EP0802267B1 - Aluminium surfaces with interference colours - Google Patents

Abstract

Interference layer contains an aluminium oxide layer and a partially transparent layer deposited on it. The novelty is that the aluminium oxide layer is an anodically produced, transparent and pore-free barrier layer with a thickness of according to the required surface colouring of the interference layer. The thickness d is 20-900 nm, and the partially transparent layer has a wavelength dependent transmission t( lambda )) which is 0.1-1. Production of the interference layer is also claimed.

Description

The present invention relates to an interference layer as a coloring surface layer of aluminum bodies containing an aluminum oxide layer and one deposited thereon semi-transparent layer. The invention further relates to a method of manufacture the interference layer according to the invention.

Interference layers, which certain length waves of the incident light by interference eliminate are known in optics as so-called filters. The manufacture of such filters usually happens by applying a high-purity, thin metal layer Glass, by subsequent deposition of a dielectric layer, and by the further Apply a semi-transparent metal layer. The deposition of the individual layers is usually done using PVD (physical vapor deposition) methods, like sputtering or vapor deposition.

The high-purity, thin metal layer is made of aluminum, for example. Al ₂ O ₃ or SiO _x layers are usually used as dielectric layers. Because of the small layer thickness, PVD-Al layers generally cannot be anodized, so that PVD-Al ₂ O ₃ or PVD-SiO ₂ are mostly used as dielectric layers. However, the application of PVD-Al ₂ O ₃ layers or PVD-SiO ₂ layers is expensive. In addition, dielectric layers which are applied to the aluminum surface by means of PVD methods sometimes have insufficient adhesion. Metals, such as high-purity aluminum, are usually used for the semi-transparent layers. The known GS method, ie the anodic oxidation of the aluminum surface with direct current in a sulfuric acid electrolyte, can also be used to produce a dielectric layer on an aluminum surface. However, the resulting protective layer usually shows a high porosity due to the method. The production of large surface layers with homogeneous coloring requires a correspondingly large constant layer thickness of the interference layer. However, it is difficult to produce a large-area dielectric layer with a constant layer thickness using the GS process.

The anodic oxide layers produced in sulfuric acid are only on pure aluminum and AlMg or AlMgSi alloys based on pure aluminum (Al ≥ 99.85% by weight) colorless and crystal clear. For less pure materials, such as Al 99.85, Al 99.8 or Al 99.5, alloy components, such as Fe or Si-rich intermetallic Phases are built into the oxide layer, which then become uncontrollable Light absorption and / or lead to light scattering and thus more or less clouded Layers, or layers with an uncontrollable coloring result.

The object of the present invention is to provide an interference layer which can be produced inexpensively to be specified as the coloring surface layer of aluminum bodies, which the previous avoids the disadvantages mentioned and enables the lightfast coloring of aluminum surfaces, or can be used as a selective reflector surface.

According to the invention, this is achieved in that the aluminum oxide layer is an anodically produced, transparent and pore-free barrier layer with a barrier layer thickness d preselected according to the desired surface color of the interference layer, the barrier layer thickness d being between 20 and 900 nm (nanometers) and the partially transparent layer being one has wavelength-dependent transmission τ (λ) that is greater than 0.01 and less than 1.

The interference layers according to the invention can, for example, on surfaces of General cargo, strips, sheets or foils made of aluminum, as well as aluminum cover layers of bodies made of composite materials, in particular aluminum cover layers of composite panels, or on any material with a - for example electrolytically - deposited Aluminum layer can be applied.

With the material aluminum, aluminum is of all purity levels in the present text as well as all aluminum alloys. In particular, the term aluminum includes everything Rolling, kneading, casting, forging and pressing alloys made of aluminum. Preferably there is pure aluminum material surface to be provided with the interference layer according to the invention With a degree of purity equal to or greater than 98.3% by weight of Al or aluminum alloys from this aluminum with at least one of the elements from the series of Si, Mg, Mn, Cu, Zn or Fe. Aluminum surfaces made from high-purity are further preferred Aluminum alloys with a purity of 99.99% by weight Al and higher, for example made of plated material, or a purity of 99.5 to 99.99 wt .-% Al.

