Method for coating a substrate, and household appliance accessory for use in the field of gastronomy

Abstract

With the objective of improving the corrosion resistance, in particular the salt spray resistance, of objects with a nickel and trivalent chromium coating, the invention proposes a method for coating a substrate with a corrosion protection layer, comprising the following working steps: providing a substrate to be coated, coating the substrate with a nickel-based preparation, coating the substrate with a trivalent chromium-based preparation, the method being characterized by a step of coating the substrate with a preparation comprising a mineral oil-based additive. A household appliance accessory that is for use in the field of gastronomy and has such a coating is also described.

Description

[0001] Method for coating a substrate and household appliance accessory for application in the gastronomic field

[0002] The invention relates to a method for coating a substrate with an anti-corrosion protective layer, comprising the following working steps: providing a substrate to be coated, coating the substrate with a nickel-based preparation, coating the substrate with a trivalent chromium-based preparation. The invention also relates to a household appliance accessory for use in the gastronomic sector, with a body structure consisting substantially of steel, with a coating comprising chromium, with an oily coating, wherein the body structure has at least one welded joint.

[0003] Until now, it was common to use hexavalent chromium (CrVl) in a chrome plating step for both metallic and plastic objects, in the form of finished or semi-finished products, i.e. having undergone at least one transformation step and having a final form, in order to give them an improved appearance and to give them better resistance to corrosion. The term hexavalent chromium CrVl or chromium(VI) oxide designates in the context of the present invention the 6th oxidation state of chromium. A chrome plating operation consists of covering a chromium substrate with a layer of greater or lesser thickness, depending on whether a layer for decorative purposes (decorative chrome plating) or as protection against wear and scratches (hard chrome plating) is desired.

[0004] Hexavalent chromium has been found to be hazardous to human health and is, among other things, carcinogenic. It is planned to ban the use of hexavalent chromium in the near future, particularly for chrome plating operations.

[0005] In order to maintain the decorative effect of the coating, it is desirable to substitute hexavalent chromium with chromium in another valence state, considered less hazardous to health, such as trivalent chromium (Crlllj). However, experiments conducted so far have shown that substrates with a coating produced from trivalent chromium have lower corrosion resistance compared to substrates treated with hexavalent chromium.

[0006] Furthermore, some chrome-plated parts are used for applications with relatively high or low temperatures compared to ambient temperatures, such as in ovens or refrigeration systems. Alternatively or additionally, some applications require food compatibility and / or corrosion resistance in saline environments.

[0007] Therefore, the invention is based on the technical problem of improving the treatment methods using trivalent chromium known until now. In particular, the present invention is based on the technical problem of providing a method for producing a coating that is non-toxic or only slightly toxic to human health, while improving the corrosion resistance of the coated product.

[0008] This problem is solved according to the invention by a method for coating a substrate with an anti-corrosion protective layer, comprising the following working steps: providing a substrate to be coated, coating the substrate with a nickel-based preparation, coating the substrate with a trivalent chromium-based preparation, the method being characterized by a step of coating the substrate with a preparation comprising a mineral oil-based additive.

[0009] The treatment of a semi-finished product such as a strip or a coil of material with an oil in order to ensure protection of said material for transport to a pre-production storage location is already known. The materials or semi-finished products thus treated are generally degreased downstream of a processing step into a finished product, i.e. the composition or surface of the finished products obtained after the processing step is substantially free of oil. It has been surprisingly found that the use of a mineral oil-based additive in a post-chrome plating treatment step of a finished product, as recommended in the method according to the invention, makes it possible to improve the anti-corrosion effect of a surface treated with trivalent chromium.In particular, the anti-corrosion resistance of metal parts having at least one weld joint which are particularly sensitive to corrosion is increased compared to an identical part which has not undergone final oil-based treatment, while guaranteeing good temperature resistance and non-toxicity when in contact with food.

