EP1943375A2

EP1943375A2 - Method for improving the corrosion resistance and lightfastness of painted aluminum oxide layers

Info

Publication number: EP1943375A2
Application number: EP06792425A
Authority: EP
Inventors: Stefan Brand; Andreas Dierdorf; Hubert Liebe; Frank Osterod; Oliver Eich; Mark Jozefowicz
Original assignee: Clariant International Ltd
Current assignee: AZ Electronic Materials Luxembourg SARL
Priority date: 2005-10-27
Filing date: 2006-10-13
Publication date: 2008-07-16
Also published as: US8057858B2; WO2007048513A3; JP2009513824A; WO2007048513A2; DE102005051755A1; TW200728508A; CA2627399A1; US20090220806A1; AR057561A1; KR20080059468A

Abstract

Disclosed is a method for producing corrosion-resistant, painted oxide layers on aluminum or aluminum alloys. According to said method, a polysilazane solution is applied to a dry oxide layer that is painted with a water-soluble, anionic color, and the coating is then hardened at a temperature ranging from 40 to 150oC.

Description

description

Process for improving the corrosion resistance and light fastness of colored aluminum oxide layers

Structures, objects or parts of aluminum or aluminum alloys provided with a protective oxide layer, in particular an oxide layer galvanically produced by anodization, are nowadays increasingly used in engineering and construction, e.g. as a component or / and for the decoration of buildings, means of transport or means of transport, or for utility or art objects. For the aesthetic design of such structures, objects or parts of these, or their oxide layers are like colored. It is therefore desirable that the colored layers have high resistance to corrosion and light and retain their colored design as long as possible.

In this case, the protective oxide layer is often produced by anodization. Depending on the intended use of the desired component, various anodization conditions are known. However, all methods have in common that a minimum layer thickness of aluminum oxide is required to ensure a corresponding corrosion protection. In addition to the destruction of the surface, a lesser quality with regard to the corrosion protection also has the disadvantage that the Aiuminiumoberfläche is unusable for decorative purposes, since a visual impairment is always the result of such an undesirable process. Such processes occur in addition to natural corrosion, especially when chemically aggressive substances reach the surface. This applies equally to colored and uncoloured surfaces.

For the inorganic, organic and electrolytic coloring of these oxide layers on aluminum or aluminum alloys, dyes of different shades are known, and the oxide layers colored therewith can be compacted in a conventional manner, for example with hot water. However, the available colors can be very different light and Have corrosive fastness, especially after prolonged exposure to sunlight or exposure to aggressive substances, so that often an undesirable impairment or even deterioration of the surface quality and in particular the color impression can occur. In particular, bright color shades of many dyes are not sufficiently light stable.

Thus, it is desired to achieve improved corrosion resistance in combination with dyeings of better fastness to light and also to bring the lightfastness of various dyeings to an overall higher level, i.e., higher color fastness. e.g. Dyes with dyes that provide weaker light fastness to bring in light fastness to the level of such dyeings that are obtainable with dyes that give very high light fastness. This is especially true for bright shades. By compaction with certain compaction means, e.g. Nickel-based at room temperature followed by hot-dip, in some cases, a certain improvement in light fastness can be achieved, which is still insufficient in many cases, especially for objects intended for outdoor architecture, so exposed to the sun for a very long time are.

It has now surprisingly been found that an improved

Corrosion resistance with improved light fastness of the colored layers can be obtained when the colored aluminum oxide layers are coated with a polysilazane-based inorganic paint. In this way, it is possible to reduce the aluminum oxide layer thickness or the amount of dye in this layer without impairing the quality of the layers.

The present invention thus relates to a process for producing corrosion-resistant, colored oxide layers on aluminum or aluminum alloys, wherein a polysilazane solution is applied to a dry oxide layer colored with a water-soluble, anionic dye and the coating is subsequently heated at a temperature in the range from 40 to 150 ⁰ C is cured. By the method according to the invention it is possible dyed To produce aluminum oxide layers with good corrosion resistance, which are characterized at the same time by a high light and UV resistance. A further advantage of the method according to the invention is that the oxide layers can be reduced in comparison to conventional methods, without the quality being reduced. Without the polysilazane treatment, these reduced layer thicknesses of the anodized colored aluminum would not be of sufficient resistance to UV radiation and corrosive attack. Also can be used by this type of treatment less UV stable, previously not suitable for outdoor use dyes or dye systems. In particular, it is possible by this procedure to expand the range of color shades of a dye. Bright shades that are applied by the known methods often show insufficient light fastness. Thus, in the case of the method described here, in particular in the case of thinly anodized, briefly colored samples, which thus show a light shade, the lightfastness is improved. At the same time the corrosion protection is improved.

