DOOR FOR A HOUSEHOLD MICROWAVE OVEN

Description

[0001] The invention relates to a door for a household microwave oven, comprising at least one perforated, electrically conductive grid, in particular a metal grid, covering a viewing opening of the door and having a plurality of micro-holes arranged in a regular pattern. The invention also relates to a household microwave oven with such a door. The invention is particularly advantageously applicable to standalone household microwave ovens and ovens with a microwave function.

[0002] For example, US 3679855 A, DE 32 31 516 A1 and EP 0 042 616 B1 disclose a door for a microwave oven having a separate perforated metal grille covering a viewing opening of the door and having a plurality of round holes arranged in a regular pattern.

[0003] WO 2016 / 179317 A1, US 4010343 A or EP 2 020 827 B1 disclose a shield for a viewing opening of a door of a microwave oven in the form of a metallic net.

[0004] DE 39 23 734 C1, DE 103 072 17 A1 disclose glass windows for doors of microwave ovens which are coated with a thin film shielding, e.g. made of aluminum, copper, tin, tin oxide, carbon nanotubes, etc.

[0005] DE 102 014 23 A1 discloses an electrically conductive coating in the visible area as a shield, wherein the coating is strip-shaped or diamond-shaped.

[0006] Shielding grilles for aircraft windows made of metal-coated polyester fibers are known from US 2014 / 0319276 A1.

[0007] EP 0 503 899 B1 discloses a microwave shield for a viewing opening of a microwave oven door in the form of a layered grid. The thickness of the grid is approximately 0.2 micrometers.

[0008] JP S54 179960 U discloses a cooking chamber wall of a microwave oven with an additional oven function. Holes with outward-facing ridges are provided in the cooking chamber wall, which have a rectangular, in particular square, basic shape with rounded corners.

[0009] The metal grids commonly used in household microwave ovens have round holes arranged in a triangular pattern, with a diameter of approximately 1.5 mm and a pitch of approximately 2.5 mm.

[0010] It is the TaskThe present invention aims to at least partially overcome the disadvantages of the prior art and, in particular, to provide a microwave-tight shield for a viewing opening of a door of a microwave oven, which shield combines a particularly advantageous combination of the properties: prevention of microwave radiation from escaping from the viewing opening, minimization of microwave losses in the shield, and good optical visibility through the shield.

[0011] This object is achieved according to the features of the independent claims. Advantageous embodiments are the subject of the dependent claims, the description, and the drawings.

[0012] The object is achieved by a door for a household microwave oven, comprising at least one perforated electrically conductive grid which covers a viewing opening of the door and has a plurality of micro-holes arranged in a regular pattern, wherein the micro-holes have a rectangular basic shape with rounded corners.

[0013] This door offers the advantage of keeping microwave losses in the shielding particularly low, maintaining good optical transparency for a frontal viewer and very good attenuation against microwave penetration. The rounded corners reduce the electrical current density induced by microwaves there compared to a pointed or sharp corner, thereby reducing microwave losses. This also has the advantage of increasing the reliability of an electrical connection across different areas of the grid. This, in turn, prevents an aging-related reduction in the shielding effect.

[0014] The rounded corners can also be referred to as defined radii, since the curves are introduced or manufactured with at least one specified radius.

[0015] The perforation of the grating is achieved by microholes. Microholes can generally be understood as holes with a width (e.g., represented by a diameter or an edge length) in the submillimeter range.

[0016] The grid can basically be an independent, e.g. prefabricated grid.

[0017] In a further development, the grid is a metal grid. The metal grid can be made entirely of metal such as steel, aluminum, and / or copper, etc., or it can be metal-coated. The metal can be or contain steel, aluminum, and / or copper (e.g., in the form of a mixture or alloy). The use of a metal grid offers the advantage that the micro-holes can be produced with low manufacturing effort and with particular precision. Alternatively, the grid can be made of carbon nanotubes or another electrically conductive material, e.g., carbon nanotubes, electrically conductive ceramic, etc.

