DE20005461U1 - Cooktop - Google Patents

Description

gl363

March 22, 2000

wi/per

F:\1JBFUL\SGWWPT\ALLO773

Schott Glass

Hattenbergstrasse 55122 Mainz

Hob

Hob

Description:

The invention relates to a hob with a transparent, uncolored glass ceramic plate or alternatively with a glass plate made of prestressed special gas as a cooking surface, which has cooking zones heated with radiant heating elements, to which decorations are attached and whose underside bears an IR-permeable layer made of a temperature-resistant paint.

Hobs with a glass ceramic plate as the cooking surface are commonplace. Typically, as shown in EP 0 220 333, they have a glass ceramic plate that is colored with ions to reduce transmission, so that the functional components of the hob located underneath the glass ceramic plate are practically invisible from above. These cooking surfaces are therefore practically not transparent and appear black when viewed from above.

Cooking surfaces made from the aforementioned glass ceramic plates are generally provided with decorations, either for purely aesthetic reasons or to demarcate functional areas, such as the cooking zones, from other areas of the cooking surface. These decorations and their application to the glass ceramic plate are described, for example, in DE 44 26 234 C 1 (= EP 0 693 464 B 1 and DE 34 33 880 C 2.

Due to the non-transparency of the colored glass ceramic plate, the decorations on the cooking surface, including the so-called fully decorated cooking surfaces known for example from DE 197 28 881 C 1 (= DE 297 11 916.8 U 1), in which the decoration almost completely covers the top of the cooking surface, are printed on the top with enamel-based ceramic colors in accordance with the above-mentioned state of the art, either typically by screen printing, or applied there using the decal technique and then fired.

The disadvantage of these known hobs with decorated glass ceramic plates is that the ceramic decorative colors can only be applied in a relatively thin layer of just a few μιλ and in this layer thickness they do not have the desired brilliance. Furthermore, due to difficulties in printing technology, especially with fully decorated hobs, the decorative design and thus the appearance of the hobs is not free of restrictions. In addition, only certain decorative colors can be used that meet practical requirements (moving pots, cleaning spilled and burnt food, etc.), since the decorations applied to the top are exposed to high levels of mechanical and chemical attack, as described for example in DE 36 00 105 C2.

Furthermore, the decorations applied to the top of the glass ceramic plate prevent the cooking surface from being as smooth as possible.

Furthermore, so-called glass hoptops are known, which have plates made of tempered soda-lime glass, which are decorated with organic colours on the underside and have holes for the installation of atmospheric gas burners. The organic colours have a relatively low temperature resistance, which is sufficient for the glass hoptops, as they are used in cold areas. For cooking surfaces with glass ceramic plates and

However, in radiantly heated cooking zones the temperatures are much higher, so that the known technology cannot be applied in this respect.

In addition, induction-heated cooking surfaces with transparent glass-ceramic plates are known which, due to the low temperatures occurring there, only have an organic, decorated underside coating that ensures non-transparency, but are undecorated in the area of the cooking zones.

From JP 7-17409 and JP 51-89517 it is known to produce glass ceramic plates used as cooking surfaces from a transparent, uncolored glass ceramic and to print the underside with a temperature-resistant color. However, this color layer only serves to create non-transparency; it simply replaces the otherwise usual coloring so that it also appears black when viewed from above. In the known case, the decorations are also applied to the top, with the corresponding disadvantages described at the beginning.

The invention is based on the object of increasing the brilliance of the decorations on cooking surfaces formed by glass ceramic plates or glass plates made of tempered special glass and of achieving a cooking surface that is as smooth as possible.

This object is achieved starting from a hob with a transparent, uncolored glass ceramic plate or a glass plate made of tempered special glass as a cooking surface, which has cooking zones heated with radiant heating elements, to which decorations are applied, and whose underside bears an IR-permeable layer made of a temperature-resistant color according to the invention in that the underside layer is designed as a color-imparting decoration and the top of the glass ceramic or glass plate is free of decoration.

