The present invention relates to a method for the surface treatment of electrically nonconducting objects.

Among the surface treatments commonly used in the art, galvanic electrodeposition processes are well-known by means of which it is possible to deposit a more or less thin metallic layer on an object for decorative, protective, or other purposes. According to methods which are by now established, these processes provide for causing an electrolytic reaction in a tank (galvanic bath) in which the object to be covered is immersed in an aqueous solution of the metal to be deposited. If the object is made of metal or in any case of electrically conducting material, it can act directly as a cathode: by applying a potential difference to the two electrodes, a flow of ions of the metal to be deposited is generated and progressively accumulates on the cathode, indeed forming the desired layer.

When instead the object is constituted by an electrically nonconducting material (for example a polymeric material), it must undergo a preliminary metalization treatment: i.e., a metallic coating substrate is deposited so that it can act as a cathode and receive the progressive accumulation of the ions of the metal to be deposited.

Typically, metalization provides first of all for the use of chromium compounds in solutions of highly corrosive sulfuric acid, so as to provide minute surface pores on the object to be coated. A colloidal palladium solution is then used to ensure the correct bonding of the metallic coating to the nonconducting material: palladium in fact subsequently acts as a catalyst for the chemical deposition of the copper or nickel contained in the solution. One then proceeds with the electrochemical galvanization of the copper or nickel and subsequently with the electrochemical plating for the desired final decoration, for example with metals such as chromium, nickel, palladium, gold, etc. However, this constructive solution is not free from drawbacks, since the toxicity (and in particular the carcinogenicity) of chromic acid has by now been acknowledged and its use is therefore by now definitely discouraged.

Some alternative solutions have been therefore proposed to overcome the drawbacks cited above and are based for example on the use of potassium permanganate, but they have not led to good results in industrial productions (for example in terms of process reliability and/or adhesion force of the metallic layers applied subsequently).

Recent studies on the methods that use trivalent chromium, deemed so far not to be a health hazard, have yielded unsatisfactory results: no advantages in industrial productions have been found and in any case it has been necessary to deal with the difficulties linked to the disposal of chromium (without however being able to exclude the forming of toxic chromium compounds during the process).

The aim of the present invention is to solve the problems described above, proposing a method that makes it possible to obtain the coating by galvanic electrodeposition of electrically nonconducting objects in an efficient and reliable manner without resorting to toxic substances.

Within this aim, an object of the invention is to propose a method that is environmentally sustainable and at the same time capable of ensuring an adequate adhesion force of the metallic coating layers.

Another object of the invention is to propose a method that makes it possible to obtain objects with adequate mechanical, chemical and physical properties, capable of passing positively the tests provided by the standards of the industrial sector to which they relate.

Another object of the invention is to propose a method that makes it possible to obtain the coating by galvanic electrodeposition of electrically nonconducting objects without resorting to steps or substances that are harmful to human beings. Another object of the invention is to propose a method that ensures high reliability in operation and is versatile and can therefore be used to coat objects made of (electrically nonconducting) materials of different types.

Another object of the invention is to propose a method that adopts a technical and structural architecture that is alternative to those of methods of the known type.

Another object of the invention is to propose a method that can be performed simply and with low cost.

Another object of the invention is to propose a method that can be performed easily starting from commonly commercially available elements and materials.

This aim and these and other objects which will become more apparent hereinafter are achieved by a method for the surface treatment of electrically nonconducting objects, comprising at least the following steps: a. performing a preliminary metalization treatment on an object made of an electrically nonconducting material, by application of a metallic substrate on the object, b. covering the object and the substrate with at least one coating layer by galvanic electrodeposition, characterized in that said preliminary treatment performed in said step a. comprises a physical vapor deposition process.

Further characteristics and advantages of the invention will become more apparent from the description of some preferred but not exclusive embodiments of the method according to the invention, illustrated by way of non-limiting example in the accompanying drawings, wherein:

Figures 1 and 2 are block diagrams that correspond to two different embodiments of the method according to the invention;

Figure 3 is a perspective view of a product obtained with the method of Figure 2;

Figure 4 is a sectional view of the object of Figure 3.

With reference to the figures, the reference numeral 1 generally designates a method for the surface treatment of electrically nonconducting objects 10. In greater detail, and as will be described in detail hereinafter, the method 1 according to the invention is aimed at obtaining the surface coating of the objects 10 by galvanic electrodeposition.

First of all, therefore, the method 1 consists, at least in a step a., in performing a preliminary metalization treatment on an object 10 made of electrically nonconducting material, for the application of a metallic substrate 11 on the object 10.

Subsequently, the method 1 consists at least, in a step b., in covering the object 10 and the substrate 11 with at least one coating layer 12 by galvanic electrodeposition (the layer 12 is applied on the substrate 11, which in turn was made to adhere beforehand to the external surface of the object 10).

As is known, galvanic electrodeposition (step b.) provides for the application of a potential difference to two electrodes, one of which, the anode, can be constituted by the metal to be deposited, by an inert metal, by graphite, or others.

