EP2646616A1

EP2646616A1 - Heating appliance covered with a self-cleaning coating and production method thereof

Info

Publication number: EP2646616A1
Application number: EP11801788.8A
Authority: EP
Inventors: Denis Paccaud
Original assignee: SEB SA
Current assignee: SEB SA
Priority date: 2010-11-29
Filing date: 2011-11-29
Publication date: 2013-10-09
Anticipated expiration: 2031-11-29
Also published as: RU2568086C2; US20130247430A1; CN103237938A; FR2968016A1; US8745904B2; RU2013123485A; WO2012072944A1; EP2646616B1; CN103237938B; FR2968016B1; PL2646616T3; HK1185388A1

Abstract

The present invention relates to a heating appliance (1) including a metal substrate (2), at least a part of which is covered with a self-cleaning coating including at least one oxidation catalyst selected from the platinoid oxides, and at least one dopant of said oxidation catalyst selected from the rare-earth oxides. According to the invention, the self-cleaning coating (4) is a bilayer coating including: an inner layer (3) at least partially covering the metal substrate (2) and including the dopant; and an outer layer (4) in contact with the ambient air and including the oxidation catalyst. The present invention also relates to a method for producing such a heating appliance.

Description

HEATING APPARATUS COVERED WITH SELF-CLEANING COATING AND METHOD OF MANUFACTURING SAME

The present invention generally relates to heating apparatus or to be heated during use and comprising a self-cleaning coating.

For the purposes of this application, the term "heating apparatus" is intended to mean any appliance, article or utensil which, during its operation, reaches a temperature of at least 65 ° C. (which is the minimum reheating temperature), and preferably at least 90 ° C. The apparatus can achieve this operating temperature by means of its own, such as a heating base built into the apparatus and provided with heating elements, or by external means. These include iron insoles, cooking appliances, ovens, grills, and cooking utensils. Among these heaters, some such as iron soles or cooking appliances have qualities of ease of use and efficiency, depending inter alia on the state and nature of the surface of their coating. With regard to iron soles, they could be improved thanks to the care given to the gliding qualities of the ironing surface, combined with those allowing the easier spreading of the linen. One way of obtaining these qualities is to use enamelled soles with a smooth-looking enamel, possibly with lines of extra thickness to promote the spreading of the fabric during the movement of the iron. It is also known to use metal soles mechanically treated and / or covered or not with a deposit to facilitate sliding.

However, in use, the sole can tarnish by carbonizing more or less diffuse on its surface ironing, and more or less incomplete, various organic fouling (especially in particulate form) that are captured by the sole by friction on the ironed fabrics. The fading of the sole, even in a not very visible manner, results in at least a partial loss of its sliding qualities. In addition, with the fouling, ironing becomes more difficult. Finally, the user apprehends to use a tarnished iron, fearing that he may alter his clothes.

Iron sole inserts are known having a hard and tough layer covered by a surface property improving layer as taught by US Patent 4,862,609. But this patent does not indicate a solution to fight against fouling.

This problem of fouling can also be encountered for other types of heating appliances, such as the walls of cooking appliances. It is known to cover them with an enamelled layer of smooth appearance, to prevent any projections of grease or food adhere to the surface of these walls. In particular, there are known enamelled self-cleaning surfaces, which may be encountered in particular in ovens and cooking utensils, as taught for example by US Pat. No. 4,029,603 or French Patent 2,400,876. However, these surfaces do not give complete satisfaction with regard to their self-cleaning properties.

To improve these properties, the Applicant has previously developed a self-cleaning coating for coating a metal surface of a heater that is more efficient in terms of catalytic activity. This coating is the subject of French patent FR 2,848,290, which describes a heating apparatus comprising a metal support, at least a portion of which is covered with a self-cleaning coating, which comprises an outer layer in contact with ambient air and comprising at least one oxidation catalyst selected from platinum oxide, and at least one inner layer, located between the metal support and the outer layer, comprising at least one catalyst of oxidation chosen from the oxides of the transition elements of group Ib. However, this self-cleaning coating has the disadvantage of requiring a large amount of platinum oxide in the outer layer to reach just satisfactory levels of catalytic activity, which in particular results in a significant increase in the cost of coating, and therefore in the end that of the heating device.

There is therefore a need for a heating appliance coating, such as a cooking appliance or an iron soleplate, in which the amount of platinoid oxides is appreciably lower, but which is more efficient in terms of Catalytic activity (ie a coating to keep the surface clean of any contamination by organic particles, and not clog up in normal use) without loss of other properties required (glossy appearance, slip and abrasion resistance of the coating).

By catalytic activity of a coating is meant, in the sense of the present invention, the ability of the outer surface of the self-cleaning coating in contact with the ambient air and with organic soils, to burn these soils, which, a burned, lose adhesion and become detached from the coating.

