EP1567807B1 - Heating device coated with a self-cleaning coating - Google Patents

Abstract

A heating device has metal walls which are at least partly covered with a self-cleaning coating having an outer layer in contact with ambient air, made of at least one oxidizing catalyst chosen from among the platinum oxides, and at least one inner layer (3) between the metallic support and the outer layer made of an oxidation catalyst chosen from the oxides of Group 1b transition elements. The catalyst in the outer layer is an oxide of palladium or platinum or a mixture of these. The catalyst in the inner layer is an oxide of copper, silver or a mixture of these. In particular, the outer layer is a palladium oxide and the inner layer a silver oxide, or the outer layer is a mixture of palladium oxide and silver oxide. The thickness of the outer layer, measured using the RBS method, is 10-500 nm, preferably 20-120 nm. The thickness of the inner layer, measured using the RBS method, is 20-50 nm. An additional intermediate layer (5) can be placed between the metallic support and the inner layer, forming a catalytically inert support made of aluminum, enamel, polytetrafluoroethylene or a mixture of these. The intermediate layer is made of enamel. The device is in the shape of a cooking device with walls which are prone to be in contact with organic dirt and the coating covers these walls. An Independent claim is included for coating the metallic support of a heating device with a self-cleaning coating as described above, by (i) heating the surface of the metallic support to 400degreesC, (ii) placing it in contact under infrared at 400-600degreesC for several seconds, (iii) spraying a solution of a catalytic precursor to form the inner layer, (iv) reheating the surface in an oven to ca. 400degreesC, (v) placing it again under infrared at 400-600degreesC for several seconds, spraying a solution of a catalytic precursor to form the outer layer, and (vii) reheat the metallic support with infrared for several minutes.

Description

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

Some heating devices, 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. .

The iron soles could be improved by the care given to the gliding qualities of the ironing surface, combined with the qualities allowing the easier spreading of the linen. One way to obtain these qualities is to use enamelled soles with a smooth-looking enamel, possibly with thicker lines to spread the fabric during the movement of the iron. Other metal soles treated mechanically and / or covered or not with a deposit to facilitate sliding can also be suitable for a satisfactory use.

However, in use, the sole can tarnish by carbonizing more or less diffuse on its ironing surface, and more or less incomplete, various organic particles captured by friction on ironed fabrics.

But when the sole is tarnished, even in a not very visible way, it partially loses its sliding qualities. Insensibly, with the clogging, ironing becomes more difficult. In addition, the user apprehends to use a tarnished iron, fearing that it can alter his clothes.

Iron sole coatings are known having a hard and resistant layer covered, as indicated by the patent. US4862609 by a layer improving the surface properties. But this patent does not indicate a solution to fight against fouling.

The walls of cooking appliances are also often covered with a smooth enamelled layer so that any splashes of grease or food do not adhere to the surface. Glazed self-cleaning surfaces are known, for example in furnaces and cooking utensils as described for example in the patent. US4029603 or the patent FR2400876 .

Baking apparatus wall claddings comprising two layers comprising the same oxidation catalyst chosen, inter alia, from among the oxides of platinoids ( US-3,566,855-A ).

However, these coatings are not entirely satisfactory as regards their self-cleaning properties.

There is therefore the need for a coating of heating apparatus such as cooking appliances or iron insoles, which keeps the surface completely covered by any contamination by organic particles, and does not clog in normal use, so as to retain its initial qualities.

• a°) une couche externe, au contact de l'air ambiant, comprenant au moins un catalyseur d'oxydation choisi parmi les oxydes de platinoïdes,
• b°) au moins une couche interne, située entre le support métallique et la couche externe, comprenant au moins un catalyseur d'oxydation choisi parmi les oxydes des éléments de transition du groupe Ib.

The present invention relates to a heating apparatus comprising a metal support of which at least a part is covered with a self-cleaning coating, characterized in that the coating comprises:

• a) an outer layer, in contact with the ambient air, comprising at least one oxidation catalyst chosen from platinum oxide,
• b) at least one inner layer, located between the metal support and the outer layer, comprising at least one oxidation catalyst chosen from the oxides of the group Ib transition elements.

