CAVITY HAVING A NON-STICK AND/OR NON-WETTING COATING, COOKING APPLIANCE COMPRISING SUCH A CAVITY AND METHOD FOR MANUFACTURING A CAVITY

Abstract

A cavity (4) for a cooking appliance (2), in particular an oven cavity (4) for a domestic oven, comprising at least one cavity wall (8a, 8b, 8c, 8d) defining a cooking chamber (6) for cooking foodstuff and having an inner surface (10) facing towards the cooking chamber (6), a central opening for placing foodstuff into the cooking chamber (6), wherein the inner surface (10) is at least partially provided with a non-stick and/or non-wetting coating (16) comprising at least a first layer (18), wherein the first layer (18) is obtained by a sol-gel process from a first composition comprising a silica sol and a silane and/or wherein the cavity (4) further comprises a heat reflection shield system (26) having at least one heat reflection shield (28) to reduce the heat radiation produced by heating elements (30) being arranged within the cavity (4) against the non-stick and/or non-wetting coating (16). A cooking appliance (2), in particular a domestic oven comprising such a cavity (4) and a method for manufacturing such a cavity (4).

Claims

1. A cavity for a cooking appliance, comprising: a cavity wall defining a cooking chamber for cooking foodstuff and having an inner surface facing towards the cooking chamber, a central opening for placing foodstuff into the cooking chamber, and a non-stick and/or non-wetting coating applied to the inner surface at least partially, wherein: the non-stick and/or non-wetting coating comprises a first layer obtained by a sol-gel process from a first composition comprising a silica sol and a silane, and/or the cavity further comprises a heat reflection shield system having a heat reflection shield to reduce heat radiation produced by heating elements arranged within the cavity against the non-stick and/or non-wetting coating.

2. The cavity according to claim 1, wherein the cavity wall is made of stainless steel, or is made of corrosive steel provided with an anticorrosive or preparation layer comprising an enamel layer and/or an aluminium layer and/or a layer comprising aluminium, wherein the first layer is applied to said anticorrosive or preparation layer.

3. The cavity according to claim 1, wherein the non-stick and/or non-wetting coating comprises a second layer applied to the first layer, wherein the second layer is obtained by a sol-gel process from a second composition comprising a silica sol, a silane and a siloxane.

4. The cavity according to claim 1, wherein in said first composition the silica sol is present in an amount of 15 to 70 wt % and/or the silane is present in an amount of 2 to 70 wt %.

5. The cavity according to claim 1, wherein the silane is an organoalkoxysilane and/or a fluoralkoxysilane.

6. The cavity according to claim 3, wherein the first composition and/or the second composition comprise or comprises an organic solvent.

7. The cavity according to claim 6, wherein the solvent is present in an amount of 10 to 60 wt % in the first composition and/or the second composition, respectively.

8. The cavity according to claim 1, wherein the first composition comprises a polydimethylsiloxane.

9. The cavity according to claim 3, wherein the siloxane is present in the second composition in an amount of 0.1 to 2 wt %.

10. The cavity according to claim 3, wherein the first composition and/or the second composition comprise or comprises pigments and/or dyes and/or filling materials and/or further additives.

11. The cavity according to claim 2, wherein the inner surface of the cavity wall and/or the anticorrosive or preparation layer has a surface roughness between Ra 0.50 μm to 5.00 μm.

12. The cavity according to claim 2, wherein the enamel layer has a thickness smaller than 50 μm, still more preferably smaller than 30 μm.

13. The cavity according to claim 1, wherein the heat reflection shield has a first part for protecting a cavity top wall and a second part for protecting a cavity side wall, wherein the first and the second part have different dimensions.

14. The cavity according to claim 1, wherein an inner surface of the heat reflection shield: is shiny with an emissivity between 0.1 and 0.6, and/or is made of a material that is temperature-resistant and/or insulating, and/or comprises two or more layers of different materials.

