EP1188350B1 - Heating element on an aluminium substrate for household appliance - Google Patents

Abstract

A heating element for a soleplate of an iron, composed of: a substrate constituted by a plate containing aluminum; an insulator covering one surface of the plate; and a heating circuit carried by the insulator, wherein the insulator includes an anodized oxide layer having a thickness between 10 and 200 microns and resistant to abrupt temperature variations of the plate.

Description

The present invention relates to heating elements for irons.

The irons usually comprise a casing made of a generally plastic handle and a hot metal soleplate which is applied to the clothes to be ironed. The sole of recent iron is composed of a flat metal bottom plate heated by an upper aluminum molded body, this body being applied to the inner face of the flat plate and having a tubular heating element. For reasons of weight, space and economy, it has sought to remove the aluminum molded body and to apply a heating element directly on the inner face of the flat plate of the sole of the iron.

Thus known patent EP555159 in which the heating element is a sandwich structure adherent to the sole. But this structure requires manufacturing time and precautions that lead to insufficiently economical production.

The enamelled steel plates are known on their internal face on which a thin-film circuit or a screen-printed circuit is deposited. But this process requires the use of vitreous compositions sufficiently insulating to withstand the voltage of the electrical sector. This type of enamel is deposited at high temperature incompatible with an aluminum substrate on the one hand and secondly the differential shrinkage after cooking of this type of enamel and the aluminum substrate induce voltages to which a flat soleplate iron can not resist without deformation.

Patent FR1584094 discloses a circuit deposited on an anodized aluminum substrate. But this embodiment where the alumina layer reaches only a few microns is not suitable for a circuit working at the voltage of the electrical sector. In addition, the use is limited to temperatures lower than those of an iron soleplate.

EP120119 discloses an aluminum substrate adapted to receive a deposited electrical circuit. A thick anodized alumina layer provides electrical isolation with silicic clogging. But if this substrate can receive an electrical or electronic circuit, there is no indication that it is adapted to withstand temperatures as high as those experienced by an iron soleplate.

EP058023 also discloses a sealing treatment of an anodized aluminum substrate. The alumina layer is clogged with an organometallic product polymerized for example by heating. But the sealant treatment required to obtain a good dielectric strength does not constitute redundant security and does not assume resistance to thermal shock encountered by an iron.

FR2763780 discloses a method of manufacturing printed circuits on an aluminum substrate where a thick layer of alumina is formed on the surface to serve as an insulator and can withstand high temperatures without appearance of defects. Clogging of the pores is not obligatory. However, if the circuit can operate when the substrate is raised to high temperature, it is specially adapted to support the implementation of integrated circuits or modules. These components, which support helps to cool, have by far no power and instant temperature variations of an iron soleplate.

US3805023 discloses a heating element having an anodized aluminum substrate. The alumina layer obtained in a weak acid bath, is dense in contact with the substrate and is an electrical barrier, while the outside of the layer is porous. In the porosities was deposited a light-sensitive product containing a precious metal which serves, after irradiation through a negative and development, of catalyst to a chemical deposition of the nickel conductive track

The use for an iron is not mentioned. A priori, the resistive tracks are deposited in replacement of the catalyst in the pores of the alumina layer. On the face of it, the external pores are quite inappropriate for a sole of steam iron working in a humid environment.

US-A-5,943,799 discloses an iron sole heating element with an insulating inner layer which comprises heating tracks, a substrate consisting of an aluminum plate and an insulating outer layer of aluminum oxide formed by electrolitic oxidation and which serves as an anti-friction layer.

The subject of the invention hereinafter is a heating element of iron soleplate. ironing, this heating element being light, compact, and economical to manufacture.

The object of the invention is achieved by a heating element for an iron soleplate, the substrate consisting of a thin plate of pure aluminum or silicon alloy or magnesium alloy is covered with an insulator on which are deposited tracks the insulation is an anodic oxidized layer of thickness between 10 and 200 microns resistant to abrupt temperature changes of the plate.

The use of aluminum makes it possible to benefit from all the advantages of this metal, in particular with regard to the temperature distribution on the sole. Aluminum, pure or alloyed with silicon having practically no magnesium is also easily enamelled. Advantageously for a good distribution of heat, the substrate of the heating element covers a large part of the inner surface of the iron soleplate, the dissipated power can be high.

Anodizing allows to benefit from an insulation naturally adherent to the support and whose expansion is compatible with the latter.

Preferably the oxidized layer is of the type obtained by anodic oxidation conducted in a solution of an acid with low electrical conductivity, with a current density of between 1 and 5 A / dm 2 at a stabilized temperature.

The use of an oxidation in a solution of low electrical conductivity acid similar to that described in the patent FR2763780 but applied to a heating element of household appliance, provides surprisingly good resistance in temperature and temperature. breakdown voltage.

