GB2082975A - Method for Colouring Oxide Layers of Aluminium or Aluminium Alloys with Organic Compounds - Google Patents

Abstract

Oxide layers of aluminium or aluminium alloys are coloured with organic compounds by introducing at least one diazo compound into pores of the oxide layer and reacting the diazo compound to form a dye. Patterns, designs, labels, signs or pictures can for example be produced by irradiating the diazo compounds incorporated in the oxide layer. The articles thus produced may be used as sign-boards, front plates, scales, circuit diagrams, traffic signs, identity cards, etc.

Description

SPECIFICATION Method for Colouring Oxide Layers of Aluminium or Aluminium Alloys With Organic Compounds The present invention relates to a method for colouring oxide layers of aluminium or aluminium alloys with organic compounds.

Aluminium or aluminium alloys are often used for labels, signs, scales, front plates, etc., and the homogeneity and porosity of the artificially produced oxide layers is generally utilised in this connection.

Dyes can be incorporated in the pores, and the homogeneity guarantees a clean uniform appearance of the coloured oxide layer. The pore openings can be sealed by a simple post-treatment, the oxide layer being treated for example with boiling water. During this treatment the aluminium oxide commonly takes up water molecules into its crystal lattice and its volume increases, thereby closing the pores.

Since this process is generally irreversible, any dye incorporated in the pores is extremely well protected.

In order to colour an oxide layer, the layer is generally brought into contact with a solution of the desired appropriate dye and allowed to absorb the latter. Other methods use for example coloured metal oxides which are produced either during the oxidation of the aluminium or afterwards in the layer. However, methods involving the vapour deposition of dyes in the layer are for example also known.

Various paths can be adopted for producing patterns or designs in the layer such as are generally required for labels and signs. By and large, two groups can be differentiated, namely direct and indirect methods.

In the direct method the dye, which is generally thickened with a colloid, is applied directly to the oxide layer, e.g. by offset printing or silk-screen printing.

In the indirect method a stencil, which covers the parts not being treated, is generally applied to the oxide layer. In this connection, one can in principle proceed either according to the positive or negative method, i.e. either cover the parts not to be coloured and then apply the dye, or firstly dye the whole layer and then cover the parts that are to remain coloured and decolourise the remainder, for example by etching or destroying the dye. The stencil may also be used for example in offset or silkscreen printing. By repeating the whole procedure multi-coloured effects can normally also be produced by both the direct and indirect methods. Combinations of both methods are also in general possible.

The dye or stencil is generally applied with mechanical printing aids. Since however the latter mostly require a printing block, such as e.g. a silk-screen plate, offset plate, dye, etc., they are expensive to produce and photographic printing methods are therefore as a rule preferred for small runs.

For the indirect method a photosensitive resist is for example used. whose solubilitv is altered in certain solvents under the influence of light. If for example an anodically oxidised aluminium plate coated in this manner is illuminated under a negative or positive and is then washed with a suitable solvent, the washed-out parts are freed and can be dyed. The direct method utilises for example the property of silver salts of being reduced by certain chemicals under the action of light and thus providing a silver image. Methods involving other light-sensitive metal salts are for example also known.

It is for example also known that various azo dyes are suitable for dyeing artificial oxide layers of aluminium. Azo dyes are formed in general when diazo compounds react with suitable organic compounds, i.e. so-called coupling agents.

The idea proposed by the present invention for producing these dyes is however novel.

A method was now found for colouring oxide layers of aluminium or aluminium alloys with organic compounds, which is characterised in that at least one diazo compound is introduced into pores of the oxide layer and reacts under the action of external influences or with at least one further organic compound introduced into the pores before or after the diazo compound, to form a dye. The oxide layers in the method according to the invention are preferably artificially produced i.e. the invention is particularly applied to anodized aluminium or aluminium alloys. The thus treated oxide layers can then also be rinsed and/or sealed.

The ability of at least one diazo compound in the oxide layer to form dyes can be altered before the formation of the dye, by irradiation with electromagnetic waves whose wavelengths correspond to the infra-red region or are shorter. The irradiation is preferably carried out with waves from the UV region.

The irradiation generally takes place after the introduction of at least one diazo compound but before the initiation of the reaction.

The preferred artificial oxide layers of aluminium or aluminium alloys can be produced by known anodizing methods. The d.c. sulphuric acid method (the so-called d.c. method) is preferred. It is in general however also possible to produce these oxide layers in other ways, such as e.g. by the a.c.

sulphuric acid method, chromic acid method. Ematal method or also by an electroless method, etc.