The aluminum surfaces can have any shape and can optionally also be structured. In the case of rolled aluminum surfaces, these can be used, for example Be treated high gloss or designer rollers. A preferred use of structured Aluminum surfaces can be found, for example, for applications in daylight lighting, for example for decorative lights, mirrors or decorative surfaces from Ceiling or wall elements, or for applications in vehicle construction, for example Decorative parts or closures. In particular, structured surfaces with structure sizes are obtained from expediently 1 nm to 1 mm and preferably from 50 nm to 100 μm to use.

It is particularly important to the invention that the barrier layer thickness corresponds to the desired one Coloring is produced in a controlled manner. To achieve the highest possible Color fastness of the interference layer, the barrier layer must also be non-porous. So that will Diffuse light scattering that is difficult to control and thus uneven color development avoided. However, the term non-porous does not mean absolute freedom from pores Roger that. Rather, the barrier layer of the interference layer according to the invention is in the essentially non-porous. It is important that the anodized aluminum oxide layer has essentially no process-related porosity. Under a procedural Porosity becomes, for example, the use of an aluminum oxide dissolving electrolyte Roger that. In the present invention, the pore-free barrier layer preferably has a porosity of less than 1% and in particular less than 0.5%.

The dielectric constant ε of the barrier layer depends, among other things. of those used to make the barrier layer used process parameters during the anodic oxidation. Conveniently the dielectric constant ε of the barrier layer is at a temperature of 20 ° C between 6 and 10.5 and preferably between 8 and 10.

The color of the aluminum surface provided with an interference layer according to the invention depends, for example, on the surface quality of the aluminum surface, on the angle of incidence of the light striking the interference layer surface, the viewing angle, the thickness of the barrier layer, the composition and the layer thickness of the partially transparent layer and the transmission τ (λ) of the partially transparent one Layer. The wavelength-dependent transmission τ (λ) is defined in the present text as the quotient τ (λ) = I / I ₀ , where I _{0 is} the light intensity of the light of the wavelength λ incident on the surface of the partially transparent layer and I is the light intensity of the from the partially transparent layer emerging light called In a preferred embodiment, the interference layer according to the invention has a transmission τ (λ) between 0.3 and 0.7.

Because of the optical properties, the layer thickness of the barrier layer is in accordance with the invention Interference layers preferably in the layer thickness range between 30 and 800 nm and particularly preferably between 35 and 500 nm.

The barrier layers of the interference layers can - over the entire interference layer surface seen - have a locally different layer thickness, so that for example optical color patterns arise on the interference layer surface. The area of the individual color sample components, i.e. Subareas of the interference layer surface with the same Barrier layer thickness, can range from submicron to - in relation to whole interference layer surface - large areas are sufficient.

In principle, all reflective materials are suitable as partially transparent layer materials. Commercial metals of all purities and in particular Ag, Al, Au, Cr, are preferred. Cu, Nb, Ni, Pt, Pd, Rh, Ta, Ti, or metal alloys containing at least one of these aforementioned elements.

The coating of the barrier layer with the partially transparent layer can, for example by physical methods, such as vapor deposition or sputtering, by chemical methods, such as CVD (chemical vapor deposition) or direct chemical deposition, or by electrochemical methods happen.

The partially transparent layer can be applied to the barrier layer over the entire surface or only Affect partial areas of the interference layer surface. For example, the sub-areas also form a grid-like network. With partially transparent layers, only partial areas of the interference layer surface, submicron structures are preferred.

The partially transparent layer can have a uniform layer thickness or a structured, i.e. a locally different layer thickness over the partially transparent layer demonstrate. In the latter case, for example, even with a uniformly thick barrier layer Color samples are generated.

The layer thickness of the partially transparent layer is expediently over the whole Interference layer surface from 0.5 to 100 nm, preferably from 1 to 80 nm and in particular from 2 to 30 nm.