[0010] It has also been found that the corrosion resistance of substrates having been treated according to the process of the invention has a corrosion resistance at least as pronounced as substrates having been treated with hexavalent chromium.

[0011] Consequently, the claimed method allows the improvement of the corrosion resistance of the treated substrate, to preserve the decorative effects of a chrome treatment, while reducing the harmful and toxic effects of methods based on the use of hexavalent chrome.

[0012] Coating the substrate with nickel prior to the trivalent chromium coating step provides increased protection against corrosion and scratches of the substrate, particularly the substrate surface. Coating with chromium gives a shiny appearance to the treated substrate and prevents yellowing of the underlying nickel. Combining nickel with chromium provides access to a wide range of colors for the final appearance of the coated substrate, while ensuring good color retention of the chosen colorimetry.

[0013] A substrate to be coated according to the invention is, preferably and in contrast to, for example, a strip or wire, an intermediate or semi-finished product, a product having undergone most of the processing steps provided for obtaining a finished product. In other words, the substrate to be coated preferably already has at least its final geometry, and has preferably undergone all the welding steps provided before the application according to the invention. Preferably, the method according to the invention corresponds to a final preparation step before the sale, packaging or storage of the then coated substrate. A substrate according to the invention may, for example, be a milled, turned, stamped, punched, extruded or other part, in particular in the form of a cable, wire, a housing, a component or part for gastronomy, packaging, automobiles, aviation, medicine, for furniture parts or others.

[0014] The term mineral oil-based additive refers, within the scope of the invention, to any type of water-soluble organic additive which has the property of not forming a film on the surface of a bath when dissolved in water. The additive used is preferably a concentrate intended for the protection against corrosion of ferrous materials. In particular, the additive used may be solvent-free and / or nitrite-free.

[0015] According to a first embodiment, the substrate to be coated has a welded junction.

[0016] The method according to the invention is particularly advantageous when applied to such substrates: it has in fact been observed that the preparation comprising a mineral oil-based additive infiltrates into interstices possibly present in the weld joints, thus making it possible to prevent the formation of corrosion in an increased manner.

[0017] The weld joint may connect portions of the substrate together, where the portions of the substrate may be made of plastic or metal. The weld joint may be a spot weld or a length weld, where the term "spot" weld is equivalent to the technical term specific to conventional welding processes. According to another embodiment, the substrate to be coated is an object at least partly made of metal, in particular made of a ferrous metal, more particularly made of steel.

[0018] A substrate of this type is, due to the possible presence of iron in its composition, susceptible to corrosion. For this reason, the claimed method is particularly advantageous for this type of substrate. Furthermore, a substrate treated according to this implementation of the method will be resistant to heat and cold, while being protected against breakage, deformation or corrosion. As a result, the longevity of the finished products resulting from the treatment is increased.

[0019] The substrate to be coated may consist essentially of one of the elements in the above list or have a surface layer consisting essentially of one of these same elements.

[0020] A substrate within the meaning of the invention may be a metal part intended for use in different fields, such as household appliances, automobiles, aeronautics, packaging, or even gastronomy in general. A substrate within the meaning of the invention may, for example, be in the form of a metal accessory for a household appliance, or a grid for holding containers such as hot pans. Furthermore, the method described may be applied, for example, to a perfume bottle cap or any other high-quality metal packaging requiring anti-corrosion protection. In the field of transport, the method according to the invention may be applied, for example, to a car grille, a bicycle frame, an airplane door, a boat part, or any other part for which corrosion protection would be a significant advantage.

[0021] In particular, one implementation of the method provides that the substrate to be coated is an accessory for a household appliance intended for use in connection with food, in particular a trellis, a grid or a metal accessory. Hexavalent chromium has been shown to be hazardous to human health and contact of an object treated with this chemical species with food intended for consumption is likely to promote carcinogenic consequences. The proposed method is therefore particularly preferable to the methods known until now, with the aim of replacing the use of the hazardous chromic species.

