Metal treatment – Process of modifying or maintaining internal physical... – Processes of coating utilizing a reactive composition which...
Reexamination Certificate
2001-08-27
2003-11-25
Sheehan, John P. (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Processes of coating utilizing a reactive composition which...
C148S243000, C148S275000, C148S276000, C148S285000, C428S472300, C427S343000, C427S419300, C205S102000, C205S148000, C205S149000, C205S201000, C205S324000
Reexamination Certificate
active
06652669
ABSTRACT:
The present invention relates to a method for producing an ultraphobic surface on aluminum as support material, and to the surface obtained thereby and to its use. In the method, the surface of an aluminum support, optionally electrochemically pickled in acidic solution with alternating voltage, is anodized, in particular by anodic oxidation, treated in hot water or water vapor at a temperature of from 50 to 100° C., optionally coated with an adhesion promoter layer and then provided with a hydrophobic or, in particular, oleophobic coating.
Ultraphobic surfaces are characterized by the fact that the contact angle of a drop of liquid, usually water, on the surface is significantly more than 90° and that the roll-off angle does not exceed 10°. Ultraphobic surfaces having a contact angle of>150° and the abovementioned roll-off angle have a very great technical advantage because, for example, they are not wettable with water or with oil, soil particles adhere to these surfaces only very poorly and these surfaces are self-cleaning. Here, self-cleaning means the ability of the surface to readily give up soil or dust particles adhering to the surface to liquids which flow over the surface.
There has therefore been no lack of attempts to provide such ultraphobic surfaces. For example, EP 476 510 A1 discloses a method for producing an ultraphobic surface in which a metal oxide film is deposited on a glass surface and is then etched using an Ar plasma. However, the surfaces produced using this method have the disadvantage that the contact angle of a drop on the surface is less than 150°. U.S. Pat. No. 5,693,236 also discloses a plurality of methods for producing ultraphobic surfaces, in which zinc oxide microneedles are applied to a surface using a binder and are then partially uncovered in various ways (e.g. by plasma treatment). The surface structured in this way is then coated with a water-repelling composition. However, surfaces structured in this way likewise only have contact angles of around up to 150°.
The object was therefore to provide ultraphobic surfaces and a method for their production which have a contact angle of≧150°, and preferably a roll-off angle of ≦10°.
Here, the roll-off angle is the angle of inclination of a fundamentally planar but structured surface toward the horizontal at which a stationary drop of water of volume 10 &mgr;l is moved as a result of the gravitational force when the surface is inclined.
The object is [lacuna] according to the invention by the provision of a method for producing an ultraphobic surface on aluminum as support material, characterized in that the surface of an aluminum support is anodized, in particular by anodic oxidation, treated in hot water or water vapor at a temperature of from 50 to 100° C., optionally coated with an adhesion promoter layer and then provided with a hydrophobic or, in particular, oleophobic coating.
For the purposes of the invention, an aluminum surface is the surface of any molding made of aluminum or made of an alloy based on aluminum, and the surface of a molding made of any material to which an aluminum layer or a layer of an alloy based on aluminum has been applied, preferably by vapor deposition. A preferred aluminum-based alloy is AlMg
3
.
A preferred alternative of the method is characterized in that, prior to the water or water vapor treatment and/or optionally the anodic oxidation in an aqueous acidic solution (≦pH 5), the surface is exposed to an electrical alternating voltage of >5 volts over a period of at least 5 sec, it also being possible for the water or water vapor treatment to be dispensed with.
The current density during the alternating voltage treatment is particularly preferably greater than 1 mA/cm
2
.
In one variant of the method, prior to the water or water vapor treatment and/or prior to the anodic oxidation and/or prior to the alternating voltage treatment, the surface is advantageously exposed to an alkaline aqueous solution (pH≧9) for at least 10 sec.