The partially transparent layer can also preferably be a sol-gel layer with a layer thickness of 0.5 to 250 µm and in particular from 0.5 to 150 µm with embedded reflective Represent particles, the dimensions of the reflecting particles preferably in the micron or submicron range and in particular in the submicron range. As reflective Particles are preferably suitable metal particles and in particular those made of Ag, Al, Au, Cr, Cu, Nb, Ni, Pt, Pd, Rh, Ta, Ti, or from metal alloys containing at least one of these aforementioned elements. The reflective particles can be uniform in the Sol-gel layer can be distributed or essentially all in one to the barrier layer surface parallel plane. In a preferred embodiment the partially transparent sol-gel layer, especially if it is essentially uniform has reflective particles distributed in the sol-gel layer, a locally different one Layer thickness. This can result in interference layers with optical color patterns. The locally different layer thickness of the partially transparent sol-gel layer can, for example be produced by roll embossing, possibly after a previous one Heat treatment in which the sol-gel layer is at least partially polymerized or cured becomes.

In order to better protect the interference layers from mechanical and chemical influences, in a preferred development they have a transparent protective layer on the side of the partially transparent layer facing away from the barrier layer. The protective layer can be any transparent layer that offers mechanical and / or chemical protection to the partially transparent layer. For example, the transparent layer is a lacquer, oxide or sol-gel layer. The lacquer layer is understood to mean, for example, a colorless, transparent, organic protective layer. Layers made of SiO ₂ , Al ₂ O ₃ , TiO ₂ or CeO _{2 are} preferred as oxide layers. In the present text, sol-gel layers are layers that are produced using a sol-gel process.

The layer thickness of such a transparent protective layer is, for example, 0.5 to 250 µm, suitably 1 to 200 µm and preferably 1 to 150 µm. The transparent one Protective layer can, for example, serve as the front end of the interference layer Protection against the effects of weather or liquids that favor corrosion (acidic Rain, bird droppings, etc.) can be applied.

The sol-gel layers have a glass-like character. Sol-gel layers contain, for example, polymerization products from organically substituted alkoxysiloxanes of the general formula Y _n Si (OR) _4-n where Y is for example a non-hydrolyzable monovalent organic group and R is for example an alkyl, aryl, alkaryl or aralkyl group, and n is a natural number from 0 to 3. If n is 1 or 2, R can be a C ₁ -C ₄ alkyl group. Y can be a phenyl group, n can be 1 and R can be a methyl group.

In another embodiment, the sol-gel layer can be a polymerization product of organically substituted alkoxy compounds of the general formula X _n AR _4-n where A is Si, Ti, Zr or Al, X is HO, alkyl-O or Cl-, R is phenyl, alkyl, alkenyl, vinyl ester or epoxy ether and n is a number of 1, 2 or 3 means. Examples of phenyl are unsubstituted phenyl, or mono-, di- or trisubstituted C ₁ -C ₉ -alkyl-substituted phenyl, for alkyl equal to methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, pentyl etc. for Alkenyl -CH = CH ₂ , allyl, 2-methylallyl, 2-butenyl etc., for vinyl ester - (CH ₂ ) ₃ -OC (= O) -C (-CH ₃ ) = CH ₂ and for epoxy ether - (CH ₂ ) ₃ -O-CH ₂ -CH (-O-) CH ₂ .

The sol-gel layers are advantageous directly or indirectly through a sol-gel process applied to the interference layer. For this purpose, for example, alkoxides and halosilanes mixed and in the presence of water and suitable catalysts hydrolyzed and condensed. After removal of water and solvent, it forms a sol that is applied to the interference layer by immersion, spinning, spraying, etc. , whereby the sol converts into a gel film, for example under influence of temperature and / or radiation. As a rule, silanes are used to form the sol, it is also possible to partially replace the silanes with compounds which instead of silicon contain titanium, zircon or aluminum. So that the hardness, density and the refractive index of the sol-gel layer can be varied. The hardness of the sol-gel layer can also be controlled using various silanes, for example by forming an inorganic network to control hardness and thermal Stability or by using an organic network to control elasticity. A sol-gel layer between the inorganic and organic polymers can be classified via the sol-gel process through targeted hydrolysis and Condensation of alkoxides, mainly of silicon, aluminum, titanium and zircon the interference layers are applied. The process turns it into an inorganic Network built up and over correspondingly derivatized silicic acid esters can additionally organic groups are built in, on the one hand for functionalization and on the other can be used to form defined organic polymer systems. In the further the sol-gel film can also be electro-coated according to the cataphoretic principle Deposition of an amine and organically modified ceramic can be deposited.

