JPS6259423B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a method for manufacturing a planar heating element in which electric heating elements are integrally embedded in an electrically insulating hollow layer, and which utilizes electric energy from heaters, cookers, dryers, etc. It provides a heat source. Conventional configurations and their problems Planar heating elements have recently come into the spotlight as heating elements that meet the needs of thinning devices and uniform heating. However, conventional planar heating elements have a structure in which the heater is wound around an insulating substrate such as mica, which has poor heat transfer to the heated object, and because the electric heating material is not sealed, there are problems with moisture resistance. , the conditions of use were limited. In addition, in recent years, there have been sheet heating elements made by forming expensive and high-melting point conductive patterns such as tungsten on raw sheets such as alumina, bonding the sheets together and sintering them, but these have excellent electrical properties. Although it can be used at high temperatures, the sintering temperature is high and there are problems with removing the electrodes. In addition, there are also devices in which a conductive pattern is formed between organic films using a paste such as carbon, and a heating element is constructed using methods such as lamination, but since the heat resistance of the resin film is low, these usually ℃, and could not be used above 200℃. There was also a problem with the lifespan. Furthermore, recently, a hollow layer has been formed on a metal substrate,
A heating element has been proposed in which a heating element is further covered with a hollow layer on the surface of the hollow layer, and the heating element is sandwiched between the hollow layers. This heating element has features such as being suitable for use in a medium to high temperature range of about 100 to 400°C because the hollow layer covering the heating element has excellent heat resistance, and is thin and expected to have a long life. However, in order to put this heating element into practical use, it is necessary to solve the problem of electrical insulation between the heating element and the metal substrate. For articles used at high temperatures, such as this type of heating element, the generally used hollow frit cannot be used as the hollow layer formed on the metal substrate from the viewpoint of electrical insulation resistance. The reason is that commonly used hollow frits contain 20 to 35% by weight of alkali metal oxides such as Na ₂ O, K ₂ O, and Li ₂ O, and therefore When used at high temperatures, the aforementioned alkaline component ions migrate, resulting in a significant deterioration of insulation resistance. In this sense, the hollow layer constituting the heating element must be formed of low-alkali frit or non-alkali frit with a low alkaline content (10% by weight or less). However, the above-mentioned low-alkali frit or non-alkali frit has a low content of alkaline components, which are excellent as easily soluble components.
Even if hollow firing is performed at a firing temperature of 0.degree. C., the hollow layer has poor fluidity and is formed in a so-called semi-fluid state, so voids inevitably exist in the hollow layer. Even if firing is performed at a higher temperature (900°C or higher) for the purpose of removing these voids, it is not very effective. The existence of these voids has an important meaning from the viewpoint of electrical properties, especially dielectric strength, and the larger the size and quantity of these voids, the more likely dielectric breakdown will occur. In other words, whether or not the voids can be reduced has a great deal to do with whether or not the aforementioned heating element can be commercialized and mass-produced. Purpose of the Invention The present invention solves the problem of voids existing in the hollow layer, especially in the hollow layer between the metal substrate and the heating element, in a heating element in which the heating element is embedded in the hollow layer as described above, and improves electrical characteristics. In particular, the purpose is to improve the dielectric strength and provide a heating element suitable for reliability and mass production. Structure of the Invention The present invention provides a first hollow layer formed on the surface of a metal substrate by firing in a non-oxidizing atmosphere, and then a heating element is covered with a second hollow layer on the surface of the hollow layer. It is characterized by being combined. DESCRIPTION OF EMBODIMENTS FIG. 1 shows the basic structure of a heating element according to the present invention. 1 is a metal plate with a first plate on both sides or one side.