• i) on chauffe la surface du support métallique à recouvrir dans un four à environ 400°C,
• ii) on place la surface du support métallique à recouvrir sous infrarouge à une température allant de 400°C à 600°C pendant quelques secondes,
• iii) on pulvérise une solution d'un précurseur de catalyseur d'oxydation choisi parmi les oxydes des éléments de transition du groupe Ib sur la surface du support métallique à recouvrir pour obtenir la couche interne,
• iv) on chauffe à nouveau la surface du support métallique à recouvrir, avec la couche interne, dans un four à environ 400°C,
• v) on place la surface du support métallique à recouvrir, avec la couche interne, sous infrarouge à une température allant de 400°C à 600°C pendant quelques secondes,
• vi) on pulvérise une solution d'un précurseur de catalyseur d'oxydation choisi parmi les oxydes de platinoïdes sur la couche interne pour obtenir la couche externe,
• vii) on recuit la surface du support métallique recouverte des couches interne et externe sous infrarouge pendant quelques minutes.

The present invention also relates to a method for covering the metal support of a heating apparatus with a self-cleaning coating as above, characterized in that it comprises the following steps:

• i) the surface of the metal support to be coated is heated in an oven at about 400.degree.
• ii) placing the surface of the metal support to be covered under infrared at a temperature ranging from 400 ° C. to 600 ° C. for a few seconds,
• iii) spraying a solution of an oxidation catalyst precursor chosen from the oxides of the group Ib transition elements on the surface of the metal support to be covered to obtain the inner layer,
• iv) re-heating the surface of the metal support to be coated, with the inner layer, in an oven at about 400 ° C,
• v) placing the surface of the metal support to be covered, with the inner layer, under infrared at a temperature ranging from 400 ° C. to 600 ° C. for a few seconds,
• vi) spraying a solution of an oxidation catalyst precursor selected from platinum oxide on the inner layer to obtain the outer layer,
• vii) annealing the surface of the metal support covered with the inner and outer layers under infrared for a few minutes.

Thanks to the invention, there is obtained an apparatus whose self-cleaning coating has a particularly excellent catalytic activity and whose adhesion to the metal support is very good.

It has indeed been found that the combination of an oxidation catalyst selected from the oxides of the Group Ib transition elements in the inner layer with an oxidation catalyst chosen from platinum oxide in the outer layer increases in the self-cleaning activity of the coating in a synergistic manner.

Thanks to the invention, the organic particles in contact with the outer layer of the coating are oxidized when the apparatus is heated. Furthermore, the synergistic effect obtained by the particular combination of an inner layer comprising a specific oxidation catalyst and an outer layer comprising a specific oxidation catalyst different from that of the inner layer makes it possible to obtain a coating having a particularly high catalytic activity. Thus, the surface of the coating is regenerated very quickly.

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.

In addition, thanks to the method of the invention and in particular through the infrared exposure of the surface of the metal support to be covered, the adhesion of the coating to the metal support is particularly good. This improved adhesion increases the friction resistance of the coating, this property being particularly advantageous in the case of an iron soleplate, for example.

For the purpose of this application, the term "heating apparatus" is intended to mean any apparatus, article or utensil which, during its operation, reaches a temperature of at least 45 ° C. and preferably at least 90 ° C. The device can reach this temperature operating by means of its own, such as a heating base integrated in the apparatus and provided with heating elements, or by external means. Such appliances are, for example, iron soles, cooking appliances, ovens, grills, kitchen utensils.

The outer layer of the coating according to the invention comprises an oxidation catalyst chosen from platinum oxide. 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. . Preferably, the outer layer comprises an oxidation catalyst selected from palladium oxides, platinum oxides and mixtures thereof.

In practice, such oxidation catalysts are well known in themselves, as well as their methods of obtaining, without it being necessary to describe in detail their methods of preparation respectively. Thus, by way of example, with respect to platinum as an oxidation catalyst, its catalytically active form can be obtained by calcination or decomposition of a chloroplatinic acid salt or any other precursor.

Of course any oxidation catalyst selected 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.

The surface of the outer layer is in direct contact with the ambient air and organic soils. 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 in organic polymer such as polyamide or polyester, any organic residue of detergent and, optionally, softener, any organic substance such as splashes of fat or food.

The oxidation catalyst selected from platinum oxide is distributed on and / or in the outer layer of the coating, where it is in contact with soiling, and in all or part of the outer layer, continuously or discontinuously.

In the case of an iron soleplate which comprises or not relief zones, the oxidation catalyst chosen from among the platinoids is distributed on the outer surface of the soleplate, intended to be brought into contact with the laundry.