Commercially available aluminium alloys or aluminium can be used in the method according to the invention. However, the quality suitable for anodic oxidation is preferably used.

An example of diazo compounds which are used in the method according to the invention and can react per se, i.e. by external influences such as an increase in temperature, irradiation, change in pH value, effect of a gas, etc., and thus form a dye is the diazo compound of 1 -amino-8-naphthol-3,6- disuiphonic acid, the so-called H acid.

However, diazo compounds which change during application to the oxide layer and form a dye may also be used in the method according to the invention.

The present invention also includes the possibility of reacting at least one diazo compound introduced into the oxide layer with a so-called coupling agent, to form a dye. Examples of suitable diazo compounds are the products known as Diazol Compounds, A, C, HC-1 , Y, etc., produced by Firma Kalle, Wiesbaden.

Examples of suitable coupling agents are the products known as coupling agents 1, 5, 13. 38, etc., produced by Firma Kalle, Wiesbaden.

Any diazo compound and any so-called coupling agent may be used in the method according to the invention.

Normally, commercially available diazo salts such as are used e.g. in diazotype processes are reacted with the appropriate commercially available coupling agents.

No limits are placed on the concentrations of the diazo compounds and coupling agents, e.g. in the form of aqueous solutions. The chosen concentration normally depends on the solubility of the diazo compound and coupling agent, the desired colour intensity of the dye that is produced, the cost factor, etc.

When light-sensitive diazo compounds are used it is generally advantageous to operate in attenuated light so that the diazo compounds are not changed.

In general, first of all the diazo compound followed by the coupling agent is applied to the oxide layer, though the reverse order is normally also possible.

One of the two above-mentioned components can thus be introduced to the oxide layer and the other component, e.g. as a solution or gas, can be allowed to act externally, the azo dye then being formed in the oxide layer.

Since the coupling of the two components often takes place only in certain pH ranges, both components can also be introduced to the layer as long as their pH value lies outside the coupling range.

In this case the dye forms as soon as the pH value is shifted by external influences, e.g. an ammonia or hydrochloric acid atmosphere, etc., to the coupling range. The coupling generally takes place in an alkaline pH range. The reaction in the pores normally occurs very rapidly, though in some cases it may take place over a prolonged period.

The components can be introduced in the following ways for example: application with a swab, immersion in solvents, spraying with a spray-gun, pouring with a pouring machine, rolling with a rolling machine, etc.

The method according to the invention is normally carried out at atmospheric pressure and ambient temperature, though higher or lower temperatures may also be employed.

As mentioned above, the treated oxide layer can in addition also be rinsed. This generally has the advantage that the soluble constituents not involved in the formation of the dye are washed out and subsequent reactions such as post-darkening or decomposition of the dye, etc., are thereby avoided.

As has also been mentioned above, the treated oxide layer can in addition also be sealed. The advantage of sealing is in general that the surface becomes insensitive to contamination and is protected against the dye or dyes being washed out, since the pores are closed. Sealing can be effected for example by impregnation or lacquering, i.e. by lacquer protection, or impregnation with a water-repelling agent, e.g. silicone, treatment with boiling water, treatment with at least one aqueous solution of suitable chemical compounds, such as e.g. nickel acetate, cobalt acetate, etc. Sealing is preferably effected by treatment with boiling water.

An advantage of the present invention is that the oxide layers can be coated with one component and various colours can be produced according to the choice of the second component.

A further advantage is the possibility of being able to produce insoluble azo dyes (pigments), which may prove to be of great advantage in the further processing, e.g. weather-fastness, bleeding in the sealing, etc.

Many diazo salts are in general light-sensitive, i.e. under the action of light they lose their capacity for forming azo dyes with coupling agents. This principle has been used for a long time in diazotyping for example: A paper coated with a light-sensitive diazo salt is usually illuminated under a positive and then reacted with a coupling agent.

As already mentioned above, the ability of at least one diazo compound in the oxide layer to form dyes can be altered by irradiation with electromagnetic waves.

If a suitable diazo salt is introduced according to the present invention into the oxide layer, and is partially or completely illuminated under a positive and reacted with a coupling agent, then in general a coloured image of the positive is formed because the diazo salt is destroyed in the illuminated areas and loses its ability to form azo dyes with coupling agents.

UV light is preferably used for the irradiation. Actinic tubes, quartz lamps, arc lamps, xenon lamps or daylight are preferably used as light sources for the irradiation.

