Removable anodising agent, in particular for local anodic oxidation of metal surfaces

Abstract

The invention relates to a removable anodizing agent, in particular for local anodic oxidation of metal surfaces, and its use, and a method for anodic oxidation by means of an anodizing agent according to the invention.

Claims

1. A removable anodising agent for anodic oxidation of a metal surface comprising: an anodising compound comprising: an inner layer and an outer adhesion promoting layer oriented towards the metal surface, the outer adhesion promoting layer having a composition different from the inner layer; an ion conducting medium containing an ion conducting component and an adhesion component, the adhesion component being in an amount selected for increasing adhesion of the anodizing agent to the metal surface prior to anodic oxidation; and one or a plurality of cohesion agents in sufficient concentration in order to allow a substantially residue-free removal of the anodising agent from the anodically oxidised metal surface; and an electrically conductive planar structure in contact with the anodising compound as the cathode; wherein the adhesion component contains a lactic acid; and wherein the anodising compound has a proportion of the ion conducting medium to the one or the plurality of cohesion agents adjusted relative to a composition and a nature of the metal surface for removal of the anodising compound including the outer adhesion-promoting layer for the substantially residue-free removal of the anodising agent from the anodically oxidised metal surface.

2. Anodising agent according to claim 1, characterized in that the cohesion agent is a water-soluble polymer or the cohesion agents are water-soluble polymers.

3. Anodising agent according to claim 2, wherein the water-soluble polymer(s) is (are) selected from the group consisting of a polyvinyl alcohol; a polysaccharide; and a polysaccharide derivative.

4. Anodising agent according to claim 3, wherein the polysaccharide derivative is selected from the group consisting of a cellulose derivative, a partially hydrolysed polyvinyl ester, a polyacrylate, a polyacrylic acid, a polyvinylpyrrolidone, a polymethacrylate, a polyamine, and a polyether.

5. Anodising agent according to claim 1, characterized in that the electrically conductive planar structure is selected from among a metal weave, a metal film, a metal net, a metal grid, a perforated sheet, a textile fabric in carbon fibers, a conductive polymer film, a metalised plastic and a metalised plastic film.

6. Anodising agent according to claim 5, further comprising: a carrier, which is in contact with the electrically conductive planar structure; wherein the carrier is selected from a weave, a fleece, a felt, a metal film and a polymer film; and wherein the anodising compound further contains one or a plurality of humectants to keep the anodising compound moist.

7. Anodising agent according to claim 1, further comprising a carrier, which is in contact with the electrically conductive planar structure.

8. Anodising agent according to claim 7, characterized in that the carrier is selected from a weave, a fleece, a felt, a metal film and a polymer film.

9. Anodising agent according to claim 1, characterized in that the anodising compound further contains one or a plurality of humectants to keep the anodising compound moist.

10. Anodising agent according to claim 1, wherein the ion conducting medium further contains at least one of a phosphoric acid, a sulfuric acid, a glycolic acid, an oxalic acid, a tartaric acid, and a citric acid.

11. Anodising agent according to claim 1 wherein anodising compound has the proportion of the ion conducting medium to the one or the plurality of cohesion agents adjusted relative to the composition and the nature of the metal surface for self-adhesion of the anodizing agent to the metal surface prior to and during anodic oxidation of the metal surface.

12. An anodising system comprising: a metal surface; and an anodising agent disposed on the metal surface; wherein the anodising agent comprises an anodising compound and an electrically conductive planar structure, the anodising compound being disposed between the metal surface and the electrically conductive planar structure, the anodising compound being in contact with the electrically conductive planar structure, and the electrically conductive planar surface being disposed separate from the metal surface; wherein the anodising compound comprises: an ion conducting medium containing an ion conducting component and an adhesion component, the adhesion component being in an amount selected for adhesion of the anodising agent to the metal surface; and one or a plurality of cohesion agents in sufficient concentration for substantially residue-free removal of the anodising agent from the metal surface following anodic oxidation of the metal surface; wherein the adhesion component is a lactic acid; and wherein the anodising compound comprises an inner layer and an outer adhesion promoting layer oriented towards the metal surface, the outer adhesion layer having a composition different from the inner layer.

