WO2021199087A1

WO2021199087A1 - Galvanic process for the electrodeposition of a protective layer, and associated bath

Info

Publication number: WO2021199087A1
Application number: PCT/IT2020/000032
Authority: WO
Inventors: Luca CAPACCIOLI; Andrea CAPACCIOLI
Original assignee: Italfimet Srl
Priority date: 2020-03-30
Filing date: 2020-03-30
Publication date: 2021-10-07
Also published as: EP4127273A1

Abstract

A galvanic process for the electrodeposition of a protective layer, which comprises a step of coating with a protective layer at least one object immersed in a galvanic bath comprising an aqueous solution. The aqueous solution comprises at least: - tin in the form of a soluble complex, in a quantity comprised between 0.5 grams and 100 grams per liter of solution, - ruthenium in the form of a soluble complex, in a quantity comprised between 0.1 grams and 50 grams per liter of solution, - a conducting salt; furthermore, during the step of coating the at least one object the aqueous solution is kept at a pH that is greater than or equal to 0.1 and lower than 7.

Description

GALVANIC PROCESS FOR THE ELECTRODEPOSITION OF A PROTECTIVE LAYER, AND ASSOCIATED BATH

The present invention relates to a galvanic process for the electrodeposition of a protective layer, and to the associated bath.

As is known, by means of a galvanic electrodeposition process it is possible to deposit a more or less thin metallic layer on an object for decorative purposes, protective purposes (in particular against corrosion), or others.

According to methods that are by now well-established, this process entails causing an electrolytic reaction in a tank (galvanic bath), in which the object to be coated (which acts as a cathode) is immersed in an aqueous solution of the metal to be deposited. In this context, the anode may be made of the very metal to be deposited, or may also be made of an inert metal or graphite. In any case, by applying a potential difference at the two electrodes, a flow of ions of the metal to be deposited is generated and the metal progressively accumulates on the cathode, indeed forming the desired layer.

Among the various metals commonly used in this context, it is known that in the field of fashion and jewelry it is customary to coat accessories and metallic objects in general with a layer of white or yellow stainless bronze, containing palladium (or other precious metals) in various percentages, in order to create a protective layer that is useful to avoid the migration of copper to the surface, which might otherwise lead to surface corrosion phenomena.

Stainless bronze has progressively replaced more traditional solutions (sharing indeed their high resistance to corrosion and wear), which entailed the use of galvanic baths containing nickel, which are now known to be capable of causing allergies and which are potentially toxic. The use of nickel is therefore now highly discouraged, if not forbidden by the relevant statutory provisions.

However, the practice of providing protective layers made of stainless bronze also is not free from drawbacks.

Typically, in fact, in order to obtain these layers it is necessary to resort to cyanide galvanic baths and this is in any case a severe problem, due both to the toxicity of the electrolytes used and to the entrainment of these substances in the subsequent treatments. The palladium baths used in the subsequent steps are in fact heavily affected by the pollution due to copper and cyanide originating from the bronzes.

The aim of the present invention is to solve the problems described above, providing a galvanic electrodeposition process that allows to deposit on an object a protective layer that ensures high resistance to corrosion and/or wear.

Within this aim, an object of the invention is to provide a galvanic bath that allows to deposit on an object a protective layer that ensures high resistance to corrosion and/or wear.

Another object of the invention is to provide a process and a galvanic bath that allow to deposit a protective layer on an object in a non-toxic and environmentally sustainable manner, without using substances that are noxious for human beings and/or for the environment.

Another object of the invention is to provide a method and a galvanic bath that have low costs, without requiring the use of palladium or other precious metals.

Another object of the invention is to provide a method (and a bath) that ensures high reliability in operation and high stability, allowing furthermore to provide protective coating layers of high quality, in terms of aesthetic appearance, mechanical performance, and not only.

Another object of the invention is to provide a process that adopts a technical and structural architecture that is alternative to those of processes of the known type.

Another object of the invention is to provide a process and a bath that can be obtained easily starting from commonly commercially available elements and materials.

Another object of the invention is to provide a process that can be performed in a simple manner.

This aim and these and other objects which will become better apparent hereinafter are achieved by a process according to claim 1, a bath according to claim 11, a protective layer according to claim 12, and a use according to claim 15.