The interference layers according to the invention are preferably suitable for lighting technology Applications, for example for creating surfaces with intense colors and / or colors dependent on the illumination and / or viewing angle for, for example decorative lights, mirrors or decorative surfaces of ceiling or wall elements. Corresponding interference layers can also be used as forgery-proof surfaces everyday objects, such as packaging or containers, be used. Such interference layers are also preferred as Surfaces of auto parts, in particular body parts, profiles or facade elements used for the construction industry, or for interior furnishings.

The present invention also relates to a method for producing the previously described Interference layer as a coloring surface layer of an aluminum body.

According to the invention, this is achieved in that the surface of the aluminum body is oxidized electrolytically in an electrolyte which does not redissolve the aluminum oxide, and the desired layer thickness d of the oxide layer formed, measured in nm, by choosing a constant electrolysis DC voltage U in volts, which is determined by d /1.6 ≤ U ≤ d /1.1 is selected, is set, and the aluminum oxide layer formed in this way is provided with a partially transparent layer on its free surface.

The production of interference layers according to the invention requires a clean aluminum surface, i.e. the aluminum surface to be electrolytically oxidized usually has to prior to the method of surface treatment according to the invention, the so-called Pretreatment.

The aluminum surfaces usually have a naturally occurring oxide layer, which is often contaminated by foreign substances due to its history. Such Foreign substances can, for example, residues of rolling aids, transport protection oils, Corrosion products or pressed-in foreign particles and the like. For the purpose of The removal of such foreign substances usually involves the aluminum surfaces Cleaning agents that exert a certain pickling attack are chemically pretreated. To In addition to acidic aqueous degreasing agents, alkaline degreasing agents are particularly suitable based on polyphosphate and borate. A cleaning with moderate to strong Material removal involves pickling or etching using strongly alkaline or acid pickling solutions, such as. Sodium hydroxide solution or a mixture of nitric acid and hydrofluoric acid. Here the natural oxide layer and with it all impurities built into it away. When using strongly attacking alkaline stains, stain deposits often arise, which have to be removed by an acidic aftertreatment. A cleaning without Surface erosion is the degreasing of the surfaces by using organic solvents or aqueous or alkaline cleaner.

Depending on the surface condition, there is also mechanical surface abrasion necessary. Such surface pretreatment can be done, for example, by grinding, Blasting, brushing or polishing are done and, if necessary, by chemical aftertreatment be supplemented.

Aluminum surfaces show a very high reflectivity in the bare metal state for light and heat rays. The smoother the surface, the higher the level Reflection and the more shiny the surface appears. You get the highest shine Pure aluminum and on special alloys, such as AlMg or AlMgSi.

A highly reflective surface is achieved, for example, by polishing, milling, or rolling with highly polished rollers in the last rolling pass, by chemical or electrolytic Shine, or by combining the aforementioned surface treatment processes reached. Polishing can be done with buffing wheels made of a soft cloth, for example and if necessary done using a polishing paste. When polishing through Rolling can take place in the last rolling pass, for example by means of engraved or etched steel rolls or by a predetermined structure and between the rolls and the rolling stock arranged means additionally a predetermined surface structure in the aluminum surface be impressed. The chemical shine happens through, for example Use of a highly concentrated mixture of acids at usually high temperatures of approx. 100 ° C. Acidic or alkaline electrolytes can be used for electrolytic shining are used, usually acidic electrolytes being preferred.

The barrier layers of the interference layers according to the invention point to aluminum surfaces a purity of 99.5 to 99.98 wt .-% no significant changes in lighting technology the surface properties of the original aluminum surfaces, i.e. the Surface condition of the aluminum surfaces, such as that present after the shine is largely retained after the application of the barrier layer. It is however, take into account that the metal purity of the surface layer, for example the glossy result of an aluminum surface can very well have an influence.

In the method according to the invention, at least the aluminum surface to be oxidized with a with regard to the desired color or with regard to the desired color structure provided predetermined surface condition and then electrically conductive liquid, the electrolyte, and as an anode to a DC voltage source connected, usually stainless steel, graphite, Lead or aluminum is used. According to the invention, the electrolyte is such that that it does not chemically dissolve the aluminum oxide formed during the electrolysis process, i.e. there is no redissolution of the aluminum oxide. In the DC field hydrogen gas develops at the cathode and oxygen gas at the anode. The one at the Oxygen formed on the aluminum surface forms a reaction with the aluminum increasingly thicker oxide layer during the process. Since the sheet resistance with the increasing thickness of the barrier layer increases rapidly, the current flow decreases accordingly quickly and the layer growth stops.

