HK1140091B - Heating apparatus and method for making the same - Google Patents

Description

Heating device and manufacturing method thereof

Cross Reference to Related Applications

The present application claims priority from the following patent applications: U.S. provisional patent application No. 60/900,994 filed on.2/13/2007 and U.S. provisional application No. 60/990,619 filed on.11/28/2007, the contents of which are incorporated herein by reference.

Technical Field

The present invention relates to a heating device and a method for manufacturing a heating element of the heating device.

Background

Low temperature conductive coatings have been proposed for some time but have not found wide commercial application due to their instability, potential cracking at high temperatures, and expensive manufacturing costs associated with the need for high vacuum vapor deposition processes to achieve uniform compositions and structures. A uniform composition, thickness and stable structure across the entire conductive layer is extremely important to maintain a consistent resistance and temperature distribution of the heating element of the heating device. A change in resistance across the conductive layer will create a temperature change/gradient and hence thermal stress in the conductive layer, destroying the stability of the structure, leading to cracking of the conductive layer, particularly in high temperature heating applications.

The application identified as Torppy et al, PCT publication No. WO00/18189(PCT publication No. WO00/1819 by Torppy et al), incorporated herein in its entirety, proposes a coating system for increasing the stability of a conductive film on a glass substrate for heating by doping tin oxide with cerium and lanthanum. However, cerium and lanthanum must be uniformly distributed within the coating to provide a stabilizing effect, but this is often difficult to achieve. Annealing at elevated temperatures for 1 hour is proposed in PCT publication WO00/18189 to help produce a uniform and stable coating. However, this method is not cost effective in manufacturing and can lead to detrimental diffusion of contaminant components from the substrate into the coating. Increasing the mole percent of cerium and lanthanum aids in the distribution of these rare earth elements, but will result in an increase in the resistance of the film, thereby reducing conductivity and power output, and limiting the practical and commercial use of the film.

The above description of the background art is helpful in understanding the heating apparatus disclosed in the present application, but is not considered to describe or constitute pertinent prior art to the heating apparatus disclosed in the present application, or to refer to the cited documents as material for patentability in view of the claims of the present application.

Disclosure of Invention

The present invention relates to a heating device comprising a heating element arranged on a substrate, said heating element comprising an electrode and a multilayer conductive coating having a nanometric thickness, wherein said multilayer conductive coating is arranged between said substrate and said electrode, said multilayer conductive coating having a structure and composition that stabilizes the properties of said heating element under high temperature conditions.

In an embodiment, the heating element of the heating device comprises a multilayer insulating coating having a thickness of nanometers, which is arranged between the multilayer conductive coating and the substrate.

In another embodiment, the heating device includes a temperature monitoring and control system integrated with the heating element of the heating device, the temperature monitoring and control system including an analog-to-digital converter for measuring temperature and a pulse width modulation driver for regulating power supply.

In yet another embodiment, the heating device further comprises a compartment defining a first air channel and a second air channel, the first air channel and the second air channel being disposed proximate to the substrate and the multilayer conductive coating, and a fan that blows hot air out of the heating device through one of the first air channel and the second air channel.

The multilayer conductive coating of the heating element of the heating device is produced by spray pyrolysis.

The spray pyrolysis may be performed at a temperature of about 650 ℃ to 750 ℃.

The spray pyrolysis may be performed at a spray pressure of about 0.4MPa to about 0.7 MPa.

The spray pyrolysis may be performed at a jet velocity of less than 1000 mm/s.

The spray pyrolysis may be performed by alternating spray passages oriented at 90 degrees to each other.

Drawings

The heating device disclosed in the present invention will be further explained with reference to the drawings and examples, wherein:

FIG. 1 is a top view of a heating element of a heating device according to an embodiment of the present invention;

FIG. 2 is a side view of the heating element shown in FIG. 1;

FIG. 3 is a high resolution scanning electron micrograph of nanostructures used to show the conductive coating of the heating element shown in FIG. 1;

FIG. 4 is a schematic circuit diagram of a control unit connected to a power supply for the heating element;

FIG. 5 is a circuit schematic of a temperature monitoring and control system having an analog-to-digital converter (ADC) and a Pulse Width Modulation (PWM) driver;

FIG. 6 is a perspective view of a heating device/furnace using a heating element according to one embodiment of the present invention;

FIG. 7 is a perspective view of a compartment (split chamber) of a heating device according to an embodiment of the present invention;

FIG. 8 is a side view of the compartment shown in FIG. 7;

figure 9 is a schematic view of a tile covered with a multi-layer nano-thickness heating film.