Further characteristics and advantages of the invention will become better apparent from the description of a preferred but not exclusive embodiment of the process and of the bath according to the invention, illustrated by way of non-limiting example in the paragraphs that follow.

The galvanic process for the electrodeposition of a protective layer comprises a step of coating with a protective layer at least one object immersed in a galvanic bath, which in turn comprises an aqueous (water- based) solution.

According to per se known methods, the process is performed by applying a potential difference to two electrodes, one of which, the cathode, is constituted by the object to be coated, while the anode can be constituted by the metal to be deposited, by an inert metal, by graphite or others. In any case, the generated flow of metal ions produces their accumulation on the object, so as to obtain progressively the forming of the desired protective layer. It is possible to immerse in the bath any number of objects (of any shape and size), insofar as allowed by the dimensions of the tank filled with the aqueous solution and by the limitations and the technical requirements of each specific situation.

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

It is appropriate to stress that the process according to the invention can be used for the deposition of a protective layer aimed at constituting a sub-layer (substrate) of the finished product that one wishes to obtain; at the same time, also in view of the high quality of the layer that, as will become apparent, the invention allows to obtain on the object to be coated (also in aesthetic terms), the invention can constitute the outer layer of the finished product. Furthermore, the possibility is not excluded to perform the process according to the invention to provide a sort of self-supporting shell, i.e., in which the object coated during the process is removed at the end of the process itself (and in which, typically but not exclusively, the finished product is indeed constituted by the deposited layer).

According to the invention, the aqueous solution comprises at least tin in the form of a soluble complex (capable therefore of constituting an adequate source of tin ions during the electrodeposition step, such as for example tin salts and/or tin compounds), in a quantity comprised between 0.5 grams and 100 grams per liter of solution.

In particular, the tin in the form of a soluble complex is selected from the group consisting of sodium stannate, potassium stannate, tin oxide, tin monoxide, tin sulfate, tin fluoborate, tin methane sulfonate, tin chloride and tin octanoate (although the adoption of different practical choices, without abandoning the protective scope claimed herein, is not excluded ).

Furthermore, according to the invention the aqueous solution comprises at least ruthenium in the form of a soluble complex (capable therefore of constituting a suitable source of ruthenium ions during the electrodeposition step, such as for example ruthenium salts and/or ruthenium compounds), in a quantity comprised between 0.1 grams and 50 grams per liter of solution.

In particular, the ruthenium in the form of a soluble complex is selected from the group consisting of ruthenium trichloride, ruthenium sulfamate, ruthenium nitrosyl nitrate, ruthenium sulfate, ruthenium phosphate, ruthenium gluconate and ruthenium oxalate (although the adoption of different practical choices, without abandoning the protective scope claimed herein, is not excluded). Moreover, according to the invention the aqueous solution comprises at least one conducting salt; in this regard, it is stressed that the aqueous solution can comprise a single specific type of conducting salt or a larger number of different conducting salts, as a function of the specific requirements.

In particular, the conducting salt is selected from the group consisting of a sulfate, a phosphate, a carboxylate, a chloride, a sulfamate, a citrate, a tartrate, an oxalate and a gluconate (although the adoption of different practical choices, without abandoning the protective scope claimed herein, is not excluded).

The method according to the invention also provides that during said step in which the object (each object) is coated with the protective layer, the aqueous solution is kept at a pH that is greater than or equal to 0.1 and lower than 7 (in other words, the aqueous solution is kept at an acid pH). It is specified that the protective scope claimed herein is extended to any substance (an acid or an aqueous solution containing an acid, for example) or practical choice that the person skilled in the art would know how to adopt, by drawing from the ordinary skills of the field, in order to keep the pH of the solution within this range.

In one embodiment of considerable practical interest, which in any case does not limit the application of the invention, the bath is kept at a constant temperature comprised between 25°C and 70°C.

Likewise, in a preferred embodiment, which in any case also does not limit the application of the invention, during the electrodeposition step the applied current density is comprised between 0.2 A/dm² and 5 A/dm².

Furthermore, the aqueous solution can comprise various and different substances, as an integration of the ones already described, in order to give the bath additional functionalities and/or optimize its particularities (and those of the resulting protective layer therewith). Some of these substances are therefore mentioned in the paragraphs that follow, but it is appropriate to stress that it is possible to add additional substances, even not directly mentioned in the present description, without thereby abandoning the protective scope claimed herein.