[0018] The viewing opening of the door can be covered by just one grille or by several grilles arranged one behind the other. The viewing opening of the door can in particular be covered by two grilles, which are arranged, for example, on a front and a back of a viewing window. If there are several grilles, their micro-holes are advantageously arranged one behind the other to maintain good visibility. It is also advantageous if the micro-holes of several grilles have the same shape and / or size. It is particularly advantageous if the several grilles have identically shaped and arranged micro-holes or patterns.

[0019] A rectangular basic shape can be understood as a shape that is rectangular except for the rounded corners. A further development is that the rectangular basic shape is a square basic shape, which allows for a particularly even distribution of the current density in the grid.

[0020] In one embodiment, the at least one perforated grid is a layer applied to a transparent door pane. This enables the provision of a particularly thin grid, in particular a metal grid. A layered metal grid is advantageously made of aluminum and / or copper or alloys thereof in order to achieve a particularly low ohmic resistance, which in turn is advantageous for good shielding performance and low losses.

[0021] It is a further development that the grid is in the form of a printed electrically conductive paint.

[0022] A further development is that the grille is a micro-contact printed grille or has been applied using micro-contact printing. Micro-contact printing offers the advantage that micrometer-sized patterns can be easily applied to the door glass. This can advantageously be done without the use of a clean room. Using a single "master" stamp, multiple identical stamps can be produced. The stamps can be used many times to produce prints with very little wear. Furthermore, very little energy is consumed to produce the prints.

[0023] A further development is that the grating is a vapor-deposited grating. CVD or PVD processes can be used for application.

[0024] A further development is that the grating is a sputtered grating. This can be done using, for example, magnetron sputtering. Magnetron sputtering can use a guided beam or a mask to apply the grating.

[0025] In microcontact printing, an electrically conductive pattern can first be applied to a door pane, and then, if necessary, its layer thickness can be increased, e.g., through electroless electroplating. The materials used for microcontact printing and electroplating can differ. In particular, the grid can consist almost entirely of the electroplated material.

[0026] The door pane can be a glass pane or a plastic pane.

[0027] One design allows the specified radius of the rounded corners to be between 7 micrometers and 15 micrometers. This has proven to be a particularly advantageous range for reducing local current density peaks in the corners while maintaining a large area of ​​the micro-holes for good transparency.

[0028] In one embodiment, the cumulative layer thickness of the at least one perforated grid is between 2 micrometers and 5 micrometers. This embodiment is based on the finding that layer thicknesses of more than five micrometers significantly reduce the precision of the micro-holes. This, in turn, impairs a targeted, uniform reduction of current density peaks and can lead to local fluctuations in optical transparency. On the other hand, it has been shown that with cumulative layer thicknesses of less than two micrometers, the ohmic resistance drops to such an extent that losses in the grid and / or leakage of microwaves through the grid increase significantly.

[0029] A "cumulative" layer thickness refers to the layer thickness of exactly one microwave-shielding grid. If several microwave-shielding grids are arranged one behind the other in the front view of the door, the "cumulative" layer thickness refers to the added or combined layer thickness of all grids.

[0030] In one embodiment, the at least one perforated grating is precisely a grating whose layer thickness is between 2.5 micrometers and 5 micrometers. This results in the advantages described above for precisely one grating. For a single layer grating made of copper, for example, a layer thickness between 2.5 micrometers and 5 micrometers may be particularly advantageous. For a single layer grating made of aluminum, for example, a layer thickness of approximately three micrometers may be particularly advantageous.

[0031] In one embodiment, the at least one perforated grille has a plurality of grilles arranged one behind the other when viewed from the front of the door, the cumulative layer thickness of which lies between 2 micrometers and 5 micrometers. This results in the advantages described above for a plurality of grilles. In particular, if two grilles are present, they can each have a layer thickness of one micrometer. Nevertheless, the upper limit of five micrometers remains, e.g., due to manufacturing tolerances in the positioning of the grilles on a viewing window, which can lead to a lateral offset of the grilles relative to one another, which in turn impairs optical transparency.

[0032] One embodiment includes the microholes being arranged in a rectangular matrix. This offers the advantage that particularly low current density peaks can be achieved. A rectangular matrix can be understood, in particular, as an arrangement in which the microholes are arranged uniformly along imaginary rows and columns extending rectangularly thereto. The microholes in adjacent rows or columns exhibit no longitudinal offset from one another—in contrast to a triangular pattern, for example.