The colored oxide layers on aluminum or aluminum alloys are produced by immersing the anodically produced, porous aluminum oxide layer in an aqueous solution of dyes and then compacting the colored layers.

As the dyes, those which are known or usable for coloring anodized alumina layers can be generally used. Furthermore, and in particular are now also such

Dyes that have only a weak or reduced light fastness and thus could not previously be used for outdoor use in the field of architecture. In particular, dyestuffs and color shades can now be used which have a light fastness of not more than 4 in the case of a conventional dyeing of anodized aluminum, since an increase of at least 3 lightfastness grades (according to ISO specification No. 2335) of the dyed layers is achieved with the aid of the process according to the invention , The anionic dyes or metal salts may be in the form of the free acids or preferably in the form of water-soluble or water-insoluble salts, for example as alkali metal, alkaline earth metal and / or ammonium salts. It is the method of adsorptive staining. This method can be carried out by various types of surface treatment (spraying, brushing or dipping) with the solutions of these dyes. It is also possible to prepare printing pastes with these dyes, which are then applied by the screen printing method or ink jet method.

Furthermore, the aluminum oxide layers produced by anodic oxidation can also be produced by metal salts according to the principle of the electrolytic dyeing process. Here, the anodized aluminum surface is colored after the anodization in a metal salt bath by attaching an AC electrical voltage. An example is the Sandocolor or Colinal process.

Another possibility is the Kombinationsfärbungs method, wherein first by the above-described method by means of metal salt solution, an electrolytically colored oxide layer is produced. In a second step, this electrolytic dye is colored in a dye bath of dissolved organic dyes or a metal salt solution. An example is the Sandalor process.

This application also applies to dyeings on anodized aluminum surfaces which have been colored according to the principle of color anodization or hard anodization. This is a process in which coloring substances are present in anodizing tanks and these substances are incorporated into the aluminum oxide layer during anodic oxidation. An example is the Permalux method or the Huwyler method.

The oxide layers to be colored are usually artificially generated

Oxide layers on aluminum or aluminum alloys. O

As aluminum alloys are primarily those in which the aluminum content predominates, especially alloys with magnesium, silicon, zinc and / or copper, e.g. Al / Mg, Al / Si, Al / Mg / Si, Al / Zn / Mg, Al / Cu / Mg and Al / Zn / Mg / Cu, preferably those in which the aluminum content is at least 90% by weight; the magnesium content is preferably

<6% by weight; the silicon content is preferably

<6% by weight; the zinc content is preferably <10% by weight; the copper content is advantageously <2 percent by weight, preferably

<0.2 weight percent.

The oxide layers formed on the metallic aluminum or on the aluminum alloys may have been produced by chemical oxidation or, preferably, galvanically by anodic oxidation. The advantage of the method described here lies in the possibility of using thin oxide layers. The processes described so far show in these thin oxide layers only a lack of stability against corrosive attack and low light fastness of the colored surfaces, especially in light shades. The anodic oxidation of the aluminum or aluminum alloy for passivation and formation of a porous layer can be carried out by known methods, using direct current and / or alternating current, and using appropriate electrolyte baths, for example with the addition of sulfuric acid, oxalic acid, chromic acid, citric acid or combinations of oxalic acid and chromic acid or sulfuric acid and oxalic acid. Such anodization processes are known in the art, eg the GS process (direct current, sulfuric acid), the GSX process (direct current, sulfuric acid with the addition of oxalic acid), the GX process (direct current, oxalic acid), the GX process with the addition of Chromic acid, the WX process (alternating current, oxalic acid), the WX-GX process (oxalic acid, first alternating current then direct current), the WS process (alternating current, sulfuric acid) and the chromic acid process (direct current, chromic acid). The current voltages are, for example, in the range of 5 to 80 volts, preferably 8 to 50 volts; the temperatures are, for example, in the range of 0 to 50 ^C C; the current density at the anode is eg in the range from 0.3 to 5 A / dm ² , D

preferably 0.5 to 4 A / dm ² , wherein in general current densities 1-2 A / dm ^{2 are} already suitable for producing a porous oxide layer; at higher voltages and current densities, for example in the range of 100 to 150 volts and> 2 A / dm ² , especially 2 to 3 A / dm ² , and at temperatures up to 20 ⁰ C particularly hard and fine-pored oxide layers can be generated, for example after "Ematal" process with oxalic acid in the presence of titanium and zirconium salts. In the production of oxide layers, which are then dyed adsorptively by electrolysis or directly with a dye, according to a preferred and in practice per se conventional procedure, the voltage in the range of 12 to 25 volts; the current density is preferably 1 to 2 A / dm ² . These anodization methods are well known in the art and also described extensively in the literature, eg in Ullmann's "Enzyklopadie der Technischen Chemie", 4th Edition, Volume 12, pages 196 to 198, or in the Sandoz brochures "Sanodal®" (Sandoz AG, Basel, Switzerland, Publication No. 9083.00.89) or "Advisor for the Adsorptive Dyeing of Anodized Aluminum" (Sandoz, Publication No. 9122.00.80).

