JPH0359984A - Heating body with positive resistance temperature coefficient - Google Patents

Abstract

PURPOSE:To prevent a crack of interfaces between metal electrode wires and a PTC resistance body by placing a high-conductive compositions whose conductivity is higher than that of the PTC resistance body, between the PTC resistance body and the metal electrode wires. CONSTITUTION:This is a (PTC) heating body with a positive resistance temperature coefficient, furnishing a PTC resistance body 1, and metal electrode wires 2 and 3 provided parallel at a specific interval opposing along the tube-form longitudinal direction of the TPC resistance body 1, and the both electrode wires 2 and 3 are covered with high-conductive compositions 4 and 5 respectively. Furthermore, the whole body is covered with an insulator 6. Consequently, a deterioration of the interfaces between the metal electrode wires 2 and 3, and the PTC resistance body 1, resulting from the thermal expansion difference by the heating when the current is applied, can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION FIELD OF INDUSTRIAL APPLICATION The present invention relates to a heating element with a positive temperature coefficient of resistance that is used as a heating appliance and a general heating device.

Conventional technology Conventional tube-shaped positive resistance temperature coefficient (hereinafter referred to as PTC)
The heating element is self-controlled to an appropriate temperature by the PTC characteristics of a PTC resistor provided between a pair of electrode wires. However, when particularly high power density is required, it is essential to improve the temperature distribution in the direction between the pair of electrode wires in order to make the temperature distribution of the heating element uniform.
As a solution to this problem, a method has been taken in which the distance between a pair of electrode wires is made closer to each other.

In FIG. 2, electrode wires 7 and 8 are parallel metal electrodes placed close to each other at a constant interval, and a PTC resistor 9 is arranged to surround these electrode wires 7.8. As a result, a high-output PTC heating element is produced.

Problems to be Solved by the Invention In general, with long-term use of such PTC heating elements, the electrical insulating layer formed mainly at the interface between the PTC resistor and the electrode wires increases the resistance of the entire heater and lowers the heat generation temperature. It had the following drawback. In particular, PTC resistors whose polymer composition is cross-linked and mixed with finely ground conductive powder are safe because they have a sea-island structure between the conductive powder and the polymer as a binder. Although it has excellent properties in terms of hardness and processing stability, it is difficult to obtain a uniform heat generation distribution, so the above-mentioned tendency was noticeable.

An object of the present invention is to improve the above-mentioned problems and to provide a PTC heating element that is safe and durable for long-term use.

Means for Solving the Problems In order to achieve the above object, the present invention provides a long tube-shaped positive electrode whose main component is a conductive composition obtained by dispersing conductive fine powder in a crystalline polymer composition. a resistor having a temperature coefficient of resistance; a pair of metal electrode wires surrounded by the resistor through a highly conductive composition having higher conductivity than the resistor and facing each other in parallel with a constant interval; The heating element has a positive temperature coefficient of resistance and includes an electric insulator covering the electrode wire.

Operation In the present invention, as described above, the metal electrode wire is surrounded and spaced at a constant interval so that a highly conductive composition having higher conductivity than the PTC resistor is interposed between the PTC resistor and the metal electrode wire. By making them face parallel,
It is possible to prevent interface cracking due to the difference in thermal expansion between the metal electrode wire and the PTC resistor, to alleviate the difference in thermal expansion, and to form a mechanism that ensures an electrically conductive path. Furthermore, it is possible to replenish the particulate conductive composition such as carbon that disappears due to the electrolytic corrosion reaction near the interface with the metal electrode wire, so it is possible to improve the resistance of the heating element due to energization.

Example Below, a PTC heating element shown as an example of the present invention is shown as □
The explanation will be based on the drawings.

In Fig. 1, metal electrode wires 2 (16 twisted copper wires with an outer diameter of 0°1 mm) are arranged in parallel at regular intervals and facing each other along the longitudinal direction of the PTC resistor tube shape of the PTC resistor resistor element. There are a metal electrode wire 3 (same configuration as the metal electrode wire 2) and a metal electrode wire 3 (same configuration as the metal electrode wire 2), each of which is coated with highly conductive compositions 4 and 5. Further, the entire body is covered with an insulator 6 (polyvinyl chloride, etc.) to form a PTC heating element.

In addition, in the said Example, the PTC resistor 1 consists of the following composition. Using polyethylene as a crystalline polymer composition, 3.5 parts by weight of dicumyl peroxide as a crosslinking agent was blended with 100 parts by weight of a kneaded low-density polyethylene containing 40% by weight of furnace black as a conductive fine powder. A particulate conductive composition having an average particle size of 60 μm was prepared by freeze-pulverizing the crosslinked product obtained by heat-treating it at 180° C. for 1 hour. Thereafter, this particulate conductive composition was prepared by kneading (la) as a crystalline polymer composition into low density polyethylene and carbon black as a conductive fine powder at a composition ratio of 28% by weight. Note that the resistor with this positive temperature coefficient of resistance is 3.2X10'Ω-cm
The volume resistivity value was shown as follows.

Further, as the highly conductive composition, a low density polyethylene composition containing 50% by weight of carbon black and exhibiting a volume resistivity of 5 to 10 Ω-cm was used.

In order to compare the example of the present invention using the above conductive composition with a sample not using such a highly conductive composition, an electric current durability test was conducted at an ambient temperature of 100° C. and an applied voltage of 200 V. The latter is soo as the time for the rate of change in resistance value to reach 50%.

However, in the above-mentioned example, even after 20,000 hours, it has not yet reached this point, indicating that the current-carrying durability is excellent.

In the above examples, low density polyethylene was shown as the base crystalline polymer composition, but polyamide, ethylene-vinyl acetate copolymer, kraft polymers such as acrylic acid and maleic acid, or styrene-butadiene may also be used. It may also be a thermoplastic elastomer such as a block copolymer.

Effects of the Invention As described above, according to the heating element having a positive temperature coefficient of resistance of the present invention, electrical connection is made between the metal electrode wire and the PTC resistor through the highly conductive composition. In addition, deterioration of the interface between the metal electrode wire and the PTC resistor due to the difference in thermal expansion due to heat generated during energization can be prevented, and a heating element with an extremely long life can be realized. In addition, the rate of change in resistance value has been greatly improved compared to conventional examples, and extremely reliable and safe self-temperature control has been achieved.
There are effects such as being able to form a heating element that has a heat-controlling effect.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a PTC heating element, not showing an embodiment of the present invention, and FIG. 2 is a sectional view of a conventional I) l'C heating element.

Claims (1)

[Claims] (1) A long tube-shaped resistor having a positive temperature coefficient of resistance higher than that of the long tube-shaped resistor whose main component is a conductive composition made by dispersing conductive fine powder in a crystalline polymer composition. A pair of metal electrode wires surrounded by the resistor through a highly conductive composition having electrical conductivity and facing each other in parallel with a certain interval, and an electrical insulator sheathing the metal electrode wires. A heating element with a characteristic positive temperature coefficient of resistance.