Anodizing Process using Ano range of Aluminium Anodining Dyes to obtain excellent color finish 

(The process is for non-electro colouring based colorants).

1.0    Ano Dyestuff for dyeing anodized Aluminium.

          The Ano dyestuffs are designed for dyeing anodized Aluminium and some of its alloys.

The procedure consists in producing artificially on the metal surface of porous oxide coating of suitable thickness, and bath dyeing of this coating in solution of Ano Dyes. Ano dyestuffs assure level dyeing of the anode coatings and give dyeing with good or very good fastnesses. The pretreatment of metal surface consist of common operations, such as:

• Mechanical working
• Degreasing with Solvents or emulsion
• Chemical or electrolytic cleaning
• Brightening of metal surface
• Chemical or electrolytic polishing
• Removing of the unsuitable oxide coat

2.0    Anodic Oxidation

Most suitable for dyeing with Ano dyestuffs are films obtained by anodic oxidation of the metal surface under the following condition:

2.1    Pretreatments: - Degreasing Etching

2.2    Anodizing

Note: The anodized surfaces should be protected from contamination and the more so from greases, as otherwise unlevel dyeing may be obtained.

3.0    Dyeing

The anodized metal required an Acid treatment in such a way. Put the anodized metal in a tank containing 10% Nitric Acid for 10-15 second. Then rinsed the panel thoroughly in running cold water to remove Nitric Acid.

3.1    Setting of the dyebath:

          The best results are obtained when dyeing in Ano dye solutions directly after, anodic oxidation. The weighted out portion of the dyestuff is pasted with small amount of cold water, diluted with boiling distilled or softened water (condensate may be used, provided it is free from oil or grease). The solution is filtered and diluted in the bath to required volume. It is recommended to maintain the temperature precisely in the range characteristic of the particular dyestuff, only exceptionally, when the dyestuff is absorbed too quickly from the bath giving unlevel dyeings, the temperature may be raised above 60 C. the volume of the is adjusted so as to provide 300-500 ml of solutions per 1 sq.dcm of the stained surface.

(We recommend todissolve the dyestuff in demineralized water. Tap water is suitable as well but the bath stability can be reduced, however.

The powder dyestuff should be completely dissolved before addition to the bath. It is best to paste it with some of hot water, stirring constantly until a homogeneous paste free from lumps is formed and then to add more hot water with continued stirring so that the paste goes slowly in to the solution.)

3.2    pH of the dyebath:

                   The optimum value for dyeing and stabilization of the dye bath is ph 4.5-5.0. The life of the dyebath is shortended by pH values beyond the tolerance region of 4.0-4.8 owing to accumulation of aluminium or ageing. Moreover lower pH values encourage bronzing of the dyeing.

3.3    Dyeing Temperature:

                   The optimum temperature for build-up of the dyestuff is 55-60 C.

At the lower temperature e.g. room temperature; a saller amount of dyestuff is adsorbed in the anodic coating in constant dyeing time. Dyeing produced at lower temperature are easier to strip, but they bleed rather more heavily in the sealing solution.

3.4    Dyeing Time:

          The dyeing process is carried on for 15-20 minute at 55-60 C. in the bath continuously agitated. Under the normal anodizing and dyeing condition, i.e.

Coating thickness                    12-15qm

Dyeing temperature                 60 C

PH                                           4.5-5.0

Dyeing concentration              5-10 gms/litre.

The saturation limit is very nearly reached after dyeing for 20 min. Longer dyeing times do not result in any significant increase in the intensity.

4.0    Sealing

                   The stained anodic coating must always be sealed. This procedure increases the resistence of these coating to corrosion, and improves the wet fastnesses of the dyeing. However there are two method of sealing is generally in practice. E.g.

4.1    Sealing in boiling water:

                   Temperature                   : Boiling

                   Time                               : 45 minute

                   Medium                          : water with 5 gms/litre sealing salt

4.1    Sealing in Nickle Sulfate:

                   Nickle Sulfate                 4.0 gms/litre

                   Sodium fluoride             1.5 gms/litre

                   PH                                  6.0

                   Temp.                             30.35 C

                   Time                               10 Minute

Final seal in hot water at pH 5.5 for 5 minute.