The flow of metal ions generated by the application of the potential difference causes their accumulation on the cathode, so as to obtain progressively the forming of the desired protective layer. When the object to be coated is electrically conducting, it acts as a cathode and receives directly the metallic coating. In the case of the present invention, in which the object 10 is electrically nonconducting, it becomes necessary to perform the preliminary metalization step a., by means of which the substrate 11 is deposited on the object 10 so that the latter can act as a cathode and in any case receive the desired coating.

It is possible to immerse in the galvanic bath in which step b. is caused to occur any number of objects 10 at will (of any shape and size), as long as it is compatible with the dimensions of the tank filled with the aqueous solution and with the limitations and the technical requirements of each specific situation.

So far, these are in any case traditional methods, which are well known in the art and to the person skilled in the art, and therefore these aspects will not be dwelt upon further.

According to the invention, the preliminary (metalization) treatment performed in step a. comprises (or consists of) a physical vapor deposition process (or PVD in acronym).

As is known, PVD processes consist of treatments aimed at depositing at least one surface coating film (the substrate 11) on objects 10 by evaporation or sublimation of a material (also known as target) from at least one source and the subsequent condensation of the target (from the vapor state) on the objects 10 to be coated (in order to obtain the desired film).

In an entirely particular and innovative manner, the invention provides for the adoption of this technology for the metalization of the object 10 (step a.), which per se is electrically nonconducting, to prepare it for electrolytic deposition (step b.). In this context, the protective scope claimed herein extends to the execution of any specific method for the execution of the PVD process (for example with a cathode or anode arc, by thermal evaporation or by electron beam).

In particular, in any case, in the preferred application of the invention the physical vapor deposition process performed in step a. is chosen of the sputtering type.

Physical vapor deposition in high vacuum, or indeed sputtering PVD is a sort of nanotechnology in which, in a chamber in which vacuum has been produced and a suitable process gas has been introduced, a beam of energetic particles (typically ions) affects, by bombarding it, a metallic bar (target), causing the emission therefrom of ions and other particles, which are thus deposited on a destination (the object 10), triggering the progressive nanometric deposition of the metallic coating film (the substrate 11).

More particularly, the physical deposition process performed in step a. (whether preferably of the sputtering type or not) provides for the sublimation or evaporation of a target material from a source; said target material is designed to form the metallic substrate 11 and is chosen from the group constituted by aluminum, copper, gold (even 18-carat gold), platinum, and palladium.

Even more particularly, in the preferred application the target material is platinum.

It should be pointed out in any case that the protective scope claimed herein also extends to the use of other target materials. In this regard, mention is made for example of the possibility to use at least one selectively from: aluminum, aluminum oxide, aluminum neodymium, aluminum silicon, tin and aluminum alloy, silver, tin and aluminum oxide, zinc and aluminum oxide, gold, boron nitride, boron carbide, graphite, cadmium sulfide, cadmium tellurium, cobalt, iron cobalt, chromium cobalt, niobium cobalt, chromium, chromium aluminum, chromium vanadium silicon, chromium tantalum aluminum, chromium molybdenum, chromium vanadium, chromium titanium, chromium silicon, copper, copper aluminum, copper gallium, copper indium gallium, copper indium gallium selenide, copper nickel, copper oxide, germanium, zinc and gallium oxide, hafnium, hafnium oxide, indium, indium alloy, indium gallium and zinc oxide, indium oxide alloy, indium and zinc oxide, iridium, molybdenum, sodium molybdenum, molybdenum niobium, nickel, nickel copper, nickel chromium, nickel chromium silicon, iron nickel, nickel niobium, nickel titanium, nickel vanadium, niobium, niobium oxide, niobium hafnium, niobium tantalum, niobium titanium, niobium zirconium, lead, platinum, platinum alloys, palladium, palladium alloys, gold, gold alloys, rhodium, copper alloys, zirconium titanate lead, ruthenium, scandium, silicon, silicon aluminum, silicon carbide, zirconium silicon alloy, silicon nitride, silica, tin, tin oxide, titanium tantalum, tantalum tungsten, titanium, titanium aluminum, titanium aluminum silicon, titanium boride, titanium carbide, titanium oxide, titanium nitride, zinc and tin oxide, titanium silicon, titanium zirconium, titanium tungsten, vanadium, tungsten, tungsten carbide, tungsten oxide, tungsten titanium, yttrium, zinc, zinc aluminum, zinc oxide, zinc and aluminum oxide, zinc sulfide, zinc tin, zirconium, zirconium oxide.

It should be noted that the method 1 can be intended for the treatment of any object 10 made of any electrically nonconducting material (choosing in the manner that is most appropriate in each instance the process parameters and the other materials involved). The execution of step a. (and subsequently of step b.) in fact does not entail particular technological limitations and therefore can be performed on substances that are even very different from each other. This ensures great versatility to the invention.

In particular, the electrically nonconducting material (of which the object 10 is composed) is chosen from the group constituted by a polymeric material, hide, and a glassy material. Treating objects 10 composed of two or more electrically nonconducting materials (be they of the type mentioned above or others) is not ruled out.