[0033] The rectangular matrix shape can, in particular, be a square matrix shape, in which the spacing between the rows and columns, or between the microholes along the columns and rows, is equal. This advantageously results in a particularly uniform distribution of the current density in the grid.

[0034] The particularly uniform distribution of the current density in the grid is also supported by the fact that the edges of the micro-holes run parallel to the rows and columns, i.e. they are not arranged in the pattern like rhombuses.

[0035] In one embodiment, the width of the strip regions of the grid delimiting the microholes is at least three times, in particular at least four times, the thickness of the grid. This provides the advantage that a particularly uniform width of the strip regions of the grid can be achieved, which further reduces an inhomogeneous current density distribution in the strip regions and thus the risk of damage to the grid. A "strip region" of the grid can be understood, in particular, as a material strip of the grid with parallel, straight longitudinal sides, the longitudinal sides of which border the microholes. The width of the material strip corresponds, in particular, to the closest distance between directly adjacent microholes in adjacent rows or columns of the matrix pattern.In a rectangular matrix pattern, the width of the column material strips ("vertical" material strips) and the width of the row material strips ("horizontal" material strips) can differ. In a square matrix pattern, their widths are the same.

[0036] This design is particularly advantageous in conjunction with a cumulative layer thickness between 2 micrometers and 5 micrometers, since with larger layer thicknesses and correspondingly larger microholes, the leakage of microwaves through the grating increases again. The reason for this may be that a higher conductivity of the grating cannot compensate for the increased permeability of the grating to microwaves due to larger microholes.

[0037] A further development is that the width of the striped areas of the grid is no more than five times, and in particular no more than four times, the thickness of the grid. This offers the advantage of particularly high transparency.

[0038] One configuration is where the pitch of adjacent microholes lies between 50 micrometers and 100 micrometers. This configuration offers the advantage of achieving a particularly favorable compromise between good transparency, low losses, and high shielding efficiency. A "pitch" of adjacent microholes can be understood, in particular, as the center-to-center distance between directly adjacent (i.e., not diagonally arranged) microholes. In a rectangular matrix pattern, the pitch along the columns and the pitch along the rows can differ. In a square matrix pattern, their pitches are the same.

[0039] In one embodiment, the microholes have an edge length between 30 micrometers and 100 micrometers, in particular between 40 micrometers and 75 micrometers. Such an edge length enables good transparency, particularly across the entire optical spectrum. Shorter edge lengths can, for example, lead to noticeable refraction of light at the edges of the microholes. Longer edge lengths can lead to a loss of image homogeneity. An edge length can be understood, in particular, as the full height or width of the microholes.

[0040] One embodiment is that the household microwave appliance is a dedicated microwave appliance ("stand-alone appliance"). Another embodiment is that the household microwave appliance is a microwave combination appliance. The microwave combination appliance can, in particular, be an oven with a microwave function. The door is then a microwave-tight oven door.

[0041] This problem is also solved by a household microwave oven that features such a door. The household microwave oven can be designed analogously to the door and offers the same advantages.

[0042] The task is further solved by a viewing window as described above.

[0043] The above-described properties, features and advantages of this invention, as well as the manner in which they are achieved, will become clearer and more clearly understood in connection with the following schematic description of an embodiment, which is explained in more detail in connection with the drawings. Fig.1 shows a front view of a section of a door according to the invention; and Fig.2 shows a front view of an enlarged section of the grille of the door from Fig.1 .

[0044] Fig.1 shows a front view of a section of a door 1 of a microwave oven G according to the invention, with a viewing window 2 in the form of, for example, a transparent plastic or glass pane 3, which is coated on one surface with a perforated metal grid 4 in layer form. The metal grid 4 can be made of, for example, aluminum or copper.

[0045] The metal grid 4 has microholes 5 arranged in a regular square matrix pattern for its perforation. The microholes 5 have a square basic shape with rounded corners.