For the purposes of the present application, the term "organic soils" means any combustible or oxidizable substance in contact with the ambient air, completely or partially. By way of example, mention may be made of any residue of synthetic fibers, as used in textile articles, for example organic polymer such as polyamide or polyester, any organic residue of detergent and optionally softening product, any organic substance such as fats or food projections.

More particularly, the subject of the present invention is a heating apparatus comprising a metal support, at least a part of which is covered with a self-cleaning coating in contact with the ambient air and comprising at least one oxidation catalyst chosen from among the oxides of platinoids. characterized in that said coating further comprises at least one dopant of said oxidation catalyst selected from rare earth oxides.

Thanks to the heating article according to the invention, an apparatus is obtained in which the self-cleaning coating has a particularly excellent catalytic activity and whose adhesion to the metallic support is very good, and which also allows the organic particles in contact with the Self-cleaning coating will be oxidized when the appliance is heated. For example, when ironing with an iron, the organic particles captured by the sole are oxidized. They are somehow burned when the iron is hot, any solid residue loses any adhesion and detaches from the sole. The sole stays clean. Similarly, in a cooking appliance such as an oven for example, the grease projections present on the wall of the oven are oxidized hot, the solid residue is detached from the wall which is kept clean.

It has also been found a synergistic effect on the catalytic activity when combining in the self-cleaning coating a dopant selected from rare earth oxides with an oxidation catalyst selected from the oxides of platinoids. So, in the In this application, the catalytic activity of the self-cleaning coating is three to five times greater than that obtained with the coating of FR 2 848 290, and this with a quantity of platinum oxide two to four times smaller. Thus, the surface of the coating is regenerated more rapidly than in the coatings described in FR 2 848 290.

By "platinoids" is meant, within the meaning of the present application, the elements having properties similar to those of platinum, and in particular, in addition to platinum, ruthenium, rhodium, palladium, osmium and iridium. .

In practice, the oxidation catalysts of the type of platinum oxides are well known in themselves, as well as their methods of obtaining, without there being any need to describe in detail their methods of preparation respectively.

Thus, by way of example, with respect to platinum oxide IV as an oxidation catalyst (hydrated platinum dioxide Pt0 ₂ -H ₂ O or Adams catalyst), its catalytically active form can be obtained by melting hexachloroplatinic acid or its ammonium salt with sodium nitrate, followed by the thermal decomposition of the platinum nitrate obtained in platinum oxide IV.

Preferably, the oxidation catalyst is chosen from palladium oxides, platinum oxides and mixtures thereof.

For the purposes of this application, the term "dopant" means an element which is not a catalyst in itself, but which has the effect of increasing and boosting the catalytic activity of said catalyst and of stabilizing the behavior of the catalyst on the catalyst. the substrate.

In the context of the present invention, the oxidation catalyst is used as a dopant in the self-cleaning coating of at least one rare earth oxide. For the purposes of the present application, the term "rare earths" is intended to mean lanthanides and yttrium having properties similar to those of lanthanum, and in particular, besides lanthanum, cerium, and yttrium.

Preferably, the dopant is selected from cerium oxides, yttrium oxide and mixtures thereof.

Of course, any oxidation catalyst and dopant retained according to the present invention must remain sufficiently stable at the operating temperature of the device, and within the limits of the useful life of the device.

According to a first advantageous embodiment of the present invention, the self-cleaning coating of the heating article according to the invention is a monolayer coating comprising at least one platinum oxide doped with yttrium oxide.

Preferably, the self-cleaning coating of the heating article according to the invention consists of palladium oxide doped with yttrium oxide. Such doping makes it possible to considerably reduce the quantity of palladium oxide while achieving a catalytic activity at least equivalent to that of the coating of FR 2848290. If the quantity of palladium oxide is identical to that of the coating of FR 2848290, then the catalytic activity is considerably improved. The effects of doping on the catalytic activity of the coating are shown by the results of Table 1 to Example 4.

According to a second particularly advantageous and preferred embodiment of the present invention, the self-cleaning coating of the heating article according to the invention is a bilayer coating comprising:

^■ an inner layer at least partially covering the metal support and including said dopant, and ■ an outer layer in contact with the ambient air and comprising the oxidation catalyst. The presence of a rare earth oxide dopant in an inner layer between the support and the layer of the coating in contact with the ambient air and containing the platinum oxide makes it possible to obtain an increase in the catalytic activity. thanks to the available oxygen in the rare earth oxide network that can diffuse into the platinum oxide layer.

In this second bilayer embodiment, the self-cleaning coating according to the invention is preferably a coating consisting of an inner layer of cerium or yttrium oxide and an outer layer of palladium oxide.