The electrolytic production of barrier layers according to the present invention permits precise control of the resulting barrier layer layer thickness. The maximum layer thickness in nanometers (nm) achieved with the method according to the invention corresponds in a first approximation to the voltage applied and measured in volts (V), ie the maximum layer thickness achieved is linearly dependent on the anodizing voltage. The exact value of the maximum layer thickness as a function of the applied DC voltage U can be determined by a simple preliminary test and is 1.1 to 1.6 nm / V, the exact values of the layer thickness depending on the voltage applied being dependent on the electrolyte used, ie its composition and its temperature, and the material composition of the surface layer of the aluminum body.

The measurement of the color tint of the interference layer surface can be done, for example, by means of a spectrometer.

By using a non-redissolving electrolyte, the barrier layers are almost non-porous, i.e. any pores that occur result, for example, from contamination in the Electrolytes or from structural defects in the aluminum surface layer, however only insignificant due to dissolution of the aluminum oxide in the electrolyte.

For example, non-redissolving electrolytes can be used in the process according to the invention organic or inorganic acids, usually diluted with water, with a pH of 2 and larger, preferably 3 and larger, in particular 4 and larger and 8.5 and smaller, preferably 7 and smaller, in particular 5.5 and smaller, can be used. To be favoured cold, i.e. at room temperature, processable electrolytes. Inorganic ones are particularly preferred or organic acids, such as sulfuric or phosphoric acid in low concentrations, Boric acid, adipic acid, citric acid or tartaric acid, or mixtures thereof, or Solutions of ammonium or sodium salts of organic or inorganic acids, in particular the named acids and their mixtures. The Solutions preferably have a total concentration of 100 g / l or less, in particular 2 to 70 g / l of ammonium or sodium salt dissolved in the electrolyte. Very particularly preferred be solutions of ammonium salts of citric or tartaric acid or Sodium salts of phosphoric acid.

A very particularly preferred electrolyte contains 1 to 5% by weight of tartaric acid, to which, for example, an amount of ammonium hydroxide (NH ₄ OH) corresponding to the desired pH value can be added.

The electrolytes are usually aqueous solutions.

The optimum electrolyte temperature for the method according to the invention depends on the one used Electrolytes off; but is generally for the quality of the barrier layer obtained of minor importance. Temperatures are used for the method according to the invention from 15 to 97 ° C and especially those between 18 and 50 ° C preferred.

The precise control of the barrier layer thickness with the method according to the invention allows, for example by means of appropriately designed, tip-shaped or plate-shaped cathodes, that is to say by controlling the locally acting anodizing potential, the production of locally different but predetermined barrier layer thicknesses, as a result of which, for example, interference layer surfaces are formed with predefined color patterns can. The DC electrolysis voltage U applied during the anodic oxidation of the aluminum surface is chosen to be different locally, so that after the partially transparent layer has been applied, a structured coloring or a color pattern with, for example, intensive colors is obtained. The locally different anodizing potential required for the production of color samples is preferably achieved by choosing a predetermined cathode shape.

The process according to the invention is particularly suitable for continuous production of interference layers through continuous electrolytic oxidation of the aluminum surface and / or continuous application of the partially transparent layer in a continuous system, preferably in an anodic strip anodizing and coating system.

Example 1:

Aluminum body with a purity of 99.90% by weight Al with a high gloss surface and Aluminum body with a purity of 99.85% by weight Al with an electrochemically roughened High-gloss surfaces are electrolytically polished and provided with a barrier layer, the electrochemically roughened high-gloss surface is also referred to as a matt gloss Surface is called. By choosing the anodizing voltage in the range from 60 to 280 V barrier layers with layer thicknesses of 78 to 364 nm are produced. Samples are provided with an approximately 10 nm thick partially transparent layer of Au or Pt. the resulting interference layer surfaces show the Al surface texture, and colors depending on the viewing angle and the thickness of the barrier layer.

