FIELD OF THE INVENTION

The present invention relates to a method of manufacturing a multilayer structure of differen metals and alloys to obtain a Mokume Gane effect on at least one surface of said structure a< well as a multilayer structure comprising alternating layers of a first layer of aluminium or of an alloy thereof and at least one further layer different from said first layer, said structure having a Mokume Gane effect on at least one surface of said structure. More specifically the present invention discloses a method for decorative enhancement of a surface of an aluminium-containing multilayer structure consisting of multiple layers of different metals or alloys in order to create a Mokume Gane (MG) structure in the surface thereof.

BACKGROUND OF THE INVENTION

In the art it is well known to obtain structures in metal objects in which the structures have been obtained by forging of two or more layers of metal plates into one compound structure. The resulting compound structure typically has certain attributes such as high strength and a layered structure available for decorative features.

The Mokume Gane effect refers to an effect obtained by a mixed-metal laminate with distinctive layered patterns and was originally developed in 17 ^th -century Japan.

KR2006013211 discloses a method for manufacturing a high-strength Cu sheet by continuously and repeatedly applying an accumulative roll-bonding process on layered Cu sheets.

US 2007/0275263 Al discloses cookware having improved uniform heat transfer over the entire cross section thereof, the cookware formed from a multilayered composite metal having a layer of stainless steel roll bonded at or near the core of the composite. The outermost layer may be a layer of roll bonded aluminium preferably having an anodized oute surface for scratch resistance and improved appearance. OBJECT OF THE INVENTION

It is an object of embodiments of the invention to provide a method to enhance the decorative effects of a surface of a multilayer structure to maximize the quality of the visual appearance thereof.

Another object of the embodiments of the invention is to provide a multilayer structure having an enhanced visual appearance.

SUMMARY OF THE INVENTION

It has been found by the present inventor(s) that by depressing and/or deforming parts of at least one surface of said multilayer structure before any of the subsequent steps of optionally grinding and/or polishing, optionally etching, anodizing and optionally dyeing and sealing of the structure, in any order, it is possible to obtain a decorative surface of a multilayer structure to obtain a Mokume Gane effect thereon.

So, in a first aspect the present invention relates to a method of manufacturing a multilayer structure of different metals and alloys to obtain a Mokume Gane effect on at least one surface of said structure, the method comprising: i) providing a multilayer structure of alternating layers of a first type of layer of aluminium or an alloy thereof and at least one further type of layer different from said first type of layer, said structure having a first and a second surface ii) Processing to provide depressions and/or deformations on parts of at least one surface of said structure; iii) Optionally grinding and/or polishing of at least one surface of the structure; iv) Optionally etching at least one surface of the structure; v) Anodizing said at least one surface of the structure to obtain a Mokume Gane effect on said surface; and vi) Optionally performing one or more of the steps of dyeing and/or sealing of the structure. In a second aspect the present invention relates to a multilayer structure of a first type of layer of aluminium or an alloy thereof and at least one further type of layer different from said first type of layer; said structure comprising alternating layers of a) a first type of layer of aluminium or an alloy of aluminium and at least one alloying metal selected from the group consisting of copper, iron, manganese, magnesium, silicon, zirconium, titanium, zinc, chromium, cerium, yttrium, and molybdenum, and b) at least one further type of layer of a material selected from the group consisting of: i) an alloy of aluminium and at least one alloying metal selected from the group consisting of copper, iron, manganese, magnesium, silicon, zirconium, titanium, zinc, chromium, cerium, yttrium, and molybdenum; and ii) aluminium or an alloy thereof comprising discrete inclusions of a material different from aluminium; or iii) a combination of i) and ii).

LEGENDS TO THE FIGURE

Fig. 1 illustrates a multilayer structure comprising four layers;

Fig. 2 illustrates said multilayer structure after forming of depressions;

Fig. 3 illustrates a top view of the multilayer structure after polishing, etching and anodizing to obtain a Mokume Gane effect;

Fig. 4 illustrates another multilayer structure comprising ten layers, in which both surfaces of the structure have been deformed; and

Fig. 5 illustrates a top view of the multilayer structure after polishing, etching and anodizing to obtain a Mokume Gane effect. DETAILED DISCLOSURE OF THE INVENTION Definitions