In this context, therefore, usefully the aqueous solution comprises at least one surfactant, preferably from the group of the amphoteric surfactants (be they anionic and/or non-ionic, or others). Even more preferably, and although other practical choices are not excluded, said surfactant is selected from the group consisting of alkyl polyoxyethylene ether, alkyl phenyl polyoxyethylene ether, polyoxyethylene alkylamine, polyoxyethylene alkylamide, polyoxyethylene fatty acid ester, polyoxyethylene polyhydric alcohol ether, surfactant block copolymer with ethylene oxide and propylene oxide, betaine, alkyl sulfate, alkyl ether sulfate, alkyl ether phosphate, alkyl sulfonate, alkyl sulfosuccinate, alkyl benzene sulfonate, polyethylene glycol, and mixtures thereof. Furthermore, preferably said surfactant (whether belonging to the group mentioned above or not) is contained in the aqueous solution preferably in a quantity comprised between 0.01 grams and 10 grams per liter of solution.

Advantageously, the aqueous solution comprises at least one complexing agent; although other embodiments are not excluded, preferably said complexing agent is selected from the group consisting of a carboxylic acid, an amino acid, a polyamine, an amine, a phosphonic acid, a sugar and/or a derivative thereof. Furthermore, preferably said complexing agent (whether it belongs or not to the group indicated above) is contained in the aqueous solution in a quantity comprised between 5 grams and 500 grams per liter of solution.

In this context, some examples of complexing agents that can be used in the context of performing the process according to the invention are: nitrilotriacetic acid, ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, 1 -hydroxy ethane 1,1-diphosphonic acid, nitrilotris(methylene) triphosphonate, sulfamic acid and/or methanesulfonic acid, mercapto succinic acid, formic acid, benzoic acid and succinic acid.

It should be noted that in one possible embodiment the aqueous solution comprises a complexing agent (an acid among the ones indicated above, another acid, or something else) indeed for the (already discussed) purpose of keeping the pH of the solution between 0.1 and 7. In this context, using methanesulfonic acid is of particular practical interest.

Favorably, the aqueous solution comprises at least one organic brightener and/or at least one inorganic brightener.

In the first option listed above, the organic brightener (which can be selected from an aromatic or non-aromatic compound) is preferably present in a quantity between 0.01 grams and 5 grams per liter of solution. Furthermore, although other embodiments are not excluded, said organic brightener is preferably selected from the group consisting of a benzene sulfanate, 3- mercaptopropionic acid, 3 -mercapto- 1-propanesulfonic acid, benzoic acid, a benzoic acid derivative, gallic acid, resorcinol, phenol and a phenol derivative.

In the second option mentioned earlier (which is alternative or in addition to the previous option), the inorganic brightener is preferably present in a quantity comprised between 0.01 grams and 5 grams per liter of solution. Furthermore, although other embodiments are not excluded, said inorganic brightener is preferably a salt of an element (metal or semimetal) selected from the group consisting of copper, zinc, rhodium, platinum, palladium, gold, gallium, germanium, bismuth, silver, thallium, tellurium, indium, iron and antimony. Like the galvanic process of electrodeposition of a protective layer, a galvanic bath comprising an aqueous solution according to what has been described so far and indeed aimed at performing said process is also subject matter of the present description.

Furthermore, a protective layer which can be obtained by means of a process and/or a bath of the type outlined so far is also subject matter of the present description.

According to the invention, said layer thus obtained comprises tin in a quantity comprised between 30% and 95% by weight and ruthenium in a quantity comprised between 5% and 70% by weight, these percentages being referred to the total weight of the layer. In other words, the protective layer according to the invention consists of (or at least comprises) an alloy of tin and ruthenium in the quantities indicated above.

More particularly, in an embodiment of considerable practical interest, the layer comprises tin in a quantity comprised between 50% and 90% by weight and preferably in a quantity equal to 80% by weight, the percentages being once again referred to the total weight of the layer.

Likewise, in an embodiment of considerable practical interest the protective layer comprises ruthenium in a quantity comprised between 5% and 30% by weight and preferably in a quantity equal to 20% by weight, the percentages being once again referred to the total weight of the layer.