Tables 1 and 2 show the results of the micro-color measurements according to DIN 5033 for High-gloss surfaces produced, different thickness barrier layers, with an approximately 10 nm thick, partially transparent metal layer are provided, in Table 1 the corresponding Values for a partially transparent layer made of Au and in Table 2 the values for a partially transparent one Layer of Pt are listed.

The micro-color measurements according to DIN 5033 are non-directional on the interference layer surface incident light. The direction of observation is against the Interference layer surface normal inclined by 8 °.

In the following tables, L *, a * and b * are color numbers. L * represents the brightness, where 0 means absolutely black and 100 absolutely white. a * denotes a value on the Red-green axis, where positive a * values indicate red and negative a * values green colors. b * shows the position of the hue on the yellow-blue axis, with positive b * values yellow and negative b * values denote blue colors. The location of a hue in the a * -b * Level thus provides information about its hue and its saturation.

The additional color specifications in the following tables relate to the visually perceptible colors at a viewing angle of 0 ° and 70 ° with respect to the interference layer surface normal. Anodizing voltage [V] Junction thickness [nm] Color (according to RAL) Micro-color measurements 0 ° 70 ° L * a * b * 60 78 Golden yellow Cadmium yellow 62.0 24.8 49.9 80 104 Heather violet Beige brown 53.9 32.7 -46.3 100 130 Light blue Red purple 77.2 -31.0 -23.4 180 234 Beige red Cadmium yellow 72.0 32.8 13.3 200 260 Heather violet Honey yellow 65.1 55.9 -32.4 220 286 Blue purple Blue purple 66.3 14.7 -30.5 240 312 Emerald green Heather violet 77.5 -57.1 17.7 260 338 Light green Blue purple 82.8 -44.3 61.4 280 364 Ocher yellow Emerald green 81.9 9.1 28.4 Anodizing voltage [V] Junction thickness [nm] Color (according to RAL) Micro-color measurements 0 ° 70 ° L * a * b * 60 78 Green Brown Silver gray 61.1 1.1 11.5 80 104 Blue purple Bastalt gray 60.2 11.3 -17.1 100 130 Light blue Navy blue 68.4 - 6.6 -35.7 180 234 Corn yellow Brown beige 59.4 21.0 2.7 200 260 Red purple Pale brown 56.3 34.0 -38.6 220 286 Violet blue Violet blue 56.9 12.8 -48.1 240 312 Patina green Blue purple 71.8 -51.6 0.4 260 338 Grass green Water blue 79.1 -43.0 32.4 280 364 Saffron yellow May green 75.2 17.9 24.6

Tables 3 and 4 show the results of the micro-color measurements according to DIN 5033 for barrier layers of various thicknesses produced on matt glossy surfaces, which are provided with a 10 nm thick, partially transparent metal layer, in Table 3 the corresponding values for a partially transparent layer Au and in Table 4 the values for a partially transparent layer of Pt are listed. Anodizing voltage [V] Junction thickness [nm] Color (according to RAL) Micro-color measurements 0 ° 70 ° L * a * b * 80 104 Heather violet Beige brown 57.8 40.5 -26.1 100 130 Light blue Red purple 77.3 -25.9 -31.5 160 208 Sulfur yellow Cadmium yellow 91.3 - 7.3 70.6 180 234 Golden yellow Cadmium yellow 81.3 16.9 55.8 200 260 Heather violet Honey yellow 70.7 53.2 -22.3 220 286 Blue purple Blue purple 70.5 15.1 -32.7 240 312 Turquoise blue Heather violet 73.7 -23.1 -12.8 260 338 Light green Blue purple 82.1 -55.9 34.7 280 364 Cadmium yellow Yellow-green 86.0 -12.6 59.0 Anodizing voltage [V] Junction thickness [nm] Color (according to RAL) Micro-color measurements 0 ° 70 ° L * a * b * 80 104 Beige brown Moss gray 55.0 13.2 - 8.5 100 130 Brilliant blue Red purple 69.0 - 1.8 -43.8 160 208 Saffron yellow Lemon yellow 84.7 7.3 39.8 180 234 Corn yellow Brown beige 75.9 8.2 22.6 200 260 bright red purple Pale brown 71.6 19.9 -15.9 220 286 Blue purple Blue purple 68.9 16.3 -33.1 240 312 Dove blue Blue purple 70.9 -15.1 -21.5 260 338 Grass green Water blue 81.1 -43.8 14.0 280 364 Zinc yellow Grass green 84.0 - 6.9 39.3

A comparison of the information found in Tables 1 and 2 with that of Tables 3 and 4 described clearly shows the influence of the surface quality of the surface layer of the aluminum body, i.e. the structure of the surface layer of the aluminum body determines the color.

