DESCRIPTION

Technical field

The present invention relates to a coating for products made of solid silver or another metal alloy and later silver-plated by an electroplating process, as defined in the preamble of claim 1.

Preferably, but without limitation, the products hereof are intended for contact with food, for example, according to Regulation (EC) No. 1935/2004 EC and Regulation (EC) No. 2003/2006.

The present invention also relates to a product intended to come into contact with food having the coating and a method of depositing the coating on such products. Background art

Silver has long been known to be used in the manufacture of products intended for contact with food, such as dishware, cutlery and tableware.

Nevertheless, the physico-chemical properties of silver and the interaction between silver products and food cause release of silver atoms into the food. As a result, an average consumer that uses these products will assume silver atoms by ingesting the food in which the silver atoms have been released.

Prior art coatings for this type of products are intended to reduce oxidation and/or sulfuration but cannot hold back and prevent release of silver atoms.

Problems of the prior art

The use of silver as a material for the manufacture or coating of products causes several problems.

First, a silver surface exposed to air is subject to oxidation and sulfuration due to its combination with sulfides or TbS. Second, these products release above 0,10 mg/kg silver atoms into food.

The deposition of prior art coatings on the silver surface to prevent oxidation and sulfuration both affects the exterior appearance of the product and its wear resistance and is not able to reduce silver release or effectively mitigate oxidation and sulfuration.

It should be noted that, according to the daily intake estimates of silver atoms as published for example in Anses (2011) (A uses (2011): Second French Total Diet Study (TDS 2), Report 1: inorganic contaminants, minerals, persistent organic pollutants, mycotoxins, and phytoestrogens ), a maximum value of silver atom release of 0.08 mg/kg was defined.

If this limit is exceeded, silver coatings and products manufactured with prior art methods increase consumers’ exposure to health risks.

Object of the invention

The object of the present invention is to provide a coating, a product intended to come into contact with food and a method of depositing the coating on the product, that can obviate the above discussed drawbacks of the prior art.

In particular, an object of the present invention is to provide a coating for silver products that can reduce the rate of silver atom release from the product while protecting and preserving the product in its intended use.

A further object of the invention is to provide a coating that can keep the original appearance (color and finish) of the product on which it is deposited unchanged.

Yet another object of the invention is to provide a coating that can mitigate oxidation and sulfuration effects on the product.

The aforementioned technical purpose and objects are substantially fulfilled by a coating, a product intended to come into contact with food and a method of depositing the coating, that comprise the technical features as disclosed in one or more of the accompanying claims.

Benefits of the invention

Advantageously, the coating, product and deposition method can reduce the release of silver into food.

Advantageously, the coating, product and deposition method can reduce consumer health risks caused by an overdose of silver.

Advantageously, the coating, product and deposition method can improve the aesthetics of the product.

Advantageously, the coating, product and deposition method can improve surface properties of the product such as transparency and mitigate oxidation and sulfuration.

BRIEF DESCRIPTION OF THE FIGURES

Further features and advantages of the present invention will result more clearly from the illustrative, non-limiting description of a preferred, non-exclusive embodiment of a coating as shown in the annexed drawings:

- Figure 1 shows a sectional schematic view of a coating deposited on the outer surface of a product according to one embodiment of the present invention;

- Figure 2 shows a sectional schematic view of a coating deposited on the outer surface of a product according to one embodiment of the present invention.

DETAIFED DESCRIPTION

Even when not expressly stated, the individual features as described with reference to the particular embodiments shall be intended as auxiliary to and/or interchangeable with other features described with reference to other exemplary embodiments.

The present invention relates to a coating 1 adapted to be deposited on an outer surface 31 of a product.

For the purposes of the present invention, the outer surface 31 of the product comprises silver atoms.

Namely, the product can be made of solid silver or a metal alloy with a silver or silver-plated outer surface.

Preferably, the outer surface 31 has a glossy or matte finish that the coating 1 is intended to maintain/preserve.

The coating 1 is formed by depositing at least one silicon oxide layer, preferably of varying stoichiometry, having a thickness of 180 to 1500 nm on the outer surface 31 of the product.

Such deposition is carried out using a machine for depositing silicon oxide layers, operating with a R parameter, which is defined as the ratio of the flow rates of O2 and the liquid precursor, which ranges from 3 to 16, and is preferably 3, 5, 12 or 16.

It should be noted that the precursor comprises silicon and/or compounds thereof which interact with oxygen to cause the formation of one or more silicon oxide layers of varying stoichiometry.

