DE4227023C1 - Colouring anodised coatings on aluminium@ objects - using 1st soln. contg. organic colouring agent and 2nd soln. contg. metal salt in which electrolytic treatment is carried out - Google Patents

Abstract

Colouring the anodised surface of Al(alloys) objects consists of dipping into a solution containing at least one organic colouring agent, followed by electrolytic treatment in a second solution containing one or more metal salts. Finally, the coating is sealed. Pref. the metal salts used in the second solution are salts of Mg, Ca, Ba, Cu, Zn, Cd, Sn, Ti, Pb, Te, Sb, W, V, Cr, Mo, Fe, Co, Ni, Mn and As. ADVANTAGE - Produces weather-resistant, well coloured layers which are fast to light. The method is easy to apply and inexpensiveee

Description

The invention relates to a multi-stage process for lightfast coloring of anodic Coatings on aluminum and aluminum alloys, being in a first stage the anodic oxidation, dip dyeing with organic dyes and in a second stage an electrolytic coloring treatment with metal salts connects.

Various methods can be used to color anodized aluminum surfaces be used. Known and described in DE-OS 38 25 213, is Dip dye treatment with organic dyes. With this procedure the organic dye adsorbed in the pores of the surface to be colored. A variety of dyes enables coloring in almost all desired colors. The However, the lightfastness of the coloring is unsatisfactory. It's also relatively difficult to achieve a uniform coloring on large areas.

The furthest of all dyeing processes have been the electrolytic Coloring of the oxide layers introduced. Here, baths containing metal salts used in which metal is electrolytically deposited in the pores of the oxide layer is stored. So u. a. in DE-OS 39 17 188, p. 3, lines 12-32 a method for Creation of colored surfaces on parts made of aluminum or aluminum alloys described, wherein as a metal salt-containing electrolyte containing tin sulfate, with Oxicarboxylic acid mixed sulfuric acid solution is used. The lightfastness this coloring is very good. With such stains, however, depending on Viewing direction and lighting create different color impressions, which in particular make flat parts appear very lively. Secondly, the spectrum is limited Hues limited.  

For this reason, diving coloring has been further developed in recent years. For example, DE-OS 39 17 188 and Galvanotechnik 82 (1991) 9, pages 3049-3050 Combination process from electrolytic coloring with subsequent adsorptive Coloring described. Such dyeing processes are also for outdoor applications got interesting. The first step in this process technology is the oxide layer colored electrolytically, whereupon a further coloring by immersion or Spray treatment with organic dyes. Such coloring must be very be carried out carefully, but then also show a good after compression Weather resistance. The advantage of this procedure is that a whole series of warm colors can be produced without the metallic inherent in the aluminum Hide appearance. A special development is the hematite shade, which has been used for some time Time is offered as a surface finish, but its light fastness is not yet full satisfied. The same would be said about other shades, such as. B. to Color shade gray.

The object of the invention is therefore to provide a new dyeing process make that in a simple, economical way the production of lightfast, colored anodic coatings on objects made of aluminum or aluminum alloys allowed.

The object is achieved according to the invention by a method in which according to Formation of the oxidic surface in a first stage treatment in one organic immersion dye bath, which is electrolytically colored with metal salts is connected downstream.

The procedure according to the invention actually enables the solution of the posed Task. It has surprisingly been found that according to the invention Process excellent weatherproof and very lightfast colored objects Aluminum and aluminum alloys are available. Initial expectations that the dyeing process according to the invention the organic dye by the subsequent electrolytic storage of the metal salt could be embedded deeper into the pore cannot be confirmed by rubbing fastness tests. It could be proven through experiments be that there is a coagulation of the organic dye. As a trigger sulfuric acid is primarily responsible for this. The one already in the pore stored  organic dye coagulates due to the subsequently introduced sulfuric acid of the electrolytic dyeing process. The metal, however, is deposited on the pore base from.

The process also has the advantage of being light and without much additional Investment effort to be feasible.

When carrying out the method according to the invention, all known ones can be used organic aluminum dyes are used. As metal salts are the salts of Magnesium, calcium, barium, copper, zinc, cadmium, tin, titanium, lead, tellurium, antimony, Bismuth, vanadium, chromium, molybdenum, iron, cobalt, nickel, manganese, silver and the like. a. conceivable. The salts are mostly in the form of their sulfates, nitrates, phosphates, hydroxides, carbonates, Borates, acetates, formates or oxalates are used. The baths can also be mixed contain of these metal salts. The usual bath additives are also conceivable here.