Even more particularly, if the method 1 is intended for the surface treatment of objects 10 made of at least one polymeric material, the latter is chosen from the group constituted by polyethylene (PE), polystyrene, polyethylene terephthalate (PET), polyvinyl chloride (PVC), polypropylene (PP), acrylonitrile-butadiene-styrene (ABS), polyamide (PA), a polycarbonate (PC), polytetrafluoroethylene (such as for example Teflon®). The object 10 can also be composed of a combination of two or more polymeric materials (whether of the type mentioned above or other).

It is specified that step b. can be performed any number of times at will and/or it is possible to provide for the application on the object 10 and on the substrate 11 in particular any number at will of coating layers 12 (constituted by any metal or alloy). In particular, therefore, in a first manner of execution of the invention, to which in practice the block diagram of Figure 1 can correspond, step b. can provide for covering the object 10 and the substrate 11 with a single coating layer 12 (by galvanic electrodeposition).

For example, said layer 12 can be made of nickel, copper (so as to avoid completely the use of nickel), or can also be made of precious metal (palladium or others), or others still.

In an embodiment of considerable practical interest, which does not in any case limit the application of the invention, step b. provides (as shown in Figure 2) first of all for applying, in a substep bl., a first coating layer 12 on the object 10 and on the substrate 11, by galvanic electrodeposition, and then applying, in a substep b2., a second coating layer 12 on the first layer 12, again by galvanic electrodeposition.

In particular, step bl. provides for the application (on the substrate 11, which in turn is made to adhere to the object 10) of a first coating layer 12 constituted by a metal chosen from the group comprising nickel and copper.

Even more particularly, step b2. provides for applying a second coating layer 12 constituted by a metal chosen from the group constituted by gold, palladium, platinum, silver.

The possibility to apply additional coating layers 12 made of any metal is in any case provided.

The embodiments of the method according to the invention are evident from what has been described so far: an object 10 made of (at least one) electrically nonconducting material is first coated, in a step a., with a metallic substrate 11, so as to render the assembly electrically conducting and thus be able to coat the latter, in a step b., with at least one coating layer 12 by galvanic electrodeposition and thus obtain a desired product 13.

The method 1 according to the invention is intended to be applied preferably in the fashion sector (merely by way of example, in Figures 3, 4 the method 1 allows the placing of a tag to be applied on bags, shoes or items of clothing in general) or in the jewelry sector, although other uses are not excluded, and are in any case within the protective scope claimed herein, for the provision of products 13 (whether finished products or even blanks) intended for other product sectors, in particular in all cases in which the metallic coating of an object 10 is required for decorative, functional or other reasons.

As mentioned, in a fully particular manner the invention provides for performing step a. by means of a PVD process (preferably a sputtering one): this avoids the use, in the metalization step a. (and in general for the entire execution of the method 1), of toxic, carcinogenic or allergenic substances, such as chromium. More generically, the method 1 is thus found to be entirely environmentally sustainable and in its steps avoids the use of substances that are dangerous or difficult to dispose of.

As shown, the method 1 is versatile, since it can certainly be used for the coating of objects 10 made of (electrically nonconducting) materials of a different type.

Likewise, the method 1 is found to be efficient and reliable, since first of all an adequate adhesion force of the substrate 11 and of the layers 12 to the respective underlying surfaces can be observed in the obtained products 13. At the same time, also as a function of the specific target used, the products 13 obtained with the method 1 according to the invention have adequate chemical, physical and mechanical properties, which are fully comparable with or superior to those that can be obtained with traditional systems.

In particular, the products obtained with the method 1 are capable of passing the tests provided by reference standards, such as for example salt spray corrosion resistance, resistance to synthetic perspiration, exposure to humid heat, resistance to corrosive gases (SO2 + NOx) and the ISO 2409 adhesion and cross-cut test.

In greater detail, the behavior and outcome of some tests conducted by the Applicants are reported hereinafter by way of example; these tests related to objects 10 constituted by heels made of ABS, on which (step a.) a substrate 11 that was in each instance different (adopting constantly different targets) was deposited and then four successive coating layers 12 (having the same composition in each test) were deposited by galvanic electrodeposition (step b.).

After the electrodeposition of the first copper layer 12, an adhesion and cross-cut test was performed in order to verify the adhesion of the substrate 11 to the electrically nonconducting object 10 and of the first layer 12 to the first substrate 11, with a positive outcome.

After completing all the electrodepositions of the other layers 12, the products 13 obtained with the various tests indicated in the preceding table were subjected to the following tests (in particular to check their resistance to corrosion).

The tests were passed successfully, with values that were comparable with, if not superior to, those that can be detected on products obtained with traditional etching.

By virtue of the invention it is thus possible to plate or in any case coat by galvanic electrodeposition objects 10 made of electrically nonconducting material without using toxic substances and obtaining in any case products 13 that have adequate performance and adhesion of the layers 12, in a tangible, objective, repeatable and standardized manner.

The invention thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the appended claims; all the details may furthermore be replaced with other technically equivalent elements.

In the exemplary embodiments shown, individual characteristics, given in relation to specific examples, may actually be interchanged with other different characteristics that exist in other exemplary embodiments.

In practice, the materials used, as well as the dimensions, may be any according to the requirements and the state of the art.

Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.