In addition, many tests in the workshop have proved the good endurance performance of this insulation in tests where the iron soleplate is subjected to many sudden colds on a wet felt, largely representative tests of a hot iron soleplate applied on a pattemouille.

In a preferred version, the substrate of the heating element is an enameled iron soleplate prior to the anodizing on its outer face intended to be in contact with the fabrics, this enameling being performed at a temperature that relaxes the metal.

Anodizing requires a relaxing treatment of the metal. Enameling the sole before anodizing saves this relaxation treatment. Preferably the enamel is protected from corrosion of the anodizing baths by a peelable protective varnish.

Preferably, the pores of the oxidized layer are filled with another metal oxide obtained by decomposition of a polymerizable organometallic product such as a silane, an organic derivative of titanium or zirconium or germanium or tin.

Although this filling is not essential with all kinds of oxidized layers, it provides additional operational safety.

In another version, the surface of the oxidized layer is impregnated with a temperature-resistant organic polymerizable product such as polyester or polyimide.

This other possibility is easier to implement and requires cooking at a lower temperature.

In a preferred version, the conductive heating tracks are serigraphed and then fired.

In another implementation of a sole heating element, the heating element having an aluminum substrate is brazed to the inner face of the iron soleplate at a temperature which allows the cooking of the tracks.

This makes it possible to obtain soles whose face in contact with the fabrics is made of stainless steel having a good distribution of heat on the surface.

The soldering is done when the tracks are freshly deposited which saves cooking of the latter.

In another version, the nickel tracks are deposited on the dense alumina layer chemically.

Any known method can be used to deposit an adherent conductive or semiconducting layer acting as a heating track. We prefer to use known methods which consist in metallizing the entire surface and then, using a photoresist mask, make the tracks by attacking the parts of this surface which must not be conductive. The advantage is that this type of process requires essentially only equipment compatible with the manufacture of printed circuits

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

In a preferred embodiment of the invention, the substrate of the heating element constitutes the sole of the iron which is a flat aluminum plate with rounded edges to facilitate sliding on the fabrics. The sole is relaxed by heat treatment, by annealing at 400 ° C, then degreased, stripped and thoroughly cleaned.

An oxide layer obtained by anodic oxidation in a solution of low electrical conductivity acid is deposited electrolytically on the inner face of the iron sole. When the deposit obtained can not serve as a bonding layer to a deposit giving good ironing qualities to the outer face intended to come into contact with the ironed fabric, this face is masked by usual means electroplating.

An oxidized layer of sufficient insulation is obtained in solutions of oxalic, citric, lactic or tartaric acid with a current density of 1 to 5 A / dm2 on the part.

In a preferred version, the insulation produced by the oxidized layer is reinforced by additional redundant insulation for greater safety.

The additional insulation layer is siliceous in a first embodiment. It can be obtained by thermal decomposition of a silane deposited on the surface of the oxide.

In a second version, the additional insulation is an oxide or a combination of oxides of metals such as titanium, zirconium, germanium, tin. It can be obtained by thermal decomposition of known precursors of these metals.

In a third version, the additional insulation is a layer of a low-melting glass such as those used to make circuits hybrids. This layer can be obtained for example by screen printing a paste 7802 from Metech and baking at 500 ° C on the oxidized layer.

The electrical circuit comprises resistive heating tracks deposited on the oxidized layer. Preferably these tracks are pastes or inks deposited by screen printing and conductive after baking. For example, it is possible to use a silver-filled polyimide paste of reference CM3321 E from Protavic which polymerises in one hour at 150 ° C. followed by one hour at 275 ° C.

Advantageously, a polyimide film covers the oxidized face and its heating tracks. This film prevents the whole from being sensitive to humidity. It is obtained for example by screen printing of a paste IM891 from the company Protavic and polymerization on the tracks.

In the simplest version the outer face of the iron sole comes into direct contact with the fabric. The metal surface is only cleaned or polished by mechanical brushing.

In a more advanced embodiment, the sole of the iron is a flat plate with rounded edges so that they are less aggressive, made of aluminum alloy with silicon where the magnesium content is less than 0.01%. This plate is enamelled on its outer surface to the iron at a temperature that anneals the aluminum and relaxes it. It is therefore not necessary to carry out relaxation treatment prior to anodization. Enameling gives good ironing characteristics to the sole. Preferably the enamel is protected at least during anodization by a peelable protective film. The sole has on its inner side insulation and tracks similar to those of the previous example.

When the user returns with an iron equipped with a sole according to the invention, the resistive heating tracks dissipate in the aluminum a significant power up to 2 kW for a sole of about 2 dm2. Aluminum has the advantage of distributing heat throughout the entire surface. Furthermore, the sole undergoes heating to the set temperature which may be greater than 250 ° C and be brought into contact with a wet cloth, see wet. Severe endurance tests show a good behavior of the sole according to the invention.

