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

Abstract

The present invention relates to a baking tray (20) or baking grid, in particular a baking tray (20) for a cooking appliance (1), having a non-stick and/or non-wetting coating (12) obtainable by a process characterised by the following steps, a) providing a baking tray (20) or baking grid having a surface, in particular having an upper surface (7a) and a bottom surface (7b), b) preferably, pretreating of the surface (7a, 7b) of the baking tray (20) or baking grid at least partially, in particular completely, for providing a surface having a roughness being suitable for applying a non-stick and/or non-wetting coating (12) by mechanical treatment, physical treatment or chemical treatment, in particular by sandblasting and/or laser treatment and/or a surface activation treatment, particularly a plasma treatment, and/or an enamelling process to form a ground layer (13), c) applying the non-stick and/or non-wetting coating (12) to the pretreated surface (7a, 7b) of the baking tray (20) or baking grid or a surface (14a) of the ground layer (13), wherein the non-stick and/or non-wetting coating (12) comprises at least one layer (17) that is obtained by a sol-gel process from a first composition comprising a silica sol and a silane. The invention further relates to a cooking appliance (1), in particular a domestic oven comprising such a baking tray (20) or baking grid and a method for manufacturing such a baking tray (20) or baking grid.

Claims

1. A baking tray or baking grid having a non-stick and/or non-wetting coating produced by a process comprising the following steps; a) providing a baking tray or baking grid having an upper surface and a bottom surface, b) optionally pretreating the surface upper surface and/or the lower surface of the baking tray or baking grid at to provide a surface roughness suitable for applying a non-stick and/or non-wetting coating by mechanical treatment, physical treatment or chemical treatment, to form a ground layer, c) applying the non-stick and/or non-wetting coating to the upper surface and/or the lower surface of the baking tray or baking grid or to a surface of the ground layer, wherein the non-stick and/or non-wetting coating comprises at least one layer that is obtained by a sol-gel process from a first composition comprising a silica sol and a silane.

2. The baking tray or baking grid according to claim 1, wherein the baking tray or baking grid is made of a corrosive material or an non-corrosive material.

3. The baking tray or baking grid according to claim 1, wherein the baking tray is provided with a protective layer applied to the upper surface and/or the lower surface of the baking tray, said protective layer is pretreated by sandblasting and/or laser treatment and/or an enamelling process for providing a surface having a roughness suitable for applying the non-stick and/or non-wetting coating and the at least one layer of the non-stick and/or non-wetting coating is applied to the surface of said protective layer.

4. The baking tray or baking grid according to claim 3, wherein the protective layer is an enamel layer and/or an aluminium layer and/or a layer comprising aluminium.

5. The baking tray or baking grid according to claim 3, wherein the protective layer has a thickness between 50 and 250 μm.

6. The baking tray or baking grid according to claim 1, wherein the ground layer is an enamel layer obtained by the enamelling process and has a layer thickness between 10 and 80 μm.

7. The baking tray or baking grid according to claim 1, wherein the upper surface and/or the lower surface of the baking tray and/or a surface of the ground layer and/or said surface the protective layer has a surface roughness between Ra 0.01 μm to 10.00 μm.

8. The baking tray or baking grid according to claim 1, wherein the non-stick and/or non-wetting coating comprises at least a first layer and a second layer, wherein the first layer of the non-stick, and/or non-wetting coating is applied to the first surface and/or the second surface of the baking tray, or to the surface of the ground layer, or to the surface of the protective layer, and wherein the second layer of the non-stick and/or non-wetting coating is applied to the first layer of the non-stick and/or non-wetting coating.

9. The baking tray or baking grid according to claim 8, wherein the second layer of the non-stick and/or non-wetting coating is obtained by a sol-gel process from a second composition comprising a silica sol, a silane and a siloxane.

10. The baking tray or baking grid according to claim 1, wherein 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 %, within the first composition.

11. The baking tray or baking grid according to claim 1, wherein the silane is an organoalkoxysilane and/or a fluoralkoxysilane.

12. The baking tray or baking grid according to claim 1, wherein the first composition comprises an organic solvent, and/or an acidic catalyst.

13. The baking tray or baking grid according to claim 12, wherein the solvent is present in said first composition in an amount of 10 to 60 wt %, and/or the catalyst is present in said first composition in an amount of 0.1 to 5 wt %.

14. The baking tray or baking grid according to claim 1, wherein the first composition comprises a siloxane.

15. The baking tray or baking grid according to claim 9, wherein the siloxane is present in said first composition in an amount of 0.1 to 2 wt %.

16. The baking tray or baking grid according to claim 1, wherein the first composition comprises pigments and/or dyes and/or filling materials and/or further additives.