The layer thickness of the porous oxide layer is advantageously in the range of 5 to 25 microns, preferably 8 to 15 microns. If the anodized aluminum or anodized aluminum alloy has been stored for a short time (e.g., 1 week or less) before dyeing, it is advantageous to wet and / or activate the substrate prior to dyeing, e.g. by treatment with a non-reducing, aqueous mineral acid, e.g. with sulfuric acid, hydrogen peroxide or nitric acid.

The dyeing is advantageously carried out at temperatures of 15-98 ° C, and advantageously more preferably at temperatures between 18 to 70 ⁰ C 20 to 60 ⁰ C. The pH of the dyeing liquor lies, for example, in the weakly acidic to weakly basic range, for example in the pH range from 3 to 8, with weakly acidic to almost neutral conditions being preferred, in particular in the pH range from 3 to 7. The dye concentration and the dyeing time can vary greatly depending on the substrate and the desired dyeing effect. For example, dye concentrations in the range from 0.01 to 50 g / l are advantageous 0.05 to 30 g / l, in particular 0.1 to 10 g / l. The dyeing time can be, for example, in the range of 10 seconds to 1.5 hours, advantageously 1 to 90 minutes, preferably 5 to 60 minutes.

The dyeings thus obtained can now be compacted or subjected directly to the coating procedure. Before densification, the dyeings are advantageously rinsed with water.

The compaction can be carried out by means of all literature-known procedures and compaction means. Advantageous are: vapor compression, hot water compression with and without deposit inhibitor, mid-temperature sealing with additives (deposit inhibitor) and / or metal salts, nickel hot compression or cold compression with and without subsequent hot water treatment. In the case of vapor compression, the aluminum parts are introduced into a container filled with water vapor, the pressure conditions being defined. A pretreatment by means of metal salts can also be carried out.

In the hot compression z. B. the aluminum parts in hot water with the addition of additives for covering prevention (Anodal SH-1) at a temperature of 96 - 100 ⁰ C densified.

In the mid-temperature compression method, for example, in water at temperatures between 70 and 90 ⁰ C and with the addition of compression accelerating and / or anti-scale additives gesealt.

When cold compaction z. As aqueous solution of nickel acetate, nickel fluoride, an alkali metal fluoride (advantageous sodium fluoride), ammonium fluoride, compression aids, metal salts (eg cobalt compounds) and / or auxiliaries such. As anionic surfactants used. The aqueous solutions of such mixtures are used at room temperature or up to 30 ⁰ C for compacting. O

Furthermore, combinations of the above-mentioned methods can be used, for example, to improve the surface quality. Among other things, for example at 70 ⁰ C in a nickel acetate, and an anionic surfactant-containing aqueous solution (nickel-hot sealing, seal salt ASL), a pre-sealing can be started. Another possibility for this pre-sealing is the use of cold-sealing. This pre-sealing is then completed by a hot dip in hot water with or without the addition of a hot water sealant (Anodal SH-1) or a mid-temperature sealing aid (Anodal SH-2) (two-stage densification ).

Following this compaction, the compacted anodized aluminum is dried. Simple wiping techniques or hot air blowers up to a temperature range of 11O ⁰ C can be used here. Other dry processes are also possible here. Drying in air is also carried out.

Following compaction, the coating is carried out with a polysilazane solution. This coating can also be applied to the un-aged aluminum surface after anodization after the coloring process.

Erflndungsgemäß be used for coating polysilazane solutions containing a solvent, a catalyst and a polysilazane or a mixture of polysilazanes of general formula 1

- (SiR'R "-NR"') _n - (1)

Here, R ', R ", R'" are the same or different and are independently hydrogen or an optionally substituted alkyl, aryl or (Trialkoxysilyl) alkyl radical, wherein it is an integer n and n is such that the polysilazane has a number average molecular weight of 150 to 150,000 g / mol.