Preferably, the doping inner layer has a thickness, measured according to the RBS method described in the examples (measuring methods) of the present application, ranging from 30 nm to 100 nm. The catalytic activity increases with the thickness of the inner layer.

The outer layer of the coating preferably has a thickness, also measured according to the RBS method described in the examples (measuring methods) of the present application, between 10 nm and 500 nm, preferably between 15 nm and 60 nm. The catalytic activity increases with the thickness of the layer until reaching a threshold effect.

Whatever the embodiment of the self-cleaning coating according to the invention, the oxidation catalyst is distributed on and / or in the outer layer and / or the monolayer of the self-cleaning coating, which is in contact with the dirt, continuously or discontinuous.

The metal support of the apparatus according to the invention can be based on any metal commonly used in the field of heating appliances such as aluminum, steel or titanium. This metal support may itself be covered with a protective layer such as a front enamel layer to be covered by the coating of the present invention.

Thus, in a preferred embodiment of the invention, the apparatus comprises an intermediate enamel protective layer located between the metal support and the self-cleaning coating, or its inner layer depending on whether the self-cleaning coating is bilayer respectively, said coating layer being intermediate protection consisting of a material selected from aluminum alloys, enamel and mixtures thereof, so that said support layer is catalytically inert with respect to oxidation.

Preferably, the intermediate protective layer is enamel with a low porosity and / or roughness, at the micrometric and / or nanometric scale. The enamel is for example a vitreous enamel. The enamel should preferably be hard, have a good glide and resist hydrolysis by hot steam.

In a preferred embodiment of the heating apparatus according to the invention, the heating apparatus is in the form of an iron soleplate comprising an ironing surface and the coating covers the ironing surface.

By ironing surface is meant, in the sense of the present invention the surface in direct contact with the laundry for the degreasing.

In another preferred embodiment of the invention, the heating apparatus is a cooking appliance comprising walls that are capable of coming into contact with organic soils and the self-cleaning coating covers these walls.

In a first mode of operation of the heating apparatus according to the invention, the catalyst acts at the operating temperature of the apparatus and the coating is kept clean as and when the use of the apparatus. In a second mode of operation of the heating apparatus according to the invention, during a phase called self-cleaning, before or after the use of the apparatus, the latter is set to a high temperature, equal to or higher than the highest operating temperatures, it is then left on standby for a predetermined time, during which the oxidation catalyst produces its effect.

The user can maintain his device regularly, without waiting for a harmful fouling.

The present invention also relates to a method for producing a heating apparatus comprising a metal support of which at least a portion is covered with a self-cleaning coating, comprising the following steps:

i. the surface of the metal support to be coated is heated to a temperature of 250 ° C. and 400 ° C. in an oven or under infrared radiation;

ii. a solution of an oxidation catalyst precursor, which is selected from platinoid salts and a dopant precursor, is sprayed onto the surface of the metal support to be coated to obtain a self-cleaning coating layer;

iii. it is cooked in an oven or under infrared radiation for a few minutes, typically between 400 ° C. and

600 ° C, the surface of the metal support covered with the self-cleaning coating layer;

said method being characterized in that it further comprises doping said self-cleaning coating layer with a dopant selected from rare earth oxides.

Doping of the oxidation catalyst is understood to mean, within the meaning of the present invention, an increase in the catalytic activity of the oxidation catalyst, as well as a stabilization of the resistance of the catalyst to the substrate. This is possible thanks to the available oxygen in the rare earth oxide network that can be used by the platinum oxide during the catalysis of the oxidation reaction.

For the purposes of the present invention, the term "precursor of the oxidation catalyst" means any chemical or physico-chemical form of the oxidation catalyst which is capable of producing the catalyst as such, or of the release by any appropriate treatment, for example by pyrolysis.

By way of example of a precursor of the oxidation catalyst that may be used in the process according to the invention, mention may especially be made of hexachloroplatinate acid, marketed by Alfa Aesar under the trade name of dihydrogen hexachloroplatinate (IV) hexahydrate, ACS, Premium, 99, 95%, Pt 37, 5% min

The application on the metal support, covered or not by an enameled layer of the catalytically active layer or layers of the self-cleaning coating is preferably by pyrolysis of an aerosol (technique usually referred to as "thermal spray"). by heating the surface to be coated and then spraying on this hot surface a solution containing a precursor of the oxidation catalyst.

According to a first advantageous embodiment of the process according to the invention, the doping of said self-cleaning coating layer is carried out during step ii of the process according to the invention, by adding to the oxidation catalyst precursor solution, a precursor dopant selected from the rare earth salts, so as to form a single-layer self-cleaning coating.

For the purposes of the present invention, the term "dopant precursor" means any chemical or physicochemical form of the dopant, which is capable of leading to the dopant as such, or of liberating it by any appropriate treatment, by example by pyrolysis.