17. The baking tray or baking grid according to claim 1, wherein at least a part of an outer surface of the coating provides an activated surface area activated by an activation process that increases surface tension within the activated surface area using plasma technology, and wherein a printing is applied to the activated surface area by means of ink technology.

18. A cooking appliance comprising: a heatable cavity, comprising at least one cavity wall defining a cooking chamber for cooking foodstuff and a central opening for placing foodstuff into the cooking chamber, heating elements for heating said cavity, a door for closing the central opening of the cavity, mounting grids and/or shelves disposed at a left cavity wall and a right cavity wall, and the baking tray or baking grid according to claim 1 mounted or mountable on said mounting grids and/or shelves.

19. A method for manufacturing a baking tray or baking grid of a cooking appliance, having a non-stick and/or non-wetting coating on a surface thereof, comprising the following steps: providing a baking tray or baking grid having an upper surface and a lower surface, pretreating the upper surface and/or the lower surface of the baking tray or baking grid by mechanical treatment, physical treatment or chemical treatment to form a first ground layer, applying at least one layer of the non-stick and/or non-wetting coating to the upper surface and/or the lower surface of the baking tray or baking grid or to a surface of the first ground layer.

20. A method for manufacturing a baking tray or baking grid according to claim 19, further comprising applying a protective layer comprising enamel and/or aluminium to the upper surface and/or the lower surface of the baking tray, and pretreating a surface of the protective layer by sandblasting and/or laser treatment and/or an enamelling process to form a second ground layer.

21. A method for manufacturing a baking tray or baking grid according to claim 20, further comprising applying an enamel powder onto the upper surface and/or lower surface of the baking tray and/or onto the surface of the protective layer, and heating the enamel powder to provide said first ground layer and/or said second ground layer with a roughness suitable for applying the non-stick and/or non-wetting coating.

22. A method for manufacturing a baking tray or baking grid according to claim 20, wherein the non-stick and/or non-wetting coating comprises a first layer and a second layer, wherein the first layer of the non-stick and/or non-wetting coating is applied to the upper surface of the baking tray or to the surface of the first ground layer or to the surface of the protective layer, and wherein the second layer of the non-stick and/or non-wetting coating is applied to the first layer of the non-stick and/or non-wetting coating.

23. A method for manufacturing a baking tray or baking grid according to claim 19, further comprising the following steps: performing an activation process using plasma technology on at least a part of an outer surface of the coating in order to provide an activated surface area, wherein the activation process increases surface tension within the activated surface area, applying a printing to the activated surface area by means of ink technology.

24. A coated baking tray or baking grid for a cooking appliance, comprising: a baking tray or baking grid made of low-carbon steel and having a fan-grid- or tray surface, said grid- or tray surface being roughened by sand-blasting or by laser treatment to achieve a first surface roughness of Ra 0.01 μm to 10.00 μm according to ISO 4287:1997; a protective layer applied over the roughened fan-cover surface, said protective layer comprising a non-corrosive material selected from enamel and aluminum and having a thickness between 50 μm and 250 μm, said protective layer having an outer surface facing away from said baking tray or baking grid; a ground layer comprising enamel applied to said outer surface of said protective layer, the ground layer having an outer surface facing away from said protective layer that has a second surface roughness up to about 3.5 μm according to ISO 4287:1997 provided by sand-blasting or by laser treatment of the outer surface of said ground layer; a first non-stick, non-wetting solgel coating layer deposited on the roughened outer surface of said ground layer, said first non-stick, non-wetting coating layer having been deposited as a first composition comprising 30 wt. % to 70 wt. % silica sol and 10 wt. % to 40 wt. % silane that underwent a first condensation reaction therebetween to yield the first solgel coating layer; and a second non-stick, non-wetting solgel coating layer deposited on an outer surface of said first non-stick, non-wetting coating layer, said second non-stick, non-wetting coating layer having been deposited as a second composition comprising 30 wt. % to 70 wt. % silica sol, 10 wt. % to 40 wt. % silane, and 0.1 wt. % to 2 wt. % siloxane that underwent a second condensation reaction therebetween to yield the second solgel coating layer; said second solgel coating layer having an outer surface configured to support foodstuff for cooking in-use, the outer surface of said second solgel coating layer having an activated surface area that has been activated using plasma technology, and a printing applied to the activated surface area by ink technology, said activated surface area having a water-contact angel of at least 95°.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0078] The present invention will be described in further detail with reference to the drawings, in which

[0079] FIG. 1 illustrates a schematic view of a cooking appliance including a baking tray according to an embodiment of the present invention,

[0080] FIG. 2 illustrates a baking tray according to one embodiment in a perspective view,

[0081] FIG. 3 illustrates a cross-sectional view of the baking tray according to a first embodiment of the invention in detail,

[0082] FIG. 4 illustrates a cross-sectional view of the baking tray according to a second embodiment of the invention in detail,

[0083] FIG. 5 illustrates a cross-sectional view of the coating according to an embodiment of the invention in detail.