For the purposes of the present invention, the R parameter is the ratio of the flow rates of O2 and the liquid precursor, but it can also be defined as the ratio of the flow rates of O2 to the solid precursor and in both cases the values are expressed in SCCM (Standard Cubic Centimeter per Minute).

It should be noted that the R parameter, as well as the thickness of the coating, affects both the transparency of the coating 1 and its adhesion to the outer surface 31 of the product.

Furthermore, the combination of the R parameter and the thickness ensures the protective properties of the coating 1, as further described below. Advantageously, the range of values of the R parameter, in combination with the thickness maximizes adhesion of the coating 1 to the outer surface 31 while maintaining excellent transparency and aesthetics of the product.

In particular, the coating 1 ensures visibility of the surface finish of the product and keeps it unchanged.

Preferably, the machine for depositing silicon oxide layers that is used to deposit the coating 1 employs the PECVD (Plasma Enhanced Chemical Deposition) technology which uses one or more radio-frequency sources. These are configured to form silicon oxide compounds SO _x of varying stoichiometry and to activate process gases.

The coating 1 so obtained and deposited using the aforementioned machine can provide a product that advantageously has a rate of release of silver atoms from the outer surface 31 of 0.1 mg/kg or less, preferably 0.08 mg/kg or less.

In other words, the coating 1 defines a coat on the outer surface 31 that limits the release of silver atoms from the outer surface 31 of the product.

Preferably, the coating 1 is deposited with the machine for depositing oxide layers operating at pressure values of 2 T 0 ³ mbar or more and source power values of 2 kW or more.

More preferably, the pressure values range from 2 T 0 ³ to 8 T 0 ³ mbar and the source power values range from 2 to 8 kW.

Still more preferably, the coating 1 is deposited with the machine for depositing oxide layers operating with precursor flows of about 10 SCCM.

This is because the use of high flow rates of precursor was found to prevent the formation a stretched coating, which has a higher breaking strength.

The use of the above operating conditions contributes, with the R parameter, to define the deposition rate of the coating 1 on the outer surface 31. Namely the deposition rate is inversely proportional to the pressure value, i.e. a decrease in pressure causes an increase of the deposition rate. Also, an increase in the precursor flow in combination with an increase in the source power causes an increase in the deposition rate. This leads to the conclusion that not all the additional precursor contributes to proportionally increase the coating growth rate, and that an optimal balance between the precursor flow and the source power may be provided to optimize the coating growth rate.

For these reasons, the coating 1 deposited with the operating parameters of the machine will improve the ability to protect the outer surface 31 and afford a silver release rate of 0.1 mg/kg or less, preferably of 0.08 mg/kg or less.

For the purposes hereof, the silver release rate was measured by an etch test for food compatibility (Test 0). Specifically, a value of 1 to 5 was assigned based on the rate of silver release according to the following assessment scheme.

In particular, the test consists in dipping the product on which the coating 1 has been deposited in etching solutions, heating to about 80°C and then analyzing the elements dispersed in the solution.

Each product undergoes three etching cycles. Preferably, the test for checking the rate of silver release shall follow the procedure standardized in accordance with the European Council (EC) Resolution CM/Res (2013) “ Metals and alloys used in food contact materials and articles

Moreover, the coating 1 deposited on the outer surface 31 of the product has been subjected to various experimental and standardized tests to assess its protective properties.

In particular, the following tests were carried out following Applicant-specific internal standards: i) Aesthetic assessment (Test 1); ii) Simulated oxidation (Test 2); iii) Wear resistance (Test 3); iv) Dishwasher resistance with general cleaning products (Test 4); v) Dishwasher resistance with silver-specific products (Test 5).

Each test allowed the deposited coating to be assessed by assigning a value from 1 to 5 according to the following assessment schemes:

As a result of the tests that have been conducted, the coating 1 was found to have a favorable aesthetic assessment in terms of both surface defects and transparency.

In addition, the tests could assess the ability of the coating 1 to resist oxidation.

When submitted to washing tests, the coating provided better conditions than the silver reference, especially when using silver-specific products.

The wear resistance test could also assess the ability of the coating 1 to protect against pitting, especially with large thicknesses.

It should be noted that the range of thicknesses E of the R parameter also afford effective adhesion of the coating 1 to the outer surface, thereby ensuring maintenance of the aforementioned properties.

