HU204308B - Process for electrolytic blue-colouring anodic oxide-layer on aluminium and it's alloys - Google Patents

Abstract

According to the present invention, the anodic oxidized aluminum or aluminum alloy is potassium ferricyanide 1-30 g / dm 3, preferably 2-20 g / dm 3 and iron 2-20 g / dm 3, preferably 2-15 g / dm3. HI) containing 0.5-2.5, preferably 1.2 to 1.4, electrolytes with an inverse electrode at an alternating voltage of 6-30 V and 0.22 A / dm2, preferably 0.2-0.5 Electrolysed with / dm2 current density, and, if desired, the pores of the resulting product are sealed in a known manner. EN 204 308 A Scope of the description: 4 pages, without illustration

Description

The present invention relates to a process for electrolytic blue dyeing of an anodic oxide layer formed on an aluminum ion and an alloy.

Several methods of coloring anodic oxide layers of aluminum and its alloys for corrosion protection to meet aesthetic needs are known.

Adsorption coloring is most common! The method of this method involves immersing the preformed aluminum workpiece 10 with a porous structure in an anodic oxide layer in a dyeing solution and painting the pores absorbed by the dye by absorbing it onto the exterior surface of the porous passages. The dyeing solution is generally an aqueous solution containing a suitable organic or dyestuff, prepared with PH. This method provides virtually unlimited color choices, but colors are not durable. Even with the use of good quality new dyes, I can't help. Thus, an attractive blue anodic oxide layer is formed in an aqueous solution of 5 g / dm ^{3 of} Sandonel turquoisePLW dye of SANDOZSwitzerland, adjusted to a pH of 5.5, but UV light, even in the case of corrosion after treatment (sealing) causes significant color fading. 25

In principle, preformed oxide film formation can be accomplished by chemically forming a colored precipitate in the pores - this is formed at the top, near the surface - but the colorant is very poorly bound to the oxide. Therefore, such a procedure is of no practical importance.

Color fast after - tinting of anodic oxide layers is accomplished by electrolytic dyeing techniques (see Figs.

235 081). These usually have alternating current in an aqueous solution containing a metal salt and an additive. The coloring agent - metal, metal oxide, metal hydroxide - is deposited at the bottom of the pores, in the base metal cycle, during the cathodic period of the current and practically does not change the color of the product after 40 outdoor applications. The color of the product thus produced preserves its metallic character, at the same time it is corrosion resistant and excellent color fastness.

Electrolytic coloring processes are widespread, but the range of colors they produce can be strongly limited. Of practical importance are the procedures for providing bronze-gray-black, copper-red-burgundy, and gold-yellow-bama hues. Other colors, such as the base colors (red, yellow, blue) and their pure combinations, have not been developed so far.

At present, there is no known electrolytic dyeing process which can be used for architectural purposes to provide a blue color with a sufficient color fastness by treating anodized oxidized aluminum. 55

It is an object of the present invention to provide a process for the subsequent blue-coloring of colorless anodic oxide layers on aluminum and its alloys with almost any color intensity ranging from light blue to dark blue, depending on the electrochemical conditions.

More specifically, the present invention relates to an electrolytic dyeing process which provides a permanent blue coloration at the bottom of the pores in the aluminum oxide layer.

In order to solve this problem, the possibility of selecting complex ferro- and ferricyanides was investigated. As is known, in the Fe ²⁺ ZFe ³⁺ and (Fe (CN) 6) ⁴ (Fe (CN) 6) ³ 'systems, four complex cyanide formation possibilities exist according to the following equations.

Fe ²⁺ + (Fe (CN) 6) ^{4 -} Fe (FE (CN) 6) ² - (1) light blue solid

3Fe ²⁺ + 2 (Fe (CN) 6) ³ - = Fe ³ (Fe (CN) ₆ ) ₂ (2) Intense Blue Solid, Tumbull Blue

4Fe ³⁺ + 3 (Fe (CN) 6) ⁴ '-Fe4 (Fe (CN) ₆ ) ₃ (3) Intense Blue Solid Compound, Berlin Blue

Fe ³⁺ + (Fe (CN) 6) ³ = Fe (Fe (CN) 6) (4) slightly brown solution

The solid compounds formed by the reaction of equations (1), (2) and (3) are formed immediately upon meeting the ions. These reactions are also used in classical analysis to detect the ions involved. Therefore, these reactions cannot be used directly for coloring. The reaction of equation (4), on the other hand, forms a soluble complex cyanide which, through electrochemical induction of an oxidation-reduction process, can form, for example, highly colored compounds in the pores which form part of the reaction equations (2) and (3). Further, in the presence of suitable organic or inorganic complexing anions, the brown solution formed in the reaction of equation (4) turns green. Meanwhile, more complex compounds are formed according to reaction equation (5) below.

