
  • electrolytic baths comprising sulfosalicylic acid mixed with sulfuric acid or metallic sulfates or an aqueous solution of sulfophthalic acid mixed with sulfuric acid or Water soluble sulfate or bisulfate have been disclosed in Japanese patent application publication No. 22,259/ 61. These electrolytic baths can provide an excellent oxide coating and a broad range of color tones, but sulfosalicylic acid and sulfophthalic acid are special chemicals and therefore the electrolytic bath becomes expensive.
  • an object of the present invention is to provide electrolytic baths capable of economically forming oxide coatings having the required colors and improved abrasion resistance and weather resistance on aluminous materials.
  • a further object of the present invention is to provide a method for forming colored oxide coatings having improved abrasion resistance and weather resistance an aluminous materials by anodizing the aluminous materials using the above described electrolytic baths.
  • a colored oxide coating having improved abrasion resistance and weather resistance can be obtained by using an electrolytic bath which is an aqueous solution containing cresolsulfonic acid and sulfuric acid or a metal sulfate in an amount equivalent to the concentration of said sulfuric acid or an aqueous solution containing cresolsulfonic acid,
  • the first aspect of the present invention consists of an electrolytic bath which is an aqueous solution containing 2.4 to 40% by weight of cresolsulfonic acid and 0.05 to 3% by Weight of sulfuric acid or a metal sul fate equivalent to the concentration of said sulfuric acid.
  • the second aspect of the present invention consists in an electrolytic bath which is an aqueous solution contain- TABLE 1 Electrolyte, weight percent Sul- [uric Cresol- Genaeid, Sulfonlc Current Time erated peracid, density, minvoltage, Shape cent percent a./dm. utes volts Appearance 0. 6 1 2 30 35-20 Corroded pores are many. 0.6 2 2 30 35-28 Corroded pores are very w. .6 2.4 2 30 30-45 Yellowish brown A .6 2 30 5 A 0.6 10 2 30 0.6 2 O 0.6 30 2 30 30-45 do A 0.6 2 30 30-45 Light yellowish A brown. 0.6 2 30 30-45 Light yellowish A brown. 0.6 2 30 30-45 Light white 0.6 2 30 30-45 ..do
  • the degree of dissociation is low and even if the voltage is increased, the oxide coating is not substantially formed on the aluminous substrate.
  • the degree of dissociation is too high and it is difficult to obtain an oxide coating having a desired color.
  • Aluminum 1100 was anodized by varying the content of sulfuric acid as shown in the following Table 2 without varying the content of cresolsulfonic acid of 10% by weight, while the temperature of the electrolytic bath was maintained at 20 C. The obtained results are shown in the following Table 2.
  • the limitation of the content of sulfuric acid or a metal sulfate is based on the reason explained in the above described bath of the first aspect of the invention.
  • the components of the electrolytic bath are cresolsulfonic acid and sulfuric acid or metal sulfates; or cresolsulfonic acid, sulfosalicylic acid and sulfuric acid or metal sulfates and therefore the electrolytic bath is inexpensive.
  • the colored oxide coating formed on the aluminum substrate has excellent abrasion resistance and weather resistance and a stable color tone.
  • oxide coatings having a broad range of color tones such as yellowish brown, bronze color, dark black, etc. can be obtained.
  • the third aspect of the present invention is a method of producing colored oxide coating on an aluminum substrate, which comprises immersing the aluminous substrate in any of the above described electrolytic baths of the first and the second aspects of this invention and passing an electric current through the electrolyte with the aluminous substrate serving as the anode.
  • the conditions for the electrolysis are as follows.
  • the concentrations of the electrolytic baths are the same as illustrated in the first and second aspects of the invention.
  • the amount of aluminum dissolved is 0.5-1.2 g./l.
  • the temperature of the bath is to C.
  • the voltage is 25 to 80 volts
  • the current density is 1 to 3 a./dm.
  • the treating time is 15 to 60 minutes.
  • a satisfactory color can not be obtained.
  • the fourth aspect of the present invention is a method of producing a light color oxide coating which comprises firstly immersing an aluminous substrate in an aqueous solution of sulfuric acid or oxalic acid and passing an electric current through the electrolyte with the aluminous substrate serving as the anode to form an oxide coating on the aluminous substrate and then, without effecting a treatment for sealing the pores in the oxide coating, anodizing the thus treated aluminous substrate in any of the above described electrolytic baths of the present invention for a short time such as less than 10 minutes.
  • the aluminous substrate is firstly anodized in an electrolytic bath which is an aqueous solution of sulfuric acid or oxalic acid to form a porous oxide coating and then the formed porous oxide coating is further anodized in any of the above described electrolytic baths of the present invention to form a thin colored oxide coating having a light color on the above described porous oxide coating.
  • the conditions of electrolysis in the above described second step follow the conditions described in the above described third aspect of this invention, except that the treating time is 5 to 10 minutes.
  • the thus obtained oxide coating is thoroughly washed with water and is subjected to a treatment for sealing the pores by 4 kg./m. of steam pressure.