[0022] A substrate according to this implementation may be intended for use in the industrial gastronomy field and / or in a particular household. Such a substrate may, for example, be a grid or shelf for a household oven, a retaining or support device to be integrated into the layout of a refrigerator or a grid for a cooking appliance such as a barbecue, a cooking or weighing basket for a kitchen appliance, a part of a coffee machine, or an air filter grid. In general, the substrate to be coated may be any type of part that has undergone a nickel and trivalent chromium coating step, and has undergone assembly by welding.

[0023] Alternatively or additionally, the treated substrate is an object at least partly made of plastic. Such a substrate may consist substantially of plastic or have a surface layer of plastic.

[0024] The process described here can therefore be applied to a wide range of products, which allows for better profitability and a relatively high return on investment for the processing chain set up to implement the process.

[0025] For example, a perfume bottle cap, a toy part, a non-structural part of a motorcycle or car can be treated by the method described herein.

[0026] According to an implementation provided within the scope of the invention, the step of coating the substrate with a preparation comprising a mineral oil-based additive is carried out as a hot rinse, where the oil-based preparation is a solution comprising demineralized water and water-soluble mineral oil, in particular with a concentration ranging from 2 parts of mineral oil-based additive per 10,000 parts of demineralized water to 2.5 parts of mineral oil-based additive per 10,000 parts of demineralized water.

[0027] This concentration range for the coating bath with mineral oil allows a compromise between the maintenance of the bath in the production line, and therefore an optimization of production costs, and the guarantee of a coating with an anti-corrosion effect sufficient to the standards imposed in general.

[0028] A higher concentration of additive in the preparation, i.e. a quantity of mineral oil-based additive in relation to the quantity of demineralized water higher than 2.5 parts of mineral oil-based additive to 10,000 parts of demineralized water, leads to rapid degradation of the coating bath and therefore requires frequent draining. With an additive concentration lower than 2 parts of mineral oil-based additive to 10,000 parts of demineralized water, the substrate is coated with a thin layer of oil, which may be insufficient for adequate resistance of the substrate to corrosion resistance tests.

[0029] The method described above is preferably carried out in such a way that the step of coating the substrate with a preparation comprising a mineral oil-based additive is carried out at a target temperature ranging from 40°C to 60°C, in particular ranging from 45°C to 55°C, preferably ranging from 47.5°C to 52.5°C, even more preferably at a target temperature of 50°C.

[0030] In doing so, the part dipped in the bath containing the preparation is heated, preferably until it reaches the target temperature. Heating to a target temperature within one of the indicated temperature ranges promotes wetting of the surface of the substrate immersed or dipped in the bath with the preparation comprising a mineral oil-based additive. As a result, filling of any gaps and cracks in the solder joints of the substrate to be coated is facilitated. Furthermore, the recommended heating of the bath also promotes the homogeneity of the preparation comprising the additive and the demineralized water. In this way, the probability of covering the substrate to be coated is improved by the proposed implementation.

[0031] A preferred implementation of the method provides that, for the step of coating the substrate with a preparation comprising a mineral oil-based additive, the substrate to be coated is exposed to the liquid oil-based preparation for a period of at least 2 minutes, preferably with an exposure time ranging from 2 to 8 minutes, even more preferably with an exposure time ranging from 2 to 5 minutes, in particular with an exposure time ranging from 2 to 4 minutes, more particularly with an exposure time ranging from 2.5 minutes to 3 minutes.

[0032] A treatment time with a value within one of the proposed ranges is a compromise between a treatment time corresponding to a lower cost of production of coated substrates and a minimum treatment time for sufficient coating of the substrate with the preparation comprising a mineral oil-based additive.

[0033] Furthermore, such an exposure time allows the substrate to reach the temperature of the preparation bath including a mineral oil-based additive, and to fully benefit from the wetting effect provided by the bath temperature.