According to a second advantageous embodiment of the method according to the invention, the doping of said self-cleaning coating layer is carried out between steps i and ii as follows:

Sputtering a solution of a dopant precursor selected from the rare earth salts onto the surface of the metal support to be coated to form an inner coating layer;

.2 reheating the surface of the metal support covered by the inner layer at a temperature of 250 ° C and 400 ° C in an oven or infrared radiation;

Typically, chlorides or nitrates, sometimes acetates if possible, are used as the dopant or oxidation catalyst salts.

Thus, in a particularly advantageous embodiment of this second embodiment according to the invention, the surface of the metal support to be covered is heated in an oven between 250 ° C and 400 ° C. A solution of the precursor of the dopant is then sprayed onto the surface of the metal support. In contact with the surface, the water evaporates, the precursor decomposes and the metal oxide formed is fixed on the support. A layer of thickness between 30 nm and 100 nm is then deposited. The thus cooled support is heated again in the oven or under infrared at a temperature between 250 ° C to 400 ° C for a few seconds. A solution of the precursor of the chosen oxidation catalyst is then sprayed over the inner layer. A layer of thickness ranging from 15 to 60 nm is deposited. The thus coated support is then annealed in an oven or under infrared for a few minutes between 400 ° C and 600 ° C, for example for five minutes. This gives a coated support whose self-cleaning properties are particularly good.

The invention will be better understood on reading the examples below and the accompanying drawings:

- Figure 1 is a sectional view of a first example of an iron soleplate according to the invention, self-cleaning bilayer coating on unglazed support,

- Figure 2 is a sectional view of a second example of iron soleplate according to the invention, self-cleaning coating bilayer on enamelled support,

FIG. 3 is a sectional view of a third example of an iron soleplate according to the invention, with self-cleaning monolayer coating on an unglazed support;

- Figure 4 is a sectional view of a fourth example of iron soleplate according to the invention, self-cleaning coating monolayer enamelled support.

FIGS. 5 to 8 show a succession of bottom views of iron insoles according to the invention, previously enamelled and then coated with a non-stick coating, which have been subjected to an abrasion resistance determination test according to the invention. EN ISO 12947-1 standard; these views serve to constitute a visual scale of evaluation of resistance to abrasion (scale described in the examples, in the paragraph "Method of determination of resistance to abrasion").

The identical elements shown in FIGS. 1 to 4 are identified by identical reference numerals. FIG. 1 shows in section a first example of an iron soleplate 1 to be ironed comprising a metal support 2 covered with an inner layer 3 and an outer layer 4, these inner and outer layers 3 constituting the covering self-cleaning. The sole also comprises a heating base 6 provided with heating elements 7. The support 2 and the base 6 are assembled by mechanical means or by gluing. The inner layer 3 comprises a dopant selected from rare earth oxides and the outer layer 4 comprises an oxidation catalyst selected from platinum oxide.

FIG. 2 shows a second example of an iron soleplate 1, which differs from the example shown in FIG. 1 by the presence of an intermediate enamel protection layer 5 covering the support 2 and being itself covered by the inner layer 3 of the self-cleaning coating.

In Figure 3, there is shown in section a third example of iron soleplate 1 to iron comprising a metal support 2 also covered with a self-cleaning coating. Unlike the iron examples shown in Figures 1 and 2, this self-cleaning coating 4 is not bilayer, but monolayer. It comprises an oxidation catalyst selected from platinum oxide and a dopant selected from rare earth oxides. As for the embodiments shown in Figures 1 and 2, the sole also comprises a heating base 6 provided with heating elements 7 and the support 2 and the base 6 are also assembled by mechanical means or by gluing.

FIG. 4 shows a fourth example of an iron soleplate 1, which differs from the example shown in FIG. 3 by the presence of an intermediate protective layer 5 made of enamel, covering the support 2 and being itself covered by the inner layer 3 of the self-cleaning coating.

Figures 5 to 8 are discussed in the examples, in the section "Method of determining the abrasion resistance".

EXAMPLES

products

^■ iron soleplates, aluminum, enamel (Comparative Example 1 and Examples 1 to 3) or unglazed (Comparative Example 2),

^■ silver nitrate, marketed by ALDRICH,

^■ Acetate of copper, marketed by VWR with the brand MERCK and under the trade name Acetate of copper monohydrate Pro analysi Assay 99, 0%,

■ Copper nitrate, marketed by VWR with the trademark MERCK and under the trade name Copper nitrate Trihydrate Pro Assay 99 analyzed, 5%,

^■ Cerium nitrate, sold by the company Alfa Aesar under the trade name of

Cerium (III) Nitrate Reacton Hexahydrate, 99, 99%,

^■ Nitrate yttrium, marketed by Alfa Aesar under the trade name Yttrium nitrate (III) hydrate 99, 99% (REO)