The coating may comprise, in addition to the oxidation catalyst chosen from platinum oxide, any inner support layer catalytically inert with respect to oxidation. This support adheres to the metal and catalytically inert support is preferably selected from aluminum or silicon compounds, such as for example alumina in divided form or particles, enamel, polytetrafluoroethylene and mixtures thereof.

In a preferred embodiment of the invention, the catalytically inert support with regard to oxidation is an 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 the penetration of hot steam or humidity.

The outer layer of the coating preferably has a thickness, measured according to the RBS method described in Example 1 of the present application, ranging from 10 nanometers to 500 nanometers, and more preferably from 20 nanometers to 120 nanometers.

The oxidation catalyst of the outer layer being active at a coating temperature greater than or equal to 90 ° C, it cleans said coating when the latter is heated at least at such a temperature.

The inner layer comprises at least one oxidation catalyst chosen from among the oxides of the group Ib transition elements, preferably selected from copper oxides, silver oxides and mixtures thereof.

In practice, such oxidation catalysts are well known in themselves, as well as their methods of obtaining, without it being necessary to describe in detail their methods of preparation respectively. By way of example, as regards silver oxide as oxidation catalyst, it is possible to use as precursor commercial silver nitrate sold by Aldrich.

Preferably, the catalytically active inner layer has a thickness, measured according to the RBS method described in Example 1 of the present application, ranging from 20 nanometers to 50 nanometers.

Preferably, the oxidation catalyst present in the inner layer has a good affinity with the oxidation catalyst present in the outer layer. Indeed, after application on the support of the inner and outer layers, the support is annealed and, during this step, the oxidation catalyst present in the inner layer may diffuse into the outer layer and the oxidation catalyst present in the outer layer may diffuse into the inner layer. In a preferred embodiment of the invention, the outer layer comprises, as oxidation catalyst, a palladium oxide and the inner layer comprises, as oxidation catalyst, a silver oxide. In a still preferred embodiment of the invention, the silver oxide has diffused into the outer layer and the outer layer thus comprises a mixture of palladium oxide and silver oxide. A particular synergistic effect on the catalytic activity of the coating has been observed in such an embodiment of the invention.

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

In another preferred embodiment of the invention, the heating apparatus is a cooking appliance comprising walls that can come into contact with organic soils and the coating covers these walls.

In a first mode of operation, the catalyst acts at the operating temperature of the apparatus and the coating is kept clean as and when the device is used.

In a second mode of operation, during a so-called self-cleaning phase, 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. is then left on hold 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 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 an enamelled layer before being covered by the coating of the present invention. Thus, in a preferred embodiment of the invention, the apparatus comprises an enamel intermediate layer located between the metal support and the catalytically active inner layer of the coating.

The application of the catalytically active inner and outer layers to the metal support, covered or not by an enameled layer, is preferably by pyrolysis, by heating the surface to be coated and spray on this hot surface of a solution containing a precursor of the oxidation catalyst.

By "precursor" is meant any chemical or physico-chemical form of the oxidation catalyst, which is likely to lead to, or to release the latter by any appropriate treatment, for example pyrolysis.

In one embodiment of the method according to the invention, the surface of the metal support to be covered is heated in an oven at about 400 ° C. and then placed very briefly, for example for a few seconds, under infrared, until a superficial temperature is reached. ranging from 400 ° C to 600 ° C. This operation softens the surface of the support and makes it possible to increase the subsequent adhesion of the coating. A solution of the precursor of the oxidation catalyst selected from Group Ib transition elements is sprayed onto the surface of the metal support. In contact with the surface, the precursor oxidizes and is fixed on the support and the water evaporates. A layer of thickness ranging from 20 to 50 nm is deposited. The support cools very quickly. It is heated again in the oven at 400 ° C and then under infrared at a temperature ranging from 400 ° C to 600 ° C for a few seconds. A solution of the precursor of the oxidation catalyst selected from the platinoids is sprayed over the inner layer. A layer of thickness ranging from 20 to 50 nm is deposited. The thus coated support is then annealed under infrared for a few minutes, for example for five minutes.

A coated support is obtained whose self-cleaning properties are particularly good.

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

FIG. 1 is a sectional view of an iron soleplate according to the invention,

Figure 2 is a sectional view of an iron soleplate according to the invention comprising an enameled protective layer.

Referring to Figure 1, is shown in section a heater 1 in the form of an iron soleplate comprising a metal support 2 covered with an inner layer 3 and an outer layer 4. The sole comprises also 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 catalyst oxidation agent chosen from the oxides of the transition elements of the group Ib and the outer layer 4 comprises an oxidation catalyst selected from the oxides of platinoids.