In one possible embodiment of the method according to the invention (mentioned here merely by way of non-limiting example of the application of the invention), the aqueous solution comprises, for each liter of solution:

- 14 g/L of tin,

- 2 g/L of ruthenium,

- 1 g/L of organic brightener,

- 10 ppm of inorganic brightener,

- 100 ppm of surfactant,

- 100 g/L of methanesulfonic acid,

- 100 g/L of sulfamic acid.

Furthermore, in this embodiment the bath is kept at a constant temperature of 40°C and the applied current density (in a Hull cell) is equal to one A/dm².

After depositing on an object the protective layer with the formulation described above for 10 minutes (thus obtaining an alloy of tin and ruthenium), the object (immersed in a nitric acid solution) does not exhibit alterations of the surface, thus showing the high degree of resistance to corrosion and oxidation.

By means of a quantitative analysis using SEM (an acronym which, as known, indicates a scanning electron microscope), the following composition of the layer (of the alloy) was found: tin in a quantity equal to 80% by weight and ruthenium in a quantity equal to 20% by weight.

The use of a protective layer as described in the preceding paragraphs, for the coating of accessories and objects in general in the fields of fashion, clothing, jewelry, costume jewelry, shoes, leatherwear, faucets, eyewear and electronics, also is subject matter of the present invention.

It should be specified in any case that the scope of protection claimed herein extends to processes and baths (and layers) which have the particularities described above but independently of the specific field of application, which therefore may be any.

The use of the bath and in general the working of the invention are in practice evident from what has been described so far.

It has in fact been shown that the process entails, according to per se traditional methods, the application of a potential difference to the electrodes immersed in the galvanic bath, wherein the object (each object) to be coated with a protective layer acts as a cathode. Indeed, the innovation of the invention, which allows to overcome the limitations of known processes, lies in the composition of the aqueous solution of the bath (in which the object to be coated is indeed immersed) and in the choice to maintain an acid pH.

The protective layer obtained by means of the process according to the invention comprises or consists of a tin-ruthenium alloy that in fact allows to provide glossy objects with a high resistance to oxidation, corrosion and wear, to be used in the field of fashion, jewelry, eyewear, faucets, electronics and in any other sector in which a substrate that is indeed resistant to oxidation and corrosion is required.

The choice to obtain this layer in a bath kept at an acid pH allows to extend for a considerable amount of time the electrodeposition step, allowing to give the protective layer a thickness of 50 microns or more (therefore very high in addition to being resistant). A layer with such a high thickness can be used effectively in all applications in which known practice would require a bath with the presence of nickel (a metal which is now discouraged since it is allergenic) or bronzes (stainless or not) containing cyanide (which are toxic). The high thickness of this deposition ensures a high resistance to corrosion and oxidation and a surprisingly high resistance to wear, which is comparable with that observed in substrates made of nickel and nickel phosphorus.

More generally, the analyses performed by the applicant have pointed out that by resorting to the invention it is possible to obtain a tin-ruthenium alloy with a thickness that is variable from 0.01 to 50 microns which withstands aggressive atmospheric conditions and increases the preservation time of the plated articles even without the use of other intermediate and/or final metals or alloys.

This layer can be used first of all as a substrate/intermediate layer between objects of various kinds, particularly containing copper, and the final finishing layer.

The high resistance to corrosion and oxidation also ensures the preservation of the aesthetic quality of the obtained protective layer, and this allows to use the latter as a final finish.

This is all the more true if one observes that the protective layer and the alloy of which it is composed provide a smooth coating to the object to be coated and prevent the diffusion of the metals from the lower layers to the finishing layer and vice versa. Therefore, a change in color over time is prevented.

The invention therefore allows to extend the life of an object without color changes, at the same time increasing its resistance in terms of durability under performance tests.

The benefits described above are obtained without having to resort to nickel, cyanide and/or other metals and materials that are noxious, toxic (for humans and/or for the environment) or allergenic. The protective layer that is deposited by virtue of the invention is therefore environmentally sustainable, non-toxic and hypoallergenic, and the risk of skin irritations in subjects that come into contact with it is therefore avoided. This allows to resort to the invention for example in fields (such as eyewear) in which baths of nickel and/or chromium that are highly toxic and allergenic are currently used in order to ensure high resistance to wear.

