EP2646616B1 - Heating appliance covered with a self-cleaning coating and production method thereof - Google Patents

Description

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 coatings are known having a hard and tough layer covered by a surface property improving layer as taught by the patent. US 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 can be found in particular in ovens and cooking utensils, as taught for example by the US patent US 4,029,603 or French FR 2,400,876 . However, these surfaces are not entirely satisfactory as regards their self-cleaning properties.

The document FR2913682 describes a self-cleaning transparent wall of heating enclosure. 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 the French patent FR 2 848 290 , which discloses 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 the group 1b. 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 as claimed in claim 1 comprising a metallic support of which at least a part is covered with a self-cleaning coating in contact with the ambient air and comprising at least one catalyst of oxidation chosen from platinum oxide, 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 with a quantity of platinum oxides of two to four times less. 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 PtO 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 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 different embodiment of the present invention, the self-cleaning coating of the heating article is a monolayer coating comprising at least one platinum oxide doped with yttrium oxide.

• ▪ une couche interne recouvrant au moins partiellement le support métallique et comprenant ledit dopant, et
• ▪ une couche externe en contact avec l'air ambiant et comprenant le catalyseur d'oxydation.

Preferably, the self-cleaning coating of the heating article according to the invention is composed 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. 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 comprising 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 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 50 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 15 and 50 nm. The catalytic activity increases with the thickness of the layer until reaching a threshold effect. In the embodiment of the self-cleaning coating according to the invention, the oxidation catalyst is distributed in the outer layer of the self-cleaning coating, which is in contact with the dirt, continuously or discontinuously.

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 between the metal support and the inner layer of the self-cleaning coating, said intermediate protective layer consisting of a material selected from aluminum alloys, enamel and mixtures thereof, so that said protective 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.

1. i. on chauffe la surface du support métallique à recouvrir à une température comprise entre 250°C et 400°C dans un four ou sous un rayonnement infrarouge ;
2. ii. on pulvérise, sur la surface du support métallique à recouvrir, une solution d'un précurseur de catalyseur d'oxydation, qui est choisi parmi des sels de platinoïdes et d'un précurseur de dopant, pour obtenir une couche de revêtement autonettoyant ;
3. iii. on cuit, dans un four ou sous rayonnement infrarouge pendant quelques minutes, typiquement entre 400°C et 600°C, la surface du support métallique recouverte de la couche de revêtement autonettoyant ;

ledit procédé étant caractérisé en ce qu'il comprend en outre le dopage de ladite couche de revêtement autonettoyant par un dopant choisi parmi les oxydes de terres rares.The user can maintain his device regularly, without waiting for a harmful fouling. A method for producing a heating apparatus comprising a metal support, at least a part of which is covered with a self-cleaning coating, comprises, according to a mode different from that of the present invention, the following steps:

1. i. the surface of the metal support to be coated is heated to a temperature of between 250 ° C. and 400 ° C. in an oven or under infrared radiation;
2. 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;
3. iii. baking, 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 means, 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 oxidation catalyst. substrate. This is possible thanks to the oxygen available in the rare earth oxide network that can be used by the platinum oxide during the catalysis of the oxidation reaction.

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 dopant precursor 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.

• i.1 on pulvérise, sur la surface du support métallique à recouvrir, une solution d'un précurseur de dopant choisi parmi les sels de terres rares, pour former une couche interne de revêtement ;
• i.2 on chauffe à nouveau la surface du support métallique recouverte par la couche interne, à une température comprise entre 250°C et 400°C dans un four ou sous un rayonnement infrarouge;

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

• i.1 spraying 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;
• i.2 reheating the surface of the metal support covered by the inner layer at a temperature between 250 ° C and 400 ° C in an oven or under 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 the invention, the surface of the metal support to be coated 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 50 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 selected oxidation catalyst is then sprayed over the inner layer. A layer of thickness ranging from 15 to 50 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.