  • a clear bronze color oxide coating having excellent abrasion resistance, corrosion resistance and weather resistance can be obtained by anodizing an aluminous substrate in the above described electrolytic bath of the present invention to form an amberish gray oxide coating and then, without sealing the pores of the oxide coating, immersing the aluminous substrate in an aqueous solution of ammonium ferric oxalate to form a reddish brown oxide coating of ferric hydroxide on the above amberish gray oxide coating, whereby these two colored oxide coatings are combined to form a clear bronze color.
  • the fifth aspect of the present invention is a method of producing the above described clear bronze color oxide coating, which comprises anodizing an aluminous substrate in the above described electrolytic bath of the present invention in a first step to form a colored oxide coating and then immersing the thus treated aluminous substrate in 1 to 10% by weight of an aqueous solution of ammonium ferric oxalate in a second step.
  • the second step of this process when the content of ammonium ferric oxalate is less than 1% by weight, the effect of addition does not occur and substantially no reddish brown ferric hydroxide is deposited on the aluminous substrate and in order to deposit ferric hydroxide, a fairly long treating time is necessary.
  • the content of ammonium ferric oxalate is more than 10% by weight, the deposit of ferric hydroxide is too rapid and it is diificult to deposit ferric hydroxide on the aluminous substrate uniformly.
  • the effect of the addition can be developed by increasing the immersion time but it has been found that the content of ammonium ferric oxalate which can form a satisfactorily colored oxide coating (more than 4.0 in NBS units) in the second step is 1 to by weight in the practical immersing time of 3 to 5 minutes.
  • an alternating current or a direct current can be used as an electric source and, if necessary it is possible to use both the currents together.
  • the conditions of the above described second step are as follows.
  • the concentration of the ammonium ferric oxalate is 1 to 10% by weight as described above, the treating temperature is 40 to 70 C. and the treating time is 3 to 10 minutes.
  • the metal sulfates to be used in the electrolytic bath of the present invention include ferric sulfate, cobalt sulfate, manganese sulfate, nickel sulfate and the like.
  • EXAMPLE 1 A thin plate of aluminum 1100 was used as a substrate and firstly subjected to a pre-treatment, in which the thin plate was immersed in a 5% by weight caustic soda solution for about 90 seconds and cleaned with water and a 10% sulfuric acid solution and then again cleaned with cold water to completely remove sulfuric acid from the thin plate.
  • the thus cleaned thin plate was anodized as the anode in an electrolytic bath containing 100 g./l. of cresolsulfonic acid and 6 g./l. of sulfuric acid in water with a direct current for about 30 minutes.
  • the bath temperature was maintained at :3" C. and the current density was 2 a./dm. and the voltage was raised from 29 volts to 42 volts.
  • the test 118 H8601 was effected as follows by means of the apparatus as shown in the attached figure. Namely, a sample 8 to be tested is fixed on a sample plate 7 by a set bolt 6.
  • a feeder 1, a funnel 3 having a taper angle of 60, an inner diameter of top portion of 70 mm. and provided with a leg portion, the length of which is 50 mm. and the inner diameter of which is 50:0.1 mm. and a conduit 5 are arranged as shown in the figure, so that abrasives falling from the feeder 1, through an outlet 2, the funnel 3 and the conduit 5 strike against the sample 8 and the surface of the sample forms an angle of to the perpendicular direction an amount of 320:10 g./min. of the abrasives having a specific gravity of more than 3.16, more than 92% of silicon carbide and free carbon of more than 1.5% are dropped on the sample 8 and the time until the coating film of the sample is broken is determined and read in second.
  • anodizing was carried out with the same composition of the electrolytic bath and the same conditions as described above except varying only the composition of aluminum alloy. Namely, aluminum alloys 6061 and 6063 were used as substrates and anodized for 30 minutes respectively. In this case, a dark black oxide coating having a thickness of 18a was formed on the aluminum alloy 6061, while a bronze oxide coating having a thickness of 18a was formed on the aluminum alloy 6063.
  • EXAMPLE 2 An aluminum 1100 previously cleaned as described in Example 1 was immersed in an electrolytic bath having the composition as shown in the following Table 4 and then the anodizing process was effected at a bath temperature of 20 C. and a current density of 2 a./dm. for 30 minutes to obtain the results as shown in Table 4. In this case, the reason why the treating time is 30 minutes is based on the fact that this time is industrially suitable for practice.
  • EXAMPLE 4 An aluminum substrate 53ST was immersed in a 5% caustic soda solution at 60 C. for 2 minutes to effect through degreasing and then cleaned with water.
  • the de- 5 greased aluminum substrate was immersed in an electrolyte consisting of a aqueous solution of sulfuric acid and anodized at a liquid temperature of C. and a current density of 1.5 a./dm. for about 20 minutes to produce a porous oxide coating of about 9 on the surface of the substrate. Then the substrate was thoroughly washed with Water without sealing the pores and thereafter immersed in an aqueous solution containing 10% cresolsulfonic acid and 0.6% sulfuric acid and anodized at a current density of 2 a./dm.
