Method of providing a coloured, anodised aluminium surface

Abstract

A method of providing a workpiece with an anodised aluminium surface with varying colour. The anodised surface is added colour, such as evenly, so that a colour concentration profile exists through the depth, where after a portion of the outer layer is removed to arrive at colour corresponding to a particular depth.

Claims

1. A method of colouring an aluminium surface, the method comprising: anodising the aluminium surface to create an anodised surface layer, introducing a particular colouring agent into a porosity of the anodised surface layer to create a coloured anodised surface layer, the coloured anodised surface layer having a first area, removing at least a portion of the coloured anodised surface layer over a second area of at least 10% of the first area of the coloured anodised surface layer so that, outside of the second area, the coloured anodised surface layer has a first thickness and, within the second area, the coloured anodised surface layer has a second thickness being lower than the first thickness, characterized in that the removing step comprises retaining at least a portion of a thickness of the coloured anodised surface layer that includes the particular colouring agent over the second area, such that the particular colouring agent is present in both the first thickness of the coloured anodised surface layer outside of the second area, and the second thickness of the coloured anodised surface layer within the second area.

2. A method according to claim 1, wherein the removing step comprises removing the portion over no more than 80% of the first area.

3. A method according to claim 1, wherein the coloured anodised surface layer has a thickness of at least 8 μm.

4. A method according to claim 1, wherein the removing step comprises one or more of sanding, sand blasting, polishing, brushing, and/or buffing of a surface of the coloured anodised surface layer.

5. A method according to claim 1, wherein the removing step comprises operating a removal tool on the portion of the coloured anodised surface layer.

6. A method according to claim 1, wherein the introducing step comprises introducing the particular colouring agent with a lower concentration thereof at larger depths in the anodised surface layer than at lower depths.

7. A method according to claim 1, wherein the introducing step comprises not introducing the particular colouring agent to a deepest portion of the anodised surface layer.

8. A method according to claim 1, wherein the introducing step comprises forming, in the coloured anodised surface layer, a maximum concentration of the particular colouring agent and where, in the first area, a concentration of no more than 10% of the maximum concentration exists at a depth of more than 15 μm from a surface of the coloured anodised surface layer.

9. A method according to claim 1, wherein the introducing step comprises adding the particular colouring agent as a fluid.

10. A method according to claim 1, wherein the introducing step comprises: initially adding a first colouring agent into the porosity, subsequently adding a second colouring agent into the porosity.

11. A workpiece having an anodised aluminium surface having a first surface part and a second surface part, wherein: the first surface part takes up at least 10% of an area of the anodised aluminium surface, the anodised aluminium surface having, at the first surface part, a first amount of a particular colouring agent per unit of area and a first thickness of the anodised aluminium surface, the second surface part takes up at least 10% of the area of the anodised aluminium surface, the anodised aluminium surface having, at the second surface part, a second amount of the aluminium colouring agent per unit of area and a second thickness of the anodised aluminium surface, and the first amount is at least 1.1 times the second amount, and the first thickness is at least 1.1 times the second thickness, characterized in that the second surface part has anodised layer thereon, wherein the particular colouring agent is present in both the first thickness the anodised aluminium surface in the first surface part, and the second thickness the anodised a aluminium surface in the second surface part.

12. A workpiece according to claim 11, wherein the anodised aluminium surface has a thickness of at least 8 μm.

13. A workpiece according to claim 11, wherein, in the first surface part, the particular colouring agent has a lower concentration thereof at larger depths in the anodised aluminium surface than at lower depths.

14. A workpiece according to claim 11, having a maximum amount of the particular colouring agent and where, in the first surface part, an amount of no more than 10% of the maximum amount exists at a depth of no more than 15 μm from a surface of the anodised aluminium surface.

15. A workpiece according to claim 11, wherein a concentration of the particular colouring agent is zero in a deepest portion of the anodised aluminium surface.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the following, preferred embodiments of the invention will be described with reference to the drawing, wherein:

(2) FIG. 1 illustrates a coloured, anodised surface,

(3) FIG. 2 illustrates the surface of FIG. 1 with a portion thereof removed, and

(4) FIG. 3 illustrates the relative dye concentration in a workpiece seen in FIG. 1.

DETAILED DESCRIPTION

(5) In FIG. 1, a cross-section of a workpiece 10 with an anodised surface layer 12 extending a predetermined depth under which the aluminium material 14 is seen. The anodised layer 12 has been dyed or coloured with a colouring agent which is provided in the pores of the anodised layer 12.

(6) The colouring agent concentration may be more or less constant through the anodised layer 12. Alternatively, the colour agent concentration may exhibit a variation in the concentration from a higher concentration at the top portion (air interface) than at larger depths.

(7) In this embodiment, it is seen that the lowest portion 13 of the anodised surface layer 12 has not received any colouring agent or has received no discernible portion thereof. This has the advantage that the colour of the underlying material 14 may be obtained while still retaining a portion of the anodic film, retaining the surface properties of the anodised layer 12.

(8) An example of the dye or colour concentration as a function of the depth from the upper surface may be seen in FIG. 3.

(9) In FIG. 2, the workpiece 10 of FIG. 1 has been exposed to mechanical processing by which a portion of the anodised surface layer 12, the portion 12′ surrounded by the dashed line, has been removed, and hence also the dye that was imbedded within it. After this process it is seen that, as the anodic layer 12 is transparent or translucent, at the surface, different shades of colour are visible at different positions of the surface. An item will be lighter at one position because the sum of dye is smaller, and not necessarily because the concentration is lower at the surface. It is noted again that the colour at a position is the sum of the dye molecules in the depth direction. Thus, a surface with a colour gradient is obtained.

