JPS6325468B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a planar heating element whose heating element is a conductive resin composition containing carbon black. Conventionally, conductive resin compositions made by blending fine metal powder or carbon black with resin such as polyethylene or polypropylene have a resistance value that has a positive temperature coefficient with respect to temperature changes, so-called
It is known that it exhibits PTC characteristics and its resistance value increases rapidly at a certain temperature. Therefore,
When used as a heating element, the temperature rises when energized, but the resistance value rapidly increases in a specific temperature range and the amount of heat generated decreases.The heating element itself exhibits a self-temperature control function, and the temperature of thermostats, temperature fuses, etc. It does not require a control element and is safe, so it is used in heaters and the like. Therefore, when using a conductive resin composition as described above as a heating element, it should be one that automatically maintains a constant temperature for a long period of time even when energized for a long time, and has excellent stability such as heat resistance under the usage environmental conditions. Must. However, this type of heating element is equipped with electrode wires that act as current-carrying conductors, so if the heating element and electrode wires are not in good contact, current will not flow to the heating element and the temperature will not rise. However, conventional synthetic resin materials for heating elements do not necessarily have good adhesion to metals such as copper and aluminum, which are the materials for electrode wires, and they gradually degrade due to oxidation of the electrodes and heat cycles. There were drawbacks such as poor adhesion between the two, increased contact resistance between the heating element and the electrode wire, and no current flowing through the heating element and no longer generating heat. As a result of intensive research on various resin materials, the present inventors found that maleic acid-modified polyolefin has good adhesion to both synthetic resins and metals, and can be used for this type of material at higher temperatures than conventional materials. Since there are different grades, it is easy to select the material depending on the purpose, and the coating material provided on the heating element can be used in combination with sufficient consideration of the difference in thermal expansion, so it is preferable as this type of resin material. This discovery led to the present invention, the gist of which is to provide a heating element formed by molding a conductive resin composition comprising at least maleic acid-modified polyolefin mixed with carbon black. The first invention of the heating element and the heating element part made of a conductive resin composition made of a maleic acid-modified polyolefin blended with carbon black and an insulating coating layer provided thereon are simultaneously extruded. This invention relates to a second invention of a method for manufacturing a shaped heating element. The maleic acid-modified polyolefin is obtained by reacting polypropylene or polyethylene with maleic acids in the presence of a radical initiator and an alkyl aromatic hydrocarbon solvent, and is, for example, a product called Admer (manufactured by Mitsui Petrochemical Industries, Ltd.). It is known as Admar NE050, Admar
There are types such as QE305. This maleic acid-modified polyolefin is uniformly blended with an appropriate amount of conductive carbon black to form a conductive synthetic resin, which is then molded into a heating element. When electrodes were attached to this and electricity was applied, it generated heat, the temperature gradually rose and the current value decreased, and in about 10 minutes, the amount of heat generated and the amount of heat dissipated were balanced and reached a steady value, and then the applied voltage was reduced considerably. However, this temperature change was small, and although the current value decreased rapidly when the applied voltage was increased, there was no major change in the surface temperature. Further, when the heating element was heated from the outside with an infrared lamp and the resistance value between the electrodes was measured in a non-energized state, the resistance value suddenly increased when the back surface temperature was around 35°C. The heating element thus obtained by blending conductive carbon black with maleic acid-modified polyolefin exhibited positive resistance-temperature characteristics, and the change in electrical resistance with temperature was as shown in FIG. In the figure, A is maleic acid-modified polyolefin made by Mitsui Petrochemical Industries, Ltd., Admer NE050 mixed with 30 parts of carbon black, and B is Admer QE305, also made by the same company, mixed with 30 parts of carbon black.
C is Admar, also made by the same company.
NE050 mixed with 50 parts of carbon black,
D indicates a mixture of Admar QE305, also made by the same company, with 50 parts of carbon black. In addition, when we investigated the softening temperature of the Admer resin, it differed depending on the base material, and it was 85 °C for low density polyethylene base material and 130 to 150 °C for polypropylene base material (both were
ASTMD1525 Vikatsu method)
It has also become clear that the self-control temperature range can be changed by changing the softening point of the base resin at a temperature at which the electrical resistance significantly increases as described above. Furthermore, the adhesion properties of these Admer resins to various base materials are as shown in Tables 1 and 2, and they have good adhesion properties to both metals and synthetic resins.