13. The anodising system of claim 12, wherein following removal of the anodizing agent from the metal surface, a thickness of a layer of the anodising compound remaining on the metal surface is an average amount of 1 m.

14. The anodising system of claim 12, wherein the anodising compound has a proportion of the ion conducting medium to the one or the plurality of cohesion agents adjusted relative to a composition and a nature of the metal surface for removal of the anodising compound including the outer adhesion-promoting layer for a substantially residue-free removal of the anodising agent from the anodically oxidised metal surface.

Description

EXEMPLARY EMBODIMENT

(1) The invention is described in more detail in the following using the exemplary embodiment and the figures, without these restricting the scope of protection of the claims.

(2) The figures show as follows:

(3) FIG. 1 a schematic representation of a preferred embodiment of the anodising agent according to the invention and its use in a method according to the invention for anodic oxidation of a metal surface;

(4) FIG. 2a a scanning electron microscope image of the surface of a test substrate in aluminium AA1050A oxidised using the anodising agent according to the invention from FIG. 1 (top view);

(5) FIG. 2b a scanning electron microscope image of the surface of a test substrate in aluminium AA1050A oxidised using the anodising agent according to the invention from FIG. 1 (surface of a cryo-rupture).

(6) The preferred embodiment shown schematically in FIG. 1 of the anodising agent according to the invention 1 comprises: an anodising compound 2; an electrically conductive planar structure 3 as the cathode; a carrier 4.

(7) Reference numeral 5 identifies the surface to be oxidised, and reference numeral 6 a direct voltage source.

(8) For production of the anodising compound 2 the following solutions 48.8 g polyvinyl alcohol solution (Mowiol 10-98, Ter Hell, 20 wt. % in water); 9.9 g polyacrylic acid solution (AC7592, Alberdingk Boley, 47 wt. % in water); 9.8 g lactic acid (87% wt. % in water) and 48.4 g phosphoric acid (40 wt. % in water)

(9) are homogenously mixed. The mixture obtained is applied in liquid form to an electrically conductive planar structure 3 in the form of a net in high-alloy steel (area 25 mm25 mm, height 0.5 mm, mesh width 0.5 mm), which has first been placed on a carrier 4 in the form of a polyethylene terephthalate film with a thickness of 100 m, and then allowed to dry. The weight loss occurring through drying is approximately 50 wt. %, in relation to the weight of the mixture applied to the net. Following drying (3 days at 23 C. and 50% relative humidity) the thickness of the anodising agent formed in this way is approximately 2 mm. The steel net 3 is approximately 1 mm below the surface of the anodising compound 2, that is to say that the thickness of the anodising compound protruding beyond the steel net is approximately 1 mm. The specific electrical volume conductivity of the anodising compound 2 is approximately 60 S/m. The anodising compound 2 is self-adhesive to the surface 5 to be anodically oxidised.

(10) The anodising agent 1 according to the invention created in this way is bonded to the surface 5 to be anodically oxidised of an object, e.g. a test substrate of aluminium AA1050A, so that the anodising compound 2 of the anodising agent 1 covers the metal surface 5 to be anodically oxidised and the electrically conductive planar structure 3 of the anodising agent 1 does not touch the metal surface 5 to be anodically oxidised.

(11) The metal surface 5 to be anodically oxidised of the test substrate of aluminium AA1050A and the steel net 3 of the anodising agent according to the invention are connected to a direct voltage source 6, wherein the metal surface 5 to be anodically oxidised is connected as an anode and the steel net 3 of the anodising agent 1 is connected as a cathode. For anodisation of the surface of the test substrate a direct voltage in the range 6 to 10 V is applied for 15 minutes.

(12) Following anodisation the anodising agent according to the invention can be removed from the substrate without leaving residues. Scanning electron microscope images of the anodically oxidised surface of the test substrate show a layer of aluminium oxide with a porous structure typical of anodised layers (FIGS. 2a and 2b). The thickness of the aluminium layer is approximately 300 nm (FIG. 2b).