Referring to Figure 2, is shown in section an iron soleplate 1 comprising a metal support 2 covered with an intermediate layer 5, an inner layer 3 and an outer layer 4. The sole also comprises a heating base 6 provided with heating elements 7, bonded to the support 2. The inner layer 3 comprises an oxidation catalyst chosen from the oxides of the transition elements of the group Ib and the outer layer 4 comprises a chosen oxidation catalyst among the oxides of platinoids. The protective layer 5 is enamel.

Example I

A clean insole iron enamelled aluminum is placed on an aluminum support of about 2 cm to best retain heat. 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, sold by Aldrich, is dissolved in water at 4 g / l and is sprayed with a pneumatic gun on the sole. A layer of about 40 to 50 nm, measured according to the RBS method, is deposited. 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 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.

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 at a temperature between 400 ° C and 600 ° C. An aqueous solution of nitric acid stabilized palladium nitrate, sold by the company Metalor, is sprayed by means of a spray gun. pneumatic on the sole. A layer of about 40 to 50 nm, measured according to the RBS method described above, is deposited.

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

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

Claims (12)

1. A heater device (1) comprising a metal substrate (2) having at least a portion covered in a self-cleaning coating, the device being characterized in that the coating comprises:

   a) an outer layer (4) in contact with ambient air, comprising at least one oxidation catalyst selected from the oxides of platinoids; and

   b) at least one inner layer (3) situated between the metal substrate (2) and the outer layer (4) and comprising at least one oxidation catalyst selected from the oxides of the transition elements of group Ib.
2. A device according to claim 1, characterized in that the oxidation catalyst of the outer layer (4) is selected from the oxides of palladium, the oxides of platinum, and mixtures thereof.
3. A device according to claim 1 or claim 2, characterized in that the oxidation catalyst of the inner layer (3) is selected from the oxides of copper, the oxides of silver, and mixtures thereof.
4. A device according to any preceding claim, characterized in that the outer layer (4) comprises as its oxidation catalyst an oxide of palladium, and the inner layer (3) comprises as its oxidation catalyst an oxide of silver.
5. A device according to claim 4, characterized in that the outer layer comprises a mixture of palladium oxide and of silver oxide.
6. A device according to any preceding claim, characterized in that the thickness of the outer layer (4), measured using the RBS method, lies in the range 10 nm to 500 nm, and more preferably in the range 20 nm to 120 nm.
7. A device according to any preceding claim, characterized in that the thickness of the inner layer (3), measured using the RBS method, lies in the range 20 nm to 50 nm.
8. A device according to any preceding claim, characterized in that it further comprises an intermediate layer (5) situated between the metal substrate (2) and the inner layer (3) of the coating, the intermediate layer constituting a substrate that is catalytically inert with respect to oxidation and that is selected from aluminum alloys, enamel, polytetrafluoroethylene, and mixtures thereof.
9. A device according to claim 8, characterized in that the intermediate layer (5) situated between the metal substrate (2) and the inner layer (3) of the coating is made of enamel.
10. A device according to any preceding claim, characterized in that it is in the form of a smoothing-iron soleplate having an ironing surface with the coating covering the ironing surface.
11. A device according to any one of claims 1 to 10, characterized in that it is in the form of a cooking device having walls likely to come into contact with organic stains, and the coating covers said walls.
12. A method of applying a self-cleaning coating to cover the metal substrate (2) of a heater device (1) according to any one of claims 1 to 10, the method being characterized in that it comprises the following steps:

    i) heating the surface of the metal substrate for covering in an oven to about 400°C;

    ii) placing the surface of the metal substrate for covering under infrared radiation at a temperature lying in the range 400°C to 600°C for a few seconds;

    iii) spraying a solution of a precursor for an oxidation catalyst selected from the oxides of the transition elements of group Ib onto the surface of the metal substrate for covering in order to obtain the inner layer (3);

    iv) re-heating the surface of the metal substrate for covering, together with its inner layer, in an oven to about 400°C;

    v) placing the surface of the metal substrate for covering, together with its inner layer, under infrared radiation at a temperature lying in the range 400°C to 600°C for a few seconds;

    vi) spraying a solution of a precursor for an oxidation catalyst selected from the oxides of platinoids on the inner layer in order to obtain the outer layer (4); and

    vii) annealing the surface of the metal substrate covered in the inner and outer layers under infrared radiation for a few minutes.

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