The decorations designed according to the invention have a very high brilliance when viewed from above, comparable to reverse glass painting. Since the decorations are applied to the underside of the glass or glass ceramic plate, the top of the plate, which forms the cooking surface, is very smooth and therefore easier to clean and operate. The choice of colors is also no longer limited by mechanical and cleaning-related requirements, since the underside of the glass or glass ceramic plate is not exposed to scratches from shifted cookware and cleaning agents or food spilling over. The freedom from the constraints of the cooking surface also offers new design options.

According to one embodiment of the invention, the temperature-resistant colors are printed on and baked on. This method of printing allows for a simple and therefore economical production of the glass or glass ceramic plate with decorations compared to other methods of applying color, whereby in the case of glass ceramic plates the typical dimpled structure makes the application of color more difficult.

According to the development of the invention, temperature-resistant paints that are suitable are paints that are based on metal and/or precious metal compounds dissolved in organic solvents and/or contain colloidal metals, so-called luster paints, precious metal resinates or generally "organometallic" paints, as well as organometallic paints that can also be pigmented as desired, as well as paints with a sol-gel-based matrix that either have a characteristic inherent color and/or can also be pigmented as desired, whereby in the hot range preferably conventional, inorganic pigments or luster, pearlescent interference pigments or any mixtures of these pigments can be used.

The above-mentioned organometallic paints, luster paints, precious metal resinates, and/or additionally pigmented organometallic paints, luster paints, precious metal resinates, and/or organic paints, colored varnishes, paints based on organically modified glasses and/or paints that consist of an organic binding matrix or sol-gel-based matrix and contain conventional organic dyes or inorganic pigments, luster, metallic effect, pearlescent or interference pigments or various mixtures of these pigments are also suitable for the cold area. The first-mentioned "organometallic" paints and paints based on a sol-gel matrix have the necessary temperature resistance to be able to permanently withstand direct radiation from the radiation elements that heat the cooking zones.

The above-mentioned colours are fired at different temperatures, depending on the colour type.

The ceramic paints that are usually used cannot be used on glass ceramic plates that are coated on the underside, as firing would significantly reduce the mechanical strength of the glass ceramic plate, so that, for example, impact loads, as can occur in practice, would lead to damage to the glass ceramic plate.

According to one embodiment of the invention, in order to achieve special color effects, in some cases decorations formed from the aforementioned organometallic solutions with metal and/or precious metal components as colors, which are generally sufficiently opaque, are deposited with organic colors or colors which consist of an organic, preferably polymeric binding matrix or matrix on a sol-gel basis and contain conventional, inorganic pigments, luster, metallic effect, pearlescent or interference pigments or various mixtures of these pigments.

Depending on the required temperature resistance, i.e. depending on whether the decorations are applied in the heated zone or in the cold area of the cooking surface, combinations of different colors are used according to a further embodiment of the invention. In principle, each of the above-mentioned colors can be used individually or - if compatible - in combination with any of the other above-mentioned colors, whereby the temperature resistance of the individual color types, the degree of transparency of the color layers and the desired color impressions influence the area of application and the color combinations.

The colours formed from organometallic solutions with metal and/or precious metal components can also be mixed with conventional, inorganic pigments, luster, metallic effect, pearlescent or interference pigments or various mixtures of these pigments to create new effects and, if required, can be back-printed with organic colours, coloured lakes, colours based on organically modified glasses and/or colours consisting of an organic, preferably polymeric binding matrix or sol-gel-based matrix and pigmented as desired.

Furthermore, combinations of transparent luster colors with precious metal colors are conceivable as suppression, especially in the cold range.

Depending on the required temperature resistance, i.e. depending on whether it is the heated zone or the cold area of the cooking surface, only the aforementioned "organometallic" colors or a combination of these colors with an organic color, a colored varnish, a color based on organically modified glasses or with colors consisting of an organic, preferably polymeric binding matrix or a sol-gel-based matrix and containing conventional, inorganic pigments, luster, metallic effect, pearlescent or interference pigments or various mixtures of these pigments are used.