Detailed Description

It is to be understood that the heating device and method of making the heating element of the present invention are not limited to the particular embodiments described below, and that various modifications and equivalent arrangements may be devised by those skilled in the art without departing from the scope of the present invention. For example, elements and/or features of different example embodiments may be combined with and/or substituted for one another without departing from the scope of this disclosure and its claims.

The phrase "multi-layer coating" or "multi-layered coating" as used herein refers to a coating having more than one layer of coating material.

The phrase "nano-thickness" as used herein refers to the thickness of each coating layer that can only be measured in the nano-level.

Fig. 1 and 2 are a top view and a side view, respectively, of a heating element of a heating device according to an embodiment of the present invention. The heating device has a heating element 10 for generating heat. The heating element 10 includes a substrate 12, a multilayer insulating coating 14, a multilayer conductive coating 16, and an electrode 18, wherein the multilayer insulating coating 14 is disposed on the substrate 12, the multilayer conductive coating 16 is disposed on the multilayer insulating coating 14, and the electrode 18 is disposed on the multilayer conductive coating 16.

In the illustrated embodiment, the substrate 12 may be made of ceramic glass or any other suitable material. It will be appreciated by those skilled in the art that ceramic glasses can withstand high temperatures and thermal shock, and are superior to other glass substrates to provide consistent and reliable high temperature heating functions.

In the illustrated embodiment, a multilayer insulating coating 14 is disposed on the surface of the ceramic glass substrate 12. The multilayer insulating coating 14 may be sol-gel derived silicon dioxide (SiO)₂) Or other suitable material. Each layer of the multilayer insulating coating 14 has a nano-thickness of about 30nm to 50 nm. The multilayer insulating coating 14 may be applied to the surface of the ceramic glass substrate 12 with a surfactant to ensure SiO coverage on the ceramic glass substrate 12₂Has 100% wetting so as to prevent the occurrence of defect sites, so that the ceramic glass substrate 12 (which is electrically conductive under high temperature conditions) is electrically isolated from the conductive coating 16, and lithium ions and other contaminant components are prevented from diffusing from the ceramic glass substrate 12 to the conductive coating 16 during heating.

Perfluoroalkyl surfactants may be used with dioctyl sodium sulfosuccinate to coat the ceramic glass substrate 12 by using spray or dip coating techniques or another suitable technique, wherein the concentration of the perfluoroalkyl surfactant is between about 0.01 and 0.001% w/w and the concentration of the dioctyl sodium sulfosuccinate is between about 0.1 and 0.01% w/w.

The SiO can be applied by dip coating or another suitable technique₂The layer is disposed on the ceramic glass substrate 12, and Tetraethylorthosilicate (TEOS) may be used as a base precursor (base pressor). Each silica sol-gel layer needs to be hydrolyzed, dried, and fired at about 500 ℃ using a staged ramp temperature cycling (staged ramp temperature cycling) to remove physical water, chemically bound water, carbon, and organic residues from the matrix to yield ultra-pure SiO with minimal defects₂And (3) a layer.

In the illustrated embodiment, a plurality of conductive coatings 16 are disposed on the insulating coating 14. The multilayer conductive coating 16 may be an oxide coating wherein the metal source used may be selected from the group consisting of tin, indium, cadmium, tungsten, titanium and vanadium doped with organometallic precursors such as monobutyl tin trichloride doped with equal amounts of donor and acceptor elements such as about 3 mol% antimony and zinc with or without other rare earth elements. Fig. 3 is a high resolution scanning electron micrograph showing the nanostructure of the conductive coating 16 of the heating element 10. It will be appreciated that the multilayer conductive coating 16 may be made of other suitable materials.