Table 5 shows the comparison of results of the micro-color measurements according to DIN 5033 for interference layers with and without a partially transparent layer for selected junction thickness values. Junction thickness [nm] Matt surface not steamed Au-steamed Pt-vaporized L * a * b * L * a * b * L * a * b * 104 90.6 -1.2 -6.4 57.8 40.5 -26.1 55.0 13.2 -8.5 234 93.1 3.7 0.3 81.3 16.9 55.8 75.9 8.2 22.6 364 94.4 -0.3 3.1 86.0 -12.6 59.0 84.0 -6.9 39.3 Junction thickness [nm] High gloss surface not steamed Au-steamed Pt-vaporized L * a * b * L * a * b * L * a * b * 104 88.0 -3.7 -5.5 53.9 32.7 -46.3 60.2 11.3 -17.1 234 87.4 3.1 -4.4 72.0 32.8 13.3 59.4 21.0 2.7 364 89.5 0.2 -0.2 81.9 9.1 28.4 75.2 17.9 24.6

Example 2:

An aluminum foil with an electrolytically polished high-gloss aluminum surface is selected by choosing the anodizing voltage in the range from 30 to 380 V according to the invention Provide barrier layers with layer thicknesses of 39 to 494 nm. The barriers will continue with a partially transparent chrome layer with a uniform for all samples Layer thickness, which is in the layer thickness range of 1 to 5 nm, provided. The application The chrome layer is made by sputtering in a belt process, the belt speed is about 25 m / min.

Table 6 shows the results of the micro-color measurements according to DIN 5033 for the interference layers described above. The comments made in Example 1 apply to the micro-color measurements. The additional color specifications according to RAL in Table 6 relate to the visually perceptible colors at a viewing angle of 0 ° and 80 ° with respect to the interference layer surface normals. Anodizing voltage [V] Junction thickness [nm] Micro-color measurements Color (according to RAL) L * a * b 0 ° 80 ° 30th 39 66 3rd 18th Olive yellow Light ivory 40 52 50 7 25th Green Brown Olive gray 50 65 38 12th 11 Nut brown beige 60 78 30th 20th -38 Midnight blue Pale brown 70 91 47 0 -45 Gentian blue Gentian blue 80 104 63 -9 -39 Sky blue Sky blue 90 117 70 -12 -32 Sky blue Violet blue 100 130 84 -15 -13 Light blue Brilliant blue 110 143 86 -15 -5 Turquoise blue Brilliant blue 120 156 89 -12 22 Green beige Bluish gray 130 169 88 -10 36 Honey yellow colorless 140 182 81 1 63 Lemon yellow Light ivory 150 195 82 0 62 Lemon yellow Light ivory 160 208 70 22 46 Saffron yellow ivory 170 221 57 47 -8th Dusky pink Sand yellow 180 234 48 61 -44 Signal violet Golden yellow 190 247 45 50 -67 Purple violet Saffron yellow 200 260 54 1 -61 Gentian blue Rose 210 273 61 -22 -50 Gentian blue Light pink 220 286 72 -48 -20 Water blue Heather violet 230 299 80 -52 11 May green Red purple 240 312 84 -44 38 Yellow-green Brilliant blue 250 325 85 -32 56 Pale yellow green Light blue 260 338 83 -9 53 Broom yellow Bright blue 270 351 77 27 13 Light pink Turquoise blue 280 364 73 42 -5 Dusky pink May green 290 377 68 57 -25 Rose Yellow-green 300 390 62 62 -40 Heather violet Sulfur yellow 310 403 60 56 -46 Traffic lane Zinc yellow 320 416 59 24th -41 Signal violet beige 330 429 68 -59 1 Water blue Light pink 340 442 72 -74 17th Mint green Hellerika violet 350 455 75 -73 27 Traffic green Heather violet 360 468 77 -60 31 Emerald green Dark purple violet 370 481 80 -30 21 Patina green Signal violet 380 494 78 10th 1 colorless Red purple