• la figure 1 est une vue en coupe d'un premier exemple de semelle de fer à repasser selon l'invention, à revêtement autonettoyant bicouche sur support non émaillé,
• la figure 2 est une vue en coupe d'un deuxième exemple de semelle de fer à repasser selon l'invention, à revêtement autonettoyant bicouche sur support émaillé,
• la figure 3 est une vue en coupe d'un troisième exemple de semelle de fer à repasser à revêtement autonettoyant monocouche sur support non émaillé
• la figure 4 est une vue en coupe d'un quatrième exemple de semelle de fer à repasser à revêtement autonettoyant monocouche sur support émaillé.
• les figures 5 à 8 représentent une succession de vues de dessous de semelles de fers à repasser selon l'invention, préalablement émaillées puis revêtues d'un revêtement antiadhésif, qui ont subi un test de détermination de la résistance à l'abrasion selon la norme EN ISO 12947-1 ; ces vues servent à constituer une échelle visuelle d'évaluation de résistance à l'abrasion (échelle décrite dans les exemples, dans le paragraphe « Méthode de détermination de la résistance à l'abrasion »).

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

• the figure 1 is a sectional view of a first example of an iron soleplate according to the invention, bilayer self-cleaning coating on unglazed support,
• the figure 2 is a sectional view of a second example of an iron soleplate according to the invention, with a two-layer self-cleaning coating on an enamelled support,
• the figure 3 is a sectional view of a third example of a single-layer self-cleaning coated iron soleplate on unglazed support
• the figure 4 is a sectional view of a fourth example of iron soleplate self-cleaning coating monolayer enamelled support.
• the Figures 5 to 8 represent a succession of bottom views of ironing insoles according to the invention, previously enamelled and then coated with a non-stick coating, which have been subjected to an abrasion resistance test according to EN ISO 12947-1. ; these views serve to constitute a visual scale of evaluation of resistance to abrasion (scale described in the examples, in the paragraph "Method of determining the resistance to abrasion").

The identical elements represented on the Figures 1 to 4 are identified by identical numerical references.

On the figure 1 , a section is shown in a first example of iron soleplate 1 to iron comprising a metal support 2 covered with an inner layer 3 and an outer layer 4, these inner layers 3 and outer 4 constituting the self-cleaning coating. 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 chosen from rare earth oxides and the outer layer 4 comprises an oxidation catalyst chosen from oxides of PGMs.

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

On the figure 3 a third example of iron soleplate 1 to be ironed is shown in section comprising a metal support 2 also covered with a self-cleaning coating. Unlike the examples of iron represented on the 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 examples of realization represented on the 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.

On the figure 4 , there is shown a fourth example of iron soleplate 1, which differs from the example shown in FIG. figure 3 by the presence of an intermediate enamel protective layer 5 covering the support 2 and itself being covered by a self-cleaning monolayer coating 4. The Figures 5 to 8 are discussed in the examples, in the section "Method of determining the abrasion resistance".

EXAMPLES products

• ▪ iron insoles, aluminum, glazed (Comparative Example 1 and Examples 1 to 3) or unglazed (Comparative Example 2),
• Silver nitrate, marketed by ALDRICH,
• ▪ Copper acetate, marketed by VWR with the trademark MERCK and under the trade name Acetate of Copper monohydrate Pro analysi Assay 99.0%,
• ▪ Copper nitrate, marketed by VWR with the trade mark MERCK and under the trade name Copper nitrate Trihydrate Pro analyzed Assay 99.5%,
• ▪ Cerium nitrate, marketed by Alfa Aesar under the trade name of Cerium (III) nitrate hexahydrate Reacton, 99.99%,
• Yttrium nitrate, marketed by Alfa Aesar under the trade name of Yttrium (III) nitrate hydrates 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 Spectroscopy) method 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 according to their energy and allows 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

• on chauffe un échantillon à 300°C, sur lequel on dépose un morceau de fibre en polymère organique fondu de 10 mg, représentatif des salissures pouvant venir contaminer la surface externe (qui est la surface catalytiquement active) du revêtement autonettoyant ;
• on dose la quantité initiale de gaz carbonique dans l'enceinte ; La variation du taux de CO₂ en fonction du temps permet de déduire l'activité catalytique du revêtement ;
• l'efficacité de la surface catalytiquement active du revêtement autonettoyant est définie par la quantité de gaz carbonique produite par heure à l'intérieur de l'enceinte par un échantillon de 10 cm². Plus précisément, la pente de la courbe représentant la variation du taux de CO₂ en fonction du temps permet de déduire l'activité catalytique du revêtement, comme cela est illustré dans le tableau 1, exemple 4