The multilayer conductive coating 16 may be disposed on the insulating film 14 using a spray pyrolysis method in which the temperature of the spray pyrolysis is controlled between about 650 ℃ and 750 ℃, the spray pressure is controlled between about 0.4 and 0.7MPa, and the thickness of each layer of the formed multi-layered nano-thickness coating is about 50 to 70nm to ensure uniform distribution of rare earth elements within the coating, thereby enhancing stability at high temperatures. Preferably, the controllable spray movement is performed on alternating spray paths oriented at about 90 ° to each other. The velocity of the jets is limited to less than 1000mm per second.

The conductive coating material in the multilayer conductive coating 16 is used to convert electrical energy to thermal energy. The applied heat generation principle is very different from conventional coil heating, in which the heat output comes from the high impedance of the metal coil, which has low heating efficiency and high power consumption. In contrast, by adjusting the composition and thickness of the coating, the electrical resistance of the coating can be controlled and the electrical conductivity can be increased, resulting in high heating efficiency with minimal energy loss.

In the illustrated embodiment, the electrode 18 is disposed on the conductive coating 16. Two spaced apart electrodes 18 are respectively disposed along two opposite sides of the conductive coating 16. The electrodes 18 may be made of glass ceramic sintered ink (glass ceramic sintered ink) in which the metal source is selected from platinum, gold, silver, palladium and copper (90-95%), and the glass frit (5-10%) is made of PbO, SiO₂、CeO₂And Li₂O and adding ethyl cellulose/ethanol organic carrier. The ink may be screen printed over the conductive coating area and optimally matched between the electrode 18, the coatings 14, 16 and the ceramic glass substrate 12 to provide consistent conductivity across the entire coating area. The ink is screen printed and baked at about 700 c for about 5 minutes to form the electrodes 18 on the heating element 10. This will prevent possible delamination of the electrodes 18 from the coatings 14, 16 and the substrate 12 which could lead to failure of the heating element 10. This method does not require a long high temperature anneal to fix the coating and the electrode.

For practical commercial and industrial use, the insulating coating 14 need not be disposed on the surface of the ceramic glass substrate 12 while performing a heating function to reach about 300 ℃ to 350 ℃. Instead, a temperature monitoring and control system is integrated with the conductive coating 16 of the heating element for optimal temperature and energy saving control. In this embodiment, the driver software, controller and Pulse Width Modulation (PWM) driver are integrated with the heating element, wherein the controller uses an analog-to-digital converter (ADC) for temperature measurement and the Pulse Width Modulation (PWM) driver for precise power control. Fig. 4 and 5 show a schematic circuit diagram of the temperature monitoring and control system.

For this temperature monitoring and control system, a heating servo system can be used to match the heating elements of the heating device and optimize its rapid and efficient heating characteristics to achieve rapid heating times (within 1 minute), accurate temperature targets (+/-5℃) and maximum energy savings (efficiency up to 90%). When the heating element of the heating device reaches the preset target temperature, the ADC and the PWM immediately respond and cut off the power supply, so that the purpose of saving energy is achieved and the exceeding of the temperature of the heating element is limited. When the temperature of the heating element drops to a preset temperature, the ADC and PWM will then respond and turn on the power supply to generate heat. The servo system thus provides continuous monitoring and control and fast response to achieve smooth powering of the heating element while optimizing its heating performance and energy saving efficiency.

Based on the composition of the coating, the heating element 10 of the heating device can be manufactured by an inexpensive deposition method in an open air environment using spray pyrolysis. In addition, the use of multi-pass control spray in forming the multi-layered conductive coating can minimize the use amount of cerium and lanthanum to less than 2.5 mol% required in the PCT publication No. WO00/18189, and can maintain the stability of the conductive coating while performing a high-temperature heating function. The movement conditions of the spray head are set, and the speed limit is lower than 1000mm per second. By means of the coating system on the ceramic glass and the specified spray treatment conditions, the heating element of the present application can achieve stable and reliable performance for practical high temperature heating functions up to about 600 ℃. The heating element of the present application may also withstand 2500 life test cycles, with a heating time of 40 minutes per cycle.

It can be determined that the spray parameters can affect the characteristics of the heating element and can set optimal conditions. Tables 1, 2 and 3 below provide relevant examples for coating areas of 150mm x 150mm, where the variables are the effective resistance and the rated power (220V) of the heating element 10.

