Thin-film structure for colouring metallic surfaces

The invention relates to a novel surface coating for oxidizable metals (especially aluminum), which is characterized in that (1) a thin layer of less than 1 μm is applied to an aluminum plate (2) by anodizing, which (3) is applied to the surface carries metallic or at least conductive particles. For protection, this structure can be covered with a layer of a lacquer or glass-like material. This nanometric structure causes a strong coloration of the cluster absorption through an optical resonance enhancement with the reflective aluminum surface. In contrast to pigment colors in the structure according to the invention, the resulting color depends on the distance between the metal particles and the mirror and not (!) Only on the intrinsic color of the particles. Unlike any color based on interference, this effect only occurs on much thinner, nanometric layers and only appears on metal-like particles.

The invention is based on a new type of coloring of aluminum, titanium or similar plates or foils using clusters and / or nanometric thin layers, with which in particular facade and body panels, but also aluminum used in the decor sector, can be optimally colored. The use in reflectors of all kinds to change the light color can also be seen as an important area of ​​application of the new product due to the pale-fast color.

In another typical application, the binding or separation of metallic particles (= clusters) can also be used as a color change. The binding or separation is converted into an easily visible optical signal through the resonance amplification of the clusters, in which the clusters interact with their mirror dipoles.

The parts of the structure according to the invention provided with reference symbols (see FIGS. 1 and 2) are assigned as follows: 1 = metal (preferably aluminum), 2 = anodized layer (0-1000 nm), 3 = metallic or metallic chromophoric particles, 4 = Protective lacquer or glass-like coating.

The structure consists of a metal layer on a carrier material, an inert spacer layer and a particle layer. In order to obtain a clear coloring, the diameter of the cluster is preferably chosen to be smaller than 40 nm; larger and asymmetrical particles can also be used with preference for broadband absorption. A change in the occupancy density of the particle layer on a molecular scale or changes in the spatial arrangement of the bound clusters on the sensor lead to the characteristic changes in the optical appearance of the surface.

Metallic or metal-like particle films with a mean cluster diameter smaller than 500 nm (preferably smaller than 40 nm, since very large particles scatter more than they absorb) have strong, narrow-band reflection minima, the spectral positions of which are extremely sensitive to the spatial arrangement, in particular the distance to an electron-conducting surface depend.

The structure can convert even the slightest changes in the surface coverage with clusters into clearly recognizable color changes, ie either into a change in absorbance at a certain wavelength or into a spectral shift in the absorption maximum.

In terms of the structure, a special effect can be observed here. While the absorption of chromophores is independent of the angle of observation, the spectral reflection minimum shifts strongly with the angle of observation. An object coated according to the invention therefore changes its color as a function of the angle of observation. This means that due to the curved surface, a passing car (e.g. Audi A8) from a distance show certain parts of the body in a metallic red color. When the car approaches, the same areas appear in blue. Due to the changing angle of incidence, the car appears in a golden hue as it drives past. Then the color change is repeated in reverse order. Similar effects would enable a completely new type of facade design when building high-rise buildings.

The particle layers can be applied, for example, by vapor deposition, sputtering, adsorptive attachment from solution, covalent coupling from solution or surface-catalyzed processes.

The material of the particles are mostly chemically stable metals such as gold, silver or copper.

In principle, other metals and alloys can also be used with different color quality, all of these or else color particles of suitable size and suitable optically resonant

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Behavior (e.g. precipitates from porphyrins, phthalocyanines, etc.) are used.

The present invention differs from the subject of the patent application "Optochemical sensor and method for its production, Austrian. Patent A 753/94 of April 12, 1994, US patent application 08/419, 615 of April 10, 1995, through the basic feature that it is not a sensor, and the use of hard anodized layers as spacer layers, the real, homogeneous color structure is achieved large, possibly curved and / or micro-rough surfaces, as well as their large-scale production.

The technological innovations according to the invention are:

• Color-stable sheets or foils or fibers or shiny metallic objects in a wide variety of freely selectable colors, • Construction of stable optical resonance structures through thin layers of absolutely reproducible thickness, • Use of anodizing processes combined with electrodynamic nanometric particle effects, • Decorative sheets or mirrored objects or objects that have different colors from different viewing directions.

The following examples describe the technical implementation:

Example 1: Surface-enhanced color effect on aluminum sheets

An oxide film is applied by anodizing to a high-gloss aluminum sheet without an anodized or protective lacquer layer. For this purpose, the aluminum sheet is immersed in 1 M boric acid, which has been adjusted to pH = 7.0 with NaOH, and connected to a voltage supply. The formation of an anodized layer of the desired color takes place, for example, in the case of “red” within a few minutes at 180 V and 2 mA / cm²,5 minutes. A very weak, slightly whitish cloudiness of the surface occurs. The sheet metal, which is coated with an anodized layer of uniform thickness, is sputtered with gold. In order to achieve optimal coloring, for example with 5 nm (mass thickness) within 10 seconds at a current strength of 40 mA and an argon pressure of 0.1 mbar.

Example 2: Surface-enhanced color effect on macroscopically curved, micro-rough aluminum foils

An oxide film is applied to a commercially available aluminum foil, which is coated on at least one side with an oxide film, by anodizing the other side. For this purpose, the aluminum foil is immersed in 1 M boric acid, which has been adjusted to pH = 7.0 with NaOH, and connected to a voltage supply. The formation of an anodized layer of the desired color takes place, for example, in the case of “yellow” within a few minutes at 120 V and 1.5 mA / cm², 5 minutes. A very weak, slightly whitish cloudiness of the surface occurs. The sheet metal covered by an anodized layer of uniform thickness is coated with metal colloids. In order to achieve an optimal coloring, the anodized layer is coated with glycidylsilane by silanizing the anodized film overnight in a silicon atmosphere via the vapor phase. The silane layer is crosslinked for 15 minutes at 105 ° C. The slide is then incubated with a solution of protein-protected metal colloids. The metal colloids are used in a concentrated solution of approx. 1% in order to guarantee the shortest possible reaction time. For example, 0.1 M phosphate pH = 4.5 is chosen as the buffer. In order to achieve the optimal coloring of the surface, it is of great importance to use colloids with the broadest possible absorption spectrum.

Example 3: Surface-protected paint panels

A colored sheet produced according to Example 1 or 2 is coated with spray or dip lacquer made of polyurethane or epoxy resin. The paint is dried and, if necessary, cured at an elevated temperature. The exact curing conditions are to be selected according to the specifications of the paint manufacturer.

Example 4: Surface-protected paint panels

A paint sheet produced according to example 1 or 2 is coated with silicate solution by spraying, spinning or dipping processes. The solvent is removed and the silicate at increased

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Temperature, glazed by UV radiation or electron beams. The exact curing conditions are to be selected according to the manufacturer's instructions