Particularly suitable are those polysilazanes in which R ', R ", R'" independently represent a radical from the group hydrogen, methyl, ethyl, propyl, iso-propyl, butyl, iso-butyl, tert-butyl, phenyl, vinyl or 3- (triethoxysilyl) propyl, 3- (trimethoxysilylpropyl).

In a preferred embodiment, perhydropolysilazanes of the formula 2 are used for the coating according to the invention.

Polysilazanes or polysilazane solutions which can be used according to the invention are used e.g. in PCT / EP 2005/011 425, which is incorporated herein by reference.

Further constituents of the polysilazane solution may be additives which influence, for example, viscosity of the formulation, substrate wetting, film formation or the bleeding behavior, and optionally inorganic nanoparticles such as, for example, SiO ₂ , TiO ₂ , ZnO, ZrO ₂ , indium tin oxide (ITO) or Al ₂ O ₃ , UV stabilizers such as HALS. Connections are used. The hardening of the polysilazane coating is preferably carried out at an oven temperature of 40 to 15O ⁰ C, preferably 50 to 120 ⁰ C, particularly preferably 60 to 110 ⁰ C. The drying time is usually 10 minutes to 12 hours, depending on the layer thickness.

In addition to curing by conventional drying, the use of drying lamps based on UV, IR or NIR technology is also possible.

The thus applied, cured Polysilazanbeschichtungen have a layer thickness of 1 to 10 .mu.m, in particular from 2 to 5 microns.

By means of the process according to the invention, it is possible to considerably improve the light fastness and corrosion resistance of the colored surfaces, which can be observed in particular with light shades or dyes having low lightfastness. Examples:

The light fastness can be determined according to ISO regulations, e.g. according to ISO Regulation No. 2135-1984, by dry-exposing a sample in exposure cycles of 100 hours of standard light exposure in an Atlas Weather-O-meter 65 WRC equipped with a xenon arc lamp or in accordance with ISO Standard No. 105 B02 (USA) by dry-exposing a sample in exposure cycles of 100 hours standard illumination in an Atlas Weather-O-meter Ci 35 A, which is equipped with a xenon arc lamp, and comparing the exposed samples with a grading pattern eg the light fastness rating = 6 of the blue scale (corresponding to about the 3rd grade according to gray scale), or determined directly with the blue scale template of grade 6, the light fastness value or the light fastness grade of a dye. If a light fastness value corresponding to the score 6 according to the blue scale is reached only after 2 exposure cycles, the pattern is rated as having a light fastness rating = 7; if this point is reached after 4 cycles, the pattern is given a certificate of authenticity of 8, and so on, as set forth in Table 1 below.

Table 1

The corrosion resistance can be determined according to the test standard ISO 3770 by means of the CASS test (Copper Accelerated Salt Spray Test). For this purpose, the coated and, for comparison, the uncoated aluminum parts, previously anodized, dyed or undyed and whitened or unsealed, sprayed according to the test standard with a copper chloride-sodium chloride solution at pH 3.1-3.3 and a temperature of 50 +/- 2 ° C for at least 24 h. The parts are then cleaned and subjected to an ISO 1462 evaluation. It is here in the polysilazane-coated samples, a significant decrease in

To observe corrosion defects, in particular a reduction in the number of holes, cracking and blistering.

In the following examples, the parts are parts by weight and the percentages by weight; the temperatures are given in degrees centigrade; the dyes are used in commercial form.

Example 1 (Reference A): A defatted and deoxidized sheet of pure aluminum is dissolved in an aqueous solution containing, in 100 parts, 16.5-22 parts of sulfuric acid and 0.5-1.5 parts of aluminum at a temperature of 17 to 21 ⁰ C, at a voltage of 12 to 20 volts with direct current, a density of 1, 0-1, 8 A / dm ² , anodized for 40 to 50 minutes. In this case, an oxide layer of about 20 to 24 microns thick is formed. After rinsing with water, the anodized aluminum sheet is dyed for 30 minutes at 60 ^° C. and a pH of 5.6 with aluminum orange G (Clariant, concentration: 3 g / l).

The dyed sheet is then rinsed with water and compacted with Anodal SH-1 (Clariant, concentration: 2 ml / l) at 98 ° for 50 min.

Example 2 (Reference B)

A degreased and deoxidized sheet of pure aluminum in an aqueous solution containing in 100 parts 16.5-22 parts of sulfuric acid and 0.5-1, 5 parts of aluminum sulfate, at a temperature of 17 to 21 ⁰ C, at a tension of 12 to 20 volts with direct current, a density of 1.0-1, 8 A / dm ² , anodized for 30 minutes. In this case, an oxide layer of about 12-14 microns thick is formed. After rinsing with water, dye the anodized Aluminum sheet for 20 minutes at 60 ⁰ C and a pH of 5.6 with aluminum orange G (Clariant, concentration: 3 g / l).