Fe ³⁺ + (Fe (CN) 6) ³ + H ⁺ + A “- H ⁺ (Fe / Fe / CN))) A (5)

The reaction product is a dark green solution. In the formula means an organic or inorganic anion. It has now been found that the coloring reaction can be best accomplished by starting with such green complex compounds, both in terms of coloration and solution stability.

In our investigations, we have found that on the basis of the above-mentioned recognitions, we can form a blue

Ferro-ferricyanide of Fe ₃ (Fe (CN) ₆ ) ₂ or ferro-ferrocyanide complex of Fe ₄ (Fe (CN) ₆ ) ₃ or a mixture thereof to expose the workpiece containing the oxide layer to an alternating current using a counter electrode in an acidic electrolyte, containing a sufficient amount of potassium ferricyanide and a suitable amount of ferric salt.

Thus, according to the invention, the process for electrolytic blue dyeing of an anodic oxide layer formed on an aluminum ion and its alloys is such that the anodized oxidized aluminum or aluminum alloy is 1-30 g / dm ³ , preferably 2-20 g / dm ³ potassium ferricyanide. g / dm ³ , preferably from 2 to 15 g / dm ^{3 of} iron (ni) salt having a pH of 0.5 to 2.5, preferably 1.2 to 1.4

EN 204308 against a counter electrode in an electrolyte of value A

It is electrolyzed at a voltage of 6 to 30 V AC and a current density of 0.2 to 2 A / dm ² , preferably 0.2 to 0.5 A / dm ² , and if necessary, the pores of the resulting product are sealed in a known manner.

Thus, the electrolytic blue dyeing is carried out in an acid electrolyte containing 1-30 g / dm ³ , preferably 2-20 g / dm ³ K ₃ (Fe (CN) ₆ ), 220 g / dm ³ , preferably 2-15 g / dm ^{3 of} ferric salt. The ferric salt may be any iron (HI) salt commonly used in electrolytic processes, such as ferric nitrate, acetate, phosphate or formate. In some cases, it may be advantageous to use an electrolyte containing ferric ammonium sulfate which tends to complex. The shade and intensity of the blue color of the oxide layer is influenced by the nature and complexing tendency of the salt-forming anion, so the appropriate ferric salt is selected with this in mind. The electrolyte may also contain one or more ferric salts within the stated concentration limits.

For the acidity of the electrolyte: organic and / or inorganic acids may be used. Adjusting the desired pH of 0.5-2.5, preferably 1.2-1.4 value of the electrolyte is about 2-25 g / dm ³ at a concentration of one or more organic or inorganic acid such as sulfuric acid, oxalic acid, phosphoric acid, acetic acid, maleic acid, sulfosalicylic acid are added. The nature of these also influences the hue and intensity of the color of the product, so these acids are also selected according to user requirements.

The electrolysis itself is carried out with alternating current, a voltage of 6-30 V and a current density of 0.2 to 2 A / dm ^2, preferably 0.20.5 A / dm ² . Any inert electrode may be used as a counter electrode. Preferably, the electrolysis is performed using a graphite electrode or a carbonaceous electrode, possibly an iron electrode. The blue coloration of the oxide layer thus takes about 1-20 minutes.

Electrolysis can be accomplished with normal sinusoidal AC, modified AC, for example, with a frequency greater than or equal to 50, and with asymmetric or non-sinusoidal alternating current combined with rectangular pulses,

Upon completion of the electrolysis, depending on the composition of the bath and the flow parameters, a light colored to dark blue product with a uniform color oxide layer is obtained.

The blue coloring of the present invention can be accomplished not only by itself, but can also be combined with other coloring methods.

If another color effect is desired, the product may be immersed in a solution of an organic dye after the electrolytic dyeing of the present invention or subjected to an electrolytic dyeing process before or after the electrolytic blue dyeing.

In this way, it is possible to combine the blue and the color that can be achieved with the other method. For example, if the process of the present invention is disclosed in U.S. Pat. Combined with the electrolytic yellow tinting described in U.S. Patent No. 4,600,128, the product is obtained in the form of an attractive green permanent oxide layer.