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

• a sample is heated at 300 ° C., on which is deposited a piece of molten organic polymer fiber of 10 mg, representative of soils that can contaminate the outer surface (which is the catalytically active surface) of the self-cleaning coating;
• the initial quantity of carbon dioxide is measured 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 amount of carbon dioxide produced per hour inside the enclosure by a sample of 10 cm ² . More precisely, 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 part coating during 3000 round trips. 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.

• ▪ la note 0 correspond à une résistance à l'abrasion excellente, pour laquelle la pièce revêtue ne présente aucune différence entre la surface abrasée et le reste du revêtement non soumis au test ;
• ▪ une note comprise entre 0 et 0,5 correspond à une résistance à l'abrasion qui peut être considérée comme acceptable ;
• ▪ si la note est supérieure à 0,5 ; les revêtements ne sont pas jugés aptes à la fonction de fer à repasser.

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 resistance to abrasion, 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 between 0 and 0.5 corresponds to an abrasion resistance that may be considered acceptable;
• ▪ if the mark is greater than 0.5 ; the coatings are not considered fit for the iron function.

• ▪ la figure 5 correspond à une semelle abrasée à laquelle la note 0 a été attribuée ; sur cette figure, on n'observe pas de différence entre les zones abrasée (constituée par une bande située entre les deux lignes en pointillées sur laquelle le patin a coulissé durant 3000 aller-retour) et non abrasée ; la résistance à l'abrasion est considérée comme étant excellente ;
• ▪ la figure 6 correspond à une semelle abrasée à laquelle la note 0,25 a été attribuée ; sur cette figure, on observe un léger éclaircissement de la zone abrasée (constituée par une bande située entre les deux lignes en pointillées) par rapport à la zone non abrasée ; la résistance à l'abrasion est considérée comme étant très satisfaisante ;
• ▪ la figure 7 correspond à une semelle abrasée à laquelle la note 0,5 a été attribuée ; sur cette figure, on observe un éclaircissement plus marqué de la zone abrasée (constituée par une bande située entre les deux lignes en pointillées) par rapport à la zone non abrasée mais qui ne laisse toutefois pas apparaître l'émail sous-jacent ; la résistance à l'abrasion est considérée comme étant acceptable ;
• ▪ la figure 8 correspond à une semelle abrasée à laquelle la note 0,75 a été attribuée ; sur cette figure, on observe un éclaircissement encore plus marqué de la zone abrasée (constituée par une bande située entre les deux lignes en pointillées) par rapport à la zone non abrasée et laissant apparaître l'émail sous jacent, celui-ci étant visible par observation à l'aide d'un microscope optique ou d'une loupe binoculaire; la résistance à l'abrasion est considérée comme étant mauvaise et non acceptable.

A panel of samples characterizing the different scores was established to facilitate the scoring, which allows for a visual scale corresponding to the scoring scale indicated above and represented on the scales. Figures 5 to 8 :

• ▪ the figure 5 corresponds to an abraded outsole to which a score of 0 has been assigned; in this figure, no difference is observed between the abraded zones (consisting of a strip situated between the two dotted lines on which the slider has slid during 3000 round-trips) and not abraded; the abrasion resistance is considered excellent;
• ▪ the figure 6 corresponds to an abraded outsole to which the score of 0.25 has been 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;
• ▪ the figure 7 corresponds to an abraded outsole to which the score of 0.5 has been 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;
• ▪ the figure 8 corresponds to an abraded outsole to which the score of 0.75 has been assigned; in this figure, an even more pronounced lightening of the abraded zone (constituted by a band situated between the two dashed lines) with respect to the non-abraded zone and revealing the underlying enamel, this being visible by observation using an optical microscope or a binocular loupe; abrasion resistance is considered bad and not acceptable.