Moreover, it is noted that the many benefits described above are obtained without necessarily resorting to palladium or other pure precious materials and therefore, with respect to the known techniques that resort to them, the protective layer according to the invention provides for a far lower production cost while ensuring a similar protection against corrosion.

The invention allows to reduce or even eliminate bronzes containing cyanide and lower production costs further, thus reducing or in some cases eliminating some steps of the subsequent treatments, which, according to known methods, use precious metal such as gold, palladium, platinum.

The choice to keep the bath at an acid pH also allows to obviate some drawbacks that are observed in some known techniques that resort to basic or alkaline baths.

In particular, the bath according to the invention exhibits high stability, without requiring continuous additions of OH- ions in order to compensate for the absorption of the CO₂ that is present in the surrounding environment, which is indeed observed in some known alkaline solutions (with consequent instability of the bath).

The acid environment renders the tin insensitive to impurities as instead might occur in a basic environment: this avoids the danger of obtaining protective layers that are dark, wrinkly and/or dusty and is a further confirmation of the quality (also aesthetic) of results that can be obtained by means of the invention.

Furthermore, it should be noted that the protective layer obtained by means of the invention has a high adherence and is not subject to passivation phenomena (as sometimes occurs by resorting to known methods), which might create problems for subsequent treatments.

The galvanic products obtained by means of the invention have been subjected to a copper diffusion test: copper migration and barrier properties are evaluated by heating the product for 48 hours at 180°C. In these conditions, the appearance of the overlying layer of precious metal has not undergone alterations and no copper diffusion phenomena have been revealed, as shown by the summary table provided hereinafter.

In general, the invention allows to avoid phenomena of diffusion of the copper that originates both from the raw material and from the galvanic copper plating and/or from the copper alloys (bronzes).

In practice it has been found that the invention fully achieves the intended aim, since resorting to a bath which uses an aqueous solution comprising tin and ruthenium, kept at an acid pH, allows to obtain a protective layer which comprises (or consists of) a tin-ruthenium alloy with low production costs, high brightness, extremely high resistance to corrosion and wear, and excellent aging behavior.

The oxidation resistance capacity of the protective layers obtained from galvanic baths according to the invention makes them applicable in various fields (whenever glossy objects and/or substrates with a high resistance to corrosion, oxidation and/or wear are required) and in particular in the fields of high fashion, clothing, costume jewelry, shoes, leatherwear, faucets, eyewear and electronics.

With specific reference to the fashion sector, the protective layer according to the invention meets all the requirements set by this field (and in particular as regards jewels and articles made of leather), as highlighted by the table in the following page, which lists the outcome of the many tests performed by the applicant on the following alloys:

- Alloy 1: 5-micron Sn-Ru alloy; - Alloy 2: 10-micron Sn-Ru alloy;

- Alloy 3: 5-micron Sn-Ru alloy + 0.2-micron palladium;

- Alloy 4: 5-micron Sn-Ru alloy + 0.2-micron gold;

- Alloy 5: 10-micron nickel + nickel phosphorous + 0.2-micron gold;

- Alloy 6: 5-micron Cu-Sn-Zn alloy + 0.2-micron palladium + 0.2- micron gold.

The invention thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the accompanying 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.

Claims

1. A galvanic process for the electrodeposition of a protective layer, which comprises a step of coating with a protective layer at least one object immersed in a galvanic bath comprising an aqueous solution, characterized in that the aqueous solution comprises at least:

- tin in the form of a soluble complex, in a quantity comprised between 0.5 grams and 100 grams per liter of solution,

- ruthenium in the form of a soluble complex, in a quantity comprised between 0.1 grams and 50 grams per liter of solution,

- a conducting salt, and in that during said step of coating the at least one object the aqueous solution is kept at a pH that is greater than or equal to 0.1 and lower than 7.

2. The process according to claim 1, characterized in that the tin in the form of a soluble complex is selected from the group consisting of sodium stannate, potassium stannate, tin oxide, tin monoxide, tin sulfate, tin fluoborate, tin methane sulfonate , tin chloride and tin octanoate.

