Highly reflecting anodised al surfaces with tailored diffuse and specular content

Abstract

The present invention relates to a method to obtain a reflective anodized aluminium surface on an object. The present invention relates in particular to a method to obtain a reflective, anodized aluminium surface having a white appearance.

1 .- 15 . (canceled) 
     
     
         16 . A method to obtain a reflective anodized aluminium surface on an object, comprising the steps:
 a. Providing the object with a top layer comprising aluminium or an aluminium alloy, the top layer comprising embedded discrete particles of a titanium or titanium oxide,   b. Subsequently anodizing said top layer to form an anodic oxide layer;   wherein said anodizing of step b. takes place in an aqueous solution of an organic acid applying a time varying signal.   
     
     
         17 . The method according to  claim 16 , wherein the particle size of the embedded discrete particles is in the range 100-500 nm, preferably in the range 150-400 nm, such as 200-300 nm. 
     
     
         18 . The method according to  claim 16 , wherein the aluminium or aluminium alloy comprises at least 95% by weight of aluminium, preferably at least 96% by weight of aluminium, such as at least 97% by weight of aluminium, such as at least 98% by weight of aluminium, more preferably at least 99% by weight of aluminium. 
     
     
         19 . The method according to  claim 16 , wherein the discrete particles of a titanium or titanium oxide are embedded by a solid state process. 
     
     
         20 . The method according to  claim 19 , wherein said solid state process is a process selected from the group consisting of friction stir processing (FSP), additive friction stir processing (AFSP), and powder metallurgy. 
     
     
         21 . The method according to  claim 16 , wherein the discrete particles of a titanium or titanium oxide are embedded by a liquid state process. 
     
     
         22 . The method according to  claim 16 , wherein the discrete particles of a titanium or titanium oxide are embedded by a vapour state process. 
     
     
         23 . The method according to  claim 16 , wherein the anodizing of step b. takes place in an aqueous solution of an organic acid selected from the group consisting of oxalic acid, succinic acid, tartaric acid, malic acid, maleic acid, formic acid, citric acid and acetic acid. 
     
     
         24 . The method according to  claim 23 , wherein the organic acid is selected from the group consisting of oxalic acid, succinic acid, tartaric acid, malic acid, maleic acid, and citric acid. 
     
     
         25 . The method according to  claim 24 , wherein the time varying signal comprises a high frequency signal in the form of a square wave signal having a frequency between 500 Hz and 5 kHz, such as around 1 kHz. 
     
     
         26 . The method according to  claim 25 , wherein the square wave signal has an amplitude between −5 V and 100 V, such as between 0 V and 40 V. 
     
     
         27 . The method according to  claim 25 , wherein the square wave signal comprises ramp up and/or ramp down times between 0 and 15% of a pulse duration. 
     
     
         28 . The method according to  claim 16 , further comprising a further step of impregnating the anodized aluminium oxide layer. 
     
     
         29 . The method according to  claim 28 , wherein said impregnation is performed by means of an impregnating substance selected from the group consisting of a silicate, a lacquer, and a sol-gel substance.