The Mokume Gane effect refers to an effect obtained by a mixed-metal laminate with distinctive layered patterns and colours and was originally developed in 17 ^th -century Japan. The term "an alloy of aluminium and at least one alloying metal" is used to describe an alloy of aluminium and one or more further metals, such as copper, iron, manganese, magnesium, silicon, zirconium, titanium, zinc, chromium, cerium, yttrium, and molybdenum. Suitable alloys comprise about 80-99 % of Al and about 1-20 % of one or more alloying metals selected from the above. The term "type of layer" means a layer having a particular composition. Thus the term "a firs type of layer of aluminium or an alloy thereof and at least one further type of layer different from said first type of layer" means that the composition of the first layer is different from the composition of the further layer. An example thereof is when the first type of layer is one particular aluminium alloy and the second type of layer is another alloy of aluminium. The term "anodising" means an electrolytic passivation process by which a part to be treated forms the anode electrode of an electrical circuit. An anodised aluminium layer may thus be obtained by passing a direct current through an electrolytic solution with the aluminium object serving as the anode.

Specific embodiments of the invention In an embodiment of the invention said multilayer structure comprises 2-6 different types of layers, such as 2, 3, or 4 different types of layers, preferably 2 or 3 different types of layers.

In an embodiment of the invention said multilayer structure is prepared by an Accumulative Roll Bonding (ARB) process.

In the present invention the Accumulative Roll Bonding (ARB) process is applied on two or more layers or plates of aluminium or an alloy of aluminium and at least one alloying metal to obtain a compound structure, wherein the structure is subsequently processed by anodizing and one or more optional additional steps to obtain the decorative Mokume Gane effect or wood structure. In an embodiment of the invention the Accumulative Roll Bonding (ARB) process is performei as a cold rolling process. Standard and well known processes are applied, processes like Accumulative Roll Bonding (ARB) is normally a cold rolling process if the two alloys are of similar type with respect to strength and hardening effect at deformation. In another embodiment of the invention the Accumulative Roll Bonding (ARB) process is performed as a hot rolling process at a temperature in the range 100-500 °C. Thus if the firs and further layers are of a different type with respect to strength and hardening effect at deformation the ARB process may be performed at elevated temperatures.

In an embodiment of the invention the method for decorative anodizing of aluminium in a multilayer structure that consists of a multilayer of different types of alloys in order to create a Mokume Gane structure in the surface, comprises creating a multilayer structure by Accumulative Roll Bonding (ARB), wherein said multilayer structure is built-up by two or more different alloys, wherein the multilayer structure is a laminate that consists of two or more layers of aluminium or an aluminium alloy in between which are organized one or more layers of another type or another alloy that behaves differently from said first layer when etching, anodizing and dyeing the multilayer structure.

One or more of the following successive processing steps may be applied on the laminated structure, the processing being: pressure to give the structure a physical form; depressing or deformation on selected points/areas on the surface to give structuring of the pattern of the Mokume Gane effect; grinding and polishing to expose the layers;

etching, anodizing and dyeing to expose the layer structure to obtain the Mokume Gane effect on the surface of the structure. The order of the individual steps may vary.

In an embodiment of the invention said multilayer structure comprises at least 2 layers, such as 4-10,000 layers, such as 4-1,000 layers, such as 8-128 layers, preferably 16-32 layers or such as 128-2048 layers, preferably 256-1024 layers. In a preferred embodiment of the invention the laminate consists of approximately 20 layers of aluminium or an alloy thereof. The first layer is the same as layers 3, 5, 7, 9 etc. and in- between are layers 2, 4, 6, 8, 10 etc. of another and different alloy that behave differently than layers 1, 3, 5, 7, 9 etc. after one or more of the steps of etching, anodizing and dyeing. To obtain the highest Mokume Gane (MG) effect the two or more types of aluminium alloys that may make up the first and further layer(s), respectively, must be different visually after one or more of the steps of etching, anodizing and dyeing in a way that develops the layer structure either by different gloss or different colour. The two or more types of layers can also be etched in different ways in order to create a relief structure that could be sensed by touching.

In the preferred embodiment the total number of layers is 5 - 30 and typically 20.

In an embodiment of the invention said first type of layer is of aluminium or an alloy of aluminium and at least one alloying metal selected from the group consisting of copper, iron, manganese, magnesium, silicon, zirconium, titanium, zinc, chromium, cerium, yttrium, and molybdenum.

In an embodiment of the invention said further type of layer, which is different from said first layer, is of a material selected from the group consisting of: i) an alloy of aluminium and at least one alloying metal selected from the group consisting of copper, iron, manganese, magnesium, silicon, zirconium, titanium, zinc, chromium, cerium, yttrium, and molybdenum, and ii) Aluminium or an alloy thereof comprising discrete inclusions of a material different from aluminium; and iii) a combination of i) and ii).