The invention is explained below using a selected example. Doing so the conventional hematite coloring process the inventive method for Hematite staining of an aluminum object compared.

1. Conventional dyeing process

200 mm long, thermoset material is used as the sample material Aluminum flat material of the alloy AlMgSi 0.5. The pretreatment is as follows:

• - polishing
• - acidic hot degreasing
• - electrolytic shine
• - Pickling in nitric acid.

Then the anodic oxidation in the sulfuric acid bath (H₂SO₄ = 180 g / l, Al = 8 g / l) at 1.5 A / dm². With an anodizing time of 40 min, a layer thickness results of approx. 20 µm.  

The normal course after an intermediate rinse is the electrolytic one Tin coloring and after a further intermediate rinse the organic dip coloring using H3LW dye from Sandoz. In Table 1 below are the Process steps of the overall process are listed individually.

Table 1

Process parameters in the conventional dyeing process for the hematite shade

2. Dyeing process according to the invention

In this case, the dip dyeing was carried out with the same pretreatment using the same material with the H3LW dye before the electrolytic tin coloring. The process parameters are shown in Table 2.  

Table 2

Process parameters in the conventional dyeing process for the hematite shade

A comparison of the colored surfaces of the aluminum flat materials showed the following Results:

a. colour

Visually, all samples are made according to both the conventional and the methods have been colored, flawlessly. The color values, measured with the Minolta color measuring device CR 200 (CIE-LAB standard) are in the range

L = 33.5-35.5,
a = 0.3-1.3,
b = 0.5 - (- 1.5).

The examined samples are within the specified tolerances of the desired one Hematite shades.

b. Apparent conductance measurement and layer thickness measurement

The apparent conductance and loss factor measurement was carried out in accordance with DIN 50 949 using the Fischer measuring device Anotest YD 8.1. The layer thickness measurement was made after Eddy current method (DIN 50 984) performed with the Isoscope MP 2 measuring device.

Apparent conductance Y = 5-6.5,
Loss factor d = 0.25-0.4,
Layer thickness S = 19-20 µm.

The electrical parameters show that the anodized layers in both Processes are well compressed. The layer thicknesses are in the expected range.

c. Lightfastness test

The light fastness was assessed according to DIN 75 202 with the Xenon device 1200 CPS determined. The total test time was 1053 hours with 13 rounds. The Radiant power was 80 W / m². While the sample colored according to the invention in Total color difference Δ E has only a slightly better tendency, it stands out at the Blue shift Δ b clearly positive from the conventionally colored sample. The yellowish color change does not take place in the coloring according to the invention.

d. Penetration depth of the organic dye

The penetration depth of the organic H3LW dye can be discontinuous Determine rubbing off the anodized layer. With the rub fastness tester FEK-VESLIC (Tracking force 9.81 N) the color was measured after every 1000 double strokes. The depth of penetration of the dye in the conventional as well as in the method according to the invention deviates only slightly. But now if you look at the blue shift Δ b as a function of the layer thickness, is the difference in the invention Process considerably less than with the conventional process. The positive effect is therefore not due to the depth of penetration of the dye, but rather likely to look for a change in dye behavior.

From the presented results, the knowledge can be derived that through a Changes in the course of the dyeing process result in significant advantages in light fastness. This relates less to the total color difference Δ E and the difference in brightness Δ L rather than a positive change in the color difference Δ b. Because the human Eye is uncomfortable when the hematite drifts into the yellowish area In addition to the objective assessment, it is also a subjective one.

Claims (4)

1. A process for the lightfast dyeing of anodic coatings on aluminum and aluminum alloys, characterized in that an object made of aluminum or an aluminum alloy which has a coating produced by anodic oxidation,

• - immersed in a first solution containing at least one organic dye ,,
• - then electrolytically colors and in a second solution containing one or more metal salts

then finally compacted. 2. The method according to claim 1, characterized in that as metal salts in the second stage, the salts of magnesium, calcium, barium, copper, zinc, Cadmium, tin, titanium, lead, tellurium, antimony, bismuth, vanadium, chrome, Molybdenum, iron, cobalt, nickel, manganese and silver can be used. 3. The method according to claim 1-2, characterized in that in the first Level of the well-known dye Sanodal jet black H3LW® and in the second stage, a divalent tin salt is used.