Advantageously, the coating 1 has an excellent oxidation resistance.

Advantageously, the coating 1 has an excellent transparency.

In other words, the coating 1 exhibits barrier properties while keeping the appearance of the tool unchanged and preventing Ag release above 0.1 mg/kg, preferably above 0.0 8mg/kg.

It should be noted that with a coating having a single silicon oxide layer, the trend of the preferred values for R is inversely proportional to the thickness. Specifically, the values of R for thicknesses below 500 nm, preferably from 100 to 200 nm, are selected from values ranging from 10 to 20, preferably from 11 to 18, more preferably from 10 to 17 and most preferably the values of R are 12 or 16.

On the other hand, the values of R for thicknesses of 500 nm and above are selected from values ranging from 0 to 9, preferably from 1 to 7, more preferably from 2 to 6 and most preferably the values of R are 3 or 5.

According to a preferred embodiment, the coating 1 comprises a silicon oxide layer 10 having a thickness that ranges of 1500 nm deposited with the machine for depositing silicon oxide layers operating with a R parameter of 3. The coating so obtained has a rate of silver atom release from the outer surface of the product that ranges from 0.021 mg/kg to 0.056 mg/kg. This result is shown in Table 1. According to one embodiment that is alternative to the above (Figure 1), the coating

1 comprises a silicon oxide layer 10 having a thickness of 500 nm deposited with the machine for depositing silicon oxide layers operating with a R parameter of 3.

The coating 1 so obtained has a rate of silver atom release from the outer surface of the product that ranges from 0.005 mg/kg to 0.061 mg/kg. These results are shown in Table 2

Table 2

Advantageously, a R parameter of 3 and a thickness selected from 1500 to 500 will provide a trade-off between transparency and adhesion of the layer to the outer surface 31.

According to a preferred embodiment, the coating 1 comprises a silicon oxide layer 10 having a thickness that ranges of 180 nm deposited with the machine for depositing silicon oxide layers operating with a R parameter of 16. The coating so obtained has a rate of silver atom release from the outer surface of the product that ranges from 0.0240 mg/kg to 0.0630 mg/kg. This result is shown in Table 3. Table 3

According to a preferred embodiment, the coating 1 comprises a silicon oxide layer 10 having a thickness that ranges of 210 nm deposited with the machine for depositing silicon oxide layers operating with a R parameter of 12. The coating so obtained has a rate of silver atom release from the outer surface of the product that ranges from 0.009 mg/kg to 0.0270 mg/kg. This result is shown in Table 4.

Table 4

According to one embodiment that is alternative to the above (Figure 2), the coating 1 comprises a multilayer structure 20 deposited on the outer surface 31 using the machine for depositing silicon oxide layers.

In particular, each silicon oxide layer 21 of the multilayer structure 21 is sequentially deposited on top of another. In other words, each silicon oxide layer 21 lies on top of the previous one and the first deposited silicon oxide layer 21 directly contacts the outer surface 31.

Preferably, the multilayer structure 20 comprises a number of silicon oxide layers 21 that ranges from 4 to 28 and has a multilayer structure thickness that ranges from 640 to 1000 nm.

In particular, the silicon oxide layers 21 have a thickness ratio of 1:1 preferably irrespective of the number of layers and the thickness of the multilayer structure 20.

Furthermore, the machine for depositing silicon oxide layers is configured to change the R parameter by alternating it with each layer.

In detail, the multilayer structure 20 is deposited with the machine for depositing silicon oxide layers operating by alternating the R parameter for each deposited silicon oxide layer 21.

Preferably, the multilayer structure comprises a number of silicon oxide layers 21 that ranges from eighteen to twenty and has a multilayer structure thickness selected from 640 to 920 nm respectively. It should be noted that the multilayer structure 20 has a selection of Rs and thicknesses of the silicon oxide layers given by the combination of the R values and thicknesses or the single-layer coating. Specifically, the multilayer structure 21 is deposited by alternately selecting the R parameter to be equal to 3 and 12.

In other words, one silicon oxide layer 21 has been deposited with a R of 3 and the next has been deposited with a R of 12.

The coating 1 comprising the multilayer structure 20 so obtained has a rate of silver atom release from the outer surface of the product that ranges from 0.000 mg/kg to 0.073 mg/kg. These results are shown in Table 5.

Table 5

More preferably, the multilayer structure comprises 4 silicon oxide layers 21 and has a multilayer structure thickness of 980 nm.

