Process for electrolytic coloration of anodized aluminium

Claim 1

A method of producing a colored anodized aluminum strip which comprises drawing aluminum in strip form successively through an anodizing stage and an electrolytic coloring stage comprising in the anodizing stage moving the strip successively past one or more anodes immersed in a sulphuric acid anodizing electrolyte and past one or more cathodes and passing direct current between said cathodes and said anodes through the strip so as to render the strip initially cathodic and subsequently anodic to develop an anodic oxide film on the surface thereof, the thus anodized strip being then passed through, in said electrolytic coloring stage, an acidic electrolyte containing a material selected from a salt of at least one of copper, tin, cobalt, nickel, chromium, iron, silver or lead, or a manganate, tellurite or selenite, and passing alternating current between at least one electrode immersed in said acidic electrolyte and said anodized strip, the circuit for said alternating current being completed through an electrode immersed in the electrolyte of the direct current anodizing stage.

Claim 2

A method of producing a colored anodized aluminum strip which comprises drawing aluminum in strip form successively through an anodizing stage and an electrolytic coloring stage comprising in the anodizing stage moving the strip successively past one or more anodes immersed in a sulphuric acid anodizing electrolyte and past one or more cathodes and passing direct current between said cathodes and said anodes through the strip so as to render the strip initially cathodic and subsequently anodic to develop an anodic oxide film on the surface thereof, the thus anodized strip being then passed through, in said electrolytic coloring stage, an acidic electrolyte containing a material selected from a salt of at least one of copper, tin, cobalt, nickel, chromium, iron, silver or lead, or a manganate, tellurite or selenite, and passing alternating current between at least one electrode immersed in said acidic electrolyte and said anodized strip, the circuit for said alternating current being completed through an electrode immersed in the electrolyte of the direct current anodizing stage.

Claim 5

A method of producing a colored anodized aluminum strip which comprises drawing aluminum in strip form successively through an anodizing electrolyte and an acidic coloring electrolyte containing a material selected from a salt of at least one of copper, tin, cobalt, nickel, chromium, iron, silver or lead or a manganate, tellurite or selenite, passing direct current between said strip and at least one cathode immersed in said anodizing electrolyte, direct current being introduced into said strip through an electrical contact at a location where said strip is substantially unanodized and passing alternating current between the anodized strip and at least one electrode immersed in the coloring electrolyte, the circuit for the alternating current being completed by contact with a substantially unanodized area of the surface of the aluminum strip to generate an asymmetric current wave form; the unanodized strip, before entry into the anodization stage, being in contact with a contact roll connected to the positive terminal of said direct current supply and an alternating current source being connected between said contact roll and the electrode in the coloring electrolyte; diode branches in parallel being included in the connection between the contact roll and the coloring electrolyte electrode, the diodes in said branches being conductive in opposite directions, the voltage drops across said diode branches when conductive being unequal whereby to generate an asymmetrical alternating current.

Claim 6

A method of producing a colored anodized aluminum strip which comprises drawing aluminum in strip form successively through an anodizing electrolyte and an acidic coloring electrolyte containing a material selected from a salt of at least one of copper, tin, cobalt, nickel, chromium, iron, silver or lead or a manganate, tellurite or selenite, passing direct current between said strip and at least one cathode immersed in said anodizing electrolyte, direct current being introduced into said strip through an electrical contact at a location where said strip is substantially unanodized and passing alternating current between the anodized strip and at least one electrode immersed in the coloring electrolyte, the circuit for the alternating current being completed by contact with a substantially unanodized area of the surface of the aluminum strip to generate an asymmetric current wave form; the unanodized strip, before entry into the anodization stage, being in contact with a contact roll connected to the positive terminal of said direct current supply and an alternating current source being connected between said contact roll and the electrode in the coloring electrolyte; diode branches in parallel being included in the connection between the contact roll and the coloring electrolyte electrode, the diodes in said branches being conductive in opposite directions, the voltage drops across said diode branches when conductive being unequal whereby to generate an asymmetrical alternating current.

Claim 7

A method of producing a colored anodized aluminum strip which comprises drawing aluminum in strip form through an anodizing stage, contacting the strip with a sulphuric acid electrolyte in said anodizing stage, said strip being drawn successively past at least one anode electrode and at least one cathode electrode, a D.C. power source being established between said anode electrode and said cathode electrode whereby said strip in rendered initially cathodic and subsequently anodic during its passage through said anodizing stage, advancing the thus anodized strip to and through an electrolytic coloring stage, contacting said strip with an acidic electrolyte containing a material selected from a salt of at least one of copper, tin, cobalt, nickel, chromium, iron, silver or lead or a manganate, tellurite or selenite and establishing an A.C. power source between said anode electrode in said anodizing stage and a counterelectrode in contact with the electrolyte in the electrocoloring stage thereby to establish alternating current with a superimposed D.C. current component flowing between said anodized strip and said counterelectrode in the electrocoloring stage.

Claim 8

A method of producing a colored anodized aluminum strip which comprises drawing aluminum in strip form through an anodizing stage, contacting the strip with a sulphuric acid electrolyte in said anodizing stage, said strip being drawn successively past at least one anode electrode and at least one cathode electrode, a D.C. power source being established between said anode electrode and said cathode electrode whereby said strip in rendered initially cathodic and subsequently anodic during its passage through said anodizing stage, advancing the thus anodized strip to and through an electrolytic coloring stage, contacting said strip with an acidic electrolyte containing a material selected from a salt of at least one of copper, tin, cobalt, nickel, chromium, iron, silver or lead or a manganate, tellurite or selenite and establishing an A.C. power source between said anode electrode in said anodizing stage and a counterelectrode in contact with the electrolyte in the electrocoloring stage thereby to establish alternating current with a superimposed D.C. current component flowing between said anodized strip and said counterelectrode in the electrocoloring stage.

Claim 10

A method of producing a colored anodized aluminum strip which comprises drawing aluminum in strip form successively through an anodizing electrolyte and an acidic coloring electrolyte containing a material selected from a salt of at least one of copper, tin, cobalt, nickel, chromium, iron, silver or lead or a manganate, tellurite or selenite, passing direct current between said strip and at least one cathode immersed in said anodizing electrolyte, direct current being introduced into said strip through an electrical contact at a location where said strip is substantially unanodized and passing alternating current between the anodized strip and at least one electrode immersed in the coloring electrolyte, the circuit for the alternating current being completed by contact with a substantially unanodized area of the surface of the aluminum strip to generate an asymmetric current wave form; the alternating-current-passing step comprising passing alternating current through the strip between at least one electrode immersed in the coloring electrolyte and out of contact with said strip and at least one electrode immersed in the anodizing electrolyte and facing a substantially unanodized area of said strip.

Claim 11

A method of producing a colored anodized aluminum strip which comprises drawing aluminum in strip form successively through an anodizing electrolyte and an acidic coloring electrolyte containing a material selected from a salt of at least one of copper, tin, cobalt, nickel, chromium, iron, silver or lead or a manganate, tellurite or selenite, passing direct current between said strip and at least one cathode immersed in said anodizing electrolyte, direct current being introduced into said strip through an electrical contact at a location where said strip is substantially unanodized and passing alternating current between the anodized strip and at least one electrode immersed in the coloring electrolyte, the circuit for the alternating current being completed by contact with a substantially unanodized area of the surface of the aluminum strip to generate an asymmetric current wave form; the alternating-current-passing step comprising passing alternating current through the strip between at least one electrode immersed in the coloring electrolyte and out of contact with said strip and at least one electrode immersed in the anodizing electrolyte and facing a substantially unanodized area of said strip.