JPH0389483A - Composition material for electric heating element - Google Patents

Abstract

PURPOSE:To prevent a danger when an electric heating element is locally heated and allow uniform heating by forming the electric heating element with carbon powder or metal powder, inorganic hydrate powder, and rubber or resin. CONSTITUTION:The kneaded paste made of carbon powder or metal powder, inorganic hydrate powder, and rubber or resin is formed in a shape with the length 500mm, width 300mm and thickness 2mm, lead wires are buried on both ends of the short side, and they are integrally molded and heat-cured to manufacture an electric heating element 1. A transparent glass 2 is provided on the front face, a mirror glass 3 is provided on the back, and a frame 4 is fitted to assemble a panel heater. The inorganic hydrate has the dehydration temperature in the range 60-300 deg.C, and it is selected among hydrates of Al, Mg and Zn. The metal is selected among Cu, Al and Fe. The inorganic hydrate with the grain size 200mum or below is used.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention is a uniform electric heating element of various shapes for use in heating,
The present invention relates to a composition for an electric heating element that can be used for freezing prevention or drying purposes. [Prior art] Conventionally, this type of electric heating element includes one in which a nichrome wire is laid out on a flat surface, and a composition in which rubber or resin is filled with electrically conductive carbon and/or carbon powder. There are some that use metal powder, and others that use a composition in which rubber or resin is filled with metal powder. [Problems to be Solved by the Invention] Electric heaters for floor heating such as nichrome wire are made of thin wires arranged in a planar shape, but they lack uniform heating. Therefore, some attempts have been made to improve thermal uniformity by using rubber or resin compositions filled with carbon, graphite, or metal powders, but rubber or resin compositions filled with carbon and/or graphite powders are Since black smoke has the property that its electrical resistance decreases as the temperature rises, if a large amount of powder is unevenly distributed,
The element is locally heated, the current in that area increases, and the temperature further increases, creating a risk of overheating and fire. A rubber or resin composition filled with metal powder may cause local overheating if a large amount of metal powder is unevenly distributed, although the metal does not have the above-mentioned properties such as carbon. The present invention improves the above-mentioned drawbacks when rubber or resin (hereinafter referred to as resin, etc.) is filled with carbon, graphite (hereinafter referred to as carbon, etc.) or metal powder, and can prevent danger even if the powder is locally unevenly distributed. Another object of the present invention is to provide a resin composition for an electric heating element that can be heated uniformly. [Means for Solving the Problems J] The present inventor has discovered that when an inorganic hydrate is dehydrated at a predetermined temperature, cracks or pores are formed in the resin composition due to the generation of moisture (gas). The present invention was achieved by paying attention to the fact that the electrical resistance of the portion increases. That is, the present invention is a composition for an electric heating element in which a resin or the like is filled with powder of carbon or metal powder (including a combination of both) and powder of inorganic hydrate. As the carbon, carbon such as artificial graphite, natural graphite, calcined coke, calcined anthracite, glassy carbon, etc. can be used, but graphite with good conductivity is preferable. These particle sizes are 1
00 μm or less is suitable. The metal powder is Cu, A1. Fe, Ni, Cr,
Mg, Ti, Si, etc. are used, but Cu, Fe, and AI are preferable from the viewpoint of electrical conductivity and economical efficiency. These particle sizes are similar to those of carbon. Inorganic hydrates are AI(OH)s, Mg(OH)
z, 5lo1nHzO1Zn (OH), etc. can be used, but it is better to dehydrate at about 60 to 300°C, and considering economic efficiency, AI (OH)
Particularly preferred is s or magnesium hydroxide. The particle size of the inorganic hydrate is suitably 200 μm or less in order to improve dispersibility. As the resin etc., rubbers such as natural rubber and chlorobrene, thermoplastic resins such as polyethylene and chlorinated polyethylene, and thermosetting resins such as phenol resins and epoxy resins are used. When mixing resin, etc., powder of carbon, etc., or metal powder, and powder of inorganic hydrate, if the resin, etc. is rubber or thermoplastic resin, the resin, etc. is semi-molten and mixed in a mixer. Thermosetting resins are mixed with powder in their liquid state before hardening. The mixed composition is molded to fit various device shapes. Thermosetting resins are cured at the same time as or after molding. The proportion of each component in the composition is preferably 5% by weight or more (hereinafter % is based on weight) in order to have the effect of dehydrating the inorganic hydrate, and carbon etc. or metal powder is preferably 50% due to its conductivity.