According to a further development of the invention, decorations are applied in multiple layers using multiple printing. This makes it possible to adjust the degree of transmission depending on the number of printing layers when printing multiple times, which allows special functional areas, such as display windows, to be displayed on the cooking surface. Metallic effects can also be achieved in this way, which are particularly desired by customers with regard to the possible combinations with stainless steel.

According to another development of the invention, the hob is designed in such a way that a laminated film, e.g. a thin aluminum film or a temperature-resistant polyester or melamine resin film, is applied with highly transparent adhesives in the cold area of the glass or glass ceramic plate and a color layer made of the temperature-resistant colors is applied only in the hot areas of the cooking zone, in particular a single-layer or multi-layer precious metal and/or luster color layer, the latter being preferred due to its higher IR transparency. Decorations can be applied to the laminated film.

According to a further embodiment of the invention, dark, opaque colors are applied in the area of the cooking zones, so that the heating elements can only be seen through when the heating elements are switched on, and therefore cannot adversely affect the appearance of the hob when it is switched off.

Further embodiments of the invention will become apparent from the description of two embodiments shown in the drawings, which also explain the invention in more detail.

Show it:

Fig. 1 in a schematic sectional view a section of

a hob with a transparent, uncoloured glass-ceramic plate, which has coatings of temperature-resistant, non-ceramic colours on the underside for creating decorations and/or symbols, and

Fig. 2 in a schematic sectional view analogous to Fig. 1 a

corresponding glass ceramic plate, which has the colour layers only in the cooking zones and a transition area and is covered with a thin aluminium foil in the cold area, and

Fig. 3 in four parts A-D different combinations of

layers of paint.

Fig. 1 shows a schematic sectional view of a section of a hob with a transparent, uncolored glass ceramic plate 1 as the cooking surface.

This glass ceramic plate 1 has at least one cooking zone 2, the hot area, indicated by a dashed line, to which an electrically operated radiant heating element 3 is assigned. The hot area 2 typically has a temperature of > approx. 350° C. It is surrounded by a ring-shaped transition zone 4, indicated by a dashed line, with a thickness of 0-25 mm and the cold area 5, in which the temperature is generally below 220° C.

According to the invention, decorations made of temperature-resistant colors are applied in different arrangements to the underside of the transparent glass ceramic plate 1, which is initially shown in general and symbolically in Fig. 1 by the layer 6, and examples of which are given in the parts of Fig. 3. This layer 6, which can also be multi-layered, consists of the previously described colors or color combinations, which have a

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have a high temperature resistance adapted to the area of the plate to which they are applied and are applied to the underside of the plate by printing.

The paints described above, which are formed from organometallic solutions with metal and/or precious metals, are film-forming paints that contain one or more precious metals - in particular platinum, palladium, gold and silver - as well as other metallic compounds dissolved in organic solvents and/or colloidal metals, and to which substances such as resins, cosolvents and/or any additives are added that affect the color, color intensity, adhesion or solubility of the luster colors. Manufacturers of such paints include Heraeus, Johnson Matthey and Cerdec. These paints are characterized by high color intensity with a low layer thickness and therefore only slightly affect the strength of the cooking surfaces. Depending on the color, the temperature resistance is between 500 and 950° C in continuous operation and can be up to 1000° C for short periods with more temperature-resistant paints.

Preferably, darker, more opaque and high-temperature-resistant colors of this type are used in the heated area of the cooking surface, cooking zone 2, which only allow the heating elements to be seen through when the plate is switched on. By printing twice or more times, the transmission in the visible spectral range can be further reduced. The infrared transmission with single printing is typically between 60-85%, depending on the type of glass ceramic and the printing screen used, which contributes to heat transfer during cooking, especially when using poor-quality dishes. This effect is supported by the fact that the material of the glass ceramic plate 1 itself already has a very high level of IR transparency. The firing takes place either in the primary firing, during the so-called ceramization, as described in DE 35 05 922 Cl, or in a special secondary firing at typically 200° C to 900° C.

preferably at approx. 460 to 650° C for less temperature-resistant colors for approx. 5 to 60 minutes, or at approx. 460° C - 900° C for more temperature-resistant colors, also for approx. 5-60 minutes. The aforementioned "organometallic" colors can also be used in the transition area 4 and in the cold area 5 of the cooking surface, i.e. outside of cooking zone 2, where the temperature load drops from approx. 350° C at the edge of the cooking zone to approx. room temperature at the outer edge of the cooking surface.

