Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
  • C25D11/02—Anodisation
  • C25D11/04—Anodisation of aluminium or alloys based thereon
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
  • C25D11/02—Anodisation
  • C25D11/04—Anodisation of aluminium or alloys based thereon
  • C25D11/18—After-treatment, e.g. pore-sealing
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/31504—Composite [nonstructural laminate]
  • Y10T428/31678—Of metal

Definitions

• the present invention relates to an interference layer as a color-imparting surface layer of aluminum bodies, comprising an aluminum oxide layer and a partially transparent layer deposited thereon.
• the invention further relates to a method for producing the interference layer according to the invention.
• Interference layers which eliminate certain longitudinal waves of the incident light through interference, are known in optics as so-called filters.
• filters are usually produced by applying a high-purity, thin metal layer on glass, by subsequent deposition of a dielectric layer, and by further applying a semitransparent metal layer.
• the deposition of the individual layers is usually carried out 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 cannot generally 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 process per se i.e. the anodic oxidation of the aluminum surface with direct current in a sulfuric acid electrolyte can be used.
• 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 layer thickness constancy of the interference layer.
• the anodic oxide layers produced in sulfuric acid are only made of pure aluminum and AlMg or AlMgSi alloys based on pure aluminum (Al ⁇ 99.85% by weight) colorless and crystal clear.
• alloy components such as Fe or Si-rich intermetallic phases, can be built into the oxide layer, which then lead to uncontrollable light absorption and / or light scattering and thus result in more or less cloudy layers or layers with an uncontrollable coloring.
• the object of the present invention is to provide an interference layer which can be produced cost-effectively as a coloring surface layer of aluminum bodies, which avoids the disadvantages mentioned above and enables the light-fast coloring of aluminum surfaces, or can be used as a selective reflector surface.
• the aluminum oxide layer is an anodically produced, transparent and pore-free barrier layer with a barrier layer thickness d preselected in accordance with 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 ⁇ ( ⁇ ) that is greater than 0.01 and less than 1.
• interference layers according to the invention can be applied, for example, to surfaces of piece goods, 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 to any materials with an aluminum layer, for example electrolytically deposited.
• the material surface to be provided with the interference layer according to the invention preferably consists of pure aluminum with a degree of purity equal to or greater than 98.3% by weight of aluminum or aluminum alloys made of this aluminum with at least one of the elements from the series of Si, Mg, Mn, Cu, Zn or Fe .
• Aluminum surfaces made of high-purity 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% by weight Al are further preferred.
• the aluminum surfaces can have any shape and can optionally also be structured. In the case of rolled aluminum surfaces, these can be treated, for example, using 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 of ceiling or wall elements, or for applications in vehicle construction, for example for decorative parts or closures.
• structured surfaces with structure sizes of expediently 1 nm to 1 mm and preferably of 50 nm to 100 ⁇ m are used.
• the barrier layer thickness is produced in a controlled manner in accordance with the desired coloring.
• the barrier layer In order to achieve the highest possible color fastness of the interference layer, the barrier layer must also be non-porous. Diffuse light scattering that is difficult to control and thus uneven color development is avoided.
• the term pore-free is not understood to mean absolute freedom from pores. Rather, the barrier layer of the interference layer according to the invention is essentially pore-free.
• the anodically produced aluminum oxide layer has essentially no process-related porosity.
• a process-related porosity means, for example, the use of an aluminum oxide-dissolving electrolyte.
• the pore-free barrier layer preferably has a porosity of less than 1% and in particular less than 0.5%.
• the dielectric constant ⁇ of the barrier layer depends, among other things. on the process parameters used to produce the barrier layer during the anodic oxidation.
• the dielectric constant ⁇ of the barrier layer at a temperature of 20 ° C. is expediently 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 properties of the aluminum surface, the angle of incidence of the light incident on 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 ⁇ ( ⁇ ) of the partially transparent Layer.
• the interference layer according to the invention has a transmission ⁇ ( ⁇ ) between 0.3 and 0.7.
• the layer thickness of the barrier layer of interference layers according to the invention is 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 — viewed over the entire interference layer surface — can 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. Partial areas of the interference layer surface with the same barrier layer thickness can range from submicron areas to large areas in relation to the entire interference layer surface.
• all reflective materials are suitable as partially transparent layer materials.
• Commercial metals of all purities and in particular Ag, Al, Au, Cr, Cu, Nb, Ni, Pt, Pd, Rh, Ta, Ti, or metal alloys containing at least one of these elements are preferred.
• the barrier layer can be coated with the partially transparent layer, 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.
• physical methods such as vapor deposition or sputtering
• chemical methods such as CVD (chemical vapor deposition) or direct chemical deposition, or by electrochemical methods.
• the partially transparent layer can be applied over the entire surface of the barrier layer or only affect partial areas of the interference layer surface.
• the partial areas can also form a grid-like network.
• Submicron structures are preferred for partially transparent layers that only affect partial areas of the interference layer surface.
• the partially transparent layer can have a uniform layer thickness or a structured, i.e. show a locally different layer thickness over the partially transparent layer. In the latter case, for example, color patterns can also be produced with a uniformly thick barrier layer.