The above is suitable. From the viewpoint of moldability, it is suitable for resin etc. to have a content of 15% or more. These upper limits are determined in relation to the remaining components, but suitably 80% for carbon etc. or metals, 35% for inorganic hydrates, and 45% for resins etc. The composition of the present invention having such a composition has a volume resistivity of 0.1-100 ΩC1, and a normal operating temperature of 45-26
It is 0°C. [Effect J: In rare cases, non-uniformity may occur in the composition, and powder may be unevenly distributed. In such cases, it can be dangerous if safety measures are not taken. When the electric heating element using the composition of the present invention is locally heated, the inorganic hydrate powder filled in it dehydrates, causing internal cracks, etc., and the current decreases due to a sudden increase in electrical resistance. As the heat generation decreases, heating above the dehydration temperature can be avoided. [Example J l) Graphite powder with a particle size of 30 μm or less and a particle size of 120 μm
The following magnesium hydroxide powders were mixed well at a weight ratio of 4:1. The mixed powder and liquid phenol resin are 7=
The mixture was kneaded at a weight ratio of 3. These three types? 1! As shown in Figure 1, the kneaded paste has a length of 500mm, a width of 300mm,
An electric heating element 1 with a lead wire was fabricated by integrally molding it to a thickness of 2 rBm and embedding copper wires to serve as lead wires 5 at both ends of the short sides, and curing with heat. Furthermore, in order to prevent electric shock and effectively dissipate heat, the front side is made of transparent plate glass 2, and the back side is made of mirror glass 3 to reflect heat.
Furthermore, a panel heater having a structure in which the electric heating element of the present invention was sandwiched was assembled by attaching frames 4 on both sides and on the top and bottom. The resistance of this panel heater at room temperature was 186Ω. 2) Copper powder with a particle size of 100 μm or less and a particle size of 150 μm
The following aluminum hydroxides were mixed well in a weight ratio of 2:1. 6: The mixed powder and chloroprene rubber compound:
They were mixed at a weight ratio of 4. This 3fi mixed compound is embedded with lead wires at both ends to make a length of 1750mm and a width of 3.
A flexible electric heating element was fabricated by roll-molding to a thickness of 00+ym and a thickness of 3 mm, and an insulating layer of woven fabric was provided thereon. The longitudinal resistance of this electric heating element at room temperature is 11
It was 6Ω. [Effect of the invention] At normal 100V, the panel heater of Example 1)
The electric heating element of Example 2) was maintained at a moderate temperature of 0°C and 65°C. Therefore, when the power supply voltage was set to 200V, in Example 1), current stopped flowing when the electric heating element reached 285°C. In Example 2), current stopped flowing when the temperature of the electric heating element reached 245°C. When the dehydration temperature of the inorganic hydrate filled in this manner is reached, fine cracks are generated inside the electric heating element of the present invention due to dehydration, the electric resistance increases, and heating above the dehydration temperature is avoided. This makes it safe to use.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view (a) showing an example of a panel heater in which the composition for an electric heating element of the present invention is used as an element, and its A-A.
It is a sectional view (b).

Claims (5)

[Claims] (1) A composition for an electric heating element comprising carbon powder or metal powder, inorganic hydrate powder, and rubber or resin. (2) The composition for an electric heating element according to claim 1, wherein the dehydration temperature of the inorganic hydrate is in the range of 60 to 300°C. (3) The composition for an electric heating element according to claim 1 or 2, wherein the inorganic hydrate is one or more of hydroxides of Al, Mg, Si, and Zn. (4) The composition for an electric heating element according to claim 1, wherein the metal is Cu, Al, or Fe. (5) The composition for an electric heating element according to any one of claims 1 to 3, wherein the inorganic hydrate is aluminum hydroxide or magnesium hydroxide with a particle size of 200 μm or less.