This aluminum surface is optionally anodically oxidized. The anodic oxidation is preferably carried out in 0.6 to 1.4 n, particularly preferably 0.9 to 1.1 n, sulfuric acid, chromic acid, oxalic acid, phosphoric acid or mixture thereof, preferably with continuous electrolyte motion under, preferably, laminar flow conditions. The electrolyte temperature is preferably 16 to 24° C., particularly preferably 19 to 21° C. The counterelectrode used is preferably an AlMg
3
medium-hard electrode. The distance of this electrode from the aluminum surface is preferably 3 to 7 cm, particularly preferably 4 to 6 cm. The current density during the oxidation is preferably adjusted to 5 to 15 mA/cm
2
, particularly preferably to 9 to 11 mA/cm
2
.
After the anodic oxidation or as the first method step, the aluminum surface is sealed with hot water or water vapor. For this purpose, the surface is exposed to hot water or water vapor at 50 to 100° C. The water or the water vapor preferably has a temperature of from 90 to 100° C. The surface is likewise preferably sealed with hot water for 300 to 1000 seconds, very particularly preferably 500 to 800 seconds. Following the treatment with hot water or water vapor, the sample is preferably dried at a preferred temperature range from 70 to 90° C. for preferably 40 to 80 minutes.
The person skilled in the art knows that the hot-water treatment can also be carried out with a water/solvent mixture, in which case the surface is then preferably exposed to the vapor mixture.
After the treatment with hot water or water vapor, the surfaces thus obtained are provided with a hydrophobic or, in particular, oleophobic coating.
For the purposes of the invention, a hydrophobic material is a material which, on a level unstructured surface, has a contact angle based on water of greater than 90°.
For the purposes of the invention, an oleophobic material is a material which, on a level unstructured surface, has a contact angle based on long-chain n-alkanes, such as n-decanè, of greater than 90°.
The ultraphobic surface preferably has a coating with a hydrophobic phobicization auxiliary, in particular an anionic, cationic, amphoteric or nonionic, surface-active compound.
Compounds to be regarded as phobicization auxiliaries are surface-active compounds of any molar mass. These compounds are preferably cationic, anionic, amphoteric or nonionic surface-active compounds, as listed, for example, in the directory “Surfactants Europa, A Dictionary of Surface Active Agents available in Europe, edited by Gordon L. Hollis, Royal Socity of Chemistry, Cambridge, 1995.
Examples of anionic phobicization auxiliaries are: alkylsulfates, ether sulfates, ether carboxylates, phosphate esters, sulfosucinates, sulfosuccinate amides, paraffinsulfonates, olefinsulfonates, sarcosinates, isothionates, taurates and lingnin-based compounds.
Examples of cationic phobicization auxiliaries are quaternary alkylammonium compounds and imidazoles.
Amphoteric phobicization auxiliaries are, for example, betaines, glycinates, propionates and imidazoles.
Examples of nonionic phobicization auxiliaries are: alkoxylates, alkyloamides, esters, amino oxides and alky polyglycosides. Also suitable are: reaction products of alkylene oxides with alkylatable compounds, such as, for example, fatty alcohols, fatty amines, fatty acids, phenols, alkylphenols, arylalkylphenols, such as styrene/phenol condensates, carboxamides and resin acids.
Particular preference is given to phobicization auxiliaries in which 1 to 100%, particularly preferably 60 to 95%, of the hydrogen atoms are substituted by fluorine atoms. Examples which may be mentioned are perfluorinated alkylsulfate, perfluorinated alkylsulfonates, perfluorinated alkylphosphonates, perfluorinated alkylphosphinates and perfluorinated carboxylic acids.
As polymeric phobicization auxiliaries for the hydrophobic coating or as polymeric hydrophobic material for the surface, preference is given to compounds with a molar mass M
w
>500 to 1,000,000, preferably 1000 to 500,000 and particularly prefe
Duff Daniel-Gordon
Gonzalez-Blanco Juan
Koehler Burkhard
Reihs Karsten
Voetz Matthias
Ohmans Andrew L.
Sheehan John P.
Sunyx Surface Nanotechnologies GmbH
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