• the layer thickness of the partially transparent layer is expediently from 0.5 to 100 nm over the entire interference layer surface, preferably from 1 to 80 nm and in particular from 2 to 30 nm.
• the partially transparent layer can also be a sol-gel layer with a layer thickness of preferably 0.5 to 250 ⁇ m and in particular of 0.5 to 150 ⁇ m with embedded reflective layers
• Suitable reflective particles are preferably metal particles and in particular those made of Ag, Al, Au, Cr, Cu, Nb, Ni, Pt, Pd, Rh, Ta, Ti, or metal alloys containing at least one of these aforementioned elements.
• the reflecting particles can be evenly distributed in the sol-gel layer or can essentially be all in a plane parallel to the barrier layer surface.
• the partially transparent sol-gel layer has a locally different layer thickness, in particular if it has reflecting particles which are essentially uniformly distributed in the sol-gel layer. This can result in interference layers with optical color patterns.
• the locally different layer thickness of the partially transparent sol-gel layer can be produced, for example, by roller embossing, if appropriate after a previously carried out heat treatment in which the sol-gel layer is at least partially polymerized or cured.
• the protective layer can be any transparent layer that offers mechanical and / or chemical protection to the partially transparent layer.
• 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.
• 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 ⁇ m, advantageously 1 to 200 ⁇ m and preferably 1 to 150 ⁇ m.
• the transparent protective layer can be applied, for example, as a front end of the interference layer to protect against the effects of the weather or liquids that favor corrosion (acid rain, bird droppings, etc.).
• 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.
• 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.
• the sol-gel layers are advantageously applied directly or indirectly to the interference layer by means of a sol-gel process.
• a sol-gel process for example, alkoxides and halosilanes are mixed and hydrolyzed and condensed in the presence of water and suitable catalysts. After removal of the water and solvent, a sol is formed which is applied to the interference layer by immersion, spinning, spraying, etc., the sol converting into a gel film, for example under the influence of temperature and / or radiation.
• silanes are used to form the sol, it is also possible to partially replace the silanes with compounds which contain titanium, zirconium or aluminum instead of the silicon. This enables the hardness, density and refractive index of the sol-gel layer to be varied.
• the hardness of the sol-gel layer can also be controlled by using different silanes, for example by forming an inorganic network to control the hardness and thermal stability or by using an organic network to control the elasticity.
• a sol-gel layer which can be classified between the inorganic and organic polymers, can be applied to the interference layers via the sol-gel process through targeted hydrolysis and condensation of alkoxides, predominantly silicon, aluminum, titanium and zirconia. The process builds up an inorganic network and, via correspondingly derivatized silicic acid esters, additional organic groups can be incorporated, which are used on the one hand for functionalization and on the other hand for the formation of defined organic polymer systems.
• the sol-gel film can also be deposited by electro-dip painting according to the principle of cataphoretic deposition of an amine and organically modified ceramic.
• the interference layers according to the invention are preferably suitable for lighting applications, for example for producing surfaces with intensive colors and / or colors dependent on the illumination and / or viewing angle, for example for decorative lights, mirrors or decorative surfaces of ceiling or wall elements.
• Corresponding interference layers can also be used as tamper-proof surfaces of everyday objects, such as packaging or containers.
• Such interference layers are furthermore preferably used as surfaces of auto parts, in particular body parts, of profiles or of facade elements for the construction industry, or for interior furnishings.
• the present invention also relates to a method for producing the interference layer described above as a color-imparting surface layer of an aluminum body.
• this is achieved in that the surface of the aluminum body is oxidized electrolytically in an electrolyte that 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.
• interference layers according to the invention requires a clean aluminum surface, i.e. the aluminum surface to be electrolytically oxidized usually has to be supplied to a surface treatment, the so-called pretreatment, prior to the method according to the invention.
• 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 be, for example, residues of rolling aids, transport protection oils, corrosion products or pressed-in foreign particles and the like.
• the aluminum surfaces are usually chemically pretreated with cleaning agents which exert a certain pickling attack.
• alkaline degreasing agents are particularly suitable based on polyphosphate and borate. Cleaning with moderate to heavy material removal is pickling or etching using strongly alkaline or acidic pickling solutions, such as sodium hydroxide solution or a mixture of nitric acid and hydrofluoric acid.
• Such surface pretreatment can be carried out, for example, by grinding, blasting, brushing or polishing and, if necessary, can be supplemented by a chemical aftertreatment.
• Aluminum surfaces show a very high reflectivity for light and heat rays in the bare metal state. The smoother the surface, the higher the specular reflection and the glossier the surface. Highest shine is achieved on high-purity aluminum and on special alloys such as AlMg or AlMgSi.
• a highly reflective surface is achieved, for example, by polishing, milling, by rolling with highly polished rollers in the last rolling pass, by chemical or electrolytic polishing, or by a combination of the aforementioned surface treatment processes.
• the polishing can be done, for example, with buffing wheels made of soft cloth and, if necessary, using a polishing paste.
• a predetermined surface structure can additionally be embossed into the aluminum surface in the last rolling pass, for example by means of engraved or etched steel rollers or by means having a predetermined structure and arranged between the rollers and the rolling stock.