Samples

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

COMPARATIVE EXAMPLE 1 PdO monolayer coating on an 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 limit 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.

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 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 on the 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 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 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 at 400 ° C and then placed for a few seconds under infrared radiation at a 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 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 on the 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 sole. 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.

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 on the 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 a silver oxide in this example and not a rare earth oxide, such as this 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 / CeO 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 on the figure 2 .

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 2 ^2nd example of PdO / Y ₂ O ₃ 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.

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.

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 also illustrated on the figure 2 .

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 3 Example of monolayer coating (PdO + Y ₂ O ₃ ) 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 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 soleplate. A layer approximately 50 to 100 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.

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 also illustrated on the figure 4 .

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 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.

• ▪ lorsque l'on utilise, dans un dépôt monocouche (exemple 3) un dopant tel que l'oxyde d'yttrium Y₂O₃, on peut diviser la quantité d'oxyde de palladium par quatre pour obtenir une activité catalytique équivalente à celle qu'on aurait avec un dépôt monocouche PdO sur support émaillé (exemple comparatif 1) ;
• ▪ lorsque l'on utilise, dans un dépôt bicouche (exemple 2) un dopant tel que l'oxyde d'yttrium Y₂O₃, on peut également diviser la quantité d'oxyde de palladium par quatre pour obtenir une activité catalytique, qui est légèrement meilleure (indice 100) à celle qu'on aurait avec un dépôt bicouche PdO sur AgO sur support émaillé (indice 95 pour l'exemple comparatif 2) ;
• ▪ avec la même quantité d'oxyde de palladium que dans le revêtement de l'exemple comparatif 1 et en utilisant comme dopant également de l'oxyde d' yttrium Y₂O₃, l'activité catalytique (exemples 2 et 3) est 1,3 à 1,4 fois (selon que l'on est en mono-ou bicouche, respectivement) supérieure à celle du revêtement de l'exemple comparatif 1,
• ▪ enfin, toujours avec la même quantité d'oxyde de palladium que dans le revêtement de FR 2848290 (exemple 1) mais en utilisant cette fois de l'oxyde de cérium CeO₂ comme dopant, l'activité catalytique (exemples 2 et 3) est 3 fois supérieure à celle du revêtement de l' exemple comparatif 1.

Tableau 1 : comparaison de l'activité catalytique des revêtements des exemples comparatifs 1 à 3 et des exemples 1 à 3 Activité catalytique sur aluminium émaillé Quantité de PdO Exemple comparatif 1 Revêtement monocouche PdO sur support émaillé Exemple comparatif 2 Revêtement bicouche PdO/AgO sur support émaillé selon FR 2848290 Exemple comparatif 3 Revêtement bicouche PdO/CuO sur support émaillé selon FR 2848290 Exemple 1 Revêtement bicouche PdO/CeO2 sur support émaillé selon l'invention Exemple 2 Revêtement bicouche Pd0/ Y₂O₃ sur support émaillé selon l'invention Exemple 3 Revêtement monocouche Pd0 + Y₂O₃ sur support émaillé 1 100 Valeur de référence ∼ 95 30 300 ∼ 140 ∼ 130 1/2 75 ∼ 70 9 190 115 115 1/4 65 60 ND 140 100 100 Légende :
ND : Non déterminé
∼ : environ The results in terms of catalytic activity, which are presented in Table 1 show that:

• When a dopant such as yttrium oxide Y ₂ O ₃ is used in a monolayer deposit (example 3), the quantity of palladium oxide can be divided by four to obtain a catalytic activity equivalent to that of one would have with a PdO monolayer deposition on 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 quantity of palladium oxide as in the coating of Comparative Example 1 and using Y ₂ O _{3 as} yttrium oxide, 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.