15. A cooking appliance comprising: the cavity for a cooking appliance according to claim 1 heatable cavity, heating elements for heating said cavity, and a door for closing the cavity.

16. A method for manufacturing a cavity of a cooking appliance, having a non-stick and/or non-wetting coating on an inner surface of a cavity wall of the cavity, comprising: applying an anticorrosive or a preparation layer comprising an enamel layer and/or an aluminium layer and/or a layer comprising aluminium to the inner surface of the cavity wall, applying a first layer of the non-stick and/or non-wetting coating to a surface of the anticorrosive or preparation layer and/or attaching a heat reflection shield system having a heat reflection shield to the inner surface of the cavity or to a heating element of the cooking appliance.

17. The method for manufacturing a cavity according to claim 16, wherein a second layer of the non-stick and/or non-wetting coating is applied to a surface of the first layer.

18. The method for manufacturing a cavity according to claim 16, wherein the inner surface of the cavity wall and/or the anticorrosive or preparation layer is or are roughened before applying the non-stick and/or non-wetting coating by laser-treatment.

19. The method for manufacturing a cavity according to claim 16, wherein the anticorrosive or preparation layer is applied to the inner surface of the cavity wall by an enameling process.

20. A cooking appliance comprising: a cooking chamber defined at least in part by a cavity side wall made of low-carbon steel and a cavity top wall, a heating element within the cooking chamber and adapted to supply heat for cooking therein, an anticorrosive layer disposed on an inner surface of said cavity side wall, a non-stick and non-wetting coating having a water-contact angle of at least 95° disposed on an inner surface of said anticorrosive layer, and a heat shield within the cooking chamber; said heat shield having an emissivity between 0.1 and 0.6 and comprising a first part adapted to reduce incidence of radiation from said heating element on said top wall, and a second part adapted to reduce incidence of radiation from said heating element on said non-stick and non-wetting coating on the side wall; said anticorrosive layer being an enamel layer having a thickness smaller than 50 μm; said non-stick and non-wetting coating comprising a first layer comprising a first matrix formed as a condensation reaction product of a first mixture comprising a silica sol and a silane, and a second layer comprising a second matrix formed as a condensation reaction product of a second mixture comprising silica sol, a silane and a siloxane, wherein the first layer of said non-stick and non-wetting coating is disposed on an inner surface of said anticorrosive layer, and the second layer of said non-stick and non-wetting coating is disposed on an inner surface of said first layer; the inner surface of said anticorrosive layer having a surface roughness of Ra 0.50 μm to 5.00 μm when measured according to ISO 4287:1997; the silane in each of said first and second mixtures comprising at least one of organoalkoxysilane or fluoralkoxysilane.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0079] The present invention will be described in further detail with reference to the drawings, in which

[0080] FIG. 1 illustrates a schematic view of a cooking appliance including a cavity according to an embodiment of the present invention,

[0081] FIG. 2 illustrates a cross-sectional view of a cavity wall in detail,

[0082] FIG. 3 illustrates a schematic view of a part of a cavity of a cooking appliance comprising a heat reflection shield system according to a first embodiment of the invention,

[0083] FIG. 4 illustrates a schematic view of a part of a cavity of a cooking appliance comprising a heat reflection shield system according to a second embodiment of the invention,

[0084] FIG. 5 illustrates a schematic view of a part of a cavity of a cooking appliance comprising a heat reflection shield system according to a third embodiment of the invention,

[0085] FIG. 6 illustrates a schematic view of a part of a cavity of a cooking appliance comprising a heat reflection shield system according to a fourth embodiment of the invention,

[0086] FIG. 7 illustrates a schematic view of a part of a cavity of a cooking appliance comprising a heat reflection shield system according to a fifth embodiment of the invention.