In the preferred embodiment the first alloy e.g. is pure aluminium, i.e. is an aluminium alloy, which appears like pure aluminium, such as an aluminium alloy with a low proportion of alloying elements, such as below 1% of e.g. silicon and/or magnesium and that has a low etch-rate and after anodizing and dyeing shows a light colour and the second alloy e.g. is aluminium with 4% Cu that will create a dark colour in the same process. The structure appears like plywood and by forming and exposing it is possible to see the layer structure and use the lines graphically to create a surface like the Mokume Gane metal known from the Samurai swords. The Mokume Gane surfaces are known from the storytellinc from the Samurai swords and can bring decorative and graphical details into the aluminium parts.

In an embodiment of the invention said further type of layer is of aluminium or an alloy thereof comprising discrete inclusions of a material different from aluminium.

In an embodiment of the invention the multilayer structure comprises a first type of aluminium layer, a further type of layer which is of aluminium or an alloy thereof comprising discrete inclusions of a material different from aluminium, and a third type of aluminium laye that behaves differently from said first layer when etching, anodizing and dyeing the multilayer structure, and wherein each of said further layers may be present in any order in the multilayer structure.

In an embodiment of the invention said inclusions are selected from the group consisting of metal particles, metal oxide particles and pigments.

The incorporation of inclusions of particles or pigments may be made to obtain a radiation scattering surface finish on an object as disclosed in more detail in applicant's copending patent application WO 2012/076467 A2, the disclosure of which is incorporated herein in its entirety. In an embodiment of the invention the discrete inclusions of a material different from aluminium may be converted to discrete radiation scattering elements through anodisation oi be oxidised to metal oxides.

In an embodiment of the invention said inclusions are provided in a volume in the range 1- 50% by volume of aluminium/aluminium alloy, more preferably in the range 1-20 % by volume of aluminium/aluminium alloy.

In an embodiment of the invention said metal particles are selected from the group consisting of copper, iron, manganese, magnesium, silicon, zirconium, titanium, zinc, chromium, cerium, yttrium, and molybdenum particles.

In an embodiment of the invention said pigments are selected from the group consisting of inorganic and organic pigments. In an embodiment of the invention said pigments are selected from the group consisting of titanium dioxide, tin oxide, zinc oxide, antimony oxide, barium sulphate, silicon dioxide, copper oxide, iron oxide, manganese dioxide, magnesium oxide, zirconium dioxide, chromiun oxide, cerium dioxide, yttrium oxide, and molybdenum oxide. In an embodiment of the invention said pigments are organic or biological pigments. Non- limiting examples thereof include Carbon Black, Phthalo Blue, Aniline dye, Mother of Pearl, Red Carmine, Magenta and Melanin.

Visible dyes can be of different luminescence, fluorescence and phosphorescence.

In an embodiment of the invention at least one surface layer of the multilayer structure according to the invention may be activated by means of an energy effect that changes the function of the surface layer. A non-limiting example thereof is a laser beam to make graphical patterns in the surface. Such processing may be used to make functional surfaces such as antennas and other communication apparatus.

In an embodiment of the invention the thickness of each layer is in the range 0.01-1000 μιη, such as 0.1-500 μιη, such as 50-500 μιη, preferably about 1-100 μιη.

In the preferred embodiment the thickness of each layer is 0.05 - 0.5 mm and typically 0.1 mm. In an embodiment of the invention the depressions and/or deformations on parts of at least one surface of the multilayer structure are obtained by mechanical processing. The forming and grinding is known as disclosed from the literature by Ian Ferguson, Mokume Gane (Jewellery Handbooks), Publisher: A&C Black (November 29, 2002),ISBN-10:

0713661569, ISBN-13: 978-0713661569.

The invention as disclosed may be used in all types of products, items, equipment and apparatus, where there is a demand for a surface with a trendy high quality look which is colourful and decorative. Examples of equipment in aluminium parts with this new Mokume Gane surface structure are but not limited to: consumer electronics, antennas and other communication apparatus, phones, jewellery, watches, control panels in cars and alike. EXAMPLE 1

Figure 1 displays an example of a layered structure (1) made of 4 sheets or plates (2, 3, 4, 5). The structure is obtained via the ARB process.

The object (1) is formed and mechanically processed e.g. by depressing on selective areas leaving the structure as displayed in Figure 2.

Figure 3 displays a top view of the object after the surface has been polished, etched and anodized given the final finish with the MG decorative effect in the selected areas of the surface (2, 3, 4).

LIST OF REFERENCES

KR2006013211

US 2007/0275263 Al