Table 1 shows the spray head movement speed of 750mms over 2, 6, 10 and 12 spray strokes^-1And the effective resistance and rated power of the heating element manufactured under the condition that the spraying pressure is 0.5 MPa.

Spray passage	2	6	10	12
					Resistor (ohm)	300	72	38	29
Rated power (W) at 220V	161	672	1273	1668

TABLE 1

Table 2 shows the variation of the effective resistance and the rated power of the heating element manufactured under the conditions of different moving speeds of the nozzle and the spraying pressure of 0.625 MPa. At a nozzle speed of 1000mm per second, the formation of the coating becomes uneven, and the heating performance thereof is unstable.

Nozzle speed (mm/s)	250	750	1000
				Resistor (ohm)	147	66	Unevenness of
Rated power (W) at 220V	329	733	-

TABLE 2

Table 3 shows the change in effective resistance and power output of the heating elements manufactured at different temperature ranges. At higher temperatures, on the order of 700 c to 750 c, lower resistance and therefore higher power output can be achieved.

Degree of Warm coating (. degree. C.)	650-700	700-750
			Resistor (ohm)	85	75
Rated power (W) at 220V	569	645

TABLE 3

The multi-layered nano-thickness coating disclosed in the present application has the following characteristics: the coating material can be deposited in an open air environment by a low cost spray process. This multi-layered nano-thickness coating system allows the heating element of the heating device to maintain a stable structure and high electrical conductivity, and thus have consistent electrical resistance and heating performance at high temperatures, even for long periods of use.

To achieve the above results, the specific selection of the composition and properties of the matrix and dopant coating materials, the process conditions for spray pyrolysis of the coated substrate surface (including temperature, movement of the spray head, nozzle design and spray pressure) requires optimum atomization of the spray material solution and deposition on the substrate surface. A multi-layer coating of nanometer thickness with high conductivity can improve the coating stability and minimize the risk of crack formation.

By using the coating compositions and processes described herein, low and high temperature/power output heating of electrical appliances including, but not limited to, electronic cooktops, electronic hot plates (laboratory hot plates), towel and clothing heating racks, electric heaters, defrosters, and warmers can be achieved.

As for the features of the nano-thickness heating element, a compact heating device such as the heating plate 70 without the conventional heating coil as shown in fig. 6 has been developed to have a thickness of less than or equal to 30 mm. The heating element is disposed on the bottom surface of the heating zone 72. The heating zone 72 may be made of ceramic glass. A temperature monitoring and control system is integrated with the heating element. Using a heating element with an effective resistance of about 50 ohms, heating 1 liter of water from 25 ℃ to 95 ℃ requires about 0.1 kilowatt-hour of energy, with an efficiency increase of about 85%.

To prevent overheating of the shell 74 and the unheated area 76 of the heater plate 70, a separate air plenum 82 as shown in FIGS. 7 and 8 may be provided in the heater plate 70. The divided duct chamber 82 defines an upper hot air duct 84 and a lower cold air duct 86. The upper hot air duct 84 is adjacent to the bottom surface of the heating zone 72 where the heating element is located. The fan 88 is used to blow hot air out of the heating device 70 through the upper hot air duct 84 as indicated by the arrows in the figure.

By using a separate air duct chamber 82, hot air and cold air are isolated in the heating plate 70. The airflow generated by the fan 88 can blow the hot air out of the upper hot air duct 84 and effectively remove the excess heat, lowering the temperature inside the heating plate 70 and the housing 74. By using a separate air duct chamber 82, the temperature can be reduced by 15 ℃ so that the temperature of the shell 74 and the unheated area 76 of the heating plate 70 is below 40 ℃, which would otherwise not be practical for use with the heating plate 70 using the nano-thickness heating elements of the present application.

The nano-thick multilayer coatings disclosed herein can be applied to other substrate materials including, but not limited to, ceramic tiles and thick glass sheets for roadway and roof defrosting, as well as wall, floor, and winter house heating, clothing and shoe heating. As shown in fig. 9, multiple layers of nano-thickness conductive coating 102 can be combined with tile 100 by a controlled spray process as previously described. A pair of electrodes 104 may also be formed by the processes described herein. On a heating element having a coated area of 150mm x 150mm, an effective resistance of about 2000 ohms can be achieved and a power output of about 25W is provided.