[0034] It is recommended to choose the exposure time according to the thickness and / or volume of the substrate: for a solid substrate with a large volume, it is advisable to choose a relatively long exposure time, so that the substrate reaches a temperature close to that of the bath. For a thin or thin-walled substrate, a relatively short time closer to 2 minutes can be chosen, thus reducing production costs. The exposure time can also be chosen according to the material composing the substrate to be coated, in particular according to the thermal conductivity of the substrate.

[0035] For a bath temperature of 50°C and an exposure time of 5 minutes, for example, a steel substrate in the form of a household oven rack may have, immediately upon leaving the bath with the preparation comprising the mineral oil-based additive, a temperature of or close to 50°C and its surface is coated with a thin layer of the preparation comprising a mineral oil-based additive.

[0036] A preferred implementation of the method provides that a drying step follows the step of coating the substrate with a preparation comprising a mineral oil-based additive.

[0037] Such a drying step allows evaporation of demineralized water from the preparation layer deposited in the previous step. At the end of the drying step, the substrate is preferably coated with nickel, chromium and demineralized oil.

[0038] 11 It is preferable that the drying step is carried out with a target temperature in the temperature range of 50°C to 110°C, preferably 60°C to 100°C, in particular 70°C to 90°C, more particularly 75°C to 85°C, more particularly a target temperature of 80°C.

[0039] This heating step allows at least partial evaporation of the demineralized water and drying of the coated substrate, for example for subsequent storage, while avoiding degradation of the mineral oil and its anticorrosive properties. The temperature range in which the target heating temperature lies is preferably chosen prior to carrying out the method, depending on the geometry of the substrate to be coated and the intended subsequent storage method. A target temperature of 80 °C, for example, is particularly suitable for a household oven rack to be coated, which is intended to be stored in a cardboard box. Furthermore, it is preferable for the drying step to last 5 to 8 minutes, in particular 6 to 7 minutes, so that at the end of the drying process the demineralized water has evaporated and only the mineral oil remains on the chrome-plated surface of the substrate.

[0040] A duration beyond this range of values ​​would have the effect of altering the anti-corrosive properties of the oil, while lowering the economic efficiency of the process.

[0041] One implementation provides that after the drying step, the coated substrate is ready for use in the gastronomic field and / or can be used in direct contact with food.

[0042] In this way, a treatment step - apart from a packaging, transport or other preparation for sale step - of the substrate or its surface is superfluous. In particular, the substrate treated with the method is a finished product ready for use and meets the usual standards for its use in the gastronomic field, in particular sufficient corrosion resistance and compatibility with foods acceptable according to the standards in place.

[0043] The substrate treated according to the invention has been tested according to the applicable standards, in particular according to the recommendations of standard NF EN 13130-1 of August 2004, of Annex V of European Union Regulation No. 10 / 2011 of January 14, 2011, of the practical guide of the European Directorate for the Quality of Medicines and Healthcare (EDQM) "Metals and Alloys", of the methodological document of the Directorate General for Competition, Consumer Affairs and the Suppression of Fraud (DGCCRF) - "Metals and Alloys", and of Regulation (EC) No. 1935 / 2004 of the European Parliament and of the Council of October 27, 2004 on materials and articles intended to come into contact with foodstuffs and repealing Directives 80 / 590 / EEC and 89 / 109 / EEC. 11 These documents are further referred to as forming an integral part of this description of the invention.The test confirmed that the release of substances from the list Silver, Aluminum, Antimony, Arsenic, Barium, Beryllium, Cadmium, Cobalt, Chromium, Copper, Tin, Iron, Lithium, Magnesium, Manganese, Mercury, Molybdenum, Nickel, Lead, Thallium, Titanium, Vanadium, Zinc for contact conditions of the simulant "artificial water" for 3 times 2 hours at reflux temperature with a first contact, a second contact and a third contact is in accordance with the limits set, in particular the limits set by the methodological document of the General Directorate for Competition, Consumer Affairs and Fraud Control (DGCCRF) - "Metals and Alloys".