Claims (16)

1. Interference layer which acts as a colouring surface layer on aluminium items, said layer containing an aluminium oxide layer and, deposited on this, a partially transparent layer,
   characterised in that,
   the aluminium oxide layer is a transparent, pore-free barrier layer produced by anodising, of predetermined thickness d corresponding to the desired surface colour of the interference layer, the thickness d of the barrier layer lying between 20 and 900 nm, and the partially transparent layer exhibiting a wavelength dependent trans-mission τ (λ) which is greater than 0,01 and smaller than 1.
2. Interference layer according to claim 1, characterised in that the thickness d of the barrier layer lies between 30 and 800 nm, in particular between 35 and 500 nm.
3. Interference layer according to claim 1 or 2, characterised in that for the purpose of creating a structured colour effect or to produce a coloured pattern, the barrier layer exhibits appropriate, predetermined, local differences in thickness.
4. Interference layer according to one of the claims 1 to 3, characterised in that the partially transparent layer of metal, in particular of Ag, Al, Au, Cr, Cu, Nb, Ni, Pt, Pd, Rh, Ta, Ti, or a metal alloy containing at least one of these mentioned elements.
5. Interference layer according to one of the claims 1 to 4, characterised in that the partially transparent layer exhibits a layer thickness of 0.5 to 100 nm, especially preferred being a thickness of 1 to 80 nm, and especially 2 to 30 nm.
6. Interference layer according to one of the claims 1 to 5, characterised in that for the purpose of creating a structured colour effect or to produce a coloured pattern, the partially transparent layer exhibits appropriate, predetermined, local differences in thickness.
7. Interference layer according to one of the claims 1 to 6, characterised in that the partially transparent layer is in the form of a lattice-shaped net, wherein the distances between the lines of the lattice-shaped net are preferably in the sub-micron range.
8. Interference layer according to claim I or 3, characterised in that the partially transparent layer is a sol-gel layer of preferably 0.5 to 250 µm with reflecting particles embedded therein, where the dimensions of the reflecting particles are preferably in the micron or sub-micron range, preferably in the sub-micron range.
9. Interference layer according to claim 8, characterised in that, for the purpose of creating optical colour patterns, the partially transparent sol-gel layer containing preferably essentially uniformly dispersed reflecting particles exhibits a structure with local differences in layer thickness.
10. Interference layer according to one of the claims 1 to 9, characterised in that the side of the partially transparent layer facing away from the barrier layer is protected from mechanical and chemical effects by means of a transparent protective layer.
11. Interference layer according to claim 10, characterised in that the transparent protective layer is a varnish, a sol-gel layer or a thin oxide layer preferably out of SiO₂, Al₂O₃ or TiO₂.
12. Process for manufacturing an interference layer according to one of the claims 1 to 9, characterised in that, the surface of the aluminium item is oxidised electrolytically in an electrolyte that does not redisolve aluminium oxide and that the desired thickness d of the resultant oxide layer, measured in nm, is obtained by choosing a constant electrolyte voltage U in volts according to the relationship d/1.6 ≤ U ≤ d/1.1 and the thus formed aluminium oxide layer is provided with a partially transparent layer on its free surface.
13. Process according to claim, 12, characterised in that, as non re-dissolving electrolyte, solutions containing organic or inorganic acids are employed, and the solutions exhibit a pH-value of 2 to 8.5
14. Process according to claim, 13, characterised in that, the non re-dissolving electrolyte is a solution of ammonium or sodium salts of organic or inorganic acids or a solution containing ammonium or sodium salts of organic or inorganic salts and the corresponding organic or inorganic acids.
15. Process according to one of the claims 12 to 14, characterised in that the electrolytic oxidation of the aluminium surface and/or the provision of the partially transparent layer is performed as a continuous process in a continuous production line, preferably in an anodic strip anodising and coating line.
16. Process according to one of the claims 12 to 15, characterised in that a locally different electrolysing direct current U is applied to the aluminium surface in order to obtain a structured colour effect or coloured pattern.