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
  • C25D11/18—After-treatment, e.g. pore-sealing
  • C25D11/24—Chemical after-treatment
  • C25D11/246—Chemical after-treatment for sealing layers
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D5/00—Processes for applying liquids or other fluent materials to surfaces to obtain special surface effects, finishes or structures
  • B05D5/06—Processes for applying liquids or other fluent materials to surfaces to obtain special surface effects, finishes or structures to obtain multicolour or other optical effects
  • B05D5/067—Metallic effect
• • 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
  • C25D11/24—Chemical after-treatment
  • C25D11/243—Chemical after-treatment using organic dyestuffs
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D2202/00—Metallic substrate
  • B05D2202/20—Metallic substrate based on light metals
  • B05D2202/25—Metallic substrate based on light metals based on Al
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D3/00—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials
  • B05D3/10—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials by other chemical means
  • B05D3/102—Pretreatment of metallic substrates

Definitions

• the present invention relates to the correction of a surface color modification caused by anodizing certain aluminum alloys and more particularly to a method of neutralizing said color modification with a dye containing sealing solution.
• a known method to eliminate or reduce this undesired cast is to lower the current density during anodizing to a level whereby the cast is diminished. This method has the disadvantages of slowing production and producing an anodic coating of inferior corrosion resistance.
• the aluminum surface instead of anodizing it.
• the aluminum is to be used for automobile bumpers, for example, it can be electroplated with nickel and chromium. Electroplating, however, is expensive and the corrosion resistance of the resulting surface is unpredictable.
• anodized aluminum is colored by applying an ink composition consisting essentially of a water soluble organic hydroxy compound having a boiling point greater than 212F., a coloring material dissolved therein. a viscosity control agent compatible with and chemically inert toward the remaining constituents in the composition and a finely divided filling agent consisting of porous particles of solid. inorganic pigment which also is chemically inert toward the remaining constituents in the composition.
• the aluminum workpiece Prior to anodizing, the aluminum workpiece can be chemically brightened if desired.
• the workpiece then is anodized at a current density sufficient to produce an anodic coating having good corrosion resistance. It is preferred to anodize at a current density between about 12 and 24 amperes per square foot for about 15 to 30 minutes. If the anodizing step causes an undesired cast to be imparted to the anodized surface, a dye is selected to neutralize that cast.
• Dyes having the color characteristics necessary to neutralize the undesired cast are selected on the basis of a color system such as the Munsell color system.
• a color system such as the Munsell color system.
• the hue corresponding to the undesired cast is found on the hue Munsell color circle.
• the color opposite the position, on that circle. of said corresponding hue, i.e. from that position, is normally the neutralizing color.
• a dye having said neutralizing color then is selected.
• Suitable dyes include the monoazo acid metallized type, among others.
• each dye must be tested to determine which dyes of those selected will not leave a color of their own'in the anodized surface. Testing may be carried out on a laboratory scale by contacting samples of anodized aluminum having the undesired cast with aqueous sealing solutions containing the individual dyes. (The composition of said solutions is defined below. The sealed samples are visually inspected and the specific dye or dyes that yield best results are thereby selected.
• the specific dye is added in a concentration of between about 3 and 30 milligrams per liter to water, thus making-up the aqueous sealing solution.
• Scaling accelerators such as metallic salts, for example. Co or Ni salts, can be added to the solution.
• the use of accelerators makes color control difficult. lt is critical that the concentration of the dye is below the value that would cause coloring of the anodized surface and is at or above the value necessary to effect neutralization of the undesired cast. Minor variations will easily establish the optimum concentration range for the specific dye. In a continuous process, the optimum concentration range is maintained with the aid of a colorimeter or spectrophotometer.
• the pH must be between about 5.5 and 6.5. Selection of a pH value is based on the desired rate of sealing. Sealing rate decreases with increased acidity. Once a pH value is selected, it must be controlled to i(). l. Sodium hydroxide or acetic acid is used to control the pH.
• the temperature of the solution must be maintained at a value sufficient to effect sealing of the anodized surface.
• a temperature between about l 80 and 2l0F. is selected and maintained at 5F.
• Sealing according to the present invention is effected by contacting the anodized aluminum with the dyecontaining sealing solution for about to 30 minutes.
• EXAMPLE A high strength aluminum alloy utilized in the manufacture of bumpers for automobiles was chemically brightened by a conventional process.
• the alloy had the following composition: 1.0 percent magnesium, 0.8 percent copper, 4.5 percent Zinc, less than 0.1 percent iron, less than 0.1 percent silicon, 0.05 percent titanium and the balance; high purity aluminum ingot.
• Anodizing was effected at a standard current denisty of 14 amperes per square foot until the anodic coating was between about 0.0004 and 0.0005 inch thick.
• the anodized product had an undesired yellow cast.
• a sealing solution having a dye concentration of about 15 milligrams per liter was maintained at a pH between 5.6 and 5.7, with sodium hydroxide and acetic acid.
• a sealing solution temperature of about 205 i 5F. was used.
• the anodized alloy was immersed in the solution for IS minutes.
• aluminum black V also known as acid black 52, a monoazo metallic dye having the chemical formula: N O SC H -xCr-Na and a color index of l5,7l I
• a method of neutralizing an undesired cast appearing in an anodized surface of an aluminum alloy by sealing said anodized surface with an aqueous solution containing a monoazo metallic dye of a color and in a concentration sufficient to neutralize said unde-, sired cast without imparting the dye color to said anodized surface wherein said solution is maintained at a pH necessary for optimum sealing and dye absorption and at a temperature between about and 2 l0 i 0.5F.
• said aluminum alloy is chemically brightened 'prior to anodizing.
• a method of neutralizing a yellow cast appearing in an anodized surface of a copper-containing aluminum alloy by sealing said anodized surface for about 15 minutes in an aqueous solution containing about 15 milligrams per liter of a monoazo metallic dye to neutralize said yellow east, wherein said solution is maintained at a pH between about 5.6 and 5.7 and at a ,tem

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• Chemical & Material Sciences (AREA)
• General Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Chemical Treatment Of Metals (AREA)
• Electrochemical Coating By Surface Reaction (AREA)

Priority Applications (9)

Applications Claiming Priority (1)

Publications (1)

Family

ID=23882228

Family Applications (1)

Country Status (9)

Cited By (1)

Citations (5)

• 1974
  • 1974-05-28 US US47411374 patent/US3874902A/en not_active Expired - Lifetime
• 1975
  • 1975-02-28 CA CA220,999A patent/CA1050211A/en not_active Expired
  • 1975-03-06 BR BR7501330A patent/BR7501330A/pt unknown
  • 1975-03-08 DE DE19752510246 patent/DE2510246A1/de active Pending
  • 1975-03-12 FR FR7507665A patent/FR2273088B1/fr not_active Expired
  • 1975-03-18 GB GB1116775A patent/GB1437709A/en not_active Expired
  • 1975-03-20 IT IT4868675A patent/IT1032374B/it active
  • 1975-04-15 JP JP4575275A patent/JPS5530079B2/ja not_active Expired
  • 1975-05-13 SE SE7505484A patent/SE7505484L/xx unknown

Patent Citations (5)

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