^An aqueous solution of nitrate of palladium stabilized with nitric acid, marketed by Metalor under the trade name Palladium Nitrate in solution procatalyst quality. Measurement methods

RBS (Rutherford Backscattering Spectroscopy) Method The RBS (Rutherford Backscattering) Method

Spectroscopy) is an analytical technique based on the elastic interaction between a ⁴ He ²⁺ ion beam and the sample particles. The high energy beam (2MeV) strikes the sample, the backscattered ions are detected at a teta angle. The spectrum thus acquired represents the intensity of the ions detected as a function of their energy and makes it possible to determine the thickness of the layer. This method is described in WK Chu and G. Langouche, MRS Bulletin, January 1993, p 32.

Method for determining the catalytic activity of the self-cleaning coating The catalytic activity of the self-cleaning coating is measured in a closed chamber as follows:

• a sample is heated to 300 ° C, on which is deposited a piece of 10 mg of molten organic polymer fiber, representative of soils that can contaminate the outer surface (which is the catalytically active surface) of the self-cleaning coating;

• we dose the initial amount of carbon dioxide in the chamber; The variation of the CO _{2 content} as a function of time makes it possible to deduce the catalytic activity of the coating;

The effectiveness of the catalytically active surface of the self-cleaning coating is defined by the quantity of carbon dioxide produced per hour inside the enclosure by a sample of 10 cm ² . More specifically, the slope of the curve representing the variation of the CO _{2 content} as a function of time makes it possible to deduce the catalytic activity of the coating, as shown in Table 1, Example 4

Method of determining abrasion resistance

The principle of this method is to slide a pad covered with a fabric on a portion of the coating during 3000 round trip. The fabric is made of wool and complies with EN ISO 12947-1.

The pad mounted at the end of a swingarm and circular shape has a contact area of 2.5 cm ² and a mass of 1.64 Kg.

The apparatus used for the test is the model sold under the trade name Taber® Linear Abrasion Tester Model 5750 by the company Taber Industries.

Depending on the wear of the coating observed after 3000 roundtrips, a score of 0 to 1 is attributed to quantify the abrasion resistance, by observation of wear under the binocular loupe and under suitable lighting:

■ the score 0 corresponds to an excellent abrasion resistance, for which the coated part has no difference between the abraded surface and the rest of the coating not subjected to the test;

A score of between 0 and 0.5 corresponds to an abrasion resistance which may be considered acceptable;

■ if the score is greater than 0.5; the coatings are not considered fit for the iron function. A panel of samples characterizing the different notes has been established to facilitate the notation, which makes it possible to produce a visual scale corresponding to the notation scale indicated above and represented in FIGS. 5 to 8:

^■ Figure 5 corresponds to an abraded outsole to which the score 0 has been assigned; in this figure, there is no difference between the abraded areas (consisting of a strip located between the two dashed lines on which the slider has slid during 3000 round-trip) and not abraded; the abrasion resistance is considered excellent;

^■ Figure 6 corresponds to an abraded outsole to which the score of 0.25 was assigned; in this figure, there is a slight lightening of the abraded area (consisting of a strip located between the two dotted lines) relative to the unabraded area; the abrasion resistance is considered to be very satisfactory;

^■ Figure 7 corresponds to an abraded outsole to which the score of 0.5 was assigned; in this figure, there is a more marked lightening of the abraded area (consisting of a strip located between the two dotted lines) relative to the unabraded area but which does not, however, reveal the underlying enamel; abrasion resistance is considered acceptable;

^■ Figure 8 corresponds to an abraded outsole to which the score of 0.75 was assigned; in this figure, an even more pronounced lightening of the abraded zone (consisting of a strip situated between the two dotted lines) with respect to the non-abraded zone and revealing the underlying enamel, the latter being visible by observation using an optical microscope or a binocular loupe; abrasion resistance is considered bad and not acceptable.

Samples

For comparison purposes, the tests presented below were carried out with iron soleplate samples each comprising a metal support 2, enamelled or not fully covered with a bilayer self-cleaning coating (Comparative Examples 1 and 2). and Examples 1 and 2 according to the invention) or monolayer (Example 3 according to the invention).

COMPARATIVE EXAMPLE 1

PdO monolayer coating on enamelled support according to the prior art A clean insole of enamelled aluminum iron is placed on a thick aluminum support serving as a heat reservoir to best limit temperature variations. The whole is heated to 400 ° C in an oven. The sole, with the support, is placed under infrared for a few seconds until reaching a surface temperature between 400 ° C and 600 ° C.

