Cooking appliance door with an inner borosilicate glass window pane and cooking appliance with said door

Abstract

The cooking appliance door has a borosilicate glass inner window pane, on which a paint layer and an infrared-reflecting layer are applied. The paint layer is high-temperature-resistant non-enamel paint with an organic or inorganic binder. In order to provide especially good adherence and high scratch resistance for the paint layer, the paint layer is applied directly on one side of the inner window pane and the infrared-reflecting layer is applied on and over this paint layer. A cooking appliance with this cooking appliance door is also part of this invention.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a cooking appliance door with an inner window pane comprising a borosilicate glass, on which a paint layer made from a high-temperature-resistant non-enamel paint with an organic or inorganic binder and an infrared-reflecting layer are applied. The invention also relates to a cooking appliance with this sort of door.

2. Description of the Related Art

A household cooking appliance, especially an oven, has a cooking chamber or compartment with an opening, which is closable by a cooking appliance door with an observation or viewing window. Cooking appliances with a door that is completely glass are known. A baking oven with an oven muffle acting as cooking compartment is a typical currently known household appliance. This sort of baking oven has been equipped to a large extent with a pyrolytic self-cleaning means, by which cooking residues are decomposed to ash at pyrolysis temperatures above 500° C.

The typical household cooking appliance door and thus its viewing window is of course heated during operation due to the comparatively high temperatures in the cooking appliance. An entirely glass appliance door, which typically comprises a glass pane packet, is also heated during operation. The same is true to a special extent during the pyrolysis occurring at extremely high temperatures in pyrolyzing baking ovens. High-quality glass is used for door panels of cooking appliances because of this high heat load. This is particularly true for the viewing windows or full glass doors for cooking appliances and baking ovens with pyrolytic self-cleaning means. A pre-stressed borosilicate glass is thus used for the inner window pane that is closest to the oven muffle. This sort of glass is characterized by a special resistance to high temperatures.

In order to keep the temperature on the outer side of the viewing window or full glass door of the cooking appliance as small as possible to reduce the danger of burns and other injuries due to contact with the outer surface of the viewing window, the viewing window is provided with a coating that reflects heat into the interior of the cooking compartment, i.e. an infrared-reflecting coating. An observation window described in U.S. Pat. No. 4,898,147 has an inner window pane made from borosilicate glass with an infrared-reflecting multilayer coating and noble gas layer between the inner and outer window panes, in order to reduce the heat transferred. A so-called “cold door” for a pyrolysis-baking oven is thus provided by means of these features. This “cold door” is defined by GIFAM DOC 266/01 by stating an upper limiting temperature, which the contacting surface of the door can have, when the outside temperature is 23° C. and the temperature in the cooking compartment is about 500° C. (with glass, less than 70° C.).

Furthermore it is known to provide the borosilicate glass inner window pane with printing made from enamel paint, comprising special writing (letters, words) and symbols, especially usage hints for the operators, particularly which indicate different cooking programs. This printed information can be located on the side of the inner window pane facing the door interior and also on the side facing the cooking compartment, as described in DE 100 07 923 C1. DE 101 43 925 A1 discloses a suitable borosilicate inner window pane for a cooking appliance door printed with enamel paint.

Conventional enamel paints melt or fuse with the glass surface during burning on the borosilicate inner window pane. Stresses are developed in the glass window pane due to the differing thermal expansion properties of the glass window pane and the printing with the enamel paint. These stresses occur in connection with interactions (ion exchange) between the enamel paint, a glass flux-based print ink and the borosilicate glass. Because of that the impact resistance of the glass window pane is degraded for impacts on the side facing away from the printed information. For that reason the above-mentioned DE 100 07 923 C1 suggests that the color printing printed with the enamel paint should be applied to the outside of the inner window pane facing or turned toward the interior of the cooking compartment. Since the current enamel paints are not heavy-metal-free, especially not lead-free, there is a danger the heavy metals, especially lead, could be volatilized in the cooking compartment at higher operating temperatures because of the color printing on the exposed side in direct contact with the cooking compartment. Furthermore the enamel paint coating has a rough, unpleasing surface.