Here, mainly "organometallic" colors are used, especially luster colors, which have a lower temperature resistance and of which a wider color spectrum - such as gold, red, green, lukewarm, various shades of gray, etc. - is available.

In a preferred embodiment, a different, e.g. lighter "organometallic" color is used for color differentiation, which may be printed with a cover layer. In one case, the cover layer is an organic color. The temperature resistance of this type of color is usually max. 180 to 300° C. This means that a gap of approx. 0 to 25 mm must be left between the cooking zone and the organic cover layer, which, in conjunction with the usually light insulation ring of the heating elements 3, is used as an additional design element to identify the cooking zone, the cooking zone marking, and can be either unprinted or printed with a more temperature-resistant color.

When using, for example, colours that contain inorganic pigments, luster, pearlescent, metallic effect or interference pigments or mixtures of different pigments and that are characterized by a metallic shine, the above-mentioned recess can be dispensed with due to the significantly higher temperature resistance of approx. 500 to 650° C compared to purely organic colours.

The above mentioned colours can be used in the cold range both in combination with the "organometallic" colours or on their own.

Depending on the top coat used, different color effects are achieved in combination with the various "organometallic" colors.

Further color design options are available by adding so-called effect pigments. The effect pigments are luster, pearlescent or interference pigments, which, unlike conventional pigments, have layers with different refractive indices and thus do not absorb and scatter light, but reflect and transmit it more or less strongly depending on the layer structure, as well as metal effect pigments, such as aluminum fiakes, which reflect light in a directed manner like a mirror. Manufacturers include E. Merck, Darmstadt, BASF, Ludwigshafen - both in Germany - as well as Mearl Corp., N.Y. USA, Karrira OY, Porl Finland, Tayca, Osaka, Japan.

It has been shown that the addition of 0 to 20% by weight of effect pigments - even in otherwise relatively dark luster colors - can clearly accentuate the metallic effect. On the other hand, too high a proportion of effect pigments (> 20% by weight) shows a deterioration in the adhesive properties, so the preferred range is between 0.1 and 10%.

In a preferred embodiment, a stainless steel effect is achieved in combination with a medium gray luster color using a silvery-colored top layer in the cold area. The usually slight brownish-yellow coloring of the glass ceramic plate gives this color combination a color expression similar to smoked glass.

Further design options arise from the use of bright organic paints in the cold area. Depending on the opacity of the paint, an additional top coat may be necessary.

Both those with a dimpled structure on the back and those with smooth surfaces on both sides are used as glass ceramic plates. The former generally have greater mechanical strength. However, the plates with smooth surfaces on both sides have the advantage that display elements such as LED LCD displays appear easy to read without additional immersion layers.

The number of layers allows the transparency to be specifically adjusted in functional zones, such as display windows.

When using almost color-neutral luster colors, e.g. anthracite, different colored displays can also be realized, which is particularly difficult with colored glass ceramic cooking surfaces, since only red tones are possible there.

In the four parts A-D of Fig. 3, various possibilities for combining color layers in the individual temperature ranges of the glass ceramic plate 1 are shown. They show:

The figure part A shows a combination of a layer 6 a of a temperature-resistant luster color in the hot area 2 with a layer 6 b of another luster color, which may also have a lower temperature resistance, in the cold area 5.

The figure part B is a combination of a layer 6a of a temperature-resistant luster paint in the hot area 2 with a layer 6c in the cold area 5, which is formed by a paint with effect pigments that is temperature-resistant up to at least 350° C.