Once again, the multilayer structure 21 has been deposited by alternately using a R parameter of 3 and a R parameter of 12.

The coating 1 so obtained has a rate of silver atom release from the outer surface of the product that ranges from 0.000 mg/kg to 0,021 mg/kg. These results are shown in Table 6

Table 6

Advantageously, the coating 1 comprising the multilayer structure 20 ensures proper adhesion to the outer surface 31 of the product, as well as a 1:1 ratio between the thicknesses of the silicon oxide layers 21 of the multilayer structure 20.

Advantageously, the multilayer structure seems to afford a better maintenance of the protective capability of the coating.

A summary scheme of the samplings A-G according to the embodiments of the present invention is shown in the following Table 7.

The scheme shows of 1 to 5 for each test a value, indicative of the property of the coating 1 according to the above assessment schemes.

'able 7

A further object of the present invention is a product intended to come into contact with food.

This product has an outer surface 31 comprising silver atoms and a coating 1 according to the present invention, as described above. These products are made of solid silver or metal alloys comprising a silver or silver- plated coat.

Thus, the outer surface 31, that would be in contact with the outside environment, i.e. food, a surface or a consumer, if no coating 1 were provided, comprises silver atoms.

Specifically, the product intended to come into contact with food has the coating 1 deposited on its outer surface 31.

Preferably, the product intended to come into contact with food comprises dishware and/or cutlery and/or tableware.

More preferably, the product intended to come into contact with food comprises all the products designed for contact with food during use, for example according to Reg. 1935/2004 EC and Reg. 2003/2006 EC.

A further object of the present invention is a method of depositing a coating 1 on an outer surface 31 comprising silver atoms of a product. Preferably, the method of depositing a coating 1 is used in coating products intended to come into contact with food.

The method comprises the step of providing one or more products intended for food contact, each having a respective outer surface 31 comprising silver atoms. Preferably, the method has a preliminary step of pre-treating the outer surface 31 to optimize deposition of the coating 1. Then, the method also provides a machine for depositing silicon oxide layers.

Preferably, the machine for depositing silicon oxide layers is configured to deposit the coating 1 according to the PECVD (Plasma Enhanced Chemical Deposition) technology, i.e. using a radio-frequency source. Once the products and the machine have been provided, the method comprises the step of introducing the products into the machine for depositing silicon oxide layers.

In order to deposit a coating 1 having the chemical and mechanical properties as defined in the present invention, the method comprises the step of selecting a value of the R parameter that ranges from 3 to 16, preferably of 3, 5, 12 or 16 on the machine for depositing silicon oxide layers.

Then, the method comprises the step of depositing a coating having at least one silicon oxide layer with a thickness ranging from 180 to 1500 nm on the outer surface 31 of the product.

Finally, the method comprises the step of unloading the products from the machine for any successive surface treatment steps.

According to the preferred embodiment in which the cover comprises a silicon oxide layer 21, the step of selecting a value of the R parameter includes selecting a single value, preferably 3, while the step of depositing includes depositing a silicon oxide layer selected from 500 to 1500 nm. This will provide a coating 1 according to sampling A or B.

According to the preferred embodiment in which the coating comprises a silicon oxide layer 21, the step of selecting a value of the R parameter includes selecting a single value, preferably 12, whereas the step of depositing includes depositing a silicon oxide layer of 180 nm. This will provide a coating 1 according to the sampling C.

According to the preferred embodiment in which the coating comprises a silicon oxide layer 21, the step of selecting a value of the R parameter includes selecting a single value, preferably 16, whereas the step of depositing includes depositing a silicon oxide layer of 210 nm. This will provide a coating 1 according to sampling D.

According to the preferred embodiment in which the coating 1 comprises a multilayer structure 20, the step of selecting a value of the R parameter includes iteratively setting the change of R for each silicon oxide layer 21 that will be deposited. Preferably, the step includes alternating the values of R of 3 and 12.

On the other hand, the step of depositing includes setting the number of layers to be deposited, the thickness ratio between the layers and the thickness of the multilayer structure to be obtained.

Preferably, the number of layers is selected from 4, 18 and 20, the ratio between the layers is selected to be equal to 1 : 1 and the thickness is selected from 980, 920 and 640 nm respectively. This will provide a coating 1 according to sampling E, F and G.

Preferably, the deposition method also comprises a step of selecting additional machine parameters such as pressure, source power, and precursor flow and of defining the rate of deposition of the coating 1.