(10) It is noted that the anodised material in itself is transparent or translucent so that the colour obtained at a given position of the surface of the workpiece 10 is an integration or sum of the colour through the layer in the thickness direction.

(11) In the upper portions of FIGS. 1 and 2, the apparent colour is illustrated.

(12) The workpiece 10 may be obtained using any of the known anodising techniques, such as exposure to an acid and a current. Anodising increases the strength of the surface and protects the aluminium against corrosion but also opens the surface creating a porosity consisting mainly of parallel pores, perpendicular to the surface, arranged in a hexagonal pattern. This porosity may be utilized to dye or colour the surface, as is well known.

(13) Introducing a colour or dye onto or into the surface, such as by dipping, spraying or painting, will allow a portion of the colour or dye to enter into the anodised surface layer 12. Subsequently, the surface may be closed by e.g. turning the anodised layer into Boehmite by dipping into hot water, making the anodised material swell to a degree where the colour material is trapped in the swelled material.

(14) As mentioned, it may be desired that the colour or die is introduced into the anodised layer with a decreasing concentration in the depth direction. This concentration distribution or function of the colour agent in the layer may be adapted or defined in a number of ways. It is known that the pore size of an anodised surface may be defined by process parameters, such as the voltage applied, and the time spent during the oxidation step of anodising. Also, the actual depth of the anodised layer may be defined by these process parameters.

(15) In the same manner, the penetration of the dye or colouring agent into the porous anodic layer may be defined or controlled, such as by selecting a colour or dye with a larger or smaller molecule size in a more or less viscous liquid, by dyeing at a higher or lower temperatures, at higher or lower dye or colour agent concentrations and even with a lower or higher pressure and flow.

(16) Having now provided a material with colouring agent in its porosity, e.g. dye, pigments, particles etc., portions of the layer may be removed to arrive at a workpiece 10 where portions of the outer surface is lighter in appearance and/or with a different hue/tone (less colouring agent and with larger colour contribution from the underlying material—typically Aluminium), corresponding to lesser amount of colouring agent because said colouring agent has been removed by a post-anodising process.

(17) It may be desired to have the thickness of the anodic layer portion in which colour resides be rather thin, i.e. that the colour has not penetrated too far into the anodised material. In this way, the work required to remove a majority of the perceived colour, such as to arrive at a colour close to that of Aluminium, will be smaller than if the colouring agent had reached deeper into the anodic film.

(18) Removal of the material 12′ may be performed in any desired manner. Milling, sanding, sand blasting or the like may be used. Preferably, the anodised layer has a thickness of 15-30 μm, so that a rather gentle process may be used which does not remove too much material too swiftly. Polishing, for example, may be used.

(19) It may be desired that the lowest or deepest layer 13 of the anodised material does not receive any colour or only an insignificant amount of colour, so that all of the coloured material may be removed to arrive at the colour of the anodised aluminium—while the remaining oxide layer has at least a minimum thickness such that satisfactory surface protection is retained.

(20) Clearly, it would be possible to introduce multiple dyes into the anodised layer. A gradual change from one perceived colour at a specific location on the surface to another perceived colour at another location on the surface is then possible if the two or more different colouring agents, dyes or colours, have reached different depths within the anodised layer. The original colour perceived when looking at the original anodised and dyed surface will be a mix of the dyes used. Removing an increasing amount of oxide from the top will remove an increasing amount of the colouring agent at the outermost portions and thus reveal an increasingly larger proportion of the colouring agent that penetrated deepest into the oxide.

(21) If the anodised and porous surface is exposed to a mix of dyes, by dipping or colouring, consisting of molecules with large differences in their ability to diffuse and/or bind, those dye molecules with highest binding affinity and highest rates of diffusion will penetrate deepest into the oxide. The molecule size difference can also be exploited: larger dye molecules will likely diffuse at different rates compared to smaller molecules, reaching different depths in the anodic film.

(22) Another method could be to first dye with one dye for a prolonged time achieving a relatively deep penetration and then dye with a second dye for a shorter time, achieving a mix of dyes near the air-oxide interface with a larger proportion of the first dye at greater depths. Rinsing between the two dyeing steps, so as to remove at least a portion of the first dye at the outermost layers, could help achieve a better layering of dyes.

(23) A third method could be to use electrolytic colouring first which forces the inorganic dye molecules into the bottom of the pores and subsequently dyeing with organic dye molecules. The penetration depth of the latter is, as previously mentioned, controlled by diffusion, and hence the organic dye molecules will not reach as deep as the electrolytic colouring, depending on the dye solution concentration, temperature and exposure time.

(24) A colouring agent may alternatively be allowed to enter farther into the porosity if an increased pressure is used for forcing the colour into the porosity, or if the temperature is higher, often lowering the viscosity, for example. In addition, as the colouring of the porosity often is an adsorption of colouring agent in the porous structure, the porosity may itself be lowered when the second colour is to be introduced into the structure, which in itself would act to prevent the second colour from reaching as deeply into the structure.

(25) Then, the first colour, defining a decrease in porosity, may act to inhibit or make difficult the introduction of the second colour to a depth past that in which the first colour is left.