【table】

[Table] The various base materials mentioned above are the Admer NE050 film (100μ thick), and when the base material is metal, it is heated at 200℃.
If the base material is other than metal, it is heat-fused at 160°C, and the adhesive strength shown on the table is the value when peeled off at a speed of 200 mm/min. In this way, a heating element made of a conductive resin composition containing maleic acid-modified polyolefin and carbon black exhibits a self-temperature control function that rapidly increases the resistance value at a certain temperature and maintains the temperature within a certain range. The self-controlling temperature range can also be changed, and since this maleic acid-modified polyolefin has good adhesion to both metals and synthetic resins, it provides strong adhesion to the insulating coating layer provided on the electrode and heating element. It is most preferable as a planar heating element that does not require a temperature control element because it maintains a constant temperature and has excellent stability. Furthermore, the structure of the planar heating element is not particularly limited and may be of various conventionally known forms, as shown in FIGS. 2 to 4. Figure 2 shows a belt-shaped one with a cocoon-shaped cross section, and Figure 3 shows a plate-shaped one. 1 is a heating element made of a conductive resin composition containing carbon black in maleic acid-modified polyolefin, and 2 is an insulating coating. The layer is made of polyethylene, polypropylene, maleic acid-modified polyolefin, or the like. It is particularly preferable that the coating layer 2 has a coefficient of thermal expansion at least equal to or higher than that of the heating element 1. 3 and 4 are electrodes made of copper, aluminum, or the like. In FIG. 4, a large number of electrodes 3 and 4 are provided on the heating element 1 to increase the area of the heating element 1. In any case, in the present invention, at least the heating element is formed from a conductive composition prepared by blending carbon black or the like with maleic acid-modified polyolefin. Example 1 After wiring the electrode wires, Admar resin (Admar QE305 manufactured by Mitsui Petrochemical Industries, Ltd.) (softening point
A pellet (conductive resin composition) obtained by kneading 100 parts of acetylene black (130°C) and a small amount of anti-aging agent is extruded to form a band-shaped heating element element 1 with a cocoon-shaped cross section as shown in FIG. I got it. Example 2 Pellet (conductive resin composition) obtained by kneading 100 parts of Admer resin (Admer QE305 manufactured by Mitsui Petrochemical Industries, Ltd.) (softening point 130°C) with 30 parts of acetylene black and a small amount of anti-aging agent. ) is obtained from a T-die with a single-letter-shaped slit, and while the extruded resin is still in a molten or softened state, an electrode wire heated to the resin temperature is placed. Cooled, thickness 0.2mm, width 500
A planar heating element 1 was obtained as shown in FIG.
This heating element exhibited resistance characteristics as shown by curve B in FIG. Next, in order to manufacture a planar heating element in which the heating element element 1 as described above is provided with an insulating coating layer 2, conventionally, the heating element element 1 is formed by an appropriate method such as extrusion, and then an insulating coating layer is formed. This is done by re-coating the coating layer 2 in a separate process. However, a conductive resin composition containing carbon black has a phenomenon in which its resistance value changes when heat is applied, and under certain conditions, the resistance value before and after thermal relaxation differs. Therefore, in the conventional production method in which the heating element 1 is extruded in the first step, the extrudate is cooled to room temperature, and the insulating coating layer 2 is re-extruded in the second step, the first step is The heating element obtained by
The second step, thermal relief, is added, and if the thermal relief conditions are close to the melting point of the heating element and within a range of ±40℃, the resistance value of the heating element will increase significantly. be. In addition, the conventional method of extruding the heating element element and then recoating it with an insulating coating layer in a separate process is not preferable in terms of productivity since the manufacturing process is divided into two processes, which is labor-intensive and has a failure rate. do not have. Therefore, preferably, a planar heating element is obtained by coating a heating element element made of a conductive resin composition prepared by blending carbon black with maleic acid-modified polyolefin and an insulating coating layer by coextrusion. By extruding the insulating coating layer and the heating element at the same time in this way, it is possible to prevent the resistance value from increasing due to the heat radiation applied to the heating element, and the resistance value can be set to any value by selecting the extrusion conditions. It's possible, and it's also good in terms of productivity. Therefore, a planar heating element having a stable and desired resistance value can be easily manufactured. Example 3 On top of the electrode wires, Admar resin (Admar QE305 manufactured by Mitsui Petrochemical Industries, Ltd.) (softening point
A heating element is obtained by extruding pellets (conductive resin composition) obtained by kneading 100 parts of acetylene black (130°C) with a small amount of anti-aging agent, and at the same time an insulating coating is applied on the heating element. A layer of polypropylene resin was extrusion coated to obtain a heating element as shown in FIG. When electricity was applied to this heating element, the surface temperature at the center point was 115℃, and the internal temperature (120℃).The resistance value calculated backward from the current value at this time was 35 million Ω, which was at room temperature of 20℃. It was four times as hot.

[Brief explanation of drawings]

FIG. 1 is a chart showing temperature changes in electrical resistance of the Admer resin heating element used, and FIGS. 2, 3, and 4 are perspective views showing other embodiments of the present invention. 1... Heat generating element, 2... Insulating coating layer, 3,
4... Electrode wire.

Claims (1)

[Scope of Claims] 1. In a planar heating element comprising an electrode, a heating element, and an insulator, at least the heating element is made of a conductive resin composition made of a maleic acid-modified polyolefin blended with carbon black. A planar heating element characterized by comprising: 2. A planar heating element characterized in that a heating element element portion made of a conductive resin composition prepared by blending carbon black with maleic acid-modified polyolefin and an insulating coating layer provided thereon are formed by co-extrusion. manufacturing method.