An aqueous nitrate solution of palladium stabilized with nitric acid is sprayed by means of a pneumatic gun on the soleplate. A layer approximately 40 to 50 nm thick, measured according to the RBS method described above, is then deposited.

After application, this single layer is annealed under infrared at 500 ° C for three minutes.

An iron sole is obtained whose self-cleaning coating adheres to the sole and has a catalytic activity, while maintaining its gliding qualities.

This iron soleplate corresponds to that illustrated in Figure 4, which corresponds to an iron soleplate according to the invention with a monolayer self-cleaning coating enamelled support. The only difference (which does not appear in this figure) is related to the absence of an oxidation catalyst in the inner layer of the self-cleaning coating, as is the case according to the present invention.

The results in terms of catalytic activity are given in Table 1, Example 4.

The results in terms of abrasion resistance are given in Table 2, Example 5.

COMPARATIVE EXAMPLE 2

PdO / AgO bilayer coating on an enamelled support according to the prior art FR 2 848 290 A clean insole of an enamelled aluminum iron is placed on a thick aluminum support serving as a heat reservoir in order to limit the temperature variations as much as possible. The whole is heated to 400 ° C in an oven. The sole, with the support, is placed under infrared for a few seconds until reaching a surface temperature between 400 ° C and 600 ° C.

Silver nitrate is dissolved in water. This silver nitrate solution is then sprayed with a pneumatic gun on the soleplate. A layer of about 40 nm to 50 nm thick, measured according to the RBS method, is then deposited.

After the application of this inner layer, the sole is again heated in the oven to 400 ° C and placed for a few seconds under a radiation infrared at a temperature between 400 ° C and 600 ° C.

After application of this outer layer, the assembly is annealed under infrared at 500 ° C for three minutes.

An iron soleplate is obtained whose self-cleaning coating adheres to the soleplate and has a catalytic activity, while maintaining its gliding qualities.

This iron soleplate corresponds to that illustrated in Figure 2, which corresponds to an iron soleplate according to the invention with a two-layer self-cleaning coating enamelled support. The only difference (which does not appear in this figure) is related to the nature of the oxidation catalyst of the inner layer of the self-cleaning coating which is a silver oxide in this example and not a rare earth oxide, such as is the case according to the present invention.

The results in terms of catalytic activity are given in Table 1, Example 4.

The results in terms of abrasion resistance are given in Table 2, Example 5.

COMPARATIVE EXAMPLE 3

PdO / CuO bilayer coating on an enamelled support, according to prior art FR 2 848 290

A clean insole of enamelled aluminum iron is placed on a thick aluminum support serving as a heat reservoir to limit temperature variations as much as possible. The whole is heated to 300 ° C in an oven. The sole, with the support, is placed under infrared for a few seconds until reaching a surface temperature between 400 ° C and 600 ° C.

Acetate or copper nitrate is dissolved in the water. This solution of acetate or copper nitrate, stabilized respectively with acetic acid or nitric acid, is then sprayed by means of a pneumatic gun on the soleplate. A layer of about 40 nm to 50 nm thick, measured according to the RBS method, is then deposited.

After the application of this inner layer, the sole is again heated in the oven at 400 ° C and then placed for a few seconds under infrared radiation at a temperature between 400 ° C and 600 ° C.

An aqueous nitric acid solution of palladium nitrate, sold by Metalor, is sprayed with a pneumatic gun on the sole. A layer approximately 40 to 50 nm thick, measured according to the RBS method described above, is then deposited.

This iron soleplate corresponds to that illustrated in Figure 2, which is that of an iron soleplate according to the invention with a two-layer self-cleaning coating enamelled support. The only difference (which does not appear in this figure) is related to the nature of the oxidation catalyst of the inner layer of the self-cleaning coating, which is an oxide in this example and not a rare earth oxide, as is the case according to the present invention.

The results in terms of catalytic activity are given and commented on in Table 1, Example 4.

The results in terms of abrasion resistance are given in Table 2, Example 5.

EXAMPLE 1

^First example of PdO / CeC> 2 bilayer coating according to the invention on enamelled support

A clean insole of enamelled aluminum iron is placed on a thick aluminum support serving as a heat reservoir to limit temperature variations as much as possible.

The whole is heated in an oven at a temperature of 300 ° C. The sole, with the support, is placed for a few seconds under infrared radiation until a surface temperature of between 300 ° C and 350 ° C.

Cerium nitrate is dissolved in water. This solution of cerium nitrate is then sprayed by means of a pneumatic gun on the sole. A layer of about 50 nm to 100 nm thick, measured according to the RBS method, is then deposited.

After the application of this inner layer, the sole is heated in the oven at 250 ° C, and then placed for a few seconds under infrared radiation at a temperature between 280 ° C and 350 ° C.

