JPH0359986A - Heating body with positive resistance temperature coefficient - Google Patents

Abstract

PURPOSE:To prevent a crack of interface depending on the thermal expansion difference between the electrode wires and a PTC resistance body by providing a pair of electrode wires opposite each other at the equal intervals wound in a spiral form along the longitudinal direction of the PTC resistance body through high conductive compositions with a conductivity higher than that of the PTC resistance body provided between the PTC resistance body and the electrode wires. CONSTITUTION:This is a (PTC) heating body with a positive resistance temperature coefficient, furnishing a pair of electrode wires 2 and 3 at the equal intervals wound in a spiral form along the longitudinal direction of the resistance body 1. The electrode wires 2 and 3 are covered with high-conductive compositions 4 and 5 respectively, and furthermore, the whole body is covered with an insulator 6. Consequently, a deterioration of the interfaces between the 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 have 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. 3, the electrode wire 7 and the electrode wire 9 are parallel linear metal electrodes provided close to each other, and between them, the PT
By arranging the C resistor 8, a high output PTC heating element appears.

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 couple the above objects, the present invention provides crystalline l''+'+1
A long tube-shaped resistor with a positive temperature coefficient of resistance whose main component is a conductive composition made by dispersing conductive fine powder in a molecular composition, and a highly conductive material with higher conductivity than this resistor. A positive temperature coefficient of resistance comprising a pair of electrode wires facing each other at equal intervals, which are spirally wound along the longitudinal direction of the resistor through a magnetic composition, and an electrical insulator sheathing the electrode wires. A heating element with

Function In the present invention, as described above, a highly conductive composition having higher conductivity than the PTC resistor is interposed between the PTC resistor and the electrode wire, and the wire is wound spirally along the longitudinal direction of the PTC resistor. By arranging a pair of equally spaced opposing electrode wires, it is possible to prevent interface cracking due to the difference in thermal expansion between the electrode wire and the PTC resistor, alleviate the difference in thermal expansion, and further improve electrical conductivity. A mechanism that secures the passage can be formed. In addition, it is possible to replenish particulate conductive composition such as carbon that disappears due to ionization reaction near the interface with the electrode wire.
The high resistance caused by energization of the heating element can be improved.

EXAMPLE Hereinafter, a PTC heating element shown as an example of the present invention will be explained based on the drawings.

In FIG. 1, a long tubular PTC resistor 1 and a pair of equally spaced electrode wires 2 (copper wires with an outer diameter of 0.1 mm) are spirally wound along the longitudinal direction of the resistor 1. 1
There are 6 wires twisted) and an electrode wire 3 (same configuration as the electrode wire 2), which are coated with highly conductive compositions 4 and 5, respectively.

That is, as shown in the cross-sectional view taken along the line AA in FIG. 2, the periphery of the electrode wire 3 is coated with the highly conductive composition 5.

Further, the entire body is covered with an insulator 6 (polyvinyl chloride) to form a PTC heating element.

Incidentally, in the above embodiment, the PTC resistor l is made 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 (Ia) 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 examples of the present invention using the above conductive composition with samples not using such a conductive composition, an electric current durability test was conducted at an ambient temperature of 100° C. and an applied voltage of 200 V. The time required for the rate of change in resistance value to reach 50% was 6500 hours in the latter case, but in the above example it was 2 hours.
Even after 1,000 hours have passed, it has not yet reached this point, indicating excellent current-carrying durability.

In the above examples, low density polyethylene was shown as the base crystalline polymer composition, but polyamide, ethylene-vinyl acetate copolymer, graft 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 electrode wire and the PTC resistor through the highly conductive composition. Therefore, it is possible to prevent deterioration of the interface between the electrode wire and the PTC resistor due to the difference in thermal expansion due to heat generation during energization, and it is possible to realize a heating element with an extremely long life. In addition, the resistance 4+'i change skewer has been greatly improved compared to the conventional example, resulting in extremely reliable and safe self-temperature BL.
; There are effects such as being able to realize a heating element having Ir+J action.

[Brief explanation of drawings]

Fig. 1 is a side view showing an embodiment of the present invention, with the insulator of the PTC photothermal body cut open to show the inside, and Fig. 2 is a side view showing the inside of the PTC photothermal body.
FIG. 3 is a side view showing the inside of a conventional P-RC heating element by cutting through the insulator thereof.

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 electrode wires facing each other at equal intervals are spirally wound along the longitudinal direction of the resistor through a highly conductive composition having electrical conductivity, and an electrical insulator sheathing the electrode wires. A heating element having a positive temperature coefficient of resistance.