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The figure part C is a combination of a layer 6 a of a temperature-resistant luster color in the hot area 2 with a layer 6 d of another luster color, which can also be more transparent, in the cold area 5, and which is partially back-printed with an organic color layer 8.

The figure part D is a combination of a layer 6 a of a temperature-resistant luster color in the hot area 2 with a layer 6 e of another temperature-resistant luster color in the transition area 4 and in the cold area 5, and which is partially back-printed with a color layer 9 which contains, for example, metallic effect pigments.

Fig. 2 shows a further embodiment with a laminated film, e.g. an aluminum foil 7 in the cold area 5 instead of a layer of paint. The aluminum foil is glued to the underside of the glass ceramic plate 1 with transparent, temperature-resistant adhesives. Examples of adhesives used are: acrylic adhesive layers, e.g. from 3M, UV-curing adhesives, or highly transparent silicone adhesives, preferably 2K systems. When lamination, care must be taken to ensure that the application is bubble-free. The adhesive layers may have to compensate for the nub structure (typically 50 to 150 /xm high), which results in a minimum layer thickness of 150 /im. When selecting the adhesive, care must also be taken to ensure that it is sufficiently resistant to water vapor, since water vapor is released from the insulation ring of the heating elements 3 during heating. The hot area 2 and the transition area 4 are provided with the layer of paint 6, as in Fig. 1.

Notwithstanding the fact that the decorations are applied to the underside of the glass/glass ceramic plate 1, additional signs or symbols may be applied to the upper side of the plate.

Preferably, however, the necessary markings, in particular the cooking zone markings, are formed on the underside of the plate, e.g. by gaps between decorations, or by adjacent, differently colored decorations.

Instead of a glass ceramic plate 1, the cooking surface can also be formed by a glass plate made of prestressed special gas, e.g. lithium aluminosilicate glass (LAS glass) or borosilicate glass.

Coating agents:

1. For the hot area:

a: Luster colours from Heraeus, D. Johnson Matthey, NL

b: Luster colours containing conventional inorganic pigments, luster metallic effect, pearlescent or interference pigments or various mixtures of these pigments

c: Sol-gel layers or pigmented sol-gel layers containing conventional inorganic pigments, luster, metallic effect, pearlescent or interference pigments or various mixtures of these pigments

d: Precious metal inks, resinates or other inks that are printed with a high degree of rasterization due to low IR transparency

2. For the cold area:

At least up to 350° C, i.e. printable directly next to the hot area (without gap)
e.g.:

a: Anti-corrosion paints with metal pigments, such as aluminium flakes

15

b: Luster colours with temperature stability up to 500° C, e.g. from Heraeus, D.; Johnson Matthey, NL.

c: Luster colours with temperature stability up to 500° C, which contain conventional inorganic pigments, luster, metallic effect, pearlescent or interference pigments or various mixtures of these pigments

d: Precious metal colours, resinates with temperature stability up to 900° C, e.g. from Johnson Matthey, Heraeus, D., Cerdec

e: Sol-gel layers or pigmented sol-gel layers containing conventional inorganic pigments, luster, metallic effect, pearlescent or interference pigments or various mixtures of these pigments.

Up to 300°C:

f: organic colours with inorganic dyes, e.g.: coloured varnishes or hydroglazes from the company Diegel, Alsfeld, D.

Up to 180° C - 220° C:

g: organic colours with organic dyes, e.g. from Heraeus, D.

h: paints based on organically modified glasses i: laminated films, e.g. aluminium foils, polyester films, melamine resin films

Furthermore, all conceivable combinations of the coating agents mentioned in and 2, e.g. in the cold range 2b+2f, 2c+2f, 2b+2a, 2b+2d, 2b+2e etc.

Depending on the type of coating, it is baked/dried/cured at different temperatures

Design elements:

1. Examples for the hot area:

For 2-ring cooking zones (small/large or round/wide roaster) between the two partial surfaces of the cooking zones:

no decoration: contrast through a highly translucent heating element when switched on or a combination with lower colour contrast, e.g.

a colour la on the surfaces with a colour Ib on the cooking zone rings:

or a combination with stronger colour contrast, e.g.

a colour Ic on the surfaces with colours la or Ib on the cooking zone rings;

rasterized color, e.g. Id in the hot area, possibly combined with la.

