JPH046079B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a planar heating element in which an electric heating element is integrally embedded in an electrically insulating hollow layer.
This heating element is used as a heat source using electrical energy in heaters, cookers, drying equipment, and the like. Conventional Structure and Problems Conventionally, sheathed heaters, quartz tube heaters, planar heating elements, and the like are known as heating elements that utilize electrical energy. Although sheathed heaters and quartz tube heaters are used for various purposes, they are not suitable for uniformly heating objects to be heated. On the other hand, 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. Yes, the conditions of use were limited. Also, in recent years,
There is a planar heating element in which a conductive pattern is formed on a raw sheet such as alumina using an expensive and high melting point conductive paste such as tungsten, and the sheets are bonded together and sintered. Although it is excellent and can be used at high temperatures, the sintering temperature is high and there are problems with removing the electrodes.
Moreover, these are expensive, often have large variations in resistance value, and have problems in manufacturing workability and productivity. In addition, there are heating elements constructed by laminating or other methods in which a conductive pattern is formed between organic films using a paste such as carbon, but these heating elements cannot be used at temperatures above 200°C. There was also a problem with longevity. Furthermore, recently, a heating element was installed on the surface of the hollow layer, and this heating element was further covered with a hollow layer.
A planar heating element in which a so-called heating element is sandwiched with a hollow layer has been proposed. This heating element has a hollow layer with excellent heat resistance and relatively good electrical insulation, so it is suitable for use in a medium to high temperature range of about 100 to 400 degrees Celsius, and is thin and can be expected to have a long life. It has the characteristics of However, the above structure has problems with the adhesion between the hollow layers, and furthermore, the insulation between the heat generating element and the metal base material is poor, so that it has not been put into practical use. Purpose of the Invention As described above, the present invention solves the problem of a planar heating element having a structure in which a heating element is sandwiched between hollow layers, and achieves a practical level of electrical insulation resistance between a metal substrate and an electric heating element. The object of the present invention is to provide a planar heating element with excellent durability and strength. Structure of the Invention The planar heating element of the present invention includes a metal substrate on which a first insulating hollow layer is formed, and an electric heating element covered and bonded to the hollow layer by a second insulating hollow layer. When the softening points of the glass frits constituting the first and second insulating hollow layers are respectively T ₁ °C and T ₂ °C,
It is characterized in that the glass frit is selected so as to satisfy the formula 0<T ₂ −T ₁ 50. DESCRIPTION OF EMBODIMENTS FIG. 1 shows the basic structure of a planar heating element according to the present invention. Reference numeral 1 denotes a metal substrate on which a first hollow layer 2 (hereinafter referred to as hollow layer) is formed on both or one side. 3 is a heating element made of a metal ribbon. This heating element 3 is covered with a second hollow layer 4 (hereinafter referred to as hollow layer), and is fixed to the hollow layer by the hollow layer. Each component will be explained in detail below. (1) Metal substrate The metal base material of the hollow substrate that constitutes the planar heating element is aluminum, aluminum die-casting, cast iron, aluminized steel, low carbon steel, steel plate for hollow hollow, or stainless steel plate. The method 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) Electric heating element The electric heating element applicable to the present invention is basically a ribbon-shaped element. It is necessary to completely cover the electric heating element with the hollow layer. For example, if a coil-shaped or thick band-shaped heating element is used, the thickness of the hollow layer 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 ribbon used in the present invention is suitably 10 to 200 μm, preferably 30 to 100 μm.
It is difficult to process thin strips of 10 μm or less into thin strips, and when manufacturing planar heating elements, the thin strips may tear, bend, or bend, resulting in extremely poor workability. . Moreover, if the thickness is 200 μm or more, in addition to the above-mentioned reasons, if a heat cycle is applied to the planar heating element, cracks may occur in the hollow layer, which is not preferable. In addition to the usual cold rolling and hot rolling methods, the 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. The etching method can be applied when the production quantity is small, and the press processing method can be applied for mass production. FIG. 2 shows an example of a patterned electric heating element. The shape of the electric heating element is
The film thickness and pattern shape can be arbitrarily determined by considering the rated power, heat generating area, temperature distribution, etc. (3) Materials for Electric Heating Element Table 1 shows the physical properties and properties of the various heat generating ribbon materials studied by the present inventors as sheet heating elements.