  • EXAMPLE 5 An aluminum substrate 28 was degreased in the same manner as described in Example 4 and then immersed in an electrolyte consisting of a 3% aqueous solution of oxalic acid and thereafter, the anodizing process was effected at a current density of 1 a./dm. with superimposed direct and alternating currents for 30 minutes to obtain a porous oxide coating of about 8,41. on the substrate. Then the substrate was cleaned with water as in Example 4 and immersed in an aqueous solution containing 10% cresolsulfonic acid and 2% ferric sulfate and the anodizing process was effected at a current density of 2 a./dm. for 5 minutes to produce an oxide coating having a thickness of 11a. In this case, the color tone of the resulting oxide coating was slightly deeper than that of the oxide coating in Example 4. Then the substrate was cleaned with water and the oxide coating was subjected to a treatment for sealing the pores under a steam pressure of 4 kg./crn.
  • these coatings are colored oxide coatings provided with abrasion reslstmeans of a fadeometer with respect to the light yellowish brown aluminum substrate of the present invention and conventional aluminum substrate colored to yellowish brown in a conventional known dyeing method, in which an oxide coating is dyed with a dyestuff.
  • EXAMPLE 6 An aluminum 28 plate having a purity of more than 99% was immersed in a 5% caustic soda solution at 60 C. for 2 minutes to thoroughly effect degreasing and then cleaned with water. Then the degreased plate was immersed in a 10% nitric acid solution at room temperature for 1 minute and cleaned with water.
  • the thus cleaned plate was immersed in a first electrolytic bath containing 100 g./l. of cresolsulfonic acid and 6 g./l. of sulfuric acid and then the anodizing process was effected under the electrolytic conditions of a liquid temperature of 20i3 C., current density of 2 a./dm. and a voltage of 20-42 volts, for 30 and 50 minutes, respectively.
  • the plate anodized for 30 minutes is referred to as plate A and the plate anodized for 50 minutes is referred to as plate B.
  • EXAMPLE 7 Aluminum 638 plates were degreased and cleaned with a caustic soda solution and nitric acid in the same manner as described in Example 6, whereafter the cleaned plates were anodized with the same first and second electrolytic baths under the same conditions as described in Example 6 for 50 minutes and 20 minutes, respectively. The obtained results were the same as those of Example 6.
  • Anodizing electrolytic bath for producing colored aluminum or aluminum alloy which is an aqueous solution of 0.5 to 10% by weight of cresol sulfonic acid, 0.5 to 5.0% by weight of sulfosalicylic acid and 0.05 to 3.0% by weight of sulfuric acid or a metal sulfate in an amount equivalent to the concentration of said sulfuric acid.
  • metal sulfate is ferric sulfate, cobalt sulfate, manganese sulfate or nickel sulfate.
  • a method for producing a colored oxide coating on aluminum or aluminum alloy which comprises electrolytically anodizing aluminum or aluminum alloy in an electrolytic bath which is an aqueous solution of 0.5 to 10% by weight of cresolsulfonic acid, 0.5 to 5.0% by weight of sulfosalicylic acid and 0.05 to 3.0% by weight of sulfuric acid or a metal sulfate in an amount equivalent to the concentration of said sulfuric acid.
  • metal sulfate is ferric sulfate, cobalt sulfate, manganese sulfate or nickel sulfate.
  • a method for producing a cooled oxide coating on aluminum or aluminum alloy which comprises electrolytically anodizing aluminum or aluminum alloy in an aqueous solution of sulfuric acid or oxalic acid to form an oxide coating on the surface of said aluminum or aluminum alloy without sealing the pores of the oxide coating and then electrolytically anodizing said oxide coated aluminum or aluminum alloy in an electrolytic bath which is an aqueous solution of 0.5 to 10% by weight of cresol- 12 sulfonic acid, 0.5 to 5.0% by weight of sulfosalicylic acid and 0.05 to 3% by weight of sulfuric acid or a metal sulfate in an amount equivalent to the concentration of said sulfuric acid.
  • metal sulfate is ferric sulfate cobalt sulfate, manganese sulfate or nickel sulfate.
  • a method for producing a bronze colored oxide coating on aluminum or aluminum alloy which comprises electrolytically anodizing aluminum or aluminum alloy in an electrolytic bath which is an aqueous solution of 0.5 to 10% by weight of cresolsulfonic acid, 0.5 to 5.0% by weight of sulfosalicylic acid and 0.05 to 3.0% by weight of sulfuric acid or a metal sulfate in an amount equivalent to the concentration of said sulfuric acid and then immersing the thus treated aluminum or aluminum alloy in a 1 to 10% by weight aqueous solution of ammonium ferric oxalate.
  • metal sulfate is ferric sulfate, cobalt sulfate, manganese sulfate or nickel sulfate.

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US842959A 1968-07-18 1969-07-18 Electrolytic bath to be used for electrolytically anodizing aluminum or aluminum alloy to form a colored oxide coating and method for anodizing said metal Expired - Lifetime US3634214A (en)

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JP5044268 1968-07-18
JP5044368 1968-07-18
JP7583968 1968-10-19
JP2506869A JPS4813220B1 (fr) 1969-04-02 1969-04-02

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DE (1) DE1936702A1 (fr)
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GB1281941A (en) 1972-07-19
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