An aqueous nitrate solution of palladium stabilized with nitric acid is sprayed by means of a pneumatic gun on the soleplate. A layer approximately 15 to 50 nm thick, measured according to the RBS method described above, is then deposited. After application of this outer layer, the assembly is annealed under infrared radiation at a temperature of 480 ° C for 4 minutes.

An iron sole is obtained whose self-cleaning coating adheres particularly well to the sole and has a very good catalytic activity, while maintaining its gliding qualities.

This iron soleplate is illustrated in Figure 2.

The results in terms of abrasion resistance are given in Table 2, Example 5. EXAMPLE 2

^2nd example bilayer coating PCIO / Y ₂ O 3 according to the invention on enameled carrier

A clean insole of enamelled aluminum iron is placed on a thick aluminum support serving as a heat reservoir to limit temperature variations as much as possible. The whole is heated in an oven at a temperature of 300 ° C. The sole, with the support, is placed for a few seconds under infrared radiation until a surface temperature of between 300 ° C and 350 ° C.

Yttrium nitrate is dissolved in water. This solution of yttrium nitrate is then sprayed with a pneumatic gun on the soleplate. A layer of about 50 nm to 100 nm thick, measured according to the RBS method, is then deposited.

After the application of this inner layer, the sole is heated in the oven at 250 ° C, and then placed for a few seconds under infrared radiation at a temperature between 280 ° C and 350 ° C. An aqueous nitrate solution of palladium stabilized with nitric acid is sprayed by means of a pneumatic gun on the soleplate. A layer approximately 15 to 50 nm thick, measured according to the RBS method described above, is then deposited.

After application of this outer layer, the assembly is annealed under infrared radiation at a temperature of 500 ° C for 4 minutes.

This iron soleplate is also illustrated in Figure 2.

The results in terms of abrasion resistance are given in Table 2, Example 5. EXAMPLE 3

Example of a single-layer coating (PCIO + Y ₂ O ₃ ) according to the invention on an enamelled support

A clean soleplate of unglazed aluminum iron is placed on a thick aluminum support serving as a heat reservoir to limit temperature variations as much as possible.

The whole is heated in an oven at a temperature of 250 ° C. The sole, with the support, is placed for a few seconds under infrared radiation until a surface temperature between 280 ° C and 350 ° C.

An aqueous solution of nitric acid stabilized palladium nitrate, in which yttrium nitrate is added as a dopant is sprayed by means of a pneumatic gun onto the sole. A layer approximately 50 to 100 nm thick, measured according to the RBS method described above, is then deposited.

This iron soleplate is also illustrated in Figure 4.

The results in terms of abrasion resistance are given in Table 2, Example 5.

EXAMPLE 4 Determination of Catalytic Activity The catalytic activity of the self-cleaning coating was determined according to the method described above for each of the coatings of Comparative Examples 1 to 3 and Examples 1 to 3.

The results, which are presented in Table 1 below, are comparative results.

They are given in relation to the catalytic activity of the self-cleaning coating of Comparative Example 1, which is assigned the index 100.

The results in terms of catalytic activity, which are presented in Table 1 show that:

^■ when used in a monolayer deposition (Example 3) a dopant such as yttria Y2O _3, we can divide the amount of palladium oxide by four to obtain equivalent catalytic activity to that we would have with a monolayer PdO deposit enamelled support (Comparative Example 1);

when a dopant such as yttrium oxide Y ₂ O ₃ is used in a bilayer deposit (example 2), the quantity of palladium oxide can also be divided by four to obtain a catalytic activity, which is slightly better (index 100) than one would have with a PdO bilayer deposit on AgO enamelled support (index 95 for Comparative Example 2);

with the same amount of palladium oxide as in the coating of Comparative Example 1 and using Y ₂ O ₃ yttrium oxide as the dopant, the catalytic activity (Examples 2 and 3) is 1.3 to 1.4 times (depending on whether one is mono-or bilayer, respectively) greater than that of the coating of Comparative Example 1, finally, always with the same amount of palladium oxide as in the coating of FR 2848290 (Example 1) but this time using cerium oxide CeO 2 as a dopant, the catalytic activity (Examples 2 and 3) is 3 times greater than that of the coating of Comparative Example 1.

Table 1: Comparison of the Catalytic Activity of the Coatings of Comparative Examples 1 and 2 and Examples 1 to 3

Legend:

ND: Not determined

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EXAMPLE 5: Determination of resistance to abrasion

The abrasion resistance of the self-cleaning coating was determined, according to the test described above according to EN ISO 12947-1, for each of the coatings of Comparative Examples 1 to 3 and Examples 1 to 3.

The results, which are presented in Table 2 below, are comparative results.

They are given in the form of a score between 0 and 1, awarded at the end of the test, after:

^■ observation of the wear of the abraded area using a binocular magnifier and under appropriate lighting, then

^■ comparison with the rating scale shown in Figures 5 to 8.