【table】

[Table] The specific resistance in the table is the measure that determines the shape of the heating element (pattern length, pattern width, ribbon thickness). Comparing the examples of iron and Inconel in the table, the resistivity of the latter is about 10 times that of the former. In other words, assuming the thickness of the ribbon is constant, iron has a pattern length of 10% compared to Inconel.
It is necessary to double the pattern width or reduce the pattern width to 1/10. If the pattern width and pattern length are constant, the same wattage cannot be obtained with iron unless the thickness is 1/10 that of Inconel. In other words, a material with a small resistivity value has a more complex shape but a thinner thickness. This greatly affects processability and workability as a planar heat generating material. Focusing on this point, the workability and processability of the planar heat generating material in the table are indicated by ○, △, and × according to the yield during pattern formation of the planar heat generating material and during installation on the hollow surface. ○ means the yield is 80% or more, △ means 30-80%,
× is 30% or less. From this result, Nos. 1 to 4 in the table have poor yields and are undesirable materials. The adhesion with the hollow layer in the table refers to the adhesion between the planar heating element and the hollow layer, and in particular,
During actual use, the lead wire may be pulled, and at that time, if the adhesion between the sheet heating element and the hollow layer is poor, the sheet heating element may easily peel off from the hollow surface, which may affect the adhesion between the two. Strength and weakness have a big impact on the product. Here, the strength of adhesion was determined by making a sample in which the heating element was covered with a hollow layer using the heating element pattern shown in Figure 2, and joining the terminal portions with spring clamps.
The weight of the spring force when the heating element peels off from the hollow layer when pulled in the vertical direction is evaluated as a measure. In the table, ○ means 3 kg or more, Δ means 3 to 1 kg, and × means 1 kg or less. This result shows that materials Nos. 1 to 3 have strong bonding strength with the hollow layer. One of the conditions for bonding the metal material and the hollow layer is that the adhesion is said to be poor unless it corrodes through thermal oxidation or reaction with the hollow strip (usually alkaline). From this point of view, the results that Nos. 1 to 3 adhere well to the hollow layer and Nos. 6 to 9 have poor adhesion seem to be appropriate. On the other hand, the stainless steel No. 5 varies greatly depending on the type of hollow layer, ranging from ○ to ×. This is due to the combination of hollow frits, the details of which will be described later. From the above results, it is preferable that the material of the planar heating element of the present invention is ferritic stainless steel. (4) Hollow layer

【table】

[Table] Table 3 Slit 100 parts by weight Clay (No. 9) 5 Sodium nitrite 0.1 Water 50 Table 2 shows the product numbers of hollow frits used by the inventors (all products from Nippon Fritt Co., Ltd.) ),
The softening temperature and standard firing temperature are shown. These frits were milled with the mill composition shown in Table 3 and milled in a ball mill for 2 hours to obtain sample slips. These slips were applied to a pretreated steel plate for hollow holes to a thickness of approximately 150 μm using a spray gun, and after drying, they were fired at a predetermined temperature for 5 minutes.
A hollow layer was formed. Furthermore, on this hollow layer, stainless steel with the pattern shown in Figure 2 is applied.
A heating element made of SUS430 (thickness: 60μm) is installed,
On top of that, a hollow strip was further applied to a thickness of about 150 μm using a spray gun, and after drying, it was baked at a predetermined temperature for 5 minutes to form a hollow layer. The experimental assignments for the hollow layer were as shown in Table 4.