<b><u> Table 1 </ u>: comparison of the catalytic activity of the coatings of Comparative Examples 1 to 3 and Examples 1 to 3 </ b> Catalytic activity on enameled aluminum Quantity of PdO Comparative Example 1 PdO monolayer coating on enamelled support Comparative Example 2 PdO / AgO two- layer coating on an enamelled support according to FR 2848290 Comparative Example 3 PdO / CuO bilayer coating on an enamelled support according to FR 2848290 Example 1 PdO / CeO2 bilayer coating on an enamelled support according to the invention Example 2 Pd0 / Y ₂ O ₃ bilayer coating on an enamelled support according to the invention Example 3 Pd0 + Y ₂ O ₃ monolayer coating on an enamelled support 1 100 Reference value ~ 95 30 300 ~ 140 ~ 130 1/2 75 ~ 70 9 190 115 115 1/4 65 60 ND 140 100 100 Legend:
ND: Not determined
~: About

EXAMPLE 5 : Determination of abrasion resistance

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.

• ▪ observation de l'usure de la zone abrasée à la loupe binoculaire et sous un éclairage adapté, puis
• ▪ comparaison avec l'échelle de notation représentée sur les figures 5 à 8.

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 under a binocular magnifying glass and under suitable lighting, then
• ▪ comparison with the rating scale represented on the Figures 5 to 8 .

• ▪ la résistance à l'abrasion est jugée excellente pour un revêtement bicouche PdO/CeO₂ sur support émaillé selon l'invention, quelle que soit la quantité d'oxyde de palladium ;
• ▪ la résistance à l'abrasion est jugée excellente pour un revêtement bicouche selon l'invention ou un revêtement monocouche, sur support émaillé, dopé par l'oxyde d'yttrium Y₂O₃ et avec une quantité d'oxyde de palladium divisée par quatre par rapport à celle de l'exemple comparatif 1 (monocouche de PdO sans dopant) ;
• ▪ la résistance à l'abrasion est jugée très satisfaisante pour un revêtement bicouche selon l'invention ou un revêtement monocouche, sur support émaillé, dopé par l'oxyde d'yttrium Y₂O₃, avec une quantité d'oxyde de palladium égale ou divisée par deux par rapport à celle de l'exemple comparatif 1 (monocouche de PdO sans dopant).

Tableau 2 : comparaison de la résistance à l'abrasion des revêtements des exemples comparatifs 1 à 3 et des exemples 1 à 3 Résistance à l'abrasion des revêtements sur aluminium émaillé Quantité de PdO Exemple comparatif 1 Revêtement monocouche PdO sur support émaillé Exemple comparatif 2 evêtement bicouche PdO/AgO sur support émaillé selon FR 2848290 Exemple comparatif 3 Revêtement bicouche PdO/CuO sur support émaillé selon FR 2848290 Exemple 1 Revêtement bicouche Pd0/CeO₂ sur support émail selon l'invention Exemple 2 Revêtement bicouche Pd0 + Y₂O₃ sur support émaillé selon l'invention Exemple 3 Revêtement monocouche Pd0/ Y₂O₃ sur support émaillé 1 > 0,75 0,25 à 0,5 0,25 à 0,5 0 0,25 0,25 1/2 0, 75 0,25 0 à 0,25 0 0,25 0,25 1/4 0,5 0,25 ND 0 0 0 Légende :
ND : Non déterminé The results in terms of abrasion resistance presented in Table 2 show that:

• ▪ the abrasion resistance is considered excellent for a PdO / CeO ₂ bilayer coating enamelled support according to the invention, regardless of the amount of palladium oxide;
• The abrasion resistance is considered excellent for a bilayer coating according to the invention or a monolayer coating, on an enamelled support, doped with yttrium oxide Y ₂ O ₃ and with an amount of palladium oxide divided by four compared to that of Comparative Example 1 (monolayer of PdO without dopant);
• The abrasion resistance is considered very satisfactory for a bilayer coating according to the invention or a monolayer coating, on enamelled support, doped with yttrium oxide Y ₂ O ₃ , with an amount of palladium oxide equal to or halved with respect to that of Comparative Example 1 (monolayer of PdO without dopant).

