JPS6366036B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a planar heating element. Many years have passed since the development of a fixed-resistance sheet heating element mainly made of carbon, and since then self-temperature control types have been added and are rapidly becoming commonplace. Its features include a fast temperature rise rate after energization and low power consumption, so it is used in industry and homes. This type of sheet heating element had the excellent features mentioned above and was expected to become popular, but the film-forming technology was not sufficient, resulting in a number of burnout accidents and fire accidents. Planar heating elements, regardless of the self-temperature control type, have a uniform temperature distribution. It is desired that the temperature range for use is wide, and that it can be used for a long time at high temperatures of 100℃ or higher, but the current sheet heating elements use synthetic resin base materials, so they can be used at temperatures of 100℃ or higher, especially 150℃. There are almost no heating elements that can be used for long periods of time at temperatures above this level, which is one of the reasons for inhibiting the development of planar heating elements. An example of a conventional sheet heating element is explained with reference to FIG. 1. After screen-printing a commercially available silver paste on the surface of a polyester substrate 1 with a thickness of about 250 μm using an automatic printing machine, it is heated to a temperature of about 180° C. in a conveyor furnace.
After baking for about 10 minutes to form a predetermined silver electrode 2, a resistance paste for a heating element prepared as follows is screen-printed on top of it using an automatic printing machine, and then baked in a conveyor furnace at a temperature of about 180°C. The heating resistor film (layer) 3 having the required thickness is formed by firing for about 10 minutes. The above resistance paste for heating elements includes, for example, about 224 g of ethylene-vinyl acetate copolymer, about 176 g of graphite with an average particle size of about 2μ, about 45 g of alumina powder, about 45 g of flame retardant, and about antimony oxide.
22.5g, anti-aging agent approx. 45g, tetralin approx. 1800g
was added to a treatment tank equipped with an electric stirrer, kept at a temperature of about 100°C while stirring for about 1 hour, and then cooled with water. The heating resistor film formed as described above is screen-printed with a solvent paste containing approximately 70% thermosetting phenolic resin and approximately 30% alumina as main components on its surface to prevent deterioration over time. Place in a furnace and bake at a temperature of about 180°C for about 10 minutes to form a phenolic resin surface coating film 4 of the required thickness.
A polyester substrate 6 with a thickness of about 150 μm is bonded onto this coating film via a heat-resistant adhesive layer 5 using a hot roller or the like to form a heating element.
The silver electrode is formed by connecting a silver-plated brass terminal 7 and a lead wire 8. In the planar heating element formed as described above, if the heating resistor film 3 is formed non-uniformly, local overheating occurs in a part of the film with an abnormally low resistance value, and heat generation occurs in that part. The resistor film melts, and then the opposing polyester substrate melts and thermally decomposes, eventually catching fire and causing a burnout accident. Such accidents are caused by the use of synthetic resin base materials with relatively low melting points of 350°C or less and flammability as constituent materials of the sheet heating elements, and the non-uniformity of the heating element resistor films mentioned above. The occurrence of accidents due to localized overheating caused by this is further exacerbated. In view of the above-mentioned drawbacks of the conventional planar heating element, the inventors have arrived at the present invention as a result of various studies. In the present invention, a base material having an electrically insulating coating film on the surface of a metal foil or plate is used, and a special electrically insulating coating film is provided on the heating resistor film. In addition, the sheet heating element is formed using a resistance paste for heating elements prepared using a special method, and has an extremely homogeneous heating resistor film throughout, and has excellent heat resistance, exceeding 200℃.
Even when used continuously for long periods of time at 250℃, there is no occurrence of accidents such as melting or burnout due to localized overheating, allowing for long-term, safe and efficient use. Hereinafter, the present invention will be described with reference to an embodiment. A silver electrode 12 is provided on the surface of an electrically insulating base material 11, and a heat generating resistor film (layer) is formed by applying a heat generating element resistance paste or the like on the upper side of this electrode. ) 13 are provided,
A heating element is formed by providing an insulating coating film 14 on the upper surface of this heating resistor film, and a terminal 17 is attached to the electrode.
If necessary, an insulating coating film 15 is further provided on the entire surface of the heating element to form a planar heating element. In this planar heating element, the base material 1 is made of aluminum, copper, brass, silver,
Organometallic compounds such as organosilsesquioxane, ethyl silicate, polytitanocarbosilane, etc. are applied to the surface of a foil with a thickness of approximately 1 to 500 μm or a plate of approximately 0.5 to 10 mm in thickness made of metal such as iron or stainless steel. After being immersed in the containing liquid or applying the containing liquid by an appropriate method, it is fired to the decomposition temperature or other required temperature to form a ceramic insulating coating film 11a for use. Various organometallic compounds other than those mentioned above can also be selected and used. The insulating coating films 14 and 15 are also formed by applying a solvent solution or other liquid containing the same metal-organic compound as the insulating coating and then baking in the same manner, and are heat-resistant, chemical-resistant, and durable insulators. A coating is obtained. The silver electrode 12 can be formed by screen-printing a commercially available silver-based conductive paste or the like in a predetermined area and then firing. The heating resistor film 13 is made of conductive material powder such as carbon or metal powder, alumina, antimony oxide or other ceramic material powder, synthetic resin binder, flame retardant, anti-aging agent, etc. as in the conventional method. Add the required amount of each to a treatment tank with a stirrer together with the required amount of tetralin or other solvent containing or not containing a surfactant, and raise the temperature to approximately 100℃ while stirring.