【table】

[Table] Column A in Table 4 shows the frit No. (No. in Table 2) used in the hollow layer, and column B shows the difference in softening point T ₂ - T ₁ of the frit used in the hollow layer.
Column C shows the adhesion evaluated by the adhesion test method shown in Table 1 above. Column 2 shows the dielectric strength voltage between the metal substrate and the heating element. The dielectric strength voltage was measured according to the dielectric strength test method stipulated in the Electrical Appliance and Materials Control Law, and those with a dielectric strength voltage of 1.5 KV or more were marked with ○, and those with a dielectric strength of 1.5 KV or more were marked with an x. The column shows the results of visual observation of the condition of the hollow end.
Those with sink marks on the edges are marked with ×, and those without are marked with ○. From the results in Table 4, the adhesion is determined by the difference in softening point of the glass frit constituting the hollow layer by -30
It can be seen that if the temperature is less than 0.degree. C., the adhesion between the heating element and the hollow layer or the hollow layer deteriorates, which is not preferable. Furthermore, it is found that in terms of electrical insulation, those having a softening point difference of 0° C. or less are not preferable. The reason for this is presumed to be due to the bubble structure generated in the hollow layer. FIG. 4 shows a schematic view of a cross-section of the hollow layer observed under a microscope. Although FIG. 4a is a cross section of only the hollow layer, it has minute bubbles 5. The main causes of these bubbles are hydrogen generated by the reaction between the metal and moisture in the slip during firing, and carbon dioxide gas generated by the oxidation of carbon in the iron. That is, the hollow layer cannot pass through without the presence of bubbles. These bubbles greatly affect the dielectric strength. Figures 4b and 4c show cross-sectional structures under conditions g and i in Table 4. That is, it can be seen that those with poor dielectric strength voltage contain large bubbles in the hollow layer below the heating element, whereas those with good dielectric strength voltage contain only small bubbles. The reason for this will be explained below. As shown in Table 2, the softening temperature of glass frit is closely related to the standard firing temperature. As shown in Fig. 4b and c, in so-called double firing, in which a hollow layer is formed by firing, a metal heating element is installed, and the hollow layer is fired. is lower than the firing temperature (softening temperature) of the layer (Fig. 4b) When the layer is fired, the layer becomes a semi-fluid state (the layer has high glass viscosity), and the bubbles in the layer are not removed sufficiently, causing further heat generation. It is thought that the bubbles grow further and become larger at the same time as the element heats up and the bubbles concentrate at the bottom of the heating element.On the other hand, the firing temperature (softening temperature) of the layer is higher than the firing temperature (softening temperature) of the layer. If the layer is high (Fig. 4c), when firing the layer, the layer will be lower than in Fig. 4b.
The glass becomes more fluid (the glass viscosity of the layer is lower), and the bubbles in the layer are sufficiently removed. In other words, it has been found that in the method of firing the layers individually through a heating element, it is necessary to make the layers sufficiently free of bubbles from the viewpoint of dielectric strength. In order to meet the above requirements, it is also possible to consider a method in which, for example, the same frit is used for each layer, and the firing temperature of only the (1) layer is increased, or the firing time of the (2) layer is extremely lengthened. The present inventors also considered this point. In the case of (1), the number of bubbles present in the layer is certainly reduced, but the flow of the glass in the layer increases and the end of the heating element is exposed, making it impossible to use it as an electrical appliance. In the case of (2) as well, the number of bubbles in the layer tended to decrease, but on the contrary, the pressure resistance deteriorated significantly. The reason is that if the firing time is extremely long, the base metal iron will diffuse into the hollow layer.
This is thought to be due to the apparent thinning of the effective hole thickness and deterioration of insulation properties. From the above points, in terms of dielectric strength, it is necessary that there be a difference in softening point between layers, and that difference is 50
If the temperature exceeds ℃, the withstand voltage will deteriorate. The reason for this is presumed to be the aforementioned diffusion of iron. At the same time, sink marks also begin to occur at the hollow end. That is, the softening point of the frit used for the layer must satisfy the formula 0<T ₂ -T ₁ ≦50. Effects of the Invention As described above, according to the present invention, a hollow-covered planar heating element having practical electrical insulation properties and durable strength can be obtained. If the sheet 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. Become. Furthermore, when used in hot water heaters, radiant heat transfer is performed, so less heat insulating material is needed at the bottom, making it possible to reduce weight and cost.

[Brief explanation of drawings]

FIG. 1 is a sectional view of the main parts showing the structure of the sheet heating element of the present invention, FIG. 2 is a plan view showing an example of the structure of the heating element, and FIG. 3 is a schematic diagram showing the cross section of the main parts of the heating element. It is a diagram. 1... Metal substrate, 2... First hollow layer, 3...
...Heating element, 4...Second hollow layer.

Claims (1)

[Claims] 1. A metal substrate on which a first insulating hollow layer is formed;
A planar heating element having an electric heating element covered and bonded with a second insulating hollow layer on the hollow layer, wherein the glass frit constituting the first and second insulating hollow layers is softened. each point
A planar heating element characterized by having a relationship that satisfies the formula 0< _T2 - _T1 ≦50 when _T1C and _T2C . 2. The planar heating element according to claim 1, wherein the electric heating element is made of ferritic stainless steel.