<b><u> Table 2 </ u>: comparison of the abrasion resistance of the coatings of Comparative Examples 1 to 3 and Examples 1 to 3 </ b> Abrasion resistance of coatings on enamelled aluminum Quantity of PdO Comparative Example 1 PdO monolayer coating on enamelled support Comparative Example 2 PdO / AgO bilayer coating on an enamelled support according to FR 2848290 Comparative Example 3 PdO / CuO bilayer coating on an enamelled support according to FR 2848290 Example 1 Pd0 / CeO ₂ bilayer coating on enamel support according to the invention Example 2 Pd0 + Y ₂ O ₃ bilayer coating on an enamelled support according to the invention Example 3 Pd0 / Y ₂ O ₃ monolayer coating on an enamelled support 1 > 0.75 0.25 to 0.5 0.25 to 0.5 0 0.25 0.25 1/2 0, 75 0.25 0 to 0.25 0 0.25 0.25 1/4 0.5 0.25 ND 0 0 0 Legend:
ND: Not determined

Claims (10)

1. Heating appliance (1) comprising a metal support (2), at least one part of which is covered by a self-cleaning coating in contact with ambient air, said coating comprising at least one oxidation catalyst chosen from among platinoid oxides and at least one dopant of said oxidation catalyst chosen from among oxides of rare earths:

   characterised in that said self-cleaning coating is a two-layer coating comprising:

   - an internal layer (3) between 50 nm and 100 nm thick at least partially covering the metal support (2) and including said dopant, and,

   - an external layer (4) between 15 nm and 50 nm thick in contact with ambient air and including said oxidation catalyst, and

   in that said external layer (4) is located on said internal layer (3).
2. Appliance according to claim 1, characterised in that the dopant is chosen from among cerium oxides, yttrium oxides and mixes of them.
3. Appliance according to claim 1 or 2, characterised in that the oxidation catalyst is chosen from among palladium oxides, platinum oxides and mixes of them.
4. Appliance according to any one of claims 1 to 3, characterised in that the self-cleaning agent is a two-layer coating comprising an internal layer 3 made of cerium oxide or yttrium oxide and an external layer made of palladium oxide.
5. Appliance according to any one of claims 1 to 4, characterised in that it also comprises an intermediate protection layer (5) located between the metal support (2) and the internal layer (3) of the self-cleaning coating, said intermediate protection layer (5) being composed of a material chosen from among aluminium alloys, enamel and mixes of them, so as to form a catalytically inert support regarding oxidation.
6. Appliance according to claim 5, characterised in that said intermediate protection layer (5) is made of enamel.
7. Appliance according to any one of claims 1 to 6, characterised in that it is in the form of the ironing plate of a warming iron including an ironing surface and in that the self-cleaning coating covers the ironing surface.
8. Appliance according to any one of claims 1 to 6, characterised in that it is the form of a cooking appliance comprising walls that might come into contact with organic dirt, said self-cleaning surface covering these walls.
9. Method of making a heating appliance (1) comprising a metal support (2), at least part of which is covered by a self-cleaning coating composed of an internal layer (3) and an external layer (4), said method being characterised in that it comprises the following steps:

   i. the surface of the metal support (2) to be coated is heated to a temperature of between 250°C and 400°C in an oven or under infrared radiation;

   ii. a solution of a doping precursor is sprayed on the surface of the metal support (2) to be coated at a temperature of between 250°C and 400°C, chosen from among salts of rare earths, to form the internal layer (3) with a coating thickness of between 50 nm and 100 nm including a dopant chosen from among oxides of rare earths;

   iii. the surface of the metal support (2) to be coated with the internal layer (3) is heated again to a temperature of between 250°C and 400°C in an oven or under infrared radiation;

   iv. a solution of an oxidation catalyst precursor is sprayed on the surface of the internal layer (3) to form the external layer (4) with a thickness of between 15 nm and 50 nm, the oxidation catalyst precursor being chosen from among platinoid salts to obtain the self-cleaning coating;

   v. the surface of the metallic support (2) coated with the self-cleaning coating is baked at a temperature of between 400°C and 600°C in an oven or under infrared radiation for a few minutes.
10. Method according to claim 9, characterised in that the doping salts or the oxidation catalyst are acetates, chlorides or nitrates.

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