It can be formed using a resistance paste for a heating element prepared by keeping it at a temperature for about 1 hour and then cooling it with water. There are also resistance pastes for heating elements prepared by the following special method. That is, a conductive material such as graphite, carbon black, or metal made into ultrafine particles with an average particle diameter of about 1 μ or less, preferably on the order of submicrons, and alumina, antimony oxide, etc., in a solvent such as xylene, carbitol, tetralin, or decalin. The required amounts of materials insoluble in the solvent such as ceramic materials, synthetic resin binders, flame retardants, anti-aging agents, and others were added to a treatment tank equipped with a stirrer, and the temperature was raised to about 100℃ while stirring.
It is prepared by maintaining it at a temperature of 0.degree. C. and treating it for a certain period of time, for example, about 1 hour, without applying ultrasonic waves or applying ultrasonic waves for an appropriate period of time, and then rapidly cooling it. The heat generating resistor paste prepared in this way has extremely good uniformity and stability, and the formed heat generating resistor film can be made homogeneous, thereby further preventing localized overheating. In the above case, if the materials added to the solvent are added as follows, a paste with even better uniformity and stability can be obtained. That is, a conductive material made into ultrafine particles and a ceramic material insoluble in the solvent are sequentially added to a solvent while stirring. After the addition, ultrasonic waves are applied to this as necessary, and then a binder, a flame retardant, It can be prepared by sequentially adding anti-aging agents and the like with stirring, applying ultrasonic waves for a certain period of time, and rapidly cooling. The applied ultrasonic waves may often be of a frequency commonly used for cleaning contaminated mechanical parts or other articles. Examples of the planar heating element of the present invention are shown below. For each example, a destructive test (500V, 30 minute load), surface temperature difference (100V, maximum temperature difference when measuring the surface temperature distribution after 30 minute energization), and estimated life (240V, 30 minute load),
(estimated from the change in characteristics after being energized for 180 days) were as shown in Table 1. Furthermore, the relationship between the thickness of the base material and the surface temperature difference (°C) for each example was as shown in FIG. Note that similar test results for the sheet heating element produced by the conventional method are also shown as a comparative example. Example 1 An aluminum foil having a thickness of 100 μm was anodized to form an alumina coating film on the surface, and then the coating film was subjected to a sealing treatment to obtain an electrically insulating base material. A commercially available silver paste was screen printed on a predetermined part of the surface of the base material using an automatic printing machine, and then baked at about 180°C for 10 minutes to provide a silver electrode. After screen-printing vinyl copolymer, graphite-based low resistance paste for 80℃ heating elements to a specified thickness using an automatic printing machine,
A heat-generating resistive film was formed by baking at ~182°C for 10 minutes.
Next, after attaching a terminal and a lead wire to the silver electrode, this was immersed in a 50% ethanol solution of organosilsesquioxane (trade name: glass resin).
After taking it out and air-drying it, it was fired for 30 minutes at a temperature of 178 to 182°C to obtain a planar heating element having a heat-resistant ceramic coating film on the entire surface. Example of blending raw materials for manufacturing resistance paste for heating elements Graphite powder (average particle size 2μ) 176g Alumina powder (average particle size 2μ) 45〃 Antimony oxide powder (average particle size 2μ) 22.5〃 Ethylene-vinyl acetate copolymer 224〃 Flame retardant 45〃 Anti-aging agent 45〃 Add the above blended raw materials to 1800 g of tetralin, heat to 100°C with stirring, mix for 1 hour, and cool with water. Example 2 As an electrically insulating base material, aluminum foil with a thickness of 200μ was immersed in a 50% organosilsesquioxane ethanol solution, then pulled out, air-dried, and baked at a temperature of 200°C for 30 minutes to coat its surface with insulation. A planar heating element was obtained in the same manner as in Example 1 except that a heating element provided with a coating was used. Example 3 An electrically insulating base material was used in which an insulating coating film was formed by spraying a 20% polytitanocarbosilane ethanol solution on the surface of a 300 μ thick aluminum foil and then baking it at a temperature of 250°C for 30 minutes. Example except that instead of organosilsesquioxane, it was immersed in a 50% alcohol solution of polytitanocarbosilane, air-dried, and then baked at a temperature of 250°C for 30 minutes to form an insulating coating film on the entire surface. A planar heating element was obtained in substantially the same manner as in Example 1. Example 4 An electrically insulating base material was used, in which a 50% alcohol solution of organosilsesquioxane was sprayed on the surface of a 400μ thick aluminum foil and an insulating coating was formed by baking at a temperature of 200±2°C for 30 minutes. And,
After soaking in a 50% alcohol solution of polytitanocarbosilane instead of organosilsesquioxane and air drying.