Finally, if desired, pore sealing aftertreatment can be used to seal the pores if this is required to increase corrosion resistance or for other reasons. To this end, the product is subjected to a known pore sealing treatment, for example, in hot water at about 100 ° C or NiF _{2 at} about 30 ° C.

The invention is illustrated by the following examples.

Example 1

A 5 x 5 cm aluminum plate having a purity of 99.5% is oxidized anodically in a solution containing 180 g / dm ³ sulfuric acid. The electrolysis was continued for 45 minutes at 16 V DC with a current density of 1.5 A / dm ² . In this way, a colorless porous oxide layer of 20 µm thickness is prepared.

Aluminum sheets with a colorless porous oxide layer are immersed in a bath containing 10 g / dm ^{3 of} potassium ferricyanide, 5 g / dm ^{3 of} ferric ammonium oxalate and 1.75 g / dm ^{3 of} sulfuric acid. The electrolytic blue coloration is performed with a 50 Hz sinusoidal AC voltage of 14 V and a current density of 0.2 A / dm ² . The counter electrode is a graphite electrode. After 10 minutes of electrolysis, a dark blue oxide layer was applied. The product was subjected to 45 minutes of hot water pore sealing post-treatment. The color will not change during this time. The product has excellent corrosion resistance and excellent color fastness.

Example 2

According to Example 1, anodized aluminum plate is immersed in an electrolyte containing 12 g / dm ^{3 of} potassium femcyanide, 4 g / dm ^{3 of} ferric ammonium sulfate and 2 g / dm ^{3 of} sulfuric acid. The blue coloring is performed with 12 V AC at a current density of 0.3 A / dm ² . After electrolysis for 10 minutes, the pores of the product were sealed as in Example 1. A blue product is obtained.

Example 3

An aluminum plate with a colorless oxide layer, 10 g / dm ^{3 of} potassium ferricyanide, 2.5 g / dm ^{3 of} ferric ammonium sulfate, 2 g / dm ^{3 of} oxalic acid and 7 g / dm ^{3 of} phosphoric acid was formed on the surface as in Example 1. immersed in electrolyte. The blue coloration is carried out at 25 V ac and 0.2 A / dm ² current density. After 5 minutes of electrolysis and 45 minutes of hot water pore seal, a light blue product is obtained.

Example 4

The procedure of Example 1 is repeated, except that the blue coloration is carried out this time with an asymmetric 20 Hz frequency. The electrolysis is continued for 10 minutes and the pores of the product are sealed as in Example 1. A light blue product is obtained.

HU 204 308 A

Example 5

An aluminum plate on which no. The electrolytic dyeing process described in Hungarian Patent Application No. 4,600,300 was applied to a golden yellow oxide layer for 3 minutes by immersion in an electrolyte containing 10 g / dm ^{3 of} potassium ferricyanide, 5 5 g / dm ^{3 of} ferric ammonium oxalate and 1.75 g / dm ^{3 of} sulfuric acid. The blue coloration was carried out as in Example 1. The product is green.

Example 6

According to Example 1, anodized aluminum plate was placed in an electrolysis bath containing 25 g / dm ^{3 of} potassium ferricyanide and 12 g / dm ^{3 of} ferric ammonium oxalate, the pH of which was adjusted to between 1.2 and 1.4 with sulfuric acid. The blasting is performed at 8 volts AC with a current density of 0.45 A / dm ^{2 for} 3 minutes. The products were subjected to a 45 minute hot water powder seal. We get deep blue products.

Claims (1)

A process for the feed trolytic blue coloring of an anodic oxide layer on aluminum and its alloys, characterized in that the anodized aluminum or aluminum alloy is oxidized in a known manner in an amount of 1-30 g / dm ³ , preferably 2-20 g / dm ³ potassium ferricyanide and 220 g / dm ³ . preferably a counter-electrode in an electrolyte adjusted to a pH of 0.5 to 2.5, preferably 1.2 to 1.4, preferably containing 2 to 15 g / dm ^{3 of} iron (HI) salt, in a known manner, at a voltage of It is electrolyzed at a current density of 22A / dm ² , preferably 0.2-0.5 A / dm ² , and if necessary, the pores of the resulting product are sealed in a known manner. Published by: National Office for Inventions, Budapest Responsible publisher: dr. Gabriella Swoboda