DETAILED DESCRIPTION

[0084] FIG. 1 illustrates a schematic view of a cooking appliance 1. Such cooking appliance 1 comprises a heatable cavity 2 having cavity walls 3 which define a cooking chamber 4 into which foodstuff may be placed for cooking or baking. The cooking chamber 4 is defined by the cavity walls 3, usually comprising a left and a right side wall, a bottom wall and an upper wall as well as a rear wall and a front wall. One of the cavity walls 3, usually the front wall (not shown in FIG. 1) comprises a central opening for placing the foodstuff into the cooking chamber 4. The central opening may be closed or opened by a door (not shown in FIG. 1) that may be a part of the front wall. The cooking appliance 1 usually further comprises also heating elements 5 presently disposed at the upper cavity wall of the cavity 2 for heating the cooking chamber 4 and therefore heating food that has been placed therein to be cooked. The cooking appliance 1 further comprises a fan cover 6 being disposed at the rear cavity wall of the cavity 2 in front of a fan 9 of the cooking appliance 1. The fan cover 6 is essentially plate shaped and comprises openings 8 for allowing a fluid to flow through. The fan cover 6 might for example be attached to the rear cavity wall by screws.

[0085] The cooking appliance 1 further comprises a control panel 10 with several operating and display elements, e.g. temperature display or oven setting knobs. Furthermore, mounting grids and shelves 11 are disposed at a left and a right cavity wall 3.

[0086] A baking tray 20 can be mounted on said mounting grids and shelves 11 for inserting foodstuff into the oven cavity 2. The baking tray 20 can be made of a corrosive material, in particular corrosive steel, or an non-corrosive material, in particular stainless steel or aluminium. An exemplary embodiment of the invention in form of a baking tray 20 is shown in FIG. 2. The baking tray 20 comprises an upper surface 7a and a bottom surface 7b. Of course, the baking tray 20 may have other shapes of different design than shown in FIG. 2, or may be designed as a grid or may further include openings (“air-fry grids”) as well as designed like further well-known variants of baking trays.

[0087] FIG. 3 shows a cross-sectional view of the baking tray 20 according to a first embodiment in which the layer structure can be seen. The baking tray 20 is obtained by a process wherein the entire surface, thus the upper surface 7a and the bottom surface 7b of the baking tray 20 is pretreated by an enamelling process to form a ground layer 13 formed by a ground coat composition that has burned to the baking tray 20 at temperatures of about 820° C. on said surface 7a, 7b. In general, the temperature for enamelling a ground enamel may be between 680 and 820° C., depending of the specific formulation of the ground enamel. In other words: The entire baking tray 20 is surrounded by the ground layer 13. Said ground layer 13 or, respectively, enamel layer, has an outer surface 14a facing away from the baking tray 20 and an inner surface 14b facing towards the baking tray 20 and shows a surface roughness Ra of about 2 to 3.5 μm at its upper surface 14a. The thickness of the ground layer 13 is about 20 μm. Ground layer 13 also shows corrosion resistant properties so that the baking tray 20 is protected against corrosion, what is in particular useful and necessary if said baking tray 20 is made of a corrosive material, for example a low carbon steel to save costs. Inventors have surprisingly found that such a small thickness and small roughness shows good adhesion properties that are sufficient for applying a non-stick and/or non-wetting coating 12 comprising at least one layer 17 that is obtained by a sol-gel process from a first composition comprising a silica sol and a silane and according to embodiments of the invention further components like solvents or additives in useful amounts as described before.

[0088] FIG. 4 shows a cross-sectional view of the baking tray 20 according to a second embodiment in which the layer structure can be seen. The baking tray 20 is presently made from a corrosive material so that a protective layer 15 is applied to the entire surface, thus the upper surface 7a and the lower surface 7b of the baking tray 20 before the pretreatment step for preventing the baking tray 20 from corrosion, the protective layer 15 having an outer surface 16a facing away from the baking tray 20 and an inner surface 16b facing towards the baking tray 20. Afterwards, for obtaining a baking tray 20 with a non-stick and/or non-wetting coating 12, said protective layer 15 is pretreated by sandblasting or laser treatment to achieve a surface roughness of the surface 16a of the protective layer between about 2 and 3.5 μm by sandblasting or a surface roughness smaller than fpm by laser treatment. Inventors have surprisingly found out that even though the surface roughness achieved by laser treatment is smaller, good adhesion behaviour can be achieved, probably due to more fine-grained structure in comparison with a sandblasted surface. The protection layer 15 has a layer thickness of about 150 μm. In particular in case that the protection layer 15 is an aluminium layer or a layer comprising aluminium, it might be useful to carry out an enamelling process to form a ground coat 13 on the surface 16a of the protective layer 15 (shown in dashed lines) to benefit from the good adhesive properties of an enamel layer made from a ground composition having a surface roughness between 2 to 3.5 μm.