A planar heating element was obtained in substantially the same manner as in Example 1, except that it was fired at 250° C. for 30 minutes to form a ceramic coating film on the entire surface. Example 5 An aluminum substrate with a thickness of 200μ was immersed in a 50% alcohol solution of ethyl silicate, then air-dried.
A planar heating element was obtained in the same manner as in Example 4, except that an insulating base material on which an insulating coating film was formed by baking this at 200° C. for 30 minutes was used. Example 6 A planar heating element was obtained in the same manner as in Example 5 except that a colored aluminum substrate with a thickness of 600 μm was used. Example 7 Example 3 on the surface of 100μ thick aluminum foil
A planar heating element was obtained in substantially the same manner as in Example 3, except that an electrically insulating base material formed in the same manner as in Example 3 was used, and a resistance paste for a heating element manufactured by the following method was used. . Manufacturing example of resistance paste for heating elements Graphite ultrafine powder 176g Commercially available graphite with an average particle size of 5μ is ground in a ball mill. Ultrafine powder with an average particle size of 0.5μ Ultrafine alumina powder 45〃 (Average particle size 0.2μ) Antimony oxide Ultrafine powder 22.5〃 (Average particle size 0.5μ when crushed in a mortar) Ethylene-vinyl acetate copolymer 224〃 Flame retardant 45〃 Anti-aging agent 4.5〃 While stirring 1800g of tetralin and raising the temperature (100℃), add the above compounded raw materials The mixture was mixed with electric stirring at a temperature of 100°C for 1 hour, cooled with water while stirring, and left at room temperature for 12 hours to obtain the desired paste. Example 8 A planar heating element was obtained in substantially the same manner as in Example 7, except that colored aluminum with a thickness of 200 μm was used and the resistance paste for the heating element was manufactured in the following manner. Stir 1800g of tetralin and raise the temperature (100g
℃), ultrafine particles of graphite, alumina, and antimony oxide, as well as the required amounts of ethylene-vinyl acetate copolymer, flame retardant, and anti-aging agent were added one after another while stirring at 100℃ for 1 hour. Ultrasonic waves (30 kilohertz) were applied to this for 10 minutes, and the paste was rapidly cooled to obtain the desired paste. Example 9 Apply a 30% alcohol solution of organosilsesquioxane to the surface of a 300μ aluminum substrate,
A planar heating element was obtained in the same manner as in Example 8, except that an insulating base material on which an insulating coating film was formed by baking at 250° C. for 30 minutes after air drying was used. Example 10 Example 9 except that a 400μ aluminum substrate was used
A planar heating element was obtained in the same manner as above. Example 11 A planar heating element was obtained in the same manner as in Example 9 except that a 600μ aluminum substrate was used. Example 12 A planar heating element was obtained in the same manner as in Example 9 except that a 1000 μm aluminum substrate was used. 【table】

[Brief explanation of drawings]

The drawings show embodiments of the present invention; FIG. 1 is a schematic cross-sectional view of a conventional planar heating element, FIG. 2 is a schematic cross-sectional view of a planar heating element of the present invention, and FIG. FIG. 4 is a cross-sectional view similar to FIG. 2 showing a modification, and FIG. 4 is a diagram showing the relationship between the thickness of the base material and the difference in surface temperature. 11 is a base material, 11a is an insulating coating film, 12 is an electrode, 13 is a heating resistor film, 14 and 15 are insulating coating films, 17 is a terminal, and 18 is a lead wire.

Claims (1)

[Scope of Claims] 1. A planar heating element in which an electrode is provided on the surface of a metal foil or metal plate provided with an electrically insulating coating film, a heating resistor film is provided, and an electrically insulating coating film is formed on the top surface of the heating resistor film. The insulating coating film is a planar heating element formed by providing a coating film of an organometallic compound on the surface and then firing it. 2. A surface heating element in which an electrode is provided on the surface of an electrically insulating base material, a heating resistor film is provided, and an electrically insulating coating is formed on the surface of the electrically insulating base material, wherein the heating resistor film is formed by ultrafine conductive particles in a solvent. Resistance paste for heating elements is obtained by adding and mixing solvent-insoluble materials such as ceramic materials, synthetic resin binders and other compounded materials, and applying or not applying ultrasonic waves to the mixture. A sheet heating element formed by uniformly coating and firing. 3. A planar heating element in which an electrode is provided on the surface of a metal base material provided with an electrically insulating coating, a heating resistor film is provided, and an electrically insulating coating is formed on the upper surface of the heating resistor film, wherein the electrically insulating coating is The film is formed by providing a coating film of an organometallic compound on the surface and then firing it, and the heating resistor film is formed by adding a material insoluble to the solvent, a synthetic resin binder, and other compounded materials in the form of ultrafine particles to a solvent. A planar heating element formed by adding and mixing, applying a resistance paste for a heating element obtained with or without applying ultrasonic waves thereto, and firing.