WO2000015005A1 - An insulated thin film heater - Google Patents

An insulated thin film heater Download PDF

Info

Publication number
WO2000015005A1
WO2000015005A1 PCT/DK1999/000466 DK9900466W WO0015005A1 WO 2000015005 A1 WO2000015005 A1 WO 2000015005A1 DK 9900466 W DK9900466 W DK 9900466W WO 0015005 A1 WO0015005 A1 WO 0015005A1
Authority
WO
WIPO (PCT)
Prior art keywords
ceramic
glass
layer
intercalated
thin film
Prior art date
Application number
PCT/DK1999/000466
Other languages
French (fr)
Inventor
Antoine Dubedout
Johan Källgren
Thoma Fich Pedersen
Richard Cooper
Original Assignee
Aktiebolaget Electrolux
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Aktiebolaget Electrolux filed Critical Aktiebolaget Electrolux
Priority to AU54085/99A priority Critical patent/AU5408599A/en
Publication of WO2000015005A1 publication Critical patent/WO2000015005A1/en

Links

Classifications

    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B3/00—Ohmic-resistance heating
    • H05B3/68—Heating arrangements specially adapted for cooking plates or analogous hot-plates
    • H05B3/74—Non-metallic plates, e.g. vitroceramic, ceramic or glassceramic hobs, also including power or control circuits
    • H05B3/748—Resistive heating elements, i.e. heating elements exposed to the air, e.g. coil wire heater

Definitions

  • the invention relates to a domestic cooktop heater of the type comprising an electrically insulating substrate connected to a thin film electrical heater.
  • a domestic cooktop heater of the above type may be made of a (typically) glass- ceramic substrate joined to a thin film electric heater.
  • This film heater may be either deposited onto the substrate, printed onto it or just brought into intimate contact with it.
  • the heater transfers heat to the substrate by conduction (it is not desired that the contact be so loose that radiation is involved), and in turn the substrate transfers heat to the cooking utensil.
  • heater comprises a dielectric material having the requisite insulating properties at the operating temperature which is applied to the glass-ceramic, and the thin film heater is deposited onto the dielectric layer.
  • the dielectric material is adhered to the glass-ceramic, effectively filling the unevennesses in the glass-ceramic surface and providing a smooth surface for the film heating element even though
  • the top surface of the glass ceramic may present protrusions or dimples. In this arrangement, the heat conduction through the dielectric material is large.
  • the lower surface of the glass-ceramic is provided with a large number of minute protrusions, thereby effectively increasing the contact area between the glass-ceramic and the dielectric layer.
  • the dielectric layer and the glass-ceramic is intercalated with a heat-conductive substance which displays flow characteristics characteristics to effectively fill any voids. This means that this layer may take up any stresses occuring due to different thermal expansion.
  • the substance of the intercalated layer is metallic.
  • a metallic layer may be deposited directly onto the glass-ceramic, and the dielectric layer is then brought into intimate contact with the metallised surface of the glass-ceramic as above.
  • the intercalated metallic layer has a perforated structure permitting the absorption of thermal stresses.
  • the intercalated metallic layer is connected to ground.
  • the intercalated metallic layer may be deposited by any known means, and its terminal may be brought out on the far side of the heating element, permitting a ground connection at a safe distance from the heating element which carries the mains voltage
  • Fig 1 shows a section through the essential layers of the invention, i e the glass ceramic with its irregularities at the bottom, the dielectric layer, and the film heater layer
  • Fig 2 shows a section through an embodiment employing an intermediate, void- filling layer
  • Fig 3 shows a section through an embodiment employing an intercalated metal layer which is grounded
  • Fig 4 shows a section through an embodiment in which the metal layer is in the form of a perforated metal foil
  • the glass ceramic layer in practice has a thickness which is several orders of magnitude larger than the thickness of the dielectric and film layers indicated
  • the glass ceramic in order to increase the contact area between the glass ceramic having a zero thermal expansion coefficient and the dielectric the glass ceramic is advantageously prepared so that it has a vast number of small protrusions at its lower side, irrespective of any profiling or other surface treatment of the top surface Increasing the surface area combined with the angles created with respect to the average surface will contribute to increasing the adhesion between the surfaces
  • the dielectric layer is provided in any industrially economical manner, however there is no need to obtain a flatness which is greater than that required for the following deposition of the thin film heater
  • the dielectric layer only has an insulating function with respect to high voltage, and this must not be obtained at the expense of increased thermal resistance
  • the dielectric layer has sufficient heat transfer properties, it will not only conduct heat from the heater to the glass ceramic but will also distribute heat "sideways" and thus contribute to an even temperature distribution.
  • Fig. 2 is shown an embodiment in which it is not the dielectric layer which has to comply with the surface irregularities but an intercalated void-filling layer.
  • a layer may be optimised for this property and for heat conduction, and hence the dielectric layer may be optimised with respect to its electrical insulating properties.
  • the surface presented to the deposition of thin film will be absolutely flat.
  • Fig. 3 is shown an embodiment in which a metallic layer is performing a bridge between the glass ceramic and the dielectric layer.
  • the metallic layer is required to be able to conduct to ground any leakage current passing through the dielectric layer in case it suffers a local breakdown.
  • the conductivity of the metallic layer must be such that the potential on the upper side of the hot glass ceramic will be below ca. 40 V. This applies in the situation where this potential is obtained as a voltage division between the impedances constituted of a person and the metallic ' layer.
  • the metallic layer is constituted of a metal foil which is perforated (shown as a broken solid curvaceous line).
  • a metal foil will be able to carry a heavier leakage current to ground than a thinly deposited layer, and also perforation is simpler to carry out as a process separate from deposition.
  • the same function may be obtained by means of a metal mesh, and the process of manufacture of this type of layer may be by means of sputtering, screen-printing, woven metal threads or punching from a metal foil.
  • a further advantage associated with a metal mesh is that the capacitive coupling between the film heater and the ground plane will be much lower than with a continuous ground plane, because the electrode area will be significantly smaller when a mesh is used.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Ceramic Engineering (AREA)
  • Surface Heating Bodies (AREA)
  • Resistance Heating (AREA)