LIST OF REFERENCE NUMERALS

[0087] 2 cooking appliance [0088] 4 cavity [0089] 6 cooking chamber [0090] 8a, b, c, d cavity wall [0091] 10 surface of the cavity wall [0092] 12 anticorrosive layer [0093] 14 surface of the anticorrosive layer [0094] 16 coating [0095] 18 first layer [0096] 20 surface of the first layer [0097] 22 second layer [0098] 24 surface of the second layer [0099] 26 heat reflection shield system [0100] 28 heat reflection shield [0101] 30 heating element [0102] 32a, 32b first, second part of the heat reflection shield [0103] 34 inner surface of the heat reflection shield system [0104] 36a, 36b layers of the heat reflection shield

DETAILED DESCRIPTION

[0105] FIG. 1 illustrates a schematic view of a cooking appliance 2. Such cooking appliance 2 comprises a heatable cavity 4 according to the present invention. The cavity 4 comprises cavity walls which define a cooking chamber 6 into which foodstuff may be placed for cooking or baking. The cooking chamber 6 is defined by the cavity walls, usually comprising a left and a right side wall, 8a and 8b, respectively, a bottom wall 8c and an upper wall 8d and a rear wall and a front wall, which are not shown in FIG. 1. One of the cavity walls, usually the front wall comprises a central opening for placing the foodstuff into the cooking chamber 6. The central opening may be closed or opened by a door that may be a part of the front wall. The cooking appliance 2 usually further comprises also heating elements (not shown in FIG. 1) for heating the cooking chamber 6 and therefore heating food that has been placed therein to be cooked. Such heating elements may be disposed at one of the cavity walls.

[0106] The cavity walls 8a, 8b, 8c, 8d are exemplary made of corrosive steel, actually a low carbon steel. In order to prevent the cavity 4 from corrosion, the cavity walls 8a, 8b, 8c, 8d are provided with an anticorrosive or preparation layer 12, in the present case an enamel layer, in particular formed by a ground coat composition, that has burned to the cavity walls 8a, 8b, 8c, 8d at temperature of 820° C. The anticorrosive or preparation layer 12 has a surface roughness of 2.5 μm and a layer thickness of 20 μm.

[0107] The cavity walls 8a, 8b, 8c, 8d are further provided with a non-stick and/or non-wetting coating 16 comprising a first layer 18 as a base layer and a second layer 22 as a top layer. The first layer 18 is applied to a surface 14 of the anticorrosive or preparation layer 12. A cross-sectional view of a cavity wall 8a is exemplary shown in detail in FIG. 2.

[0108] Both, the first layer 18 and the second layer 22 are obtained by a sol-gel process. For production of the first layer 16, a colloidal silica sol, which is pure SiO.sub.2, an organoalkoxysilane, which is an organic-inorganic hybrid material and presently methyltrimethyoxysilane, and an acid catalyst, presently acetic acid are mixed and stirred for about 2 hours at room temperature in order to effect a condensation reaction. The weight proportion of organoalkoxysilane is about 10 to 40 wt %, silica sol is present in an amount of 30 to 70 wt %. Adding acetic acid in an amount of 0.1 to 2 wt % is sufficient for accelerating the condensation reaction.

[0109] Then, a solvent, presently propanol, is added in an amount of 10 to 40 wt %. Pigments are added and further additives can be additionally added at this step.

[0110] For production of the second layer 22, colloidal silica sol, siloxane and a solvent, even here propanol, are mixed. Organoalkoxysilane and an acid catalyst, presently acetic acid are then added. Even said mixture is mixed and stirred for about 2 hours at room temperature. The weight proportion of organoalkoxysilane is about 10 to 40 wt %, silica sol is present in an amount of 30 to 70 wt %, acetic acid is present in an amount of 0.1 to 2 wt %. Siloxane, presently polydimethylsiloxane, is added in an amount of 0.1 to 2 wt %.

[0111] Then, a solvent, presently even here propanol, is added in an amount of 10 to 40 wt %. Pigments are added and further additives can be additionally added at this step.