In another embodiment, the substrate of the heating element is an aluminum flat plate which is expanded and which receives an oxidized layer obtained by anodic oxidation in a solution of an acid with low electrical conductivity, as in the previous examples. . In the same way the oxidized layer can receive additional insulation if necessary, then the tracks are deposited and cooked as needed.

The heating element obtained is bonded to the inner face of an iron soleplate formed by a thin enamelled aluminum plate on its outer face. Advantageously, a silicone adhesive is used which is compatible with the temperatures of use of the soleplate. This assembly has the advantage of being compatible with that of existing iron fabrications comprising a heating body stuck on a sole.

In another embodiment, the substrate of the heating element is an aluminum flat plate which is expanded and which receives an oxidized layer obtained by anodic oxidation in a solution of an acid with low electrical conductivity, as in the previous examples. . In the same way the oxidized layer can receive additional insulation if necessary, before depositing the tracks.

The heating element obtained is brazed on the inner face of an iron soleplate constituted by a thin plate of stainless steel. Advantageously, a solder melting at a temperature which fires the deposited tracks and / or the protective deposit is used, making the operation more economical. This operation is made possible by a rigorous control of the atmosphere in which it takes place.

In a different version, the heating element obtained is fixed on the inner face of an iron soleplate constituted by a thin stainless steel plate whose outer edges are rolled to come to rest on the heating element and maintain it. in known manner. The heat transfer between the heating element and the soleplate is provided by a thin layer of conductive heat-resistant adhesive such as a silicone adhesive.

This gives a sole that has the same advantages as that of the previous example, but with another presentation.

In another version, the sole of the iron is a flat plate with rounded edges so that they are less aggressive, made of aluminum alloy with silicon where the magnesium content is less than 0.01%. This plate is enamelled on its outer surface to the iron at a temperature that anneals the aluminum and relaxes it. It is therefore not necessary to carry out relaxation treatment prior to anodization. Enameling gives good ironing characteristics to the sole. Preferably the enamel is protected at least during anodization by a peelable protective film. The sole has on its inner face an oxidized insulating layer similar to that of the previous examples.

On this insulating layer, preferably unplugged or incompletely clogged, nickel tracks have been deposited. To do this the surface is sensitized by a solution containing palladium chloride or a commercial precursor distributed for example by the company SHIPLEY. The surface is then quenched in a metallization bath comprising nickel sulphate and reducing agents, and overcoated with nickel. The surface is then masked with a photosensitive resin, exposed to ultraviolet light through a pattern that reproduces the desired tracks, and revealed by a sodium bath to remove the exposed parts of the mask. The nickel free surface is then attacked for example by a solution of iron perchloride which leaves only the tracks. The remains of masking resin are removed with acetone. These operations, which are partly compatible with printed circuit manufacturing equipment, are carried out according to the rules of the art with the necessary precautions and intermediate rinses.

The connections are then brazed on the tracks by known means.

Compared to the tracks obtained by serigraphy, the tracks obtained by chemical deposition of nickel do not require firing.

The application of this invention is mainly intended for the field of irons, but it may however be envisaged to apply it in a similar way, with some obvious adaptations, to the outer face of a bottom of tank intended to heat the iron. water in a kettle or oil in a deep fryer.

Claims (8)

1. A heater element for a smoothing iron, whose substrate is constituted by a thin plate of aluminum that is pure or alloyed with silicon, or alloyed with magnesium and is covered with an insulator on which heater tracks are deposited, said heater element being characterized in that the insulator is an anodic oxidized layer of thickness lying in the range 10 µm to 200 µm and is resistant to sudden variations in the temperature of the plate.
2. A heater element according to claim 1, characterized in that the oxidized layer is of the type obtained by anodic oxidation performed in a solution of an acid that is weakly electrically conductive, with a current density lying in the range 1 A/dm² to 5 A/dm² at a stabilized temperature.
3. A heater element according to claim 1 or claim 2, characterized in that the pores in the oxidized layer are filled with another metal oxide obtained by decomposition of a polymerizable organometallic substance such as a silane, or an organic derivative of titanium or of zirconium or of germanium or of tin.
4. A heater element according to any one of claims 1 to 3, characterized in that the surface of the oxidized layer is impregnated with a glass having a low melting point.
5. A heater element according to any preceding claim, characterized in that it has tracks that are screen printed on the oxidized layer.
6. A heater element according to any one of claims 1 to 4, characterized in that it has metal heater tracks deposited chemically on the oxidized layer.
7. A heater element according to any one of claims 1 to 6, characterized in that it is brazed to the inside face of the soleplate of the iron at a temperature that enables the tracks to be baked.
8. A heater element according to any one of claims 1 to 6, characterized in that the substrate of the heater element is a smoothing iron soleplate that is enameled prior to anodizing on its face that is designed to be in contact with the ironing, the enameling being performed at a temperature that relaxes the metal.