Abstract

The invention addresses the problem of insulating a glass-ceramic so that no dangerous voltages occur due to heat-provoked increasing conductivity of the glass-ceramic when it is connected to a mains supply. By intercalating a suitable stress-absorbing layer it is possible to deposit a stable insulating layer.

Description

thinspc
An insulated thin film heater.
The invention relates to a domestic cooktop heater of the type comprising an electrically insulating substrate connected to a thin film electrical heater.
A domestic cooktop heater of the above type may be made of a (typically) glass- ceramic substrate joined to a thin film electric heater. This film heater may be either deposited onto the substrate, printed onto it or just brought into intimate contact with it. When it is energised, the heater transfers heat to the substrate by conduction (it is not desired that the contact be so loose that radiation is involved), and in turn the substrate transfers heat to the cooking utensil.
Existing glass-ceramic is known to be electrically conductive at the operating temperature, and since the user may touch a metallic cooking utensil or even the surface, it is necessary to provide an electrical insulation between the electrically heated film and the cooktop surface. At the operating temperature IEC regulations set a minimum break-down voltage requirement at 3750V AC (or 1250V AC if a grounded connection is interposed between the film and the cooking utensil). A film heater in this construction must hence comprise a specific electrically insulating layer.
Various solutions have been proposed in the past, however, no solution is presently available commercially for bonding any known high temperature electrical insulator to a glass-ceramic substrate with the capability to withstand thermal cycling from 20°C to 400°C providing a commercial life-time for the cooktop. The thermal coefficient of expansion of a glass-ceramic is near zero, and this puts a heavy requirement for any material it is desired to adhere to such a substrate. It should either present a similar low thermal coefficient of expansion or tolerate the resulting stresses. Under no circumstances must cycling provoke cracks in the glass-ceramic. According to the invention, heater comprises a dielectric material having the requisite insulating properties at the operating temperature which is applied to the glass-ceramic, and the thin film heater is deposited onto the dielectric layer. The dielectric material is adhered to the glass-ceramic, effectively filling the unevennesses in the glass-ceramic surface and providing a smooth surface for the film heating element even though The top surface of the glass ceramic may present protrusions or dimples. In this arrangement, the heat conduction through the dielectric material is large.
According to an advantageous embodiment of the invention, the lower surface of the glass-ceramic is provided with a large number of minute protrusions, thereby effectively increasing the contact area between the glass-ceramic and the dielectric layer.
In a further advantageous embodiment of the invention, the dielectric layer and the glass-ceramic is intercalated with a heat-conductive substance which displays flow characteristics characteristics to effectively fill any voids. This means that this layer may take up any stresses occuring due to different thermal expansion.
According to a further embodiment of the invention, the substance of the intercalated layer is metallic. Such a metallic layer may be deposited directly onto the glass-ceramic, and the dielectric layer is then brought into intimate contact with the metallised surface of the glass-ceramic as above.
In a further advantageous embodiment the intercalated metallic layer has a perforated structure permitting the absorption of thermal stresses.