[0112] For manufacturing a cavity 4 having a non-stick and/or non-wetting coating 16 on an inner surface 10 of the cavity walls 8a, 8b, 8c, 8d, the anticorrosive or preparation layer 12, presently an enamel layer is applied to the inner surface 10 of the cavity walls 8a, 8b, 8c, 8d in a first step. In order to improve adhesion properties of the inner surface 10 of the cavity walls 8a, 8b, 8c, 8d, the latter is roughened before applying the anticorrosive or preparation layer 12 by laser treatment.

[0113] In a second step, the first layer 18 is applied to the surface 14 of the anticorrosive or preparation layer 12. In order to improve adhesion properties of the anticorrosive or preparation layer 12, the latter is prepared by an enameling process.

[0114] In a third step, the second layer 22 is applied to the surface 20 of the first layer 18. The first layer 16 as well as the second layer 22 are sprayed on the surface 14 of the anticorrosive or preparation layer 12 or the surface 20 of the first layer 16 and dried. The first layer 16 is preferably at least still wet during the second layer 22 is applied.

[0115] The present invention, thus a cavity having a non-stick and/or non-wetting coating and a cooking appliance having such a cavity shows an improved cleaning behaviour. The cavity or the coating respectively is abrasion-resistant and shows a greater surface hardness what leads to an increased lifetime. Furthermore the coating has shown a good adhesion on the cavity wall, in particular on the surface of the anticorrosive layer. As the coating is produced by a sol-gel process, a (second) burning step at high temperatures is not necessary.

[0116] The cavity 4 further comprises a heat reflection shield system 26 having at least one heat reflection shield 28 to reduce the heat radiation produced by heating elements 30 being arranged within the cavity 4 against the non-stick and/or non-wetting coating 16. Each of the FIGS. 3 to 7 shows a part of the cavity 4 with different embodiments of such a heat reflection shield system 26.

[0117] According to FIG. 3, the cavity 4 comprises a heat reflection shield system 26 with one heat reflection shield 28 that is applied to an outside rod of the heating element 30. The heat reflection shield 28 has a first part 32a for protecting a cavity top wall 8d and a second part 32b for protecting a cavity side wall 8a. The first and the second part 32a, 32b have different dimensions, the second part 32b that extends downwards the cavity side wall has larger extension than the first part 32a. The heat reflection shield 28 is made of a material being temperature-resistant, light and insulating.

[0118] FIG. 4 shows a cavity 4 having a heat reflection shield system 26 with exemplary two heat reflection shields 28 each being applied to a heating rod of the heating element 30. A heat reflection shield 28 can be applied to all rods of the heating element 30. The heat reflection shield 28 is made of a material being temperature-resistant, light and insulating.

[0119] FIG. 5 shows an alternative embodiment, wherein a whole plate 28 is applied on top of the heating element 30 as a whole heat reflection shield 28. The heat reflection shield 28 according to FIG. 4 and FIG. 5 have the same functional geometry. The heat reflection shield 28 is made of a material being temperature-resistant, light and insulating.

[0120] FIG. 6 shows an embodiment wherein the heat reflection shield 28 comprises two layers 36a, 36b made of different materials. The inner layer 36b is the stiff carrying geometry, the outer layer 36a is the light isolating material with low radiation.

[0121] FIG. 7 shows an embodiment wherein the heat reflection shield 28 has such a shape that two rods of the heating element 30 are isolated from each other by said heat reflection shield 28.

[0122] All of the above heat reflection shields 28 have an inner surface 34 that is shiny with an emissivity between 0.1 and 0.6.

[0123] Although illustrative embodiments of the present invention have been described herein with reference to the accompanying drawings, it is to be understood that the present invention is not limited to those precise embodiments, and that various other changes and modifications may be affected therein by one skilled in the art without departing from the scope or spirit of the invention. All such changes and modifications are intended to be included within the scope of the invention as defined by the appended claims.