Subsequently, the colored sheet is rinsed with water and with Anodal SH-1 (Clariant, concentration: 2 ml / l) at 100 ⁰ C for 60 and 30 min. compacted.

Example 3:

It is prepared analogously to Example 1, a further sample, which is provided after densification and drying with a polysilazane. For this, the dyed, anodized aluminum sheet is now immersed in a solution of NL 120 A-20® (Clariant) for a few seconds and carefully pulled out. After a brief dripping, the sample is dried at 12O ⁰ C for 3 h.

Example 4:

It is prepared analogously to Example 1, a further sample, which is provided after densification and drying with a polysilazane. For this purpose, a mixture of a nanoparticulate ZnO dispersion (20 mol%) in dibutyl ether and a polysilazane solution NL 120 A-20® (20 mol%) in dibutyl ether in a ratio of 1: 1 is prepared. The dried, colored, anodized aluminum sheet is then immersed in the above mixture for a few seconds and carefully pulled out. After a brief dripping, the sample is dried at 11O ⁰ C for 3 hours.

Example 5: (reduced anodized starch, PHPS)

It is prepared analogously to Example 2, a further sample, which is provided after densification and drying with a polysilazane. For this purpose, the dyed, anodized aluminum sheet is now immersed for a few seconds in a solution of NL 120 A-20 (Clariant) and carefully pulled out. After a brief drain, the sample is dried at 12O ⁰ C for 2 h.

EXAMPLE 6 A further sample is prepared analogously to Example 2, which is provided with a polysilazane layer after compaction and drying. For this purpose, a mixture of a nanoparticulate ZnO dispersion (20 mol%) in dibutyl ether and a polysilazane solution NL 120 A-20® (20 mol%) in dibutyl ether in a ratio of 1: 1 produced. The dried, colored, anodized aluminum sheet is then immersed in the above mixture for a few seconds and carefully pulled out. After a brief drain, the sample is dried at 110 ⁰ C for 3 hours. Example 7: A further sample is prepared analogously to Example 2, which is provided with a polysilazane layer after compaction and drying. For this, the dyed, anodized aluminum sheet is now immersed in a solution of NP 110-10® (Clariant) for a few seconds and carefully pulled out. After a brief drain, the sample is dried at 100 ⁰ C for 3 h.

Example Anodizing strength (μm) System Corrosion test Light fastness, 100 h

(Atlas CI35)

B 1 (Ref. A) 20-24 without 3

B 2 (ref. B) 12-14 without 2 B B 33 2 200--2244 NL-120 A-20> 6

B 4 20-24 NL-120 A-20 / ZnO> 6

B5 12-14 NL-120 A-20> 6

B6 12-14 NL-120 A-20 / ZnO> 6

B7 12-14 NP-120 A-20> 6

Claims

claims:

1. A process for the preparation of corrosion-resistant, colored oxide layers on aluminum or aluminum alloys, characterized in that applied to a dry, dyed with a water-soluble, anionic dye oxide layer, a Polysilazanlösung and then cured the coating at a temperature in the range of 40 to 150 ⁰ C. becomes.

2. The method according to claim 1, characterized in that for

Coating a polysilazane solution containing a solvent, a catalyst and a polysilazane or a mixture of polysilazanes of the general formula 1

- (SiR'R "-NR '") _n - (1)

is used,

wherein R ', R ", R'" are the same or different and are independently hydrogen or an optionally substituted alkyl, aryl, vinyl or (Trialkoxysilyl) alkyl radical, wherein n is an integer, and n is dimensioned so that the polysilazane has a number average molecular weight of 150 to 150,000 g / mol.

3. The method according to claim 1 or 2, characterized in that the oxide layer has a thickness in the range of 5 to 30 microns.

4. The method according to at least one of the preceding claims, characterized in that the polysilazane coating after curing has a layer thickness of 1 to 10 microns.

5. The method according to at least one of the preceding claims, characterized in that the oxide layer is produced by anodization.

6. The method according to at least one of the preceding claims, characterized in that the polysilazane solution contains additives for influencing the viscosity of the formulation, the substrate wetting, the film formation or the Ablüftverhaltens and optionally inorganic nanoparticles and / or UV stabilizers.

7. The method according to at least one of the preceding claims, characterized in that in a dye which has a light fastness of at most 4, an improvement in light fastness to at least 3 light fastness marks is achieved (measured according to ISO Regulation No. 2135-1984).