In a further advantageous embodiment the intercalated metallic layer is connected to ground. This has the distinct advantage that according to IEC the demands on the insulating properties of the dielectric layer are considerably reduced, because the construction now fulfils the condition of grounding. The intercalated metallic layer may be deposited by any known means, and its terminal may be brought out on the far side of the heating element, permitting a ground connection at a safe distance from the heating element which carries the mains voltage
The invention will be described in detail in the following with reference to an example and drawings, in which
Fig 1 shows a section through the essential layers of the invention, i e the glass ceramic with its irregularities at the bottom, the dielectric layer, and the film heater layer
Fig 2 shows a section through an embodiment employing an intermediate, void- filling layer,
Fig 3 shows a section through an embodiment employing an intercalated metal layer which is grounded, and
Fig 4 shows a section through an embodiment in which the metal layer is in the form of a perforated metal foil
In all the figures, the glass ceramic layer in practice has a thickness which is several orders of magnitude larger than the thickness of the dielectric and film layers indicated As shown in Fig 1, in order to increase the contact area between the glass ceramic having a zero thermal expansion coefficient and the dielectric the glass ceramic is advantageously prepared so that it has a vast number of small protrusions at its lower side, irrespective of any profiling or other surface treatment of the top surface Increasing the surface area combined with the angles created with respect to the average surface will contribute to increasing the adhesion between the surfaces The dielectric layer is provided in any industrially economical manner, however there is no need to obtain a flatness which is greater than that required for the following deposition of the thin film heater The dielectric layer only has an insulating function with respect to high voltage, and this must not be obtained at the expense of increased thermal resistance However, in case the dielectric layer has sufficient heat transfer properties, it will not only conduct heat from the heater to the glass ceramic but will also distribute heat "sideways" and thus contribute to an even temperature distribution.
In Fig. 2 is shown an embodiment in which it is not the dielectric layer which has to comply with the surface irregularities but an intercalated void-filling layer. Such a layer may be optimised for this property and for heat conduction, and hence the dielectric layer may be optimised with respect to its electrical insulating properties. In this case, the surface presented to the deposition of thin film will be absolutely flat.
In Fig. 3 is shown an embodiment in which a metallic layer is performing a bridge between the glass ceramic and the dielectric layer. The metallic layer is required to be able to conduct to ground any leakage current passing through the dielectric layer in case it suffers a local breakdown. The conductivity of the metallic layer must be such that the potential on the upper side of the hot glass ceramic will be below ca. 40 V. This applies in the situation where this potential is obtained as a voltage division between the impedances constituted of a person and the metallic ' layer.
In Fig. 4 is shown that the metallic layer is constituted of a metal foil which is perforated (shown as a broken solid curvaceous line). A metal foil will be able to carry a heavier leakage current to ground than a thinly deposited layer, and also perforation is simpler to carry out as a process separate from deposition. The same function may be obtained by means of a metal mesh, and the process of manufacture of this type of layer may be by means of sputtering, screen-printing, woven metal threads or punching from a metal foil.
A further advantage associated with a metal mesh is that the capacitive coupling between the film heater and the ground plane will be much lower than with a continuous ground plane, because the electrode area will be significantly smaller when a mesh is used.