There is no enamel print or enamel for printing currently known for borosilicate glass, which (1) is heavy-metal-free, (2) has a smooth aesthetically pleasing surface and (3) maintains the impact resistance of the borosilicate glass pane, when the impacts occur on the side facing away or opposite from the printing. As a result, non-enamel paint with organic (e.g. silicones or fluoropolymers) or inorganic (e.g. water glass; sol-gel binders) binders was develop, which in contrast to the conventional enamel paint is not bonded with the glass surface by melting. These non-ceramic paints are described in the old Patent application DE 103 13 630, whose subject matter is incorporated herein by explicit reference thereto.

This paint is only a SiO₂-based paint with carbon particles, which are coated or enveloped by SiO₂, as pigment, as is described in DE 195 25 658 C1.

Up to now the color printing on inner window panes of borosilicate viewing windows with infrared-reflecting coatings provided by the above-described non-enamel paints has been applied directly to the infrared-reflecting coating. This leads to certain process uncertainties and unreliabilities, since the adherence of the paint developed for direct application to borosilicate glass is not guaranteed on an infrared-reflecting coating. The infrared-reflecting coating usually comprises a tin oxide material, which differs significantly from a borosilicate glass. Furthermore the above-described paint coating is not very resistant to scratching.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a cooking appliance door of the above-described type with an inner window pane comprising borosilicate glass, which has an infrared-reflecting coating and printing, such that the printing reliably adheres to the window pane and resists scratching.

This object and others, which will be made more apparent hereinafter, are attained in a cooking appliance door with an inner window pane comprising a borosilicate glass, on which a paint layer, which comprises a high-temperature-resistant non-enamel paint with an organic or inorganic binder, and an infrared-reflecting layer are applied.

According to the invention surprisingly the paint layer is applied directly on one side of the inner window pane and the infrared-reflecting layer is applied on and/or over this paint layer.

The present invention also includes a cooking appliance with the above-described cooking appliance door according to the invention.

Because of the critical feature of the invention, i.e. the application of infrared-reflecting layer after applying the color printing or paint layer to the inner window pane, one very advantageously obtains a resistant color printing on the inner window pane of borosilicate glass. Besides greater adherence of the paint layer on the glass substrate the color printing is also scratch-resistant, since the infrared-reflecting layer is very hard and thus mechanically protects the printed information provided by the non-enamel paint. Furthermore use of the non-enamel paint in this manner also maintains the impact strength for impacts occurring on the side of the inner window pane opposite from the side bearing the printing. The printing also can be provided on the side of the inner window pane facing away from or opposite from the cooking compartment. In that case there are no interactions between the coating and the cooking compartment.

Of course the color printing can also be provided on the side of the inner window pane closest to or facing the cooking compartment, especially with the infrared-reflecting coating covering the color printing. Thus the occurrence of printing with paint portions in the cooking compartment is at least reduced.

DE 101 62 220 A1 discloses a two-layer coating on a glass pane for a cooking appliance door. This two-layer coating comprises a first dark, especially black colored, heat-radiating layer and above it a second white colored heat reflecting layer. The second layer should reflect a substantial part of the radiated heat back into the oven. In contrast heat, which reaches the glass pane, should be radiated away by the first dark layer.

DE 101 62 220 A1 does not provide any hint or suggestion of a paint coating made from non-enamel paint or a solution of the associated adherence problems due to the foregoing problems.

BRIEF DESCRIPTION OF THE DRAWING

The objects, features and advantages of the invention will now be illustrated in more detail with the aid of the following description of the preferred embodiment, with reference to the following figures, in which

FIG. 1 is a diagrammatic cutaway cross-sectional view through an inner window pane of an observation window of a cooking appliance door or a completely glass door, especially a cooking oven door; and

FIG. 2 is a schematic cross-sectional view through one embodiment of a cooking appliance including a cooking appliance door according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