An insulating hollow layer 2 is formed. Reference numeral 3 denotes a thin strip-shaped metal heating element, which is installed on the surface of the hollow layer 2 and further covered with a second hollow layer 4, thereby creating a structure in which the heating element 3 is sandwiched between the hollow layers 2 and 4. . Each component will be explained below. (1) Metal base material The metal base material of the hollow substrate that constitutes the heating element is aluminum, aluminum die-cast, cast iron, aluminized steel, low carbon steel, hollow steel plate, or stainless steel plate, depending on the selection. The length is determined based on the usage conditions, usage temperature, shape of the base material, and workability, and pretreatment is performed as necessary. The following explanation will focus on steel plates for hollow holes. (2) Electronic heating element Electric heating elements are basically ribbon-shaped. It is necessary to completely cover the surface of the electric heating element with the hollow layer 4. For example, if a coil-shaped or thick band-shaped heating element is used, the thickness of the hollow layer 4 becomes correspondingly large. As a result, the adhesion of the hollow layer is extremely reduced, and the hollow layer is easily peeled off by an external shock, exposing the electric heating element. The thickness of the heating element ribbon is suitably 10 to 200 μm, preferably 30 to 100 μm. In addition to the usual methods of cold rolling and hot rolling, metal can be made into a thin ribbon using an ultra-quenching method. Etching and press working are suitable methods for forming a thin metal strip into a desired pattern. FIG. 2 shows an example of a patterned electric heating element. The film thickness and pattern shape of the electric heating element are determined in consideration of the rated power, heating area, temperature distribution, etc. Various electric heating materials can be used for the electric heating element, but the specific resistance and coefficient of thermal expansion, which are factors that determine the shape of the heating element (pattern width, length, thickness), etc., must be at appropriate values. has
In addition, a material with excellent adhesion to the hollow layer and workability is selected. From these points of view, 20
Ferritic stainless steel having a specific resistance of 60 μΩ·cm at ℃ and a thermal expansion coefficient of 104×10 ⁻⁷ deg ⁻¹ at 100° C. is most preferable. (3) Insulating hollow layer As a factor that determines the electrical properties of the heating element, the electrical properties (insulation resistance, dielectric strength voltage, etc.) of the insulating hollow layer interposed between the heating element and the metal substrate are important points. In addition to the thickness of the hollow layer, the volume resistivity of the glass frit is an important factor that determines the insulation resistance. It is expressed by the following formula. R _v = ρ _v・d/A (1) R _v : Insulation resistance ρ _v : Volume resistivity A : Heating element area d : Thickness of the hollow layer Here, the thickness of the hollow layer is determined from the viewpoint of hollow adhesion. It is determined from 100 to 500 at most.
It is about μm. From this point of view, in order to improve the insulation resistance of the insulating hollow layer, it is necessary to construct the insulating hollow layer with a glass frit having excellent volume resistivity, and the selection of the glass frit becomes important. Next, a specific example will be explained. First, as the frit for forming the hollow layer, low-alkali frit XG-4 manufactured by Nippon Frit Co., Ltd. with an alkali component of 5% by weight was used. This frit was made into the mill composition shown in Table 1,
Milling was performed using a ball mill for 2 hours to obtain slips. Pretreated size of these slips: 100×
Approximately 150μm with a spray gun on a 100mm hollow steel plate
After drying, it was baked at a predetermined temperature for 5 minutes to form an insulating hollow layer. Furthermore, on this hollow layer, stainless steel with the pattern shown in Figure 2 is applied.
A heating element made of SUS430 (thickness: 60 μm) was installed, and on top of it, the hollow strip used for the insulating hollow layer was applied to a thickness of about 150 μm using a spray gun. After drying, it was baked at a specified temperature for 5 minutes. The heating element was covered with a hollow layer.

[Table] At this time, various changes were made to the enameled firing atmosphere,
The dielectric strength voltage between the heating element and the steel plate was measured. The results are shown in Table 2. Here, the dielectric strength voltage was measured according to the dielectric strength test method specified in the Electrical Appliance and Material Control Law.

