Patent GB-1069168-A (GB)
Title: Composite coated aluminium articles
IPC: C25D11/06
Filed: 1964-10-30
Abstract: A process for producing a composite coated aluminium article having an aluminium base, an intermediate layer of aluminium oxide and an outer layer of a fluorinated hydrocarbon polymer comprises (1) cleaning the surface of an aluminium substrate, (2) anodically oxidizing the cleaned substrate in an aqueous electrolyte containing from 15 to 18 ounces per gallon of sulphuric acid at a temperature from 25 DEG  to 40 DEG F., at least 1 cubic foot of air per gallon of electrolyte per minute being passed through the electrolyte, the impressed voltage between the cathode and the aluminium anode being from 24 to 90 volts and the anode current density from 25 to 60 amps per square foot, the oxidation being continued until the oxide layer is at least 0.0005 ins. thick, (3) immersing the oxidized aluminium in an aqueous suspension of a fluorinated hydrocarbon polymer, the particles of said polymer being up to 2 microns in diameter, the suspension being at a temperature of at least 140 DEG F., until the polymer fills the interstices of the oxide layer and forms an outer coating at least 0.0001 in. thick.  The cleaning step may comprise immersion in a hot sodium hydroxide solution followed by immersion in a chromic acid-nitric acid aqueous solution followed by rinsing.  The anodizing bath may also contain a carboxylic acid, such as oxalic acid, malonic acid or succinic acid. A sugar, for example, sucrose, may also be added.  The fluorinated hydrocarbon polymer may be polytetrafluoroethylene or tetrafluoropolyethylenehexafluoropolypropylene copolymer.  The coated article is air dried and may subsequently be baked. Additional thicknesses of the fluorinated hydrocarbon may then be applied by spraying. Examples are given of coating an aluminium plate and an aluminium frying pan.ALSO:A process for producing a composite coated aluminium article having an aluminium base, an intermediate layer of aluminium oxide and an outer layer of a fluorinated hydrocarbon polymer comprises (1) cleaning the surface of an aluminium substrate, (2) anodically oxidising the cleaned substrate in an aqueous electrolyte containing from 15 to 18 ounces per gallon of sulphuric acid at a temperature from 25 DEG  to 70 DEG F., at least 1 cubic foot of air per gallon of electrolyte per minute being passed through the electrolyte, the impressed voltage between the cathode and the aluminium anode being from 24 to 90 volts and the anode current density from 25 to 60 amps perr square foot, the oxidation being continued until the oxide layer is at least 0.0005 ins. thick, (3) immersing the oxidised aluminium in an aqueous suspension of a fluorinated hydrocarbon polymer, the particles of said polymer being up to 2 microns in diameter, the suspension being at a temperature of at least 140 DEG F., until the polymer fills the interstices of the oxide layer and forms an outer coating at least 0.0001 in. thick. the cleaning step may comprise immersion in a hot sodium hydroxide solution followed by immersion in a chromic acid-nitric acid aqueous solution followed by rinsing.  The anodising bath may also contain a carboxylic acid, such as oxalic acid, malonic acid or succinic acid. A sugar, for example, sucrose, may also be added.  The fluorinated hydrocarbon polymer may be polytetrafluoroethylene or tetrafluoropolyethylenehexafluoropolypropylene copolymer.  The caoted article is air dried and may subsequently be baked. Additional thicknesses of the fluorinated hydrocarbon may then be applied by spraying.  Examples are given of coating an aluminium plate and an aluminium frying pan.