The results in terms of abrasion resistance presented in Table 1 show that:

^■ the abrasion resistance is found to be excellent for a two-layer coating PdO / CE02 enamelled support of the invention, regardless of the amount of palladium oxide;

^■ the abrasion resistance is found to be excellent for a mono- or bilayer coating on enameled support of the invention, doped with yttria Y2O ₃ and with an amount of palladium oxide divided by four relative to that of Comparative Example 1 (monolayer of PdO without dopant);

^■ the abrasion resistance is considered very satisfactory for a mono- or bilayer coating on enameled carrier according the invention, doped with yttrium oxide Y2O ₃ , with an amount of palladium oxide equal to or halved with respect to that of Comparative Example 1 (monolayer of PdO 5 without dopant).

Table 2: Comparison of the Abrasion Resistance of the Coatings of Comparative Examples 1 and 2 and Examples 1 to 3

Legend:

ND: Not determined

Claims

1. Heating apparatus (1) comprising a metal support (2) at least a portion of which is covered with a self-cleaning coating (4) in contact with the ambient air, said coating (4) comprising at least one oxidation catalyst selected from platinum oxide and at least one dopant of said oxidation catalyst chosen from rare earth oxides,

characterized in that said self-cleaning coating (4) is a bilayer coating comprising: an inner layer (3) at least partially covering the metal support (2) and comprising said dopant, and

An outer layer (4) in contact with the ambient air and comprising said oxidation catalyst.

2. Apparatus according to claim 1, characterized in that the dopant is selected from cerium oxides, yttrium oxides, and mixtures thereof.

3. Apparatus according to claims 1 or 2, the oxidation catalyst is selected from palladium oxides, platinum oxides and mixtures thereof.

4. Apparatus according to any one of claims 1 to 3, characterized in that said self-cleaning coating (4) is a bilayer coating consisting of an inner layer 3 of cerium oxide or yttrium and a layer external 4 of palladium oxide.

5. Apparatus according to any one of claims 1 to 4, characterized in that the thickness of the outer layer (4), measured according to the RBS method, is between 10 nm and 500 nm, and preferably between 15 nm and 60 nm.

6. Apparatus according to any one of claims 1 to 4, characterized in that the thickness of the inner layer (3), measured according to the RBS method, is between 30 nm and 60 nm.

7. Apparatus according to any one of claims 1 to 6, characterized in that it further comprises an intermediate protective layer (5) between the metal support (2) and the inner layer (3) of the self-cleaning coating ( 4), said intermediate protective layer (5) consisting of a material selected from aluminum alloys, enamel and mixtures thereof, so as to constitute a catalytically inert carrier with respect to oxidation.

8. Apparatus according to claim 7, characterized in that said intermediate protective layer (5) is enamel.

9. Apparatus according to any one of claims 1 to 8, characterized in that it is in the form of an iron soleplate comprising an ironing surface and that the self-cleaning coating covers the ironing surface.

10. Apparatus according to any one of claims 1 to 8, characterized in that it is in the form of a cooking apparatus comprising walls capable of coming into contact with organic soils, said self-cleaning coating covering these walls.

11. A method for producing a heating apparatus (1) comprising a metal support (2) of which at least a part is covered with a self-cleaning coating (4), comprising the following steps:

i. the surface of the metal support (2) to be coated at a temperature of between 300 ° C and 400 ° C is heated in an oven or under infrared radiation;

ii. a solution of an oxidation catalyst precursor is sprayed onto the surface of the metal support (2) to be coated and sprayed onto the surface of the support which is selected from platinoid salts to obtain a self-cleaning coating layer. (4)

iii. the surface of the metal support (2) covered with the self-cleaning coating layer (4) is baked, in an oven or under infrared radiation for a few minutes,

said method being characterized by further comprising doping said self-cleaning coating layer (4) with a dopant selected from rare earth oxides.

12. Method according to claim 11, characterized in that the doping and fixing of said layer (4) self-cleaning coating is carried out in step ii, by adding to the oxidation catalyst precursor solution, a dopant precursor selected from the rare earth salts, so as to form a monolayer self-cleaning coating (4).

13. The method of claim 11, characterized in that the doping and fixing of said layer (4) self-cleaning coating is carried out between steps i and ii as follows: a solution of a dopant precursor selected from the rare earth salts is sprayed onto the surface of the metal support (2) to be coated, to form an inner layer (3) of coating,

the surface of the metal support (2) covered by the inner layer (3) is reheated to a temperature of between 250 ° C. and 400 ° C. in an infrared radiation oven.

14. Process according to any one of Claims 11 to 13, characterized in that the dopant or oxidation catalyst salts are acetates, chlorides or nitrates.