Claims

PATENT CL IMS
1. A domestic cooktop heater of the type comprising an electrically insulating substrate connected to a thin film electrical heater characterised in that it further comprises a dielectric material having the requisite insulating properties at the operating temperature which is applied to the glass-ceramic, and the thin film heater is deposited onto the dielectric layer.
2. A cooktop according to claim 1, characterised in that the lower surface of the glass-ceramic is provided with a large number of minute protrusions,
3. A cooktop according to claim 1 or 2, characterised in that the dielectric layer and the glass-ceramic is intercalated with a heat-conductive substance which displays flow characteristics to effectively fill any voids.
4. A cooktop according to claim 3, characterise in that the substance of the intercalated layer is metallic.
5. A cooktop according to claim 4, characterised in that the intercalated metallic layer has a perforated structure permitting the absorption of thermal stresses
6. A cooktop according to claim 4 or 5, characterised in that the intercalated metallic layer is connected to ground.
7. A cooktop according to claim 5 and 6, characterised in that the intercalated metallic layer is in the form of a metal foil.
PCT/DK1999/000466 1998-09-03 1999-09-03 An insulated thin film heater WO2000015005A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU54085/99A AU5408599A (en) 1998-09-03 1999-09-03 An insulated thin film heater

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DKPA199801115 1998-09-03
DKPA199801115 1998-09-03

Publications (1)

Publication Number Publication Date
WO2000015005A1 true WO2000015005A1 (en) 2000-03-16

Family

ID=8101183

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/DK1999/000466 WO2000015005A1 (en) 1998-09-03 1999-09-03 An insulated thin film heater

Country Status (2)

Country Link
AU (1) AU5408599A (en)
WO (1) WO2000015005A1 (en)

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE10110793A1 (en) * 2001-03-06 2002-10-02 Schott Glas Ceramic cooking system with glass ceramic plate, insulation layer and heating elements
DE10242481C1 (en) * 2002-09-13 2003-12-04 Schott Glas Glass ceramic hob comprises low-expansion sintered glass ceramic containing specified high percentage of cordierite in main crystal phase
FR2848289A1 (en) * 2002-12-05 2004-06-11 Schott Glas Oven chamber, has heated partition of glass or vitro ceramic material with metallic conducting layer, supported by lateral guides
DE10110792B4 (en) * 2001-03-06 2004-09-23 Schott Glas Ceramic cooking system with glass ceramic plate, insulation layer and heating elements
DE10207515B4 (en) * 2002-02-22 2004-12-02 Schott Ag Cooking system with a cooking surface and a holder
WO2005055663A1 (en) * 2003-12-02 2005-06-16 Schott Ag Heating device, in particular ceramic hob and method for producing a device of this type
WO2008047199A2 (en) * 2006-10-18 2008-04-24 Inglass S.P.A. Ceramic or glass cooktop with integrated heater
ES2388866A1 (en) * 2009-10-01 2012-10-19 BSH Electrodomésticos España S.A. Cooking hob with a metallicly covered cover plate. (Machine-translation by Google Translate, not legally binding)