[0046] The corners have a given radius R, as in Fig.2 shown. The radius R here is between 7 micrometers and 15 micrometers, while an edge length K of the microholes 5 can be, in particular, between 40 micrometers and 75 micrometers. A pitch L of adjacent microholes is, in particular, between 50 micrometers and 100 micrometers.

[0047] In addition, a width W1, W2 of the vertical strip regions 6 and horizontal strip regions 7 of the metal grid 4 delimiting the microholes 5 is each at least three times, in particular four times, as large as a layer thickness of the metal grid 4 (extending perpendicular to the plane of the sheet), which lies between 2.5 micrometers and 5 micrometers. The widths are the same here, but can also be different in principle.

[0048] In particular, the following variants of the metal grid 4 can be used: variant 1 2 3 4 5 Pitch L [µm] 100 100 65 65 50 Width W [µm] 25 35 20 15 10 Radius R [µm] 15 15 10 10 7 metal Al Al Cu Cu Cu Layer thickness [µm] 3 3 5 5 2,5 Transparency [%] 54,6 40,3 45,9 57,1 62,5 Microwave transmittance [dB] at 2.45 GHz -59,6 -63,9 -68,3 -64,5 -63,8

[0049] All variants exhibit a transparency (determined as the ratio of the transmitted luminous flux compared to a door without grille 4) of more than 40%, which is significantly better than the 28% achieved with the most commonly used metal grilles. The best shielding of microwave radiation is achieved with variant 3.

[0050] Of course, the present invention is not limited to the embodiment shown.

[0051] In general, "a", "an", etc. can be understood as a singular or a plural, in particular in the sense of "at least one" or "one or more", etc., as long as this is not explicitly excluded, e.g. by the expression "exactly one", etc.

[0052] A numerical value may also include the exact number stated as well as a usual tolerance range, as long as this is not explicitly excluded. List of reference symbols

[0053] 1Door 2Viewing window 3Window 4Metal grille 5Micro hole 6Vertical stripe area 7Horizontal stripe area GMicrowave oven KKedge length LPitch RRadius W1Width of vertical stripe areas W2Width of horizontal stripe areas

Claims

1. Door (1) for a household microwave appliance (G), having at least one perforated electrically conductive lattice (4), in particular metal lattice, which covers a viewing opening of the door (1) and has a plurality of microholes (5) arranged in a regular pattern, characterised in that the microholes (5) have a rectangular, in particular square, basic shape with rounded corners.

2. Door (1) according to claim 1, characterised in that the at least one perforated lattice (4) is a layer applied to a transparent door pane (3).

3. Door (1) according to one of the preceding claims, characterised in that a predefined radius (R) of the rounded corners lies between 7 micrometres and 15 micrometres.

4. Door (1) according to one of the preceding claims, characterised in that a cumulative layer thickness of the at least one perforated lattice (4) lies between 2 micrometres and 5 micrometres.

5. Door (1) according to claim 4, characterised in that the at least one perforated lattice (4) is exactly one lattice, the layer thickness of which lies between 2.5 micrometres and 5 micrometres.

6. Door (1) according to claim 4, characterised in that the at least one lattice has a plurality of lattices arranged one behind the other on the door (1) in a front view, the cumulative layer thickness of which lies between 2 micrometres and 5 micrometres.

7. Door (1) according to one of the preceding claims, characterised in that the microholes (5) are arranged in a rectangular matrix shape.

8. Door (1) according to one of the preceding claims, characterised in that a width (W1, W2) of strip regions (6, 7) of the lattice (4) which delimit the microholes (5) is at least three times, in particular at least four times as great as a thickness of the lattice (4).

9. Door (1) according to one of the preceding claims, characterised in that a pitch (L) of adjacent microholes (5) lies between 50 micrometres and 100 micrometres.

10. Door (1) according to one of the preceding claims, characterised in that the microholes (5) have an edge length (K) between 30 micrometres and 100 micrometres, in particular between 40 micrometres and 75 micrometres.

11. Door (1) according to one of the preceding claims, characterised in that the household microwave appliance (G) is a dedicated microwave appliance or a microwave combination appliance, in particular oven with microwave functionality.