[0089] FIG. 5 shows a cross-sectional view of the baking tray 20 according to a third embodiment, that differs from the first embodiment according to FIG. 3 in that the non-stick and/or non-wetting coating 12 comprises a first and a second layer 17, 18, wherein the first layer 17 is applied to the surface 14a of the ground layer 13 and wherein the second layer 18 is applied to the first layer 17. The second layer 18 is obtained by a sol-gel process from a second composition comprising a silica sol, a silane and a siloxane. Both layers 17, 18 have an outer surface 17a, 18a facing away from the baking tray 20 and an inner surface 17b, 18b facing towards the baking tray 20.

[0090] As a matter of course, even a baking tray 20 according to the second embodiment shown in FIG. 4 might have a non-stick and/or non-wetting coating 12 comprising a first and a second layer 17, 18, wherein the first layer 17 is applied to the surface 16a of the protective layer 15 and wherein the second layer 18 is applied to the first layer 17.

[0091] Both, the first layer 17 and, if present, the second layer 18 are obtained by a sol-gel process. For production of the first layer 17, 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.

[0092] 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.

[0093] For production of the second layer 18, 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 %.

[0094] 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.

[0095] For manufacturing a baking tray 20 having a non-stick and/or non-wetting coating 12 on its surface 7a, 7b a baking tray 20 having an upper surface 7a, an bottom surface 7b is provided. In a further step, the surface 7a, 7b of the baking tray 20 is pretreated in order to provide good adhesion properties and surface roughness for subsequent apply of the non-stick and/or non-wetting coating 12 (FIG. 3). Additionally or in an alternative, a protective layer 15 is applied to the surface 7a, 7b of the baking tray 20 and said protective layer 15 is pretreated (FIG. 4). Pretreatment of the surface 7a, 7b of the baking tray 20 or, if present, the surface 16a, 16b of the protective layer 15 is carried out in particular by sandblasting, laser treatment or an enamelling process for forming a ground layer 13.

[0096] The enamelling process is in particular carried out by applying an enamel powder onto the upper surface 7a of the baking tray 20 and/or onto the surface 16a, 16b of the protective layer 15, and heating the enamel powder for providing a ground layer 13 with a surface 14a having a roughness being suitable for applying the non-stick and/or non-wetting coating 12.

[0097] Afterwards, at least one layer of the non-stick and/or non-wetting coating 12 is applied to the upper surface 7a of the baking tray 20 or, if present, to the upper surface 16a of the protective layer 15 or the surface 14a of the ground layer 13.

[0098] In case of applying a non-stick and/or non-wetting coating 12 comprising at least two layers 17, 18 (FIG. 5), the first layer 17 is applied to the surface 7a, 7b of the baking tray 20 or the surface 14a of the ground layer 13 or the surface 16a of the protective layer 15, and the second layer 18 is applied to the first layer 17.

[0099] The present invention, thus a baking tray 20 having a non-stick and/or non-wetting coating 12 and a baking tray 20 having such a coating 12 shows an improved cleaning behaviour. The coating 12 is abrasion-resistant and shows a greater surface hardness what leads to an increased lifetime. Furthermore, the coating 12 has shown a good adhesion properties on the baking tray 20, in particular on the surface 14a of the ground layer 13 or the surface 16a of the protective layer 15. As the coating 12 is produced by a sol-gel process, a (second) burning step at high temperatures is not necessary.

[0100] The baking tray 20 may further comprise a printing (not shown) that is applied, in particular by ink technology, to the surface of the coating 12, in particular to a surface area that has been activated by using plasma technology in order to increase the surface tension.

[0101] 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.

LIST OF REFERENCE NUMERALS

[0102] 1 cooking appliance [0103] 2 cavity [0104] 3 cavity wall [0105] 4 cooking chamber [0106] 5 heating element [0107] 6 fan cover [0108] 7a upper surface of the baking tray [0109] 7b bottom surface of the baking tray [0110] 8 openings [0111] 9 fan [0112] 10 control panel [0113] 11 mounting grids and shelves [0114] 12 non-stick and/or non-wetting coating [0115] 13 ground layer [0116] 14a surface of the ground layer [0117] 14b bottom surface of the ground layer [0118] 15 protective layer [0119] 16a inner surface of the protective layer [0120] 16b outer surface of the protective layer [0121] 17 first layer of the non-stick and/or non-wetting coating [0122] 17a inner surface of the first layer [0123] 17b outer surface of the first layer [0124] 18 second layer of the non-stick and/or non-wetting coating [0125] 18a outer surface of the second layer [0126] 18b inner surface of the second layer [0127] 20 baking tray