Citations (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3694622A (en) * 1971-01-07 1972-09-26 Ralph L Bentley Heater
US3869596A (en) * 1973-09-28 1975-03-04 Safeway Products Inc Cookware heater
US4032750A (en) * 1976-03-26 1977-06-28 General Electric Company Flat plate heating unit with foil heating means
DE3105065A1 (en) * 1981-02-12 1982-08-19 Licentia Patent-Verwaltungs-Gmbh, 6000 Frankfurt Glass-ceramic hotplate
DE4109569A1 (en) * 1991-03-22 1992-09-24 Buchtal Gmbh Electric heating plate for cooking hob - has metal plate with printed conductor pattern beneath thermally conductive cover layer
US5252809A (en) * 1991-02-26 1993-10-12 Lapin-Demin Gmbh Panel heating element and process for its production
US5508495A (en) * 1990-10-15 1996-04-16 Yahav; Shimon Domestic cooking apparatus
DE19711541A1 (en) * 1997-03-20 1998-09-24 Ako Werke Gmbh & Co Electric hotplate
EP0951202A2 (en) * 1998-04-17 1999-10-20 BSH Bosch und Siemens Hausgeräte GmbH Cooking plate with electrically conductive ceramic plate

Patent Citations (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3694622A (en) * 1971-01-07 1972-09-26 Ralph L Bentley Heater
US3869596A (en) * 1973-09-28 1975-03-04 Safeway Products Inc Cookware heater
US4032750A (en) * 1976-03-26 1977-06-28 General Electric Company Flat plate heating unit with foil heating means
DE3105065A1 (en) * 1981-02-12 1982-08-19 Licentia Patent-Verwaltungs-Gmbh, 6000 Frankfurt Glass-ceramic hotplate
US5508495A (en) * 1990-10-15 1996-04-16 Yahav; Shimon Domestic cooking apparatus
US5252809A (en) * 1991-02-26 1993-10-12 Lapin-Demin Gmbh Panel heating element and process for its production
DE4109569A1 (en) * 1991-03-22 1992-09-24 Buchtal Gmbh Electric heating plate for cooking hob - has metal plate with printed conductor pattern beneath thermally conductive cover layer
DE19711541A1 (en) * 1997-03-20 1998-09-24 Ako Werke Gmbh & Co Electric hotplate
EP0951202A2 (en) * 1998-04-17 1999-10-20 BSH Bosch und Siemens Hausgeräte GmbH Cooking plate with electrically conductive ceramic plate

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE10110793A1 (en) * 2001-03-06 2002-10-02 Schott Glas Ceramic cooking system with glass ceramic plate, insulation layer and heating elements
DE10110792B4 (en) * 2001-03-06 2004-09-23 Schott Glas Ceramic cooking system with glass ceramic plate, insulation layer and heating elements
DE10207515B4 (en) * 2002-02-22 2004-12-02 Schott Ag Cooking system with a cooking surface and a holder
DE10242481C1 (en) * 2002-09-13 2003-12-04 Schott Glas Glass ceramic hob comprises low-expansion sintered glass ceramic containing specified high percentage of cordierite in main crystal phase
FR2848289A1 (en) * 2002-12-05 2004-06-11 Schott Glas Oven chamber, has heated partition of glass or vitro ceramic material with metallic conducting layer, supported by lateral guides
WO2005055663A1 (en) * 2003-12-02 2005-06-16 Schott Ag Heating device, in particular ceramic hob and method for producing a device of this type
WO2008047199A2 (en) * 2006-10-18 2008-04-24 Inglass S.P.A. Ceramic or glass cooktop with integrated heater
WO2008047199A3 (en) * 2006-10-18 2008-07-10 Inglass Spa Ceramic or glass cooktop with integrated heater
ES2388866A1 (en) * 2009-10-01 2012-10-19 BSH Electrodomésticos España S.A. Cooking hob with a metallicly covered cover plate. (Machine-translation by Google Translate, not legally binding)

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Publication number Publication date
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