Normally, no limits are placed on the combination possibilities between the diazo compounds, coupling agents and irradiation; thus, it is for example possible to firstly incorporate the diazo compound in the oxide layer, change this in the desired way and manner by irradiation, and then react the resultant compound with the coupling agent. It is however also possible to introduce both components to the oxide layer and then carry out the irradiation. As already mentioned above, many other combination possibilities for colour formation may be employed in the method according to the invention.

By irradiating the diazo compounds incorporated in the oxide layer, patterns, designs, symbols, characters or pictures may be formed for example. The articles thereby produced may be used as signboards, front plates, scales, circuit diagrams, traffic signs, identity cards, etc.

The durability of these articles produced by the method according to the invention is at the very least that of a normal anodized plate quality, but is generally far superior to this.

The present invention is illustrated in more detail with the aid of the following examples.

Example 1 A previously chemically delustred aluminium or aluminium alloy sheet suitable for decorative anodic oxidation was oxidised anodically by the conventional d.c. sulphuric acid method under the following conditions: Electrolyte 180 g/l electrolyte Sulphuric acid Aluminium 5-1 5 g/l electrolyte Temperature 1 9-220C Current density 1.5 A/dm2 Duration 30 minutes After the oxidation the sheet was treated for 5 minutes in 15 to 20% nitric acid and was then rinsed and dried.

A solution of fast blue salt BB (diazotised 4-amino-2,5 diethoxybenzanilide zinc double salt) 10 9 Approx. 90% acetic acid to 100 ml was applied with a swab for 1 minute to the oxide layer. The layer was allowed to dry naturally and was then dried with a warm air blower. A positive was placed on the sheet and illuminated from a distance of 60 cm with a quartz lamp.for 30 seconds.

The illuminated sheet was dipped in a solution of: Phloroglucin 5g Distilled water to 100 ml 25% ammonia solution to pH 10 The image immediately appeared, being blackish-brown on a light background. The sheet was next thoroughly rinsed with water and then conventionally sealed with warm water at 96 to 1 000C for 30 minutes.

Example 2 A sheet was treated according to Example 1, but was immersed in the following solution after the illumination: 2,3-naphthoic acid morpholinopropylamide (Firma Kalle, Wiesbaden: Coupling agent 38) 3g Distilled water to 100 mi 25% ammonia solution to pH 10 A violet image immediately appeared, which to some extent lost its reddish tinge and became blue after rinsing with water and sealing.

Example 3 A sheet anodically oxidised according to Example 1 was painted with the following solution: 4-diazo-dimethylaniline zinc chloride (Firmal Kalle, Wiesbaden: Diazo A) 5 9 Hexylresorcinol 5g Approx. 90% acetic acid 30 g Methyl alcohol to approx. 100 ml After 30 seconds the sheet was rubbed dry with a dry swab, and then illuminated under a positive as described in Example 1. The illuminated sheet was covered with blotting paper, impregnated with the following solution, and then thoroughly dried.

Ammonium bicarbonate 10 9 Polyvinyl alcohol (M4/88 Hoechst) as a 10% solution in ethanol 1 ml 25% ammonia solution 20 ml Distilled water to 100 ml The whole was then pressed together for 20 seconds with a hot plate (e.g. iron) heated to approx.

1200C The image developed as a darkish brown colour but after the subsequent rinsing adopted a khakibrown colour which it also retained after the sealing.

Example 4 The following solution was poured over a sheet pretreated and anodically oxidised according to Example 1: 2,4,2',4t-tetraoxy-diphenylsulphide (Firma Kalle, Wiesbaden: Coupling agent 2) 4g 4-diazo-2-methylphenylpyrrolidine ZnCI2 (Firma Kalle, Wiesbaden: Diazo Y) 6g Thiourea 4g Approx. 90% acetic acid 5 ml Saturated methanolic NaHSO3 solution 5 ml Butyl glycol 15 ml Methanol to 100 ml After drying, the sheet was illuminated as in Example 1, but the illumination time was 1 minute instead of 30 seconds. The illuminated sheet was then heat treated for 1 minute at 1 40 C. A dark brown image was formed, which was not changed even by the subsequent rinsing and sealing.