[Table] The firing in an air atmosphere in Table 2 is performed using a normal batch furnace, and the firing in a non-oxidizing atmosphere of the present invention is performed in a firing furnace in which nitrogen, argon, hydrogen, etc. are flowed. It was fired in As is clear from Table 2, the dielectric strength of conventional planar heating elements fired in an oxidizing atmosphere is as low as 1kV or less, and those that have been fired at a higher firing temperature to remove voids in the hollow layer are not as effective. It showed no effect. On the other hand, the heating element of the present invention fired in a non-oxidizing atmosphere had significantly improved dielectric strength compared to the heating element fired in an oxidizing atmosphere commonly used in the past. In addition, in the above example, the firing conditions were the same as those for the first and second hollow layers, but for Nos. 3 to 8, even if the second hollow layer was fired in air, the dielectric strength characteristics remained the same. Indicated. In order to analyze the reason for the improved dielectric strength, we took cross-sectional photographs of them. The results are illustrated in Figure 3. Figure 3a is a cross section of a heating element fired in an oxidizing atmosphere, and Figure 3b is a cross section of the heating element fired in a non-oxidizing atmosphere. As is clear from FIG. 3, the size and number of voids 5 in the hollow layer are significantly different, and both the size and number of voids in the hollow layer fired in a conventional oxidizing atmosphere are large. Recognize. As the non-oxidizing atmosphere, argon, helium, nitrogen, hydrogen, vacuum, etc. can be considered, but nitrogen is preferable from the viewpoint of cost, mass productivity, and safety. The causes of voids when fired in an oxidizing atmosphere are (1) generation of CO ₂ gas due to oxidation of C in the steel sheet, and (2) inhibition of softening and flow of glass particles due to thermal oxidation of the steel sheet during the firing process. can be mentioned. Regarding factor 1, since low alkali glass is used, the softening fluidity is poor, and the generated CO ₂ gas remains in the hollow layer. The void generation mechanism described in (2) above is illustrated in FIG. In an oxidizing atmosphere, the growth of the oxide layer 7 of the steel sheet begins at the same time as the glass particles 6 begin to soften and flow during firing. At this time, iron oxides begin to dissolve and diffuse into the glass. When iron oxide dissolves in glass, its softening point rises, making it difficult to melt at a certain temperature, and voids remain mixed in the hollow layer in a semi-sintered state. This is the reason why if the firing temperature is further increased in order to remove these voids, the iron oxide layer will only increase, making it more difficult to melt and not being as effective. When firing is performed in a non-oxidizing atmosphere as in the present invention, the formation of an oxide layer on the steel sheet is eliminated, and as a result, the glass frit softens and flows at a predetermined temperature without increasing the softening temperature, thereby preventing the inclusion of voids. It can be avoided. For the above reasons, it is thought that the present invention reduces the size and amount of voids in the hollow layer, and improves the dielectric strength voltage, compared to the conventional method. In addition to improving the dielectric strength mentioned above, the method of the present invention does not cause thermal oxidation of the lead extraction part of the heating element, and has excellent effects on spot welding properties and life characteristics. However, in the method of the present invention, if the second hollow layer is also fired in a non-oxidizing atmosphere, single-sided hollowing becomes possible. An example thereof is shown in FIG. FIG. 5a shows a configuration according to the conventional method, and FIG. 5b shows a configuration according to the method of the present invention. That is, in the conventional method, double-sided hollowing is essential from the viewpoint of thermal oxidation and corrosion, but in the method of the present invention, single-sided hollowing is possible because the base material is not subjected to thermal oxidation during firing. This makes it possible to reduce the weight. Effects of the Invention As described above, according to the present invention, the electrical characteristics,
In particular, the dielectric strength can be significantly improved. Further, it is possible to prevent thermal oxidation of the lead portion of the heating element, improve the spot weldability and lifespan of the lead wire, and also enable single-sided hollowing, which was previously impossible. Furthermore, if the heating element of the present invention is replaced with an infrared lamp for a tower kotatsu, not only can the heater part be made much thinner, but also health heating can be achieved by emitting high-quality far infrared rays from the hollow layer. . Furthermore, when used in a hot warmer, radiant heat transfer is performed, so less heat insulating material can be used at the bottom, making it possible to reduce weight and cost.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a main part showing the basic structure of a heating element according to the present invention, FIG. 2 is a plan view showing an example of a pattern of a heating element, FIG. Figure 4 is a diagram explaining the void generation mechanism.
FIG. 5 is a sectional view of a main part showing a comparison of the basic configurations of heating elements. 1... Metal substrate, 2... First hollow layer, 3...
...Heating element, 4...Second hollow layer.

Claims (1)

[Scope of Claims] 1. A method comprising the steps of: forming a first hollow layer on a metal substrate; and covering and bonding an electric heating element with a second hollow layer on the hollow layer; A method for manufacturing a heating element, characterized in that the first hollow layer is fired in a non-oxidizing atmosphere. 2. The method for producing a heating element according to claim 1, wherein the non-oxidizing atmosphere is nitrogen, argon, helium, hydrogen or vacuum. 3. The method of manufacturing a heating element according to claim 1, wherein the second hollow layer is fired in a non-oxidizing atmosphere.