The nano-thickness multilayer coatings disclosed herein are applicable to the automotive industry including, but not limited to, engine heating for easy start-up in winter, heating and defrosting of dashboards, mirrors and windshields.

The nano-thickness multilayer coatings disclosed herein may also be applied in the aerospace industry, including but not limited to heating and defrosting of aircraft wings and cabins during winter.

The coating system of the present application can be integrated into ac, dc power supplies and/or solar energy systems for heat generating functions. Conventional heating elements typically have a high electrical resistance and therefore are powered by a dc power source, with low current, and do not produce sufficient consistent energy throughout the heating and cooking zones. By the controlled spray treatment, the conductivity of the heating film can be improved and the resistance can be reduced to 10 ohm or less. By using a direct current power supply and/or an integrated solar power supply, sufficient heat can be generated to perform the actual heating function. By using a 24V dc power supply, the heating element described herein can reach a temperature of 150 ℃ in 2 minutes and generate enough heat to perform the heating, cooking and warming functions. By using a 12V dc power supply, a temperature of 150 ℃ can be reached within 8 minutes.

For a heating device powered by an ac power source, rapid and efficient heating to temperatures up to 600 c is possible with low power consumption. Heating devices that may be used include, but are not limited to, stoves, heating plates, heaters, and defrosting and warming devices. Due to high energy efficiency, the saved electric energy consumption is nearly 30%, and the method also provides remarkable benefits for reducing pollution and global warming in the aspect of environment and simultaneously helps consumers to reduce electric charge expenditure.

In stove and hotplate applications, fast and efficient heating is comparable to and outperforms electromagnetic induction heating technology. The heating element of the present application does not generate electromagnetic radiation and dryness (induction heating uses electromagnetic induction) compared to induction heating, and has a lower material cost (induction heating uses an expensive copper coil). Further, the coating materials and methods disclosed herein are of low cost and have no limitations on cooking utensils (induction heating can only be achieved on high-grade stainless steel utensils). The heating device of the present application is light in weight and can be of a universal design.

While the invention has been described with reference to several embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the invention.

Claims (28)

1. A heating device comprising a heating element disposed on a substrate, wherein the heating element comprises an electrode and a multi-layer conductive coating having a nano-thickness, wherein the multi-layer conductive coating is disposed between the substrate and the electrode, the multi-layer conductive coating having a structure and composition that stabilizes the performance of the heating element under high temperature conditions; the electrode comprises a glass-ceramic sintered ink comprising a metal source selected from the group consisting of platinum, gold, silver, palladium, and copper; the heating element includes a multi-layer insulating coating having a nano-thickness disposed between the multi-layer conductive coating and the substrate.

2. The heating device of claim 1, wherein the multilayer conductive coating comprises an oxide coating comprising a metal source selected from the group consisting of tin, indium, cadmium, tungsten, titanium, and vanadium.

3. The heating device of claim 1, wherein the multi-layer insulating coating comprises sol-gel derived silica.

4. The heating device of claim 1, further comprising a surfactant disposed on the substrate, the surfactant comprising a perfluoroalkyl surfactant at a concentration of between 0.01 and 0.001% w/w, for use with dioctyl sodium sulfosuccinate at a concentration of between 0.1 and 0.01% w/w.

5. The heating device of claim 1, further comprising a temperature monitoring and control system integrated with the heating element of the heating device, the temperature monitoring and control system comprising an analog-to-digital converter for measuring temperature and a pulse width modulation driver for regulating power supply.

6. The heating device of claim 1, further comprising a compartment defining a first air path and a second air path, the first and second air paths being disposed proximate the substrate and the multilayer conductive coating, and a fan that blows hot air out of the heating device through one of the first and second air paths.

7. The heating device of claim 1, wherein each layer of the plurality of conductive coatings has a thickness of 50 to 70 nm.