• the chemical shine occurs, for example, by using a highly concentrated acid mixture at usually high temperatures of approx. 100 ° C.
• Acidic or alkaline electrolytes can be used for the electrolytic luster, with acidic electrolytes usually being preferred.
• the barrier layers of the interference layers according to the invention show on aluminum surfaces with a purity of 99.5 to 99.98% by weight no significant changes in the lighting properties of the surface properties of the original aluminum surfaces, that is to say the surface condition of the aluminum surfaces, as is present, for example, after the shine, remains largely after the application of the barrier layer receive. It is however, it must be taken into account that the metal purity of the surface layer, for example on the gloss result of an aluminum surface, can very well have an influence.
• the aluminum surface to be oxidized is provided with a surface state predetermined with respect to the desired color or with respect to the desired color structure and then placed in an electrically conductive liquid, the electrolyte, and connected as an anode to a direct voltage source, usually stainless steel as the negative electrode , Graphite, lead or aluminum is used.
• the electrolyte is such that it does not chemically dissolve the aluminum oxide formed during the electrolysis process, i.e. there is no redissolution of the aluminum oxide.
• hydrogen gas develops at the cathode and oxygen gas at the anode.
• the oxygen that forms on the aluminum surface forms an oxide layer that becomes increasingly thicker as a result of the reaction with the aluminum. Since the layer resistance increases rapidly with increasing thickness of the barrier layer, the current flow decreases correspondingly 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 as a function of the applied voltage 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 color tint of the interference layer surface can be measured, for example, using a spectrometer.
• non-redissolving electrolyte means that the barrier layers are almost pore-free, i.e. any pores that occur result, for example, from contamination in the electrolyte or from structural defects in the aluminum surface layer, but only insignificantly through dissolution of the aluminum oxide in the electrolyte.
• the non-redissolving electrolytes used in the process according to the invention are, for example, organic or inorganic acids, generally diluted with water, with a pH of 2 and greater, preferably 3 and greater, in particular 4 and greater and 8.5 and less, preferably 7 and less, especially 5.5 and smaller, can be used. Cold, i.e. at room temperature, processable electrolytes.
• Inorganic or organic acids such as sulfuric or phosphoric acid in low concentration, 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 acids mentioned by name and mixtures thereof, are particularly preferred .
• 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. Solutions of ammonium salts of citric or tartaric acid or sodium salts of phosphoric acid are very particularly preferred.
• 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.
• NH 4 OH ammonium hydroxide
• the electrolytes are usually aqueous solutions.
• the optimum electrolyte temperature for the method according to the invention depends on the electrolyte used; but is generally of minor importance for the quality of the barrier layer obtained. Temperatures of 15 to 97 ° C. and in particular those between 18 and 50 ° C. are preferred for the process according to the invention.
• 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 method according to the invention is particularly suitable for the continuous production of interference layers by 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.
• Aluminum bodies with a purity of 99.90% by weight Al with a high-gloss surface and aluminum bodies with a purity of 99.85% by weight Al with an electrochemically roughened high-gloss surface are electrolytically polished and provided with a barrier layer, the electro-chemically roughened high-gloss surface hereinafter being referred to as a matt, glossy surface becomes.
• the anodizing voltage in the range from 60 to 280 V
• barrier layers with layer thicknesses of 78 to 364 nm are produced.
• the samples are provided with an approximately 10 nm thick, partially transparent layer of Au or Pt. the resulting interference layer surfaces show colors which are dependent on the Al surface quality, as well as on the viewing angle and on the barrier layer thickness.
• Tables 1 and 2 show the results of the micro-color measurements according to DIN 5033 for barrier layers of different thicknesses produced on high-gloss surfaces, which are provided with an approximately 10 nm thick, partially transparent metal layer, in Table 1 the corresponding values for a partially transparent layer made of Au and in Table 2 the values for a partially transparent Pt layer are listed.
• micro-color measurements in accordance with DIN 5033 are carried out with the light hitting the interference layer surface in a non-directional manner.
• the direction of observation is inclined by 8 ° against the interference layer surface normal.
• 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 denote red and negative a * values denote green colors.
• b * shows the position of the hue on the yellow-blue axis, whereby positive b * values indicate yellow and negative b * values indicate blue colors.
• the position of a hue in the a * - b * plane thus provides information about its hue and saturation.
• Tables 3 and 4 show the results of the micro-color measurements according to DIN 5033 for barrier layers of different 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 Table 4 shows the values for a partially transparent layer of Pt, Table 3 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
• 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.
• Table 5 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
• An aluminum foil with an electrolytically polished high-gloss aluminum surface is provided with barrier layers according to the invention with layer thicknesses of 39 to 494 nm by choosing the anodizing voltage in the range from 30 to 380 V.
• the barrier layers are further provided with a partially transparent chrome layer with a layer thickness uniform for all samples, which lies in the layer thickness range from 1 to 5 nm.
• the application the chrome layer is made by sputtering in a belt process, the belt speed being approximately 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 RAL color specifications 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.

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• 1996
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