This inner window pane 1 is exposed to the highest temperatures because it is immediately adjacent to the hot oven muffle or cooking compartment 30 (FIG. 2) during operation of the cooking appliance 10. This is especially true during pyrolytic self-cleaning, in which temperatures of over 500° C. are present in the cooking compartment 30. Because of this reason the inner window pane 1 of the cooking appliance door 20 is made from borosilicate glass, preferably from a pre-stressed borosilicate glass, which has a high resistance to these high temperatures and a small thermal expansion coefficient. The color printing or paint layer 2 is printed on one side of the inner window pane, which is an interior side as shown in this embodiment. The color printing or paint layer 2 can form a colored surface or also letters or symbols, which provide a hint or suggestion for the operator, especially of different cooking programs that the cooking appliance can perform. The color printing or paint layer 2 is made from the above-described non-enamel paint, which is applied directly to the inner surface of the borosilicate glass of the inner window pane by a printing process, especially a screen printing process and burned in after that. The layer thickness is preferably in a range of 10 to 15 μm. The printing preferably occurs in a dot matrix or pattern.

Subsequently an infrared-reflecting coating 3 is applied to the color printing or paint layer 2, for example by a hot spraying process. This coating 3 typically contains tin oxide as “effective ingredient” and is usually formed in a know way, e.g. in regard to coating thickness, etc. These IR-reflecting coatings are especially known for heat-resistant glazing (e.g. K-GLAS® or OPTIFLOAT® mirror glass), and for example are described in DE 198 25 437 A1. Since the infrared-reflecting layer 3 is very hard, the scratch-resistance of the color printing 2 is high, and the adherence of the color printing directly on the glass surface is very high.

The preferred embodiment shown in the sole Figure has only a single IR-reflecting coating and a single color printing or paint layer. It is understandable however that another embodiment could have more than one of each of these layers.

FIG. 2 shows a cooking appliance 10 including a simplified representation of a cooking appliance door 20 according to the invention. The cooking appliance door 20 includes an inner window pane 1 made of borosilicate glass. As explained above, the inner window pane 1 is first provided with color printing or a paint layer 2 on its surface closest to or facing the cooking compartment 30. Then an infrared-reflecting coating 3 is provided on the inner surface of the inner window pane 1 by a hot spraying method, so that the coating 3 completely covers the color printing or paint layer 2.

The disclosure in German Patent Application 103 44 442.4-16 of Sep. 25, 2003 is incorporated here by reference. This German Patent Application describes the invention described hereinabove and claimed in the claims appended hereinbelow and provides the basis for a claim of priority for the instant invention under 35 U.S.C. 119.

While the invention has been illustrated and described as embodied in a cooking appliance door with an inner window pane made of borosilicate glass and a cooking appliance containing that door, it is not intended to be limited to the details shown, since various modifications and changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior this invention.

Claims

1. A cooking appliance door comprising an inner window pane (1), said inner window pane comprising borosilicate glass;

at least one paint layer (2) applied directly to a surface on one side of said inner window pane, wherein said at least one paint layer (2) comprises a high-temperature-resistant non-enamel paint with an organic or inorganic binder; and

at least one infrared-reflecting layer (3) applied on said at least one paint layer (2) on said one side of the inner window pane.

2. The cooking appliance as defined in claim 1, wherein said at least one paint layer (2) has a thickness of from 10 to 15 μm.

3. The cooking appliance as defined in claim 1 or 2, wherein said at least one paint layer (2) is printed on the inner window pane (1).

4. The cooking appliance as defined in claim 1, wherein said at least one infrared-reflecting layer (3) contains tin oxide.

5. The cooking appliance as defined in claim 1 or 4, wherein said at least one infrared-reflecting layer (3) is applied to the at least one paint layer (2) by a hot spraying process.

6. A cooking appliance (10) comprising a cooking compartment (30) with an opening for placing cooking materials in the cooking compartment (30) and a cooking appliance door (20) for closing said opening;

wherein said cooking appliance door (20) comprises an inner window pane (1) made of a borosilicate glass, at least one paint layer (2) applied directly to a surface on one side of said inner window pane, said at least one paint layer (2) comprising a high-temperature-resistant non-enamel paint with an organic or inorganic binder and at least one infrared-reflecting layer (3) applied on said at least one paint layer (2) on said one side of the inner window pane.

7. The cooking appliance as defined in claim 6, wherein said at least one paint layer (2) has a thickness of from 10 to 15 μm.

8. The cooking appliance as defined in claim 6, wherein said at least one infrared-reflecting layer (3) contains tin oxide.