Example 5 An anodically oxidised, unsealed sheet with an oxide sheet at least 18 ym thick was sprayed with the following solution: 4-diazo-2,5-diethoxyphenylmorpholine 1/2 ZnCl2 (Firma Kalle, Wiesbaden: Diazo HC) 10g Distilled water to 100 ml After drying, an acetate foil was placed on top of the sheet, which was wetted on the sheet side with the following solution and then dried: #-naphthylamine 5g Urea 10g 10% ethyl cellulose solution in ethanol 15 ml Butyl glycol 15 ml Methanol to 100 ml On pressing the sheet and foil together for 20 seconds with a hot plate (e.g. iron) heated to 1200 C, an orange colour developed in the layer which remained unaltered even after the subsequent rinsing and sealing.

Example 6 An anodically oxidised, unsealed sheet with an oxide layer at least 15 ym thick was brushed (tampon) with the following solution for 1 minute: 4-diazo-diethylaniline ZnCI2 (Firma Kalle, Wiesbaden: Diazo C) 10 9 Urea 59 Distilled water to 100 ml The sheet was then scraped with a sharply ground rubber doctor knife and dried. After illumination the sheet was covered with an acetate foil whose side facing the sheet was wetted with the following solution and allowed to dry thoroughly: 1 ,8-naphthylenediamine 5g 10% ethyl cellulose solution in ethanol 15 ml Butyl glycol 10 ml Methanol to 100 ml A hot plate (e.g. iron) heated to 1 300C was pressed on the foil for 20 seconds. The image developed as a red colour on the unilluminated areas.This colour remained unchanged even after subsequent rinsing with water and sealing.

Example 7 A sheet was treated as in Example 6, but instead of the foil of Example 6 a piece of foil from Example 5 which had not yet been subjected to the heat treatment was used. An orange image was formed which withstood undamaged all subsequent treatments.

Example 8 A sheet pretreated and anodically oxidised according to Example 1 was painted for 1 minute with a solution having the following composition: 4-diazo-diethylaniline ZnCI2 10g 2,5-dimethyl-4-dimethylaminomethylphenol HCI (Firma Kalle, Wiesbaden: Coupling agent 13) 6g Adipic acid lg Distilled water to 100 ml and was then rubbed dry with a dry swab. After illumination under a positive (according to Example 1) the sheet was placed in a closed vessel in which 25% ammonia solution evaporated in an open dish.

The evaporated ammonia displaced the pH value of the diazo/coupling agent mixture towards the coupling ravage (from acid to alkaline). A yellow image of the positive was formed in a short time. After 5 minutes the sheet was removed from the vessel, rinsed and sealed.

Example 9 An anodically oxidised, unsealed sheet with an oxide layer at least 1 5 ym thick was coated with the following solution for at least 1 minute: 4-diazo-dimethylaniline zinc double salt (Firma Kalle, Wiesbaden: Diazo A) 2 9 Sodium salt of 2,7-dioxynaphthalene-3,6-disulpho acid (Firma Kalle, Coupling agent 5) 4g Distilled water to 100 ml and then scraped with a sharp rubber doctor knife and dried. The sheet was illuminated according to Example 8 and developed.

After developing in the ammonia atmosphere, the image of the positive was blue, while after sealing it became violet.

Example 10 A sheet was treated according to Example 8, but at the end of treatment instead of sealing according to Example 9 it was coated once more and processed further. The sign was then triple coloured. After the sealing the colours were yellow (solution of Example 8), violet (Example 9) and light brown (at those regions where the two colours overlapped).

Claims (9)

Claims

1. A method of colouring an oxide layer on the surface of aluminium or an aluminium alloy with an organic compound, which method comprises introducing at least one diazo compound into the pores of the oxide layer and reacting the diazo compound in the pores of the oxide layer to form a dye.

2. A method as claimed in claim 1, wherein the diazo compound is self reactive to form the dye and is reacted to form the dye by alteration of the external conditions.

3. A method as claimed in claim 1, wherein the diazo compound is reacted with a coupling agent to form the dye.

4. A method as claimed in any one of claims 1 to 3, wherein the oxide layers are artificially produced.

5. A method as claimed in any one of claims 1 to 4, wherein the oxide layer is subsequently rinsed and/or sealed.

6. A method as claimed in any one of claims 1 to 5, wherein after introduction of the diazo compound into said pores and before formation of said dye, at least part of said oxide layer is exposed to infra-red or shorter wavelength electromagnetic radiation whereby the dye forming properties of at least one diazo compound in the pores are altered.

7. A method as claimed in claim 6, wherein the electromagnetic radiation is U.V. light

8. A method as claimed in either claims 6 or claim 7, wherein the said exposure takes place after introduction of at least one diazo compound but before initiation of the reaction.

9. A method as claimed in any one of claims 1 to 8 and substantially as hereinbefore described.