[0044] A particular implementation of the method provides that an electrolysis passivation step follows the coating step with a trivalent chromium-based preparation and precedes a substrate coating step with a preparation comprising a mineral oil-based additive.

[0045] The use of hexavalent chromium for a coating has the effect of passivating the coated surface, i.e. it contributes to improving the corrosion resistance of said surface. By substituting hexavalent chromium for trivalent chromium, the passivation effect and therefore the corrosion inhibition effect is largely lost. To compensate for this loss of anticorrosive property, the invention proposes an intermediate step, i.e. after the deposition of trivalent chromium and before the deposition of oil on the surface of the substrate to be protected, of passivation by electrolysis.

[0046] Generally speaking, electrochemical passivation of a steel part has the effect of eliminating the ferrous part on the surface of the part and oxidizing the metallic chromium present in the part into chromium oxide.

[0047] Experiments have shown that the introduction of a passivation step after the application of trivalent chromium has the effect of exacerbating the corrosion inhibiting properties of the trivalent chromium-based coating, to at least equal those of a hexavalent chromium-based coating, or even to supplant them. In particular, the resistance over time to the neutral salt spray test according to ISO 9227 with an acceptable corrosion threshold is prolonged for a substrate having undergone a passivation step.

[0048] For this passivation step, it is advisable to use a preparation based on demineralized water, to which additives are added, in particular based on trivalent chromium salts. In particular, a first additive with a concentration ranging from 23 to 27 ml per liter of preparation, a second additive containing trivalent chromium salts with a concentration ranging from 12 to 18 ml per liter of preparation and a third additive with a concentration ranging from 0.3 to 0.7 ml per liter of preparation can be provided. The first additive is consumed by entrainment of the bath, the second additive based on trivalent chromium salts is used for the assembly of the bath and the third additive is provided to limit the formation of impurities in the passivation bath.Before mixing the respective additives with a solute for preparing the corresponding baths, the first additive is preferably in liquid form, the second additive and the third additive are each preferably in solid form.

[0049] Furthermore, a working temperature range of 25°C to 30°C, a working pH range of 9.3 to 9.8 and a time range of 120 to 180 seconds are preferred for this passivation step.

[0050] An exemplary implementation for the passivation step consists of exposure to the passivation preparation for a period of time ranging from 2 to 4 minutes, preferably ranging from 2.5 to 3 minutes in an electrolysis bath, where an anode and a cathode are provided and separated by a distance in a range of 100 to 180 mm, preferably a distance of about 120 mm.

[0051] The above-mentioned technical problem is also solved within the scope of the invention by a household appliance accessory for use in the gastronomic field, with a body structure consisting substantially of steel and with a trivalent chromium-based coating, wherein the body structure has at least one weld joint, characterized in that an oily coating is provided, and in that the distribution of the oily coating is substantially limited to the area of ​​the at least one weld joint.

[0052] An accessory according to the invention not only has the advantage of presenting an improved appearance provided by the combined coating of nickel and chromium while being harmless to human health, but also corrosion resistance sufficiently good to compete with a coating based on hexavalent chromium.

[0053] In particular, the welded joints of the accessory structure are generally more vulnerable to corrosion than solid surfaces of the same structure. This vulnerability is explained by variations in surface texture such as cracks, crevices or material irregularities at the welded joints, which are conducive to the formation of corrosion. By coating the welded surfaces or at least the welded joints of the accessory with an oily coating, these material and / or texture irregularities are partly filled by the oil, thus preventing the onset of corrosion by contact with air or water.

[0054] An accessory within the meaning of the invention is preferably a finished product, in contrast to a semi-finished product which requires at least one additional processing step before it can be used by an end consumer. The accessory may, for example, take the form of a grid for an electric household oven, a cooking basket for a food processor, or any other example included in the definition for a substrate to be coated which can be used in the gastronomic field as mentioned above.