3. The process according to claim 1 or 2, characterized in that the ruthenium in the form of a soluble complex is selected from the group consisting of ruthenium trichloride, ruthenium sulfamate, ruthenium nitrosyl nitrate, ruthenium sulfate, ruthenium phosphate, ruthenium gluconate and ruthenium oxalate.

4. The process according to one or more of the preceding claims, characterized in that the conducting salt is selected from the group consisting of a sulfate, a phosphate, a carboxylate, a chloride, a sulfamate, a citrate, a tartrate, an oxalate and a gluconate.

5. The process according to one or more of the preceding claims, characterized in that the bath is kept at a constant temperature comprised between 25°C and 70°C.

6. The process according to one or more of the preceding claims, characterized in that during the electrodeposition step the applied current density is comprised between 0.2 A/dm² and 5 A/dm².

7. The process according to one or more of the preceding claims, characterized in that the aqueous solution comprises at least one surfactant, preferably selected from the group of amphoteric surfactants and even more preferably selected from the group consisting of alkyl polyoxyethylene ether, alkyl phenyl polyoxyethylene ether, polyoxyethylene alkylamine, polyoxyethylene alkylamide, polyoxyethylene fatty acid ester, polyoxyethylene polyhydric alcohol ether, surfactant block copolymer with ethylene oxide and propylene oxide, betaine, alkyl sulfate, alkyl ether sulfate, alkyl ether phosphate, alkyl sulfonate, alkyl sulfosuccinate, alkyl benzene sulfonate, polyethylene glycol, and mixtures thereof, the surfactant being contained in the aqueous solution preferably in a quantity comprised between 0.01 grams and 10 grams per liter of solution.

8. The process according to one or more of the preceding claims, characterized in that the aqueous solution comprises at least one complexing agent, preferably selected from the group consisting of a carboxylic acid, an amino acid, a polyamine, an amine, a phosphonic acid, a sugar and/or a derivative thereof, the complexing agent being contained in the aqueous solution preferably in a quantity comprised between 5 grams and 500 grams per liter of solution.

9. The process according to one or more of the preceding claims, characterized in that the aqueous solution comprises at least one organic brightener, preferably in a quantity comprised between 0.01 grams and 5 grams per liter of solution, and/or at least one inorganic brightener, preferably in a quantity comprised between 0.01 g and 5 grams per liter of solution, the organic brightener being preferably selected from the group consisting of a benzene sulfanate, 3-mercaptopropionic acid, 3-mercapto-l-propanesulfonic acid, benzoic acid, a derivative of benzoic acid, gallic acid, resorcinol, phenol and a phenol derivative, the inorganic brightener being preferably a salt of an element selected from the group consisting of copper, zinc, rhodium, platinum, palladium, gold, gallium, germanium, bismuth, silver, thallium, tellurium, indium, iron and antimony.

10. The process according to claim 9, characterized in that the aqueous solution comprises, for each liter of solution:

- 14 g/L of tin,

- 2 g/L of ruthenium,

- 1 g/L of organic brightener,

- 10 ppm of inorganic brighter, - 100 ppm of surfactant,

- 100 g/L of methanesulfonic acid,

- 100 g/L of sulfamic acid, the bath being kept at a constant temperature of 40°C, the applied current density being equal to 1 A/dm².

11. A galvanic bath for performing a galvanic process of electrodeposition of a protective layer, characterized in that it comprises an aqueous solution as defined in one or more of the preceding claims.

12. A protective layer, obtainable by means of a process and/or a bath according to one or more of the preceding claims, characterized in that it comprises

- tin in a quantity comprised between 30% and 95% by weight,

- ruthenium in a quantity comprised between 5% and 70% by weight, the percentages being referred to the total weight of said layer.

13. The protective layer according to claim 12, characterized in that it comprises tin in a quantity comprised between 50% and 90% by weight, and preferably in a quantity equal to 80% by weight, the percentages being referred to the total weight of said layer.

14. The protective layer according to claim 12, characterized in that it comprises ruthenium in a quantity comprised between 5% and 30% by weight and preferably in a quantity equal to 20% by weight, the percentages being referred to the total weight of said layer.

15. Use of a protective layer according to one or more of claims 12 to 14 for coating accessories and objects in general in the fields of fashion, clothing, jewelry, costume jewelry, shoes, leatherwear, faucets, eyewear, and electronics.