8. A heating device comprising a heating element disposed on a substrate, wherein the heating element comprises an electrode and a multi-layer conductive coating having a nano-thickness, wherein the multi-layer conductive coating is disposed between the substrate and the electrode, the multi-layer conductive coating being produced by spray pyrolysis having a structure and composition that stabilizes the performance of the heating element under high temperature conditions; the spray pyrolysis is performed under a spray pressure of 0.4MPa to 0.7 MPa; the heating element includes a multi-layer insulating coating having a nano-thickness disposed between the multi-layer conductive coating and the substrate.

9. The heating device according to claim 8, wherein the spray pyrolysis is performed at a temperature of 650 ℃ to 750 ℃.

10. The heating device of claim 8, wherein the spray pyrolysis is performed at a jet velocity of less than 1000 mm/s.

11. The heating device according to claim 8, characterized in that the spray pyrolysis is performed by alternating spray paths in directions of 90 degrees to each other.

12. The heating device of claim 8, wherein the electrode is disposed on the multilayer conductive coating by screen printing.

13. The heating apparatus as claimed in claim 8, wherein the electrode is formed by screen printing ink and baking at 700 ℃ for 5 minutes.

14. The heating device according to claim 8, wherein the plurality of insulating coatings are disposed on the substrate by dip coating using tetraethoxysilane as a base precursor, and each layer of the plurality of insulating coatings is hydrolyzed, dried, and fired at 500 ℃.

15. The heating device of claim 8, further comprising a temperature monitoring and control system integrated with the heating element of the heating device, the temperature monitoring and control system comprising an analog-to-digital converter for measuring temperature and a pulse width modulation driver for regulating power supply.

16. The heating device of claim 8, further comprising a compartment defining a first air path and a second air path, the first and second air paths being disposed proximate the substrate and the multilayer conductive coating, and a fan that blows hot air out of the heating device through one of the first and second air paths.

17. A method of making a heating element for a heating device, comprising the steps of:

arranging a substrate;

generating a multilayer conductive coating by spray pyrolysis; and

disposing an electrode on the conductive coating;

the electrode comprises a glass-ceramic sintered ink comprising a metal source selected from the group consisting of platinum, gold, silver, palladium, and copper; further comprising: a multi-layer insulating coating having a thickness of nanometers is disposed on the substrate.

18. The method of manufacturing a heating element of a heating apparatus according to claim 17, wherein the spray pyrolysis is performed at a temperature of 650 ℃ to 750 ℃.

19. The method of manufacturing a heating element of a heating apparatus according to claim 17, wherein the spray pyrolysis is performed under a spray pressure of 0.4MPa to 0.7 MPa.

20. The method of claim 17, wherein the spray pyrolysis is performed at a jet velocity of less than 1000 mm/s.

21. Method for manufacturing a heating element of a heating device according to claim 17, characterized in that the spray pyrolysis is performed by alternating spray paths in directions of 90 degrees to each other.

22. The method of manufacturing a heating element of a heating apparatus according to claim 17, wherein the plurality of insulating coatings are disposed on the substrate by dip coating using tetraethoxysilane as a base precursor, and each layer of the plurality of insulating coatings is hydrolyzed, dried, and fired at 500 ℃.

23. A method of making a heating element for a heating device as claimed in claim 17, wherein the multi-layer conductive coating comprises an oxide coating comprising a metal source selected from tin, indium, cadmium, tungsten, titanium and vanadium.

24. A method of making a heating element for a heating device as claimed in claim 17, wherein the heating element comprises a multi-layer insulating coating having a nano-thickness disposed between the multi-layer conductive coating and the substrate.

25. A method of making a heating element for a heating device as claimed in claim 17, wherein the multi-layer insulating coating comprises sol-gel derived silica.

26. A method of making a heating element for a heating device as recited in claim 17, further comprising disposing a surfactant on the substrate, the surfactant comprising a perfluoroalkyl surfactant at a concentration of between 0.01 and 0.001% w/w, in combination with dioctyl sodium sulfosuccinate at a concentration of between 0.1 and 0.01% w/w.

27. A method of manufacturing a heating element of a heating device according to claim 17, wherein the electrode is provided on the multilayer conductive coating by screen printing.

28. A method of manufacturing a heating element of a heating apparatus according to claim 17, wherein the electrode is formed by screen-printing an ink and baking at 700 ℃ for 5 minutes.