[0055] The invention is described in more detail and more specifically below with the support of examples, which however do not limit the present invention. An example of implementation of the method is implemented as follows: a substrate to be coated and in the form of a steel grid for a domestic oven is loaded onto a transport support animated by a robot, then led by the robot to a processing line.

[0056] The overall processing line comprises a preparation line and a deposition line itself, the preparation line preceding a deposition line. The grid loaded onto the robot is taken to the first bath of the preparation line for degreasing, the aim of which is to rid the grid of any grease traces accumulated during the processing, transport and / or storage steps of the grid before the coating process is carried out. The substrate then undergoes the following preparation steps in order, for each of which a tank containing a corresponding preparation is provided: a) rinsing, b) acid pickling, c) rinsing, d) electrolytic degreasing and / or degreasing under electric current with a rectifier and then e) rinsing.

[0057] The household oven rack thus prepared is led by the robot to the deposition line also comprising a series of successive treatment steps, arranged as follows: f) depassivation bath, g) rinsing, h) bath with a nickel-based preparation for a semi-glossy nickel coating i) bath with a nickel-based preparation for a glossy nickel coating, j) rinsing, k) activation bath to prepare the surface of the substrate to receive chromium, l] spray rinsing, m] bath with trivalent chromium-based preparation, n] dip rinsing, spray rinsing, passivation bath under current, o] hot rinsing with preparation comprising a mineral oil-based additive, and drying.

[0058] The rinsing steps are carried out with demineralized water to ensure as much as possible electrochemical neutrality of the wet surface of the substrate to be coated, in this case the household oven grill.

[0059] The bath with a nickel-based preparation for a semi-glossy nickel coating in position h) of the deposition line has a boric acid content in the range of 45.0 to 50.0 g / L, a nickel chloride content of 55.0 to 65.0 g / L, a nickel content of 65 to 80 g / L and a nickel sulfate content of 240 to 300 g / L.

[0060] The bath with a nickel-based preparation for a bright nickel coating in position i] of the deposition line has a boric acid content in the range of 45.0 to 50.0 g / L, a nickel chloride content of 55.0 to 65.0 g / L, a nickel content of 70 to 80 g / L and a nickel sulfate content of 250 to 300 g / L.

[0061] At the exit of these nickel baths, the substrate to be coated, here the household oven rack, has a total nickel coating between 12 and 19 pm thick, which can be distributed for example between approximately 8 pm thick of semi-bright chrome and approximately 7 pm of bright nickel.

[0062] The trivalent chromium bath has a target temperature in the range of 50 to 55 °C, a current density in the range of 8 to 12 Amperes per dm 2 , and an anode-to-cathode distance in the range of 100 to 180 mm, preferably a distance of about 120 mm. The household oven rack with a nickel layer is dipped for a total time of 4 to 5 minutes in the trivalent chromium bath.

[0063] After the trivalent chromium bath, the household oven rack has a layer of chromium with a thickness ranging from 2 to 4 pm, preferably ranging from 2 to 3 pm thick.

[0064] 11 It should be noted that the term “bath” within the meaning of the above explanations designates a quenching step in one or more liquids distributed in one or more tanks, where the liquids have a similar composition. In other words, a “trivalent chromium bath” can for example be carried out in two quenches, each in an oven containing a liquid preparation of similar composition, to extend the total quenching time of the substrate to be coated while avoiding an overall slowdown of the processing chain.

[0065] The concentration of the respective preparations in the tanks corresponding to the successive baths is monitored and adjusted regularly, in order to ensure that the contents are within predefined tolerance ranges.

[0066] After the last step of the deposition line, i.e. after drying, the treated domestic oven rack is unloaded from the robot and the transport support is freed from any layers of products collected during the successive baths of the treatment line, so that it can be put back into operation in a new treatment cycle with a substrate free of nickel / chrome coating.