2. Examples for the cold area:

transparent luster colours from la, Ib, 2b, 2c with silvery underprint, so that a delicate veil of colour appears over a metallic opaque background

Spot-like printed luster colours of various colours with a white or grey underprint to simulate rock structures

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black luster color printed only on the stud tips with a full-surface underprint in a strong organic color, e.g. grass green. Combination of opaque and transparent luster colors next to each other to enable viewing windows onto certain components in the hob system, printed or unprinted film laminates in the cold area.

Claims (13)

1. Hob with a transparent, uncolored glass ceramic plate (1) or glass plate made of toughened special glass as a cooking surface, which has cooking zones (2) heated by radiant heating elements (3), to which decorations are applied and whose underside bears an IR-permeable layer (6, 8), characterized in that the underside layer (6) is designed as a color-imparting decoration (6, 8) and the upper side of the glass ceramic or glass plate (1) is free of decoration. 2. Cooking surface according to claim 1, characterized in that the underside layer (6) - in the area of the cooking zones (2) (hot area) is made of a material which is resistant to temperatures greater than approximately 350°C, typically greater than 500°C, and - in the area of the cooking surface outside the cooking zones (2) (cold area) is made of a material which is resistant to temperatures below approx. 350°C. 3. Cooking surface according to claim 1 or 2, characterized in that the underside layer (6), at least in the hot area, is made up of colors consisting of organometallic solutions with complexed and/or colloidal metal and/or precious metal components (luster colors, precious metal resinates), which optionally contain pigments or mixtures of pigments. 4. Cooking surface according to claim 1 or 2, characterized in that the underside layer (6) consists, at least in the hot region, of sol-gel layers which optionally contain pigments or mixtures of pigments. 5. Cooking surface according to one of claims 2 to 4, characterized in that in the cold region (5) and/or in the transition region (4), in which temperatures of up to approximately 350°C are reached, the underside layer (6) consists of luster colors, optionally pigmented, or other organometallic colors, in particular precious metal resinates, anti-corrosive colors, optionally pigmented, or sol-gel layers, optionally pigmented, which are resistant at least up to this temperature. 6. Cooktop according to one of claims 2 to 4, characterized in that in the cold region (5) and/or in the transition region (4), in which temperatures of up to approximately 300°C are reached, the underside layer (6) consists of organic colors, such as colored varnishes, colors based on organically modified glasses and/or colors which consist of an organic, preferably polymeric binding matrix or sol-gel-based matrix and contain conventional, inorganic pigments, luster, metallic effect, pearlescent or interference pigments or various mixtures of these pigments. 7. Cooking surface according to one of claims 3 to 6, characterized in that the underside layer (6) in the hot, transition and cold areas (2, 4, 5) each consists of a combination of the temperature-resistant colors for the area. 8. Hob according to one of claims 1 to 7, characterized in that the underside layer (6) is multi-layered. 9. Cooking surface according to one of claims 1 to 8, characterized in that the underside layer (6) is backed by a covering layer (8) of a different color. 10. Cooking surface according to one of claims 1 to 9, characterized in that the marking of the cooking zones (2) is formed by recesses in the underside layer (6) or by different colors/color contrasts in the layer. 11. Hob according to one of claims 1 to 10, characterized in that display windows, in particular for residual heat display, for colored LEDs or LCDs, are formed in the underside layer. 12. Hob according to one of claims 1 to 11, characterized in that in the cold area (5) of the glass or glass ceramic plate (1) a film, preferably an aluminum film (7) or a stainless steel or a corresponding temperature-resistant plastic film, such as a polyester film or melamine resin film, is laminated with highly transparent adhesives and only in the hot areas (2) a color layer (6) made of the corresponding temperature-resistant colors is applied. 13. Hob according to claim 12, characterized in that decorations are printed on the film.