[0067] The treated grid has a decorative and protective nickel / chromium coating, the corrosion-inhibiting properties of which are enhanced by a mineral oil-based coating, the latter substantially covering the welded joints of the grid at the intersections of its tenons. Two identically produced and treated steel grids, one of which underwent a final coating step with a preparation comprising a mineral oil-based additive and the other not, were tested with a salt spray for a period of 72 hours and at a test temperature of 35°C, in accordance with ISO 9227. At the end of this test, the untreated grid is corroded at the welded areas, whereas the grid treated by the method according to the invention is not corroded.

[0068] It is specified that the arrangement of the steps of the method indicated above can be modified, while being included in the object of the present invention.

Claims

Demands 1. A process for coating a substrate with an anti-corrosion protective layer, comprising the following working steps: making available a substrate to be coated, coating the substrate with a nickel-based preparation, coating the substrate with a trivalent chromium-based preparation, characterized by a step of coating the substrate with a preparation comprising a mineral oil-based additive, where the substrate is dipped into a tank containing the preparation comprising a mineral oil-based additive.

2. A method according to claim 1, characterized in that the substrate to be coated has a welded joint.

3. A method according to any one of claims 1 or 2, characterized in that the substrate to be coated is an object at least partly based on metal, in particular based on a ferrous metal, more particularly based on steel.

4. A method according to any one of claims 1 to 3, characterized in that the substrate to be coated is an accessory for a household appliance intended for use in connection with food, in particular a trellis, a grid or a metal accessory.

5. A method according to any one of claims 1 or 2, characterized in that the substrate is an object at least partly based on plastic material.

6. A method according to any one of claims 1 to 5, characterized in that the step of coating the substrate with a preparation comprising a mineral oil-based additive is carried out as a hot rinse, where the oil-based preparation is a solution comprising demineralized water and water-soluble mineral oil, in particular with a concentration ranging from 2 parts of mineral oil-based additive to 10,000 parts of demineralized water to 2.5 parts of mineral oil-based additive to 10,000 parts of demineralized water.

7. A process according to any one of claims 1 to 6, characterized in that the step of coating the substrate with a preparation comprising a mineral oil-based additive is carried out at a target temperature of 40 °C to 60 °C, in particular from 45 °C to 55 °C, preferably from 47.5 °C to 52.5 °C, all the more preferred to a target temperature of 50 °C.

8. A method according to any one of claims 1 to 7, characterized in that, for the step of coating the substrate with a preparation comprising a mineral oil-based additive, the substrate to be coated is exposed to the liquid oil-based preparation for a period of at least 2 minutes, preferably with an exposure time of 2 to 8 minutes, even more preferably with an exposure time of 2 to 5 minutes, in particular with an exposure time of 2 to 4 minutes, more particularly with an exposure time of 2.5 to 3 minutes.

9. A process according to any one of claims 1 to 8, characterized in that a drying step follows the step of coating the substrate with a preparation comprising a mineral oil-based additive.

10. A process according to claim 9, characterized in that the drying step is carried out with a target temperature in the temperature range of 50 °C to 110 °C, preferably from 60 °C to 100 °C, in particular from 70 °C to 90 °C, more particularly from 75 °C to 85 °C, more particularly a target temperature of 80 °C. A process according to any one of claims 9 or 10, characterized in that the drying step has a duration of 5 to 8 minutes, in particular 6 to 7 minutes. A process according to any one of claims 9 to 11, characterized in that after the drying step, the coated substrate is ready for use in the food industry and / or can be used in direct contact with food. A process according to any one of claims 1 to 12, characterized in that an electrolytic passivation step follows the coating step with a trivalent chromium-based preparation and precedes the coating step of the substrate with a preparation comprising a mineral oil-based additive.Accessory for a household appliance for use in the food service industry, with a body structure made substantially of steel and with a trivalent chromium-based coating, where the body structure has at least one weld joint, characterized in that an oily coating is provided, and in that the distribution of the oily coating is substantially limited to the area of ​​at least one weld joint.